diff --git a/sprout/weed/attr_cnv.hpp b/sprout/weed/attr_cnv.hpp
index 2109dbf5..9fd2222a 100644
--- a/sprout/weed/attr_cnv.hpp
+++ b/sprout/weed/attr_cnv.hpp
@@ -3,6 +3,7 @@
 
 #include <sprout/config.hpp>
 #include <sprout/weed/attr_cnv/times.hpp>
+#include <sprout/weed/attr_cnv/negate.hpp>
 #include <sprout/weed/attr_cnv/shift_left.hpp>
 #include <sprout/weed/attr_cnv/modulus.hpp>
 #include <sprout/weed/attr_cnv/bitwise_or.hpp>
diff --git a/sprout/weed/attr_cnv/negate.hpp b/sprout/weed/attr_cnv/negate.hpp
new file mode 100644
index 00000000..3d62685b
--- /dev/null
+++ b/sprout/weed/attr_cnv/negate.hpp
@@ -0,0 +1,28 @@
+#ifndef SPROUT_WEED_ATTR_CNV_NEGATE_HPP
+#define SPROUT_WEED_ATTR_CNV_NEGATE_HPP
+
+#include <type_traits>
+#include <sprout/config.hpp>
+#include <sprout/weed/unused.hpp>
+#include <sprout/weed/traits/type/is_unused.hpp>
+#include <sprout/weed/attr_cnv/result_of/negate.hpp>
+
+namespace sprout {
+	namespace weed {
+		namespace attr_cnv {
+			//
+			// negate
+			//
+			// !unused -> unused
+			template<typename T>
+			SPROUT_CONSTEXPR inline typename std::enable_if<
+				sprout::weed::traits::is_unused<T>::value,
+				typename sprout::weed::attr_cnv::result_of::negate<T>::type
+			>::type negate(T const& t, bool cond) {
+				return sprout::weed::unused();
+			}
+		}	// namespace attr_cnv
+	}	// namespace weed
+}	// namespace sprout
+
+#endif	// #ifndef SPROUT_WEED_ATTR_CNV_NEGATE_HPP
diff --git a/sprout/weed/attr_cnv/result_of.hpp b/sprout/weed/attr_cnv/result_of.hpp
index 0e672018..953b3559 100644
--- a/sprout/weed/attr_cnv/result_of.hpp
+++ b/sprout/weed/attr_cnv/result_of.hpp
@@ -3,6 +3,7 @@
 
 #include <sprout/config.hpp>
 #include <sprout/weed/attr_cnv/result_of/times.hpp>
+#include <sprout/weed/attr_cnv/result_of/negate.hpp>
 #include <sprout/weed/attr_cnv/result_of/shift_left.hpp>
 #include <sprout/weed/attr_cnv/result_of/modulus.hpp>
 #include <sprout/weed/attr_cnv/result_of/bitwise_or.hpp>
diff --git a/sprout/weed/attr_cnv/result_of/negate.hpp b/sprout/weed/attr_cnv/result_of/negate.hpp
new file mode 100644
index 00000000..226d9848
--- /dev/null
+++ b/sprout/weed/attr_cnv/result_of/negate.hpp
@@ -0,0 +1,34 @@
+#ifndef SPROUT_WEED_ATTR_CNV_RESULT_OF_NEGATE_HPP
+#define SPROUT_WEED_ATTR_CNV_RESULT_OF_NEGATE_HPP
+
+#include <type_traits>
+#include <sprout/config.hpp>
+#include <sprout/weed/unused.hpp>
+#include <sprout/weed/traits/type/is_unused.hpp>
+
+namespace sprout {
+	namespace weed {
+		namespace attr_cnv {
+			namespace result_of {
+				//
+				// negate
+				//
+				template<typename T, typename = void>
+				struct negate;
+				// -unused -> unused
+				template<typename T>
+				struct negate<
+					T,
+					typename std::enable_if<
+						sprout::weed::traits::is_unused<T>::value
+					>::type
+				> {
+				public:
+					typedef sprout::weed::unused type;
+				};
+			}	// namespace result_of
+		}	// namespace attr_cnv
+	}	// namespace weed
+}	// namespace sprout
+
+#endif	// #ifndef SPROUT_WEED_ATTR_CNV_RESULT_OF_NEGATE_HPP
diff --git a/sprout/weed/context/parse_context/operator.hpp b/sprout/weed/context/parse_context/operator.hpp
index e2b4ce25..97e53ae9 100644
--- a/sprout/weed/context/parse_context/operator.hpp
+++ b/sprout/weed/context/parse_context/operator.hpp
@@ -3,11 +3,13 @@
 
 #include <sprout/config.hpp>
 #include <sprout/weed/context/parse_context/operator/unary_plus.hpp>
+#include <sprout/weed/context/parse_context/operator/negate.hpp>
 #include <sprout/weed/context/parse_context/operator/dereference.hpp>
 #include <sprout/weed/context/parse_context/operator/address_of.hpp>
