1 files changed, 143 insertions, 0 deletions
diff --git a/src/boost/libs/hana/example/misc/restricted_function.cpp b/src/boost/libs/hana/example/misc/restricted_function.cpp
new file mode 100644
index 000000000..6a290489b
--- /dev/null
+++ b/src/boost/libs/hana/example/misc/restricted_function.cpp
@@ -0,0 +1,143 @@
+// 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/all_of.hpp>
+#include <boost/hana/assert.hpp>
+#include <boost/hana/cartesian_product.hpp>
+#include <boost/hana/contains.hpp>
+#include <boost/hana/core/to.hpp>
+#include <boost/hana/equal.hpp>
+#include <boost/hana/functional/demux.hpp>
+#include <boost/hana/fuse.hpp>
+#include <boost/hana/integral_constant.hpp>
+#include <boost/hana/minus.hpp>
+#include <boost/hana/mod.hpp>
+#include <boost/hana/not.hpp>
+#include <boost/hana/not_equal.hpp>
+#include <boost/hana/or.hpp>
+#include <boost/hana/plus.hpp>
+#include <boost/hana/set.hpp>
+#include <boost/hana/transform.hpp>
+#include <boost/hana/tuple.hpp>
+namespace hana = boost::hana;
+using namespace hana::literals;
+
+
+// A function that can have an arbitrary compile-time set of values as a domain
+// and co-domain. This is most likely purely of theoretical interest, but it
+// allows creating functions with very complex domains and co-domains that are
+// computed at compile-time.
+
+struct Function { };
+
+template <typename Domain, typename Codomain, typename F>
+struct function_type {
+    using hana_tag = Function;
+
+    Domain domain_;
+    Codomain codomain_;
+    F f_;
+
+    template <typename X>
+    constexpr auto operator()(X x) const {
+        BOOST_HANA_CONSTANT_ASSERT(boost::hana::contains(domain_, x));
+        return f_(x);
+    }
+};
+
+template <typename ...F, typename ...G>
+constexpr auto operator==(function_type<F...> f, function_type<G...> g)
+{ return hana::equal(f, g); }
+
+template <typename ...F, typename ...G>
+constexpr auto operator!=(function_type<F...> f, function_type<G...> g)
+{ return hana::not_equal(f, g); }
+
+
+auto function = [](auto domain, auto codomain) {
+    return [=](auto definition) {
+        return function_type<decltype(domain), decltype(codomain), decltype(definition)>{
+            domain, codomain, definition
+        };
+    };
+};
+
+template <typename Function>
+constexpr auto domain(Function f)
+{ return f.domain_; }
+
+template <typename Function>
+constexpr auto codomain(Function f)
+{ return f.codomain_; }
+
+template <typename Function>
+constexpr auto range(Function f) {
+    // We must convert to hana::tuple first because hana::set is not a Functor
+    return hana::to_set(hana::transform(hana::to_tuple(domain(f)), f));
+}
+
+template <typename P, typename Q>
+constexpr auto implies(P p, Q q) {
+    return hana::or_(hana::not_(p), q);
+}
+
+template <typename F>
+constexpr auto is_injective(F f) {
+    auto dom = hana::to_tuple(domain(f));
+    auto pairs = hana::cartesian_product(hana::make_tuple(dom, dom));
+    return hana::all_of(pairs, hana::fuse([&](auto x, auto y) {
+        return implies(hana::not_equal(x, y), hana::not_equal(f(x), f(y)));
+    }));
+}
+
+template <typename F>
+constexpr auto is_onto(F f) {
+    return codomain(f) == range(f);
+}
+
+namespace boost { namespace hana {
+    template <>
+    struct equal_impl<Function, Function> {
+        template <typename F, typename G>
+        static constexpr auto apply(F f, G g) {
+            return domain(f) == domain(g) &&
+                   hana::all_of(domain(f), hana::demux(hana::equal)(f, g));
+        }
+    };
+}} // end namespace boost::hana
+
+int main() {
+    auto f = function(hana::make_set(1_c, 2_c, 3_c), hana::make_set(1_c, 2_c, 3_c, 4_c, 5_c, 6_c))(
+        [](auto x) { return x + 1_c; }
+    );
+
+    auto g = function(hana::make_set(1_c, 2_c, 3_c), hana::make_set(2_c, 3_c, 4_c))(
+        [](auto x) { return x + 1_c; }
+    );
+
+    auto h = function(hana::make_set(1_c, 2_c, 3_c), hana::make_set(0_c, 1_c, 2_c))(
+        [](auto x) { return x - 1_c; }
+    );
+
+    BOOST_HANA_CONSTANT_CHECK(f == g);
+    BOOST_HANA_CONSTANT_CHECK(f != h);
+    BOOST_HANA_CONSTANT_CHECK(f(1_c) == 2_c);
+
+    BOOST_HANA_CONSTANT_CHECK(range(f) == hana::make_set(4_c, 3_c, 2_c));
+    BOOST_HANA_CONSTANT_CHECK(range(g) == hana::make_set(2_c, 3_c, 4_c));
+    BOOST_HANA_CONSTANT_CHECK(range(h) == hana::make_set(0_c, 1_c, 2_c));
+
+    BOOST_HANA_CONSTANT_CHECK(hana::not_(is_onto(f)));
+    BOOST_HANA_CONSTANT_CHECK(is_onto(g));
+    BOOST_HANA_CONSTANT_CHECK(is_onto(h));
+
+    auto even = function(hana::make_set(1_c, 2_c, 3_c), hana::make_set(hana::true_c, hana::false_c))(
+        [](auto x) { return x % 2_c == 0_c; }
+    );
+
+    BOOST_HANA_CONSTANT_CHECK(is_injective(f));
+    BOOST_HANA_CONSTANT_CHECK(is_injective(g));
+    BOOST_HANA_CONSTANT_CHECK(is_injective(h));
+    BOOST_HANA_CONSTANT_CHECK(hana::not_(is_injective(even)));
+}