hw5: monads, some problems

Author: MAnyKey

ITMOPrelude/Monads.hs

@@ -0,0 +1,29 @@
+{-# LANGUAGE NoImplicitPrelude, FlexibleInstances, UndecidableInstances #-}
+module ITMOPrelude.Monads where
+
+import ITMOPrelude.Category
+
+id x = x
+
+class MonadFish m where
+  returnFish :: a -> m a
+  (>=>) :: (a -> m b) -> (b -> m c) -> a -> m c
+
+instance Monad m => Functor m where
+  fmap f x = x >>= f
+
+class Functor m => MonadJoin m where
+  returnJoin :: a -> m a
+  join :: m (m a) -> m a
+  
+instance Monad m => MonadFish m where
+  returnFish = return
+  f >=> g = \a -> f a >>= \b -> g b
+
+instance MonadFish m => Monad m where
+  return = returnFish  
+  ma >>= f = id >=> f ma
+
+instance MonadJoin m => Monad m where
+  return = returnJoin
+  f >>= g = join (fmap g f)