Monad.purs

module Main where

import Effect.Console (log)

type Monad m = { return :: forall a. a -> m a
               , bind :: forall a b. m a -> (a -> m b) -> m b }

data Id a = Id a

id :: Monad Id
id = { return : Id
     , bind : \ma f -> case ma of Id a -> f a }

data Maybe a = Nothing | Just a

maybe :: Monad Maybe
maybe = { return : Just
  , bind : \ma f -> case ma of
      Nothing -> Nothing
      Just a -> f a
  }

test :: forall m. Monad m -> m Number
test = \m -> m.bind (m.return 1.0) (\n1 ->
        m.bind (m.return "Test") (\n2 ->
        m.return n1))

test1 = test id

test2 = test maybe

main = log "Done"