diff --git a/sprout/tuple.hpp b/sprout/tuple.hpp
index 5bb157b4..ca3016d4 100644
--- a/sprout/tuple.hpp
+++ b/sprout/tuple.hpp
@@ -3,6 +3,6 @@
 
 #include <sprout/config.hpp>
 #include <sprout/tuple/tuple.hpp>
-#include <sprout/tuple/tuple_comparison.hpp>
+#include <sprout/tuple/traits.hpp>
 
 #endif	// #ifndef SPROUT_TUPLE_HPP
diff --git a/sprout/tuple/operation/append_back.hpp b/sprout/tuple/operation/append_back.hpp
index d27582af..d264fa3b 100644
--- a/sprout/tuple/operation/append_back.hpp
+++ b/sprout/tuple/operation/append_back.hpp
@@ -4,8 +4,9 @@
 #include <cstddef>
 #include <sprout/config.hpp>
 #include <sprout/index_tuple.hpp>
-#include <sprout/tuple/traits.hpp>
+#include <sprout/tuple/tuple.hpp>
 #include <sprout/tuple/functions.hpp>
+#include <sprout/type/operation/append_back.hpp>
 
 namespace sprout {
 	namespace tuples {
@@ -14,25 +15,9 @@ namespace sprout {
 			// append_back
 			//
 			template<typename Tuple, typename InputTuple>
-			struct append_back {
-			private:
-				template<typename IndexTuple1, typename IndexTuple2>
-				struct apply_impl;
-				template<std::ptrdiff_t... Indexes1, std::ptrdiff_t... Indexes2>
-				struct apply_impl<sprout::index_tuple<Indexes1...>, sprout::index_tuple<Indexes2...> >
-					: public sprout::tuples::rebind_types<
-						Tuple
-					>::template apply<
-						typename sprout::tuples::tuple_element<Indexes1, Tuple>::type...,
-						typename sprout::tuples::tuple_element<Indexes2, InputTuple>::type...
-					>
-				{};
-			public:
-				typedef typename apply_impl<
-					typename sprout::index_range<0, sprout::tuples::tuple_size<Tuple>::value>::type,
-					typename sprout::index_range<0, sprout::tuples::tuple_size<InputTuple>::value>::type
-				>::type type;
-			};
+			struct append_back
+				: public sprout::types::append_back<Tuple, InputTuple>
+			{};
 		}	// namespace result_of
 
 		namespace detail {
diff --git a/sprout/tuple/operation/append_front.hpp b/sprout/tuple/operation/append_front.hpp
index 2028991b..de1e059a 100644
--- a/sprout/tuple/operation/append_front.hpp
+++ b/sprout/tuple/operation/append_front.hpp
@@ -4,8 +4,9 @@
 #include <cstddef>
 #include <sprout/config.hpp>
 #include <sprout/index_tuple.hpp>
-#include <sprout/tuple/traits.hpp>
+#include <sprout/tuple/tuple.hpp>
 #include <sprout/tuple/functions.hpp>
+#include <sprout/type/operation/append_front.hpp>
 
 namespace sprout {
 	namespace tuples {
@@ -14,25 +15,9 @@ namespace sprout {
 			// append_front
 			//
 			template<typename Tuple, typename InputTuple>
-			struct append_front {
-			private:
-				template<typename IndexTuple1, typename IndexTuple2>
-				struct apply_impl;
-				template<std::ptrdiff_t... Indexes1, std::ptrdiff_t... Indexes2>
-				struct apply_impl<sprout::index_tuple<Indexes1...>, sprout::index_tuple<Indexes2...> >
-					: public sprout::tuples::rebind_types<
-						Tuple
-					>::template apply<
-						typename sprout::tuples::tuple_element<Indexes2, InputTuple>::type...,
-						typename sprout::tuples::tuple_element<Indexes1, Tuple>::type...
-					>
-				{};
-			public:
-				typedef typename apply_impl<
-					typename sprout::index_range<0, sprout::tuples::tuple_size<Tuple>::value>::type,
-					typename sprout::index_range<0, sprout::tuples::tuple_size<InputTuple>::value>::type
-				>::type type;
-			};
+			struct append_front
+				: public sprout::types::append_front<Tuple, InputTuple>
+			{};
 		}	// namespace result_of
 
 		namespace detail {
diff --git a/sprout/tuple/operation/push_back.hpp b/sprout/tuple/operation/push_back.hpp
index a69a370d..91c875e7 100644
--- a/sprout/tuple/operation/push_back.hpp
+++ b/sprout/tuple/operation/push_back.hpp
@@ -4,8 +4,9 @@
 #include <cstddef>
 #include <sprout/config.hpp>
 #include <sprout/index_tuple.hpp>
-#include <sprout/tuple/traits.hpp>
+#include <sprout/tuple/tuple.hpp>
 #include <sprout/tuple/functions.hpp>
+#include <sprout/type/operation/push_back.hpp>
 
 namespace sprout {
 	namespace tuples {
@@ -14,24 +15,9 @@ namespace sprout {
 			// push_back
 			//
 			template<typename Tuple, typename T>
-			struct push_back {
-			private:
-				template<typename IndexTuple>
-				struct apply_impl;
-				template<std::ptrdiff_t... Indexes>
-				struct apply_impl<sprout::index_tuple<Indexes...>>
-					: public sprout::tuples::rebind_types<
-						Tuple
-					>::template apply<
-						typename sprout::tuples::tuple_element<Indexes, Tuple>::type...,
-						T
-					>
-				{};
-			public:
-				typedef typename apply_impl<
-					typename sprout::index_range<0, sprout::tuples::tuple_size<Tuple>::value>::type
-				>::type type;
-			};
+			struct push_back
+				: public sprout::types::push_back<Tuple, T>
+			{};
 		}	// namespace result_of
 
 		namespace detail {
diff --git a/sprout/tuple/operation/push_front.hpp b/sprout/tuple/operation/push_front.hpp
index 8592a9a7..ae91ca92 100644
--- a/sprout/tuple/operation/push_front.hpp
+++ b/sprout/tuple/operation/push_front.hpp
@@ -4,8 +4,9 @@
 #include <cstddef>
 #include <sprout/config.hpp>
 #include <sprout/index_tuple.hpp>
-#include <sprout/tuple/traits.hpp>
+#include <sprout/tuple/tuple.hpp>
 #include <sprout/tuple/functions.hpp>
+#include <sprout/type/operation/push_front.hpp>
 
