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  1. auto Y_ = [](auto h) {
  2. 	return ([](auto f) { return f(f); })
  3. 	([h](auto f) {
  4. 		return h([f](auto ... n) {
  5. 			return f(f)(n...);
  6. 		});
  7. 	});
  8. };
  9.  
  10. #define REC(NAME, FUN) Y_([](auto NAME){ return [NAME] FUN;})
  11.  
  12. //////////////////////////////////////////////
  13.  
  14. #include <iostream>
  15.  
  16. int main()
  17. {
  18. 	// EXAMPLES
  19.  
  20. 	// factorial
  21. 	auto fact = REC(g,
  22. 		(auto n) {
  23. 			if (n < 2) return 1;
  24. 			return n * g(n - 1);
  25. 		});
  26.  
  27. 	// fibonacci
  28. 	auto fib = REC(g,
  29. 		(auto n) -> int {
  30. 			return n > 1 ? g(n - 1) + g(n - 2) : n;
  31. 		});
  32.  
  33. 	// binomial coefficient
  34. 	auto comb = REC(g,
  35. 		(auto x, auto y) {
  36. 			if (y == 0 || x == y) return 1;
  37. 			return g(x - 1, y - 1) + g(x - 1, y);
  38. 		});
  39.  
  40. 	std::cout << fact(6)     << "\n";
  41. 	std::cout << fib(10)     << "\n";
  42. 	std::cout << comb(10, 4) << "\n";
  43.  
  44. 	return 0;
  45. }
  46.  
Success #stdin #stdout 0s 3148KB
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https://ideone.com/De3hCN
language:
C++14 (gcc 8.3)
created:
8 years ago
visibility:
secret

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