mirror of
https://github.com/boostorg/hana.git
synced 2026-01-31 08:12:16 +00:00
5211da5a5d
- Improve the documentation and tests of Lazy - Add missing `operator!` to Logical's documentation - In `eval_if`, evaluate branches with `eval` for more flexibility - Use `lazy` instead of ugly workarounds in Sequence and Iterable
69 lines
1.3 KiB
C++
69 lines
1.3 KiB
C++
/*
|
|
@copyright Louis Dionne 2015
|
|
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/bool.hpp>
|
|
#include <boost/hana/config.hpp>
|
|
#include <boost/hana/enumerable.hpp>
|
|
#include <boost/hana/functional/placeholder.hpp>
|
|
#include <boost/hana/lazy.hpp>
|
|
|
|
#include <sstream>
|
|
using namespace boost::hana;
|
|
|
|
|
|
int main() {
|
|
|
|
{
|
|
|
|
//! [lazy]
|
|
BOOST_HANA_CONSTEXPR_LAMBDA auto f = lazy([](auto x) {
|
|
return 1 / x;
|
|
});
|
|
BOOST_HANA_CONSTEXPR_LAMBDA auto g = lazy([](auto x) {
|
|
return x + 1;
|
|
});
|
|
|
|
BOOST_HANA_CONSTEXPR_CHECK(eval(if_(false_, f(0), g(0))) == 0 + 1);
|
|
//! [lazy]
|
|
|
|
}{
|
|
|
|
//! [eval]
|
|
static_assert(eval(lazy(_ + 1)(3)) == 4, "");
|
|
//! [eval]
|
|
|
|
}{
|
|
|
|
//! [functor]
|
|
static_assert(eval(transform(lazy(4 / _)(1), _ * 3)) == (4 / 1) * 3, "");
|
|
|
|
transform(lazy(4 / _)(0), _ * 3); // never evaluated
|
|
//! [functor]
|
|
|
|
}{
|
|
|
|
//! [comonad]
|
|
std::stringstream s("1 2 3");
|
|
auto i = lazy([&] {
|
|
int i;
|
|
s >> i;
|
|
return i;
|
|
})();
|
|
|
|
auto i_plus_one = extend(i, [](auto lazy_int) {
|
|
return succ(eval(lazy_int));
|
|
});
|
|
|
|
BOOST_HANA_RUNTIME_CHECK(extract(i_plus_one) == 2);
|
|
BOOST_HANA_RUNTIME_CHECK(extract(i_plus_one) == 3);
|
|
BOOST_HANA_RUNTIME_CHECK(extract(i_plus_one) == 4);
|
|
//! [comonad]
|
|
|
|
}
|
|
|
|
}
|