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  1. #include <stdio.h>
  2. #include <functional>
  3.  
  4. using namespace std;
  5.  
  6. template<typename A, typename B>
  7. using F = function<A(B)>;
  8.  
  9. template<typename A>
  10. using CN = F<F<A, A>, F<A, A>>;
  11.  
  12. template<typename A>
  13. CN<A> zero() {
  14.  return [](F<A,A>) -> F<A,A> {
  15.     return [](A i) -> A {return i;};
  16.  };
  17. }
  18.  
  19. template<typename A>
  20. CN<A> inc(CN<A> n) {
  21.     return [=](F<A,A> f) -> F<A,A> {
  22.         return [=](A a) -> A {
  23.             return n(f)(f(a));
  24.         };
  25.     };
  26. }
  27.  
  28. template<typename A>
  29. CN<A> operator*(CN<A> a, CN<A> b) {
  30.     return [=](F<A,A> f) -> F<A,A> {
  31.         return b(a(f));
  32.     };
  33. }
  34.  
  35. template<typename A>
  36. CN<A> operator+(CN<A> a, CN<A> b) {
  37.     return [=](F<A,A> f) -> F<A,A> {
  38.         return [=](A i) -> A {
  39.             auto i1 = a(f)(i);
  40.             return b(f)(i1);
  41.         };
  42.     };
  43. }
  44.  
  45. CN<unsigned int> i2c(unsigned int n) {
  46. 	auto l = zero<unsigned int>();
  47. 	for(int i = 0; i<n; i++)
  48. 		l = inc(l);
  49. 	return l;
  50. }
  51.  
  52. unsigned int c2i(CN<int> n) {
  53.     auto n2 = n([&](int a)->int {return a+1;});
  54.     return n2(0);
  55. }
  56.  
  57. int multiply(unsigned int a, unsigned int b) {
  58. 	return c2i(i2c(a) * i2c(b));
  59. }
  60.  
  61. int main() {
  62. 	unsigned int a, b;
  63. 	a = 4;
  64. 	b = 3;
  65. 	printf("%d*%d=%d", a, b, multiply(a, b));
  66. 	return 0;
  67. }
Success #stdin #stdout 0s 3420KB
comments (?)
stdin
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Standard input is empty
stdout
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4*3=12
https://ideone.com/Y7KCZx
language:
C++14 (gcc 8.3)
created:
10 years ago
visibility:
public

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