C/C++ Users Group Library 1996 July/C-C++ Users Group Library July 1996.iso/vol_200/232_01/userman

Text File | 1987-06-15 | 21.0 KB | 861 lines

.ds CM
.TL
A Little Smalltalk
User Manual
.AU
Timothy A. Budd
.po +0.2i
.nr PO +0.2i
.NH 1
Introduction
.PP
This manual is intended as an aid in using the Little Smalltalk system.
It is not intended to be used as an introduction to the Smalltalk
language.
Little Smalltalk is largely (with exceptions listed in a later section)
a subset of the Smalltalk-80\s-2\u*\d\s+2 language described
.FS
* Smalltalk-80 is a trademark of the Xerox Corporation.
.FE
in [.Smalltalk blue.].
A complete description of the classes included in the Little Smalltalk system
and the messages they accept is given in Appendix 1.
.NH 1
Running the system
.PP
The Little Smalltalk system is invoked by typing the command \fBst\fP.
The system is interactive \- that is, the user types an expression at the
keyboard and the system responds by evaluating the expression and typing
the result.
For example,
typing the expression \fB3 + 4\fP results in the value \fB7\fP being
displayed on
the output.  Execution is terminated by typing control\-D.  A sample
execution session is shown in Figure 1.
.KF
.sp
.DS B
% st
Little Smalltalk
    3 + 4
7
    ^D
%
.DE
.sp
.ce
\fBFigure 1:\fP A Sample Little Smalltalk Session
.sp
.KE
.PP
Instance variables for the command level can be created by
assigning a value to a new variable name.  Thereafter that variable can
be used at the command level, although it is not known within the scope
of any method.  The variable ``last'' always contains the value
returned by the last expression typed.
Figure 2 shows the creation of a variable.
Note that the assignment arrow is formed as a two character sequence.
.KF
.sp
.DS B
.ta 5m
    newvar <\(mi 2 / 3
    newvar
0.666667
    2 raisedTo: newvar + (4 / 3)
4
    last
4
.DE
.sp
.ce
\fBFigure 2:\fP Creating Variables
.sp
.KE
.PP
The default behavior is for the value of expressions,
with the exception of assignments, to be typed
automatically as they are evaluated.
This behavior can be modified either by using the \-d flag
(see Appendix 2), or by passing a message to the pseudo
variable \fBsmalltalk\fP (see Appendix 1).
.PP
Class descriptions must be read in from files, they cannot be entered
interactively.  Class descriptions are entered using a system directive.
For example, to include a class description contained in a file named
\fBnewclass.st\fP, the following system directive should be issued:
.sp
.ce
)i newclass.st
.sp
A list of files containing class descriptions can also be given as
arguments to the st command.  The command
.DS B
%st file\s-2\d1\u\s+2 ... file\s-2\dn\u\s+2
.DE
is equivalent to the sequence
.DS B
.ta 5m
%st
Little Smalltalk
    )i file\s-2\d1\u\s+2
    ...
    )i file\s-2\dn\u\s+2
.DE
.PP
A table of system directives is given in Figure 3.
.KF
.sp
.TS
center box;
l lw(4.5i).

)e filename    T{
Edit the named file.  The Little Smalltalk system will suspend, leaving
the user in an editor for making changes to the named file.  Upon leaving
the editor the named file will automatically be included, as if the )i
directive had been typed.
T}

)g filename    T{
Search for an entry in the system library area matching the filename.
If found, the class descriptions in the library entry are included.
This command is useful for including commonly used classes that are not
part of the standard prelude, such as classes for statistics applications
or graphics.
T}

)i filename    T{
Include the named file.  The file must contain one or more class descriptions.
The class descriptions are parsed, and if syntactically legal new
instances of class \fBClass\fP are added to the Smalltalk system.
T}

)l filename    T{
Load a previously saved environment from the named file.
The current values of all variables are overridden.
The file must have been created using the )s directive (below).
T}

)r filename    T{
Read the named file.  The file must contain Smalltalk statements, as
would be typed at the keyboard.  The effect is just as if the lines
of the file had been typed at the keyboard.  The file cannot contain
class descriptions.
T}

