compat/meta: add basic template metaprogramming header

2 files changed, 54 insertions, 0 deletions

diff --git a/compat/meta.hpp b/compat/meta.hpp
new file mode 100644
index 00000000..b1c1dd1a
--- /dev/null
+++ b/compat/meta.hpp
@@ -0,0 +1,53 @@
+#pragma once
+
+#include <tuple>
+
+namespace meta {
+
+namespace detail {
+
+    template<typename x, typename y>
+    struct reverse_;
+
+    template<typename x0, typename... xs, template<typename...> class x, typename... ys>
+    struct reverse_<x<x0, xs...>, x<ys...>>
+    {
+        using type = typename reverse_<x<xs...>, x<x0, ys...>>::type;
+    };
+
+    template<template<typename...> class x, typename... ys>
+    struct reverse_<x<>, x<ys...>>
+    {
+        using type = x<ys...>;
+    };
+
+    template<template<typename...> class inst, typename x>
+    struct lift_;
+
+    template<template<typename...> class inst, template<typename...> class x, typename... xs>
+    struct lift_<inst, x<xs...>>
+    {
+        using type = inst<xs...>;
+    };
+}
+
+
+template<typename... xs>
+using reverse = typename detail::reverse_<std::tuple<xs...>, std::tuple<>>::type;
+
+template<template<typename...> class inst, class x>
+using lift = typename detail::lift_<inst, x>::type;
+
+template<typename x, typename... xs>
+using first = x;
+
+template<typename x, typename... xs>
+using rest = std::tuple<xs...>;
+
+template<typename... xs>
+using butlast = reverse<rest<reverse<xs...>>>;
+
+template<typename... xs>
+using last = lift<first, reverse<xs...>>;
+
+}
diff --git a/compat/util.hpp b/compat/util.hpp
index 60427b53..3adebd5b 100644
--- a/compat/util.hpp
+++ b/compat/util.hpp
@@ -2,6 +2,7 @@
 
 #include "ndebug-guard.hpp"
 #include "run-in-thread.hpp"
+#include "meta.hpp"
 
 #include <memory>
 #include <cmath>