ProfitPress Mega CDROM2 …eeware (MSDOS)(1992)(Eng)/ProfitPress-MegaCDROM2.B6I/APPS/DATABASE/REXL210.ZIP/APPENDIX.DOC

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                          RExL  Version 2.10


          A Rule-based Applications Development Environment

                                 From


                         The Software Loft,
                         Lough Guitane,
                         Killarney,
                         Co. Kerry,
                         Ireland.            Tel: [+353] 64-54014

               Internet:      [e-mail]

               Compuserve:    100042,1237




            -- Part II -- The Appendices to the Manual --




     Information in this  document is subject  to change  without
     notice and does  not represent a commitment  on the part  of
     The Software Loft.   The software  described in this  manual
     may be  used and  copied within  the  terms of  the  license
     agreement.

     Turbo C, Turbo Pascal and Sidekick are registered trademarks
     of  Borland  International.    dBase  III+  and  dBase   are
     registered trademarks of Ashton-Tate.

     (C)  Copyright,  The  Software  Loft,  1992.    All   rights
     reserved.  If you have  any difficulties, please contact  us
     at the following address:

               The Software Loft
               Lough Guitane
               Killarney
               Co. Kerry
               Ireland             Telephone: [+353] 64-54014

               Internet:      [e-mail]

               Compuserve:    100042,1237





































                            Contents



          Chapter 1  Function Families                     3
             1.1  Introduction . . . . . . . . . . . . . . 3
             1.2  Array handling . . . . . . . . . . . . . 3
             1.3  Binary operations  . . . . . . . . . . . 4
             1.4  Database operations  . . . . . . . . . . 4
             1.5  Date and time manipulation . . . . . . . 5
             1.6  RExL error handling functions  . . . . . 6
             1.7  Keyboard handling functions  . . . . . . 7
             1.8  Operating system interface functions . . 7
             1.9  Financial functions  . . . . . . . . . . 8
             1.10  Mathematical functions  . . . . . . . . 8
             1.11  Screen handling functions . . . . . . . 9
             1.12  Miscellaneous functions . . . . . . . . 9

          Chapter 2  The Database Module                  11
             2.1  Introduction to Databases  . . . . . .  11
             2.2  Indexes  . . . . . . . . . . . . . . .  13
             2.3  Using Database Files . . . . . . . . .  15
                2.3.1  Opening and selecting files . . .  15
                2.3.2  Reading and writing to files  . .  16
                   2.3.2.1  Using functions  . . . . . .  16
                   2.3.2.2  Direct field access  . . . .  18
                2.3.3  Moving around in a file . . . . .  20
                2.3.4  Miscellaneous functions . . . . .  20
                   2.3.4.1  Statistical analysis of
                            data . . . . . . . . . . . .  20
                   2.3.4.2  Deletion of information  . .  20
                   2.3.4.3  Other functions  . . . . . .  21

          Chapter 3  Function Reference                   23

          Chapter 4  Keystroke reference                  95
             4.1  Editor keystrokes  . . . . . . . . . .  95
             4.2  Screen designer keystrokes . . . . . .  97
             4.3  Debugger keystrokes  . . . . . . . . .  99





                                  i



          Chapter 5  Error Messages                      103
             5.1  Error messages common to runtime and
                  editor . . . . . . . . . . . . . . . . 103
                5.1.1  Bad help file format  . . . . . . 103
                5.1.2  Cannot locate system  . . . . . . 103
                5.1.3  Cannot open print file  . . . . . 103
                5.1.4  Couldn't open file  . . . . . . . 103
                5.1.5  Macros nested too deep (20=max) . 104
                5.1.6  Help file index is not loaded . . 104
                5.1.7  Unable to locate help file  . . . 104
                5.1.8  Macro recursion not allowed . . . 104
                5.1.9  Error loading configuration
                       file  . . . . . . . . . . . . . . 104
                5.1.10  Zero memory allocation
                        request! . . . . . . . . . . . . 104
                5.1.11  Not enough memory to perform
                        selected operation . . . . . . . 105
                5.1.12  This window is not movable . . . 105
                5.1.13  No directories available . . . . 105
                5.1.14  No files in directory  . . . . . 105
                5.1.15  No macros defined  . . . . . . . 105
                5.1.16  --- Out of memory ---  . . . . . 105
                5.1.17  No screens defined . . . . . . . 105
                5.1.18  Not enough memory to load
                        system . . . . . . . . . . . . . 105
                5.1.19  No unused rules available  . . . 105
                5.1.20  No unused screens available  . . 106
                5.1.21  No variables defined . . . . . . 106
                5.1.22  Rule is not used in current
                        listing  . . . . . . . . . . . . 106
                5.1.23  Error saving configuration
                        file . . . . . . . . . . . . . . 106
                5.1.24  Screen is not used in current
                        listing  . . . . . . . . . . . . 106
                5.1.25  Screen file is corrupt . . . . . 106
                5.1.26  Too many files open  . . . . . . 107
                5.1.27  Too many keys in macro
                        (500=max)  . . . . . . . . . . . 107
                5.1.28  Variable is not used in current
                        listing  . . . . . . . . . . . . 107
                5.1.29  Wrong source file format . . . . 107
                5.1.30  Wrong screen file format . . . . 107
                5.1.31  Error opening screen file  . . . 107
             5.2  Error messages unique to editor  . . . 107
                5.2.1  Incorrect format in listing
                       file  . . . . . . . . . . . . . . 107
                5.2.2  Cannot nest fields  . . . . . . . 108



                                  ii



                5.2.3  Can only delete recursed rule from
                       first level of recursion  . . . . 108
                5.2.4  Unable to locate runtime module . 108
                5.2.5  Area crosses fields . . . . . . . 108
                5.2.6  Can't have a field of this type in
                       this screen . . . . . . . . . . . 108
                5.2.7  Illegal array dimension . . . . . 109
                5.2.8  Maximum number of fields
                       reached . . . . . . . . . . . . . 109
                5.2.9  Memory low, should save now!  . . 109
                5.2.10  Not used in listing  . . . . . . 109
                5.2.11  This is the main rule and is called
                        to start the kbs . . . . . . . . 109
                5.2.12  Cannot change rule name to one
                        already existing . . . . . . . . 109
                5.2.13  This screen already exists . . . 109
                5.2.14  Toggle fields must be more than 5
                        and less than 75 characters
                        wide . . . . . . . . . . . . . . 110
                5.2.15  Unable to create screen file . . 110
                5.2.16  Error saving file  . . . . . . . 110
                5.2.17  Error loading file . . . . . . . 110
                5.2.18  Error loading screen file  . . . 110
                5.2.19  Cannot change name of Main
                        Program  . . . . . . . . . . . . 110
             5.3  Error messages unique to runtime-
                  debugger . . . . . . . . . . . . . . . 110
                5.3.1  Array bounds overflow . . . . . . 110
                5.3.2  Can't set a breakpoint here . . . 111
                5.3.3  Cannot open printer for output  . 111
                5.3.4  Cannot find editor  . . . . . . . 111
                5.3.5  Divide by zero  . . . . . . . . . 111
                5.3.6  String-numeric collision  . . . . 111
                5.3.7  Can't have string for radio button
                       parameter . . . . . . . . . . . . 112
                5.3.8  Stack underflow . . . . . . . . . 112
                5.3.9  Stack overflow  . . . . . . . . . 112
                5.3.10  Numeric value out of range . . . 112
                5.3.11  Rule stack overflow  . . . . . . 112
                5.3.12  Invalid database file handle . . 112
                5.3.13  Unable to allocate rule stack  . 112
                5.3.14  Math error : Parameter out of range
                        in function XXX  . . . . . . . . 113
                5.3.15  Math error : Parameter singularity
                        in function XXX  . . . . . . . . 113
                5.3.16  Math error : numeric overflow  . 113
                5.3.17  Math error : numeric underflow . 113
                5.3.18  Math error : precision loss  . . 113


                                 iii



             5.4  Critical Errors  . . . . . . . . . . . 113
                5.4.1  Write protect error . . . . . . . 114
                5.4.2  Drive not ready . . . . . . . . . 114
                5.4.3  Printer out of paper  . . . . . . 114
                5.4.4  Write fault . . . . . . . . . . . 114
                5.4.5  Read fault  . . . . . . . . . . . 114
                5.4.6  General Failure . . . . . . . . . 114
                5.4.7  Sector not found  . . . . . . . . 114
                5.4.8  Unknown unit  . . . . . . . . . . 115
                5.4.9  Unknown command . . . . . . . . . 115
                5.4.10  CRC error  . . . . . . . . . . . 115
                5.4.11  Bad request structure length . . 115
                5.4.12  Seek error . . . . . . . . . . . 115
                5.4.13  Unknown media type . . . . . . . 115

          Chapter 6  Extra Utilities                     117
             6.1  RExLPC . . . . . . . . . . . . . . . . 117
             6.2  RDU  . . . . . . . . . . . . . . . . . 118
                6.2.1  Introduction  . . . . . . . . . . 119
                6.2.2  Loading and Running . . . . . . . 119
                6.2.3  RDU menu system . . . . . . . . . 119
                   6.2.3.1  File Menu  . . . . . . . . . 119
                6.2.4  Edit Menu . . . . . . . . . . . . 120
                6.2.5  Search Menu . . . . . . . . . . . 122
                6.2.6  Utilities Menu  . . . . . . . . . 124
                6.2.7  Options Menu  . . . . . . . . . . 126
             6.3  RExLRD . . . . . . . . . . . . . . . . 127
             6.4  RExLRT . . . . . . . . . . . . . . . . 128
             6.5  ScrList  . . . . . . . . . . . . . . . 129
             6.6  ScrGrab  . . . . . . . . . . . . . . . 130
             6.7  ScrXtrct . . . . . . . . . . . . . . . 131
             6.8  ScrAdd . . . . . . . . . . . . . . . . 132
             6.9  MI . . . . . . . . . . . . . . . . . . 132
             6.10  KbdSpeed  . . . . . . . . . . . . . . 134
             6.11  KbdScan . . . . . . . . . . . . . . . 135

          Chapter 7  Afterword                           137













                                  iv









                             Tables


          Table 1.1: Functions in AR function family . . . 3
          Table 1.2: Functions in BT function family . . . 4
          Table 1.3: Functions in DB function family . . . 5
          Table 1.4: Functions in DT function family . . . 5
          Table 1.5: Functions in ER function family . . . 6
          Table 1.6: Functions in KB function family . . . 7
          Table 1.7: Functions in OS function family . . . 8
          Table 1.8: Financial functions . . . . . . . . . 8
          Table 1.9: Math functions  . . . . . . . . . . . 9
          Table 1.10: Screen functions . . . . . . . . . . 9
          Table 1.11: Miscellaneous functions  . . . . . .10
          Table 2.1: Simple Database Record Structure  . .12
          Table 2.2: dBase Expression Compatibility with
                     RExL  . . . . . . . . . . . . . . . .14
          Table 2.3: Miscellaneous Database Functions  . .21
          Table 3.1: ARsize() Input Indexing . . . . . . .26
          Table 3.2: BEEP() Frequencies  . . . . . . . . .29
          Table 3.3: Color Attribute Codes . . . . . . . .30
          Table 3.4: DISPLAY() escape sequences  . . . . .50
          Table 3.5: Valid Format Specifiers for
                     DTformat()  . . . . . . . . . . . . .54
          Table 3.6: OSdir() File Attribute Coding . . . .74
          Table 3.7: OSdriveok() return values . . . . . .75
          Table 3.8: OSstat() Return Indexing  . . . . . .78
          Table 3.9: CPU Type Return Coding  . . . . . . .79
          Table 3.10: Coprocessor Type Return Coding . . .79
          Table 3.11: Video Adapter Type Return Coding . .79
          Table 3.12: Color Attribute Codes  . . . . . . .81
          Table 4.1: Cursor movement keys  . . . . . . . .95
          Table 4.2: Hilite bar movement keys  . . . . . .95
          Table 4.3: Modifier keys . . . . . . . . . . . .96
          Table 4.4: Editor list keys  . . . . . . . . . .96
          Table 4.5: Editor miscellaneous keys . . . . . .96
          Table 4.6: Screen designer movement keys . . . .97
          Table 4.7: Screen designer field definition
                     keys  . . . . . . . . . . . . . . . .97
          Table 4.8: Screen designer line draw keys  . . .98
          Table 4.9: Screen designer miscellaneous keys  .98
          Table 4.10: Screen designer block mark keys  . .99


                                  v



          Table 4.11: Debugger hilite bar movement keys  .99
          Table 4.12: Debugger list keys . . . . . . . . .99
          Table 4.13: Debugger miscellaneous keys  . . . 100
          Table 4.14: KB function return values  . . . . 101
          Table 6.1: Keystrokes in structure create  . . 124













































                                  vi
       - Appendices.                         Page: 3 -








                              Chapter 1

                          Function Families


     1.1  Introduction


     This appendix gives a brief  introduction to the use of  and
     the design behind  the the seven  function families in  RExL
     and the various miscellaneous functions.


     1.2  Array handling


     There are nine functions which are used to manipulate arrays
     and determine information about them.  The functions are  as
     follows:

              Table 1.1: Functions in AR function family

     ARavg()        ARcount()      ARinit()
     ARmax()        ARmin()        ARsize()
     ARstd()        ARsum()        ARvar()

     The functions fall into two groups, the smaller first  group
     has two  functions  in  it:  ARinit()  and  ARsize().    The
     ARinit() function is used to  initialise the contents of  an
     array, while the second determines, at runtime, the size  of
     a particular dimension of an array.

     The other functions in this family are used for  statistical
     analysis of the contents of the arrays.  The function  names
     are based upon  similar functions  found in  Lotus 123,  and
     where appropriate, the parameter lists are the same.








      - RExL  Version 2.10  Copyright 1992, The Software Loft -
       - Appendices.                         Page: 4 -


     1.3  Binary operations


     There are six functions, using the initial letters BT  which
     are used to perform binary operations.  The functions are as
     follows:

              Table 1.2: Functions in BT function family

     BTand()        BTnot()        BTor()
     BTshl()        BTshr()        BTxor()

     The function  names  are  based  upon  the  equivalent  8086
     assembly language functions.   All the BT functions  convert
     their  parameters  to  sixteen  bit  words,  any  parameters
     greater than 65535  being set  to 65535  and any  parameters
     less than 1 being set to 0.

     Typically, these functions are used in conjunction with  the
     four memory access  functions, PEEK(),  PEEKW(), POKE()  and
     POKEW() to determine  information which  cannot be  obtained
     through the other system functions.

     For example, to determine if the NumLock state is active  or
     not, the following line could be used:

               [Expr] NumLockOn:=BTand(PEEK(0,1047),32)

     The use of the memory access functions should be avoided  if
     you intend  your  application  to run  on  widely  different
     machines.


     1.4  Database operations


     The thirty-nine dBase file and index manipulation  functions
     use the initial letters DB.  The functions are as follows:












      - RExL  Version 2.10  Copyright 1992, The Software Loft -
       - Appendices.                         Page: 5 -


              Table 1.3: Functions in DB function family

     DBappend()     DBavg()        DBbottom()
     DBcloseall()   DBclosedbf()   DBclosendx()
     DBcount()      DBcountflds()  DBdelete()
     DBdeleted()    DBexact()      DBgo()
     DBlocate()     DBmax()        DBmin()
     DBmkdbf()      DBmkndx()      DBnext()
     DBpack()       DBprev()       DBrecall()
     DBreccount()   DBrecno()      DBreindex()
     DBreplace()    DBrnum()       DBrstr$()
     DBseek()       DBseldbf()     DBselndx()
     DBskip()       DBstd()        DBstruct()
     DBsum()        DBtop()        DBusedbf()
     DBusendx()     DBvar()        DBzap()

     Because of the size and complexity of the database module in
     RExL, it is treated on its own in the next appendix.


     1.5  Date and time manipulation


     The eighteen date  and time manipulation  functions use  the
     initial letters DT.  The functions are as follows:

              Table 1.4: Functions in DT function family

     DTdate()       DTdate$()      DTdatevalue()
     DTday$()       DTdayno()      DTformat()
     DThourno()     DTminuteno()   DTmonth$()
     DTmonthno()    DTnow()        DTsecondno()
     DTsetdate()    DTsettime()    DTtime()
     DTtime$()      DTtimevalue()  DTyearno()

     The date functions  are again, based  largely upon those  in
     Lotus 123, with a few minor inconsistencies removed.

     The date  module can  use dates  in  any of  the three  most
     common date formats, European,  American and Japanese.   The
     exact format which is in use initially is determined by  the
     settings in the CONFIG.SYS file  in your machine.  If  there
     is no  specific format  set up,  then the  date format  will
     default to American.  The DTformat() command can be used  to
     set the  date and  time formats  and separators  explicitly,
     overriding the defaults.




      - RExL  Version 2.10  Copyright 1992, The Software Loft -
       - Appendices.                         Page: 6 -


     Date and  time  information  are  stored  in  RExL  as  real
     numbers.  The integer portion  of a date-time number is  the
     Julian day number  while the  fractional part  is the  time,
     expressed as a fraction of 24 hours.

     The Julian day number of a particular date is the number  of
     days elapsed since and including the first of January,  4713
     BC (the  reasons for  this exact  date being  chosen as  the
     origin are  historically amusing).   The  Julian day  number
     system is used widely in date calculations and should not be
     confused with the Julian Calendar.   The algorithms used  in
     RExL to calculate the Julian day number do not take  account
     of the ten  day transition from the  Julian Calendar to  the
     Gregorian  Calendar  which  occurred  from  October  5th  to
     October 15th  in 1582  in Rome  and at  various other  later
     dates around the rest of the world.

     Dates before 0 AD cannot be represented in RExL.  Apart from
     any other  considerations, there  was no  standard  calendar
     then, rendering calculations somewhat useless.

     Date and time functions which  return a date or time  number
     will return zero if the date or time was invalid.


     1.6  RExL error handling functions


     The five error  handling functions use  the initial  letters
     ER. The functions are as follows:

              Table 1.5: Functions in ER function family

     ERclear()      ERmsg$()       ERnum()
     ERok()         ERwatch()

     Whenever an error  occurs in  the runtime  portion of  RExL,
     internal variables save the text of the error and the  error
     number.  These  variables can be  interrogated by using  the
     ERmsg$() function (to  retrieve the text  of the error)  and
     ERnum() (to retrieve the error code).

     If no  errors have  occurred, then  calls to  ERmsg$()  will
     return an  empty string  and calls  to ERnum()  will  return
     zero.  Once an error has occurred, the text and error number
     remain fixed until the next error occurs, an application  is
     LOAD()'ed or the ERclear() function is used.



      - RExL  Version 2.10  Copyright 1992, The Software Loft -
       - Appendices.                         Page: 7 -


     While the  development of  an  application is  in  progress,
     errors should be left on, to detect errors such as divide by
     zero, which  would otherwise  not be  seen.   In  the  final
     distribution version, the error display can be disabled with
     the ERwatch() function.


     1.7  Keyboard handling functions


     The five keyboard handling functions use the initial letters
     KB.  The functions are as follows:

              Table 1.6: Functions in KB function family

     KBclear()      KBlast()
     KBread()       KBready()
     KBwait()

     The IBM PC uses a keyboard buffer to store keystrokes  until
     they can be processed by a program.  The normal size of  the
     buffer is 15 keystrokes.  The KBclear() function resets  and
     empties the  keyboard buffer,  while the  KBready()  reports
     whether a keystroke is pending  in the keyboard buffer.  The
     other two functions  in the  group are  used for  retrieving
     keystrokes from the  buffer, optionally  waiting a  variable
     time span for one.   When a screen has been terminated,  the
     KBlast() function  can be  used to  determine the  keystroke
     which caused its termination.

     If a keystroke returned by RExL is a character key, then the
     ASCII code of  the character will  be returned  immediately.
     Keys that  do not  have ASCII  codes, such  as the  function
     keys, return a more complex coding, the details of which are
     not necessary. The complete  list of function return  values
     is listed in appendix D, with the other keystrokes RExL  can
     return.   Note that  the <Insert>  key  is captured  by  the
     runtime module and is not returned to the application.


     1.8  Operating system interface functions


     The thirteen operating system interface functions, which use
     the initial letter code OS, are as follows:





      - RExL  Version 2.10  Copyright 1992, The Software Loft -
       - Appendices.                         Page: 8 -


              Table 1.7: Functions in OS function family

     OScd()         OScmd()   OScopy()
     OSdel()        OSdir()   OSdrive()
     OSexists()     OSmd()    OSnumber()
     OSrd()         OSren()   OSstat()
     OSwd$()

     These functions  perform  most  of the  operations  commonly
     needed to interface  with the operating  system under  which
     RExL is  working.    The commands  are  modelled  after  the
     corresponding DOS commands and require the same parameters.

     The OSstat()  function is  the only  function in  the  group
     which has no direct DOS counterpart.  It returns the  status
     of the machine,  including the  processor, co-processor  and
     display adapter type as well as the operating system version
     and information about the currently selected disk.


     1.9  Financial functions


     The financial functions in RExL are used in the  calculation
     of ordinary annuities.   There are  seven functions in  this
     group which does not use a common initial two-letter group.

                    Table 1.8: Financial functions

     CTERM()        FV()
     PMT()          PV()
     RATE()         SLN()
     SYD()          TERM()

     The functions in  this group are based  upon those in  Lotus
     123.  The annuity due for the FV() and PV() functions may be
     calculated easily by multiplying the result of the  ordinary
     annuity by the expression 1+rate, where rate is the periodic
     interest rate.


     1.10  Mathematical functions


     As with the financial functions,  the math functions do  not
     have a  common  initial  letter pair.  The  thirty-one  math
     functions are as follows:



      - RExL  Version 2.10  Copyright 1992, The Software Loft -
       - Appendices.                         Page: 9 -


                      Table 1.9: Math functions

     ABS()     ACOS()    AND()
     ASIN()    ATAN()    CEIL()
     COS()     DEG()     DIV()
     EQV()     EXP()     FALSE()
     FLOOR()   IMP()     LOG()
     LOG10()   MAX()     MIN()
     MOD()     NOT()     OR()
     PI()      POW()     RAD()
     RAND()    ROUND()   SEED()
     SIN()     SQRT()    TAN()
     TRUE()    XOR()

     All math functions  requiring an angle  parameter must  have
     the angle expressed in radian measure.  The RAD() and  DEG()
     functions can be used to convert degrees to radians and vice
     versa.


     1.11  Screen handling functions


     The functions in this section are used for handling screens:
     input, output, box drawing and painting areas as well as for
     loading screens.  There are fifteen functions in this group:

                     Table 1.10: Screen functions

     BEEP()         CODE()         ATTRXY()
     BOX()          CHAR$()        CHARXY$()
     CLS()          DISPLAY()      FILL()
     GOTOXY()       INPUT()        INPUT$()
     INVERSE()      LOADSCR()      PAINT()


     1.12  Miscellaneous functions


     This final group of functions  fall into no clearly  defined
     grouping.  The functions in the group are as follows:









      - RExL  Version 2.10  Copyright 1992, The Software Loft -
       - Appendices.                         Page: 10 -


                 Table 1.11: Miscellaneous functions

     ESCWATCH()     EXACT()        FIND()
     IIF()          IF$()          INIT()
     LEFT$()        LENGTH()       LOAD()
     LOWER$()       MID$()         OUTPUT()
     PAUSE()        PEEK()         PEEKW()
     POKE()         POKEW()        QUIT()
     REPEAT$()      REPLACE$()     RIGHT$()
     SOUNDEX$()     STRING$()      SUFFIX$()
     TRIM$()        UPPER$()       VALUE()
     VERSION()






































      - RExL  Version 2.10  Copyright 1992, The Software Loft -
       - Appendices.                         Page: 11 -








                              Chapter 2

                         The Database Module


     The database function family, the largest single grouping of
     functions, in RExL is fully compatible with the database and
     index file format used in dBase III+.  Since this feature is
     central to RExL,  it's treated on its  own in this  appendix
     which contains  a  complete  introduction  to  the  database
     facilities in RExL.


     2.1  Introduction to Databases


     There are a few terms relating to databases which need to be
     understood before we can move on to the next section.

     Most database formats, including the dBase format used here,
     store their information in fixed fields.  A field is  simply
     storage area of fixed length (known as the field size) which
     is referenced from  RExL through a  field name.   The  field
     names follow the  same conventions as  RExL variable  names,
     save that the  dollar character `$'  is not  used to  denote
     strings. The maximum width of a field name in the dBase file
     format is ten characters.

