the Maybe monad

example.coffee

Maybe = require './Maybe'

Maybe(1) # => Maybe(1)
Maybe({a: 1})('a') # => Maybe(1)

Maybe({a: 1})('a').value # => 1

Maybe({a: 1})('b') # => Nothing
Maybe({a: 1})('b')('c')('d')('e') # => Nothing

obj = {a: 1, setA: (val) -> @a = val; this}
Maybe(obj)('setA', 2)('a') # => Maybe(2)
Maybe(obj)('setA') # => Maybe(obj.setA)
Maybe(obj)('setA')._(3) # => Maybe(obj)
obj.a # => 3

maybe.coffee

maybeToString = () ->
  if @value?
    "Maybe(#{@value.toString()})"
  else
    'Nothing'

maybeSend = (args...) ->
  value = @value
  if typeof value is 'function'
    Maybe value(args...)
  else
    Nothing

Maybe = (value) ->
  console.log "Maybe(#{value})"
  maybe = (slot, args...) ->
    console.log "(#{value}):maybe(#{slot})"

    unless value?
      return Nothing

    newValue = value[slot]
    if typeof newValue is 'function'
      console.log "bind:(#{newValue}):(#{value})"
      newValue = newValue.bind(value)

    maybeNewValue = Maybe newValue

    if args.length
      maybeNewValue = maybeNewValue.send(args...)

    return maybeNewValue

  maybe.value = value
  maybe.toString = maybeToString
  maybe._ = maybe.send = maybeSend

  maybe

exports.Maybe = Maybe
Nothing = exports.Nothing = Maybe.Nothing = Maybe()