all tasks

Task/Y-combinator/Objective-C/y-combinator.m

@@ -0,0 +1,42 @@
+#import <Foundation/Foundation.h>
+
+typedef int (^Func)(int);
+typedef Func (^FuncFunc)(Func);
+typedef Func (^RecursiveFunc)(id); // hide recursive typing behind dynamic typing
+
+Func fix (FuncFunc f) {
+  RecursiveFunc r =
+    ^(id y) {
+      RecursiveFunc w = y; // cast value back into desired type
+      return f(^(int x) {
+        return w(w)(x);
+      });
+    };
+  return r(r);
+}
+
+int main (int argc, const char *argv[]) {
+  NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];
+
+  FuncFunc almost_fac = ^Func(Func f) {
+    return [[^(int n) {
+      if (n <= 1) return 1;
+      return n * f(n - 1);
+    } copy] autorelease];
+  };
+
+  FuncFunc almost_fib = ^Func(Func f) {
+    return [[^(int n) {
+      if (n <= 2) return 1;
+      return  f(n - 1) + f(n - 2);
+    } copy] autorelease];
+  };
+
+  Func fib = fix(almost_fib);
+  Func fac = fix(almost_fac);
+  NSLog(@"fib(10) = %d", fib(10));
+  NSLog(@"fac(10) = %d", fac(10));
+
+  [pool release];
+  return 0;
+}