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9928dea216
That concept was added more for completeness than for actual usefulness, since I have not used it a single time since its creation. Given the complexity of the library, I think it is better to remove it and shrink the library to a more useful core than giving too many features that contribute to bloat. Also, the laws were difficult to check and it hence Traversable models were not very well tested anyway. I can always roll this back if someone shows me how Traversable is actually useful for metaprogramming.
119 lines
2.6 KiB
C++
119 lines
2.6 KiB
C++
/*
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@copyright Louis Dionne 2015
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Distributed under the Boost Software License, Version 1.0.
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(See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
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*/
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#include <boost/hana/assert.hpp>
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#include <boost/hana/bool.hpp>
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#include <boost/hana/config.hpp>
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#include <boost/hana/either.hpp>
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#include <boost/hana/integral_constant.hpp>
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#include <boost/hana/tuple.hpp>
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#include <string>
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using namespace boost::hana;
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using namespace std::literals;
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int main() {
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{
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//! [comparable]
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BOOST_HANA_CONSTEXPR_CHECK(left('x') == left('x'));
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BOOST_HANA_CONSTANT_CHECK(right('x') != left('x'));
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BOOST_HANA_CONSTEXPR_CHECK(right('x') == right('x'));
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BOOST_HANA_CONSTEXPR_CHECK(right('x') != right('y'));
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//! [comparable]
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}{
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//! [orderable]
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// left is always less than right, regardless of what's in it
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BOOST_HANA_CONSTANT_CHECK(left(2000) < right(2));
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// when comparing two lefts or two rights, we compare the contents
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BOOST_HANA_CONSTEXPR_CHECK(left(2) < left(2000));
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BOOST_HANA_CONSTEXPR_CHECK(right(2) < right(2000));
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//! [orderable]
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}{
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//! [functor]
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auto safe_div = infix([](auto x, auto y) {
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return eval_if(y == int_<0>,
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[] { return left("division by zero"s); },
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[=](auto _) { return right(x / _(y)); }
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);
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});
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BOOST_HANA_CONSTANT_CHECK(
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transform(int_<6> ^safe_div^ int_<3>, succ) == right(int_<3>)
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);
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BOOST_HANA_RUNTIME_CHECK(
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transform(int_<6> ^safe_div^ int_<0>, succ) == left("division by zero"s)
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);
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//! [functor]
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}{
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//! [monad]
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auto safe_div = [](auto x, auto y) {
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return eval_if(y == int_<0>,
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[] { return left("division by zero"s); },
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[=](auto _) { return right(x / _(y)); }
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);
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};
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auto safe_dec = [](auto x) {
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return eval_if(x == int_<0>,
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[] { return left("negative value"s); },
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[=](auto _) { return right(_(x) - int_<1>); }
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);
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};
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BOOST_HANA_RUNTIME_CHECK(
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(safe_div(int_<4>, int_<0>) | safe_dec) == left("division by zero"s)
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);
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BOOST_HANA_RUNTIME_CHECK(
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(safe_div(int_<0>, int_<2>) | safe_dec) == left("negative value"s)
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);
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BOOST_HANA_CONSTANT_CHECK(
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(safe_div(int_<4>, int_<2>) | safe_dec) == right(int_<1>)
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);
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//! [monad]
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}{
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//! [foldable]
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BOOST_HANA_CONSTANT_CHECK(unpack(left('x'), make<Tuple>) == make<Tuple>());
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BOOST_HANA_CONSTEXPR_CHECK(unpack(right('x'), make<Tuple>) == make<Tuple>('x'));
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//! [foldable]
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}{
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//! [either]
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BOOST_HANA_CONSTEXPR_CHECK(either(succ, pred, left(1)) == 2);
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BOOST_HANA_CONSTEXPR_CHECK(either(succ, pred, right(1)) == 0);
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//! [either]
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}{
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//! [left]
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constexpr auto left_value = left('x');
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//! [left]
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//! [right]
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constexpr auto right_value = right('x');
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//! [right]
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(void)left_value;
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(void)right_value;
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}
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}
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