Index: boost/proto/proto_fwd.hpp
===================================================================
--- boost/proto/proto_fwd.hpp	(revision 74374)
+++ boost/proto/proto_fwd.hpp	(working copy)
@@ -269,6 +269,9 @@
 
     using namespace tagns_;
 
+    template<typename Expr>
+    struct tag_of;
+
     ////////////////////////////////////////////////////////////////////////////////////////////////
     struct _;
 
@@ -359,7 +362,7 @@
     template<typename Condition, typename Then = _, typename Else = not_<_> >
     struct if_;
 
-    template<typename Cases>
+    template<typename Cases, typename Transform = tag_of<_>() >
     struct switch_;
 
     template<typename T>
@@ -462,9 +465,6 @@
     struct is_sub_domain_of;
 
     template<typename Expr>
-    struct tag_of;
-
-    template<typename Expr>
     struct arity_of;
 
     template<typename T, typename Void = void>
@@ -741,7 +741,7 @@
     template<typename Grammar>
     struct pass_through;
 
-    template<typename Grammar = detail::_default>
+    template<typename Grammar = detail::_default >
     struct _default;
 
     struct _expr;
Index: boost/proto/matches.hpp
===================================================================
--- boost/proto/matches.hpp	(revision 74374)
+++ boost/proto/matches.hpp	(working copy)
@@ -10,6 +10,7 @@
 #ifndef BOOST_PROTO_MATCHES_HPP_EAN_11_03_2006
 #define BOOST_PROTO_MATCHES_HPP_EAN_11_03_2006
 
+
 #include <boost/config.hpp>
 #include <boost/detail/workaround.hpp>
 #include <boost/preprocessor/cat.hpp>
@@ -402,16 +403,40 @@
         {};
 
         // handle proto::switch_
-        template<typename Expr, typename Tag, typename Args, long Arity, typename Cases>
-        struct matches_<Expr, proto::basic_expr<Tag, Args, Arity>, switch_<Cases> >
-          : matches_<
-                Expr
-              , proto::basic_expr<Tag, Args, Arity>
-              , typename Cases::template case_<Tag>::proto_grammar
-            >
+        template< typename Expr, typename Tag, typename Args, long Arity
+                , typename Cases, typename Transform
+                >
+        struct matches_ < Expr, proto::basic_expr<Tag, Args, Arity>
+                        , switch_<Cases,Transform>
+                        >
+        : matches_< Expr
+                  , proto::basic_expr<Tag, Args, Arity>
+                  , typename
+                    Cases::template case_<typename
+                                          when<_,Transform>::template
+                                          impl<Expr,int,int>::result_type
+                                         >::proto_grammar
+                  >
         {
-            typedef typename Cases::template case_<Tag> which;
+          typedef when<_,Transform> applicant;
+          typedef typename applicant::template impl<Expr,int,int>::result_type selected_type;
+          typedef typename Cases::template case_<selected_type> which;
         };
+
+        template< typename Expr, typename Tag, typename Args, long Arity
+                , typename Cases
+                >
+        struct matches_ < Expr, proto::basic_expr<Tag, Args, Arity>
+                        , switch_<Cases>
+                        >
+        : matches_< Expr
+                  , proto::basic_expr<Tag, Args, Arity>
+                  , typename  Cases::template
+                              case_<Tag>::proto_grammar
+                  >
+        {
+          typedef typename Cases::template case_<Tag> which;
+        };
     }
 