     Each field can be one of the following four different types:

         o  Numeric: which are used to store numeric  information
            within a fixed number of  digits.  The maximum  field
            width of  a numeric  field is  nineteen digits.    If
            there are decimal  fractions to be  stored, then  the
            field must contain space for a decimal point and  the
            field must also have a fixed decimal fraction  width,
            at most two less than the size of the field.

         o  String: These fields are  used to store character  or
            string information with a maximum field width of  255
            characters.   Because of  the limit  of 80  character
            long strings  in the  current  release of  RExL,  any


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            fields  which  are  wider  then  80  characters   are
            truncated.

         o  Date: This field,  used to store  dates, has a  fixed
            field width  of  8  characters.  Since  there  is  no
            intrinsic  date  type  in   RExL,  date  fields   are
            converted to Julian day numbers, compatible with  the
            date system in use elsewhere in RExL.

         o  Logical: This  final field  type stores  yes-no  type
            logical information.  As with the date fields,  there
            is no intrinsic logical data type in RExL, so logical
            information is  returned as  a  numeric type,  0  for
            False and 1 for True.

     Traditionally, to avoid having to repeat the field types too
     often, the types are abbreviated  to single letter: `N'  for
     numeric, `C'  for  character,  `D'  for  date  and  `L'  for
     logical.  The memo type, which is not commonly used in dBase
     applications, is not supported in RExL.

     Fields  are   collected   together   to  form   records   of
     information.

     Whenever an application  has a database  open for use,  RExL
     maintains a pointer, known as  the record pointer, into  the
     database pointing  at the  record which  all operations  are
     based upon.   When a database  is first  opened, the  record
     pointer is placed at the first record in the database.

     As a  complete example  of a  record structure,  a  customer
     database might be designed as follows:

             Table 2.1: Simple Database Record Structure

     Field Name     Type      Width          Decimal Places
     CUSTNAME       `C'       30
     BALANCE        `N'       8                   2
     MAILSHOT       `L'       1
     NEXTBILL       `D'       8

     The above  database structure  demonstrates the  use of  the
     four different field types.  When databases are created, the
     width of the  logical and date  fields is set  automatically
     and does not have to be specified, the same is true for  the
     decimal places specifier in character field types.




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     Databases are  stored  on  disk with  a  file  extension  of
     ".DBF",  so  the   above  structure  could   be  stored   as
     "CUSTOMER.DBF".


     2.2  Indexes


     Databases are  designed for  the  storage and  retrieval  of
     large amounts of information.  If the information is held in
     an random  manner  (like  a shuffled  pack  of  cards)  then
     searching for a  particular item of  information can  become
     prohibitively slow if there are large numbers of records  in
     the database. The dBase file format specifies a way in which
     indexes may be  generated through  which it  is possible  to
     access information rapidly in a large database.

     An index file, used to store the indexing information, is  a
     separate DOS file (using the extension ".NDX") which is used
     in tandem  with a  database file  to allow  rapid access  to
     specific information.   This  rapid  access is  achieved  by
     storing the indexing information in strict order (alphabetic
     or date or numeric).

     The function of the index file is analogous to a card  index
     system in a library, where  a box contains a sorted list  of
     cards, one  for each  book in  the library.   When  somebody
     looks for a  book, the card  index can  be searched  quickly
     (since it is sorted) and upon finding the wanted book  name,
     the card will contain some information on how to locate  the
     book in  the  library.  In  the same  way,  the  index  file
     contains sorted information  together with  pointers to  the
     records in the database which  match the information in  the
     index file.

     The index  is  generated  using an  index  expression  which
     defines the order in which  the records in the database  are
     to be  retrieved in.   Initially,  when the  index is  first
     created, the index expression  is evaluated for all  records
     in  the  database.    Subsequently,  whenever  a  record  is
     modified, added or removed from  the database, the index  is
     updated to reflect the new contents of the database.

     In the example from the end of the previous section, if  the
     developer decided that  the records were  to be sorted  with
     respect to the name of the customer, then an index could  be
     generated with the  index expression CUSTNAME.   Thus,  when
     the user  of the  end system  wanted  to view  a  particular


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     customer's record, the customer  name would be entered,  the
     name would then  be searched for  in the  index file and  if
     located, would then be returned to the user of the system.

     Since the index  files used by  RExL may  also be used  with
     dBase, Clipper and other packages which adhere to the ".NDX"
     standard, the search expression  must be a dBase  expression
     and not a  RExL expression. The  simplest dBase  expressions
     are simply  field  names  and for  most  purposes,  this  is
     sufficient.  The  RExL call  to generate  the customer  name
     index from the previous paragraph would be as follows:

                 [Expr] DBmkndx("CUSTndx","CUSTNAME")

     This  would  create  an  index  file  called  "CUSTndx.NDX",
     sorting  the  records  with  respect  to  the  field   named
     "CUSTNAME".

     The dBase expression parser built into RExL also copes  with
     more complicated expressions involving dBase function  calls
     and mathematical  operators.   The following  table gives  a
     brief summary  of  the  functions and  operators  supported:
     (dBase  does  not   follow  the   dollar  character   string
     convention, so some of the  functions in the table may  seem
     slightly at odds with the rest of RExL.)

         Table 2.2: dBase Expression Compatibility with RExL

     Function       Meaning
     * + - / ^      Ordinary mathematical operators
     >= <= >
     < = <>         Ordinary relational operators
     DATE()         Return system date as `D'
     DELETED()      Return delete of current record as `L'
     DTOC()         Convert date field to `C'. (not recommended)
     DTOS()         Convert date field to `C'. (recommended)
     CTOD()         Convert string to date.
     IIF()          Equivalent to RExL IIF()
     RECNO()        Returns the current record number
     RECCOUNT()     Returns the number of records in the database
     STR()          Convert number to string as STRING$()
     SUBSTR()       Equivalent to RExL MID$()
     TIME()         Return system time
     VAL()          Convert string to number
     UPPER()        Equivalent to UPPER$()
     SOUNDEX()      Equivalent to SOUNDEX$()




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     The  DTOC()  function  is  supported,  although  is  is  not
     recommended as  an  index  expression function:    Since  it
     returns the  year  as a  two  digits  instead of  four,  the
     function can only cope with  dates in a single century.  The
     DTOS() function returns the date as a string with the format
     "yyyymmdd" (y for year,  m for month and  d for day) and  is
     therefore more suitable for indexing since it can deal  with
     multiple centuries.

     A full description of the database functions above is beyond
     the scope of this introduction.   Consult your dBase  manual
     for precise  details on  how these  functions and  operators
     operate.


     2.3  Using Database Files


     2.3.1  Opening and selecting files

     The handling of database files  is based largely around  the
     concept of  file  handles, which  are  very similar  to  the
     notion of work-spaces used in the dBase documentation.  When
     a data file is opened (using DBusedbf()) or an index file is
     opened (using DBusendx()), a file handle (a reference number
     greater than zero)  is returned to  RExL, through which  the
     application can make references to that file or index.   The
     advantage of the file handle system is that a  theoretically
     arbitrary number of  files and indexes may  be kept open  at
     any one time and any file or index can be referenced through
     its file handle.   In practice  however, the  number of  DOS
     files which may be opened simultaneously is limited (by DOS)
     to twenty,  five of  which cannot  be reassigned,  so up  to
     fifteen database and index files may be open simultaneously.
     (Note that  in  version  2.10,  it  is  possible  to  access
     multiple database  files  without  having to  make  repeated
     calls to DBseldbf().)

     speech For  example, assuming  that  the database  file  and
     index file from the previous sections have been created  and
     exist in the work directory.  The following code can be used
     to open and select the two files:

     [Expr] DBFhandle:=DBusedbf("customer")
     [Expr] NDXhandle:=DBusendx("custndx")
     [Expr] DBseldbf(DBFhandle)
     [Expr] DBselndx(NDXhandle)
     [Expr] DBtop()


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     The first line opens the  customer database and returns  the
     database file handle  which RExL has  assigned to  it.   The
     second line opens the index file and assigns the index  file
     handle  to  NDXhandle.    Next,  the  database  file  opened
     previously is selected  or made  the current  work file,  at
     this point the records are  not yet sorted, since the  index
     file has not been selected. The fourth line applies the sort
     order to the current database.  Finally, the current  record
     number is set to the first record in the database (it's good
     practice always to know what the current record is).

     In a real-life application,  the return values of  DBFhandle
     and NDXhandle would  be checked for  validity, to make  sure
     that they had been opened correctly.

     2.3.2  Reading and writing to files

     There are two  ways in which information  can be written  to
     and read  from  database  files.    The  first  method  uses
     specific functions to read and  write database files and  is
     compatible with RExL version 2.00, but is cumbersome to use.
     The second, newer and more efficient method is to use the  @
     notation introduced  in  version  2.10, generally  known  as
     `direct field access'.  The  next two subsections deal  with
     both methods.

     2.3.2.1  Using functions

     There are four  functions which are used  to read and  write
     the currently selected database file.  These are DBappend(),
     used to  append a  blank  record to  the  end of  the  file,
     DBreplace() to write to the file and DBrnum() and  DBrstr$()
     to read from it.

     a) Writing to a file

     The DBreplace() command requires  two parameters, the  first
     is the field name while  the second parameter, which may  be
     either string or  numeric in  type, specifies  the value  to
     place into the  field.  This function  is equivalent to  the
     dBase  command  REPLACE.    The  action  of  DBreplace()  is
     slightly more complicated than it may at first seem.   First
     of all, if the field is numeric and the number being written
     is too wide  for the field,  then the field  will be set  to
     zero.  If the field  is string and the string being  written
     is too long, then it will be truncated.




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     It is also possible to write string values to numeric fields
     (although the strings must clearly contain numeric value for
     this to work) and to write numeric values to string  fields,
     where \rexl\  will  attempt to  convert  the number  into  a
     string before writing  it to  the field.   Generally,  these
     cross-breed replacements should be avoided where possible.

     For logical fields, a value of \true\ will be written to the
     field if the second parameter is numeric and non zero, or if
     it is string and equal to  "Y" "y" "T" or "t". In all  other
     cases, the value written will be  false.  If the field is  a
     date field,  then the  second parameter  will be  internally
     converted to a date number and written to the field.

     The DBappend()  command is  used to  place a  new and  blank
     record at the end of  the currently selected database  file.
     If this  has been  performed successfully,  then the  record
     pointer will be placed there.

     b) Reading from a file

     The two functions DBrnum() and DBrstr$() are used to extract
     information from the current  record.  DBrnum() returns  the
     field expressed as a number, where possible, while DBrstr$()
     returns the field  expressed as  a string,  which is  always
     possible.

     DBrstr$() is subject to much the same caveats as DBreplace()
     as regards reading strings: If  the field contains a  string
     longer than 80  characters, then it will  be truncated.   As
     with DBreplace()  it is  possible, but  not recommended,  to
     perform cross-breed reading, from  numeric fields to  string
     variables and string fields to numeric values.

     When the two  field reading  functions are  applied to  date
     fields, the  return value  will be  the value  of the  field
     converted to the appropriate  type.  Thus DBrstr$()  applied
     to a date  field will return  a date  string in the  current
     date format, while  a call to DBrnum()  applied to the  same
     field  will  return  the  Julian  day  number  of  the  date
     specified in the field.

     The two functions  can also  be applied  to logical  fields,
     where DBrnum() will return 1.0 for a true value in the field
     and 0.0 for a false value. DBrstr$ will return "Y" for  true
     and "N" for false.




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     2.3.2.2  Direct field access

     a) Basics

     The `@' operator is used to access database fields  directly
     and is mapped  internally to a call  to either DBrstr$()  or
     DBrnum().  There  are two forms of  the operator, the  first
     which corresponds  to DBrstr$(),  is `@$'  and is  used  for
     accessing the value  of a field  as a  string.  The  second,
     taking the place of the DBrnum() function, is the `@' symbol
     on its own and is used to access  the value of a field as  a
     string.

     To use the access operator, it is simply placed at the start
     of the database  field name. For  example, to  read a  field
     called `CUSTNO', and  assign its  value to  a variable,  the
     following expression could be written:

               [Expr] customer:=@custno

     Similarly, the contents of a character field may be returned
     to a string as follows:

               [Expr] name$:=@$name

     where `NAME' is a character field.

     As with  the read  functions  DBrstr$() and  DBrnum(),  full
     cross-type read operations  are permitted.   This again,  is
     most noticeable  when  using  date fields:    using  the  @$
     operator on a  date field will  return a  date string  while
     using the @  operator will return the  Julian Day Number  of
     the date specified in the field.

     Information may  also be  written to  the database  file  in
     exactly the same manner as it is read, so that a string  may
     be assigned to a string field using:

               [Expr] @$name:="Joe Smith"

     and to a numeric field using:

               [Expr] @age:=24


     b) Accessing multiple database files




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     The syntax of  the @  operator can  be extended  to allow  a
     single   token   to    access   multiple   database    files
     simultaneously.   The  general  format  of  the  extended  @
     operator is:

               Numeric value:      @<num_variable>.<field>
     and
               String value:       @$<num_variable>.<field>

     where <num_variable>  is a  simple (ie.  non-array)  numeric
     variable whose value is the file handle for a database file,
     the dot is a full stop character and <field> is the name  of
     the field whose value is being assigned or retrieved.

     If, for  example,  two database  files  had been  opened  as
     follows:

               db_one:=dbusedbf("customer")
               db_two:=dbusedbf("orders")

     then a character  field, NAME, in the  customer file can  be
     accessed using the expression:

               @$db_one.name

     while a numeric field `ORDERVAL'  in the orders file can  be
     accessed using:

               @db_two.orderval

     Note again  that only  simple numeric  variables can  appear
     between the  @symbol  and the  full  stop.   Direct  numeric
     values, expressions and arrays are not allowed.

     This extension to  the format of  the @  operator is a  very
     powerful feature and extends  considerably the power of  the
     language in interrogating database files.  In particular, it
     does away with  the need  to select  and reselect  different
     database files in  order to use  them and  also reduces  the
     likelihood of introducing bugs by having the wrong  database
     open at a particular time.

     Perhaps its  greatest benefit  is that  it allows  a  single
     screen to access  multiple database  files, something  which
     was extremely cumbersome in the previous version.





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     2.3.3  Moving around in a file

     There are  six functions  used to  move the  record  pointer
     within the file  from one record  to another.   With all  of
     these functions, the movement is carried out with respect to
     the current index file, if one is open.

     The first two  functions, DBtop() and  DBbottom(), move  the
     record pointer to  the first and  last records  in the  file
     while DBprev()  and  DBnext()  move the  previous  and  next
     records.

     DBskip() will skip, forward or backward through the file  by
     a specified number of  records.  If an  index is open,  then
     index ordering will  be used.  DBgo() is  used to  go to  an
     absolute record  number, but  unlike DBskip(),  it does  not
     obey any index.

     There are two functions used to find information in a  file.
     The first of these, DBlocate() is used to locate a  specific
     string or  number  in a  database  field (date  and  logical
     fields are  not currently  supported by  DBlocate()).   This
     function is based upon the LOCATE command in dBase.

     In a large file, locating a record may take some time, since
     it must read  and check every  record to  see if the  search
     condition is  met.    It  is  therefore  usually  better  to
     generate an index and use  it with the DBseek() function  to
     find information.  DBseek(), based upon the SEEK command  in
     dBase, is used  to find information  in a  file through  its
     current index.   Because the index  file is  kept in  strict
     order, the seek can be performed very rapidly.

     2.3.4  Miscellaneous functions

     2.3.4.1  Statistical analysis of data

     There  are  seven  functions,  based  largely  upon  similar
     functions in Lotus 123, which  can be used to perform  basic
     statistical analysis upon the data in a database file.   The
     functions, covered fully in  the function reference, are  as
     follows:  DBavg(),  DBcount(),  DBstd(),  DBsum(),  DBvar(),
     DBmax() and DBmin().

     2.3.4.2  Deletion of information

     Four  functions  are   used  to  control   the  removal   of
     information  from  database  files.  These  are  DBdelete(),


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     DBdeleted(),  DBpack()  and  DBrecall().  When  a  call   to
     DBdelete() is made to delete a record, the record is  marked
     for deletion  and  not  physically removed  from  the  file.
     Thus, a further call to DBrecall() can be made to unmark the
     record to return it to its normal status.

     The DBdeleted() function can be used to determine whether  a
     record has  been  marked  for deletion  or  not,  while  the
     DBpack() function will permanently  remove all records  from
     the database which have been marked for deletion.

     2.3.4.3  Other functions

     There are nine  other functions  in the  database packed  in
     RExL which are used to  perform maintenance on the  database
     file itself.  These functions are

             Table 2.3: Miscellaneous Database Functions

     Function       Use
     DBcountflds()  Returns the number of fields in the database
     DBexact()      Turn database case sensitivity on and off
     DBmkdbf()      Create a database
     DBmkndx()      Create an index file
     DBreindex()    Re-create an index file
     DBreccount()   Return the number of records in a database
     DBrecno()      Return the current record number
     DBstruct()     Return the current database structure
     DBzap()        Remove all records from a database

     By default, the database module is case sensitive,  contrary
     to the rest of RExL.   This is for reasons of  compatibility
     with dBase  which  is  case  sensitive.    However,  if  the
     database files  will  not  be used  with  dBase,  then  case
     sensitivity can  be  safely set  to  off.   If  index  files
     generated with  case sensitivity  off are  used with  dBase,
     then the  results are  unpredictable, since  the index  file
     format is not identical.












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                              Chapter 3

                          Function Reference


     --------------------------------------------------------------------

     ABS(number)

     ABS()  returns  the  absolute  value  (or  modulus)  of  the
     parameter.

     Returns:  The parameter expressed as a positive number

     See also: FLOOR CEIL ROUND

     Example:  val:=ABS(-10) Returns 10 to the variable val

     Example:  val:=ABS(10) Returns 10 to the variable val

     --------------------------------------------------------------------

     ACOS(number)

     Returns the arc-cosine of the parameter. The return value is
     expressed in radians. To convert radians to degrees, use the
     DEG() function. The value returned  will be in the range  of
     zero radians to pi radians.

     Returns:  A number

     See also: ASIN ATAN DEG

     Example:  val:=ACOS(0.5) Returns 1.04719775 radians to val.

     --------------------------------------------------------------------
     AND(log1,log2)

     AND() performs a logical AND operation upon the two  logical
     parameters passed to the function and returns the result  of
     the  test.  The  function  returns  True  if  both   logical
     parameters are True otherwise it returns False.


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     Returns:  A number

     See also: NOT EQV XOR OR IMP

     Example:  val:=AND(TRUE(),FALSE())

               Returns False to to the variable val.

     ---------------------------------------------------------------------
     ARavg(num[#],start,end)

     ARavg() returns  the  average of  the  elements of  the  one
     dimensional numeric  array parameter  between the  specified
     start and end elements. Note that unlike ARcount(),  ARavg()
     takes account of zero values in its calculation.

     In order  to  determine if  the  value  for the  average  is
     meaningful, you should also calculate the standard deviation
     of the data, using the ARstd() function.

     Returns:  A number

     See also: ARcount ARsum DBavg

     Example:  avg:=ARavg(score[#],0,9)

               Returns, to  the  variable  avg,  the  average  of
     score[#] over the first to tenth elements inclusive.

     ---------------------------------------------------------------------
     ARcount(numstr[#],start,end)

     ARcount() counts the elements  of the one dimensional  array
     parameter which are  nonzero, if  the array  is numeric,  or
     nonempty, if  the array  is of  type  string. The  count  is
     performed between  the  specified  start  and  end  elements
     inclusive.

     Returns:  The number of nonempty elements

     See also: ARavg ARsum DBcount

     Example:  n:=ARcount(name$[#],0,2)

               Returns, to the variable n, the number of nonempty
     strings in the string array, name$[#], between the first and
     third elements.



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     ---------------------------------------------------------------------
     ARinit(numstr[#])

     ARinit() clears all  elements of an  array, setting  numeric
     array values  to  0  and  string array  values  to  "".  The
     function accepts arrays of any dimension.

     Returns:  True

     Example:  ARinit(name$[#])

               Resets all elements of name$[#] to "".

     ---------------------------------------------------------------------

     ARmax(num[#],start,end)

     ARmax() returns  the  maximum  value of  the  numeric  array
     parameter between the specified start and end elements.

     Returns:  A number

     See also: ARcount ARmin

     Example:  mmax:=ARmax(score[#],0,9)

               Returns, to the variable  mmax, the maximum  value
     of the  numeric  array  score[#] over  the  first  to  tenth
     elements inclusive.

     ---------------------------------------------------------------------

     ARmin(num[#],start,end)

     ARmin() returns  the  minimum  value of  the  numeric  array
     parameter between the specified start and end elements.

     Returns:  A number

     See also: ARcount ARmax

     Example:  mmin:=ARmin(score[#],0,9)

               Returns, to the variable  mmin, the minimum  value
     of the  numeric  array  score[#] over  the  first  to  tenth
     elements inclusive.

     ---------------------------------------------------------------------


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     ARsize(numstr[#],dimension)

     ARsize() returns the  size of  the specified  array, in  the
     specified dimension. The dimensions are defined as follows:

                  Table 3.1: ARsize() Input Indexing

     Dimension           Meaning
          1              x dimension (first dimension)
          2              y dimension (second dimension)
          3              z dimension (third dimension)

     Returns:  The size of the specified dimension

     Example:  ARsize(name$[#],1)

               Returns the size of the first, or x, dimension  of
     the string array name$[#].

     ---------------------------------------------------------------------

     ARstd(num[#],start,end)

     ARstd() returns  the population  standard deviation  of  the
     values  in  num[#]  between  the  specified  start  and  end
     elements,  inclusive.  This  function  uses  the  n   method
     (biased)  to  determine  the   standard  deviation  of   the
     population data.

     The standard deviation can be thought of as a measure of the
     validity of the average of the set of data. If the deviation
     is small,  then the  average is  good, if  the deviation  is
     large, then the value for the average could be meaningless.

     Returns:  A number

     See also: ARvar ARavg ARcount

     Example:  std:=ARstd(score[#],0,9)

               Returns,  to  the   variable  std,  the   standard
     deviation of the value of  score[#] over the first to  tenth
     elements inclusive.

     ---------------------------------------------------------------------

     ARsum(num[#],start,end)



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     ARsum() returns the summation of the elements in the  num[#]
     array  between  the  specified   start  and  end   elements,
     inclusive.

     Returns:  A number

     See also: ARvar ARstd ARavg ARcount

     Example:  sum:=ARsum(score[#],0,9)

               Returns, to the variable sum, the sum of the first
     ten elements of the array score[#]

     ---------------------------------------------------------------------

     ARvar(num[#],start,end)

     ARvar() returns  the population  variance of  the values  in
     num[#]  between  the  specified  start  and  end   elements,
     inclusive. This  function  uses  the n  method  (biased)  to
     determine the standard deviation of the population data.

     ARvar() is  also  equal  to the  sqaure  of  the  population
     standard deviation of the array, as returned by the  ARstd()
     function.

     Returns:  A number

     See also: ARstd ARavg ARcount

     Example:  var:=ARvar(score[#],0,9)

               Returns, to  the    variable var,  the  population
     variance of the value of  the array score[#] over the  first
     to tenth elements inclusive.

     ---------------------------------------------------------------------

     ASIN(number)

     Returns the inverse sine of the parameter. The return  value
     is expressed in radians and  can range in value from from  -
     pi/2 to pi/2.

     Returns:  A number

     See also: ACOS, ATAN



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     Example:  val:=ASIN(0.5)

               Returns 0.52335987756 radians to val

     ---------------------------------------------------------------------

     ATAN(number)

     Returns the  inverse tangent  of the  parameter. The  return
     value is expressed  in radians and can  range from -pi/2  to
     pi/2.

     Returns:  A number

     See also: ASIN, ACOS

     Example:  val:=ATAN(0.5)

               Returns 0.463647609 radians to val

     ---------------------------------------------------------------------

     ATTRXY(xpos, ypos)

     This function returns the attribute (or color value) of  the
     character displayed at position (xpos,ypos).  The entry  for
     BOX() has a table of color values which can be used to  work
     out the actual colors used on the screen.

     Returns:  A number between 0 and 255

     See also: PAINT CHARXY

     Example:  col:=ATTRXY(10,10)

               Returns the attribute  value of  the character  at
     screen co-ordinates (10,10).

