diff --git a/sprout/type_traits/detail/invoke.hpp b/sprout/type_traits/detail/invoke.hpp
new file mode 100644
index 00000000..45267ffb
--- /dev/null
+++ b/sprout/type_traits/detail/invoke.hpp
@@ -0,0 +1,73 @@
+/*=============================================================================
+  Copyright (c) 2011-2017 Bolero MURAKAMI
+  https://github.com/bolero-MURAKAMI/Sprout
+
+  Distributed under the Boost Software License, Version 1.0. (See accompanying
+  file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+=============================================================================*/
+#ifndef SPROUT_TYPE_TRAITS_DETAIL_INVOKE_HPP
+#define SPROUT_TYPE_TRAITS_DETAIL_INVOKE_HPP
+
+#include <utility>
+#include <sprout/config.hpp>
+#include <sprout/type_traits/identity.hpp>
+#include <sprout/type_traits/voider.hpp>
+#include <sprout/detail/nil_base.hpp>
+#include <sprout/utility/implicit_cast.hpp>
+
+namespace sprout {
+	namespace detail {
+		template<typename F, typename... Args>
+		inline SPROUT_CONSTEXPR decltype(std::declval<F>()(std::declval<Args>()...))
+		invoke(F&&, Args&&...) SPROUT_NOEXCEPT_IF_EXPR(std::declval<F>()(std::declval<Args>()...));
+
+		template<typename Base, typename T, typename Derived>
+		inline SPROUT_CONSTEXPR decltype(std::declval<Derived>().*(std::declval<T Base::*>()))
+		invoke(T Base::*, Derived&&) SPROUT_NOEXCEPT_IF_EXPR(std::declval<Derived>().*(std::declval<T Base::*>()));
+
+		template<typename PMD, typename Pointer>
+		inline SPROUT_CONSTEXPR decltype((*std::declval<Pointer>()).*(std::declval<PMD>()))
+		invoke(PMD&&, Pointer&&) SPROUT_NOEXCEPT_IF_EXPR((*std::declval<Pointer>()).*(std::declval<PMD>()));
+
+		template<typename Base, typename T, typename Derived, typename... Args>
+		inline SPROUT_CONSTEXPR decltype((std::declval<Derived>().*(std::declval<T Base::*>()))(std::declval<Args>()...))
+		invoke(T Base::*, Derived&&, Args&&...) SPROUT_NOEXCEPT_IF_EXPR((std::declval<Derived>().*(std::declval<T Base::*>()))(std::declval<Args>()...));
+
+		template<typename PMF, typename Pointer, typename... Args>
+		inline SPROUT_CONSTEXPR decltype(((*std::declval<Pointer>()).*(std::declval<PMF>()))(std::declval<Args>()...))
+		invoke(PMF&& pmf, Pointer&& ptr, Args&&... args) SPROUT_NOEXCEPT_IF_EXPR(((*std::declval<Pointer>()).*(std::declval<PMF>()))(std::declval<Args>()...));
+
+		template<typename R, typename F, typename... Args>
+		inline SPROUT_CONSTEXPR R
+		invoke(F&&, Args&&...) SPROUT_NOEXCEPT_IF_EXPR(R(std::declval<F>()(std::declval<Args>()...)));
+
+		template<typename R, typename Base, typename T, typename Derived>
+		inline SPROUT_CONSTEXPR decltype(R(std::declval<Derived>().*(std::declval<T Base::*>())))
+		invoke(T Base::*, Derived&&) SPROUT_NOEXCEPT_IF_EXPR(R(std::declval<Derived>().*(std::declval<T Base::*>())));
+
+		template<typename R, typename PMD, typename Pointer>
+		inline SPROUT_CONSTEXPR decltype(R((*std::declval<Pointer>()).*(std::declval<PMD>())))
+		invoke(PMD&&, Pointer&&) SPROUT_NOEXCEPT_IF_EXPR(R((*std::declval<Pointer>()).*(std::declval<PMD>())));
+
+		template<typename R, typename Base, typename T, typename Derived, typename... Args>
+		inline SPROUT_CONSTEXPR decltype(R((std::declval<Derived>().*(std::declval<T Base::*>()))(std::declval<Args>()...)))
