Initial data commit

Task/Y-combinator/Java/y-combinator-1.java

@@ -0,0 +1,25 @@
+import java.util.function.Function;
+
+public interface YCombinator {
+  interface RecursiveFunction<F> extends Function<RecursiveFunction<F>, F> { }
+  public static <A,B> Function<A,B> Y(Function<Function<A,B>, Function<A,B>> f) {
+    RecursiveFunction<Function<A,B>> r = w -> f.apply(x -> w.apply(w).apply(x));
+    return r.apply(r);
+  }
+
+  public static void main(String... arguments) {
+    Function<Integer,Integer> fib = Y(f -> n ->
+      (n <= 2)
+        ? 1
+        : (f.apply(n - 1) + f.apply(n - 2))
+    );
+    Function<Integer,Integer> fac = Y(f -> n ->
+      (n <= 1)
+        ? 1
+        : (n * f.apply(n - 1))
+    );
+
+    System.out.println("fib(10) = " + fib.apply(10));
+    System.out.println("fac(10) = " + fac.apply(10));
+  }
+}