option.js

// `unit` is `return` from Haskell
// `bind` is `>>=` from Haskell, or `flatMap` from Scala

var None = {
  bind:      function (fn)        { return this;      },
  unit:      function (v)         { return Option(v); },
  getOrElse: function (elseValue) { return elseValue; }
};

var Some = function (value) {
  return {
    bind:      function (fn) { return fn.call(this, value); },
    unit:      function (v)  { return Option(v);            },
    getOrElse: function (_)  { return value;                }
  }
};

var Option = function (value) {
  return (value === null || value === undefined) ? None : Some(value);
};

var n = Option(5).bind(function (n) { return this.unit(n + 1); })
                 .bind(function (n) { return this.unit(n + 2); })
              // .bind(function (n) { return this.unit(null);  })
                 .bind(function (n) { return this.unit(n + 3); })
                 .getOrElse("something returned None along the way");

console.log(n === 11);