Maybe monad in CoffeeScript.

maybe.coffee

MONAD = (modifier) ->
  prototype = Object.create null
  unit = (value) ->
    monad = Object.create prototype
    monad.bind = (func, args...) -> func(value, args...)
    modifier(monad, value) if typeof modifier is 'function'
    monad

  unit.lift = (name, func) ->
    prototype[name] = (args...) ->
      unit @bind(func, args...)
    unit
  unit


PRINT = (args...) -> print x.toUpperCase() for x in args

# id = MONAD().lift('print', PRINT)     # construct an identity monad without modifier
# monad = id null
# monad.print()                         # complains!

modifier = (monad, value) ->
  if not value?
    monad.is_null = true
    monad.bind = -> monad               # do nothing w/ bound funcs on null values

maybe = MONAD(modifier)                 # construct the maybe monad
  .lift('print', PRINT)

monad = maybe 'hi!'
monad.print()

monad = maybe null
monad.print()                           # doesn't complain!