SweetJS

Sweet brings the hygienic macros of languages like Scheme and Rust to JavaScript. Macros allow you to sweeten the syntax of JavaScript and craft the language you’ve always wanted.

Website | Source | Paper: "Sweeten Your JavaScript: Hygienic Macros for ES5" and Paper: "An Operational Semantics for JavaScript"

Install:

npm install -g @sweet-js/cli @sweet-js/helpers

... puts sjs binary into global scope, which does transpilation of source.

Examples

Let:

syntax let = function (ctx) {
  let ident = ctx.next().value;
  ctx.next(); // eat `=`
  let init = ctx.expand('expr').value;
  return #`
    (function (${ident}) {
      ${ctx}
    }(${init}))
  `
};

let bb8 = new Droid('BB-8', 'orange');
console.log(bb8.beep());

Conditional:

import { unwrap, isKeyword } from '@sweet-js/helpers' for syntax;

syntax cond = function (ctx) {
  let bodyCtx = ctx.contextify(ctx.next().value);

  let result = #``;
  for (let stx of bodyCtx) { // <2>
    if (isKeyword(stx) && unwrap(stx).value === 'case') {
      let test = bodyCtx.expand('expr').value;
      // eat `:`
      bodyCtx.next();
      let r = bodyCtx.expand('expr').value;
      result = result.concat(#`${test} ? ${r} :`);
    } else if (isKeyword(stx) && unwrap(stx).value === 'default') {
      // eat `:`
      bodyCtx.next();
      let r = bodyCtx.expand('expr').value;
      result = result.concat(#`${r}`);
    } else {
      throw new Error('unknown syntax: ' + stx);
    }
  }
  return result;
};

let x = null;
let realTypeof = cond {
  case x === null: 'null'
  case Array.isArray(x): 'array'
  case typeof x === 'object': 'object'
  default: typeof x
}

Operators:

operator >>= left 1 = (left, right) => {
  return #`${left}.then(${right})`;
};

fetch('/foo.json') >>= resp => { return resp.json() }
                   >>= json => { return processJson(json) }

Tags: library browser nodejs

Last modified 16 December 2024

SweetJS

Semantic macros for ECMAScript.

Examples