)s filename    T{
Save the current state in the named file.  The values of all variables
are saved, and can later be reloaded using the )l directive (above).
T}

)!string    T{
Execute the remainder of the line following the exclamation point
as a Unix\s-2\u*\d\s+2 command.  Nothing is done with the output of the command,
nor is the returning status of the command recorded.
T}

.TE
.sp
.ce
\fBFigure 3:\fP System Directives
.sp
.KE
.PP
Note that the )e system directive invokes an editor on a file
containing class descriptions, and then automatically includes the file
when the editor is exited.
Classes also respond to the message \fBedit\fP, which will have the same
effect as the )e directive applied to the file containing the class
description.
Thus the typical debug/edit/debug cycle
involves repeated uses of the )e directive or the \fBedit\fP message
until a desired outcome is achieved.
The editor invoked by the )e directive can be changed by setting
the EDITOR variable in the users environment.
.NH 1
Differences between Little Smalltalk and the Smalltalk-80 system
.PP
This section describes the differences between the language accepted by
the Little Smalltalk system and the language described in
[.Smalltalk blue.].  The principal reasons for these changes are
as follows:
.IP size 6.5m
Classes which are largely unnecessary, or which could be easily
simulated by other classes (e.g. Association, SortedCollection) have
been eliminated in the interest of keeping the size of the standard
library as small as possible.  Similarly, indexed instance variables are
not supported, since to do so would increase the size of every object in
the system, and they can be easily simulated in those classes in which
they are important (see below).
.IP portability
Classes which depend upon particular hardware (e.g. BitBlt) are not included
as part of the Little Smalltalk system.  The basic system assumes nothing
more than ascii terminals.
.IP representation
The need for a textual representation for class descriptions required some
small additions to the syntax for class methods (see Appendix 3).
Similarly, the fact that classes and subclasses can be separately parsed,
in either order, forced some changes in the scoping rules for instance
variables.
.PP
The following sections describe these changes in more detail.
.NH 2
No Browser
.PP
The Smalltalk-80 Programming Environment described in [.Smalltalk orange.]
is not included as part of the Little Smalltalk system.  The Little
Smalltalk system is designed to be little, easily portable, and to
rely on nothing more than basic terminal capabilities.
.NH 2
Internal Representation Different
.PP
The internal representations of objects, including processes, interpreters,
and bytecodes, is entirely different in the Little Smalltalk system from
the Smalltalk-80 system described in [.Smalltalk blue.].
.FS
* Unix is a trademark of Bell Laboratories.
.FE
.NH 2
Fewer Classes
.PP
Many of the classes described in [.Smalltalk blue.] are not included as
part of the Little Smalltalk basic system.  Some of these are not
necessary because of the decision not to include the editor, browser,
and so on as part of the basic system.  Others are omitted in the interest
of keeping the standard library of classes small.  A complete list
of included classes for the Little Smalltalk system is given in Appendix 1.
.NH 2
No Class Protocol
.PP
Protocol for all classes is defined as part of class \fBClass\fP.
It is not possible to redefine class protocol as part of a class description,
only instance protocol.
The notion of metaclasses is not supported.
.NH 2
Cascades Different
.PP
The semantics of cascades has been simplified and generalized.
The result of a cascaded expression is always the result of the expression
to the left of the first semicolon, which is also the receiver for each
subsequent continuation.  Continuations can include multiple messages.
A rather nonsensical, but illustrative, example is the following:
.DS B
2 + 3 ; \(mi 7 + 3 ; * 4
.DE
.LP
The result of this expression is 5 (the value yielded by 2 + 3).  5 is also
the receiver for the message \(mi 7, and that result (\(mi2) is in turn the
receiver for the message + 3.  This last result is thrown away.  5 is then
again used as the receiver for the message * 4, the result of which is also
thrown away.
.NH 2
Instance Variable Name Scope
.PP
In the language described in [.Smalltalk blue.], an instance variable is
known not only to the class protocol in which it is declared, but is also
valid in methods defined for any subclasses of that class.
In the Little Smalltalk system an instance variable can be referenced only
within the protocol for the class in which it is declared.
.NH 2
Indexed Instance Variables
.PP
Implicitly defined indexed instance variables are not supported.
In any class for which these are desired they can be easily simulated by
including an additional instance variable, containing an Array, and
including the following methods:
.DS B
.ta 4m 8m
Class Whatever
| indexVars |
[
    new: size
        indexVars <\(mi Array new: size

