48 lines
1.3 KiB
C++
48 lines
1.3 KiB
C++
// Copyright Louis Dionne 2013-2017
|
|
// Distributed under the Boost Software License, Version 1.0.
|
|
// (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
|
|
|
|
#include <boost/hana/assert.hpp>
|
|
#include <boost/hana/chain.hpp>
|
|
#include <boost/hana/eval.hpp>
|
|
#include <boost/hana/lazy.hpp>
|
|
|
|
#include <functional>
|
|
#include <iostream>
|
|
#include <sstream>
|
|
namespace hana = boost::hana;
|
|
|
|
|
|
template <typename T>
|
|
T read_(std::istream& stream) {
|
|
T x;
|
|
stream >> x;
|
|
std::cout << "read " << x << " from the stream\n";
|
|
return x;
|
|
}
|
|
|
|
int main() {
|
|
std::stringstream ss;
|
|
int in = 123;
|
|
|
|
std::cout << "creating the monadic chain...\n";
|
|
auto out = hana::make_lazy(read_<int>)(std::ref(ss))
|
|
| [](auto x) {
|
|
std::cout << "performing x + 1...\n";
|
|
return hana::make_lazy(x + 1);
|
|
}
|
|
| [](auto x) {
|
|
std::cout << "performing x / 2...\n";
|
|
return hana::make_lazy(x / 2);
|
|
};
|
|
|
|
std::cout << "putting " << in << " in the stream...\n";
|
|
ss << in; // nothing is evaluated yet
|
|
|
|
std::cout << "evaluating the monadic chain...\n";
|
|
auto eout = hana::eval(out);
|
|
|
|
std::cout << "the result of the monadic chain is " << eout << "\n";
|
|
BOOST_HANA_RUNTIME_CHECK(eout == (in + 1) / 2);
|
|
}
|