Add the Monoid type class

example/monoid/plus.cpp

@@ -0,0 +1,17 @@
+/*
+@copyright Louis Dionne 2014
+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/detail/assert.hpp>
+#include <boost/hana/integral.hpp>
+using namespace boost::hana;
+
+
+int main() {
+    //! [main]
+    BOOST_HANA_CONSTANT_ASSERT(plus(int_<3>, int_<5>) == int_<8>);
+    BOOST_HANA_CONSTEXPR_ASSERT(plus(1, 2) == 3);
+    //! [main]
+}