+		invoke(T Base::*, Derived&&, Args&&...) SPROUT_NOEXCEPT_IF_EXPR(R((std::declval<Derived>().*(std::declval<T Base::*>()))(std::declval<Args>()...)));
+
+		template<typename R, typename PMF, typename Pointer, typename... Args>
+		inline SPROUT_CONSTEXPR decltype(R(((*std::declval<Pointer>()).*(std::declval<PMF>()))(std::declval<Args>()...)))
+		invoke(PMF&& pmf, Pointer&& ptr, Args&&... args) SPROUT_NOEXCEPT_IF_EXPR(R(((*std::declval<Pointer>()).*(std::declval<PMF>()))(std::declval<Args>()...)));
+	}	// namespace detail
+
+	namespace detail {
+		template<typename Void, typename F, typename... Args>
+		struct invoke_result
+			: public sprout::detail::nil_base
+		{};
+		template<typename F, typename... Args>
+		struct invoke_result<typename sprout::voider<decltype(sprout::detail::invoke(std::declval<F>(), std::declval<Args>()...))>::type, F, Args...>
+			: public sprout::identity<decltype(sprout::detail::invoke(std::declval<F>(), std::declval<Args>()...))>
+		{};
+	}	// namespace detail
+}	// namespace sprout
+
+#endif	// #ifndef SPROUT_TYPE_TRAITS_DETAIL_INVOKE_HPP
diff --git a/sprout/type_traits/invoke_result.hpp b/sprout/type_traits/invoke_result.hpp
index 14310fcf..537c8876 100644
--- a/sprout/type_traits/invoke_result.hpp
+++ b/sprout/type_traits/invoke_result.hpp
@@ -9,7 +9,7 @@
 #define SPROUT_TYPE_TRAITS_INVOKE_RESULT_HPP
 
 #include <sprout/config.hpp>
-#include <sprout/type_traits/result_of.hpp>
+#include <sprout/type_traits/detail/invoke.hpp>
 
 namespace sprout {
 	//
diff --git a/sprout/type_traits/is_invocable.hpp b/sprout/type_traits/is_invocable.hpp
new file mode 100644
index 00000000..2a83b805
--- /dev/null
+++ b/sprout/type_traits/is_invocable.hpp
@@ -0,0 +1,43 @@
+/*=============================================================================
+  Copyright (c) 2011-2017 Bolero MURAKAMI
+  https://github.com/bolero-MURAKAMI/Sprout
+
+  Distributed under the Boost Software License, Version 1.0. (See accompanying
+  file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+=============================================================================*/
+#ifndef SPROUT_TYPE_TRAITS_IS_INVOCABLE_HPP
+#define SPROUT_TYPE_TRAITS_IS_INVOCABLE_HPP
+
+#include <sprout/config.hpp>
+#include <sprout/type_traits/integral_constant.hpp>
+#include <sprout/type_traits/invoke_result.hpp>
+#include <sprout/type_traits/voider.hpp>
+
+namespace sprout {
+	//
+	// is_invocable
+	//
+	namespace detail {
+		template<typename Result, typename = void>
+		struct is_invocable_impl
+			: public sprout::false_type
+		{};
+		template<typename Result>
+		struct is_invocable_impl<Result, typename sprout::voider<typename Result::type>::type>
+			: public sprout::true_type
+		{};
+	}	// namespace detail
+	template<typename F, typename... Args>
+	struct is_invocable
+		: public sprout::detail::is_invocable_impl<
+			sprout::invoke_result<F, Args...>
+		>::type
+	{};
+
+#if SPROUT_USE_VARIABLE_TEMPLATES
+	template<typename F, typename... Args>
+	SPROUT_STATIC_CONSTEXPR bool is_invocable_v = sprout::is_invocable<F, Args...>::value;
+#endif	// #if SPROUT_USE_VARIABLE_TEMPLATES
+}	// namespace sprout
+
+#endif	// #ifndef SPROUT_TYPE_TRAITS_IS_INVOCABLE_HPP
diff --git a/sprout/type_traits/is_invocable_r.hpp b/sprout/type_traits/is_invocable_r.hpp
new file mode 100644
index 00000000..def53dba
