Checking Instance knowledge

Haskell Excercises & Code/MFAM - Practice/monad.hs

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+module MonadicStuff where
+
+-- Checking udnerstanding of Monad instance for Maybe
+-- To write Monad. we need to write ApplICATIVE
+-- To write applicative we need Functor
+--import Data.Maybe
+
+instance Functor Maybe where
+    fmap f Nothing  = Nothing
+    fmap f (Just x) = Just (f x)
+
+instance Applicative Maybe where
+    pure x = Just x
+    -- pure id <*> v = v
+    -- pure should not change the underlying values
+    Nothing <*> _ = Nothing
+    _ <*> Nothing = Nothing
+    Just f <*> Just n = Just (f n)
+
+instance Monad Maybe where
+    return = Just
+    Nothing >>= f = Nothing
+    (Just n) >>= f = f n