 #include <sprout/weed/context/parse_context/operator/logical_not.hpp>
 #include <sprout/weed/context/parse_context/operator/shift_left.hpp>
 #include <sprout/weed/context/parse_context/operator/modulus.hpp>
+#include <sprout/weed/context/parse_context/operator/minus.hpp>
 #include <sprout/weed/context/parse_context/operator/bitwise_or.hpp>
 
 #endif	// #ifndef SPROUT_WEED_CONTEXT_PARSE_CONTEXT_OPERATOR_HPP
diff --git a/sprout/weed/context/parse_context/operator/minus.hpp b/sprout/weed/context/parse_context/operator/minus.hpp
new file mode 100644
index 00000000..3a4a32d8
--- /dev/null
+++ b/sprout/weed/context/parse_context/operator/minus.hpp
@@ -0,0 +1,67 @@
+#ifndef SPROUT_WEED_CONTEXT_PARSE_CONTEXT_TERMINAL_OPERATOR_MINUS_HPP
+#define SPROUT_WEED_CONTEXT_PARSE_CONTEXT_TERMINAL_OPERATOR_MINUS_HPP
+
+#include <type_traits>
+#include <sprout/config.hpp>
+#include <sprout/tuple/tuple.hpp>
+#include <sprout/weed/eval_result.hpp>
+#include <sprout/weed/expr/tag.hpp>
+#include <sprout/weed/expr/eval.hpp>
+#include <sprout/weed/traits/expr/tag_of.hpp>
+#include <sprout/weed/traits/parser/attribute_of.hpp>
+#include <sprout/weed/context/parse_context_fwd.hpp>
+
+namespace sprout {
+	namespace weed {
+		//
+		// parse_context::eval
+		//
+		template<typename Iterator>
+		template<typename Expr>
+		struct parse_context<Iterator>::eval<
+			Expr,
+			typename std::enable_if<
+				std::is_same<
+					typename sprout::weed::traits::tag_of<Expr>::type,
+					sprout::weed::tag::minus
+				>::value
+			>::type
+		> {
+		private:
+			typedef sprout::weed::parse_context<Iterator> context_type;
+		public:
+			typedef typename sprout::weed::traits::attribute_of<Expr, Iterator, context_type>::type attribute_type;
+			typedef sprout::weed::eval_result<context_type, Iterator, attribute_type> result_type;
+		private:
+			template<typename Result1>
+			SPROUT_CONSTEXPR result_type call_1(
+				typename Expr::args_type const& args,
+				context_type const& ctx,
+				Result1 const& res
+				) const
+			{
+				return res.success() && !sprout::weed::eval(sprout::tuples::get<1>(args), ctx).success()
+					? res
+					: result_type(false, ctx.begin(), attribute_type(), ctx)
+					;
+			}
+			SPROUT_CONSTEXPR result_type call(
+				typename Expr::args_type const& args,
+				context_type const& ctx
+				) const
+			{
+				return call_1(args, ctx, sprout::weed::eval(sprout::tuples::get<0>(args), ctx));
+			}
+		public:
+			SPROUT_CONSTEXPR result_type operator()(
+				Expr const& expr,
+				context_type const& ctx
+				) const
+			{
+				return call(expr.args(), ctx);
+			}
+		};
+	}	// namespace weed
+}	// namespace sprout
+
+#endif	// #ifndef SPROUT_WEED_CONTEXT_PARSE_CONTEXT_TERMINAL_OPERATOR_MINUS_HPP
diff --git a/sprout/weed/context/parse_context/operator/negate.hpp b/sprout/weed/context/parse_context/operator/negate.hpp
new file mode 100644
index 00000000..d74606f9
--- /dev/null
+++ b/sprout/weed/context/parse_context/operator/negate.hpp
@@ -0,0 +1,62 @@
+#ifndef SPROUT_WEED_CONTEXT_PARSE_CONTEXT_TERMINAL_OPERATOR_NEGATE_HPP
+#define SPROUT_WEED_CONTEXT_PARSE_CONTEXT_TERMINAL_OPERATOR_NEGATE_HPP
+
+#include <type_traits>
+#include <sprout/config.hpp>
+#include <sprout/tuple/tuple.hpp>
+#include <sprout/weed/eval_result.hpp>
+#include <sprout/weed/expr/tag.hpp>
+#include <sprout/weed/expr/eval.hpp>
+#include <sprout/weed/attr_cnv/negate.hpp>
+#include <sprout/weed/traits/expr/tag_of.hpp>
+#include <sprout/weed/traits/parser/attribute_of.hpp>
+#include <sprout/weed/context/parse_context_fwd.hpp>
+
+namespace sprout {
+	namespace weed {
+		//
