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- // 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/eval.hpp>
- #include <boost/hana/extend.hpp>
- #include <boost/hana/extract.hpp>
- #include <boost/hana/lazy.hpp>
- #include <functional>
- #include <istream>
- #include <sstream>
- namespace hana = boost::hana;
- template <typename T>
- T read_one(std::istream& s) {
- T value;
- s >> value;
- return value;
- }
- int main() {
- std::stringstream s;
- s << "1 2 3";
- auto from_stream = hana::extend(hana::make_lazy(read_one<int>)(std::ref(s)), [](auto i) {
- return hana::eval(i) + 1;
- });
- BOOST_HANA_RUNTIME_CHECK(hana::extract(from_stream) == 2);
- BOOST_HANA_RUNTIME_CHECK(hana::extract(from_stream) == 3);
- BOOST_HANA_RUNTIME_CHECK(hana::extract(from_stream) == 4);
- }
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