YALI.js

Yet Another Lox Interpreter. Javascript Implementation

Lox is a Dynamically Typed Programming Language created by Bob Nystrom for his excellent book Crafting Interpreters.

This is yet another Javascript Implementation.

Try it out in the Playground!

Installation

$ npm install yali.js

CLI Usage

File

$ yali loxfile.lox

REPL

$ yali
> print "No semicolons needed!"

loxfmt

$ loxfmt --write --indent="  " loxfile.lox

lox2python

$ lox2python loxfile.lox --out="a.py"

OR

$ lox2python loxfile.lox | python

Embedding in your JS App

The main interface of YALI.js is a run method that will tokenize, parse, and interpret your lox source code, all in one function.

run(source_code, environment = new Environment(), printfn = console.log, debug = false)

You can pass in an environment object, which lets you define built-in variables and functions like so:

const { run, Environment } = require('yali')
const env = new Environment()
env.setBuiltin('owner', 'dberezin')
env.setBuiltin('meaning_of_life', 42)
env.setBuiltin('alert', (interpreter, arg) => alert(arg[0]))

You can also pass in a printfn that will be called for every print statement. Here's an example for capitalizing each word in the stdout:

run(
  'print "hello world";',
  new Environment(),
  out => console.log(out.split(' ').map(_.capitalize).join(' '))
)
> Hello World

Parsing

YALI.js also provides a parse function to tokenize and parse lox source code, returning an array of AST nodes that can be manipulated as desired. See any of the transpiler examples for reference.

Contribute

For any bugs and feature requests please open an issue. For code contributions please create a pull request. Enjoy!