List: add span, group and group_by

example/list/span.cpp

@@ -0,0 +1,37 @@
+/*
+@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/detail/constexpr.hpp>
+#include <boost/hana/functional.hpp>
+#include <boost/hana/integral.hpp>
+#include <boost/hana/list/instance.hpp>
+#include <boost/hana/pair.hpp>
+using namespace boost::hana;
+
+
+int main() {
+    //! [main]
+    BOOST_HANA_CONSTEXPR_LAMBDA auto xs = list(int_<1>, int_<2>, int_<3>, int_<4>);
+    BOOST_HANA_CONSTANT_ASSERT(
+        span(xs, _ < int_<3>)
+        ==
+        pair(list(int_<1>, int_<2>), list(int_<3>, int_<4>))
+    );
+
+    BOOST_HANA_CONSTANT_ASSERT(
+        span(xs, _ < int_<0>)
+        ==
+        pair(list(), xs)
+    );
+
+    BOOST_HANA_CONSTANT_ASSERT(
+        span(xs, _ < int_<5>)
+        ==
+        pair(xs, list())
+    );
+    //! [main]
+}