|    at: location
        \(ua indexVars at: location

|    at: location put: value
        indexVars at: location put: value

    ...
.sp
.DE
.PP
The message new: can be used with any class, with an effect similar to
new.  That is, if a new instance of the class is created by sending the
message new: to the class variable, the message is immediately passed
on to the new instance, and the result returned is used as the result of
the creation message.
.NH 2
No Pool Variables
.PP
The concepts of pool variables, global variables, or class variables are
not supported.
In their place there is a new pseudo-variable, \fBsmalltalk\fP, which
responds to the messages \fBat:\fP and \fBat:put:\fP.
The keys for this collection can be arbitrary.
Although this facility is available, its use is often a sign of poor
program design, and should be avoided.
.NH 2
No Associations
.PP
The class Dictionary stores keys and values separately, rather than
as instances of Association.  The class Association, and all messages
referring to Associations have been removed.
.NH 2
Generators in place of Streams
.PP
The notion of stream has been replaced by the slightly different notion of
\fIgenerators\fP, in particular the use of the messages \fIfirst\fP
and \fInext\fP in subclasses of \fBCollection\fP.
External files are supported by an explicit class \fBFile\fP.
.NH 2
Primitives Different
.PP
Both the syntax and the use of primitives has been changed.
Primitives provide an interface between the Smalltalk world and the
underlying system, permitting the execution of operations that cannot be
specified in Smalltalk.  In Little Smalltalk, primitives cannot fail and
must return a value (although they may, in error situations, print an error
message and return \fBnil\fP).
The syntax for primitives has been altered to permit the specification of
primitives with an arbitrary number of arguments.  The format for a
primitive call is as follows:
.DS B
<primitive \fBnumber\fP \fIargumentlist\fP >
.DE
Where \fBnumber\fP is the number of the primitive to be executed
(which must be a value between 1 and 255),
and \fIargumentlist\fP is a list of Smalltalk primary expressions (see
Appendix 2).  Appendix 4 lists the meanings of each of the currently
recognized primitive numbers.
.NH 2
Byte Arrays
.PP
A new syntax has been created for defining an array composed entirely of
unsigned integers in the range 0-255.  These arrays are given a very
tight encoding.  The syntax is a pound sign, followed by a left square
brace, followed by a sequence of numbers in the range 0 to 255, followed by
a right square brace.
.DS B
#[ \fInumbers\fP ]
.DE
.LP
Byte Arrays are used extensively internally.
.NH 2
New Pseudo Variables
.PP
In addition to the pseudo variable \fBsmalltalk\fP already mentioned,
another pseudo variable, \fBselfProcess\fP, has beed added to the Little
Smalltalk system.  \fBselfProcess\fP returns the currently executing process,
which can then be passed as an argument to a semaphore, or
be used as a receiver for a message valid for class \fBProcess\fP.
Like \fBself\fP and \fBsuper\fP, \fBselfProcess\fP cannot be used at
the command level.
.NH 2
No Dependency
.PP
The notion of dependency, and automatic dependency updating, is not
included in Little Smalltalk.
.[]
.ds CH
.bp
.SH
.ce 2
Appendix 1
Class Descriptions
.PP
The messages accepted by the classes included in the Little Smalltalk
standard library are described in the following pages.
A list of the classes
defined, where indentation is used to imply subclassing, is given below:
.DS I
.ta 3m 6m 9m 12m 15m
Object
    UndefinedObject
    Symbol
    Boolean
        True
        False
    Magnitude
        Char
        Number
            Integer
            Float
        Radian
        Point
    Random
    Collection
        Bag
        Set
        KeyedCollection
            Dictionary
                Smalltalk
            File
            SequenceableCollection
                Interval
                LinkedList
                    Semaphore
                File
                ArrayedCollection
                    Array
                    ByteArray
                    String
    Block
    Class
    Process
.DE
.PP
In the descriptions of each message the following notes may occur:
.IP \fId\fP
Indicates the effect of the message differs slightly from that given
in [.Smalltalk blue.].
.IP \fIn\fP
Indicates the message is not included as part of the language defined
in [.Smalltalk blue.].
.IP \fIr\fP
Indicates the protocol for the message overrides a protocol given in
some superclass.  Only where the logical effect of this overriding is
important is the message given a second time; some messages, such as
copy, are overridden in many classes but are not described in the documentation
because the logical effect remains the same.
.bp
.SH
.ce 2
Appendix 2
Man Page
.PP
A Unix man page for the st command is given on the following page.
.bp
.SH
.ce 2
Appendix 3
Syntax Charts
.PP
Syntax charts for the language accepted by the Little Smalltalk system
are described on the following pages.
The following is an example class description:
.DS B
Class Set :Collection
| dict |
[
        new
                dict <\(mi Dictionary new