--- /dev/null
+++ b/sprout/type_traits/is_invocable_r.hpp
@@ -0,0 +1,46 @@
+/*=============================================================================
+  Copyright (c) 2011-2017 Bolero MURAKAMI
+  https://github.com/bolero-MURAKAMI/Sprout
+
+  Distributed under the Boost Software License, Version 1.0. (See accompanying
+  file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+=============================================================================*/
+#ifndef SPROUT_TYPE_TRAITS_IS_INVOCABLE_R_HPP
+#define SPROUT_TYPE_TRAITS_IS_INVOCABLE_R_HPP
+
+#include <type_traits>
+#include <sprout/config.hpp>
+#include <sprout/type_traits/integral_constant.hpp>
+#include <sprout/type_traits/invoke_result.hpp>
+#include <sprout/type_traits/voider.hpp>
+
+namespace sprout {
+	//
+	// is_invocable_r
+	//
+	namespace detail {
+		template<typename R, typename Result, typename = void>
+		struct is_invocable_r_impl
+			: public sprout::false_type
+		{};
+		template<typename R, typename Result>
+		struct is_invocable_r_impl<R, Result, typename sprout::voider<typename Result::type>::type>
+			: public sprout::bool_constant<
+				std::is_void<R>::value || std::is_convertible<typename Result::type, R>::value
+			>
+		{};
+	}	// namespace detail
+	template<typename R, typename F, typename... Args>
+	struct is_invocable_r
+		: public sprout::detail::is_invocable_r_impl<
+			R, sprout::invoke_result<F, Args...>
+		>::type
+	{};
+
+#if SPROUT_USE_VARIABLE_TEMPLATES
+	template<typename R, typename F, typename... Args>
+	SPROUT_STATIC_CONSTEXPR bool is_invocable_r_v = sprout::is_invocable_r<R, F, Args...>::value;
+#endif	// #if SPROUT_USE_VARIABLE_TEMPLATES
+}	// namespace sprout
+
+#endif	// #ifndef SPROUT_TYPE_TRAITS_IS_INVOCABLE_R_HPP
diff --git a/sprout/type_traits/is_nothrow_invocable.hpp b/sprout/type_traits/is_nothrow_invocable.hpp
new file mode 100644
index 00000000..7521f0df
--- /dev/null
+++ b/sprout/type_traits/is_nothrow_invocable.hpp
@@ -0,0 +1,45 @@
+/*=============================================================================
+  Copyright (c) 2011-2017 Bolero MURAKAMI
+  https://github.com/bolero-MURAKAMI/Sprout
+
+  Distributed under the Boost Software License, Version 1.0. (See accompanying
+  file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+=============================================================================*/
+#ifndef SPROUT_TYPE_TRAITS_IS_NOTHROW_INVOCABLE_HPP
+#define SPROUT_TYPE_TRAITS_IS_NOTHROW_INVOCABLE_HPP
+
+#include <sprout/config.hpp>
+#include <sprout/type_traits/integral_constant.hpp>
+#include <sprout/type_traits/invoke_result.hpp>
+#include <sprout/type_traits/detail/invoke.hpp>
+
+namespace sprout {
+	//
+	// is_nothrow_invocable
+	//
+	namespace detail {
+		template<bool Cond, typename F, typename... Args>
+		struct is_nothrow_invocable_impl
+			: public sprout::false_type
+		{};
+		template<typename F, typename... Args>
+		struct is_nothrow_invocable_impl<true, F, Args...>
+			: public sprout::bool_constant<
+				SPROUT_NOEXCEPT_EXPR(sprout::detail::invoke(std::declval<F>(), std::declval<Args>()...))
+			>
+		{};
+	}	// namespace detail
+	template<typename F, typename... Args>
+	struct is_nothrow_invocable
+		: public sprout::detail::is_nothrow_invocable_impl<
+			sprout::is_invocable<F, Args...>::value, F, Args...
