do-notation using sweet.js

do.sjs

macro $do {
    case { $y:expr } => {
        $y
    }
    case { $x:ident <- $y:expr $rest ... } => { 
        λ['>=']($y, function($x) {
            return $do { $rest ... }
        });
    }
}

// Using the bilby.js functional programming library:
// https://github.com/pufuwozu/bilby.js
var λ = require('./bilby');

// Haskell:
//
// do
//   x <- [1, 2]
//   y <- [x, x]
//   [y * 2, y * 3]
//
// [2,3,2,3,4,6,4,6]

// sweet.js:

// Can't use arrays directly because of https://github.com/mozilla/sweet.js/issues/28
// Need to manually replace a, b and c in output with array expressions.

var list = $do {
  x <- a // [1, 2]
  y <- b // [x, x]
  c // [y * 2, y * 3]
};
console.log(list);

// [ 2, 3, 2, 3, 4, 6, 4, 6 ]

This is awesome! Nice job

Note: the "can't use arrays directly" bit isn't an issue anymore apparently: sweet-js/sweet-core#28
For anyone coming here in the future you might want to check out: https://github.com/fantasyland/sweet-fantasies/blob/master/src/do.sjs