1 files changed, 50 insertions, 0 deletions
diff --git a/src/boost/libs/hana/example/optional/applicative.complex.cpp b/src/boost/libs/hana/example/optional/applicative.complex.cpp
new file mode 100644
index 000000000..f8eb84a73
--- /dev/null
+++ b/src/boost/libs/hana/example/optional/applicative.complex.cpp
@@ -0,0 +1,50 @@
+// 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/ap.hpp>
+#include <boost/hana/assert.hpp>
+#include <boost/hana/bool.hpp>
+#include <boost/hana/config.hpp>
+#include <boost/hana/equal.hpp>
+#include <boost/hana/if.hpp>
+#include <boost/hana/lift.hpp>
+#include <boost/hana/optional.hpp>
+namespace hana = boost::hana;
+
+
+template <char op>
+constexpr auto function = hana::nothing;
+
+template <>
+BOOST_HANA_CONSTEXPR_LAMBDA auto function<'+'> = hana::just([](auto x, auto y) {
+    return x + y;
+});
+
+template <>
+BOOST_HANA_CONSTEXPR_LAMBDA auto function<'-'> = hana::just([](auto x, auto y) {
+    return x - y;
+});
+
+// and so on...
+
+template <char n>
+constexpr auto digit = hana::if_(hana::bool_c<(n >= '0' && n <= '9')>,
+    hana::just(static_cast<int>(n - 48)),
+    hana::nothing
+);
+
+template <char x, char op, char y>
+BOOST_HANA_CONSTEXPR_LAMBDA auto evaluate = hana::ap(function<op>, digit<x>, digit<y>);
+
+int main() {
+    BOOST_HANA_CONSTEXPR_CHECK(evaluate<'1', '+', '2'> == hana::just(1 + 2));
+    BOOST_HANA_CONSTEXPR_CHECK(evaluate<'4', '-', '2'> == hana::just(4 - 2));
+
+    BOOST_HANA_CONSTANT_CHECK(evaluate<'?', '+', '2'> == hana::nothing);
+    BOOST_HANA_CONSTANT_CHECK(evaluate<'1', '?', '2'> == hana::nothing);
+    BOOST_HANA_CONSTANT_CHECK(evaluate<'1', '+', '?'> == hana::nothing);
+    BOOST_HANA_CONSTANT_CHECK(evaluate<'?', '?', '?'> == hana::nothing);
+
+    static_assert(hana::lift<hana::optional_tag>(123) == hana::just(123), "");
+}