ceph/src/boost/libs/hana/example/lazy/comonad.cpp

   1 // Copyright Louis Dionne 2013-2017
   2 // Distributed under the Boost Software License, Version 1.0.
   3 // (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
   4
   5 #include <boost/hana/assert.hpp>
   6 #include <boost/hana/eval.hpp>
   7 #include <boost/hana/extend.hpp>
   8 #include <boost/hana/extract.hpp>
   9 #include <boost/hana/lazy.hpp>
  10
  11 #include <sstream>
  12 namespace hana = boost::hana;
  13
  14
  15 int main() {
  16     std::stringstream s("1 2 3");
  17     auto i = hana::make_lazy([&] {
  18         int i;
  19         s >> i;
  20         return i;
  21     })();
  22
  23     auto i_plus_one = hana::extend(i, [](auto lazy_int) {
  24         return hana::eval(lazy_int) + 1;
  25     });
  26
  27     BOOST_HANA_RUNTIME_CHECK(hana::extract(i_plus_one) == 2);
  28     BOOST_HANA_RUNTIME_CHECK(hana::extract(i_plus_one) == 3);
  29     BOOST_HANA_RUNTIME_CHECK(hana::extract(i_plus_one) == 4);
  30 }