 namespace sprout {
 	namespace tuples {
@@ -14,24 +15,9 @@ namespace sprout {
 			// push_front
 			//
 			template<typename Tuple, typename T>
-			struct push_front {
-			private:
-				template<typename IndexTuple>
-				struct apply_impl;
-				template<std::ptrdiff_t... Indexes>
-				struct apply_impl<sprout::index_tuple<Indexes...>>
-					: public sprout::tuples::rebind_types<
-						Tuple
-					>::template apply<
-						T,
-						typename sprout::tuples::tuple_element<Indexes, Tuple>::type...
-					>
-				{};
-			public:
-				typedef typename apply_impl<
-					typename sprout::index_range<0, sprout::tuples::tuple_size<Tuple>::value>::type
-				>::type type;
-			};
+			struct push_front
+				: public sprout::types::push_front<Tuple, T>
+			{};
 		}	// namespace result_of
 
 		namespace detail {
diff --git a/sprout/tuple/traits.hpp b/sprout/tuple/traits.hpp
index eab70a34..8aadb17f 100644
--- a/sprout/tuple/traits.hpp
+++ b/sprout/tuple/traits.hpp
@@ -3,6 +3,7 @@
 
 #include <sprout/config.hpp>
 #include <sprout/tuple/tuple.hpp>
+#include <sprout/type/rebind_types.hpp>
 
 namespace sprout {
 	namespace tuples {
@@ -24,20 +25,9 @@ namespace sprout {
 		// rebind_types
 		//
 		template<typename Tuple>
-		struct rebind_types {
-		public:
-			template<typename... Types>
-			struct apply;
-		};
-		template<typename... Ts>
-		struct rebind_types<sprout::tuples::tuple<Ts...> > {
-		public:
-			template<typename... Types>
-			struct apply {
-			public:
-				typedef sprout::tuples::tuple<Types...> type;
-			};
-		};
+		struct rebind_types
+			: public sprout::types::rebind_types<Tuple>
+		{};
 
 		//
 		// clone_functor
@@ -93,7 +83,6 @@ namespace sprout {
 	}	// namespace tuples
 
 	using sprout::tuples::tuple_traits;
-	using sprout::tuples::rebind_types;
 }	// namespace sprout
 
 #endif	// #ifndef SPROUT_TUPLE_TRAITS_HPP
diff --git a/sprout/tuple/tuple.hpp b/sprout/tuple/tuple.hpp
index 4b26406d..1661c759 100644
--- a/sprout/tuple/tuple.hpp
+++ b/sprout/tuple/tuple.hpp
@@ -229,7 +229,7 @@ namespace sprout {
 				: inherited_type(static_cast<sprout::tuples::detail::tuple_impl<0, UTypes...>&&>(t))
 			{}
 			// tuple assignment
-			tuple& operator=(const tuple& rhs) {
+			tuple& operator=(tuple const& rhs) {
 				static_cast<inherited_type&>(*this) = rhs;
 				return *this;
 			}
@@ -248,7 +248,7 @@ namespace sprout {
 				return *this;
 			}
 			// tuple swap
-			void swap(tuple& other) SPROUT_NOEXCEPT_EXPR(SPROUT_NOEXCEPT_EXPR(other.swap(other))) {
+			void swap(tuple& other) SPROUT_NOEXCEPT_EXPR(SPROUT_NOEXCEPT_EXPR(inherited_type::swap(other))) {
 				inherited_type::swap(other);
 			}
 		};
@@ -426,4 +426,6 @@ namespace sprout {
 	using sprout::tuples::get;
 }	// namespace sprout
 
