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Notes on the Book 'Starting Forth' by Brodie -------------------------------------------- L.O.V.E. Forth matches closely the Forth 83 standard, as does the book 'Starting Forth'. Here are some notes on differences between L.O.V.E. Forth and the words and examples described in this book (2nd edition is assumed). Remember to type HELP (wordname) or the Alt-F1 key if you have any difficulty. Chapter 3 Working with Forth --------- It is necessary to have the block disk words included in L.O.V.E. Forth in order to use many of the words described in this chapter. The shareware DEMO program has these included. To include them in BARE system type: INCLUDE" LOADBLK.TXT" (enter) . Many users will, of coarse, prefer to use text files using their favorite text editor to compose programs. To open a new screens file when using block disk words type: OPEN-NEW" myfile.scr" (enter) . This will create a brand new file named MYFILE.SCR (or the name of your choice). To extend the file to include more screens, type: n SCREENS (enter) where n is the total number you want (maximum is 32767, but don't type that many unless you have a BIG disk). For more information see the file SOURCE.DOC. To switch on the printer type the word PR-ON. This causes all activity to be both printed and displayed. Type PR-OFF when done. The printer LPT1 is used. There is a word called L which is like LIST but is much faster. LN lists the next screen up, LB lists back one, and EL edits the current last screen displayed in this way (see EDITOR below). There is no word TRIAD. The word SHOW displays a range of screens rapidly on the display. To use it type the first screen and last screen followed by the word SHOW. The EDITOR described in 'Starting Forth' is antiquated and is no longer used in most forth systems. L.O.V.E. Forth has a full screen (one screen) editor with cursor control and other features. To use it type: n EDIT where n is the screen number you wish to edit. Type Ctrl-X to get help. Chapter 7 A number of kinds of numbers --------- L.O.V.E. Forth stores the decimal place in a variable called DPL. If no decimal point was used in the last number converted, DPL contains -1. M/ has a slightly different meaning in L.O.V.E. Forth M*/ must be loaded from the file MISC.TXT (it is loaded with the block disk words). It assumes the Forth '79 conventions for division. Chapter 8 Variables constants and arrays --------- Note that the dictionary structure is different in L.O.V.E. Forth than what is shown here. ? is not defined. Try: : ? @ . ; L.O.V.E. Forth defines defines double number words such as 2! 2@ 2DUP etc. also as D! D@ DDUP which may be more meaningful names in some applications. Chapter 9 Under the hood --------- The dictionary structure is different in L.O.V.E. Forth from what is shown. The word ' returns the compilation address of the following word in the thread segment. This doesn't matter, really. Words such as EXECUTE and vectored execution as described, all work as expected. The word DUMP in L.O.V.E. Forth works from the data segment. You can use it to show your data. Use TS:DUMP to see the portion of your words that are in the thread segment (give it the compilation address), HS:DUMP from the head segment (>NAME may be used to convert the compilation address) and CS:DUMP from the code segment (machine code). The word @EXECUTE is not present. The structure of dictionary entries varies from what is shown in the book. The main differences occur because L.O.V.E. Forth divides each word out between various segments. More is said in accompanying technical notes, but here is a summary. The dictionary head, including the NAME and LINK as described go into the HEAD SEGMENT. The CODE POINTER and BODY go into the THREAD SEGMENT. There is one exception. VARIABLEs and other data words have their BODY (ie. the data) stored in the DATA SEGMENT (or VS: for 'variables segment'). When an assembler is used, it's resulting code goes into the CODE SEGMENT. The parameter and return stacks are contained in the STACK SEGMENT. The word >BODY takes the address from ' (ie. the compilation address) and returns an address in the data segment (eg. address of data for a VARIABLE). The word TS:>BODY takes the address from ' and returns an address in the thread segment (eg. the body of a colon definition). There is no error checking in these words, if there isn't, for example, a data segment field for the word that was 'ed the address returned