Generators for do-notation

do.js

var sequence = (M, ms)=> ms.reduce(
  (m1, m2)=> do(M, function*() {
    var x  = yield m1;
    var xs = yield m2;
    return x.concat(xs);
  }), M.of([]));

// should be eqv to

var sequence = (M, ms)=> ms.reduce(
  (m1, m2)=> {
    m1.chain((x)  => {
    m2.chain((xs) => {
    return M.of(x.concat(xs));
  }}}, M.of([]));

function doom(M, fn) {
  var g = fn();
  var loop = (x)=> {
    var {value, done} = g.next(x);
    return done ? M.of(value) : value.chain(loop);
  };
  return loop();
}