     ---------------------------------------------------------------------
     BEEP(frequency,time)

     Sounds the  computer's internal  speaker. The  frequency  is
     measured in  Hertz  and  time  is  measured  in  millseconds
     (thousandths of a second). If the time parameter is set to 0
     then the  sound  will be  generated  until another  call  to
     BEEP() is made.  If time  set to -1, the beeper is  switched
     off. The following  is a  table of  natural frequencies  and
     their corresponding musical notes.   time can be as long  as


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     65534 milliseconds, or  about 65  seconds.   A frequence  of
     440Hz is A below Middle C.

                    Table 3.2: BEEP() Frequencies

       Note   Frequency Note   Frequency
          C    130.810   C    523.250
          D    146.830   D    587.330
          E    164.810   E    659.260
          F    174.610   F    698.460
          G    196.000   G    783.990
          A    220.000   A    880.000
          B    246.940   B    987.770
          C    261.630   C    1046.500
          D    293.660   D    1174.700
          E    329.630   E    1318.500
          F    349.230   F    1396.900
          G    392.000   G    1568.000
          A    440.000   A    1760.000
          B    493.880   B    1975.500

     Returns:  True

     Example:  BEEP(523.250,1000)

               Sounds the beeper at middle C for one second.

     ---------------------------------------------------------------------

     BOX(x, y, w, h, color, type)

     Draws a character box on screen. The parameters specify  the
     coordinates of the top left corner and the desired width and
     height of the box. The sixth parameter specifies the type of
     box: type is zero for a single line box and one for a double
     line box. The color  parameter specifies the attribute  with
     which the box is to be  drawn. The interior of the box  will
     be filled with spaces.  Attributes are calculated by  adding
     the color number of the background (paper color) to that  of
     the foreground  (ink) color.  The  following are  the  color
     numbers:









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                   Table 3.3: Color Attribute Codes

     Color     Foreground     Background
     Black          0              0
     Blue           1              16
     Green          2              32
     Cyan           3              48
     Red            4              64
     Magenta        5              80
     Brown          6              96
     Light Gray     7              112
     Dark Gray      8              (128)
     Light Blue     9              (144)
     Light Green    10             (160)
     Light Cyan     11             (176)
     Light Red      12             (192)
     Light Mgnta    13             (208)
     Yellow         14             (224)
     White          15             (240)
     Blink          128            -

     If the  last  screen  displayed  during  execution  had  the
     flash-intensity bit set to `intensity', then a further eight
     background colors, indicated above by the bracketed numbers,
     are available, at  the expense  of blinking.  Note that  the
     background colors are derived from the foreground colors  by
     multiplying by sixteen.

     Returns:  True

     See also: PAINT INVERSE

     Example:  BOX(0,0,79,24,31,1)

               Draws a double lined white on blue box around  the
     screen.

     ---------------------------------------------------------------------

     BTand(bit1,bit2)

     BTand() performs  a  bitwise  and  operation  upon  the  two
     parameters. As with all the bit manipulation functions,  the
     values are  internally converted  to sixteen  bit words,  so
     numbers greated than 65535 are treated as 65535 and  numbers
     less than 1 are treated as zero.

     Returns:  A number between 0 and 65535


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     See also: BTnot BTor BTshl BTshr BTxor

     Example:  bt:=BTand(6,4)

               Returns a value of 4 to the variable bt

     ---------------------------------------------------------------------

     BTnot(bits)

     BTnot() performs  a  bitwise 16  bit  NOT operation  on  its
     numeric parameter.

     Returns:  A number between 0 and 65535

     See also: BTand BTor BTshl BTshr BTxor

     Example:  bt:=BTnot(65535) Returns  a  value  of  1  to  the
     variable bt

     ---------------------------------------------------------------------

     BTor(bit1,bit2)

     BTor() performs a bitwise or operation upon two  sixteen-bit
     parameters.

     Returns:  A number between 0 and 65535

     See also: BTnot BTand BTshl BTshr BTxor

     Example:  bt:=BTor(6,4)

               Returns a value of 6 to the variable bt

     ---------------------------------------------------------------------

     BTshl(bit1,bit2)

     BTshl() performs a bitwise left shift of the first parameter
     by the number of bits specified by the second parameter. The
     return value of BTshl() is equivalent to the product of  the
     first parameter and  two raised to the  power of the  second
     parameter.

     Returns:  A number between 0 and 65535

     See also: BTnot BTor BTand BTshr BTxor


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     Example:  bt:=BTshl(2,2)

               Returns a value of 8 to the variable bt

     ---------------------------------------------------------------------

     BTshr(bit1,bit2)

     BTshr()  performs  a  bitwise  right  shift  of  the   first
     paremeter by  the number  of bits  specified by  the  second
     parameter. The return value of BTshr() is equivalent to  the
     quotient of the first parameter divided by two raised to the
     power of the second parameter.

     Returns:  A number between 0 and 65535

     See also: BTnot BTor BTshl BTand BTxor

     Example:  bt:=BTshr(8,2)

               Returns a value of 2 to the variable bt

     ---------------------------------------------------------------------

     BTxor(bit1,bit2)

     BTxor() performs a bitwise  exclusive or operation upon  the
     two sixteen bit parameters.

     Returns:  A number between 0 and 65535

     See also: BTnot BTor BTshl BTshr BTand

     Example:  bt:=BTxor(32767,16)

               Returns a value of 32751 to the variable bt

     ---------------------------------------------------------------------

     CEIL(number)

     CEIL()  returns  the  smallest   number  greater  than   the
     parameter.

     Returns:  A number

     See also: FLOOR



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     Example:  a:=CEIL(5.5)

               Returns the value 6.0 to the variable a.

     ---------------------------------------------------------------------

     CHAR$(asciicode)

     Returns the ASCII character whose ASCII code is asciicode.

     Returns:  A one-character string

     See also: CODE

     Example:  t$:=CODE(65)

               Returns the letter "A", whose ASCII code is 65, to
     the variable t$.

     ---------------------------------------------------------------------

     CHARXY$(xpos,ypos)

     CHARXY$() returns the ASCII code of the character  displayed
     at the  screen coordinates  (xpos,ypos). The  top left  hand
     corner of the screen is position (0,0) and the bottom  right
     corner is position (79,24).

     Returns:  A number

     See also: CHAR$ ATTRXY

     Example:  asciival:=CHARXY(0,0)

               Assigns the ascii value of the character displayed
     at position (0,0), the top left corner.

     ---------------------------------------------------------------------

     CLS()

     CLS() clears the screen. The screen will be set to white  on
     black and the cursor  position will be set  to the top  left
     hand corner.

     Returns:  True

     Example:  CLS()


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               Clears the screen.

     ---------------------------------------------------------------------
     CODE(character$)

     Returns the ASCII  code of the  first letter  of the  string
     parameter.  See appendix F for a table of ASCII codes.

     Returns:  A number

     See also: CHAR$

     Example:  asciival:=CODE("A")

               Returns 65  to asciival,  the ASCII  code for  the
     letter "A".

     ---------------------------------------------------------------------

     COS(angle)

     Calculates the  cosine  of the  angle,  where the  angle  is
     measured in radians. The return  value will be in the  range
     of -1  to 1.  The ACOS()  function  is used  to convert  the
     cosine of an angle to the angle.

     Returns:  A number

     Example:  val:=COS(0.5)

               Returns 0.8775825619 to the variable val.

     ---------------------------------------------------------------------

     CTERM(rate, end, start)

     CTERM() returns the number of compound periods it would take
     for the start value, at the specified interest rate to  grow
     to the end  value. The  rate should  be the  specified as  a
     decimal fraction rather than a percentage.

     Returns:  A number

     See also: FV PMT PV RATE TERM

     Example:  yrs:=CTERM(0.1,100,10)




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       - Appendices.                         Page: 35 -


               Returns 24.1588 interest  periods to the  variable
     yrs, indicating that it would  take 24 years and two  months
     for an amount of $10  to grow to $100 at  a rate of 10%  per
     annum.

     ---------------------------------------------------------------------

     DBappend(none)

     Adds a new blank record to the end of the currently selected
     database file.

     Returns:  True if successful, False otherwise

     See also: DBreplace

     Example:  DBappend()

     ---------------------------------------------------------------------

     DBavg(field$,start,end)

     DBavg() returns the average of  the fields of the  currently
     open database, between the specified start and end   fields.
     (Note that  unlike  the  function DBcount(),  DBavg()  takes
     account of zero values). Note that the specified field  must
     be numeric and not string.

     Returns:  A number

     See also: DBcount DBsum DBavg

     Example:  avg:=DBavg("AMOUNT",1,10)

               avg is assigned the average of the field  "AMOUNT"
     in the current database between the first and tenth  records
     inclusive.

     ---------------------------------------------------------------------

     DBbottom()

     Places  the  record  pointer  at  the  last  record  in  the
     currently selected database file in index order.

     Returns:  True if successful, False otherwise

     See also: DBtop


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     Example:  DBbottom()

               This will go  to the  last record  in the  current
     database using the current index.

     ---------------------------------------------------------------------

     DBcloseall()

     Closes all  open  database and  index  files. It  is  better
     practice to close each file separately using DBclosedbf().

     Returns:  True if successful, False otherwise.

     Example:  DBcloseall()

     ---------------------------------------------------------------------

     DBclosedbf()

     Closes the currently  open database file.  Any active  index
     files will also  be closed.  It will  fail if  there are  no
     files open.

     Returns:  True if successful, False otherwise

     See also: DBcloseall DBclosendx

     Example:  DBclosedbf()

     ---------------------------------------------------------------------

     DBclosendx(num)

     Closes the index  file addressed  by the  index file  handle
     num.

     Returns:  True if successful, False otherwise

     See also: DBusendx

     Example:  DBclosendx(names)

               Closes the index file  linked to the index  handle
     names.

     ---------------------------------------------------------------------



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     DBcount(field$,start,end)

     DBcount()  counts  the  fields   of  the  currently   active
     database,  between  the  specified  start  and  end  records
     elements, which are  nonzero, if  the field  is numeric,  or
     nonempty, if the field is of type string.

     Returns:  The number of nonempty fields

     See also: DBavg DBsum DBcount

     Example:  n:=DBcount("DONATION",1,DBreccount())

               n  is  assigned  the  number  of  records  in  the
     currently open database which have nonempty DONATION fields.

     ---------------------------------------------------------------------

     DBcountflds()

     DBcountflds() returns the  number of fields  in a record  in
     the currently selected database file. This function is  most
     useful for determining if a call to DBstruct() would  result
     in an error from too many fields in the database.

     Returns:  A number

     Example:  ARsize(name$[#],1)<DBcountflds()

               This line fails if the size of the name$[#]  array
     is smaller than the number  of fields in the database.  This
     is a  useful check  to perform  whenever an  application  is
     dealing with unknown databases.

     ---------------------------------------------------------------------

     DBdelete()

     Marks the current record in the currently open database  for
     deletion. It may  be physically deleted  using the  DBpack()
     command and  recalled  from  deletion using  the  DBrecall()
     function.

     Returns:  True if successful, False otherwise

     See also: DBpack DBrecall DBdeleted

     Example:  DBdelete()


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       - Appendices.                         Page: 38 -


     ---------------------------------------------------------------------

     DBdeleted()

     Returns True if  the current database  record is marked  for
     deletion.

     Returns:  True if marked, False otherwise

     See also: DBpack DBrecall DBdelete

     Example:  DBdeleted()

     ---------------------------------------------------------------------

     DBexact(number)

     DBexact() switches case sensitivity off, if the parameter is
     zero or  on for  nonzero values.  By default,  the  database
     module is  case sensitive,  to maintain  compatibility  with
     dBase index files.  If you intend to  use the same  database
     and  index  files   with  dBase,  you   should  leave   case
     sensitivity on.

     Returns:  True

     Example:  DBexact(0)

               Switches case sensitivity  off, to follow the RExL
     convention.

     ---------------------------------------------------------------------
     DBgo(recnum)

     DBgo() moves  the current  record pointer  to record  number
     recnum in  the  currently  selected database.  The  function
     returns false if  the specified record  number is less  than
     one or greater than the number of records in the database.

     Returns:  True if successful, False otherwise

     See also: DBrecno DBskip

     Example:  DBgo(DBreccount())

               This positions  the  record  pointer at  the  last
     record in the currently selected database. This performs the
     same action as DBbottom().


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       - Appendices.                         Page: 39 -


     ---------------------------------------------------------------------

     DBlocate(field$,numstr,start,direction)

     DBlocate() will locate  the number or  string numstr in  the
     field  field$,  in  the  currently  open  database.   Unlike
     DBseek(), it does not  require an index to  be open and  the
     search can be  carried out  on any  field in  the file.  The
     search starts from record number start and moving  backwards
     if direction is negative and  forwards if zero or  positive.
     In the  current release,  only numeric  and string  database
     fields may be used with DBlocate().

     Returns:  True if located successfully, False otherwise

     See also: DBseek

     Example:  DBlocate("CUST","MCCA01",0,1)

               Tries to  find the  string  "MCCA01" in  the  CUST
     field of the current database starting from the first record
     in the database moving forward.

     Example:  DBlocate("CUSTNUM",1234)

               Tries to find the number 1234 in the field CUSTNUM
     in the current database.

     ---------------------------------------------------------------------

     DBmax(field$,start,end)

     DBmax()  returns  the  maximum  value  of  the  field  named
     "field$" in  the  current  database, between  the  specified
     start and end records. Note that the specified field must be
     numeric and not string.

     Returns:  A number

     See also: DBcount DBsum DBavg DBmin

     Example:  q:=DBmax("PAYMENT",1,10)

               Returns, to the variable  q, the maximum value  of
     the PAYMENT field in the current database between the  first
     and tenth records, inclusive.

     ---------------------------------------------------------------------


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       - Appendices.                         Page: 40 -


     DBmin(field$,start,end)

     DBmin() returns the minimum value of the field specified  by
     field$ in the current database, between the specified  start
     and end records. The specified field must be numeric.

     Returns:  A number

     See also: DBcount DBsum DBavg DBmax

     Example:  q:=DBmin("PAYMENT",1,10)

               Returns, to the variable  q, the minimum value  of
     the PAYMENT field in the current database between the  first
     and tenth records, inclusive.

     ---------------------------------------------------------------------

     DBmkdbf(name$,num,n$[#],t$[#],len[#],dec[#])

     DBmkdbf() creates a new database file name$ with num  number
     of fields. The specifictions for the fields are contained in
     the arrays passed  to the  function: The  first array  n$[#]
     specifies the list  of field names in  the file, the  second
     t$[#] defines the  types of  the fields  ("C" for  character
     fields, "N" for  numeric, "D" for date  and "L" for  logical
     fields), the third array contains field widths and the final
     array specifies  the number  of decimal  places for  numeric
     fields.

     Returns:  True if successful, False otherwise.

     Example:  DBmkdbf("NEWFILE",4,n$[#],t$[#],len[#],dec[#])

               Creates a database  called NEWFILE.DBF, with  four
     fields as defined by the arrays.

     ---------------------------------------------------------------------

     DBmkndx(indexname$,keyname$)

     Creates an index file  for the currently selected  database.
     The first parameter  specifies a  file name  and the  second
     specifies a field name to index it on. The file extension of
     the index file will be  ".NDX". irrespective of whether  one
     was specified or not.  The index will be opened after it has
     been created.



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       - Appendices.                         Page: 41 -


     Returns:  True if successful, False otherwise

     See also: DBusendx

     Example:  idx:=DBmkndx("test","name")

               Creates an  index called  "test.ndx" which  orders
     the currently selected database on the NAME field.

     ---------------------------------------------------------------------

     DBnext()

     Increments the record pointer to  the next record, in  index
     order if an index  is open. It will  return an error if  the
     record pointer is already at the end of the file.

     Returns:  True if successfully moved, False otherwise

     See also: DBprev

     Example:  DBnext()

               Goes to the  next record in  the current  database
     using the current index.

     ---------------------------------------------------------------------

     DBpack()

     Removes all the records in the currently open database  file
     which have  been marked  for deletion  using the  DBdelete()
     function.    Deleted  records   cannot  be  recovered   with
     DBrecall() after a call to this function has been made.

     Returns:  True if successful, False otherwise

     See also: DBrecall DBdelete

     Example:  DBpack()

               Deletes all records marked for deletion.

     ---------------------------------------------------------------------

     DBprev()




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       - Appendices.                         Page: 42 -


     Decrements the  current  record  pointer  to  point  at  the
     previous record,  in index  order if  one is  open. It  will
     return an  error if  the record  pointer is  already at  the
     beginning of the file.

     Returns:  True if successfully moved, False otherwise

     See also: DBnext

     Example:  DBprev()

     ---------------------------------------------------------------------

     DBrecall()

     Undoes the  effect of  a DBdelete()  call by  resetting  the
     deletion marker on the current  record. The record will  not
     then be removed in a subsequent call to DBpack().

     Returns:  True

     See also: DBpack DBdelete

     Example:  DBrecall()

               Recalls the current record from deletion.

     ---------------------------------------------------------------------

     DBreccount()

     Returns the  number of  records  in the  currently  selected
     database.

     Returns:  A number

     See also: DBrecno DBgo

     Example:  maxrec:=DBreccount()

               Sets the variable maxrec to the number of  records
     in the database.

     ---------------------------------------------------------------------

     DBrecno()




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       - Appendices.                         Page: 43 -


     Returns the number  of the current  record in the  currently
     selected database.

     Returns:  A number

     See also: DBreccount DBgo

     Example:  currec:=DBrecno()

               Sets the  variable  currec  to the  current  recor
     number.

     ---------------------------------------------------------------------

     DBreindex(indexhandle)

     Reindexes an  index  file  addressed  by  indexhandle.  This
     command is used if you  have an index file which has  become
     out of date  with respect  to its  corresponding data  file,
     caused by adding or deleting records from the database while
     having the index closed.

     Returns:  True if successful, False otherwise

     See also: DBmkndx

     Example:  DBreindex(ihandle)

               Reindexes the index file  referenced by the  index
     handle ihandle.

     ---------------------------------------------------------------------

     DBreplace(fieldname$, numstr)

     Writes the string or number numstr to the field specified by
     fieldname$. The value will be stored accurate to the  number
     of places available in  the data file, or  as zero if it  is
     too large.  See the  `Introduction  to Databases'  for  more
     information on how this function behaves.

     Returns:  True if successful, False otherwise

     See also: DBrstr$ DBrnum

     Example:  DBreplace("custcode",10)

               Writes the value 10 to the CUSTCODE field.


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       - Appendices.                         Page: 44 -


     Example:  DBreplace("custname","RH")

               Writes the string "RH" to the CUSTNAME field.

     ---------------------------------------------------------------------

     DBrnum(fieldname$)

     Returns the value of the field named fieldname$ as a number.
     See the `Introduction to Databases' for more information  on
     how this  function behaves.  This function  is included  for
     compatibility with  earlier versions  of RExL  and has  been
     superceded by the `@' and `@$' operators.

     Returns:  A number

     See also: DBrstr$

     Example:  a:=DBrnum("custcode")

               Returns the  value of  the field  CUSTCODE to  the
     variable a.

     ---------------------------------------------------------------------

     DBrseek(dbf_handle, numstr)

     DBrseek() finds  an  index key  value  of the  type  variant
     parameter numstr  in the  database  file referenced  by  the
     handle dbf_handle. If  the seek  value in  numstr is  longer
     than the index key expression,  then the seek value will  be
     truncated. If the database file has no index attached to  it
     then an error will be generated and the function will fail.

     This function is extremely powerful as it adds a measure  of
     relational database capability to RExL.

     Returns:  1 if a successful seek was performed
               2 if a partial match was located
               0 if no match could be found.

     See also: DBlocate DBseek

     Example:  [Expr] DBseek(cust, "Robin")

               Positions the record pointer  at the first  record
     in the database  file referenced  by the  file handle  cust,
     which contains a key field value of "Robin".


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       - Appendices.                         Page: 45 -


     Example:  [Expr] DBseek(orders,@cust.orderno)

               Finds the first occurrence  (in the database  file
     referenced by the  file handle orders) of  the value in  the
     orderno field of the database file referenced by the  handle
     cust. This   example illustrates  the  power  of  DBrseek(),
     where the  contents  of one  database  can   be   used    to
     retrieve  information immediately from another database.

     ---------------------------------------------------------------------

     DBrstr$(fieldname$)

     Returns the value of the field named fieldname$ as a string.
     See the `Introduction to Databases' for more information  on
     how this  function behaves.  This function  is included  for
     compatibility with  earlier versions  of RExL  and has  been
     superceded by the `@' and `@$' operators.

     Returns:  A string

     See also: DBrnum

     Example:  a$:=DBrstr$("custname")

               Returns the  value of  the field  CUSTNAME to  the
     variable a$.

     ---------------------------------------------------------------------

     DBseek(numstr)

     Finds a  matching key  value in  a numeric  or string  field
     using the  current index.  A value  will be  found which  is
     accurate to the fields width. If there is no index file open
     and selected, then this function call will fail.

     Returns:  1 if  successful, 2  for partial  match, 0  if  no
     match

     See also: DBlocate

     Example:  DBseek(37.2)

               Positions the record pointer  at the first  record
     in the database which contains a key field value of 37.2.

     Example:  DBseek("String")


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               Finds the first occurrence of the string  "String"
     in the index key field.

     ---------------------------------------------------------------------

     DBseldbf(filehandle)

     Selects the database file addressed by filehandle and  makes
     it the current database.   The file handle is linked to  the
     file using the  DBusedbf() command.  If there  was an  index
     file associated  with  the  database, then  the  index  will
     automatically be selected.

     Returns:  True if successful, false otherwise

     See also: DBusedbf

     Example:  DBseldbf(names)

               Makes the file linked to the file handle names the
     currently selected database file.

     ---------------------------------------------------------------------

     DBselndx(ihandle)

     Selects an open index file,  referenced by the index  handle
     ihandle,  with  which  to   order  the  currently   selected
     database. The number passed is the index handle generated by
     DBusendx().

     Returns:  True if successful, false otherwise

     See also: DBusendx DBclosendx

     Example:  DBselndx(names)

               Selects the  index file  referenced by  the  index
     file handle  names  and applies  it  to the  currently  open
     database.

     ---------------------------------------------------------------------

     DBskip(numrecs)

     Skips past  the next  numrecs number  of records,  in  index
     order if one is open. It will return an error if you attempt
     to skip beyond the end of the file.


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     Returns:  True if successful, False otherwise

     See also: DBgo

     Example:  DBskip(1)

               Goes to the next record in index order.

     ---------------------------------------------------------------------

     DBstd(field$,start,end)

     DBstd() returns  the population  standard deviation  of  the
     field$ field  in the  current database,  over the  range  of
     start to end  fields. The  specified field  must be  numeric
     type and not string. The deviation is calculated using the n
     method (unbiased), as in the ARstd() function.

     Returns:  A number

     See also: DBvar DBsum DBavg

     Example:  stddev:=DBstd("PAYMENT",1,10)

               Returns, to  the  variable  stddev,  the  standard
     deviation of  the  PAYMENT  field in  the  current  database
     between the first and tenth records, inclusive.

     ---------------------------------------------------------------------

     DBstruct(n$[#],t$[#],len[#],dec[#])

     Returns the number of fields in the currently open database.
     The parameters  return a  list of  the field  names,  types,
     widths and defined decimal places. The function will  return
     with an error if the arrays  are not big enough to hold  the
     information required.

     Returns:  Number of fields if successful, False otherwise

     See also: DBcountflds

     Example:  n:=DBstruct(n$[#],t$[#],len[#],dec[#])

               Returns the number  of fields in  the database  to
     the variable n and places the names of the fields in  n$[#],
     the field types  in t$[#], their lengths  in len[#] and  the
     decimal field width of numeric fields in dec[#].


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     ---------------------------------------------------------------------

     DBsum(field$,start,end)

     DBsum() returns the  sum of the  field named  field$ in  the
     current database, over  the range of  start to end  records.
     The specified field must be of numeric type.

     Returns:  A number

     See also: DBcount DBavg

     Example:  sum:=DBsum("PAYMENT",1,DBreccount())

               Returns, to the sumiable sum, the sum of "PAYMENT"
     field in the current database for all records in the file.

     ---------------------------------------------------------------------

     DBtop()

     Positions the  record pointer  at the  first record  in  the
     currently open database.  If there  is an  index active,  it
     will go to the first record in this index. An error will  be
     reported if  no  database  has  been  selected,  or  if  the
     database is empty when the returned value will be zero.