+		// parse_context::eval
+		//
+		template<typename Iterator>
+		template<typename Expr>
+		struct parse_context<Iterator>::eval<
+			Expr,
+			typename std::enable_if<
+				std::is_same<
+					typename sprout::weed::traits::tag_of<Expr>::type,
+					sprout::weed::tag::negate
+				>::value
+			>::type
+		> {
+		private:
+			typedef sprout::weed::parse_context<Iterator> context_type;
+		public:
+			typedef typename sprout::weed::traits::attribute_of<Expr, Iterator, context_type>::type attribute_type;
+			typedef sprout::weed::eval_result<context_type, Iterator, attribute_type> result_type;
+		private:
+			template<typename Result>
+			SPROUT_CONSTEXPR result_type call(
+				context_type const& ctx,
+				Result const& res
+				) const
+			{
+				return result_type(
+					true,
+					res.current(),
+					sprout::weed::attr_cnv::negate(res.attr(), res.success()),
+					res.success() ? context_type(ctx, res.current()) : ctx
+					);
+			}
+		public:
+			SPROUT_CONSTEXPR result_type operator()(
+				Expr const& expr,
+				context_type const& ctx
+				) const
+			{
+				return call(ctx, sprout::weed::eval(sprout::tuples::get<0>(expr.args()), ctx));
+			}
+		};
+	}	// namespace weed
+}	// namespace sprout
+
+#endif	// #ifndef SPROUT_WEED_CONTEXT_PARSE_CONTEXT_TERMINAL_OPERATOR_NEGATE_HPP
diff --git a/sprout/weed/expr/tag.hpp b/sprout/weed/expr/tag.hpp
index fb6286b6..384388c5 100644
--- a/sprout/weed/expr/tag.hpp
+++ b/sprout/weed/expr/tag.hpp
@@ -8,11 +8,13 @@ namespace sprout {
 		namespace tag {
 			struct terminal {};
 			struct unary_plus {};
+			struct negate {};
 			struct dereference {};
 			struct address_of {};
 			struct logical_not {};
 			struct shift_left {};
 			struct modulus {};
+			struct minus {};
 			struct bitwise_or {};
 		}	// namespace tag
 	}	// namespace weed
diff --git a/sprout/weed/operator.hpp b/sprout/weed/operator.hpp
index 0c56f223..ba4e1473 100644
--- a/sprout/weed/operator.hpp
+++ b/sprout/weed/operator.hpp
@@ -3,11 +3,13 @@
 
 #include <sprout/config.hpp>
 #include <sprout/weed/operator/unary_plus.hpp>
+#include <sprout/weed/operator/negate.hpp>
 #include <sprout/weed/operator/dereference.hpp>
 #include <sprout/weed/operator/address_of.hpp>
 #include <sprout/weed/operator/logical_not.hpp>
 #include <sprout/weed/operator/shift_left.hpp>
 #include <sprout/weed/operator/modulus.hpp>
+#include <sprout/weed/operator/minus.hpp>
 #include <sprout/weed/operator/bitwise_or.hpp>
 
 #endif	// #ifndef SPROUT_WEED_OPERATOR_HPP
diff --git a/sprout/weed/operator/address_of.hpp b/sprout/weed/operator/address_of.hpp
index 5df73480..5c4b66e0 100644
--- a/sprout/weed/operator/address_of.hpp
+++ b/sprout/weed/operator/address_of.hpp
@@ -26,7 +26,7 @@ namespace sprout {
 		SPROUT_CONSTEXPR inline typename sprout::weed::traits::expr_of<
 			sprout::weed::tag::address_of,
 			Arg
-		>::type operator!(Arg&& arg) {
+		>::type operator&(Arg&& arg) {
 			return sprout::weed::make_expr<sprout::weed::tag::address_of>(
 				sprout::forward<Arg>(arg)
 				);
diff --git a/sprout/weed/operator/minus.hpp b/sprout/weed/operator/minus.hpp
new file mode 100644
index 00000000..9c73d7cc
--- /dev/null
+++ b/sprout/weed/operator/minus.hpp
@@ -0,0 +1,43 @@
+#ifndef SPROUT_WEED_OPERATOR_MINUS_HPP
+#define SPROUT_WEED_OPERATOR_MINUS_HPP
+
+#include <type_traits>
+#include <sprout/config.hpp>
+#include <sprout/utility/forward.hpp>
+#include <sprout/weed/expr/tag.hpp>
+#include <sprout/weed/expr/make_expr.hpp>
+#include <sprout/weed/traits/expr/expr_of.hpp>
+#include <sprout/weed/traits/parser/is_parser.hpp>
+#include <sprout/weed/detail/uncvref.hpp>
