Monad

var Monad = function(x) {
  this.value = x
}

Monad.prototype.of = function(x) {
  return new Container(x)
}

Monad.prototype.isNothing = function() {
  return (this.__value === null || this.__value === undefined)
}

Monad.prototype.map = function(f) {
  return this.isNothing() ? new Maybe(null) : Maybe.of(f(this.__value))
}

Monad.prototype.join = function() {
  return this.isNothing() ? Monad.of(null) : this.__value
}