Iterable: refactor docs and make FoldableInstance a detail of implementation

example/iterable/drop_while.cpp

@@ -0,0 +1,30 @@
+/*
+@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/constexpr.hpp>
+#include <boost/hana/detail/static_assert.hpp>
+#include <boost/hana/integral.hpp>
+#include <boost/hana/list/instance.hpp>
+#include <boost/hana/range.hpp>
+using namespace boost::hana;
+using namespace literals;
+
+
+int main() {
+    //! [main]
+    BOOST_HANA_CONSTEXPR_LAMBDA auto negative = [](auto x) {
+        return x < int_<0>;
+    };
+
+    BOOST_HANA_STATIC_ASSERT(
+        drop_while(negative, range(int_<-3>, int_<6>)) == range(int_<0>, int_<6>)
+    );
+
+    BOOST_HANA_STATIC_ASSERT(
+        drop_while(negative, list(1_c, -2_c, 4_c, 5_c)) == list(1_c, -2_c, 4_c, 5_c)
+    );
+    //! [main]
+}