MyMaybe.hs

module MyMaybe where

data MyMaybe a = MyJust a | MyNothing deriving Show

instance Monad MyMaybe where

  return m = MyJust m
  (>>=) m f = case m of
                MyJust a -> f a
                MyNothing -> MyNothing


mylookup :: (Eq k) => k -> [(k, v)] -> MyMaybe v
mylookup k ms = foldr (\(key, v) acc -> if k == key then MyJust v else acc) MyNothing ms