will be meaningless. See the file COMPAT.DOC for more information on changing the values of constants and other issues related to the compatibility of L.O.V.E. Forth. The memory map of L.O.V.E. Forth is quit different from that shown. Each segment in L.O.V.E. Forth has it's own dictionary pointer. They are only incremented in segments where data are added. It suffices to say here simply that the more code you add, the farther up the dictionary points move. Try the command MEM-MAP to see the L.O.V.E. Forth segments and how full they are. L.O.V.E. Forth does not have an 'electives block'. It has however many other files of useful code that you may compile such as the block words mentioned above. ALLOT, HERE and PAD work with the VS: in L.O.V.E. Forth. The variable DP is reserved for the thread segment and should not be manipulated casually. The word EMPTY is not present. SP@ and S0 are present but return addresses in the STACK SEGMENT. Therefore, if we wanted to access the stack area we would use SS:@ not @ as described. TIB returns an address the VS: and works as described. There are no USER VARIABLES. BLOCK BUFFERS are in high memory as described (in the VS: too). Vocabularies are very similar to what is described. There are several provided. ROOT (which contains some words for manipulating vocabularies), FORTH (with the majority of standard words), MSDOS (with file handling and other words to access DOS), VIRTUAL (with words for handling virtual vocabularies), TOOLBOX (with programming utilities). There are also vocabularies which are loaded instantly when referenced, called virtual vocabularies. These are ASSEMBLER, UTILITIES, EDITOR, SCREEN-UTILS (the latter two are only available when block words are loaded). A major difference between L.O.V.E. Forth and what is described, is that the vocabulary search order in L.O.V.E. Forth is implemented as a vocabulary stack, the top being the first one searched. Executing a vocabulary (ie. the word) makes it the first one in the search order. The word ALSO allows a vocabulary to be added to the search order. VDROP removes the top one. CONTEXT always holds the top of the vocabulary stack. ONLY resets the vocabulary stack to just ROOT. The word DEFINITIONS works as expected. CONTEXT (ie. the top of the vocabulary stack) becomes the vocabulary into which new definitions are added. Use ORDER to display the current search order, WORDS displays words from the CONTEXT vocabulary, WORDS> followed by any vocabulary name, displays words from that vocabulary. The word DEVELOP resets the vocabularies to ROOT, FORTH, and TOOLBOX which is the usual order for normal programming and experimention. (If in doubt, type DEVELOP). Chapter 10 I/O any you ---------- Make sure the block disk words are loaded with INCLUDE" LOADBLK.TXT" The word >TYPE is not defined. Though CMOVE and CMOVE> are included, the word BMOVE (same arguments) is much more useful. It checks prior to the move, whether there will be any bytes written over by the move, and adjusts the direction of the move accordingly. (For all that explanation, the overhead is very slight). The word BLANK is not included. Try: : BLANK BL FILL ; L.O.V.E. Forth defines two words to check for keypresses. The word QTERM simply checks for a key and returns a flag, true if there is one available for KEY. The word ?TERMINAL does the same thing, but removes it if one is found. The word NUMBER only recognizes a decimal point within a number being converted. The word STRING is not provided, but the word ," (comma-quote) provides this function. The word LIT" is also not provided. The word " (quote) provides this function, note that it returns just an address and can be executed from the keyboard as well (it places the string at PAD). Note that all string words allow the inclusion of control characters using UNIX conventions. See the file STRINGS.DOC for more information. Chapter 11 Extending the Compiler with Defining and Compiling Words ---------- The example given for dot" will not operate in L.O.V.E. Forth because string literals are actually stored in the VS:. B." would work however, if the word BRIGHT were available. The word ASCII is provided and is state-smart. Chapter 12 3-1/2 Examples ---------- The words ASCII and \ are already provided. The word ," is defined differently in the second example. Either define STRING as ," first, or use " instead of ," . The rpn assember provided with L83 has a similar implementation, but remember that code goes into the code segment.