diff --git a/src/libsyntax/ext/base.rs b/src/libsyntax/ext/base.rs
index 2a7f8c8865b..b387694c6c1 100644
--- a/src/libsyntax/ext/base.rs
+++ b/src/libsyntax/ext/base.rs
@@ -202,131 +202,107 @@ pub fn syntax_expander_table() -> SyntaxEnv {
 // One of these is made during expansion and incrementally updated as we go;
 // when a macro expansion occurs, the resulting nodes have the backtrace()
 // -> expn_info of their expansion context stored into their span.
-pub trait ext_ctxt {
-    fn codemap(&self) -> @CodeMap;
-    fn parse_sess(&self) -> @mut parse::ParseSess;
-    fn cfg(&self) -> ast::crate_cfg;
-    fn call_site(&self) -> span;
-    fn print_backtrace(&self);
-    fn backtrace(&self) -> Option<@ExpnInfo>;
-    fn mod_push(&self, mod_name: ast::ident);
-    fn mod_pop(&self);
-    fn mod_path(&self) -> ~[ast::ident];
-    fn bt_push(&self, ei: codemap::ExpnInfo);
-    fn bt_pop(&self);
-    fn span_fatal(&self, sp: span, msg: &str) -> !;
-    fn span_err(&self, sp: span, msg: &str);
-    fn span_warn(&self, sp: span, msg: &str);
-    fn span_unimpl(&self, sp: span, msg: &str) -> !;
-    fn span_bug(&self, sp: span, msg: &str) -> !;
-    fn bug(&self, msg: &str) -> !;
-    fn next_id(&self) -> ast::node_id;
-    fn trace_macros(&self) -> bool;
-    fn set_trace_macros(&self, x: bool);
-    /* for unhygienic identifier transformation */
-    fn str_of(&self, id: ast::ident) -> ~str;
-    fn ident_of(&self, st: &str) -> ast::ident;
+pub struct ext_ctxt {
+    parse_sess: @mut parse::ParseSess,
+    cfg: ast::crate_cfg,
+    backtrace: @mut Option<@ExpnInfo>,
+
+    // These two @mut's should really not be here,
+    // but the self types for CtxtRepr are all wrong
+    // and there are bugs in the code for object
+    // types that make this hard to get right at the
+    // moment. - nmatsakis
+    mod_path: @mut ~[ast::ident],
+    trace_mac: @mut bool
 }
 
-pub fn mk_ctxt(parse_sess: @mut parse::ParseSess, cfg: ast::crate_cfg)
-            -> @ext_ctxt {
-    struct CtxtRepr {
-        parse_sess: @mut parse::ParseSess,
-        cfg: ast::crate_cfg,
-        backtrace: @mut Option<@ExpnInfo>,
-
-        // These two @mut's should really not be here,
-        // but the self types for CtxtRepr are all wrong
-        // and there are bugs in the code for object
-        // types that make this hard to get right at the
-        // moment. - nmatsakis
-        mod_path: @mut ~[ast::ident],
-        trace_mac: @mut bool
-    }
-    impl ext_ctxt for CtxtRepr {
-        fn codemap(&self) -> @CodeMap { self.parse_sess.cm }
-        fn parse_sess(&self) -> @mut parse::ParseSess { self.parse_sess }
-        fn cfg(&self) -> ast::crate_cfg { copy self.cfg }
-        fn call_site(&self) -> span {
-            match *self.backtrace {
-                Some(@ExpandedFrom(CallInfo {call_site: cs, _})) => cs,
-                None => self.bug("missing top span")
-            }
+pub impl ext_ctxt {
+    fn codemap(&self) -> @CodeMap { self.parse_sess.cm }
+    fn parse_sess(&self) -> @mut parse::ParseSess { self.parse_sess }
+    fn cfg(&self) -> ast::crate_cfg { copy self.cfg }
+    fn call_site(&self) -> span {
+        match *self.backtrace {
+            Some(@ExpandedFrom(CallInfo {call_site: cs, _})) => cs,
+            None => self.bug("missing top span")
         }
-        fn print_backtrace(&self) { }
-        fn backtrace(&self) -> Option<@ExpnInfo> { *self.backtrace }
-        fn mod_push(&self, i: ast::ident) { self.mod_path.push(i); }
-        fn mod_pop(&self) { self.mod_path.pop(); }
-        fn mod_path(&self) -> ~[ast::ident] { copy *self.mod_path }
-        fn bt_push(&self, ei: codemap::ExpnInfo) {
-            match ei {
-              ExpandedFrom(CallInfo {call_site: cs, callee: ref callee}) => {
+    }
+    fn print_backtrace(&self) { }
+    fn backtrace(&self) -> Option<@ExpnInfo> { *self.backtrace }
+    fn mod_push(&self, i: ast::ident) { self.mod_path.push(i); }
+    fn mod_pop(&self) { self.mod_path.pop(); }
+    fn mod_path(&self) -> ~[ast::ident] { copy *self.mod_path }
+    fn bt_push(&self, ei: codemap::ExpnInfo) {
+        match ei {
+            ExpandedFrom(CallInfo {call_site: cs, callee: ref callee}) => {
                 *self.backtrace =
