all tasks

Task/Y-combinator/Standard-ML/y-combinator.ml

@@ -0,0 +1,21 @@
+- datatype 'a mu = Roll of ('a mu -> 'a)
+  fun unroll (Roll x) = x
+
+  fun fix f = (fn x => fn a => f (unroll x x) a) (Roll (fn x => fn a => f (unroll x x) a))
+
+  fun fac f 0 = 1
+    | fac f n = n * f (n-1)
+
+  fun fib f 0 = 0
+    | fib f 1 = 1
+    | fib f n = f (n-1) + f (n-2)
+;
+datatype 'a mu = Roll of 'a mu -> 'a
+val unroll = fn : 'a mu -> 'a mu -> 'a
+val fix = fn : (('a -> 'b) -> 'a -> 'b) -> 'a -> 'b
+val fac = fn : (int -> int) -> int -> int
+val fib = fn : (int -> int) -> int -> int
+- List.tabulate (10, fix fac);
+val it = [1,1,2,6,24,120,720,5040,40320,362880] : int list
+- List.tabulate (10, fix fib);
+val it = [0,1,1,2,3,5,8,13,21,34] : int list