+
+namespace sprout {
+	namespace weed {
+		//
+		// operator-
+		//
+		template<
+			typename Arg1,
+			typename Arg2,
+			typename = typename std::enable_if<
+				sprout::weed::traits::is_parser<
+					typename sprout::weed::detail::uncvref<Arg1>::type
+				>::value
+				&& sprout::weed::traits::is_parser<
+					typename sprout::weed::detail::uncvref<Arg2>::type
+				>::value
+			>::type
+		>
+		SPROUT_CONSTEXPR inline typename sprout::weed::traits::expr_of<
+			sprout::weed::tag::minus,
+			Arg1,
+			Arg2
+		>::type operator-(Arg1&& arg1, Arg2&& arg2) {
+			return sprout::weed::make_expr<sprout::weed::tag::minus>(
+				sprout::forward<Arg1>(arg1),
+				sprout::forward<Arg2>(arg2)
+				);
+		}
+	}	// namespace weed
+}	// namespace sprout
+
+#endif	// #ifndef SPROUT_WEED_OPERATOR_MINUS_HPP
diff --git a/sprout/weed/operator/negate.hpp b/sprout/weed/operator/negate.hpp
new file mode 100644
index 00000000..c8e3be79
--- /dev/null
+++ b/sprout/weed/operator/negate.hpp
@@ -0,0 +1,37 @@
+#ifndef SPROUT_WEED_OPERATOR_NEGATE_HPP
+#define SPROUT_WEED_OPERATOR_NEGATE_HPP
+
+#include <type_traits>
+#include <sprout/config.hpp>
+#include <sprout/utility/forward.hpp>
+#include <sprout/weed/expr/tag.hpp>
+#include <sprout/weed/expr/make_expr.hpp>
+#include <sprout/weed/traits/expr/expr_of.hpp>
+#include <sprout/weed/traits/parser/is_parser.hpp>
+#include <sprout/weed/detail/uncvref.hpp>
+
+namespace sprout {
+	namespace weed {
+		//
+		// operator-
+		//
+		template<
+			typename Arg,
+			typename = typename std::enable_if<
+				sprout::weed::traits::is_parser<
+					typename sprout::weed::detail::uncvref<Arg>::type
+				>::value
+			>::type
+		>
+		SPROUT_CONSTEXPR inline typename sprout::weed::traits::expr_of<
+			sprout::weed::tag::negate,
+			Arg
+		>::type operator-(Arg&& arg) {
+			return sprout::weed::make_expr<sprout::weed::tag::negate>(
+				sprout::forward<Arg>(arg)
+				);
+		}
+	}	// namespace weed
+}	// namespace sprout
+
+#endif	// #ifndef SPROUT_WEED_OPERATOR_NEGATE_HPP
diff --git a/sprout/weed/traits/parser/attribute_of.hpp b/sprout/weed/traits/parser/attribute_of.hpp
index db74f5e4..52e4a85c 100644
--- a/sprout/weed/traits/parser/attribute_of.hpp
+++ b/sprout/weed/traits/parser/attribute_of.hpp
@@ -71,6 +71,12 @@ namespace sprout {
 				>
 			{};
 			template<typename Arg, typename Iterator, typename Context>
+			struct attribute_of<sprout::weed::expr<sprout::weed::tag::negate, Arg>, Iterator, Context>
+				: public sprout::weed::attr_cnv::result_of::negate<
+					typename sprout::weed::traits::attribute_of<Arg, Iterator, Context>::type
+				>
+			{};
+			template<typename Arg, typename Iterator, typename Context>
 			struct attribute_of<sprout::weed::expr<sprout::weed::tag::dereference, Arg>, Iterator, Context>
 				: public sprout::weed::attr_cnv::result_of::times<
 					sprout::weed::traits::limit_of<Arg, Iterator, Context>::value,
@@ -102,6 +108,11 @@ namespace sprout {
 				>
 			{};
 			template<typename Arg1, typename Arg2, typename Iterator, typename Context>
+			struct attribute_of<sprout::weed::expr<sprout::weed::tag::minus, Arg1, Arg2>, Iterator, Context> {
+			public:
+				typedef typename sprout::weed::traits::attribute_of<Arg1, Iterator, Context>::type type;
+			};
+			template<typename Arg1, typename Arg2, typename Iterator, typename Context>
 			struct attribute_of<sprout::weed::expr<sprout::weed::tag::bitwise_or, Arg1, Arg2>, Iterator, Context>
 				: public sprout::weed::attr_cnv::result_of::bitwise_or<
 					typename sprout::weed::traits::attribute_of<Arg1, Iterator, Context>::type,