Add solutions to the composing types chapter

Author: BoeingX

src/ComposingTypes/Twinplicative/Exercise.hs

@@ -0,0 +1,13 @@
+module ComposingTypes.Twinplicative.Exercise where
+    
+import Control.Applicative (liftA2)
+
+newtype Compose f g a = Compose { getCompose :: f (g a) }
+    deriving (Eq, Show)
+
+instance (Functor f, Functor g) => Functor (Compose f g) where
+    fmap f (Compose fga) = Compose $ (fmap . fmap) f fga
+
+instance (Applicative f, Applicative g) => Applicative (Compose f g) where
+    pure = Compose . pure . pure
+    Compose fgab <*> Compose fga = Compose $ liftA2 (<*>) fgab fga