June 2018 Update

Task/Y-combinator/Elm/y-combinator.elm

@@ -0,0 +1,18 @@
+import Html exposing (text)
+
+type Mu a b = Roll (Mu a b -> a -> b)
+
+unroll : Mu a b -> (Mu a b -> a -> b)
+unroll (Roll x) = x
+
+fix : ((a -> b) -> (a -> b)) -> (a -> b)
+fix f = let g r = f (\v -> unroll r r v)
+        in g (Roll g)
+
+fac : Int -> Int
+fac = fix <|
+    \f n -> if n <= 0
+            then 1
+            else n * f (n - 1)
+
+main = text <| toString <| fac 5