+#include <sprout/tuple/tuple_comparison.hpp>
+
 #endif	// #ifndef SPROUT_TUPLE_TUPLE_HPP
diff --git a/sprout/tuple/tuple_comparison.hpp b/sprout/tuple/tuple_comparison.hpp
index bbc97351..7d7d0e57 100644
--- a/sprout/tuple/tuple_comparison.hpp
+++ b/sprout/tuple/tuple_comparison.hpp
@@ -46,7 +46,7 @@ namespace sprout {
 			};
 		}	// namespace detail
 		template<typename... TTypes, typename... UTypes>
-		bool SPROUT_CONSTEXPR inline operator==(
+		SPROUT_CONSTEXPR inline bool operator==(
 			sprout::tuples::tuple<TTypes...> const& lhs,
 			sprout::tuples::tuple<UTypes...> const& rhs
 			)
@@ -62,7 +62,7 @@ namespace sprout {
 				>::eq(lhs, rhs);
 		}
 		template<typename... TTypes, typename... UTypes>
-		bool SPROUT_CONSTEXPR inline operator<(
+		SPROUT_CONSTEXPR inline bool operator<(
 			sprout::tuples::tuple<TTypes...> const& lhs,
 			sprout::tuples::tuple<UTypes...> const& rhs
 			)
@@ -78,7 +78,7 @@ namespace sprout {
 				>::less(lhs, rhs);
 		}
 		template<typename... TTypes, typename... UTypes>
-		bool SPROUT_CONSTEXPR inline operator!=(
+		SPROUT_CONSTEXPR inline bool operator!=(
 			sprout::tuples::tuple<TTypes...> const& lhs,
 			sprout::tuples::tuple<UTypes...> const& rhs
 			)
@@ -86,7 +86,7 @@ namespace sprout {
 			return !(lhs == rhs);
 		}
 		template<typename... TTypes, typename... UTypes>
-		bool SPROUT_CONSTEXPR inline operator>(
+		SPROUT_CONSTEXPR inline bool operator>(
 			sprout::tuples::tuple<TTypes...> const& lhs,
 			sprout::tuples::tuple<UTypes...> const& rhs
 			)
@@ -94,7 +94,7 @@ namespace sprout {
 			return rhs < lhs;
 		}
 		template<typename... TTypes, typename... UTypes>
-		bool SPROUT_CONSTEXPR inline operator<=(
+		SPROUT_CONSTEXPR inline bool operator<=(
 			sprout::tuples::tuple<TTypes...> const& lhs,
 			sprout::tuples::tuple<UTypes...> const& rhs
 			)
@@ -102,7 +102,7 @@ namespace sprout {
 			return !(rhs < lhs);
 		}
 		template<typename... TTypes, typename... UTypes>
-		bool SPROUT_CONSTEXPR inline operator>=(
+		SPROUT_CONSTEXPR inline bool operator>=(
 			sprout::tuples::tuple<TTypes...> const& lhs,
 			sprout::tuples::tuple<UTypes...> const& rhs
 			)
diff --git a/sprout/type.hpp b/sprout/type.hpp
new file mode 100644
index 00000000..34e2206a
--- /dev/null
+++ b/sprout/type.hpp
@@ -0,0 +1,11 @@
+#ifndef SPROUT_TYPE_HPP
+#define SPROUT_TYPE_HPP
+
+#include <sprout/config.hpp>
+#include <sprout/type/tuple.hpp>
+#include <sprout/type/type_tuple.hpp>
+#include <sprout/type/rebind_types.hpp>
+#include <sprout/type/algorithm.hpp>
+#include <sprout/type/operation.hpp>
+
+#endif	// #ifndef SPROUT_TYPE_HPP
diff --git a/sprout/type/algorithm.hpp b/sprout/type/algorithm.hpp
new file mode 100644
index 00000000..8a816908
--- /dev/null
+++ b/sprout/type/algorithm.hpp
@@ -0,0 +1,7 @@
+#ifndef SPROUT_TYPE_ALGORITHM_HPP
+#define SPROUT_TYPE_ALGORITHM_HPP
+
+#include <sprout/config.hpp>
+#include <sprout/type/algorithm/find_index.hpp>
+
+#endif	// #ifndef SPROUT_TYPE_ALGORITHM_HPP
diff --git a/sprout/type/algorithm/find_index.hpp b/sprout/type/algorithm/find_index.hpp
new file mode 100644
index 00000000..0b925d0f
--- /dev/null
+++ b/sprout/type/algorithm/find_index.hpp
@@ -0,0 +1,49 @@
+#ifndef SPROUT_TYPE_ALGORITHM_FIND_INDEX_HPP
+#define SPROUT_TYPE_ALGORITHM_FIND_INDEX_HPP
+
+#include <cstddef>
+#include <type_traits>
+#include <sprout/config.hpp>
+#include <sprout/type/tuple.hpp>
+
+namespace sprout {
+	namespace types {
+		namespace detail {
+			template<typename Tuple, typename T, std::size_t I, typename = void>
+			struct find_index_impl;
+			template<typename Tuple, typename T, std::size_t I>
+			struct find_index_impl<
+				Tuple,
+				T,
+				I,
+				typename std::enable_if<
+					I == sprout::types::tuple_size<Tuple>::value
+					|| std::is_same<typename sprout::types::tuple_element<I, Tuple>::type, T>::value
+				>::type
+			>
+				: public std::integral_constant<std::size_t, I>
+			{};
+			template<typename Tuple, typename T, std::size_t I>
+			struct find_index_impl<
+				Tuple,
+				T,
+				I,
+				typename std::enable_if<
+					I != sprout::types::tuple_size<Tuple>::value
+					&& !std::is_same<typename sprout::types::tuple_element<I, Tuple>::type, T>::value
+				>::type
+			>
+				: public sprout::types::detail::find_index_impl<Tuple, T, I + 1>
+			{};
+		}	// namespace detail
+		//
+		// find_index
+		//
+		template<typename Tuple, typename T>
+		struct find_index
+			: public sprout::types::detail::find_index_impl<Tuple, T, 0>
+		{};
+	}	// namespace types
+}	// namespace sprout
+
+#endif	// #ifndef SPROUT_TYPE_ALGORITHM_FIND_INDEX_HPP
diff --git a/sprout/type/iterator.hpp b/sprout/type/iterator.hpp
new file mode 100644
index 00000000..fd7f2f7f
--- /dev/null
+++ b/sprout/type/iterator.hpp
@@ -0,0 +1,9 @@
+#ifndef SPROUT_TYPE_ITERATOR_HPP
+#define SPROUT_TYPE_ITERATOR_HPP
+
+#include <sprout/config.hpp>
+#include <sprout/type/iterator/next.hpp>
+#include <sprout/type/iterator/prev.hpp>
+#include <sprout/type/iterator/deref.hpp>
+
+#endif	// #ifndef SPROUT_TYPE_ITERATOR_HPP
diff --git a/sprout/type/iterator/deref.hpp b/sprout/type/iterator/deref.hpp
new file mode 100644
