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Forth
Forth

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Forth is a programming language that uses a stack-based metaphor in an effort to reduce memory requirements as much as possible. In contrast to languages like [Basic], the parser never has to "look ahead" to find additional data in order to see if a command is properly entered, any data it could need has to be pushed onto the stack as well. This greatly reduces the size of the parser, and as a result, leaves more room free for programs.
Forth is a cancatenative stack-based programming language.
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Another key aspect of the language was Forth's inherently multitasking design. The program could set up separate stacks and feed different code into each one. The Forth kernel would run each of these stacks in turn, so all Forth programs had access to these features. This made writing multithreaded code very easy, so one could, for instance, have a thread reading the joystick as it moved, and then read that value in a game loop in another stack.
Stack-based languages simplify the language's parser considerably because the data for an instruction always appears in the source code before the instructions that will use it. To see why this helps, consider this typical line of [Basic]:\\
\\
{{A = 10 + 20 * B}}\\
\\
To perform this line, the interpreter has to read the entire line, look up the value of B (let's say 3), realize that the * has to be performed before + and order the instructions correctly, and then finally convert those into instructions something like:\\
\\
{{get(B,temp1)}} - get the value in B and store it in temp1\\
{{multiply(20,temp1,temp2)}} - multiply that value by 20 and store the result in temp2\\
{{add(10,temp2,temp3)}} - add 10 to temp2 and store the result in temp3 \\
{{put(temp3,A)}} - store the value of temp3 into the variable A\\
\\
In contrast, in a stack-based system, the programmer organizes the code in the fashion it will ultimately be performed. The equivalent would be something like:\\
\\
{{B 20 mul}}\\
{{10 add}}\\
\\
When this code is performed, the interpreter pushes the value of B on the stack, then 20. It then encounters the mul, which removes the last two items, the 3 and 20, multiplies them, and puts the result back on the stack. Next, it pushes 10 on the stack, leaving the top two locations containing 60 and 10. It then encounters add, taking the two values, adding them, and putting the result back on the stack. The top of the stack now contains the result, 70.
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The downside to the stack-based approach is that it makes the language difficult to understand by mere mortals. Even tutorials purporting to show how simple it was often ended in an unreadable mess. As a result, Forth was subject to perhaps one of the longest running fanboi wars since APL was invented. Constantly derided by practically everyone in the industry, it saw some interest in spite of this, but little commercial software emerged. The singular exception is the PostScript system, which is essentially a version of Forth modified to produce graphics output.
Notice that the stack-based version ''has no temporary values'', and only reads a single instruction at a time, not an entire line of code. As a result, the parser is much simpler, smaller and requires less memory to run. This, in turn, generally makes it much faster, comparable to compiled programs.
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The Atari 8-bits were being sold right in the middle of this battle, and as a result there was a fair amount of support on the platform and some interest in the press.
Another key aspect of the language is Forth's inherently multitasking design. The program could set up separate stacks and feed different code into each one. The Forth kernel would run each of these stacks in turn, so all Forth programs had access to these features. This made writing multithreaded code very easy, so one could, for instance, have a thread reading the joystick as it moved, and then read that value in a game loop in another stack.
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!! Tutorials
!! Forth Systems for the Atari
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* [Einfuehrung in Forth 83]
* [FOCO65|https://github.com/piotr-wiszowaty/foco65] a Forth Cross-Compiler written in Python that translates into XASM assembly language
* [SPL] (Simple Programming Language) a Forth-ish compiler written in Python that translates into Assembly language
* [X-FORTH] - a FIG Forth variant, currently maintained
* [VolksForth] - a powerful Forth83 standards Forth for Atari 8bit, Atari ST, MS-DOS, CP/M, C=64, C=16/116/Plus4, still maintained
* [ANTIC Forth]
* [valFORTH]
* [English Software Company FORTH]
** [Page 6 Review of ES Forth|http://page6.org/archive/issue_14/page_34.htm]
* [Extended Atari FIG-Forth APX20029]
* [Mesa Forth]
* [QS Forth]
* [Graphic Forth] - A ANTIC / Fig-FORTH 1.4s Version with special Graphics Extensions.
* [FIG Forth 1.1]
* [FIG Forth 1.0D]
* [fig-FORTH1.4S-1.atr]
* [fig-FORTH1.4S-2.atr]
* [ProForth] Apple II (6502 Source)
* [SNAUT]
* [Forth Compiler from Frank Ostrowski]
* [CoinOp FORTH]
* [Elcomp Forth_DOS 25.atr]; Atari Version of Elcomp-Forth by E.Floegel & H.C.Wagner, 1982
* [Grafs Atari-Forth DOS 2.5.atr|Grafs_Atari-Forth_DOS_2.5.atr]; from Andreas Graf ca. 1990
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!! Forth Books
* [Using Fig FORTH On The Atari 800 By Stephen A. Cohen|https://archive.org/details/UsingFigFORTHOnTheAtari800ByStephenACohen]
* [APX 20157 FORTH Turtle Graphics Plus Manual by William D. Volk|https://archive.org/details/APX20157FORTHTurtleGraphicsPlusManual]
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!! Forth Systems for the Atari
!! Tutorials
* [Einfuehrung in Forth 83]
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* [FOCO65|https://github.com/piotr-wiszowaty/foco65] a Forth Cross-Compiler written in Python that translates into XASM assembly language
* [SPL] (Simple Programming Language) a Forth-ish compiler written in Python that translates into Assembly language
* [X-FORTH] - a FIG Forth variant, currently maintained
* [VolksForth] - a powerful Forth83 standards Forth for Atari 8bit, Atari ST, MS-DOS, CP/M, C=64, C=16/116/Plus4, still maintained
* [ANTIC Forth]
* [valFORTH]
* [English Software Company FORTH]
** [Page 6 Review of ES Forth|http://page6.org/archive/issue_14/page_34.htm]
* [Extended Atari FIG-Forth APX20029]
* [Mesa Forth]
* [QS Forth]
* [Graphic Forth] - A ANTIC / Fig-FORTH 1.4s Version with special Graphics Extensions.
* [FIG Forth 1.1]
* [FIG Forth 1.0D]
* [fig-FORTH1.4S-1.atr]
* [fig-FORTH1.4S-2.atr]
* [ProForth] Apple II (6502 Source)
* [SNAUT]
* [Forth Compiler from Frank Ostrowski]
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This page (revision-82) was last changed on 03-Jan-2024 15:31 by bartgo  Top