     Returns:  True if successfully moved, False otherwise

     See also: DBbottom

     Example:  DBtop()

     ---------------------------------------------------------------------

     DBusedbf(filename$)

     DBusedbf() opens  a  database file  for  use and  returns  a
     database file handle with which the file may be accessed.  A
     database file may be made current by selecting the  database
     handle using DBseldbf().

     Returns:  Database  file   handle   if   successful,   False
     otherwise

     See also: DBseldbf DBclosedbf

     Example:  f:=DBusedbf("test")


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               Opens  a  database  file  called  "TEST.DBF"   and
     returns its file handle to the variable f.

     ---------------------------------------------------------------------

     DBusendx(indexname$)

     DBusendx() opens an  index file for  use with the  currently
     selected database file and returns an index file handle. The
     default and necessary index file extension is ".NDX",  which
     is aupplied automatically  if omitted.   When the index  has
     been opened using this function,  it may be activated  using
     the DBselndx() command.

     Returns:  Index file handle, False if error

     See also: DBclosendx DBselndx

     Example:  idx:=DBusendx("test")

               Returns  an  index  handle  to  the  variable  idx
     through which the index file "TEST.NDX" may be accessed.

     ---------------------------------------------------------------------
     DBvar(field$,start,end)

     DBvar() returns the population variance of the field$  field
     in the  current database,  over the  range of  start to  end
     fields. The specified  field must  be numeric  type and  not
     string. The  variance  is  calculated  using  the  n  method
     (unbiased), as in he ARvar() function.

     Returns:  A number

     See also: DBstd DBsum DBavg

     Example:  var:=DBvar("PAYMENT",1,10)

               Returns,  to  the   variable  var,  the   standard
     deviation of  the  field  named  "PAYMENT"  in  the  current
     database between the first and tenth records, inclusive.

     ---------------------------------------------------------------------

     DBzap()





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     DBzap()  removes  all  records  from  the  currently  active
     database, irrespective of the  status of the deletion  flag.
     Use this command with care!

     Returns:  True if successful, False otherwise

     See also: DBpack DBdelete

     Example:  DBzap()

               Erases the contents of the current database.

     ---------------------------------------------------------------------

     DEG(radianangle)

     Converts from radian angle measure to degrees. Note that all
     trigonometric functions in RExL use radian measure for input
     and output.

     Returns:  A number

     See also: RAD

     Example:  degangle:=DEG(0.5)

               Returns 28.64788 degrees to the variable degangle.

     ---------------------------------------------------------------------

     DISPLAY(text$)

     Displays text$ at  the current cursor  position. The  cursor
     position may be set using the GOTOXY() function.   DISPLAY()
     also uses a number of `escape sequences' which are identical
     those found in the C language.  An escape sequence  consists
     of a backslash followed by  some character.  In the  current
     version four escape sequences are defined:

                Table 3.4: DISPLAY() escape sequences

     \t   Move one tab stop to the right
     \n   Move to beginning of next line
          scrolling the screen if needed
     \a   Ring the terminal bell
     \\   Output the backslash character

     Returns:  True


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     Example:  DISPLAY("Hello, world\n\t")

               Displays the  string  "Hello, world",  moving  the
     cursor down one line and one tab stop to the right.

     ---------------------------------------------------------------------

     DIV(number, divisor)

     Returns the  result of  the integer  division of  the  first
     number by  the second.  Both parameters  must be  less  than
     2,147,483,647 for this function to produce a correct  value,
     otherwise an overflow will occur.

     Returns:  A number

     See also: MOD

     Example:  x:=DIV(25,3)

               Returns 8 to the variable x.

     ---------------------------------------------------------------------

     DTdate(year,month,day)

     DTdate() takes  three parameters,  year, month  and  day-of-
     month and returns the julian  day number of that date, or  0
     if the date is invalid. See the section on date functions in
     appendix A for information on Julian day numbers.

     Returns:  A number

     See also: DTdate$ DTdatevalue

     Example:  days:=DTdatevalue(1991,11,2)

               Returns the internal date number for the second of
     November, 1991.

     ---------------------------------------------------------------------

     DTdate$(daynumber)

     DTdate$() will return a date string representing the date of
     the Julian day number daynumber. Ensure that the date format
     is set  up  correctly  by  using  the  DTformat()  function,



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     otherwise your application may misinterpret the date  string
     returned.

     Returns:  True if successful, False otherwise

     See also: DTformat DTdatevalue

     Example:  a$:=DTdate$(DTnow())

               If the date  is the  5th of  December, 1991,  then
     this call  returns  "5/12/1991"  with European  date  format
     current,  "12/05/1991"   with   American  date   format   or
     "1991/12/05" with Japanese format current.

     ---------------------------------------------------------------------

     DTdatevalue(date$)

     DTdatevalue() takes a single string parameter, interprets it
     as a date string according  to the current date format,  and
     returns the Julian day number of that date.  Take care  that
     the date format is set  correctly for your country by  using
     DTformat().

     Returns:  A number

     See also: DTdate$

     Example:  days:=DTdatevalue("2.1.1900")

               Returns 2  to the  variable days  if the  European
     date is the default (2nd of January), otherwise returns 33 (
     1st of February in American format).

     ---------------------------------------------------------------------

     DTday$(date)

     DTday$() will return the name of the day specified by  date,
     interpreted as a Julian day number.

     Returns:  A string

     Example:  day$:=DTday$(DTnow())

               Returns  the  name   of  today  (ie   "Wednesday",
     "Thursday" and so on) to the variable day$.



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     ---------------------------------------------------------------------

     DTdayno(date)

     DTdayno() will  return the  day-of-month for  the  specified
     internal date number.

     Returns:  A number between 1 and 31

     Example:  d:=DTdayno(DTnow())

               Returns the number of the current day of the month
     to the variable d.

     ---------------------------------------------------------------------

     DTdayofyear(date)

     DTdayofyear() takes a Julian Day Number, `date', and returns
     the day number of the year in which that date fell.

     Returns:  A number from 1 to 366

     See also: DTdayno

     Example:  d:=DTdayofyear(DTdatevalue("01-01-1992"))

               Returns 1 to d

     Example:  d:=DTdayofyear(DTdatevalue("29-02-1992"))

               Returns 60 to d

     ---------------------------------------------------------------------

     DTformat(formatnumber,time$,date$)

     Sets the  format  and separator  for  date strings  and  the
     separator only for time strings.  Failure to set the  format
     correctly  could  lead  to  unpredictable  results  if  your
     application depends on a specific date format. Valid  values
     for formatnumber are as follows:








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          Table 3.5: Valid Format Specifiers for DTformat()

     0    Return format in use
     1    mm/dd/yyyy (American standard)
     2    dd/mm/yyyy (European standard)
     3    yyyy/mm/dd (Japanese standard)

     time$ and date$ define the number separators for use in time
     strings and date strings respectively. By default, these are
     set up from  values specified in  the country  line of  your
     "CONFIG.SYS" file.   If  you want  to  leave either  of  the
     separators unchanged, pass the empty string, "".

     Returns:  True if  valid parameters  passed and  set,  False
     otherwise

     Example:  DTformat(1,":","/")

               This line  sets the  current  date format  to  the
     American standard  of mm/dd/yyyy,  the time  separator to  a
     colon (to give  time strings like  "13:00:00") and the  date
     separator to a forward slash.

     ---------------------------------------------------------------------

     DThourno(time)

     DThourno() will return the hour of the time specified by the
     parameter, expressed in RExL's internal time format.

     Returns:  A number between 0 and 23

     See also: DTminuteno DTsecondno

     Example:  d:=DThourno(DTnow())

               Returns the current hour to the variable d.

     ---------------------------------------------------------------------

     DTminuteno(time)

     DTminuteno()  will  return  the  minute  specified  by   the
     parameter, expressed in RExL's internal time format.

     Returns:  A number between 0 and 59

     See also: DThourno DTsecondno


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     Example:  d:=DTminuteno(DTnow())

               Returns the number  of the current  minute to  the
     variable d.

     ---------------------------------------------------------------------

     DTmonth$(datenum)

     DTmonth$() returns  the name  of the  month upon  which  the
     specified Julian day number datenum, fell.

     Returns:  A string

     See also: Date functions

     Example:  mth$:=DTmonth$(DTnow())

               This will set mth$ to  be the name of the  current
     month.

     ---------------------------------------------------------------------

     DTmonthno(date)

     DTmonthno() will return the month-of-year for the  specified
     Julian day number.

     Returns:  A number between 1 and 12

     Example:  d:=DTmonthno(DTnow())

               Returns the  number of  the current  month of  the
     year to the variable d.

     ---------------------------------------------------------------------

     DTnow()

     Returns the RExL's internal date  and time in the form of  a
     real number. The  integer part of the  number is the  Julian
     day number and the decimal fraction part is the current time
     of day,  expressed in  direct  fractional form.  Appendix  A
     gives more information on the Julian day numbering system.

     Returns:  A number




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     Example:  a$:=DTdate$(DTnow()) Will set a$ to be the current
     date in the current date format as set by DTformat().

     ---------------------------------------------------------------------

     DTsecondno(time)

     DTsecondno()  will  return  the  second  specified  by   the
     parameter, expressed in RExL's internal time format.

     Returns:  A number between 0 and 59

     See also: DThourno DTminuteno

     Example:  d:=DTsecondno(DTnow())

               Returns the number  of the current  second to  the
     variable d.

     ---------------------------------------------------------------------

     DTsetdate(newdate)

     Initializes the system  date to  the date  specified in  the
     numeric parameter interpreted as a Julian day number.

     Returns:  True if successful, False otherwise

     See also: DTdate$

     Example:  DTsetdate(DTnow()+7)

               Set the date to be one week in the future.

     ---------------------------------------------------------------------

     DTsettime(newtime)

     DTsettime() sets the system time.   The time is measured  in
     decimal  fractions  of  a  day.    See  appendix  A  for   a
     description of RExL's time format.

     Returns:  True

     See also: DTtime$ DTtime

     Example:  DTsettime(0.5) Sets the time to be midday.



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     ---------------------------------------------------------------------

     DTtime(hour,minute,second)

     DTtime() takes the specified hour, minute and second  values
     and returns the internal time fraction representing the time
     specified. If the  time is invalid,  then the function  will
     return zero.

     Returns:  A time fraction

     See also: DTtimevalue DTtime$

     Example:  DTsettime(DTtime(13,0,0))

               This will set the current  time to one o'clock  in
     the afternoon.

     ---------------------------------------------------------------------

     DTtime$(dayfrac)

     DTtime() converts the dayfrac numeric parameter from  RExL's
     internal format to a time string using the currently  active
     time separators.

     Returns:  A string

     See also: DTtimevalue DTtime

     Example:  newtime$:=DTtime$(0.5)

               This will set newtime$ to be "12:00:00".

     ---------------------------------------------------------------------

     DTtimevalue(t$)

     Converts the specified time  string to RExL's internal  time
     format. If the time is invalid the function returns a  value
     of 0.

     Returns:  A number

     See also: DTtime$ DTtime

     Example:  frac:=DTtimevalue("13:00:00")



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               This   will   set   frac   to   RExL's    internal
     representation of one o'clock in the afternoon, 0.5416667.

     ---------------------------------------------------------------------

     DTyearno(date)

     DTyearno() will return the year for the specified Julian day
     number.

     Returns:  A number

     Example:  d:=DTyearno(DTnow())

               Returns the  number of  the  current year  to  the
     variable d.

     ---------------------------------------------------------------------

     EQV(log1,log2)

     EQV() performs  a  logical  equivalence test  upon  the  two
     logical parameters  passed  to  the function.  The  function
     returns True if both logical parameters are True or if  both
     are False, otherwise it returns False.  Note that EQV(l1,l2)
     is equivalent to NOT(XOR(l1,l2)).

     Returns:  A number

     See also: NOT AND XOR OR IMP

     Example:  val:=EQV(TRUE(),FALSE())

               Returns False to to the variable val

     ---------------------------------------------------------------------

     ERclear()

     ERclear() clears  all  error  flags so  that  ERmsg$()  will
     return a empty string and ERok() will return True, until the
     next error occurs.

     Returns:  True

     See also: ERwatch ERok ERmsg$

     Example:  ERclear()


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     ---------------------------------------------------------------------

     ERmsg$()

     Return the last error message  generated, or a empty  string
     if there has been no errors since starting or since the last
     use of the ERclear() function.

     Returns:  A string

     See also: ERwatch ERok

     Example:  a$:=ERmsg$()

               Returns an  empty string  if  there have  been  no
     errors since the  start of execution,  or the  last call  to
     ERclear().

     ---------------------------------------------------------------------

     ERnum()

     ERnum()  returns  the  error   number  of  the  last   error
     generated, or zero  if there  has been  no errors  generated
     since the last  call to ERclear()  or since the  application
     began.  This  function should be  used with  care since  the
     error numbers may change in future versions of RExL.

     Returns:  A number

     See also: ERwatch ERok ERmsg$

     Example:  ERnum()

     ---------------------------------------------------------------------

     ERok()

     ERok() will return true if no error has been reported  since
     starting or  the last  ERclear(). It  is used  to check  for
     `hidden' failures such as divide-by-0's (and so on) which do
     not fail statements, and hence are more difficult to detect.

     Returns:  True if error has occurred, False otherwise

     See also: ERmsg$ ERwatch

     Example:  ERok()


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     ---------------------------------------------------------------------

     ERwatch(number)

     ERwatch() turns the error reporting  feature on and off.  If
     the numeric  parameter  is  non-zero, then  errors  will  be
     displayed on the bottom line of the screen as is the default
     condition of RExL. If the parameter is zero, error reporting
     will be  disabled, although  the error  messages and  number
     will be set up regardless.

     Returns:  True

     See also: ERok ERmsg$

     Example:  ERwatch(TRUE())

               Enable error reporting.

     ---------------------------------------------------------------------

     ESCWATCH(number)

     ESCWATCH() is used to enable and disable the trapping of the
     <Esc> and <Alt-D> keys  during execution of an  application.
     In the default condition of on (a value for number of 1), an
     `error' is flagged, prompting the user to see if he wants to
     terminate the application.  If the parameter  is zero,  then
     RExL will  not scan  for the  key.  During debugging  of  an
     application, it's best to leave watching on.

     Returns:  True

     Example:  ESCWATCH(TRUE())

               Monitor the  <Esc> and  <Alt-D> keys  for  presses
     during execution of an application.

     ---------------------------------------------------------------------

     EXACT(num)

     EXACT() defines whether the string comparisons and tests are
     carried  out  respecting  the  case  of  the  letters  being
     compared (when num = 1)  or irrespective of case (num =  0).
     In its default condition, RExL is not sensitive to the  case
     of letters.



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     Returns:  True

     Example:  EXACT(TRUE())

               Turns on case sensitivity.

     ---------------------------------------------------------------------

     EXP(number)

     Returns the  exponential e  (2.71828) to  the power  of  the
     single numeric parameter.

     Returns:  A number

     See also: LOG

     Example:  x:=EXP(1)

               Returns 2.718281828 to the variable x.

     ---------------------------------------------------------------------

     FALSE()

     Returns the value zero. It is used to fail a rule or part of
     a rule.

     Returns:  False

     See also: TRUE NOT

     Example:  value:=NOT(FALSE())

               Returns 1 to the variable value.

     ---------------------------------------------------------------------

     FILL(x, y, w, h, char$)

     Fills an area  of the screen  with the specified  character.
     The  first  four  parameters  specify  the  horizontal   and
     vertical coordinates of  the top left  hand corner (x,y)  of
     the bounding box and its width w and height h  respectively.
     The fifth parameter  specifies the ASCII  character to  fill
     the area with. The attributes of the box remain unchanged by
     this command.



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     Returns:  True

     See also: PAINT BOX

     Example:  FILL(0,0,79,24,"A")

               Fills the screen with the letter A.

     ---------------------------------------------------------------------

     FIND(substr$, superstr$)

     Locates the first occurrence of substr$ within superstr$. If
     the substring is  not in superstr$,  then the function  will
     return False. The value returned is zero based, meaning that
     if the substring  starts at  the first  character, then  the
     return value will be zero. This behaviour is comatible  with
     C language, where all string positions are zero-based.

     Returns:  String index if located, -1 otherwise

     Example:  pos:=FIND("lo","Hello")

               Returns a value of 3 to the variable pos.

     ---------------------------------------------------------------------

     FLOOR(number)

     FLOOR() returns  the largest  number less  than the  numeric
     parameter.

     Returns:  A number

     See also: CEIL

     Example:  a:=FLOOR(5.5)

               Returns the value 5.0 to the variable a.

     ---------------------------------------------------------------------

     FV(pmt,rate,periods)

     Calculates the future value of equal payments of amount  pmt
     of a simple ordinary annuity, earning at a periodic interest
     rate for the  number of payment  periods. The interest  rate
     should be expressed as a decimal rather than a percentage.


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     Returns:  A number

     Example:  x:=FV(1000,0.1,10)

               Returns $15937.43 to the variable x.

     ---------------------------------------------------------------------

     GOTOXY(xpos, ypos)

     Positions  the  text  cursor  on  the  text  screen  at  the
     specified  horizontal  co-ordinate  xpos  and  vertical  co-
     ordinate ypos, taking (0,0) to be the top right hand  corner
     of the screen.   If the  coordinates are  out of range,  the
     GOTOXY() will return False.

     Returns:  True if successful, False otherwise

     See also: DISPLAY

     Example:  GOTOXY(0,0)

               Sets the cursor to the top left hand corner of the
     screen.

     --------------------------------------------------------------------

     HELP(log)

     HELP() is used to turn  the online help feature on and  off.
     When `log' is true, <F1>  will display the currently  active
     help screen when pressed from within a dialog screen.   When
     `log' is  false, <F1>  keystrokes will  be returned  to  the
     application.

     Returns:  True

     Example:  HELP(1)

               Turns on <F1> monitoring.
     ---------------------------------------------------------------------

     IIF(boolexp, anstrue, ansfalse)

     Returns one of the parameters anstrue or ansfalse  depending
     on the value of the  boolean expression passed as the  first
     parameter, boolexp. If the boolexp is true (non-zero),  then



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     anstrue is returned,  otherwise ansfalse  is returned.  This
     behaviour is compatible with the Clipper IF command.

     Returns:  Either of the second two parameters

     See also: IIF$

     Example:  a:=IIF(x,1,2)

               If the value of x is non-zero, then A is  assigned
     the value 1, otherwise the value 2.

     ---------------------------------------------------------------------

     IIF$(boolexp, anstrue$, ansfalse$)

     IIF$()  will  return  anstrue$  if  the  boolean  expression
     boolexp is true,  or ansfalse$, if boolexp  is false.   This
     behaviour is compatible with the Clipper IF command.

     Returns:  A string

     See also: IIF

     Example:  a$:=IIF$(x,"Y","N")

               If the value of x is non-zero, then A$ is assigned
     the value "Y", otherwise the value "N".

     ---------------------------------------------------------------------

     IMP(log1,log2)

     IMP() performs  a  logical  implication test  upon  the  two
     logical parameters  passed  to  the function.  The  function
     returns True if the first  parameter is True and the  second
     is False, otherwise it returns False.

     Returns:  A number

     See also: NOT AND XOR OR EQV

     Example:  val:=IMP(TRUE(),FALSE())

               Returns True to to the variable val.

     ---------------------------------------------------------------------



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     INIT()

     Clears out all variables currently defined, setting  numeric
     variables to 0.0 and setting strings to zero length.

     Returns:  True

     Example:  INIT()

     ---------------------------------------------------------------------

     INPUT(x,y,w,p,value)

     Generates an input field of width w and decimal precision  p
     at  the  horizontal  and  vertical  coordinates  (x,y).  The
     initial value of the input is value  The attribute at  (x,y)
     will be extended to the width of the input. If value is  too
     large to display in the  assigned area, then overwriting  of
     the surrounding screen may occur.   The input area will  not
     be affected by this. The maximum width of input is 19 digits
     and the maximum precision is 17 digits.

     Returns:  The number input

     See also: INPUT$

     Example:  n:=INPUT(5,10,10,2,1.2)

               Accepts the input of a number a column 5, row  10,
     with a width of 10  places and including room for 2  decimal
     places, with an  initial value of  1.2. The  number will  be
     stored in the variable n.

     ---------------------------------------------------------------------

     INPUT$(x,y,width,value$)

     Generates a string input field of width w at the  horizontal
     and  vertical  coordinates  (x,y)  specified,  setting   the
     initial value of the input to value$.

     Returns:  The string input

     See also: INPUT

     Example:  t$:=INPUT$(5,10,10,"Test")




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               Accepts input of a string at column 5 row 10, with
     a width of 10 places and an initial value of "Test".

     ---------------------------------------------------------------------

     INVERSE(x1, y1, x2, y2)

     Inverts the attributes of an  area of screen. The first  two
     parameters define the top left  corner. The last two  define
     the bottom right corner. If you invert the same area  twice,
     you will be  left with the  same area. This  can be used  to
     flash an  area.    The inverse  attribute  is  generated  by
     xor'ing the current attribute with 7Fh.

     Returns:  True

     Example:  INVERSE(0,0,79,24)

               Inverts the attributes for the whole screen.

     ---------------------------------------------------------------------

     KBclear()

     Clears all keystrokes from the keyboard buffer.

     Returns:  True

     Example:  KBclear()

     ---------------------------------------------------------------------

     KBlast()

     KBlast() returns the last keystroke typed by the user.   The
     function can be used to determine the keystroke which caused
     the termination of a dialog screen (for example, if the user
     pressed <PgUp>, <PgDn>, <Enter> and so on).  If no keys have
     been pressed since the application started running, or since
     the last  call of  KBclear(), then  KBlast() returns  False.
     See appendix D for a list of return values.

     Returns:  Key code  for  last  key pressed,  False  if  none
     present

     See also: KBwait

     Example:  key:=KBlast()


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     ---------------------------------------------------------------------

     KBread()

     Waits until  a key  is pressed  and  then returns  the  code
     associated with it. If the key is a character key, the ASCII
     code will be returned, otherwise, the internal code for  the
     key will be returned.  See  appendix D for a list of  return
     values.

     Returns:  Key code for key pressed

     See also: KBwait

     Example:  key:=KBread()

               Waits for a key to be pressed and returns keyboard
     code in the variable key.

     ---------------------------------------------------------------------

     KBready()

     KBready() returns the value of a keystroke, if one is  ready
     and waiting in the keyboard  buffer. If there is no  pending
     keystroke, the function returns immediately with a value  of
     zero, otherwise it returns the keystroke code, as listed  in
     appendix D.

     Returns:  Key code for key waiting, zero otherwise

     Example:  KeyWaiting:=KBready()

     ---------------------------------------------------------------------

     KBwait(time)

     Waits for the specified number of seconds time for a key  to
     be pressed. The  function then returns  the coded value  for
     that key or zero if no key was pressed.  See appendix D  for
     a list of keystroke codes.

     Returns:  Key code if key pressed, False if no key pressed

     Example:  key:=KBwait()

     ---------------------------------------------------------------------



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     LEFT$(str$,num)

     Returns a  string  comprising  the leftmost  num  number  of
     characters from the string str$. If the number specified  is
     greater than the length of the string then the entire string
     will be copied.

     Returns:  A string

     See also: RIGHT$ MID$

     Example:  a$:=LEFT$("Hello",2)

               This sets a$ to be "He"

     ---------------------------------------------------------------------

     LENGTH(string$)

     Returns the length  of a  character string  string$. If  the
     string is empty, then the value 0 will be returned

     Returns:  A number

     Example:  lgth:=LENGTH("System")

               This will set lgth to be 6.

     ---------------------------------------------------------------------

     LOAD(filename$)

     Loads in and  passes control to  another listing. LOAD()  is
     not nested so that when the second listing finishes, control
     is not  passed  back to  the  original listing.  LOAD()  may
     return False if the second  listing is too big, or does  not
     exist.  If the specified application image does not exist in
     the current directory, then the  list of paths specified  in
     the RExL environment variable will be searched in  sequence.
     If the  application  is  located,  then  all  databases  are
     closed, the internal error variables are reset and execution
     begins at the master rule of the new application.  The stack
     of screens stored by PUSHSCR() and POPSCR() are not cleared,
     so screenfuls  of  information  may be  passed  between  two
     applications.

     Applications  compiled  with   the  postfix  compiler   must
     exercise caution  when using  the  LOAD function,  which  is


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     implemented slightly  differently  in  the  executable  file
     library.  The section on  the postfix compiler RExLPC  gives
     more details on this.

     Returns:  False if listing could not load

     Example:  LOAD("2ndpart")

               Loads and passes control to the application  image
     with the DOS file name "2ndpart.rxl".

