Monads in plain CoffeeScript http://modernjavascript.blogspot.com.es/2013/06/monads-in-plain-javascript.html

monad.coffee

Maybe = (@value) ->
Maybe::ret = -> @value
Maybe::bind = (fn) ->
  if @value? then (fn @value) else undefined
Maybe.lift = (fn) -> (val) -> new Maybe (fn val)

addOne = (val) -> val + 1
maybeAddOne = Maybe.lift addOne

Maybe.lift2 = (fn) -> (M1, M2) ->
  helper = M1.bind (val1) ->
    M2.bind (val2) ->
      fn val1, val2
  new Maybe helper

add = (a, b) -> a + b
m1 = new Maybe 1
m2 = new Maybe 2
m3 = new Maybe undefined

liftM2Add = Maybe.lift2 add

console.log liftM2Add(m1, m2).ret()
console.log liftM2Add(m3, m2).ret()
console.log liftM2Add(m1, m3).ret()