Awesome
monad_do
Emulation of DO
syntax sugar for monads in C++
Code example
#include <boost/optional.hpp>
#include <iostream>
#include <utility>
#include <cassert>
using namespace std;
using namespace boost;
// Identity Monad:
template<typename T>
struct Identity
{
T data;
template<typename F> friend auto operator>>=(Identity m, F f)
{
return f(m.data);
}
};
// Maybe Monad:
template<typename F, typename T>
auto operator>>=(optional<T> m, F f)
{
return m ? f(m.get()) : m;
}
template<template<typename> class Monad>
auto run()
{
return
DO(Monad,
(x, unit(1))
(y, unit(2))
(z, DO(Monad,
(x, unit(5))
(_, unit(x - 2))
))
(_, unit(x + y + z))
);
}
int main()
{
assert( run<Identity>().data == 6 );
assert( run<optional>().get() == 6 );
assert
(
not DO(optional,
(x, unit(1))
(y, unit(2))
(z, DO(optional,
(x, make_optional(false, 5))
(_, unit(x - 2))
))
(_, unit(x + y + z))
)
);
cout << "DONE" << endl;
}