Experimental haskell in javascript interpreter. Many haskell features are not implemented. This projects mainly exists to be able to write and interpret Tidal Cycles code in the browser, as part of Strudel.

Installation

Via Script Tag

You can load the library directly from a script tag via unpkg:

<script src="https://unpkg.com/hs2js@0.0.3"></script>
<button id="hello">hello</button>
<script>
  hs2js.setBase('https://unpkg.com/hs2js@0.0.3/dist/');
  hs2js.loadParser();
  document.getElementById('hello').addEventListener('click', () => {
    hs2js.evaluate('alert "hello from haskell!"');
  });
</script>

Via npm

You need to add postinstall to your package.json script to copy the parser to your public folder:

{
  "scripts": {
    "postinstall": "cp node_modules/hs2js/dist/tree-sitter.wasm public && cp node_modules/hs2js/dist/tree-sitter-haskell.wasm public"
  }
}

Depending on your setup, replace public with the folder that will serve your assets to /. Then install the package:

npm i hs2js

and use it:

import * as hs2js from 'hs2js';
hs2js.loadParser();
document.getElementById('hello').addEventListener('click', () => {
  hs2js.evaluate('alert "hello from haskell!"');
});

API

These are all functions exported by the package:

evaluate

Evaluates a piece of haskell code

code: valid haskell code
scope: global scope, defaults to globalThis. Allows you to pass an object of your own functions / variables from JS to Haskell.
ops: mapping for custom infix operator

Example:

// simple
hs2js.evaluate(`2 + 2`).then(console.log) // log 4
// passing variables via scope:
hs2js.evaluate(`a + b`, { a: 1, b: 2 }).then(console.log); // logs 3
// custom operator
hs2js.evaluate(`2 |* 3`, {}, { '|*': (l, r) => l * r }).then(console.log); // logs 6

parse

Parses a piece of haskell code, returning its AST representation.

Example:

hs2js.parse(`2 + 2`).then(ast=>console.log(ast.toString()))
// (haskell declarations: (declarations (top_splice (apply function: (variable) argument: (literal (integer))))))

run

Evaluates rootNode of haskell AST (used by evaluate internally).

rootNode: haskell AST root node, as returned by parse
scope: see evaluate
ops: see evaluate

Example:

async function main() {
  const ast = await hs2js.parse(`2 + 3`);
  const res = hs2js.run(ast.rootNode);
  console.log(res);
}
main(); // logs 5

loadParser

Loads and caches the parser by fetching tree-sitter.wasm and tree-sitter-haskell.wasm. This function is called internally by parse but calling it yourself might make the parser be ready faster, depending on your application.

hs2js.loadParser().then(() => console.log('parser loaded'))

setBase

Sets the base path where the WASM files are expected by loadParser. Defaults to /. Expects tree-sitter.wasm and tree-sitter-haskell.wasm to be present. Can either be a relative path or a URL.

hs2js.setBase('https://unpkg.com/hs2js@0.0.4/dist/');
hs2js.loadParser(); 
/* loads 
- https://unpkg.com/hs2js@0.0.4/dist/tree-sitter.wasm
- https://unpkg.com/hs2js@0.0.4/dist/tree-sitter-haskell.wasm
*/