index 00000000..7c1f139b
--- /dev/null
+++ b/sprout/type/iterator/deref.hpp
@@ -0,0 +1,19 @@
+#ifndef SPROUT_TYPE_ITERATOR_DEREF_HPP
+#define SPROUT_TYPE_ITERATOR_DEREF_HPP
+
+#include <sprout/config.hpp>
+
+namespace sprout {
+	namespace types {
+		//
+		// deref
+		//
+		template<typename Iterator>
+		struct deref {
+		public:
+			typedef typename Iterator::type type;
+		};
+	}	// namespace types
+}	// namespace sprout
+
+#endif	// #ifndef SPROUT_TYPE_ITERATOR_DEREF_HPP
diff --git a/sprout/type/iterator/index_iterator.hpp b/sprout/type/iterator/index_iterator.hpp
new file mode 100644
index 00000000..70252b34
--- /dev/null
+++ b/sprout/type/iterator/index_iterator.hpp
@@ -0,0 +1,91 @@
+#ifndef SPROUT_TYPE_ITERATOR_INDEX_ITERATOR_HPP
+#define SPROUT_TYPE_ITERATOR_INDEX_ITERATOR_HPP
+
+#include <cstddef>
+#include <type_traits>
+#include <sprout/config.hpp>
+#include <sprout/type/tuple.hpp>
+#include <sprout/type/void.hpp>
+
+namespace sprout {
+	namespace types {
+		template<typename Tuple, std::ptrdiff_t Index>
+		struct index_iterator;
+
+		namespace detail {
+			//
+			// index_iterator_impl
+			//
+			template<typename Tuple, std::ptrdiff_t Index, typename = void>
+			struct index_iterator_impl;
+			template<typename Tuple, std::ptrdiff_t Index>
+			struct index_iterator_impl<
+				Tuple,
+				Index,
+				typename std::enable_if<
+					sprout::types::tuple_size<Tuple>::value == 0
+					|| (Index < 0)
+					|| (Index > sprout::types::tuple_size<Tuple>::value)
+				>::type
+			> {
+			public:
+				typedef sprout::types::void_ type;
+				typedef sprout::types::void_ next;
+				typedef sprout::types::void_ prev;
+			};
+			template<typename Tuple, std::ptrdiff_t Index>
+			struct index_iterator_impl<
+				Tuple,
+				Index,
+				typename std::enable_if<
+					sprout::types::tuple_size<Tuple>::value != 0
+					&& Index == 0
+				>::type
+			> {
+			public:
+				typedef typename sprout::types::tuple_element<Index, Tuple>::type type;
+				typedef sprout::types::index_iterator<Tuple, Index + 1> next;
+				typedef sprout::types::void_ prev;
+			};
+			template<typename Tuple, std::ptrdiff_t Index>
+			struct index_iterator_impl<
+				Tuple,
+				Index,
+				typename std::enable_if<
+					sprout::types::tuple_size<Tuple>::value != 0
+					&& Index == sprout::types::tuple_size<Tuple>::value
+				>::type
+			> {
+			public:
+				typedef sprout::types::void_ type;
+				typedef sprout::types::void_ next;
+				typedef sprout::types::index_iterator<Tuple, sprout::types::tuple_size<Tuple>::value - 1> prev;
+			};
+			template<typename Tuple, std::ptrdiff_t Index>
+			struct index_iterator_impl<
+				Tuple,
+				Index,
+				typename std::enable_if<
+					sprout::types::tuple_size<Tuple>::value != 0
+					&& (Index > 0)
+					&& (Index < sprout::types::tuple_size<Tuple>::value)
+				>::type
+			> {
+			public:
+				typedef typename sprout::types::tuple_element<Index, Tuple>::type type;
+				typedef sprout::types::index_iterator<Tuple, Index + 1> next;
+				typedef sprout::types::index_iterator<Tuple, Index - 1> prev;
+			};
+		}	// namespace detail
+		//
+		// index_iterator
+		//
+		template<typename Tuple, std::ptrdiff_t Index>
+		struct index_iterator
+			: public sprout::types::detail::index_iterator_impl<Tuple, Index>
+			, public std::integral_constant<std::ptrdiff_t, Index>
+		{};
+	}	// namespace types
+}	// namespace sprout
+
+#endif	// #ifndef SPROUT_TYPE_ITERATOR_INDEX_ITERATOR_HPP
diff --git a/sprout/type/iterator/next.hpp b/sprout/type/iterator/next.hpp
new file mode 100644
index 00000000..bcc969b0
--- /dev/null
+++ b/sprout/type/iterator/next.hpp
@@ -0,0 +1,19 @@
+#ifndef SPROUT_TYPE_ITERATOR_NEXT_HPP
+#define SPROUT_TYPE_ITERATOR_NEXT_HPP
+
+#include <sprout/config.hpp>
+
+namespace sprout {
+	namespace types {
+		//
+		// next
+		//
+		template<typename Iterator>
+		struct next {
+		public:
+			typedef typename Iterator::next type;
+		};
+	}	// namespace types
+}	// namespace sprout
+
+#endif	// #ifndef SPROUT_TYPE_ITERATOR_NEXT_HPP
diff --git a/sprout/type/iterator/prev.hpp b/sprout/type/iterator/prev.hpp
new file mode 100644
index 00000000..8ed91cb2
--- /dev/null
+++ b/sprout/type/iterator/prev.hpp
@@ -0,0 +1,19 @@
+#ifndef SPROUT_TYPE_ITERATOR_PREV_HPP
+#define SPROUT_TYPE_ITERATOR_PREV_HPP
+
+#include <sprout/config.hpp>
+
+namespace sprout {
+	namespace types {
+		//
+		// prev
+		//
+		template<typename Iterator>
+		struct prev {
+		public:
+			typedef typename Iterator::prev type;
+		};
+	}	// namespace types
+}	// namespace sprout
+
+#endif	// #ifndef SPROUT_TYPE_ITERATOR_PREV_HPP
diff --git a/sprout/type/operation.hpp b/sprout/type/operation.hpp
new file mode 100644
index 00000000..387e3e5c
--- /dev/null
+++ b/sprout/type/operation.hpp
@@ -0,0 +1,10 @@
+#ifndef SPROUT_TYPE_OPERATION_HPP
+#define SPROUT_TYPE_OPERATION_HPP
+
+#include <sprout/config.hpp>
+#include <sprout/type/operation/append_back.hpp>
+#include <sprout/type/operation/append_front.hpp>
+#include <sprout/type/operation/push_back.hpp>
+#include <sprout/type/operation/push_front.hpp>
+
+#endif	// #ifndef SPROUT_TYPE_OPERATION_HPP
