JavaScript back and Forth

Aliaksei Chapyzhenka

JavaScript back and Forth

Aliaksei Chapyzhenka drom.io/fday15

We turn out water into wine
It's something we do all the time
It doesn't cost a single dime
And it's beautiful...

Crash Test Dummies

Forth is everywhere

Forth runs everywhere

from micro-controllers to rockets

"everywhere" is changing over time

JavaScript is everywhere

Can we translate Forth <--> JavaScript?

JavaScipt is new "everywhere"

PC client (browser)
server, cloud (node.js)
mobile phone, tablet, Apps
Embedded. IoT, etc.

Dev boards: tessel.io, espruino.com
Runtimes: kinomajs, iot.js, v7

Some JavaScript facts

Dynamic, do all at runtime
Untyped, everything is var
Interpreted, no explicit compile stage, binary or bytecode
Multi-pardigm, imperative, OO, functional
Async programming with callbacks
Streams, UNIX concept. (stdin/stdout)
originally developed in 10 days in May 1995

JavaScript AST

JavaScript code can be represented in form of Abstract Syntax Tree (AST)
Parser, code generator, traversal utilites, will use it.
Mozilla-AST and Shift-AST , are the most popular AST formats
AST can be represented in JSON format
AST used in all following experiments

JavaScript arithmetic

Main numeric value format is float64, tricks to do i32, u32, f32.

x | 0 --> i32
x >>> 0 --> u32
+x --> f64
Math.fround(x) --> f32

TypedArrays can be used to store signed / unsigned {8, 16, 32}, f32, f64
asm.js and WebAssembly new ways to be closer to CPU.

case 1: Forth interpreter in JavaScript

Standard Forth interpreter in JavaScript
JavaScript as an Assembler
Forth as a stream, non-blocking IO
embed Forth inside web page or server
Working torwards ANS94 and Forth2012 compliance.

Forth in JS -- challenges

Organize vocabulary with JS structures, array, object.
Forth control structures are complex, JS has no branches, has to use break
CREATE DOES> magic
Double and mixed integer arithmetic. i64, u64

case 2: JavaScript to Forth

Proof of concept prototype
Needs serious CFG and SSA pipeline
Migrating to the Sea of Nodes tools
May switch to WebAssembly: wast-parser, wast-pipeline

case 3: CodeMirror

CodeMirror is a versatile text editor implemented in JavaScript for the browser

Supports 100+ languages including Forth

Runs lightweight Forth interpreter to do proper coloring

Conclusions

Yes, one can mix JavaScript and Forth
Allows full web-based Forth IDE
A stepping stone in my Stack Processor reserach (Quark).
All free and Open Source