chapter 16 - added a module for functor laws

Author: mukeshsoni

chapter16/FunctorLaws.hs

@@ -0,0 +1,22 @@
+import Test.QuickCheck
+import Test.QuickCheck.Function
+
+functorIdentity :: (Functor f, Eq (f a)) =>
+                        f a -> Bool
+functorIdentity f = fmap id f == f
+
+functorCompose :: (Functor f, Eq (f c)) =>
+                       (a -> b)
+                    -> (b -> c)
+                    -> f a
+                    -> Bool
+functorCompose f g x =
+    (fmap g (fmap f x)) == fmap (g . f) x
+
+functorCompose' :: (Eq (f c), Functor f) =>
+                       f a
+                    -> Fun a b
+                    -> Fun b c
+                    -> Bool
+functorCompose' x (Fun _ f) (Fun _ g) =
+    (fmap g (fmap f x)) == fmap (g . f) x