Initial data commit

Task/Y-combinator/D/y-combinator.d

@@ -0,0 +1,25 @@
+import std.stdio, std.traits, std.algorithm, std.range;
+
+auto Y(S, T...)(S delegate(T) delegate(S delegate(T)) f) {
+    static struct F {
+        S delegate(T) delegate(F) f;
+        alias f this;
+    }
+    return (x => x(x))(F(x => f((T v) => x(x)(v))));
+}
+
+void main() { // Demo code:
+    auto factorial = Y((int delegate(int) self) =>
+        (int n) => 0 == n ? 1 : n * self(n - 1)
+    );
+
+    auto ackermann = Y((ulong delegate(ulong, ulong) self) =>
+        (ulong m, ulong n) {
+            if (m == 0) return n + 1;
+            if (n == 0) return self(m - 1, 1);
+            return self(m - 1, self(m, n - 1));
+    });
+
+    writeln("factorial: ", 10.iota.map!factorial);
+    writeln("ackermann(3, 5): ", ackermann(3, 5));
+}