maybe.coffee

class Maybe
    bind: (f) ->
        if @_value is undefined then Nothing else f(@_value)

    ret: (x) -> Just(x)

    fmap: (f) ->
        if @_value is undefined then Nothing else Just(f(@_value))

Just = (x) ->
    m = new Maybe()
    m._value = x
    m

Nothing = Just(undefined)

bind = (m, f) -> m.bind(f)
ret = (m, x) -> m.ret(x)
fmap = (f, f_) -> f.fmap(f_)