Maybeモナドみたいなものが作りたかった | Codetter（こーどったー）

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
#include <cstdio>
#include <boost/optional.hpp>
#include <boost/type_traits.hpp>
#include <boost/utility/result_of.hpp>
template <typename T>
struct is_optional : public boost::false_type
{ };
template <typename T>
struct is_optional<boost::optional<T> > : public boost::true_type
{ };
template <typename T, typename F,
    typename Reserver = typename boost::disable_if<is_optional<typename boost::result_of<F(T)>::type>>::type,
    typename Reserver2 = typename boost::disable_if<boost::is_void<typename boost::result_of<F(T)>::type>>::type
>
inline boost::optional<typename boost::result_of<F(T)>::type> operator >> (boost::optional<T> val, F func)
{
    if (val) {
        return func(*val);
    } else {
        return boost::none;
    }
}
template <typename T, typename F, typename Reserver = typename boost::enable_if<is_optional<typename boost::result_of<F(T)>::type>>::type>
inline typename boost::result_of<F(T)>::type operator >> (boost::optional<T> val, F func)
{
    if (val) {
        return func(*val);
    } else {
        return boost::none;
    }
}
template <typename T, typename F, typename Reserver = typename boost::enable_if<boost::is_void<typename boost::result_of<F(T)>::type>>::type>
inline void operator >> (boost::optional<T> val, F func)
{
    if (val) {
        return func(*val);
    }
}
boost::optional<int> testFunc(int n) {
    return (n % 2 == 0)? n/2 : boost::optional<int>();
}
int testFunc2(int n) {
    return n / 2;
}
int main(int argc, const char * argv[])
{
    testFunc(32)
    >> [] (int r) { return testFunc(r); }
    >> [] (int r) { return testFunc2(r); }
    >> [] (int r) { std::printf("%d", r); }
    ;
}
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX