[exercise] 8.7

Author: Dev-XYS

chapter08-Declaring-types-and-classes/7.hs

@@ -0,0 +1,8 @@
+data Maybe' a = Nothing' | Just' a
+
+instance Eq a => Eq (Maybe' a) where
+ Nothing' == Nothing' = True
+ (Just' x) == (Just' y) = x == y
+ _ == _ = False
+
+-- Instance declaration of list is omitted.