Fix chapter 25

25-composing-types/25-composing-types.md

@@ -0,0 +1,10 @@
+# 25 Composing Types
+
+## 25.4 Twinplicative
+
+see [src/gotcha.hs](./src/gotcha.hs)
+
+## 25.6 Compose Instances
+
+- see [src/gotcha.hs](./src/gotcha.hs)
+- see [src/bifunctor.hs](./src/bifunctor.hs)

25-composing-types/25.4-twinplicative.md

@@ -1,2 +0,0 @@
-# GOTCHA! Exercise time
-see src/gotcha.hs

25-composing-types/25.6-compose-instances.md

@@ -1,5 +0,0 @@
-# Exercises: Compose Instances
-see src/gotcha.hs
-
-## Bifunctor
-see src/bifunctor.hs

25-composing-types/src/gotcha.hs

@@ -16,6 +16,11 @@ 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
 
+myApply :: (Applicative f, Applicative g)
+        => Compose f g (a -> b) -> Compose f g a -> Compose f g b
+myApply (Compose h) (Compose c) =
+    Compose $ (fmap (<*>) h) <*> c
+
 instance (Applicative f, Applicative g) => Applicative (Compose f g) where
     pure :: a -> Compose f g a
     pure a = Compose $ pure (pure a)