                     Some(@ExpandedFrom(CallInfo {
                         call_site: span {lo: cs.lo, hi: cs.hi,
                                          expn_info: *self.backtrace},
                         callee: copy *callee}));
-              }
             }
         }
-        fn bt_pop(&self) {
-            match *self.backtrace {
-              Some(@ExpandedFrom(CallInfo {
-                  call_site: span {expn_info: prev, _}, _
-              })) => {
-                *self.backtrace = prev
-              }
-              _ => self.bug("tried to pop without a push")
-            }
-        }
-        fn span_fatal(&self, sp: span, msg: &str) -> ! {
-            self.print_backtrace();
-            self.parse_sess.span_diagnostic.span_fatal(sp, msg);
-        }
-        fn span_err(&self, sp: span, msg: &str) {
-            self.print_backtrace();
-            self.parse_sess.span_diagnostic.span_err(sp, msg);
-        }
-        fn span_warn(&self, sp: span, msg: &str) {
-            self.print_backtrace();
-            self.parse_sess.span_diagnostic.span_warn(sp, msg);
-        }
-        fn span_unimpl(&self, sp: span, msg: &str) -> ! {
-            self.print_backtrace();
-            self.parse_sess.span_diagnostic.span_unimpl(sp, msg);
-        }
-        fn span_bug(&self, sp: span, msg: &str) -> ! {
-            self.print_backtrace();
-            self.parse_sess.span_diagnostic.span_bug(sp, msg);
-        }
-        fn bug(&self, msg: &str) -> ! {
-            self.print_backtrace();
-            self.parse_sess.span_diagnostic.handler().bug(msg);
-        }
-        fn next_id(&self) -> ast::node_id {
-            return parse::next_node_id(self.parse_sess);
-        }
-        fn trace_macros(&self) -> bool {
-            *self.trace_mac
-        }
-        fn set_trace_macros(&self, x: bool) {
-            *self.trace_mac = x
-        }
-        fn str_of(&self, id: ast::ident) -> ~str {
-            copy *self.parse_sess.interner.get(id)
-        }
-        fn ident_of(&self, st: &str) -> ast::ident {
-            self.parse_sess.interner.intern(st)
-        }
     }
-    let imp: @CtxtRepr = @CtxtRepr {
+    fn bt_pop(&self) {
+        match *self.backtrace {
+            Some(@ExpandedFrom(
+                CallInfo {
+                    call_site: span {expn_info: prev, _}, _
+                })) => {
+                *self.backtrace = prev
+            }
+            _ => self.bug("tried to pop without a push")
+        }
+    }
+    fn span_fatal(&self, sp: span, msg: &str) -> ! {
+        self.print_backtrace();
+        self.parse_sess.span_diagnostic.span_fatal(sp, msg);
+    }
+    fn span_err(&self, sp: span, msg: &str) {
+        self.print_backtrace();
+        self.parse_sess.span_diagnostic.span_err(sp, msg);
+    }
+    fn span_warn(&self, sp: span, msg: &str) {
+        self.print_backtrace();
+        self.parse_sess.span_diagnostic.span_warn(sp, msg);
+    }
+    fn span_unimpl(&self, sp: span, msg: &str) -> ! {
+        self.print_backtrace();
+        self.parse_sess.span_diagnostic.span_unimpl(sp, msg);
+    }
+    fn span_bug(&self, sp: span, msg: &str) -> ! {
+        self.print_backtrace();
+        self.parse_sess.span_diagnostic.span_bug(sp, msg);
+    }
+    fn bug(&self, msg: &str) -> ! {
+        self.print_backtrace();
+        self.parse_sess.span_diagnostic.handler().bug(msg);
+    }
+    fn next_id(&self) -> ast::node_id {
+        parse::next_node_id(self.parse_sess)
+    }
+    fn trace_macros(&self) -> bool {
+        *self.trace_mac
+    }
+    fn set_trace_macros(&self, x: bool) {
+        *self.trace_mac = x
+    }
+    fn str_of(&self, id: ast::ident) -> ~str {
+        copy *self.parse_sess.interner.get(id)
+    }
+    fn ident_of(&self, st: &str) -> ast::ident {
+        self.parse_sess.interner.intern(st)
+    }
+}
+
+pub fn mk_ctxt(parse_sess: @mut parse::ParseSess, cfg: ast::crate_cfg)
+    -> @ext_ctxt {
+    @ext_ctxt {
         parse_sess: parse_sess,
         cfg: cfg,
         backtrace: @mut None,
         mod_path: @mut ~[],
         trace_mac: @mut false
-    };
-    ((imp) as @ext_ctxt)
+    }
 }
 
 pub fn expr_to_str(cx: @ext_ctxt, expr: @ast::expr, err_msg: ~str) -> ~str {