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SimForth

License: GPL v3 CI testing

SimForth is a non serious and personal Forth interpreter in the category of token forth. It has been developed in C++11. SimForth is compiled and installed as:

  • A basic standalone Forth interpreter (in the same way than gforth, pforth, ...), running on the console and offering you the choice between an interactive prompt or interpreting scripts (from files or string). For more information, see the document
  • A shared library that allows you to embed a Forth interpreter in your personal C++ projects like shown in this example. You can extend the original Forth C++ class to create a personal Forth like shown in this example.
  • A Forth IDE made in GTK+ (work in progress, it contains minimal features).
  • A proof of concept of a tiny spreadsheet GTK+. standalone using SimForth instead of Visual Basic.

Documentation

SimForth comes with some documentation inside the folder doc:

Features

SimForth is not a Forth conceived to be embedded in micro-controllers. It is a token threaded forth developed in C++ and token threaded forth makes the slower Forth interpreters and C++ makes the binary bigger. SimForth has been made for offering GIS and spreadsheet extensions (still in gestation) not to follow the Forth standard. The core of SimForth is for the moment not complete and some words are currently in development. As consequence, SimForth is not 100% compliant to ANSI-Forth 2012.

I am a Forth noob, SimForth has its own personal touch concerning the implementation of the interpreter, dictionary, input buffer, some features have been discarded (source editor, user variable, vocabulary) and some design issues are still present. Certainly, purists will not agree with my way of having implemented it. See deviations.

Implemented in SimForth:

  • Standalone Forth. See sub-project.
  • Shared library for your C++ project desiring to embed a Forth interpreter.
  • No Return-Stack manipulation but auxiliary stack manipulation (makes Forth less crashy).
  • The Data-Stack is mixing integer and floatting-point values: no separated floating point stack, no floatting-point words. Standard words such addition or times will use floatting point when needed. I did not want floatting-point words since this increase the number of primitives and make the code less readable.
  • Can import C code and interface C functions from external libraries. See documentation.
  • Minimal Forth system Glossary doc: , code: .
  • Display colorful and human-friendly error messages (more than gforth).
  • Display colorful dictionary. See screenshot.
  • Basic colorful debugger. See screenshot.
  • Interactive mode, interpret files and C++ strings.
  • Auto-completion of words in the interactive mode.
  • History of commands in the interactive mode.
  • (WIP) Basic GTK+ IDE (auto-completion, color, dictionary and stack display). See screenshot.
  • Basic GTK+ spreadsheet standalone using SimForth instead of Visual Basic. See sub-project.
  • Basic self-tests made in Forth. See code. Continuous integration scripts.
  • Can execute basic Legacy OpenGL code. See code.
  • Data-Stack mixing integer and float values (no separated floating point stack).
  • Max number of characters for a word is 32. Unicode words can be accepted while this feature is not really tested.
  • Save and load dump dictionary.

To be fixed / Work in progress:

  • See issue
  • Words to be implemented: locals, throw, catch, multi-tasking ...
  • Forth structures are not compatible with C structure.
  • Little/Big endian compatibility when dictionary is saved. For the moment only AMD64-style architecture is managed.

Known issues:

  • Disastrous dictionary byte manipulation.
  • Dictionary having C functions loaded from shared libraries cannot be saved/loaded since pointers are not exported.

Q/A

  • Why SimForth? When I started to develop SimTaDyn I wanted a scripting language with GIS primitives for managing my maps. SimForth was originally used in my student project named SimTaDyn which is a Geographic Information System (GIS) in which maps can be manipulated as a spreadsheet and where Forth replaces the Excel Visual Basic, the scripting language for formulas stored in spreadsheet cells. I am currently moving apart SimTaDyn code as modules and the Forth interpreter is one of these external parts. SimTaDyn is still a work in progress project but now, SimForth has its own git repo and I hope have it's own life and used for my other projects.

  • Why not using Lua or Python or Julia? Because Forth code is compact, has no syntax (thanks to the reverse polish notation (RPN) and therefore, a Forth script is enough minimalist to be embedded in cells of spreadsheets in the same way of Excel Visual Basic. Minimalist does not mean weak functionalities: Forth is coming from embedded systems in 70's and has been used in astronomy, it has a very tiny footprint memory: up to 64 KiB for classic Forth. This size includes the interpreter and the virtual machine holding the byte code shared with the memory. In kind of way, a spreadsheet cell is kind of micro-controller: compactness is the key! This reduced size is possible mainly because the interpreter does not have to manage complex language syntax. In addition, this language can self-evolving its syntax (metaprogramming), living in a multi-tasking virtual machine that can easily be dumped in a file and shared. Forth is therefore more power than Excel Visual Basic. Lua or Python or Julia are a size more complex and heavy while offering a more friendly syntax and powerful libraries.

  • Why developing another Forth interpreter? Why not simply using gforth? In 2004, as a student, I wanted to learn Forth after my father gave me the book "FORTH" by W. P. Salman, O. Tisserand and B. Toulout, Editions Eyrolles, 1983. SimTaDyn started as a one-year student project and making a Forth interpreter was a good idea to impress my teachers (while, in fact, they were not all impressed by the beauty of Forth ... and by SimTaDyn). The other reason was the code source of gforth is too obscure for me, pforth can easily be crashed and I did not know at this time the uncrushable 4th. In addition, I wanted to develop my own Forth managing my desired features and, as a noob, to implement core features in C and interface them with Forth words. They usually do that in Python so why not in Forth!

  • Why using C++ for developing Forth? Should not be better if written in assembly? Yes, assembly would have been a better choice but I wanted to have a portable Forth and use the inheritance of C++ to implement easily different Forth interpreters (from classic Forth to a specialized Forth for GIS).

  • So why using SimForth? SimForth is the scripting language for SimTaDyn and should be used from SimTaDyn only since SimForth, used as standalone, is less powerful than any serious Forth interpreter and it is two times slower than pforth, five compared to gforth. See benchmark. In my opinion, SimForth used as shared library, offers a simpler API than gforth.

Gallery

  • Dictionary (console)

doc/img/Dictionary.png

  • Debugger (console)

doc/img/Debugger.png

  • GTK+ IDE

doc/img/IDE.png