TypeClasses.hs

module Main (


) where
import Control.Monad.Either

f :: (Monad m) ⇒ Int →   m Int
f 0  = fail "I don't like zeros"
f x  = return x

example1 m =
    case m of
    Nothing →  putStrLn "Nothing"
    Just i  →  putStrLn (show i)

example2 m=
    case m of
    Left msg →  putStrLn msg
    Right i  →  putStrLn (show i)

intermediate :: (Monad m) ⇒   m Int
intermediate= f 0 ↠ λ i →  return (i+1)

main =    example1 intermediate >> example2 intermediate --prints Nothing
                                                         --Example: I don't like zeros