     ---------------------------------------------------------------------

     LOADSCR(filename$, x, y)

     Loads in  a small  area of  the  screen from  the  specified
     filename. The  x  and y  coordinates  specify the  top  left
     corner of where the screen is to appear. Any fields that are
     contained with the  screen will  then be  activated. If  you
     wish to load the screen to its original x or y position then
     set the relevant parameter to  -1.  Any parts of the  screen
     being loaded  which  do not  fit  will  be ignored  and  not
     displayed.

     Returns:  True if loaded ok, False otherwise

     See also: SAVESCR

     Example:  LOADSCR(n$,10,-1)

               Get the screen named n$ and place it at column  10
     with the row being the same as that from where it was saved.

     ---------------------------------------------------------------------

     LOG(number)

     Returns the natural logarithm (log  to base e (2.71828))  of
     the parameter.

     Returns:  A number

     See also: EXP

     Example:  nl:=LOG(0.51)

               This will set nl to be -0.673344553



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     ---------------------------------------------------------------------

     LOG10(number)

     Returns the base-10 logarithm of the parameter.

     Returns:  A number

     Example:  lg:=LOG10(0.51)

               This will set lg to be -0.292429824

     ---------------------------------------------------------------------

     LOWER$(string$)

     LOWER$() returns the  parameter string  translated in  lower
     case.  The  European ASCII characters are  left as they  are
     and are not translated to lower case.

     Returns:  A string

     See also: UPPER$

     Example:  a$:=LOWER$("hELlO")

               Returns the string "hello" to a$.

     ---------------------------------------------------------------------

     MAX(num1, num2)

     Returns the larger of the two numeric parameters.

     Returns:  A number

     See also: MIN

     Example:  bigger:=MAX(5,4)

               This will set bigger to be 5

     ---------------------------------------------------------------------

     MID$(source$, start, count)

     Returns count characters,  starting at  position start  from
     the string source$. If start  is past the end of the  string


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     or count is less than or equal to zero, then an empty string
     is returned.

     Returns:  A string

     See also: LEFT$ RIGHT$

     Example:  a$:=MID$("ABCDEF",2,2)

               This will set a$ to be "CD"

     ---------------------------------------------------------------------

     MIN(number1, number2)

     Returns the smaller of the two parameters.

     Returns:  A number

     See also: MAX

     Example:  small:=MIN(5,4)

               This will set small to be 4.

     ---------------------------------------------------------------------

     MOD(number1, number2)

     Returns the remainder of the division of number2 by number1.
     Mathematically, this operation is known as modulo division.

     Returns:  A number

     See also: DIV

     Example:  remainder:=MOD(10,3)

               This will set remainder to be 1.

     ---------------------------------------------------------------------

     NOT(boolean)

     Returns  the  logical  inverse  of  the  parameter:  If  the
     parameter evaluates to false, the function will return True,
     otherwise it will return False.



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     Returns:  True or False

     See also: BTnot

     Example:  NOT(TRUE()) Returns False.

     ---------------------------------------------------------------------

     OR(log1,log2)

     OR() performs a logical OR  upon the two logical  parameters
     passed to the function. The function returns True if  either
     of the two logical parameters are True otherwise it  returns
     False.

     Returns:  A number

     See also: NOT EQV XOR AND IMP

     Example:  val:=OR(TRUE(),FALSE())

               Returns False to to the variable val.

     ---------------------------------------------------------------------

     OScd(path$)

     Changes directory to  the path  specified by  path$. If  the
     directory cannot  be  accessed  then  the  function  returns
     false, otherwise  true.  To  change the  current  drive  use
     OSdrive().

     Returns:  True if successful, False otherwise

     See also: OSdrive OSrd OSmd

     Example:  OScd("\rexl\demo")

               Sets the directory to be \rexl\demo on the default
     drive.

     ---------------------------------------------------------------------

     OScmd(command$)

     Allows external programs to be loaded and run. The parameter
     contains the program name and  any parameters which must  be
     passed to it.  OScmd() returns True if the command  executed


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       - Appendices.                         Page: 73 -


     and False if  it failed to do  so.  Note  that RExL must  be
     able to access the command  interpreter to run the  command.
     The command interpreter is  usually the file  "COMMAND.COM",
     located in  the root  directory of  the  boot drive  and  is
     referenced by the COMSPEC environment variable.

     Returns:  True if successful, False otherwise

     Example:  OScmd("edit c:\autoexec.bat")

               Executes the program  or batch  file named  "edit"
     and  passes  the  string   "c:\autoexec.bat"  to  it  as   a
     parameter.

     ---------------------------------------------------------------------

     OScopy(source$,dest$)

     Copys a  file from  the source$  to dest$.  The  destination
     parameter, unlike its  MS-DOS equivalent,  must contain  the
     name of the file to which the file will be copied. The  wild
     card characters ? and  are not allowed in either  parameter.
     If you need  to perform a  wild card  copy, use the  OScmd()
     function.

     Returns:  True if successful, False otherwise

     See also: OScmd

     Example:  OScopy("TEST.DOC","\T.TXT")

               Copies a file "TEST.DOC" in the current  directory
     to the root directory, naming it "T.TXT".

     ---------------------------------------------------------------------

     OSdel(filename$)

     Deletes the specified file from  the disk. If the file  does
     not exist, or could not  be deleted then this function  will
     return false, otherwise true.  filename$ may specify a  full
     path including drive specifier.

     Returns:  True if successful, False otherwise

     See also: OSexists

     Example:  OSdel("TEST.RXL")


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       - Appendices.                         Page: 74 -


               Deletes the file called "TEST.RXL" in the  current
     directory.

     ---------------------------------------------------------------------

     OSdir(mask$, attr, n$[#], sz[#], dt[#], at[#])

     OSdir() is used to obtain  DOS diretory listings from  disk.
     The first parameter specifies the  DOS file mask to use  for
     the search and  may include  drive and  path designators  as
     well as wild card characters. The second parameter specifies
     the file attribute  to search for. To  search for more  than
     one file  type,  add  the search  attributes  together.  The
     following table gives the valid search attributes:

               Table 3.6: OSdir() File Attribute Coding

     Attribute Code      Meaning
     1                   Read only attribute
     2                   Hidden file
     4                   System file
     8                   Volume label
     16                  Directory
     32                  Archive
     64                  All files

     If you  are  unsure  about  the meanings  of  any  of  these
     attributes, consult your DOS manual.

     The results of  the search are  placed in  the arrays:  file
     names in n$[#], file sizes in sz[#], file dates and times in
     dt[#] and file attributes in  at[#].  The return value  from
     OSdir() is the number  of files returned in  the array.   If
     any  of  the  arrays  are  not  large  enough  to  hold  the
     information required,  then an  array bounds  error eill  be
     generated and the function  will return without looking  for
     any more files.

     Returns:  The number  of files  found or  zero if  no  files
     located

     See also: OSexists

     Example:  OSdir("*.rxl",64,n$[#],sz[#],dt[#],at[#])

               Returns lists of all of the RExL application image
     files  in   the  current directory.  The files may have  any
     attribute.


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       - Appendices.                         Page: 75 -


     Example:  OSdir("T?.RXL",64,n$[#],sz[#],dt[#],at[#])

               Returns a list  of all of  the RExL  files in  the
     current directory, whose names  have two letters, the  first
     of which is "T"

     ---------------------------------------------------------------------

     OSdrive(drive$)

     Selects a new current disk drive. The parameter should be  a
     two character  string, the  first character  of which  is  a
     drive letter and the second a colon. The return value of the
     function is the ASCII character code of the drive  selected.
     If the drive was not  successfully selected, then the  value
     returned will be the ASCII code of the current drive letter.
     Passing an empty string in  place of drive$ will return  the
     current drive with no change made.

     Returns:  True if successful, False otherwise

     See also: OScd OSwd$

     Example:  OSdrive("C:")

               Sets the current or default drive to be C:

     ---------------------------------------------------------------------

     OSdriveok(dstr$)

     OSdriveok() tests a disk drive, normally a floppy drive,  to
     determine if it  is ready  to be  written to  or read  from.
     `dstr$' specifies the DOS disk drive to test.  The  function
     can return  one  of  a  range  of  values,  giving  explicit
     information about  why  the disk  drive  is not  ready.  The
     following table  gives the  exact  return values  and  their
     meanings:

                 Table 3.7: OSdriveok() return values

          -1        Wrong parameters
          0         Drive loaded and ready to read or write
          1         Drive door open or diskette inserted upside down
          2         Diskette is unformatted
          3         Write protected
          4         Undetermined



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       - Appendices.                         Page: 76 -


     Note that  unlike  almost  all other  rexl  functions,  this
     function returns zero if the test performed was successful.

     Returns:  A number

     See also: OSdrive

     Example:  !OSdriveok("A:")

               Returns true if  drive A: is  not write  protected
     and is ready for access.

     ---------------------------------------------------------------------

     OSexists(filename$)

     Checks to see  if the specified  file exists. filename$  can
     contain a full pathname and drive specification.

     Returns:  True if file exists, False otherwise

     See also: OSdir

     Example:  OSexists("c:\command.com")

               Tests to see if  the file "COMMAND.COM" exists  in
     the root diretory of the C: drive.

     ---------------------------------------------------------------------

     OSmd(dirname$)

     OSmd()  will  make  a  DOS  directory.  The  single   string
     parameter specifies  the  directory  name to  make  and  may
     contain a drive letter.  As in the DOS  md command, you  may
     only make one directory level at a time.

     Returns:  True if successful, False otherwise

     See also: OSrd

     Example:  OSmd("\test")

               Makes  a  directory  called  "test"  in  the  root
     directory of the current drive.

     ---------------------------------------------------------------------



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       - Appendices.                         Page: 77 -


     OSnumber()

     This function  returns a  value indicating  which  operating
     system RExL is currently running under. Currently, the  only
     value returned is 1, for MS-DOS, but future versions of RExL
     running  under  different  operating  systems  will   return
     different values.  Use  OSstat() to determine the  operating
     system version number.

     Returns:  1 for MS-DOS

     See also: OSstat

     Example:  sys:=OSnumber()

               Sets sys equal  to 1  if the  operating system  is
     MS-DOS.

     ---------------------------------------------------------------------

     OSrd(dirname$)

     OSrd() will  remove  a  DOS  directory.  The  single  string
     parameter specifies the  directory name to  be deleted.  The
     string  can  contain  a  drive   letter  and  a  full   path
     specification.

     Returns:  True if successful, False otherwise

     See also: OSmd

     Example:  OSrd("c:\test")

               Removes a directory called  "\test" from the  root
     directory of the C: drive.

     ---------------------------------------------------------------------

     OSren(source$,dest$)

     This function will rename the  file named source$ to  dest$.
     The parameters may specify a directory paths, so that  files
     may be moved  from one directory  to another using  OSren().
     Note that, as in DOS,  the destination file must not  exist,
     or the function will fail.

     Returns:  True if successful, otherwise False.



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       - Appendices.                         Page: 78 -


     See also: OScopy OSdel

     Example:  OSren("TEST.TXT","TEST.BAK")

               Changes  the  name  of  the  file  "TEST.TXT"   to
     "TEST.BAK".

     ---------------------------------------------------------------------

     OSstat(ar[#])

     OSstat() returns  seven  items  of  information,  about  the
     current  status  of  the  machine,  to  the  specified   one
     dimensional numeric array.

     The information returned is as follows:

                 Table 3.8: OSstat() Return Indexing

     Array Index    Meaning
     0              Disk space free on current drive
     1              Total disk space on current drive
     2              Total number of disk drives available
     3              Largest block of free memory available
     4              Current DOS version
     5              CPU type
     6              Coprocessor type
     7              Video adapter type

     If the  current disk  is  large, then  DOS  may take  a  few
     seconds to determine the its free space and total size.   If
     the current disk is not  valid, for example, a floppy  drive
     with an open door, then  a critical error will be  generated
     and a value  of zero will  be returned for  the size of  the
     disk.

     The DOS version  is returned as  a real  number of the  form
     x.yy where x is the major version number and yy is the minor
     version number.











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       - Appendices.                         Page: 79 -


                  Table 3.9: CPU Type Return Coding

     Return Value   Processor Type
     0              Intel 8088
     1              Intel 8086
     2              NEC V20
     3              NEC V30
     4              Intel 80188
     5              Intel 80186
     6              Intel 80286
     7              Intel 80386
     8              Intel 80486

              Table 3.10: Coprocessor Type Return Coding

     Return Value Coprocessor Type
     0              None installed
     1              Intel 8087
     2              Intel 80287
     3              Intel 80387

             Table 3.11: Video Adapter Type Return Coding

     Return Value   Video Adapter type
     0              Monochrome
     1              CGA adapter
     2              EGA adapter
     3              VGA adapter

     Returns:  True if array large enough, False otherwise

     See also: OSdir OSnumber

     Example:  OSstat(Stat[#])

               Returns  the  above  information  to  the  stat[#]
     array.

     ---------------------------------------------------------------------

     OSwd$()

     Returns a string containing the current directory path.  The
     string will also contain the current drive letter.

     Returns:  A string

     See also: OSdir OScd


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       - Appendices.                         Page: 80 -


     Example:  d$:=OSwd$()

     ---------------------------------------------------------------------

     OUTPUT(device$)

     Sets the default output device for print requests. Since the
     string is passed directly to DOS  it can be a file on  disk.
     By default the  printer output device  is the device  driver
     "PRN". If you are  using a parallel/centronics type  printer
     then you may wish to use the command:

                        [Expr] OUTPUT("LPT1")

     or if you are using a serially connected printer:

                        [Expr] OUTPUT("COM1")

     These two functions explicitly  state which type of  printer
     you will be using. Using  the generic PRN device you  should
     have less problems  when people connect  different types  of
     printers. Making it a variable would allow you to modify  to
     set up a option for the user to select the output device.

     Returns:  True

     Example:  OUTPUT("DUMP.DOC") Assigns all  printer output  to
     the file "DUMP.DOC"

     ---------------------------------------------------------------------

     PAINT(x, y, w, h, att, mask)

     PAINT() changes the attributes of a box whose top left  hand
     corner is  (x,y) and  whose width  and  height are  w and  h
     respectively.  When  changing  the  attribute  byte  on  the
     screen, PAINT() performs a boolean AND on the byte with  the
     mask and then adds the  attribute which has been ANDed  with
     the  inverted   mask.  The   result  of   this   complicated
     manoeuvering is that  any color can  be filtered  in or  out
     from either background or foreground. If you wish to  change
     foreground only  set  the mask  to  be  240, to  change  the
     background only,  set  it  to  15. If  you  want  to  change
     everything in the area set the mask to be 0.

     The following table  lists the colors which  can be used  on
     color monitors:



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       - Appendices.                         Page: 81 -


                  Table 3.12: Color Attribute Codes

          Color     Foreground          Background
          Black          0              0
          Blue           1              16
          Green          2              32
          Cyan           3              48
          Red            4              64
          Magenta        5              80
          Brown          6              96
          Light Gray     7              112
          Dark Gray      8              (128)
          Light Blue     9              (144)
          Light Green    10             (160)
          Light Cyan     11             (176)
          Light Red      12             (192)
          Light Mgnta    13             (208)
          Yellow         14             (224)
          White          15             (240)
          Blink          128            -

     If the  last  screen  displayed  during  execution  had  the
     flash-intensity bit set to `intensity', then a further eight
     background colors, indicated above by the bracketed numbers,
     are available, at  the expense  of blinking.  Note that  the
     background colors are derived from the foreground colors  by
     multiplying by sixteen.

     Some early CGA  systems do not  support the  flash-intensity
     toggle, so distribution packages which may be used on  these
     adapters should not use this feature.

     Returns:  True

     See also: INVERSE FILL

     Example:  PAINT(0,0,79,24,31,0)

               This will set the entire screen to bright white on
     a blue background.

     Example:  PAINT(0,0,79,24,15,240)

               This  changes  all  foreground  colors  to  white,
     leaving background colors unchanged.

     ---------------------------------------------------------------------



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       - Appendices.                         Page: 82 -


     PAUSE(time)

     Halts execution  of the  application  for a  specified  time
     before  execution  continues.  The   time  is  measured   in
     milliseconds (thousandths of a second).

     Returns:  True

     Example:  PAUSE(1500)

               Halts the system for a second and a half.

     ---------------------------------------------------------------------

     PEEK(seg,ofs)

     PEEK() returns the value of the byte at the memory  location
     referenced by a segment value of seg and an offset value  of
     ofs.  Consult a DOS  reference if you are not familiar  with
     the concept of offsets and segmentation.

     Returns:  A number from 0 to 255

     See also: PEEKW POKE POKEW

     Example:  DisplayType:=PEEK(0,1097)

               This   expression   returns,   to   the   variable
     DisplayType, the type of display attached to your  computer.
     The value  will  be  3 for  a  color  display and  7  for  a
     monochrome display.

     ---------------------------------------------------------------------

     PEEKW(seg,ofs)

     PEEKW() returns the  value of the  sixteen bit  word at  the
     memory location referenced by a segment value of seg and  an
     offset value of ofs.  Consult a DOS reference if you are not
     familiar with the concept of offsets and segmentation.

     Returns:  A number from 0 to 65535

     See also: PEEK POKE POKEW

     Example:  CharAttr:=PEEKW(47104,0)




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               This expression returns, to the variable CharAttr,
     the first character and attribute  pair of a color  display.
     The attribute will  be in the upper  byte and the  character
     will be in the lower byte.

     ---------------------------------------------------------------------

     PI()

     Returns the value of pi, 3.14159265358979.

     Returns:  True

     Example:  degs:=rads*180/PI()

               Returns the value  of rads  radians, expressed  in
     degrees to the variable  degs. This expression performs  the
     same action as the DEG() function.

     ---------------------------------------------------------------------

     PMT(prin,rate,periods)

     Calculates  the  equal  periodic  payment  for  an  ordinary
     annuity with an initial principal of prin, at the  specified
     rate, for  periods  payments.  The  interest  rate  must  be
     expressed  as  a   decimal  fraction,  rather   than  as   a
     percentage.

     Returns:  A number

     Example:  amt:=PMT(1000,0.1,10) Stores the value $162.75  to
     the variable amt.

     ---------------------------------------------------------------------

     POKE(seg,ofs,value)

     POKE() will  place the  byte value  at the  memory  location
     referenced by a segment value of seg and an offset value  of
     ofs.  This function should  be used with care, since  poking
     to random areas of the computer's memory may corrupt DOS and
     cause unpredictable behaviour.   Consult your DOS  reference
     if you  are not  familiar with  the concept  of offsets  and
     segmentation.

     Returns:  True



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     See also: PEEKW PEEK POKEW

     Example:  POKE(0,1047,0)

               This expression  pokes  a  value of  zero  to  the
     keyboard flags byte at 0417h in the BIOS data segment.  This
     will turn off insert status, caps lock and num lock.

     ---------------------------------------------------------------------

     POKEW(seg,ofs,value)

     POKEW() will place the sixteen bit word value at the  memory
     location referenced by a segment value of seg and an  offset
     value of ofs. Use this  function with care, since poking  to
     random areas of  the computer's memory  may corrupt DOS  and
     cause unpredictable behaviour.   Consult your DOS  reference
     if you  are not  familiar with  the concept  of offsets  and
     segmentation.

     Returns:  True

     See also: PEEKW PEEK POKE

     Example:  POKEW(47104,0,0)

               This expression pokes a value of zero to the first
     character and  attribute  pair at  the  start of  the  color
     display memory area. This is displayed as a black space.

     ---------------------------------------------------------------------

     POPSCR()

     POPSCR() restores the screen from  a temporary work area  in
     memory. The PUSHSCR() function is used to save the screen in
     memory. Up to ten  screens may be saved  and restored, on  a
     first-in, last-out or stack based basis.

     Returns:  True if successful, false otherwise.

     See also: PUSHSCR

     Example:  POPSCR()

               Restores contents of screen.

     ---------------------------------------------------------------------


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     POW(number, exponent)

     Returns the value of number raised to the power of exponent.
     This function is included for reasons of compatibility  with
     the C language.

     Returns:  True

     Example:  v:=POW(10,2)

               Returns 100 to  the variable  v.   Note that  this
     operation can also be carried out using the `raise to power'
     operator, the caret, ^, so  that the above expression  could
     be rewritten as follows:

     Example:  v:=10^2

     ---------------------------------------------------------------------

     PUSHSCR()

     PUSHSCR() saves the current screen in a temporary work  area
     in memory. The information saved consists only of a  picture
     of the screen and  does not save any  fields.  The  POPSCR()
     function is used to restore a screen from memory.  Up to ten
     screens may be saved and  restored, on a first-in,  last-out
     or stack based basis.

     Returns:  True if successful, false otherwise.

     See also: POPSCR

     Example:  PUSHSCR()

               Saves contents of screen.

     ---------------------------------------------------------------------

     PV(pmt, rate, periods)

     Calculates the  present  value  of equal  pmt  in  a  simple
     ordinary annuity at the specified interest rate for a number
     of periods. As  with all financial  functions, the  interest
     rate must be expressed as a decimal fraction, rather than as
     a percentage.

     Returns:  A number



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     Example:  amt:=PV(1000,0.1,10)

               Stores $6144.57 to the variable amt.

     ---------------------------------------------------------------------

     QUIT()

     Halts the  execution  of  the current  application.  If  the
     runtime debugger was called from within the editor, then the
     editor wil be restarted,  otherwise, the module will  return
     to DOS.

     Returns:  N/A

     Example:  QUIT()

               Halts the  application  and  then returns  to  the
     operating system or editor.

     ---------------------------------------------------------------------

     RAD(angle)

     Converts an angle  expressed in degrees  into an  equivalent
     angle in radians.  All trigonometric functions  in RExL  use
     radians as input.

     Returns:  A number

     See also: DEG

     Example:  r:=RAD(180)

               This  assigns  the   value  of   pi,  the   radian
     equivalent of 180 degrees, to the variable r.

     ---------------------------------------------------------------------

     RAND()

     Returns a pseudo-random  number between 0  and 1. Each  time
     the inference  engine  starts a  seed  set to  generate  the
     sequence. Since  the seed  is always  the same,  the  random
     number generator follows the same sequence. You can set your
     own seed value by using the SEED() function.

     Returns:  A number


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     See also: SEED

     Example:  num:=FLOOR(RAND()*80)+10

               Assigns an random whole  number between 10 and  90
     to the variable num.

     ---------------------------------------------------------------------

     RATE(fv, pv, periods)

     Calculates the periodic  interest rate necessary  for pv  to
     grow to fv over a fixed number of compounding periods.

     Returns:  A number

     Example:  val:=RATE(1000,100,10)

               Assigns  the  value  0.2589  (or  25.89%)  to  the
     variable val.

     ---------------------------------------------------------------------

     REPEAT$(str$,times)

     REPEAT$() returns a  string consisting of  a source  string,
     str$, repeated times times. If the string would need to grow
     beyond the maximum string length  of 80 characters, it  will
     be truncated.

     Returns:  A string

     Example:  a$:=REPEAT$("-",5) Assigns the  string "-----"  to
     a$.

     ---------------------------------------------------------------------

     REPLACE$(str$,start,chars,repl$)

     REPLACE$() takes a source string, str$, removes chars number
     of characters  from  it,  starting at  position  start  from
     within the string and inserts the replacement string,  repl$
     into the  source in  that position.  If  repl$ is  an  empty
     string, then the  nett effect of REPLACE$()  is to remove  a
     substring from a  parent string.   If repl$  is empty,  then
     str$ will be terminated at position start.




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     Note that all  string indexing  numbers (such  as the  start
     parameter above)  are zero  based,  meaning that  the  first
     character is as position zero, not at position one as is the
     default in some other computer languages.

     Returns:  A string

     Example:  a$:=REPLACE$("Hello",0,2,"Ha") Assigns the  string
     "Hallo" to the variable a$.  It removes two characters  from
     the string "Hello", starting at position 0, giving "llo" and
     inserts the  string "Ha"  at position  0 to  give the  final
     string "Hallo".

     ---------------------------------------------------------------------

     RIGHT$(str$, number)

     Returns the rightmost number  of characters from the  string
     str$.

     Returns:  A string

     See also: LEFT$ MID$

     Example:  a$:=RIGHT$("Hello",2)

               Assigns the string "lo" to the variable a$.

     ---------------------------------------------------------------------
     ROUND(number, places)

     Truncates the  first parameter  to the  number of  specified
     places of decimals,  or if  places is  negative, the  output
     will be to that number of significant digits.

