Move over test from compiler repo

Author: paf31

examples/Tree.purs.hs

@@ -0,0 +1,19 @@
+module Main where
+
+  import Prelude
+  import Data.Foldable
+  import Data.Monoid
+
+  data Tree a = Node a | Branch (Tree a) (Tree a)
+
+  instance foldableTree :: Foldable Tree where
+    foldr f z (Node x)     = x `f` z
+    foldr f z (Branch l r) = foldr f (foldr f z r) l
+
+    foldl f z (Node x)     = z `f` x
+    foldl f z (Branch l r) = foldl f (foldl f z l) r
+
+    foldMap f (Node x)     = f x
+    foldMap f (Branch l r) = foldMap f l <> foldMap f r
+
+  main = Debug.Trace.print <<< sum $ Branch (Node 1) (Branch (Node 2) (Node 3))