diff --git a/src/libserialize/json.rs b/src/libserialize/json.rs
index 7919ac0eff16..37bd11ba59f4 100644
--- a/src/libserialize/json.rs
+++ b/src/libserialize/json.rs
@@ -458,17 +458,19 @@ impl<'a> ::Encoder<io::IoError> for Encoder<'a> {
         escape_str(self.writer, v)
     }
 
-    fn emit_enum(&mut self,
-                 _name: &str,
-                 f: |&mut Encoder<'a>| -> EncodeResult) -> EncodeResult {
+    fn emit_enum<F>(&mut self, _name: &str, f: F) -> EncodeResult where
+        F: FnOnce(&mut Encoder<'a>) -> EncodeResult,
+    {
         f(self)
     }
 
-    fn emit_enum_variant(&mut self,
-                         name: &str,
-                         _id: uint,
-                         cnt: uint,
-                         f: |&mut Encoder<'a>| -> EncodeResult) -> EncodeResult {
+    fn emit_enum_variant<F>(&mut self,
+                            name: &str,
+                            _id: uint,
+                            cnt: uint,
+                            f: F) -> EncodeResult where
+        F: FnOnce(&mut Encoder<'a>) -> EncodeResult,
+    {
         // enums are encoded as strings or objects
         // Bunny => "Bunny"
         // Kangaroo(34,"William") => {"variant": "Kangaroo", "fields": [34,"William"]}
@@ -483,100 +485,113 @@ impl<'a> ::Encoder<io::IoError> for Encoder<'a> {
         }
     }
 
-    fn emit_enum_variant_arg(&mut self,
-                             idx: uint,
-                             f: |&mut Encoder<'a>| -> EncodeResult) -> EncodeResult {
+    fn emit_enum_variant_arg<F>(&mut self, idx: uint, f: F) -> EncodeResult where
+        F: FnOnce(&mut Encoder<'a>) -> EncodeResult,
+    {
         if idx != 0 {
             try!(write!(self.writer, ","));
         }
         f(self)
     }
 
-    fn emit_enum_struct_variant(&mut self,
-                                name: &str,
-                                id: uint,
-                                cnt: uint,
-                                f: |&mut Encoder<'a>| -> EncodeResult) -> EncodeResult {
+    fn emit_enum_struct_variant<F>(&mut self,
+                                   name: &str,
+                                   id: uint,
+                                   cnt: uint,
+                                   f: F) -> EncodeResult where
+        F: FnOnce(&mut Encoder<'a>) -> EncodeResult,
+    {
         self.emit_enum_variant(name, id, cnt, f)
     }
 
-    fn emit_enum_struct_variant_field(&mut self,
-                                      _: &str,
-                                      idx: uint,
-                                      f: |&mut Encoder<'a>| -> EncodeResult) -> EncodeResult {
+    fn emit_enum_struct_variant_field<F>(&mut self,
+                                         _: &str,
+                                         idx: uint,
+                                         f: F) -> EncodeResult where
+        F: FnOnce(&mut Encoder<'a>) -> EncodeResult,
+    {
         self.emit_enum_variant_arg(idx, f)
     }
 
-    fn emit_struct(&mut self,
-                   _: &str,
-                   _: uint,
-                   f: |&mut Encoder<'a>| -> EncodeResult) -> EncodeResult {
+    fn emit_struct<F>(&mut self, _: &str, _: uint, f: F) -> EncodeResult where
+        F: FnOnce(&mut Encoder<'a>) -> EncodeResult,
+    {
         try!(write!(self.writer, "{{"));
         try!(f(self));
         write!(self.writer, "}}")
     }
 
-    fn emit_struct_field(&mut self,
-                         name: &str,
-                         idx: uint,
-                         f: |&mut Encoder<'a>| -> EncodeResult) -> EncodeResult {
+    fn emit_struct_field<F>(&mut self, name: &str, idx: uint, f: F) -> EncodeResult where
+        F: FnOnce(&mut Encoder<'a>) -> EncodeResult,
+    {
         if idx != 0 { try!(write!(self.writer, ",")); }
         try!(escape_str(self.writer, name));
         try!(write!(self.writer, ":"));
         f(self)
     }
 
-    fn emit_tuple(&mut self, len: uint, f: |&mut Encoder<'a>| -> EncodeResult) -> EncodeResult {
+    fn emit_tuple<F>(&mut self, len: uint, f: F) -> EncodeResult where
+        F: FnOnce(&mut Encoder<'a>) -> EncodeResult,
+    {
         self.emit_seq(len, f)
     }
-    fn emit_tuple_arg(&mut self,
-                      idx: uint,
-                      f: |&mut Encoder<'a>| -> EncodeResult) -> EncodeResult {
+    fn emit_tuple_arg<F>(&mut self, idx: uint, f: F) -> EncodeResult where
+        F: FnOnce(&mut Encoder<'a>) -> EncodeResult,
+    {
         self.emit_seq_elt(idx, f)
     }
 
