Add remaining haskell book exercises

1 files changed, 38 insertions, 0 deletions

diff --git a/Haskell-book/18/Instance/src/PhhhbbtttEither.hs b/Haskell-book/18/Instance/src/PhhhbbtttEither.hs
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+++ b/Haskell-book/18/Instance/src/PhhhbbtttEither.hs
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+{-# LANGUAGE NoImplicitPrelude #-}
+module PhhhbbtttEither where
+
+import Prelude ( Monad(..)
+               , Functor(..)
+               , Applicative(..)
+               , Eq(..)
+               , ($)
+               , Show(..) )
+import Test.QuickCheck
+import Test.QuickCheck.Checkers
+
+data PhhhbbtttEither b a =
+        Left a
+      | Right b
+      deriving (Eq, Show)
+
+instance Functor (PhhhbbtttEither b) where
+    fmap f (Right x) = Right x
+    fmap f (Left x) = Left $ f x
+
+instance Applicative (PhhhbbtttEither b) where
+    pure x = Left x
+    Right f <*> _ = Right f
+    Left f <*> x = fmap f x
+
+instance Monad (PhhhbbtttEither b) where
+    return = pure
+    (Right x) >>= f = Right x
+    (Left x) >>= f = f x
+
+instance (Arbitrary a, Arbitrary b) => Arbitrary (PhhhbbtttEither b a) where
+    arbitrary = frequency [ (1, fmap Right arbitrary)
+                          , (1, fmap Left arbitrary)
+                          ]
+
+instance (Eq a, Eq b) => EqProp (PhhhbbtttEither b a) where
+    (=-=) = eq