|       add: newElement
                dict at: newElement
                     ifAbsent: [dict at: newElement put: 1]

|       remove: oldElement ifAbsent: exceptionBlock
        dict removeKey: oldElement ifAbsent: exceptionBlock

|       size
                \(ua dict size

|       occurrencesOf: anElement
                \(ua dict at: anElement ifAbsent: [0]

|       first
                dict first.
        \(ua dict currentKey

|       next
                dict next.
        \(ua dict currentKey

]
.DE
.bp
.SH
.ce 2
Appendix 4
Primitive Numbers
.PP
The following chart gives the function performed by each primitive in the
Little Smalltalk system.
.SH
Information about objects
.IP 0
(not used )
.IP 1
class of an object
.IP 2
superobject of an object
.IP 3
test if class responds to new
.IP 4
size of object
.IP 5
hash value
.IP 6
test if two built-in objects are of the same type
.IP 7
object equality testing ( == )
.IP 8
various switch toggles
.IP 9
numerical generality testing
.SH
Integer manipulation
.IP 10
integer addition (both args must be integer)
.IP 11
integer subtraction
.IP 12
integer < test
.IP 13
integer > test
.IP 14
integer \(<= test
.IP 15
integer \(>= test
.IP 16
integer = test
.IP 17
integer ~= test
.IP 18
integer multiplication
.IP 19
integer //
.SH
Bit manipulation and other integer valued functions
.IP 20
gcd:
.IP 21
bitAt:
.IP 22
bitOr:
.IP 23
bitAnd:
.IP 24
bitXor:
.IP 25
bitShift:
.IP 26
radix:
.IP 27
not used
.IP 28
integer quo:
.IP 29
integer rem:
.SH
Other integer functions
.IP 30
doPrimitive:withArguments:
.IP 31
not used
.IP 32
convert random integer to random float
.IP 33
bitInvert
.IP 34
highBit
.IP 35
randomNumber (argument is seed )
.IP 36
asCharacter
.IP 37
asString
.IP 38
factorial
.IP 39
asFloat
.SH
Character manipulation
.IP 40
not used
.IP 41.
not used
.IP 42
character < test
.IP 43
character > test
.IP 44
character \(<= test
.IP 45
character \(>= test
.IP 46
character = test
.IP 47
character ~= test
.IP 48
not used
.IP 49
not used
.SH
Character unary functions
.IP 50
digitValue
.IP 51
isVowel
.IP 52
isLetter
.IP 53
isLowerCase
.IP 54
isUpperCase
.IP 55
isSeparator
.IP 56
isAlphaNumeric
.IP 57
caseShift
.IP 58
asString
.IP 59
asciiValue
.SH
Floating point manipulation
.IP 60
floating point addition (both args must be float)
.IP 61
floating point subtraction
.IP 62
floating point < test
.IP 63
floating point > test
.IP 64
floating point \(<= test
.IP 65
floating point \(>= test
.IP 66
floating point = test
.IP 67
floating point ~= test
.IP 68
floating point multiplication
.IP 69
floating point division
.SH
Other floating point operations
.IP 70
ln
.IP 71
sqrt
.IP 72
floor
.IP 73
ceiling
.IP 74
not used
.IP 75
integerPart
.IP 76
fractionalPart
.IP 77
gamma
.IP 78
asString
.IP 79
exp
.SH
Other numerical functions
.IP 80
normalize number to be within 0 and 2\(*p.
.IP 81
sin
.IP 82
cos
.IP 83
not used
.IP 84
arcSin
.IP 85
arcCos
.IP 86
arcTan
.IP 87
not used
.IP 88
raisedTo:
.IP 89
radix:
.SH
Symbol Commands
.IP 90.
not used
.IP 91
symbol comparison, returns true or false.
.IP 92
printString
.IP 93
asString
.IP 94
print (used internally)
.IP 95
not used
.IP 96
not used
.IP 97
build a new class, arguments are class name, superclass name, instance
