bbforth

luchak • 2023-07-11*2023-07-11 21:17* •

BBS>

PICO-8>Work in Progress

This cart is a barebones Forth implementation in 279 tokens. It could be smaller, it could be more usable, but I haven't really touched it in weeks, so here you go. Probably full of bugs.

Features

eval() function
Interpret and compile modes - extend syntax in Forth!
if/then (implemented in Forth)
A few useful comments, including some commented-out utility functions and basic smoke test.

Non-features / shortcomings

else (you can add this in Forth)
Arithmetic (you can add this for 11 tokens per binop, or 9 tokens if you're willing to use valid Lua identifiers as operator names)
Looping (you can probably add this for the cost of a few arithmetic/comparison operators, then add the syntax in Forth for no token cost)
Passing args or returning values when calling Lua functions from Forth (depending on how fancy you want to get, probably takes 20-50 tokens for a reasonable wrapper)
[ and ] are spelled _lb and _rb for some reason.
The inner interpreter works in a non-standard way that will make it hard to call arbitrary Forth from Lua outside of eval - this is probably worth rethinking.

A few ways to make it smaller

A few functions could probably be moved from Lua to the initial Forth definitions as-is, although since : and ; depend on them this will be a bit messy.
With the right Forth/Lua binding util, even more functions could probably be moved.
With some internal representation changes, even _interp and eval could probably be (mostly) boostrapped.

Anyway, enjoy. This may not be useful for very much, but the question of how little material you need to bootstrap a reasonable eval is still kind of a fun question.