Do2.js

 // Do works with any Monad that implements the fantasy-land spec
//    https://github.com/fantasyland/fantasy-land#monad
function Do(Type) { return (a, ...fns) => {
  function doIt(as, fns) {
    const [fn, ...rest] = fns;
    if(rest.length === 0) {
      return as['fantasy-land/chain'](a2s => {
        return Type['fantasy-land/of'](fn.apply(null, a2s));
      });
    } else {
      return as['fantasy-land/chain'](a2s => {
        const aPrime = fn.apply(null, a2s);
        return doIt(aPrime['fantasy-land/map']((aP) => [aP, ...a2s]), rest);
      });
    }
  }
  return doIt(a['fantasy-land/map'](a2 => [a2]), fns);
}}

/**
 * Maybe from https://github.com/origamitower/folktale
 */
const Maybe = require('folktale/maybe');
const maybe = 
  Do(Maybe)(
    Maybe.Just(5),
    (five) => Maybe.Just(7),
    (seven, five) => Maybe.Just(seven + five),
    (added, seven, five) => Maybe.Just(added * seven * five),
    (multiplied, added, seven, five) => {
      // last function is just 'mapped', so we can return anything and have
      //   it wrapped in Type["fantasy-land/of"]()
      return multiplied + added + seven + five;
    }
  );
console.log(maybe) // folktale:Maybe.Just({ value: 444 })  ((5 + 7) * 5 * 7) + (5 + 7) + 5 + 7