diff --git a/sprout/type/operation/append_back.hpp b/sprout/type/operation/append_back.hpp
new file mode 100644
index 00000000..eacb67f2
--- /dev/null
+++ b/sprout/type/operation/append_back.hpp
@@ -0,0 +1,38 @@
+#ifndef SPROUT_TYPE_OPERATION_APPEND_BACK_HPP
+#define SPROUT_TYPE_OPERATION_APPEND_BACK_HPP
+
+#include <cstddef>
+#include <sprout/config.hpp>
+#include <sprout/index_tuple.hpp>
+#include <sprout/type/tuple.hpp>
+#include <sprout/type/rebind_types.hpp>
+
+namespace sprout {
+	namespace types {
+		//
+		// append_back
+		//
+		template<typename Tuple, typename InputTuple>
+		struct append_back {
+		private:
+			template<typename IndexTuple1, typename IndexTuple2>
+			struct apply_impl;
+			template<std::ptrdiff_t... Indexes1, std::ptrdiff_t... Indexes2>
+			struct apply_impl<sprout::index_tuple<Indexes1...>, sprout::index_tuple<Indexes2...> >
+				: public sprout::types::rebind_types<
+					Tuple
+				>::template apply<
+					typename sprout::types::tuple_element<Indexes1, Tuple>::type...,
+					typename sprout::types::tuple_element<Indexes2, InputTuple>::type...
+				>
+			{};
+		public:
+			typedef typename apply_impl<
+				typename sprout::index_range<0, sprout::types::tuple_size<Tuple>::value>::type,
+				typename sprout::index_range<0, sprout::types::tuple_size<InputTuple>::value>::type
+			>::type type;
+		};
+	}	// namespace types
+}	// namespace sprout
+
+#endif	// #ifndef SPROUT_TYPE_OPERATION_APPEND_BACK_HPP
diff --git a/sprout/type/operation/append_front.hpp b/sprout/type/operation/append_front.hpp
new file mode 100644
index 00000000..a59d0607
--- /dev/null
+++ b/sprout/type/operation/append_front.hpp
@@ -0,0 +1,38 @@
+#ifndef SPROUT_TYPE_OPERATION_APPEND_FRONT_HPP
+#define SPROUT_TYPE_OPERATION_APPEND_FRONT_HPP
+
+#include <cstddef>
+#include <sprout/config.hpp>
+#include <sprout/index_tuple.hpp>
+#include <sprout/type/tuple.hpp>
+#include <sprout/type/rebind_types.hpp>
+
+namespace sprout {
+	namespace types {
+		//
+		// append_front
+		//
+		template<typename Tuple, typename InputTuple>
+		struct append_front {
+		private:
+			template<typename IndexTuple1, typename IndexTuple2>
+			struct apply_impl;
+			template<std::ptrdiff_t... Indexes1, std::ptrdiff_t... Indexes2>
+			struct apply_impl<sprout::index_tuple<Indexes1...>, sprout::index_tuple<Indexes2...> >
+				: public sprout::types::rebind_types<
+					Tuple
+				>::template apply<
+					typename sprout::types::tuple_element<Indexes2, InputTuple>::type...,
+					typename sprout::types::tuple_element<Indexes1, Tuple>::type...
+				>
+			{};
+		public:
+			typedef typename apply_impl<
+				typename sprout::index_range<0, sprout::types::tuple_size<Tuple>::value>::type,
+				typename sprout::index_range<0, sprout::types::tuple_size<InputTuple>::value>::type
+			>::type type;
+		};
+	}	// namespace types
+}	// namespace sprout
+
+#endif	// #ifndef SPROUT_TYPE_OPERATION_APPEND_FRONT_HPP
diff --git a/sprout/type/operation/push_back.hpp b/sprout/type/operation/push_back.hpp
new file mode 100644
index 00000000..78e3ebba
--- /dev/null
+++ b/sprout/type/operation/push_back.hpp
@@ -0,0 +1,37 @@
+#ifndef SPROUT_TYPE_OPERATION_PUSH_BACK_HPP
+#define SPROUT_TYPE_OPERATION_PUSH_BACK_HPP
+
+#include <cstddef>
+#include <sprout/config.hpp>
+#include <sprout/index_tuple.hpp>
+#include <sprout/type/tuple.hpp>
+#include <sprout/type/rebind_types.hpp>
+
+namespace sprout {
+	namespace types {
+		//
+		// push_back
+		//
+		template<typename Tuple, typename T>
+		struct push_back {
+		private:
+			template<typename IndexTuple>
+			struct apply_impl;
+			template<std::ptrdiff_t... Indexes>
+			struct apply_impl<sprout::index_tuple<Indexes...> >
+				: public sprout::types::rebind_types<
+					Tuple
+				>::template apply<
+					typename sprout::types::tuple_element<Indexes, Tuple>::type...,
+					T
+				>
+			{};
+		public:
+			typedef typename apply_impl<
+				typename sprout::index_range<0, sprout::types::tuple_size<Tuple>::value>::type
+			>::type type;
+		};
+	}	// namespace types
+}	// namespace sprout
+
+#endif	// #ifndef SPROUT_TYPE_OPERATION_PUSH_BACK_HPP
diff --git a/sprout/type/operation/push_front.hpp b/sprout/type/operation/push_front.hpp
new file mode 100644
index 00000000..5e9ef938
--- /dev/null
+++ b/sprout/type/operation/push_front.hpp
@@ -0,0 +1,37 @@
+#ifndef SPROUT_TYPE_OPERATION_PUSH_FRONT_HPP
+#define SPROUT_TYPE_OPERATION_PUSH_FRONT_HPP
+
+#include <cstddef>
+#include <sprout/config.hpp>
+#include <sprout/index_tuple.hpp>
+#include <sprout/type/tuple.hpp>
+#include <sprout/type/rebind_types.hpp>
+
+namespace sprout {
+	namespace types {
+		//
+		// push_front
+		//
+		template<typename Tuple, typename T>
+		struct push_front {
+		private:
+			template<typename IndexTuple>
+			struct apply_impl;
+			template<std::ptrdiff_t... Indexes>
+			struct apply_impl<sprout::index_tuple<Indexes...> >
+				: public sprout::types::rebind_types<
+					Tuple
+				>::template apply<
+					T,
+					typename sprout::types::tuple_element<Indexes, Tuple>::type...
+				>
+			{};
+		public:
+			typedef typename apply_impl<
+				typename sprout::index_range<0, sprout::types::tuple_size<Tuple>::value>::type
