brendanator / jsforth

Forth implemented in js

jsForth

An implementation of Forth in JavaScript

Try it out here

ANS Forth

jsForth implements the full core ANS standard

The following word sets are implemented:

• Core words - fully implemented
  • All tests pass except some integer multiplication/division edge cases where the ANS spec differs from the results given by the long package
• Core plus words - fully implemented and all tests pass
• Core extension words - fully implemented and all tests pass

The ANS Forth tests can be run using npm run test or in the intepreter with the following Forth code

include test/verbose-tester.fth
include https://raw.githubusercontent.com/gerryjackson/forth2012-test-suite/master/src/core.fr

The complete test suite is available here

JavaScript interoperability

• global variable access js /document
• array access js .0.2
• property access js .name
• property setting js .name!
• function calling js .sin{1}
• method calling js /document.getElementById{1}
• new with params js .new{1}

Threading model - trampolined threading

All of the standard threading models require call or jump to execute the next instruction. In JavaScript these both translate into functions calls in tail position. Without tail call optimisation this will lead to a stack overflow. Therefore jsForth uses a trampoline to execute instructions.

ECMAScript 6 specifies tail call optimisation, but unfortunately most browsers don't support it yet.

jsforth's Issues

REFILL returns incorrect true flag

On success, refill doesn't return -1, but something like 1. When true flag should be -1 for all the standard words.

JavaScript Strings in Interop

I am attempting to figure out how to convert a counted string (such as from using s" in a definition) into a JavaScript string so that I can call external JavaScript functions that require strings as input. However, I cannot seem to get it working. Here is what I am trying to do:

: test123 s" statusTarget" ;
statusTarget is the ID of an element on the DOM in my test page

test123
Two numbers are now on the stack, representing the counted string

js /document.getElementById{2}
This pops TOS and NOS, but only returns null (where it should have returned something relating to the found element).

I have checked that document.getElementById('statusText') works in the console, however I cannot manage to get the JS interop code to do the same thing. Browsing through js-interop.js seems to indicate that there isn't currently a function to do this conversion, as there are no examples of how to this in the comments at the top. Other JS functions seem to work as long as they only take numbers as input.

I would have attempted to implement this myself, but I cannot yet figure out how strings are stored in Forth's virtual memory, so I am a bit lost (the address on the stack is always some large negative number). Am I overlooking something or is this not yet implemented?

P.S. Great code by the way! jsForth works really well otherwise.

non-destructive display of stack

It would be nice if the ".s" command was supported in the browser interpreter so that we could look at the stuff in the stack without deleting it.

S" doesn't work like in other forths

Hey @brendanator

First off - your Forth rocks! 😎 I've played with building Forths for numerous platforms, and I've enjoyed playing with a lot of pre-existing Forths too. For people like me who don't get how the whole "threading" thing works, creating a full ANS Forth is nothing short of incredible. Very, very cool!

Having said that, I've kinda got two issues in one here:

1. The main issue - the only one that's really an issue per se - is that S" doesn't put the pointer and length on the stack... at least, not in the demo page. For example, if I'm in Gforth, and I type s" Forth" .s, I'll get output like 1234567 5 (the 5 being the length of the word "Forth" and the other number being a pointer to the string in memory). That's not happening here.
2. This may (and probably should, sorry) be a separate issue, but how would strings work with JS interop? It could be you hve an example somewhere and I just haven't seen it yet, but my first thought was something like s" Message here" /js alert{1} and it would show an alert("Message here"). If you need some tutorials, I'd be happy to contribute those once I know what the heck I'm doing. 😆

Anyway, thanks again for the awesome #Forth ! I can't wait to wire this up to something like xterm.js, build a nice little API of words around a canvas, and doo all kinds of crazy fun stuff with this thing. 😃