RosettaCodeData/Task/Y-combinator/Objective-C/y-combinator-1.m

#import <Foundation/Foundation.h>

typedef int (^Func)(int);
typedef Func (^FuncFunc)(Func);
typedef Func (^RecursiveFunc)(id); // hide recursive typing behind dynamic typing

Func Y(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[]) {
  @autoreleasepool {

    Func fib = Y(^Func(Func f) {
      return ^(int n) {
        if (n <= 2) return 1;
        return  f(n - 1) + f(n - 2);
      };
    });
    Func fac = Y(^Func(Func f) {
      return ^(int n) {
        if (n <= 1) return 1;
        return n * f(n - 1);
      };
    });

    Func fib = fix(almost_fib);
    Func fac = fix(almost_fac);
    NSLog(@"fib(10) = %d", fib(10));
    NSLog(@"fac(10) = %d", fac(10));

  }
  return 0;
}