     Returns:  A number

     See also: FLOOR CEIL

     Example:  num:=ROUND(1.546,2)

               Assigns num to be 1.55

     Example:  num:=ROUND(213.2,-1)

               Assigns num to be 210.0

     ---------------------------------------------------------------------


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     SEED(Value)

     Sets the  seed for  the  pseudo-random number  generator  in
     RExL.  This  is  set,  by  default,  at  the  start  of   an
     application to a constant  value (resulting in a  repeatable
     array of random  numbers), but you can  make your seed  more
     random by using some function of date and time.  Value  must
     be in the range of 0 to 65535.

     Returns:  True

     See also: RAND

     Example:  SEED((DTminuteno()+DTsecondno())*65535/120)

               This expression randomly assign the seed value  to
     one of 120 different values.

     ---------------------------------------------------------------------

     SIN(angle)

     Calculates the sine of the angle angle, measured in radians.

     Returns:  A number

     See also: COS TAN RAD DEG

     Example:  value:=SIN(0.5)

               Assigns the  value  0.4794255386 to  the  variable
     value.

     ---------------------------------------------------------------------

     SLN(cost, salvage, life)

     Calculates the  straight  line,  or  constant,  depreciation
     allowance of  an  asset  per  period.  The  first  parameter
     specifies the initial cost, the second, the salvage value at
     the end of the item's life and the third parameter gives the
     expected life of the item.

     Returns:  A number

     Example:  depr:=SLN(5000,1500,5)

               Assigns 700 to the variable depr.


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     ---------------------------------------------------------------------

     SOUNDEX$(string)

     SOUNDEX$()  calculates  the  soundex  code  of  the   string
     parameter. The soundex code of a string is a four  character
     string, having  an  initial letter  (equal  to that  of  the
     source string) followed by a  three digit code, which  codes
     for the phonetic value of that string.

     SOUNDEX$() is most usually used in conjunction with database
     applications, where the precise  spelling of search keys  is
     not known,  or  where  there is  an  significant  chance  of
     misspelling of a search key.

     Returns:  A four letter string

     Example:  search1$:=SOUNDEX$("smith")

     Example:  search2$:=SOUNDEX$("smythe")

               Both search1$ and search2$ are assigned the  value
     of "S530", the soundex code of both strings.

     ---------------------------------------------------------------------

     SQRT(number)

     Calculates the square root of  a number. The number must  be
     zero or greater as the  square root of a negative number  is
     undefined.

     Returns:  A positive number

     Example:  num:=SQRT(9)

               Assigns the value 3 to the variable num.

     ---------------------------------------------------------------------

     STRING$(number, width, places)

     Returns number converted to a string of the specified  width
     and number of  decimal places. The  width must also  include
     space for a decimal  point and minus sign.  If the width  is
     larger than  the  resulting number  then  it will  be  right
     justified. If width is less than it then the string will  be
     truncated.  If  the  width  is  zero,  the  number  will  be


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       - Appendices.                         Page: 91 -


     converted to the format most suitable, that is omitting  the
     decimal point and  fraction if none  exists or inserting  an
     exponent if the number is too large for normal display.

     Returns:  A string

     Example:  num$:=STRING$(-5.2,4,1)  This   will  assign   the
     string "-5.2" to the variable num$.

     ---------------------------------------------------------------------

     SUFFIX$(num)

     SUFFIX$() returns  the  parameter  as  a  string,  with  the
     appropriate

     numeric suffix added.   This  function is  most useful  when
     applied to dates.

     Returns:  A string

     Example:  a$:=SUFFIX$(12)

               Returns the string "12th" to the variable a$

     ---------------------------------------------------------------------

     SYD(cost, salvage, life, period)

     Calculates the sum of  the year's depreciation allowance  of
     an asset for a specified of period, given the original cost,
     the salvage value at  the end of its  life of life  periods.
     The life is  measured in the  same units  as periods and  it
     typically the number of years of expected life.

     Returns:  A number

     Example:  x:=SYD(1000,100,9,3)

               Returns the value 140 to the variable x.

     ---------------------------------------------------------------------

     TAN(angle)

     Calculates the trigonometrical  tangent of  an angle,  where
     the angle is measured in radians.



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       - Appendices.                         Page: 92 -


     Returns:  A number

     Example:  value:=TAN(0.5)

               This will  assign the  value 0.5463024898  to  the
     variable value.

     ---------------------------------------------------------------------

     TERM(pmt, rate, fv)

     TERM() calculates  and  returns  the number  of  periods  of
     payment, each payment of amount pmt needed to reach fv at  a
     periodic interest rate, rate.  The rate parameter should  be
     expressed as a decimal  fraction, the percentage divided  by
     100.

     Returns:  A number

     Example:  num:=TERM(50,0.15,5000)

               Assigns the value 19.837 to the variable num.

     ---------------------------------------------------------------------

     TRIM$(str$,trimtype)

     TRIM$()  returns  the  string  parameter  str$  with  spaces
     removed from it, according  to the numeric parameter.  Legal
     values for trimtype are as follows:

     trimtype       Meaning
     0              Remove spaces from both ends of the string
     1              Remove spaces from the right end only
     2              Remove spaces from the left end only

     Returns:  A string

     Example:  a$:=TRIM$(" <-> ",0)

               Returns the string "<->" to a$.

     Example:  a$:=TRIM$(" <-> ",1)

               Returns the string " <->" to a$.

     Example:  a$:=TRIM$(" <-> ",2)



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       - Appendices.                         Page: 93 -


               Returns the string "<-> " to a$.

     ---------------------------------------------------------------------

     TRUE()

     Returns the value True. If  you place this as the first  and
     only line of a OR condition  in a rule, then that rule  will
     always evaluate to True.

     Returns:  True

     See also: FALSE

     Example:  TRUE()

     ---------------------------------------------------------------------

     UPPER$(string$)

     UPPER$()  returns  the  parameter  string  in  upper   case.
     European accented  characters  are  not translated  by  this
     function.

     Returns:  A string

     See also: LOWER$

     Example:  a$:=UPPER$("hello")

               Returns the string "HELLO" to a$.

     ---------------------------------------------------------------------

     VALUE(number$)

     VALUE() converts a string, number$, to a number. It  returns
     the converted  number if  successful or  0 if  there was  an
     error.  number$ may contain exponents using the e+99 format.

     Returns:  True if successful, False otherwise

     Example:  num:=VALUE("5.23")

               Assigns a value of 5.23 to the variable num

     ---------------------------------------------------------------------



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       - Appendices.                         Page: 94 -


     VERSION()

     Returns  the  version  number   of  RExL  under  which   the
     application is running.

     Returns:  A number

     Example:  ver:=VERSION()

               Sets the variable  ver to be x.yy  where x is  the
     major version number and yy is the minor version number.

     ---------------------------------------------------------------------

     XOR(log1,log2)

     XOR() performs a logical  exclusive-or upon the two  logical
     parameters passed to the function. The function returns True
     if the two parameters are  of different logical values,  and
     False otherwise.

     Returns:  A number

     See also: AND NOT EQV OR IMP

     Example:  val:=XOR(TRUE(),FALSE())

               Returns False to to the variable val.






















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                              Chapter 4

                         Keystroke reference


     4.1  Editor keystrokes


                   Table 4.1: Cursor movement keys

     <F1>                Context sensitive help
     <Left>              Move one character left
     <Right>             Move one character right
     <Home>              Move to start of input
     <End>               Move to end of input
     <Ctrl-Left>         Move to previous word
     <Ctrl-Right>        Move to next word
     <Backspace>         Delete character to left
     <Del>               Delete character to right
     <Shift-Enter>       Place string in scrap
     <Shift-Ins>         Paste string from scrap
     <Ctrl-U>            Undo changes to string
     <Scroll-Lock>       Move window (if applicable)
     <Alt-Equals>        Toggle macro recording
     <Alt-Minus>         Select playback macro

                 Table 4.2: Hilite bar movement keys

     <Up>, <Down>        Move one line up and down
     <PgUp>              Move up 20 lines
     <PgDn>              Move down 20 lines
     <Ctrl-Home>         Move to top of screen
     <Ctrl-End>          Move to end of screen
     <Ctrl-PgUp>         Move to to of rule
     <Tab>               Expand rule definition
     <Shift-Tab>         Contract rule definition
     <Alt-D>, <Ctrl-Y>   Delete line
     <Alt-B>             Insert blank line






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       - Appendices.                         Page: 96 -


                       Table 4.3: Modifier keys

     <Ctrl-E>,<F4>  Start expression
     <F10>          Select screen type
     <Ctrl-O>       Make rule one-pass
     <Ctrl-M>       Toggle [Multi]
     <Ctrl-S>       Toggle [Single]
     <Ctrl-N>       Toggle [Not]
     <Ctrl-W>       Toggle [While]
     <Ctrl-B>       Toggle [BackTo]
     <Ctrl-Z>       Toggle [Zap]

                     Table 4.4: Editor list keys

     <Alt-Z>,<Shift-F2>  Rule list
          <Ctrl-R>            Rule reference list
          <Tab>               Expand and enter rule
     <Alt-S>, <Shift-F3> Screen list
          <Ctrl-S>            Screen reference list
          <Tab>               Locate and position at 1st occurrence
     <Alt-U>, <Shift-F4> Unused rule list
          <Tab>               Enter rule definition
          <Ctrl-Y>, <Del>, <Alt-D> Delete rule
     <Shift-F5>          Unused screen list
          <Ctrl-Y>, <Del>,<Alt-D>  Delete screen from file
     <Alt-V>, <Shift-F6>      Variable list
          <Ctrl-R>            Variable rule-ref list
          <Tab>               Alter array dimensions
     <Ctrl-F,<Shift-F7>       Function list

                 Table 4.5: Editor miscellaneous keys

     <Alt-X>        Quit editor
     <Alt-G>        Graphic rule display
     <Alt-F5>       Show user screen
     <Ctrl-F8>      Toggle breakpoint
     <Ctrl-R>       Rule reference
     <F2>           Save application
     <F3>           Load new application
     <F9>           Debug application
     <Ctrl-F9>      Run application (no debugger)









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       - Appendices.                         Page: 97 -


     4.2  Screen designer keystrokes


               Table 4.6: Screen designer movement keys

     <Tab>          ten characters right
     <Shift-Tab>    ten characters left
     <Left>         one characters left
     <Right>        one characters right
     <Up>           one characters up
     <Down>         one characters down
     <PgUp>         to top of screen
     <Ctrl-Home>    to top of screen
     <PgDn>         to bottom of screen
     <Ctrl-End>     to end of screen
     <Ctrl-PgUp>    to top left hand corner of screen
     <Ctrl-PgDn>    to top left hand corner of screen
     <Home>         to left of screen
     <End>          to right of screen
     <Ctrl-Right>   one word right
     <Ctrl-Left>    one word left
     <Enter>        next line, to right of nearest box if possible
     <Del>          Delete character to right
     <Backspace>    Delete character to left

           Table 4.7: Screen designer field definition keys

     <Alt-F>        Display expression attached to hilited field
     <Ctrl-M>       Define menu field
     <Ctrl-T>       Define toggle list field
     <Ctrl-R>       Define radio button field
     <Ctrl-O>       Define output field
     <Ctrl-I>       Define input field
     <Ctrl-F>       Define new field $ Field control menu
     <Ctrl-C>       Define check box field
     <F10>          Edit field expression














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       - Appendices.                         Page: 98 -


              Table 4.8: Screen designer line draw keys

     <Space>, <Right>    One character right
     <Left>              One character left
     <Down>              One line down
     <Up>                One line up
     <Enter>, <Esc>      End line draw
     <Del>               Toggle delete mode
     <Alt-1>             Force horizontal emphasis to one line
     <Alt-2>             Force horizontal emphasis to two lines
     <Alt-3>             Force vertical emphasis to one line
     <Alt-4>             Force vertical emphasis to two lines

            Table 4.9: Screen designer miscellaneous keys

     <Alt-M>        Begin block mark
     <F7>           Begin block mark
     <Ctrl-S>       Show screen designer status
     <Ctrl-Y>       Delete characters & fields on line
                    Second time, delete entire line
     <F2>           Save screen
     <F3>           Load new screen
     <Alt-X>        Exit from screen designer
     <Esc>          Exit from screen designer
     <Alt-V>, <Shift-F6>      Variable list
     <Alt-Z>, <Shift-F2>      Rule list
     <Alt-S>, <Shift-F3>      Screen list
     <Alt-L>        Enter line draw mode
     <Alt-D>        Delete hilited field
     <Alt-T>        Toggle flash-intensity
     <Alt-R>        Remark last block



















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       - Appendices.                         Page: 99 -


             Table 4.10: Screen designer block mark keys

     <End>          Extend block mark to right of screen
     <Home>         Extend block mark to left of screen
     <PgDn>, <Ctrl-End>  Extend block mark to bottom of screen
     <PgUp>, <Ctrl-Home> Extend block mark to top of screen
     <Ctrl-PgDn>    Extend block mark to bottom-right of screen
     <Ctrl-PgUp>    Extend block mark to top-left of screen
     <Up>           Extend block mark one line up
     <Down>         Extend block mark one line down
     <Right>        Extend block mark one line right
     <Left>         Extend block mark one line left
     <Tab>          Extend block mark ten characters right
     <Shift-Tab>    Extend block mark ten characters left
     <F8>, <Enter>, <Alt-M>   Select marked block
     <Esc>          Terminate block mark
     <Alt-D>, <Ctrl-Y>, <Del> Delete marked block
     <Alt-B>        Draw box in marked block


     4.3  Debugger keystrokes


            Table 4.11: Debugger hilite bar movement keys

     <Tab>          Expand rule definition
     <Shift-Tab>    Contract rule definition
     <Left>         Move cursor left one character
     <Right>        Move cursor right one character
     <PgUp>         Move up 20 lines
     <PgDn>         Move down 20 lines
     <Up>           Move up one line
     <Enter>        Move down one line
     <Down>         Move down one line
     <Ctrl-Home>    Move to top of screen
     <Ctrl-End>     Move to end of screen
     <Ctrl-PgUp>    Move to top of rule

                    Table 4.12: Debugger list keys

     <Alt-Z>, <Shift-F2>      Rule list
     <Tab>                    Expand rule definition
     <Alt-S>, <Shift-F3>      Screen list
     <Alt-U, <Shift-F4>       Unused rule list
     <Shift-F5>               Unused screen list
     <Alt-V>, <Shift-F6>      Variable list
     <Ctrl-F>, <Shift-F7>     Function list



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       - Appendices.                         Page: 100 -


               Table 4.13: Debugger miscellaneous keys

     <Alt-X>                  Quit debugger
     <Alt-F5>                 Show user screen
     <Ctrl-E>, <Ctrl-F4>      Evaluate expression
     <Ctrl-W>, <Ctrl-F7>      Add watch
     <Alt-F7>                 Animate debugger
     <F4>                     Execute to cursor
     <F5>                     Expand debugger window
     <F6>                     Toggle windows
     <F7>                     Trace execution
     <F8>                     Step execution
     <F9>                     Run program
     <Ctrl-F9>                Remove all breakpoints and run program
     <Ctrl-F8>                Toggle breakpoint
     <Space>                  Trace execution
     <Ctrl-O>                 Return cursor to origin
     <Alt-Equals>             Toggle macro recording
     <Alt-Minus>              Select playback macro
     <Alt-D>, <Ctrl-Break>    Pass control to debugger






























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       - Appendices.                         Page: 102 -


                Table 4.14: KB function return values

     <Backspace>    8        <Left>          331     <Alt-4>          379
     <Tab>          9        <Right>         333     <Alt-5>          380
     <Enter>        13       <End>           335     <Alt-6>          381
     <Esc>          27       <Down>          336     <Alt-7>          382
     <Shift-Tab>    271      <PgDn>          337     <Alt-8>          383
     <Alt-Q>        272      <Del>           339     <Alt-9>          384
     <Alt-W>        273      <Shift-F1>      340     <Alt-0>          385
     <Alt-E>        274      <Shift-F2>      341     <Alt-Minus>      386
     <Alt-R>        275      <Shift-F3>      342     <Alt-Equals>     387
     <Alt-T>        276      <Shift-F4>      343     <Ctrl-PgUp>      388
     <Alt-Y>        277      <Shift-F5>      344     <Shift-Insert>   500
     <Alt-U>        278      <Shift-F6>      345     <Shift-End>      501
     <Alt-I>        279      <Shift-F7>      346     <Shift-Down>     502
     <Alt-O>        280      <Shift-F8>      347     <Shift-PgDn>     503
     <Alt-P>        281      <Shift-F9>      348     <Shift-Left>     504
     <Alt-A>        286      <Shift-F10>     349     <Shift-Right>    506
     <Alt-S>        287      <Ctrl-F1>       350     <Shift-Home>     507
     <Alt-D>        288      <Ctrl-F2>       351     <Shift-Up>       508
     <Alt-F>        289      <Ctrl-F3>       352     <Shift-PgUp>     509
     <Alt-G>        290      <Ctrl-F4>       353     <Shift-Enter>    510
     <Alt-H>        291      <Ctrl-F5>       354     <Ctrl-A>         601
     <Alt-J>        292      <Ctrl-F6>       355     <Ctrl-B>         602
     <Alt-K>        293      <Ctrl-F7>       356     <Ctrl-C>         603
     <Alt-L>        294      <Ctrl-F8>       357     <Ctrl-D>         604
     <Alt-Z>        300      <Ctrl-F9>       358     <Ctrl-E>         605
     <Alt-X>        301      <Ctrl-F10>      359     <Ctrl-F>         606
     <Alt-C>        302      <Alt-F1>        360     <Ctrl-G>         607
     <Alt-V>        303      <Alt-F2>        361     <Ctrl-J>         610
     <Alt-B>        304      <Alt-F3>        362     <Ctrl-K>         611
     <Alt-N>        305      <Alt-F4>        363     <Ctrl-L>         612
     <Alt-M>        306      <Alt-F5>        364     <Ctrl-N>         614
     <F1>           315      <Alt-F6>        365     <Ctrl-O>         615
     <F2>           316      <Alt-F7>        366     <Ctrl-P>         616
     <F3>           317      <Alt-F8>        367     <Ctrl-Q>         617
     <F4>           318      <Alt-F9>        368     <Ctrl-R>         618
     <F5>           319      <Alt-F10>       369     <Ctrl-S>         619
     <F6>           320      <Ctrl-Left>     371     <Ctrl-T>         620
     <F7>           321      <Ctrl-Right>    372     <Ctrl-U>         621
     <F8>           322      <Ctrl-End>      373     <Ctrl-V>         622
     <F9>           323      <Ctrl-PgDn>     374     <Ctrl-W>         623
     <F10>          324      <Ctrl-Home>     375     <Ctrl-X>         624
     <Home>         327      <Alt-1>         376     <Ctrl-Y>         625
     <Up>           328      <Alt-2>         377     <Ctrl-Z>         626
     <PgUp>         329      <Alt-3>         378     <Ctrl-Enter>     700




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       - Appendices.                         Page: 103 -








                              Chapter 5

                            Error Messages


     5.1  Error messages common to runtime and editor


     5.1.1  Bad help file format

     The help file has become corrupted somehow.  The only way to
     remove this error is to restore a copy of the help file from
     the distribution disks, or  archive file which you  received
     your copy of RExL in.

     5.1.2  Cannot locate system

     RExL cannot shell to DOS because it cannot locate the system
     files which are required.  This is most likely to be  caused
     by the  COMSPEC environment  variable set  incorrectly.   It
     should contain the  name, directory and  drive of your  main
     command processor.   Try issuing the  following DOS  command
     from the  normal DOS  prompt, if  none  of the  above  makes
     sense.

     set comspec=c:\command.com

     5.1.3  Cannot open print file

     RExL is unable to open the file which was specified  instead
     of the printer. Generally, this is caused by running out  of
     file handles.   This condition can  be rectified by  placing
     the following line in your CONFIG.SYS file:

     files=20

     5.1.4  Couldn't open file

     RExL is unable to open some file. Generally, this is  caused
     by running  out of  file handles.    This condition  can  be
     rectified by placing the  following line in your  CONFIG.SYS
     file:


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       - Appendices.                         Page: 104 -


     files=20

     5.1.5  Macros nested too deep (20=max)

     You're most unlikely to encounter this error.  It  indicates
     that you are trying to  execute a macro from within a  macro
     from within a  macro etc,  to a  level of  twenty deep,  the
     maximum allowable.

     5.1.6  Help file index is not loaded

     If RExL  was unable  to locate  the  help file,  this  error
     message will  be  displayed if  any  of  the help  keys  are
     pressed.

     5.1.7  Unable to locate help file

     When the editor starts up, it preloads a portion of the help
     file to allow  more rapid access to  the information in  it.
     If the editor is not able to locate the help file in the  in
     the  current  directory  or  the  or  list  of   directories
     specified in  the REXL  environment variable,  then it  will
     isue this error message.

     Automatic  preloading  can  be   disabled  by  setting   the
     Options|Help menu option to slow.

     5.1.8  Macro recursion not allowed

     RExL will not allow  a macro being defined  to call a  macro
     which in turn executes the keystroke which is being defined.
     This is to prevent infinite recursion of the macro facility.

     5.1.9  Error loading configuration file

     The  RExL  configuration  file   REXL.CFG  in  the   current
     directory is invalid or could not be loaded for some reason.
     The  configuration  file  format  changes  from  version  to
     version, so this error may  appear if you run a new  version
     of RExL without  deleting the  old configuration  file.   If
     this occursm, just ignore the error and it won't re-appear.

     5.1.10  Zero memory allocation request!

     For some reason, a zero length request has been made to  the
     memory allocator.  This should never occur, thus  indicating
     a bug if  it does.   Note  down the  exact circumstances  in
     which the error occurred and report it to us.


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       - Appendices.                         Page: 105 -


     5.1.11  Not enough memory to perform selected operation

     There is not enough memory available for RExL to do whatever
     you just asked it to.   If you have any TSR programs  loaded
     in memory, then unload them, re-enter RExL and try again.

     5.1.12  This window is not movable

     You have just tried to  move a window which is not  movable.
     Generally, the only unmovable windows are the system menus.

     5.1.13  No directories available

     RExL is  unable to  locate any  directories in  the  current
     directory for the File|Change directory menu.  This  warning
     only occurs if  you are  in the  root directory  of a  drive
     which has no subdirectories.

     5.1.14  No files in directory

     This error in a file  selection menu if the specified  drive
     and directory  do  not  contain any  directories  nor  files
     matching the stipulated file specification.

     5.1.15  No macros defined

     The Options|Save macro file menu option has been chosen  but
     there are no macros currently defined in memory to be saved.

     5.1.16  --- Out of memory ---

     RExL has run out of memory in some critical operation  where
     memory must be  present.  The  best course  of action it  to
     quit RExL  as  soon as  possible,  remove any  TSR  programs
     resident and to retry.

     5.1.17  No screens defined

     You have requested the screen list, but there are no screens
     present to make the list from.

     5.1.18  Not enough memory to load system

     The DOS  command processor  COMMAND.COM requires  a  certain
     amount of memory  to run, depending on  the version of  DOS.
     If there is not enough memory present then this warning will
     appear.



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       - Appendices.                         Page: 106 -


     5.1.19  No unused rules available

     You have  selected  the  unused  rule  list,  but  RExL  has
     determined that all rules are used in the listing.  Remember
     that recursive rules are taken  to be used, irrespective  of
     whether they are called by  any other rules.  When  scanning
     for unused rules, RExL also checks the line buffer to locate
     rules, marking them as used if any are present.

     5.1.20  No unused screens available

     You have  selected  the unused  screen  list, but  RExL  has
     determined that all  screens defined in  the current  screen
     file are  used in  the listing.   When  scanning for  unused
     screens, RExL also checks the line buffer to locate screens,
     marking them as used if any are present.

     5.1.21  No variables defined

     You have  selected  the variable  list,  but RExL  has  been
     unable to find any variables in its internal list.

     5.1.22  Rule is not used in current listing

     RExL has tried and failed to find any references to the rule
     for which you  have just  requested a  reference list.  This
     error can  occur from  the editor  window when  <Ctrl-R>  is
     pressed, or in the rule list, with the same keystroke.

     5.1.23  Error saving configuration file

     RExL was unable  to save the  configuration file,  REXL.CFG,
     correctly.  If a partial  file was saved, then it should  be
     deleted since  it  will generate  an  error when  RExL  next
     starts from that directory.

