FoldablesHEADmaster

1 files changed, 11 insertions, 0 deletions

diff --git a/monad/h3.hs b/monad/h3.hs
new file mode 100644
index 0000000..9439331
--- /dev/null
+++ b/monad/h3.hs
@@ -0,0 +1,11 @@
+data Free f a = Var a
+              | Node (f (Free f a))
+
+instance Functor f => Functor (Free f) where
+    fmap g (Var a) = g a
+    fmap g (Node a) = fmap g a
+
+instance Functor f => Monad (Free f) where
+    return a = Var a
+    (Var a) >>= g = g a
+    (Node a) >>= g = fmap g a