+			>::type type;
+		};
+	}	// namespace types
+}	// namespace sprout
+
+#endif	// #ifndef SPROUT_TYPE_OPERATION_PUSH_FRONT_HPP
diff --git a/sprout/type/rebind_types.hpp b/sprout/type/rebind_types.hpp
new file mode 100644
index 00000000..e44e69ef
--- /dev/null
+++ b/sprout/type/rebind_types.hpp
@@ -0,0 +1,29 @@
+#ifndef SPROUT_TYPE_REBIND_TYPES_HPP
+#define SPROUT_TYPE_REBIND_TYPES_HPP
+
+#include <sprout/config.hpp>
+#include <sprout/type/type_tuple.hpp>
+
+namespace sprout {
+	namespace types {
+		//
+		// rebind_types
+		//
+		template<typename Tuple>
+		struct rebind_types;
+
+		template<typename... Ts>
+		struct rebind_types<sprout::types::type_tuple<Ts...> > {
+		public:
+			template<typename... Types>
+			struct apply {
+			public:
+				typedef sprout::types::type_tuple<Types...> type;
+			};
+		};
+	}	// namespace types
+
+	using sprout::types::rebind_types;
+}	// namespace sprout
+
+#endif	// #ifndef SPROUT_TYPE_REBIND_TYPES_HPP
diff --git a/sprout/type/seq/algorithm.hpp b/sprout/type/seq/algorithm.hpp
new file mode 100644
index 00000000..fd3fd892
--- /dev/null
+++ b/sprout/type/seq/algorithm.hpp
@@ -0,0 +1,7 @@
+#ifndef SPROUT_TYPE_SEQ_ALGORITHM_HPP
+#define SPROUT_TYPE_SEQ_ALGORITHM_HPP
+
+#include <sprout/config.hpp>
+#include <sprout/type/seq/algorithm/find.hpp>
+
+#endif	// #ifndef SPROUT_TYPE_SEQ_ALGORITHM_HPP
diff --git a/sprout/type/seq/algorithm/find.hpp b/sprout/type/seq/algorithm/find.hpp
new file mode 100644
index 00000000..89195fc7
--- /dev/null
+++ b/sprout/type/seq/algorithm/find.hpp
@@ -0,0 +1,71 @@
+#ifndef SPROUT_TYPE_SEQ_ALGORITHM_FIND_HPP
+#define SPROUT_TYPE_SEQ_ALGORITHM_FIND_HPP
+
+#include <type_traits>
+#include <sprout/config.hpp>
+#include <sprout/type/tuple.hpp>
+
+namespace sprout {
+	namespace types {
+		namespace seq {
+			namespace detail {
+				template<typename First, typename Last, typename T, typename = void>
+				struct find_impl;
+				template<typename First, typename Last, typename T>
+				struct find_impl<
+					First,
+					Last,
+					T,
+					typename std::enable_if<
+						std::is_same<First, Last>::value
+					>::type
+				> {
+				public:
+					typedef Last type;
+				};
+				template<typename First, typename Last, typename T>
+				struct find_impl<
+					First,
+					Last,
+					T,
+					typename std::enable_if<
+						!std::is_same<First, Last>::value
+						&& std::is_same<typename sprout::types::deref<First>::type, T>::value
+					>::type
+				> {
+				public:
+					typedef First type;
+				};
+				template<typename First, typename Last, typename T>
+				struct find_impl<
+					First,
+					Last,
+					T,
+					typename std::enable_if<
+						!std::is_same<First, Last>::value
+						&& !std::is_same<typename sprout::types::deref<First>::type, T>::value
+					>::type
+				>
+					: public sprout::types::seq::detail::find_impl<
+						typename sprout::types::next<First>::type,
+						Last,
+						T
+					>
+				{};
+			}	// namespace detail
+			//
+			// find
+			//
+			template<typename ForwardSequence, typename T>
+			struct find
+				: public sprout::types::seq::detail::find_impl<
+					typename sprout::types::begin<ForwardSequence>::type,
+					typename sprout::types::end<ForwardSequence>::type,
+					T
+				>
+			{};
+		}	// namespace seq
+	}	// namespace types
+}	// namespace sprout
+
+#endif	// #ifndef SPROUT_TYPE_SEQ_ALGORITHM_FIND_HPP
diff --git a/sprout/type/tuple.hpp b/sprout/type/tuple.hpp
new file mode 100644
index 00000000..c3cbd29f
--- /dev/null
+++ b/sprout/type/tuple.hpp
@@ -0,0 +1,42 @@
+#ifndef SPROUT_TYPE_TUPLE_HPP
+#define SPROUT_TYPE_TUPLE_HPP
+
+#include <cstddef>
+#include <tuple>
+#include <sprout/config.hpp>
+
+namespace sprout {
+	namespace types {
+		//
+		// begin
+		//
+		template<typename T>
+		struct begin {
+			typedef typename T::begin type;
+		};
+		//
+		// end
+		//
+		template<typename T>
+		struct end {
+			typedef typename T::end type;
+		};
+
+		//
+		// tuple_size
+		//
+		template<typename T>
+		struct tuple_size
+			: public std::tuple_size<T>
+		{};
+		//
+		// tuple_element
+		//
+		template<std::size_t I, typename T>
+		struct tuple_element
+			: public std::tuple_element<I, T>
+		{};
+	}	// namespace types
+}	// namespace sprout
+
+#endif	// #ifndef SPROUT_TYPE_TUPLE_HPP
diff --git a/sprout/type/type_tuple.hpp b/sprout/type/type_tuple.hpp
new file mode 100644
index 00000000..9ddafdb5
--- /dev/null
+++ b/sprout/type/type_tuple.hpp
@@ -0,0 +1,60 @@
+#ifndef SPROUT_TYPE_TYPE_TUPLE_HPP
+#define SPROUT_TYPE_TYPE_TUPLE_HPP
+
+#include <cstddef>
+#include <tuple>
+#include <type_traits>
+#include <sprout/config.hpp>
+#include <sprout/type/tuple.hpp>
+#include <sprout/type/iterator.hpp>
+#include <sprout/type/iterator/index_iterator.hpp>
+
+namespace sprout {
+	namespace types {
+		//
+		// type_tuple
+		//
+		template<typename... Types>
+		struct type_tuple {
+		public:
+			typedef sprout::types::index_iterator<type_tuple, 0> begin;
+			typedef sprout::types::index_iterator<type_tuple, sizeof...(Types)> end;
+		};
+
+		namespace detail {
+			template<std::size_t I, typename T>
+			struct tuple_element_impl;
