Data commit

Task/Anonymous-recursion/Java/anonymous-recursion-2.java

@@ -0,0 +1,25 @@
+import java.util.function.Function;
+
+@FunctionalInterface
+interface SelfApplicable<OUTPUT> {
+    OUTPUT apply(SelfApplicable<OUTPUT> input);
+}
+
+class Utils {
+    public static <INPUT, OUTPUT> SelfApplicable<Function<Function<Function<INPUT, OUTPUT>, Function<INPUT, OUTPUT>>, Function<INPUT, OUTPUT>>> y() {
+        return y -> f -> x -> f.apply(y.apply(y).apply(f)).apply(x);
+    }
+
+    public static <INPUT, OUTPUT> Function<Function<Function<INPUT, OUTPUT>, Function<INPUT, OUTPUT>>, Function<INPUT, OUTPUT>> fix() {
+        return Utils.<INPUT, OUTPUT>y().apply(Utils.<INPUT, OUTPUT>y());
+    }
+
+    public static long fib(int m) {
+        if (m < 0)
+            throw new IllegalArgumentException("n can not be a negative number");
+
+        return Utils.<Integer, Long>fix().apply(
+                f -> n -> (n < 2) ? n : (f.apply(n - 1) + f.apply(n - 2))
+        ).apply(m);
+    }
+}