+		>::type
+	{};
+
+#if SPROUT_USE_VARIABLE_TEMPLATES
+	template<typename F, typename... Args>
+	SPROUT_STATIC_CONSTEXPR bool is_nothrow_invocable_v = sprout::is_nothrow_invocable<F, Args...>::value;
+#endif	// #if SPROUT_USE_VARIABLE_TEMPLATES
+}	// namespace sprout
+
+#endif	// #ifndef SPROUT_TYPE_TRAITS_IS_NOTHROW_INVOCABLE_HPP
diff --git a/sprout/type_traits/is_nothrow_invocable_r.hpp b/sprout/type_traits/is_nothrow_invocable_r.hpp
new file mode 100644
index 00000000..9a5ea95e
--- /dev/null
+++ b/sprout/type_traits/is_nothrow_invocable_r.hpp
@@ -0,0 +1,47 @@
+/*=============================================================================
+  Copyright (c) 2011-2017 Bolero MURAKAMI
+  https://github.com/bolero-MURAKAMI/Sprout
+
+  Distributed under the Boost Software License, Version 1.0. (See accompanying
+  file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+=============================================================================*/
+#ifndef SPROUT_TYPE_TRAITS_IS_NOTHROW_INVOCABLE_R_HPP
+#define SPROUT_TYPE_TRAITS_IS_NOTHROW_INVOCABLE_R_HPP
+
+#include <type_traits>
+#include <sprout/config.hpp>
+#include <sprout/type_traits/integral_constant.hpp>
+#include <sprout/type_traits/invoke_result.hpp>
+#include <sprout/type_traits/voider.hpp>
+#include <sprout/type_traits/detail/invoke.hpp>
+
+namespace sprout {
+	//
+	// is_nothrow_invocable_r
+	//
+	namespace detail {
+		template<bool Cond, typename R, typename F, typename... Args>
+		struct is_nothrow_invocable_r_impl
+			: public sprout::false_type
+		{};
+		template<typename R, typename F, typename... Args>
+		struct is_nothrow_invocable_r_impl<true, R, F, Args...>
+			: public sprout::bool_constant<
+				SPROUT_NOEXCEPT_EXPR(sprout::detail::invoke<R>(std::declval<F>(), std::declval<Args>()...))
+			>
+		{};
+	}	// namespace detail
+	template<typename R, typename F, typename... Args>
+	struct is_nothrow_invocable_r
+		: public sprout::detail::is_nothrow_invocable_r_impl<
+			sprout::is_invocable_r<R, F, Args...>::value, R, F, Args...
+		>::type
+	{};
+
+#if SPROUT_USE_VARIABLE_TEMPLATES
+	template<typename R, typename F, typename... Args>
+	SPROUT_STATIC_CONSTEXPR bool is_nothrow_invocable_r_v = sprout::is_nothrow_invocable_r<R, F, Args...>::value;
+#endif	// #if SPROUT_USE_VARIABLE_TEMPLATES
+}	// namespace sprout
+
+#endif	// #ifndef SPROUT_TYPE_TRAITS_IS_NOTHROW_INVOCABLE_R_HPP
diff --git a/sprout/type_traits/relationship.hpp b/sprout/type_traits/relationship.hpp
index e152bb86..3f0652fb 100644
--- a/sprout/type_traits/relationship.hpp
+++ b/sprout/type_traits/relationship.hpp
@@ -13,6 +13,10 @@
 #include <sprout/type_traits/is_same.hpp>
 #include <sprout/type_traits/is_base_of.hpp>
 #include <sprout/type_traits/is_convertible.hpp>
+#include <sprout/type_traits/is_invocable.hpp>
+#include <sprout/type_traits/is_invocable_r.hpp>
+#include <sprout/type_traits/is_nothrow_invocable.hpp>
+#include <sprout/type_traits/is_nothrow_invocable_r.hpp>
 
 #include <sprout/type_traits/is_const_cast_convertible.hpp>
 #include <sprout/type_traits/is_convert_constructible.hpp>
diff --git a/sprout/type_traits/result_of.hpp b/sprout/type_traits/result_of.hpp
index 41bf7ab4..4cef0cde 100644
--- a/sprout/type_traits/result_of.hpp
+++ b/sprout/type_traits/result_of.hpp
@@ -8,42 +8,10 @@
 #ifndef SPROUT_TYPE_TRAITS_RESULT_OF_HPP
 #define SPROUT_TYPE_TRAITS_RESULT_OF_HPP
 
-#include <utility>
 #include <sprout/config.hpp>
-#include <sprout/type_traits/identity.hpp>
+#include <sprout/type_traits/detail/invoke.hpp>
 
 namespace sprout {
-	namespace detail {
-		template<typename F, typename... Args>
-		inline SPROUT_CONSTEXPR decltype(std::declval<F>()(std::declval<Args>()...))