+			template<typename Head, typename... Tail>
+			struct tuple_element_impl<0, sprout::types::type_tuple<Head, Tail...> > {
+			public:
+				typedef Head type;
+			};
+			template<std::size_t I, typename Head, typename... Tail>
+			struct tuple_element_impl<I, sprout::types::type_tuple<Head, Tail...> >
+				: public sprout::types::detail::tuple_element_impl<I - 1, sprout::types::type_tuple<Tail...> >
+			{};
+		}	// namespace detail
+	}	// namespace types
+
+	using sprout::types::type_tuple;
+}	// namespace sprout
+
+namespace std {
+	//
+	// tuple_size
+	//
+	template<typename... Types>
+	struct tuple_size<sprout::types::type_tuple<Types...> >
+		: public std::integral_constant<std::size_t, sizeof...(Types)>
+	{};
+
+	//
+	// tuple_element
+	//
+	template<std::size_t I, typename... Types>
+	struct tuple_element<I, sprout::types::type_tuple<Types...> >
+		: public sprout::types::detail::tuple_element_impl<I, sprout::types::type_tuple<Types...> >
+	{};
+}	// namespace std
+
+#endif	// #ifndef SPROUT_TYPE_TYPE_TUPLE_HPP
diff --git a/sprout/type/void.hpp b/sprout/type/void.hpp
new file mode 100644
index 00000000..1e3f60a1
--- /dev/null
+++ b/sprout/type/void.hpp
@@ -0,0 +1,15 @@
+#ifndef SPROUT_TYPE_VOID_HPP
+#define SPROUT_TYPE_VOID_HPP
+
+#include <sprout/config.hpp>
+
+namespace sprout {
+	namespace types {
+		//
+		// void_
+		//
+		struct void_ {};
+	}	// namespace types
+}	// namespace sprout
+
+#endif	// #ifndef SPROUT_TYPE_VOID_HPP
diff --git a/sprout/variant.hpp b/sprout/variant.hpp
new file mode 100644
index 00000000..c9c77ab2
--- /dev/null
+++ b/sprout/variant.hpp
@@ -0,0 +1,8 @@
+#ifndef SPROUT_VARIANT_HPP
+#define SPROUT_VARIANT_HPP
+
+#include <sprout/config.hpp>
+#include <sprout/variant/variant.hpp>
+#include <sprout/variant/get.hpp>
+
+#endif	// #ifndef SPROUT_VARIANT_HPP
diff --git a/sprout/variant/get.hpp b/sprout/variant/get.hpp
new file mode 100644
index 00000000..99e34800
--- /dev/null
+++ b/sprout/variant/get.hpp
@@ -0,0 +1,21 @@
+#ifndef SPROUT_VARIANT_GET_HPP
+#define SPROUT_VARIANT_GET_HPP
+
+#include <sprout/config.hpp>
+#include <sprout/variant/variant.hpp>
+
+namespace sprout {
+	//
+	// get
+	//
+	template<typename U, typename... Types>
+	SPROUT_CONSTEXPR U const& get(sprout::variant<Types...> const& operand) {
+		return operand.template get<U>();
+	}
+	template<typename U, typename... Types>
+	U& get(sprout::variant<Types...>& operand) {
+		return operand.template get<U>();
+	}
+}	// namespace sprout
+
+#endif	// #ifndef SPROUT_VARIANT_GET_HPP
diff --git a/sprout/variant/variant.hpp b/sprout/variant/variant.hpp
new file mode 100644
index 00000000..3439b47c
--- /dev/null
+++ b/sprout/variant/variant.hpp
@@ -0,0 +1,233 @@
+#ifndef SPROUT_VARIANT_VARIANT_HPP
+#define SPROUT_VARIANT_VARIANT_HPP
+
+#include <cstddef>
+#include <utility>
+#include <stdexcept>
+#include <sprout/config.hpp>
+#include <sprout/index_tuple.hpp>
+#include <sprout/utility/operation.hpp>
+#include <sprout/tuple/tuple.hpp>
+#include <sprout/tuple/functions.hpp>
+#include <sprout/type/algorithm/find_index.hpp>
+
+namespace sprout {
+	namespace detail {
+		template<typename... Types>
+		class variant_impl {
+		protected:
+			typedef sprout::tuples::tuple<Types...> tuple_type;;
+		private:
+			template<typename T, std::ptrdiff_t... Indexes>
+			static SPROUT_CONSTEXPR tuple_type init(T&& operand, sprout::index_tuple<Indexes...>) {
+				return sprout::tuples::make_clone<tuple_type>(
+					typename sprout::tuples::tuple_element<Indexes, tuple_type>::type()...,
+					sprout::forward<T>(operand)
+					);
+			}
+		protected:
+			tuple_type tuple_;
+			int which_;
+		protected:
+			SPROUT_CONSTEXPR variant_impl()
+				: tuple_()
+				, which_()
+			{}
+			template<typename T, typename Index>
+			SPROUT_CONSTEXPR variant_impl(T&& operand, Index)
+				: tuple_(init(sprout::forward<T>(operand), typename sprout::index_range<0, Index::value>::type()))
+				, which_(Index::value)
+			{
+				static_assert(Index::value < sizeof...(Types), "variant<>: invalid operand");
+			}
+			void swap(variant_impl& other) SPROUT_NOEXCEPT_EXPR(
+				SPROUT_NOEXCEPT_EXPR(swap(std::declval<tuple_type&>(), std::declval<tuple_type&>()))
+				)
+			{
+				using std::swap;
+				swap(tuple_, other.tuple_);
+				swap(which_, other.which_);
+			}
+			variant_impl& operator=(variant_impl const&) = default;
+		};
+	}	// namespace detail
+	//
+	// variant
+	//
+	template<typename... Types>
+	class variant
+		: private sprout::detail::variant_impl<Types...>
+	{
+	private:
+		typedef sprout::detail::variant_impl<Types...> impl_type;;
+	public:
+		typedef typename impl_type::tuple_type tuple_type;;
+	private:
+		template<int I>
+		static SPROUT_CONSTEXPR typename std::enable_if<
+			I == sizeof...(Types),
+			bool
+		>::type eq(tuple_type const& l, tuple_type const& r, int which) {
+			return false;
+		}
+		template<int I>
+		static SPROUT_CONSTEXPR typename std::enable_if<
+			I != sizeof...(Types),
+			bool
+		>::type eq(tuple_type const& l, tuple_type const& r, int which) {
+			return I == which
+				? sprout::tuples::get<I>(l) == sprout::tuples::get<I>(r)
+				: eq<I + 1>(l, r, which)