     /// \brief A Boolean metafunction that evaluates whether a given
@@ -449,6 +474,9 @@
     ///     not match \c T.
     /// \li An expression \c E matches <tt>switch_\<C\></tt> if
     ///     \c E matches <tt>C::case_\<E::proto_tag\></tt>.
+    /// \li An expression \c E matches <tt>switch_\<C,T\></tt> if
+    ///     the result type of the transform \c T on \c E matches
+    ///     <tt>C::case_\<boost::result_of\<T(E)\>::type\></tt>.
     ///
     /// A terminal expression <tt>expr\<AT,term\<A\> \></tt> matches
     /// a grammar <tt>expr\<BT,term\<B\> \></tt> if \c BT is \c AT or
@@ -784,27 +812,47 @@
     /// When applying <tt>switch_\<C\></tt> as a transform with an
     /// expression \c e of type \c E, state \c s and data \c d, it is
     /// equivalent to <tt>C::case_\<E::proto_tag\>()(e, s, d)</tt>.
+    template<typename Cases, typename Transform>
+    struct switch_ : transform< switch_<Cases,Transform> >
+    {
+      typedef switch_ proto_grammar;
+      typedef when<_,Transform> applicant;
+
+      template<typename Expr, typename State, typename Data>
+      struct impl
+      : Cases::template
+        case_ < typename applicant::template impl<Expr,State,Data>::result_type
+              >::template impl<Expr, State, Data>
+      {};
+
+      template<typename Expr, typename State, typename Data>
+      struct impl<Expr &, State, Data>
+      : Cases::template
+        case_ <typename applicant::template impl<Expr,State,Data>::result_type
+              >::template impl<Expr &, State, Data>
+      {};
+    };
+
     template<typename Cases>
-    struct switch_ : transform<switch_<Cases> >
+    struct switch_<Cases> : transform< switch_<Cases> >
     {
-        typedef switch_ proto_grammar;
+      typedef switch_ proto_grammar;
+      /// \param e An expression
+      /// \param s The current state
+      /// \param d A data of arbitrary type
+      /// \pre <tt>matches\<Expr,switch_\>::value</tt> is \c true.
+      /// \return <tt>which()(e, s, d)</tt>, where <tt>which</tt> is
+      /// <tt>Cases::case_<typename Expr::proto_tag></tt>
 
-        /// \param e An expression
-        /// \param s The current state
-        /// \param d A data of arbitrary type
-        /// \pre <tt>matches\<Expr,switch_\>::value</tt> is \c true.
-        /// \return <tt>which()(e, s, d)</tt>, where <tt>which</tt> is
-        /// <tt>Cases::case_<typename Expr::proto_tag></tt>
+      template<typename Expr, typename State, typename Data>
+      struct impl
+      : Cases::template case_<typename Expr::proto_tag>::template impl<Expr, State, Data>
+      {};
 
-        template<typename Expr, typename State, typename Data>
-        struct impl
-          : Cases::template case_<typename Expr::proto_tag>::template impl<Expr, State, Data>
-        {};
-
-        template<typename Expr, typename State, typename Data>
-        struct impl<Expr &, State, Data>
-          : Cases::template case_<typename Expr::proto_tag>::template impl<Expr &, State, Data>
-        {};
+      template<typename Expr, typename State, typename Data>
+      struct impl<Expr &, State, Data>
+      : Cases::template case_<typename Expr::proto_tag>::template impl<Expr &, State, Data>
+      {};
     };
 
     /// \brief For forcing exact matches of terminal types.
@@ -901,8 +949,8 @@
 
     /// INTERNAL ONLY
     ///
-    template<typename Cases>
-    struct is_callable<switch_<Cases> >
+    template<typename Cases, typename Transform>
+    struct is_callable<switch_<Cases,Transform> >
       : mpl::true_
     {};
 
Index: libs/proto/test/Jamfile.v2
===================================================================
--- libs/proto/test/Jamfile.v2	(revision 74374)
+++ libs/proto/test/Jamfile.v2	(working copy)
@@ -31,6 +31,7 @@
         [ run make_expr.cpp ]
         [ run matches.cpp ]
         [ run flatten.cpp ]
+        [ run new_switch.cpp ]
         [ run toy_spirit.cpp ]
         [ run toy_spirit2.cpp ]
         [ run make.cpp ]