variables, messages, methods, context size.
.IP 98
insert an object into class dictionary, first argument is symbol,
second argument is class definition
.IP 99
find an object in class dictionary.  argument is symbol.
.SH
String operations
.IP 100
string length
.IP 101
string compare, case important \- return \(mi1, 0 or 1.
.IP 102
string compare, case not important
.IP 103
string catenation
.IP 104
string at:
.IP 105
string at:put:
.IP 106
copyFrom:length:
.IP 107
copy (new string with same chars)
.IP 108
asSymbol
.IP 109
string printString
.SH
Array manipulation
.IP 110
build an untyped object of given size, argument is integer size.
.IP 111
index variable get (first argument is object, second is index)
.IP 112
index variable put (first argument is object, second is index,
third argument is expression)
.IP 113
object grow (returns a new object with same instance variable values
as first argument, but with second argument tacked on end as new instance variable)
.IP 114
build an instance of \fBArray\fP of the given size.
.IP 115
new string of given size
.IP 116
ByteArray new:
.IP 117
ByteArray size
.IP 118
ByteArray at:
.IP 119
ByteArray at:put:
.SH
Output and error messages
.IP 120
print string with no return
.IP 121
print string with return
.IP 122
general error - first argument is receiver, second is error string
.IP 123
print string on error output (with return)
.IP 124
not used
.IP 125
unix system call
.IP 126
print a string at a specific point on the terminal
.IP 127
block return without surrounding context
.IP 128
reference count less than zero, first argument is guilty object
.IP 129
does not respond error, first argument is receiver, second is message.
.SH
File operations
.IP 130
file open, first argument is name, second argument is mode
.IP 131
file read
.IP 132
file write
.IP 133
set file mode, first argument is file, second is mode indicator (anInteger)
.IP 134
compute file size in bytes
.IP 135
file set location (at:) second argument is location (anInteger)
.IP 136
return current file offset in bytes
.IP 137
not used
.IP 138
not used
.IP 139
not used
.SH
Process management
.IP 140
block execute (trapped by interpreter)
.IP 141
new process (withArguments:)
.IP 142
terminate a process
.IP 143
perform:withArguments: (trapped by interpreter)
.IP 144.
not used
.IP 145
set state
.IP 146
return state
.IP 148
start atomic action
.IP 149
end atomic action
.SH
Operations on classes
.IP 150
class edit
.IP 151
superclass of a class
.IP 152
class name (a Symbol)
.IP 153
new instance of a class
.IP 154
list all commands class responds to
.IP 155
respondsTo: , second argument is a symbol
.IP 156
class view (drop into editor, but no include)
.IP 157
class list
.IP 158
variables (returns an array of symbols)
.IP 159
not used
.SH
Date and Time
.IP 160
current date and time as string
.IP 161
seconds time counter
.IP 162
clear the screen
.SH
Plot(3) interface
.IP 170
clear the screen
.IP 171
move the cursor (move(x,y))
.IP 172
draw a line (cont(x,y))
.IP 173
draw a point (point(x,y))
.IP 174
draw a circle (circle(x,y,r))
.IP 175
draw an arc (arc(x,y,x0,y0,x1,y1))
.IP 176
establish the coordinate space (space(a,b,c,d))
.IP 177
draw a line (line(a,b,c,d))
.IP 178
print a label (label(s))
.IP 179
establish a line type (linemod(s))