     5.1.24  Screen is not used in current listing

     RExL has  tried and  failed to  find any  references to  the
     screen for which you have  just requested a reference  list.
     This error can  occur in the screen  list, when <Ctrl-R>  is
     pressed.

     5.1.25  Screen file is corrupt

     The screen file has somehow  become corrupted and no  longer
     can be read by REXL. The  only action which can be taken  is
     to restore the screen file from your last backup.


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       - Appendices.                         Page: 107 -


     5.1.26  Too many files open

     RExL has failed when attempting  to enter a DOS shell  since
     it was unable to open the command processor file because  of
     lack of available file handles.  Close some files and retry.

     5.1.27  Too many keys in macro (500=max)

     RExL can store up to 500 keystrokes in a single macro.  This
     error appears if you have  attempted to go past this  limit.
     If you  require that  more than  500  keystrokes are  to  be
     played back, then you should define one macro which does the
     first section  and  then  calls a  macro  which  does  those
     remaining.

     5.1.28  Variable is not used in current listing

     You have tried to get RExL to generate a variable  reference
     list for a  variable which does not  have any references  in
     the listing.   Note that RExL  does not  look in the  screen
     file for variables, so that  a variable which is  apparently
     unused may be present in some screen.

     5.1.29  Wrong source file format

     RExL  application  listing  files  change  format  from  one
     version to another.  This error is generated if you  attempt
     to load an application file  saved from one version of  RExL
     into  another  version.     To  transfer  listings   between
     versions, use the Import|ASCII load and save options.

     5.1.30  Wrong screen file format

     The editor has  attempted to load  an incorrectly  formatted
     screen from a screen file.  This is usually caused by  using
     different versions of RExL.   Use the Import|ASCII load  and
     save menu  options to  move applications  between  different
     versions of RExL.

     5.1.31  Error opening screen file

     RExL was unable to open the screen file associated with  the
     current application.   This is  probably due  to having  too
     many files open.  Close some files and try again.






      - RExL  Version 2.10  Copyright 1992, The Software Loft -
       - Appendices.                         Page: 108 -


     5.2  Error messages unique to editor


     5.2.1  Incorrect format in listing file

     RExL has found some incorrectly formatted item in the  ASCII
     listing file, which  it is unable to  process.  ASCII  files
     are not intended for editing with text editors and  attempts
     to do so may produce errors such as this one.

     5.2.2  Cannot nest fields

     All field types, except menu fields, cannot nest or  overlay
     each other.

     5.2.3  Can only delete recursed rule from first level of
     recursion

     A rule which is in the rule stack cannot have lines  deleted
     from it,  since  they  might  corrupt  the  rule  stack  and
     possibly crash  RExL.    This error  is  generated  when  an
     attempt is made to delete  a block from a recursive rule  or
     to delete a line from a recursive rule.

     If the line or lines must be deleted, then you should return
     to the root  (by pressing <Shift-Tab>  repeatedly) and  then
     entering the  rule by  selecting it  in  the rule  list  and
     pressing <Tab>.

     5.2.4  Unable to locate runtime module

     RExL has tried  to run the runtime  and debugger module  but
     was unable to find it.  When searching, RExL first  searches
     the current  directory, then  the directory  or  directories
     specified by the REXL environment variable, and finally  the
     entire DOS path.  Only when all of these have been  searched
     unsuccessfully, will this error message be displayed.

     5.2.5  Area crosses fields

     An attempt has been made to move or copy a block of text and
     fields from one place  on the screen to  another and in  the
     process overlaying  some previously  defined fields.    RExL
     does not allow this and issues this message when it occurs.






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       - Appendices.                         Page: 109 -


     5.2.6  Can't have a field of this type in this screen

     You have tried to define a field of a type not permitted  in
     the current screen.   Consult the  table in  the chapter  on
     using the screen designer to find out the valid combinations
     of field type and screen type.

     5.2.7  Illegal array dimension

     When entering the  size of  an array  dimension, an  invalid
     number was entered.  Re-enter the number and try again.

     5.2.8  Maximum number of fields reached

     Screens can contain  a maximum of  127 fields.   Any  screen
     which contains more than that amount should be  re-designed,
     since the screen updating  process may become noticeable  on
     slow PC's.

     5.2.9  Memory low, should save now!

     The amount of  memory available  in RExL's  memory pool  has
     gone below  2,000  bytes.    In  order  to  save  a  listing
     successfully, RExL needs  about 1,000 bytes,  so saving  and
     quitting now would be a good idea.

     5.2.10  Not used in listing

     You have tried  to enter a  rule which  is defined, but  not
     used, in the current listing.

     5.2.11  This is the main rule and is called to start the kbs

     You have  attempted to  find rule  references for  the  main
     program rule. This is only a diagnostic message.

     5.2.12  Cannot change rule name to one already existing

     Normally, RExL allows for and automatically compensates  for
     the changing of the name of any rule in an application.   It
     does not, however, allow  a rule name to  be changed to  one
     which exists already, since a name conflict would arise. Any
     changes made to the rule name are undone.







      - RExL  Version 2.10  Copyright 1992, The Software Loft -
       - Appendices.                         Page: 110 -


     5.2.13  This screen already exists

     As with rule names previously, it is not possible to  change
     the name  of a  screen to  one  which already  exists.   Any
     changes made to the screen name are undone.

     5.2.14  Toggle fields must be more than 5 and less than 75
     characters wide

     The width  of  toggle  fields  must  be  between  6  and  74
     characters inclusive.

     5.2.15  Unable to create screen file

     RExL was  unable to  create a  screen  file to  go with  the
     current application.   This  is  probably caused  either  by
     having no  disk space  left, or  by having  no file  handles
     available.


     5.2.16  Error saving file

     RExL was,  for  some  reason, unable  to  save  the  current
     application to disk successfully.   This is probably  caused
     either by having no  disk space left, or  by having no  file
     handles available.

     5.2.17  Error loading file

     RExL was, for  some reason,  unable to  load an  application
     from disk successfully.  This  is probably caused by  having
     no file handles available.

     5.2.18  Error loading screen file

     RExL was unable to load the screen file associated with  the
     current application.

     5.2.19  Cannot change name of Main Program

     It is  not possible,  in the  current  version of  RExL,  to
     change the name of the root rule.








      - RExL  Version 2.10  Copyright 1992, The Software Loft -
       - Appendices.                         Page: 111 -


     5.3  Error messages unique to runtime-debugger


     5.3.1  Array bounds overflow

     The runtime  module has  detected an  attempt to  access  an
     array element beyond the defined bounds of the array.  Array
     bounds can be set  in the editor from  the variable list  by
     selecting the array, pressing <Tab> and entering the size of
     the array.

     5.3.2  Can't set a breakpoint here

     A breakpoint can only be  set on a line which will  actually
     be  executed.    These  lines  include  rules,  screens  and
     expressions but do not include blank lines.

     5.3.3  Cannot open printer for output

     Cannot write to print device
     Cannot close print device ,

     The printer device cannot be  opened for output, written  to
     or closed.  If output is directed to the printer, then  make
     sure that it is connected and online.  Alternatively, if the
     printer destination has been set using the OUTPUT() command,
     then make sure that the filename is valid.

     5.3.4  Cannot find editor

     You have run the debugger from the editor or you have passed
     the -e  option on  the command  line,  but the  debugger  is
     unable to locate  the editor.   The debugger will  terminate
     when this  message  is  cleared.   When  searching  for  the
     editor, RExL searches the current directory, the directories
     specified in  the REXL  environment directory  and then  the
     entire DOS path.

     5.3.5  Divide by zero

     Your  application  has  attempted  a  to  divide  a  numeric
     expression by  zero,  which  is  a  computationally  invalid
     operation.

     5.3.6  String-numeric collision

     This error should never occur  in normal operation of  RExL.
     It indicated  that an  internal parsing  error has  occurred


      - RExL  Version 2.10  Copyright 1992, The Software Loft -
       - Appendices.                         Page: 112 -


     during the assignment  of some quantity of  to another.   If
     you receive this error, then contact us.

     5.3.7  Can't have string for radio button parameter

     Only numeric variables are valid radio button LValues.  This
     error is  kept for  reasons  of compatibility  with  earlier
     versions of RExL.

     5.3.8  Stack underflow

     This error  should not  occur.   It  indicated that  one  of
     RExL's  internal  stacks  (numeric,  string  or  array)  has
     underflowed.  If you receive this error, then contact us.

     5.3.9  Stack overflow

     This error  should not  occur.   It  indicated that  one  of
     RExL's  internal  stacks  (numeric,  string  or  array)  has
     overflowed.  If you receive this error, then contact us.

     5.3.10  Numeric value out of range

     Certain mathematical functions require that their parameters
     be within certain ranges.   For example, the LOG()  function
     is only defined for values  greater than zero, and  attempts
     to find logiarithms  of numbers  less thanor  equal to  zero
     will generate this error.

     5.3.11  Rule stack overflow

     You have  tried  to  recurse beyond  the  maximum  limit  of
     recursion.   By default,  the limit  is 100  entries on  the
     stack, but it can be increased from within the editor  using
     the Options|Rule stack menu option  or by specifying the  -s
     option on the command line to the debugger.

     5.3.12  Invalid database file handle

     An operation  involving  database  file handles  has  failed
     because an  invalid file  handle was  passed.    This  error
     generally occurs in expressions using RExL's @variable.field
     construction, when  <variable>  does  not  contain  a  valid
     database file handle.






      - RExL  Version 2.10  Copyright 1992, The Software Loft -
       - Appendices.                         Page: 113 -


     5.3.13  Unable to allocate rule stack

     The runtime and debugger module has been unable to  allocate
     enough memory to the runtime stack and consequently will not
     attempt to run the application.   Make sure that you're  not
     passing some over-large  value to the  module either on  the
     command line, with the -s option, or from within the  editor
     using the Options|Rule stack option.

     5.3.14  Math error : Parameter out of range in function XXX

     The function XXX has been passed a value which is out of the
     range for  which the  function is  defined.   The  functions
     which can  generate this  error  are SIN(),  COS(),  ACOS(),
     ASIN(), TAN(), ATAN(), LOG() and LOG10().

     5.3.15  Math error : Parameter singularity in function XXX

     Certain functions, while defined across certain ranges  have
     values within the range for which the return value generates
     a singularity.    For example,  the  TAN() function  is  not
     defined for PI/2  radians and an  attempt to calculate  this
     value would cause this error to be generated.

     5.3.16  Math error : numeric overflow

     You have tried to generate a result greater than the maximum
     value which RExL can cope with, about 2.7E308, absolute.

     5.3.17  Math error : numeric underflow

     This error indicates  that the result  of a calculation  has
     underflown and cannot  be represented accurately.  Generally
     speaking, a numeric underflow will return a zero value.

     5.3.18  Math error : precision loss

     This error indicates that a calculation has not been carried
     out to  a sufficient  degree of  accuracy.   This  generally
     occurs  when   evaluating  functions   close  to   parameter
     singularities.


     5.4  Critical Errors


     These errors occur  when some item  of hardware attached  to
     your PC does not appear to be functioning correctly.   These


      - RExL  Version 2.10  Copyright 1992, The Software Loft -
       - Appendices.                         Page: 114 -


     errors are entirely  DOS generated  and RExL  itself can  do
     little to  rectify  them.   Like  the other  error  messages
     above, these are trappable using the ERok() function.  These
     errors are  listed in  increasing order  of obscurity,  with
     errors at the bottom of the list being the most unlikely  to
     occur.

     5.4.1  Write protect error

     An attempt has  been made to  write information  to a  write
     protected disk.   Remove  the   write  protect tab  and  try
     again.

     5.4.2  Drive not ready

     The disk drive accessed in the last operation was not ready.
     Make sure that the disk  is inserted correctly, is  properly
     formatted and can be read from the drive.

     5.4.3  Printer out of paper

     The printer  device  has  returned  an  error  code  to  DOS
     indicating  that  something  was  wrong  with  the  printer.
     Possible causes include no paper in the printer, the printer
     being turned off or off line or a paper jam.

     5.4.4  Write fault

     DOS has tried  to write to  some block  or character  device
     driver but  the driver  returned an  error code,  indicating
     that it was unable to  perform the operation.  When  applied
     to printers, it generally means that the printer has run out
     of paper or has been turned off during a print run.

     5.4.5  Read fault

     DOS has tried  to read from some  block or character  device
     driver but  the driver  returned an  error code,  indicating
     that it was unable to perform the operation.

     5.4.6  General Failure

     This is a  general purpose catch-all  error message,  saying
     that something went wrong, but DOS was unable to figure  out
     exactly what.   When applied  to disks,  it generally  means
     that the disk is not formatted or is not of the correct size
     for the disk drive.



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       - Appendices.                         Page: 115 -


     5.4.7  Sector not found

     This error indicates that a sector on a  disk has been found
     to be invalid, probably caused by a corruption of some  type
     on the disk in question.

     5.4.8  Unknown unit

     A request has been made by DOS to some device which does not
     exist or has not responded.

     5.4.9  Unknown command

     An IOCTL request  has been made to  some block or  character
     device driver  but the  command was  not recognised  by  the
     driver.

     5.4.10  CRC error

     The cyclic redundancy  check on  disk reads  and writes  has
     failed, indicating a  faulty drive  or improperly  formatted
     disk.

     5.4.11  Bad request structure length

     An IOCTL request  has been made to  some block or  character
     device driver but  the format  of the  request structure  is
     incorrect.

     5.4.12  Seek error

     BIOS was unable to locate the disk sector requested in a DOS
     call.

     5.4.13  Unknown media type

     The disk which has just been accessed does not have a  valid
     media identifier.  This is usually caused by using Unix (and
     other system) formatted floppy disks.











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       - Appendices.                         Page: 117 -








                              Chapter 6

                           Extra Utilities


     This appendix documents  the extra  utilities supplied  with
     RExL which  are  only  available  in  the  fully  registered
     version.


     6.1  RExLPC


     RExLPC is a  utility which will  combine a RExL  application
     image file, its  associated screen file  and a special  stub
     file into a single standalone executable file, suitable  for
     distribution.  It  is provided  as a  neater alternative  to
     RExLRT, described  further on  in this  chapter.  Typically,
     RExLRT is  used  to  distribute applications  which  can  be
     modified  by   the   end-user,   or  may   require   on-site
     modification by the  developer.  On  the other hand,  RExLPC
     can be  used  to provide  a  single, faster  DOS  executable
     application which  cannot  be  decompiled.  Backups  of  the
     original versions of  the application must  be kept if  they
     may need to be modified at a later date

     As a  rough guide  to performance  gains, RExL  applications
     converted with  RExLPC will  run code  approximately two  to
     four times as fast as REXLRD and REXLRT will.  Corresponding
     C programs will  run about  half as  fast to  twice as  fast
     again.   For database  operations, the  speed gain  will  be
     small because most time is  spent within the database  code,
     which is common both the stub and the other executables.

     RExLPC takes two parameters on  the command line, the  first
     specifies the RExL application  file to be converted,  while
     the second parameter specifies the DOS executable file to be
     created.  The base stub file REXLSTUB.COD must be accessible
     either through the REXL environment  variable or on the  DOS
     PATH.   While  the postfix  compiler  is running,  it  posts
     progress reports on the screen, to keep you informed of  how
     far it  has  got.    When the  compiler  finishes,  it  will


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     generate an  executable  file  as specified  by  the  second
     command line parameter.  If an executable file of this  name
     exists already, then  it will  be overwritten.  Applications
     should be fully working and debugged when passed through the
     compiler.

     The resulting executable file can be copied, distributed and
     run like any other DOS executable.

     The process involved in conversion is as follows.   Firstly,
     the screen file and application images are loaded as  normal
     and  the  stub  file  is  copied  to  the  specified  output
     executable file.  Then the postfix compiler module  postfix-
     compiles the application and  appends the generated code  to
     the stub file.  Finally, the screen file is postfix compiled
     and then appended  to the  stub.   The resulting  executable
     file can be copied, distributed  and run like any other  DOS
     executable and does not require any of the files (which were
     required to build it) to be present when the program is run.
     As with  all other  RExL executable  files, you  should  not
     attempt to  compress  the  file  with  compressors  such  as
     PKLite, DIET, LZexe and such  like because of the nature  of
     the files.

     Finally, a minor point of incompatibility with RExL:  RExLPC
     does not supports the LOAD() function as it exists in  RExL,
     because of the different .RXL and .EXE internal formats.  In
     the compiled version, the LOAD()  function will look for  an
     executable file of  the same name  as the application  image
     and load and  execute that instead.   This  seems to be  the
     most acceptable  solution  and  will work  transparently  if
     multiple  applications   are   converted   and   distributed
     together.  If  this is  not satisfactory,  then the  OScmd()
     function can be  used to run  the runtime  (or the  runtime-
     debugger module), passing it the name of the application  to
     run.

     For example,  the  command  LOAD("TEST")  which,  in  normal
     circumstances  would   load   an  application   image   file
     "TEST.RXL", would be interpreted by RExLPC as a call to load
     and  run  the   file  "TEST.EXE",   overlaying  the   caller
     application (unlike a call to OScmd(), where the application
     regains  control  when   the  called  program   terminates).
     Alternatively, the command OScmd() could be used to run  the
     application using a call such as: OScmd("rexlrt test").





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     6.2  RDU


     6.2.1  Introduction

     RDU, the  RExL Database  Utility, is  a standalone  database
     manager which can  be used to  manage dBase III+  compatible
     files.  It can create  and modify database structures,  edit
     and browse database files and create and maintain dBase III+
     index files.

     RDU is quite simple  to operate and is  based upon the  same
     interface as other RExL programming tools.

     6.2.2  Loading and Running

     RDU is loaded  by typing  RDU at  the DOS  prompt and  needs
     about 180k  of  DOS memory  to  run.   To  start work  on  a
     database file  immediately, rather  than having  to use  the
     menu system to load one, you can simply pass the name of the
     database on  the command  line.   For example,  to load  and
     start work on a database named "CUSTOMER.DBF", issue the DOS
     command `RDU customer'.  The default and necessary extension
     of ".DBF" will  be automatically  appended for  you, so  you
     don't need to specify it.

     When RDU  has  loaded, you'll  be  presented with  the  main
     screen which is similar to RExL's editor.

     There are five  pull down  menus in  RDU which  are used  to
     control the program.   The next  five sections will  explain
     each menu.

     6.2.3  RDU menu system

     6.2.3.1  File Menu

     There are seven  options in this menu,  based upon those  in
     the File Menu of RExL's editor.  The options are as follows:

         o  Use File: When selected, this option pops up a dialog
            box prompting for a database  file to open.  You  can
            either  enter  a  database  name  directly  or  press
            <Enter> and select from a list.  When a database file
            has been selected,  it can be  edited using the  Edit
            menu.




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         o  Use Index:  When  a  database  has  been  opened  and
            selected, an index file can  be opened, to order  the
            contents of the  database. When this  menu option  is
            selected, a file name  dialog box appears,  prompting
            for an index  file to  open.   As with  the Use  File
            option, an  index name  can be  entered directly  or,
            upon pressing <Enter>, an  index file can be  selcted
            from a list. If there is no database open, then  this
            option cannot be used.

         o  Remove: This choice allows you to delete a file  from
            disk. You may need to do  this is you want to save  a
            file on disk, but are unable to do so through a  lack
            of disk space.

         o  Change Dir: This option will allow you to change  the
            active directory.  The format  used here is much  the
            same as that used in the file name input routine, the
            only  differences  being  that  no  file  names   are
            displayed in  the list  and that  the current  active
            path  (drive  name  with  full  directory)  will   be
            displayed on the  status line  at the  bottom of  the
            screen.

         o  Default Drive:  When this  option is  chosen, a  menu
            will pop up displaying the list of available DOS disk
            drives. As with  the directory  selection above,  the
            current  active  path  is  displayed  on  the  status
            display line at the bottom of the screen.

         o  OS Shell: If you  want to run a  DOS command, but  do
            not wish to  exit from RDU  permanently, choose  this
            option to go into a  DOS shell. While you are in  the
            shell, you should not,  under any circumstances,  run
            any T$SR programs (such  as Sidekick, ScrGrab and  so
            forth), since these programs change critical area  of
            the computer's  memory which  may cause  it to  crash
            unpredictably when you  return to RDU.  When you  are
            finished in the shell, type `exit' at the DOS  prompt
            to return.

         o  Quit: This option terminates  RDU and returns you  to
            DOS permanently.  Since any  work done is written  to
            the database immediately, there is no `File has  been
            changed' type prompt  generated when  this option  is
            selected.




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     6.2.4  Edit Menu

     This six  option menu  is used  to control  the editing  and
     deletion of  information  in  the  database  file  currently
     selceted.   If there  is no  database  file open,  then  the
     options in this menu may not be used.

     The first  two  options,  edit  and  browse,  are  used  for
     changing and viewing information in the current database and
     are both `variations on a theme'.  In either of these modes,
     the fields in  the database are displayed  on the left  hand
     side of  the  screen and  the  contents  of the  fields  are
     displayed to the right of the field names.

     The <PgUp> and <PgDn> keys are used to move to the next  and
     previous records respectively,  while <Ctrl-PgUp> moves  the
     record pointer to  the top of  the database and  <Ctrl-PgDn>
     moves it to the last record.

     If there are more fields in the database than can be  fitted
     on the screen, then <Ctrl-Home> moves the first field in the
     database to the  top of the  screen, while <Ctrl-End>  moves
     the last field to the bottom line of the screen.

     In browse mode, it is  not possible to edit the contents  of
     the database  and  there  is therefore  no  cursor  visible.
     Pressing <Up> and <Down>  will move increment and  decrement
     the top field on the  screen, if there are more fields  than
     can be fitted, otherwise the  keys have no effect in  browse
     mode.

     In edit mode, <Up> and <Down> move to the previous and  next
     fields in the database, scrolling the field list, if needed.
     <Tab> and <Shift-Tab>  perform the same  action as <Up>  and
     <Down>.  If <Down> or <Enter> is pressed on the final  field
     in the  record, when  the record  pointer  is at  the  final
     record in the database, then the prompt Append records? will
     appear.  If the Yes  option is selected, then a record  will
     be appended to  the database and  editing will proceed  from
     the new record. If the no option is selected, then no record
     will be added.

     When editing date fields, the date entered will be displayed
     and must be entered in the format appropriate to the country
     set up on your machine.  If a valid date is entered, then it
     will be silently  converted to a dBase  date and written  to
     the database  file.   RDU will  not  allow you  to enter  an
     invalid date.


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     Logical fields are one character wide and treat values of Y,
     y, T and t as true and all other characters as false.   True
     values are  stored  as  Y  and false  values  as  N  in  the
     database.

     Character fields may be from  1 to 255 characters wide.   If
     the field width of the field being edited is greater than 67
     characters, then a small arrow will be displayed before  the
     start of  the edit  area.   The arrow  can be  one of  three
     characters, depending on  whether the edit  area extends  to
     the  left  of  the  currently  displayed  area  (uses  ASCII
     character 27), whether it extends on both sides (uses  ASCII
     character 29), or whether it extends to the left (uses ascii
     character 26).

     Any changes made  to the database  file are  written to  the
     file immediately.

     The six options in the Edit menu are as follows:

         o  Edit record:  Enters  RDU's record editing  facility,
            as described above.

         o  Browse record: Enters RDU's record display  facility,
            as described  above.  The  contents of  the  database
            cannot be changed when using this mode.

         o  Delete record:  This option will set the delete  flag
            of the  current  record.    Because  this  option  is
            relatively common, the <Alt-D> keystroke can be  used
            to toggle  this flag.   Note  that when  a record  is
            marked for  deletion, it  is not  physically  removed
            from the database.

         o  Recall deleted record:  This option clears the delete
            flag for the current record in the current  database.
            <Alt-D> can be  used to clear  the delete  flag on  a
            record, if it has been set.

         o  Pack database:  All records marked for deletion in  a
            database will be  removed when it  is packed.   After
            this operation, the records  cannot be recalled  from
            deletion using the Recall menu option.

         o  Zap database:  This  menu option permanently  removes
            all records  in  a  database. As  with  packing,  the
            records cannot be retrieved afterward.



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     6.2.5  Search Menu

     The search  menu  is used  for  searching for  and  locating
     information in database files.   There are three options  in
     this menu:

         o  Locate string: This option is  used to search for  an
            occurrence of a string within a field in the  current
            database.

            When the  option  is  chosen,  a  menu  will  pop  up
            containing the names of all the fields in the current
            database.  The  field selected here  will be the  one
            searched in during the  searching operation.  Once  a
            field has  been selected,  a dialog  box will  appear
            prompting for a string to  locate.  The dialog  input
            area will be as wide as the field being searched in.