+				;
+		}
+		template<int I>
+		static SPROUT_CONSTEXPR typename std::enable_if<
+			static_cast<std::size_t>(I) == sizeof...(Types),
+			bool
+		>::type lt(tuple_type const& l, tuple_type const& r, int which) {
+			return false;
+		}
+		template<int I>
+		static SPROUT_CONSTEXPR typename std::enable_if<
+			static_cast<std::size_t>(I) != sizeof...(Types),
+			bool
+		>::type lt(tuple_type const& l, tuple_type const& r, int which) {
+			return I == which
+				? sprout::tuples::get<I>(l) < sprout::tuples::get<I>(r)
+				: lt<I + 1>(l, r, which)
+				;
+		}
+		template<int I, typename Elem, typename Traits>
+		static typename std::enable_if<
+			static_cast<std::size_t>(I) == sizeof...(Types),
+			std::basic_ostream<Elem, Traits>&
+		>::type output(std::basic_ostream<Elem, Traits>& os, tuple_type const& t, int which) {
+			return os;
+		}
+		template<int I, typename Elem, typename Traits>
+		static typename std::enable_if<
+			static_cast<std::size_t>(I) != sizeof...(Types),
+			std::basic_ostream<Elem, Traits>&
+		>::type output(std::basic_ostream<Elem, Traits>& os, tuple_type const& t, int which) {
+			return I == which
+				? os << sprout::tuples::get<I>(t)
+				: output<I + 1>(os, t, which)
+				;
+		}
+	private:
+		using impl_type::tuple_;
+		using impl_type::which_;
+	public:
+		// construct/copy/destruct
+		SPROUT_CONSTEXPR variant()
+			: impl_type()
+		{}
+		variant(variant const&) = default;
+		template<typename T>
+		SPROUT_CONSTEXPR variant(T&& operand)
+			: impl_type(sprout::forward<T>(operand), sprout::types::find_index<tuple_type, T>())
+		{}
+		// modifiers
+		void swap(variant& other) SPROUT_NOEXCEPT_EXPR(SPROUT_NOEXCEPT_EXPR(impl_type::swap(other))) {
+			impl_type::swap(other);
+		}
+		variant& operator=(variant const& rhs) {
+			static_cast<impl_type&>(*this) = rhs;
+			return *this;
+		}
+		variant& operator=(variant&& rhs) SPROUT_NOEXCEPT_EXPR(std::is_nothrow_move_assignable<impl_type>::value) {
+			static_cast<impl_type&>(*this) = sprout::move(rhs);
+			return *this;
+		}
+		template<typename T>
+		variant& operator=(T&& rhs) {
+			static_cast<impl_type&>(*this) = variant(sprout::forward<T>(rhs));
+			return *this;
+		}
+		// queries
+		SPROUT_CONSTEXPR int which() const {
+			return which_;
+		}
+		SPROUT_CONSTEXPR bool empty() const {
+			return sizeof...(Types) == 0;
+		}
+		// relational
+		friend SPROUT_CONSTEXPR bool operator==(variant const& lhs, variant const& rhs) {
+			return lhs.which_ == rhs.which_ && eq<0>(lhs.tuple_, rhs.tuple_, lhs.which_);
+		}
+		friend SPROUT_CONSTEXPR bool operator!=(variant const& lhs, variant const& rhs) {
+			return !(lhs == rhs);
+		}
+		friend SPROUT_CONSTEXPR bool operator<(variant const& lhs, variant const& rhs) {
+			return lhs.which_ < rhs.which_
+				|| (lhs.which_ == rhs.which_ && lt<0>(lhs.tuple_, rhs.tuple_, lhs.which_))
+				;
+		}
+		friend SPROUT_CONSTEXPR bool operator>(variant const& lhs, variant const& rhs) {
+			return rhs < lhs;
+		}
+		friend SPROUT_CONSTEXPR bool operator<=(variant const& lhs, variant const& rhs) {
+			return !(rhs < lhs);
+		}
+		friend SPROUT_CONSTEXPR bool operator>=(variant const& lhs, variant const& rhs) {
+			return !(lhs < rhs);
+		}
+
+		template<typename Elem, typename Traits>
+		friend std::basic_ostream<Elem, Traits>& operator<<(std::basic_ostream<Elem, Traits>& lhs, variant const& rhs) {
+			return output<0>(lhs, rhs.tuple_, rhs.which_);
+		}
+		template<typename U>
+		SPROUT_CONSTEXPR typename std::enable_if<
+			sprout::types::find_index<tuple_type, U>::value != sizeof...(Types),
+			U const&
+		>::type get() const {
+			return sprout::types::find_index<tuple_type, U>::value == static_cast<std::size_t>(which_)
+				? sprout::tuples::get<sprout::types::find_index<tuple_type, U>::value>(tuple_)
+				: (throw std::domain_error("variant<>: bad get"), sprout::tuples::get<sprout::types::find_index<tuple_type, U>::value>(tuple_))
+				;
+		}
+		template<typename U>
+		typename std::enable_if<
+			sprout::types::find_index<tuple_type, U>::value != sizeof...(Types),
+			U&
+		>::type get() {
+			return sprout::types::find_index<tuple_type, U>::value == which_
+				? sprout::tuples::get<sprout::types::find_index<tuple_type, U>::value>(tuple_)
+				: (throw std::domain_error("variant<>: bad get"), sprout::tuples::get<sprout::types::find_index<tuple_type, U>::value>(tuple_))
+				;
+		}
+	};
+
+	//
+	// swap
+	//
+	template<typename... Types>
+	inline void swap(
+		sprout::variant<Types...>& lhs,
+		sprout::variant<Types...>& rhs
+		) SPROUT_NOEXCEPT_EXPR(SPROUT_NOEXCEPT_EXPR(lhs.swap(rhs)))
+	{
+		lhs.swap(rhs);
+	}
+}	// namespace sprout
+
+namespace std {
+	//
+	// tuple_size
+	//
+	template<typename... Types>
+	struct tuple_size<sprout::variant<Types...> >
+		: public std::tuple_size<typename sprout::variant<Types...>::tuple_tyep>
+	{};
+
+	//
+	// tuple_element
+	//
+	template<std::size_t I, typename... Types>
+	struct tuple_element<I, sprout::variant<Types...> >
+		: public std::tuple_element<I, typename sprout::variant<Types...>::tuple_tyep>
+	{};
+}	// namespace std
+
+#endif	// #ifndef SPROUT_VARIANT_VARIANT_HPP