Maybe Monad COCO

Maybe.coco

import math

class Maybe

data Just(n) from Maybe
data Nothing() from Maybe

@addpattern(fmap)
def fmap(f, Nothing()) = Nothing()

@addpattern(fmap)
def fmap(f, Just(n))   = Just(f(n))

def apply(f: Maybe, a: Maybe):
    match (Just(ff), Just(aa)) in (f, a):
        return Just(ff(aa))
    else:
        return Nothing()

def bind(f, Nothing()) = Nothing()

@addpattern
def bind(f, Just(a)) = f(a)


maybeValue = Just(10)

maybeFunction = Just(x -> x ** 2)
maybeFunction2 = Just(math.sqrt)

def valueToMaybe(v: int) -> Maybe:
    if v < 100:
        return Just(v)
    return Nothing()

maybeValue |> fmap$(x -> x ** 2) |> apply$(maybeFunction) |> print


f = x -> x * 2

# Composition
(f..f..f..f)(5) |> print