            When a  search string  has been  entered, the  record
            pointer will  be reset  to the  top of  the file  and
            searching will  begin  from there.    If a  match  is
            found, then the matching record will be displayed and
            a prompt box will  appear, asking whether the  search
            should continue  from that  location to  try to  find
            another occurrence of the string.

            The record counter in the bottom right of the  screen
            is constantly updated during  the search to keep  you
            informed of its progress.

         o  Seek string: This  option is used to  seek for a  key
            string in an index file.  When selected, a dialog box
            appears, prompting for a string to seek for.

            If the seek  is successful, then  the record  pointer
            wil be  placed at  the  record whose  key  expression
            matches that entered.  If it is unsuccessful, then an
            error message will be displayed.

            Since records are in index  order when an index  file
            is open, you  will not  be prompted  to continue  the
            seek when it has successfully found something.

         o  Go to record:  This  option will prompt for a  record
            number to jump to.  If the record number specified is
            less than 1 or greater than the number of records  in
            the  database,  then   no  action   will  be   taken.
            Otherwise, the  record pointer  will  be set  to  the


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            specified record number.   The record  number is  not
            dependant on any index files open.

     6.2.6  Utilities Menu

     This menu has six options as follows:

         o  Create  database:  This  option  is  used  to  create
            database structures.  When  it  is  first  chosen,  a
            dialog box appears prompting for a file name to  call
            the structure which is about to be created.  When one
            has  been  entered  the  creation  of  the  structure
            begins.

         o  The structure creation  box has four  columns in  it.
            The first is  for field names,  the second for  field
            types, the  third  for  field widths  and  the  final
            column for field decimal places.

         o  For logical and date fields, the field width is fixed
            at one  and eight  characters respectively,  with  no
            decimal places.  The dialog will not allow figures to
            be entered in  the final  two columns  for these  two
            field types.  Similarly, it is not possible to  enter
            decimal field widths for character fields.   RDU will
            not allow duplicate field names  to exist in a  file,
            displaying an error if this is attempted.

         o  The keystrokes used are as follows:

                  Table 6.1: Keystrokes in structure create

            <Shift-Tab>    Go to previous input area in field
             <Tab>         Go to next input area in field
             <Enter>       Go to next input area, creating field
                           if already on last input area
             <Up>          Go to same input area in field above
             <Down>        Go to same input area in field below
             <Alt-D>       Delete field definition

         o  The field type  can be toggled  by pressing  <Space>.
            Alternatively, pressing  the field  type letter  will
            set the type:  `C' for character fields, `D' for date
            fields, `N' for  numeric fields and  `L' for  logical
            fields.





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         o  When the field definitions have been created, move to
            the final field in the structure and press <Enter> to
            create the strucure on disk.

         o  Once the  structure has  been created,  the  File/Use
            database menu options can be used to open and  select
            the file just created.

         o  Modify structure  This choice operates in exactly the
            same way as the previous option for creating database
            files.  The structure of the current database will be
            placed in the database creation  box where it can  be
            modified using the same keystrokes as before.

         o  If the type of a  field is changed, then RDU will  do
            its best to preserve the  contents of the field.   In
            particular, date fields  converted to numeric  fields
            will  have  their  contents  changed  to  Julian  day
            numbers, used elsewhere in RExL, while numeric fields
            (changed to  date fields)  will  be assumed  to  hold
            Julian day numbers and processed accordingly.

         o  If the  width  of  any field  is  reduced,  then  the
            contents will be  truncated to  fit.   If numbers  in
            numeric fields  no  longer  fit, then  they  will  be
            replaced with asterisks.

         o  When the desired changes have been made to the  file,
            press <Enter> on  the empty field at  the end of  the
            list to make the changes permanent.

         o  Create index: This choice is used to create an  index
            file for the database which is currently open.   When
            this menu option is selected, you will be prompted to
            enter an index key expression, which may contain  any
            of the dBase III functions supported in RExL and  the
            fields in  the  current  database.    As  an  aid-de-
            memoire, <F10> lists the fields in the database while
            <Ctrl-F> can be used to list the functions  available
            to you.  If the expression entered is not valid, then
            an error will be generated.

         o  When a syntactically valid  index key expression  has
            been entered, you  will be  prompted for  a DOS  file
            name to save the index file under. If one is entered,
            then index generation will proceed.




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         o  While the index file is being generated, its progress
            will be displayed in a progress box in the center  of
            the  screen.    Because   of  the  method  used   for
            generation of index files, sorting may be slow if the
            file is already in order, however, if the file is not
            sorted,  then  the  index  will  be  generated   very
            rapidly.

         o  Reindex:   This option  will reindex  an index  file.
            This operation  may  need  to be  carried  out  if  a
            database file has been modified while its  associated
            index file was closed.  If there is no database  file
            or index  file open,  then  this option  performs  no
            action.

         o  Statistics:   This option  displays statistics  about
            the database  and index  files currently  open.   The
            first line displays the name of the current database,
            the second  displays the  name of  the current  index
            file, if one is open.

         o  The third and fourth lines show the number of  fields
            and records, respectively, in the database. The fifth
            line displays  the date  of the  last update  to  the
            database file, while the final line shows the size of
            the database header record.

         o  Field list:  This  option  lists the  fields  in  the
            current database. The display  format is exactly  the
            same as  in the  database create  option above,  with
            field names in the first column, types in the second,
            widths in the third and decimal places in the fourth.

     6.2.7  Options Menu

     This menu is fundamentally the  same as that in the  editor.
     It has five options as follows:

         o  Load macros:  Any macro definitions you define may be
            saved to  disk for  later retrieval  using this  menu
            option. The macro file format is constant across  the
            RExL product  range, so  that macros  defined in  the
            editor may be used in the debugger or in the database
            manager and  so on.   Macros  are explained  in  more
            detail at the start of the chapter on the editor.





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         o  Save macros:  This option  allows you to save  macros
            which can then be reloaded at some future time  using
            the load option above.

         o  Beep  off:    By  default,  RExL  beeps  whenever  it
            encounters an error. This  beeping can be toggled  on
            and off by selecting this option.

         o  Exploding windows In its normal state, all windows in
            RExL open  instantaneously  upon  activation.    This
            option can be  used to  make windows  `grow' to  full
            size on the screen.  This is only a visual effect and
            has no effect upon the application.

         o  Case sensitivity:  By  default, all database  indexes
            and searches are  carried out  with case  sensitivity
            on, to follow the dBase convention.  However, this is
            contrary to  the case-insensitivity  in the  rest  of
            RExL.  If dBase  compatibility is not required,  then
            the case sensitivity  may be turned  off.  Note  that
            the  case-sensitivity   feature  only   affects   the
            generation of index files.


     6.3  RExLRD


     RExLRD is the combined runtime  and debugger module for  the
     RExL programming  environment and  is called  by the  editor
     whenever the application is run.  RExLRD uses the  following
     command line syntax:

                 RExLRD [-d] [-k] [-e] <filename.rxl>

     The options are used as follows:

         o  -d:
            The `d' parameter will cause the debugger to start up
            in debug mode,  as if  the user  had pressed  <Alt-D>
            during loading of  the application.   This switch  is
            passed  invisibly  by  the  editor  to  the  debugger
            whenever  the  debugger  is  called  via  the   Debug
            application option in the Run menu in the editor.

         o  -e:
            The `e' option will return control to the editor when
            the debugger terminates.   Whenever the editor  calls
            the debugger, this option  is silently passed to  the


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            debugger, so  that the  debugger will  return to  the
            editor when it terminates.

         o  -k:
            This `k' option  is used to  tell the runtime  module
            not to watch  out for the  two keystrokes of  <Alt-D>
            and <Esc>,  which  are normally  monitored.  (<Alt-D>
            will interrupt the run module and relinquish  control
            to the  debugger  while  pressing  <Esc>  twice  will
            terminate the application.)

         o  -l:
            This `l' option  is used to  tell the runtime  module
            that it is  running on an  LCD display.   If you  are
            running the  debugger  from  the  editor,  then  this
            option will be passed  automatically, but if you  are
            running it from the DOS  command line, then you  need
            to include it specifically.

         o  -s:
            This `s'  option  is used  to  set  the size  of  the
            runtime  stack  to   be  used   when  executing   the
            application.   Be  default  the  size  is  100  stack
            entries, but if your application uses recursion  then
            this value should be increased.  If you need as  much
            memory as posible,  then this value  may be  reduced:
            Each stack entry  requires eight  bytes of  permanent
            storage.  The required stack size is placed after the
            `s'.  For example, to set a stack size of 30 entries,
            the command line option `-s30' should be passed.


     6.4  RExLRT


     RExLRT  is  the  runtime  module  of  the  RExL  programming
     environment.  If it used for running the systems written  in
     RExL. It  is  about  one-third  smaller  than  the  combined
     runtime-debugger module and it  runs applications about  10%
     to 15%  faster.  The  command  line  syntax  for  RExLRT  is
     identical to that for the debugger, with the only difference
     being that <Alt-D>  does not pass  control to the  debugger,
     since there is none.

     RExLRT  is  used  in  preference  to  the  executable   file
     generator, RExLPC described earlier, when it is necessary to
     have  separate  application  image,  screen  and  executable
     files.   Typically,  this  program  is  used  to  distribute


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     unfinished   applications   which   may   require    on-site
     modifications.

     Note also, that  REXLRT supports the  LOAD() function  call,
     whereas RExLPC does not,  because of the differing  internal
     formats.


     6.5  ScrList


     ScrList lists the contents of  screen files and outputs  the
     contents to the standard output device, usually the monitor.
     The format of the output file listing is as follows:

     The block  number  of every  block  in  the screen  file  is
     printed first,  immediately followed  by a  colon.   If  the
     block is in use  as a screen, then  the screen name will  be
     printed surrounded by quotes.   If the block is not in  use,
     then the message (Block is not used) will be displayed.

     The next line displays the position and size of the block in
     the screen  file in  the format  [x,y]->[x+w,y+h] where  the
     screen was originally saved from position (x,y) with a block
     width and  height of  w and  h respectively.  The number  of
     fields defined in the block follows next.

     The rest of the line is concerned with internal information:
     bsz is the size of the  current block, ofs is the offset  of
     the block within the  screen file while fsz  is the size  of
     the block used up by the screen, the difference between  bsz
     and fsz being unused.  As an integrity check, the sum of the
     current block's offset and block size should equal the  next
     blocks offset.

     The remaining lines  in a screen's  list display the  fields
     defined in the screen.   Firstly, the type  of the field  is
     listed, followed by a colon and the position and  dimensions
     of the  field,  in the  format  of  (x,y) [w,h],  where  the
     symbols have their usual meanings.

     If the field is a menu field, then ScrList will move to  the
     next  field   immediately.     Otherwise,   the   expression
     associated with the field  is displayed, enclosed in  square
     brackets.  Note that since  the screen file itself  contains
     no variable  name information,  the  names of  variables  in
     expressions cannot  be  determined  and they  are  therefore
     displayed  as   variable  reference   numbers,   immediately


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     preceded by a hash  # symbol.  If  you require a listing  of
     the  expressions  attached  to   all  the  fields  in   your
     application, then use the `Import/Save ASCII' option in  the
     editor.  If the field  is a toggle list, then the  different
     options in  the  list will  be  displayed on  the  following
     lines, again enclosed in square brackets.

     The following is  an extract from a  typical example of  the
     output from ScrList showing all the salient features:

     6:"Is Data ok?"
      [28,11]- [51,17] -   3  fields    (fsz:  221,  ofs:   2395,
     bsz:221)
          Menu  : (24, 4) [21x 1] : [#1]
          MArea : (35,14) [ 7x 1]
          MArea : (35,15) [ 7x 1]
     7:"Enter Names and Question 1"
      [ 0, 0]- [79,24] -  7 fields  (fsz:  901, ofs:  2616,  bsz:
     901)
          Input : (24, 4) [21x 1] : [#2]
          Input : (24, 5) [ 9x 1] : [#3]
          Toggle: (24, 6) [15x 1] : [#4]
               [Civil Eng]
               [Science]
               [Electrical]
               [Mechanical]
               [Agriculture]
          Input : (24, 7) [11x 1] : [#5]
          Input : (18,13) [ 1x 1] : [#0[1,1]]
          Check : (18,14) [ 3x 1] : [#6]
          Radio : (18,15) [ 3x 4] : [#7]


     6.6  ScrGrab


     ScrGrab is a  terminate and stay  resident utility which  is
     used to grab text screens from the monitor and to place  the
     contents in files compatible with RExL's ".SCR" format.  The
     ScrAdd utility can be used to combine screen files together.
     Typical applications of ScrGrab and ScrAdd are demonstration
     programs like that supplied with RExL, bug reports  supplied
     with screen dumps and so on.

     When loaded in  memory, ScrGrab  uses about  2,500 bytes  of
     memory.   When it  is  no longer  required,  it and  can  be
     unloaded from memory from the command line.



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     The  command  line  arguments  which  ScrGrab  uses  are  as
     follows:

            -h and -? Show command line help

            -u        Unload  from  memory.    If  further   T&SR
            programs have  been  loaded  since ScrGrab,  then  it
            cannot be unloaded since  doing so would corrupt  DOS
            and most likely crash the machine.

            -k....:   This  option  is   used  to   set  up   the
            keystroke,  by  default  <Alt-G>,  which  will  cause
            ScrGrab to save a screen to disk.  Unless you have  a
            keyboard scan  code table,  you'll need  to used  the
            KbdScan utility to determine the exact four character
            keyboard scan  code to  supply here.   Refer  to  the
            section on Scan for more information.

            -d:       Requests  ScrGrab  to  report  the  current
            defaults which it is using. The first line gives  the
            activating scan code, in a format compatible with the
            output from KbdScan while the next line gives the DOS
            paragraph  where  the  program   is  loaded.     This
            information is purely  technical and is  not of  much
            use.

     You  should  not  run  any  T&SR  programs  from  within  an
     operating system shell, such as when the `File/OS shell'  is
     selected from the editor, since T&SR's perform surgery  upon
     DOS  which  will  cause  it   to  crash  if  the  shell   is
     subsequently terminated using the DOS exit command.


     6.7  ScrXtrct


     ScrXtrct is a utility which  can extract and place a  screen
     from one screen file into another screen file.  The  general
     command line format of this command are:

                   ScrXtrct OldScr ScreenNo NewScr

     where OldScr is  the screen  file from  which screen  number
     ScreenNo will be extracted and placed into the NewScr screen
     file, erasing NewScr if it already exists.  Unlike the  rest
     of RExL,  ScreenNo  is  one-based, meaning  that  the  first
     screen is  number 1,  the second  number 2  and so  on.   If
     OldScr contains a number of screens and you are not sure  of


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     the reference number  of the screen you  want, then you  can
     use the ScrList utility to list them along with their screen
     numbers.


     6.8  ScrAdd


     ScrAdd is a  utility which can  extract and  place a  screen
     from one screen file into another screen file.  The  general
     command line format of this command are:

                    ScrAdd OldScr ScreenNo NewScr

     where OldScr is  the screen  file from  which screen  number
     ScreenNo will be extracted and placed into the NewScr screen
     file.  Note that, as  with ScrXtrct, ScreenNo is  one-based.
     If OldScr contains a number of screens, then you can use the
     ScrList  utility  to  list  them  along  with  their  screen
     numbers.

     If the name of the screen specified clashes with one in  the
     new screen file,  then you will  be promted  to enter a  new
     name for the screen being added.

     ScrAdd does not perform  any of the optimization  operations
     carried out in  the editor upon screen  files when they  are
     being modified.   Instead, it simply  appends the screen  to
     NewScr.

     ScrAdd is  generally used  in combination  with ScrGrab  and
     ScrXtrct to move screens from one screen file to the next.


     6.9  MI


     MI,  short  for   memory  information,  displays   pertinent
     information about the state of DOS and the programs resident
     in your  PC.   The following  is  a typical  display of  the
     output from MI:


     MI  Version 2.1  Copyright (c) 1992, The Software Loft
     -------- -------- ------------ --------------
     PSP addr Size     Owner        Hooked vectors
     -------- -------- ------------ --------------
     0008     24,048   [  Dos  ]


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     084E     2,368    [ Shell ]    22 23 24 2E EF
              64       [ Free  ]
     084E     752      [ Shell ]
     0AA6     128      [  Dos  ]
     0921     6,208    edos.com     2F
     0AA6     2,592    edos.com
     0B54     2,320    scrgrab.com  09 16 21 28
     0BE7     606,768  [ Free  ]
     ------------  ----------------------  ----------------------
     Memory        Total bytes             Available bytes
     ------------  ----------------------  ----------------------
     Conventional  655,360     (640k)      606,592     (592k)
     Expanded      EMS not responding
     Extended      3,145,728   (3,072k)    0           (0k)
     XMS           2,048,000   (2,000k)    2,048,000   (2,000k)
     HMA allocated, EBDA not present
     There are  12,102,400 (out  of  120,946,944) bytes  free  on
     drive N:


     The first  section of  the display  gives information  about
     memory control blocks (MCB's) in  low DOS memory, between  0
     and 640k.  It lists the hexadecimal address of the owner  of
     the MCB in `PSP addr' column, the amount of memory owned  by
     the block  in the  `Size' column,  the name  of the  program
     which owns the PSP in the `Owner' column.  The final  column
     lists, in  hexadecimal,  the  interrupt  vectors  which  are
     hooked into  the memory  controlled by  the MCB.   From  the
     above display, we  can see that ScrGrab  hooks the high  and
     low  priority  keyboard  interrupts,  the  main  DOS  server
     interrupt  and  the  DOSok  interrupt.    A  DOS   technical
     reference will  tell  you  the  meanings  and  uses  of  the
     different interrupt numbers.

     DOS  itself  also  owns  blocks  of  memory  and  these  are
     signalled by  owners of  `[Dos]',  for blocks  with  invalid
     environments and  `[Shell]', for  blocks which  do not  have
     program names attached to them.

     The second section  of the output from  MI lists the  amount
     memory available  in each  of the  different memory  schemes
     used in the  PC. The listing is  divided into five  columns:
     The first gives the type  of memory about to be listed,  the
     second gives the total amount of memory allocatable and  the
     fourth gives the amout of memory remaining unallocated.  The
     third  and  fifth  columns   convert  the  byte  counts   to
     measurements in kilobytes (bytes divided by 1024).



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     Conventional memory  extends  from  0 to  640k,  unless  VGA
     graphics memory  has  been  used to  backfill  DOS  to  736k
     (generally, it isn't).   The  available conventional  figure
     will always be  slightly less than that  noted as [Free]  in
     the first section of the listing.  This is because the first
     section lists as free the memory used by the environment  of
     the currently active program, while the second does not.

     The next line gives the amount of expanded memory (LIM  EMS)
     in your system.  It interrogates the status of int 67h which
     controls the interface  to the memory.   If  this vector  is
     NULL, then the  message `None' will  be displayed.   If  the
     vector exists, but  does not respond in  the way it  should,
     then the message `EMS not responding' will be displayed.

     The third line in this  section gives the amount of  vanilla
     extended memory available and free.  The total is read  from
     the CMOS setup information in  your PC, while the amount  of
     free memory is taken from int 15h/fn 88h.  The final line in
     the memory display gives the amount of XMS (Extended  Memory
     System) in your machine.

     The second last line  gives the on/off status  of the DOS  5
     HMA (High Memory Arena) and that of the EBDA (Extended  BIOS
     Data Area) which is normally  only present on PS/2,  Compaq,
     Digital and Olivetti PC's.

     The final line gives the  total disk space and the space  on
     the currently selected  disk drive.   MI  can optionally  be
     followed by  a  drive  letter  to  specify  a  drive,  whose
     statistics are displayed instead of the current drive.   For
     example the line MI  a: will list the  free space and  total
     drive space on the A: drive rather than the current drive.

     MI takes one of two optional command line parameters, -c and
     -m.

     The -c parameter instructs MI  to display the CPU type,  the
     floating point coprocessor type, the video adapter type.  If
     the  processor is  an Intel 80386 or  above, then a  message
     will be  displayed saying whether or not the CPU is  running
     in protected mode.

     The  -m  parameter  causes  the  normal  `condensed'  memory
     control block  display  to be  displayed  in its  low  level
     unprocessed  form.  When  -m  is  specified,  no  memory  or
     capacities are determined.



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     6.10  KbdSpeed


     KbdSpeed is a small utility to set the keyboard repeat  rate
     on AT class computers with  extended keyboards.  The  format
     of the command is as follows:

                       KbdSpeed <letter><digit>

     where letter  is  a  letter in  the  range  `a' to  `z'  and
     controls the repeat rate, with `a' at 30 repeats per  second
     and `z' meaning 5  repeats per second. digit  is a digit  in
     the range `1' to `4'  specifying the delay before  repeating
     occurs.   1  specifies  a delay  of  1/4  seconds, up  to  4
     specifying a delay of 1 second.

     To set the keyboard to  repeat at 30 characters per  second,
     with a delay of 1/4  seconds before auto repeat occurs,  the
     following command would be issued:

                             KbdSpeed a1

     If you run KbsSpeed from within MicroSoft Windows, then  the
     program will have no effect, since Windows resets the  rates
     of its own accord, ignoring any preset values.

     KbdSpeed is most useful in RExL when designing screens where
     the cursor  may  need to  make  large movements  around  the
     screen.  The normal repeat rate of 10 characters per  second
     then becomes an irritation.


     6.11  KbdScan


     KbdScan is another small utility which reads from keystrokes
     from the keyboard and displays  the keyboard scan code,  the
     BIOS keystroke return  value and the TSR  hotkey code.   The
     information is displayed on three sucessive lines.

     The format of the command is as follows:

                             KbdScan [-x]

     This utility  is provided  so that  the activating  keyboard
     scan code for  ScrGrab can be  changed.  If  you want to  do
     this, take the TSR hotkey  code displayed on the final  line



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     of display and place it  as the parameter to the -k  command
     line option to ScrGrab.

     The following is  output from KbdScan,  with <Alt-0> as  the
     last key pressed:

     KbdScan  Version 2.1  (C) Copyright 1992, The Software Loft
     Press any key, ESC (twice) aborts :
     Shift/scan code   :088b
     BIOS return value :8100
     TSR hotkey code   :0881

     To change the  activating keystroke in  ScrGrab to  <Alt-0>,
     the following command would be issued.

                            ScrGrab -k0881

     Finally, ScrGrab accepts  the command line  option `-x'.  If
     this option is included,  ScrGrab will read keystrokes  from
     an extended 101-102 key keyboard.  This is only supplied  as
     an extra feature, and is not used in RExL.





























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                              Chapter 7

                              Afterword


     This appendix  gives a  few pointers  to the  directions  in
     which the Software Loft hopes  to go when developing  future
     versions of RExL.   Any suggestions  for features which  you
     would like  to  see  incorporated  would  be  most  welcome.
     Please  remember  that  without  your  support,  we   cannot
     continue to  supply you  with  low cost,  quality  software.
     Thank you.

         o  New features  in the  screen  designer.   These  will
            include pictures for  input and output  (as in  dBase
            compatible languages) as well as undo.

         o  Improve the  speed  of the  runtime-debugger  module.
            Currently, we  have  a  better  expression  evaluator
            undergoing tests and  we hope  to include  it in  the
            next major release.

         o  Mouse handling.

         o  More features in the debugger:  Break on  expression,
            pass count  breakpoints,  break on  variable  access.
            VGA 43 and 50 line mode support.

         o  More features  in  the  editor: Search  and  replace,
            lines  longer  than   65  characters,  and   function
            references (similar to  variable references).   Color
            installation program  to  set  up  colors  of  menus,
            windows and various other  system parameters. VGA  43
            and 50 line mode support.

         o  Language: rules attached to variables.  Every time  a
            variable is either accessed  or changed, its rule  is
            called.  User defined RExL  functions.  Link in  with
            C, assembly language and Pascal.




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         o  Add  true  relational  capability  to  the   database
            module.  Most  of the code required  is in place  for
            this.

         o  A portable runtime module to allow the programmer  to
            write applications in  DOS and to  port the  finished
            product to  Unix,  and  other  text  based  operating
            systems.

         o  A windows version  of RExL.   The current version  of
            RExL has taken fourteen months  for us to write.   We
            hope to be able to  port most of the code to  Windows
            easily enough  and  to  have an  alpha  test  version
            running sometime around September of 1992.

























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