-		invoke(F&&, Args&&...);
-
-		template<typename Base, typename T, typename Derived>
-		inline SPROUT_CONSTEXPR decltype(std::declval<Derived>().*(std::declval<T Base::*>()))
-		invoke(T Base::*, Derived&&);
-
-		template<typename PMD, typename Pointer>
-		inline SPROUT_CONSTEXPR decltype((*std::declval<Pointer>()).*(std::declval<PMD>()))
-		invoke(PMD&&, Pointer&&);
-
-		template<typename Base, typename T, typename Derived, typename... Args>
-		inline SPROUT_CONSTEXPR decltype((std::declval<Derived>().*(std::declval<T Base::*>()))(std::declval<Args>()...))
-		invoke(T Base::*, Derived&&, Args&&...);
-
-		template<typename PMF, typename Pointer, typename... Args>
-		inline SPROUT_CONSTEXPR decltype(((*std::declval<Pointer>()).*(std::declval<PMF>()))(std::declval<Args>()...))
-		invoke(PMF&& pmf, Pointer&& ptr, Args&&... args);
-	}	// namespace detail
-
-	namespace detail {
-		template<typename Void, typename, typename...>
-		struct invoke_result {};
-		template<typename F, typename...Args>
-		struct invoke_result<decltype(void(sprout::detail::invoke(std::declval<F>(), std::declval<Args>()...))), F, Args...>
-			: public sprout::identity<decltype(sprout::detail::invoke(std::declval<F>(), std::declval<Args>()...))>
-		{};
-	}	// namespace detail
-
 	//
 	// result_of
 	//
diff --git a/sprout/type_traits/void_t.hpp b/sprout/type_traits/void_t.hpp
new file mode 100644
index 00000000..2c09b956
--- /dev/null
+++ b/sprout/type_traits/void_t.hpp
@@ -0,0 +1,14 @@
+/*=============================================================================
+  Copyright (c) 2011-2017 Bolero MURAKAMI
+  https://github.com/bolero-MURAKAMI/Sprout
+
+  Distributed under the Boost Software License, Version 1.0. (See accompanying
+  file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+=============================================================================*/
+#ifndef SPROUT_TYPE_TRAITS_VOID_T_HPP
+#define SPROUT_TYPE_TRAITS_VOID_T_HPP
+
+#include <sprout/config.hpp>
+#include <sprout/type_traits/voider.hpp>
+
+#endif	// #ifndef SPROUT_TYPE_TRAITS_VOID_T_HPP
diff --git a/testspr/print.hpp b/testspr/print.hpp
index a027aefe..5485219d 100644
--- a/testspr/print.hpp
+++ b/testspr/print.hpp
@@ -15,6 +15,8 @@
 #include <iostream>
 #include <iomanip>
 #include <sprout/config.hpp>
+#include <sprout/preprocessor/config.hpp>
+#include <sprout/preprocessor/stringize.hpp>
 #include <sprout/container.hpp>
 #include <sprout/detail/io/ios_state.hpp>
 #include <testspr/typeinfo.hpp>
@@ -181,4 +183,15 @@ namespace testspr {
 	}
 }	// namespace testspr
 
+//
+// TESTSPR_PRINT_EXPR
+//
+#if SPROUT_PP_VARIADICS
+#	define TESTSPR_PRINT_EXPR(...) \
+		::testspr::print_ln(SPROUT_PP_STRINGIZE((__VA_ARGS__)), " => ", __VA_ARGS__)
+#else
+#	define TESTSPR_PRINT_EXPR(EXPR) \
+		::testspr::print_ln(SPROUT_PP_STRINGIZE((EXPR)), " => ", EXPR)
+#endif
+
 #endif	// #ifndef TESTSPR_PRINT_HPP