-    fn emit_tuple_struct(&mut self,
-                         _name: &str,
-                         len: uint,
-                         f: |&mut Encoder<'a>| -> EncodeResult) -> EncodeResult {
+    fn emit_tuple_struct<F>(&mut self, _name: &str, len: uint, f: F) -> EncodeResult where
+        F: FnOnce(&mut Encoder<'a>) -> EncodeResult,
+    {
         self.emit_seq(len, f)
     }
-    fn emit_tuple_struct_arg(&mut self,
-                             idx: uint,
-                             f: |&mut Encoder<'a>| -> EncodeResult) -> EncodeResult {
+    fn emit_tuple_struct_arg<F>(&mut self, idx: uint, f: F) -> EncodeResult where
+        F: FnOnce(&mut Encoder<'a>) -> EncodeResult,
+    {
         self.emit_seq_elt(idx, f)
     }
 
-    fn emit_option(&mut self, f: |&mut Encoder<'a>| -> EncodeResult) -> EncodeResult {
+    fn emit_option<F>(&mut self, f: F) -> EncodeResult where
+        F: FnOnce(&mut Encoder<'a>) -> EncodeResult,
+    {
         f(self)
     }
     fn emit_option_none(&mut self) -> EncodeResult { self.emit_nil() }
-    fn emit_option_some(&mut self, f: |&mut Encoder<'a>| -> EncodeResult) -> EncodeResult {
+    fn emit_option_some<F>(&mut self, f: F) -> EncodeResult where
+        F: FnOnce(&mut Encoder<'a>) -> EncodeResult,
+    {
         f(self)
     }
 
-    fn emit_seq(&mut self, _len: uint, f: |&mut Encoder<'a>| -> EncodeResult) -> EncodeResult {
+    fn emit_seq<F>(&mut self, _len: uint, f: F) -> EncodeResult where
+        F: FnOnce(&mut Encoder<'a>) -> EncodeResult,
+    {
         try!(write!(self.writer, "["));
         try!(f(self));
         write!(self.writer, "]")
     }
 
-    fn emit_seq_elt(&mut self, idx: uint, f: |&mut Encoder<'a>| -> EncodeResult) -> EncodeResult {
+    fn emit_seq_elt<F>(&mut self, idx: uint, f: F) -> EncodeResult where
+        F: FnOnce(&mut Encoder<'a>) -> EncodeResult,
+    {
         if idx != 0 {
             try!(write!(self.writer, ","));
         }
         f(self)
     }
 
-    fn emit_map(&mut self, _len: uint, f: |&mut Encoder<'a>| -> EncodeResult) -> EncodeResult {
+    fn emit_map<F>(&mut self, _len: uint, f: F) -> EncodeResult where
+        F: FnOnce(&mut Encoder<'a>) -> EncodeResult,
+    {
         try!(write!(self.writer, "{{"));
         try!(f(self));
         write!(self.writer, "}}")
     }
 
-    fn emit_map_elt_key(&mut self,
-                        idx: uint,
-                        f: |&mut Encoder<'a>| -> EncodeResult) -> EncodeResult {
+    fn emit_map_elt_key<F>(&mut self, idx: uint, mut f: F) -> EncodeResult where
+        F: FnMut(&mut Encoder<'a>) -> EncodeResult,
+    {
         if idx != 0 { try!(write!(self.writer, ",")) }
         // ref #12967, make sure to wrap a key in double quotes,
         // in the event that its of a type that omits them (eg numbers)
@@ -594,9 +609,9 @@ impl<'a> ::Encoder<io::IoError> for Encoder<'a> {
         Ok(())
     }
 
-    fn emit_map_elt_val(&mut self,
-                        _idx: uint,
-                        f: |&mut Encoder<'a>| -> EncodeResult) -> EncodeResult {
+    fn emit_map_elt_val<F>(&mut self, _idx: uint, f: F) -> EncodeResult where
+        F: FnOnce(&mut Encoder<'a>) -> EncodeResult,
+    {
         try!(write!(self.writer, ":"));
         f(self)
     }
@@ -663,17 +678,20 @@ impl<'a> ::Encoder<io::IoError> for PrettyEncoder<'a> {
         escape_str(self.writer, v)
     }
 
-    fn emit_enum(&mut self,
-                 _name: &str,
-                 f: |&mut PrettyEncoder<'a>| -> EncodeResult) -> EncodeResult {
+    fn emit_enum<F>(&mut self, _name: &str, f: F) -> EncodeResult where
+        F: FnOnce(&mut PrettyEncoder<'a>) -> EncodeResult,
+    {
         f(self)
     }
 
-    fn emit_enum_variant(&mut self,
-                         name: &str,
-                         _id: uint,
-                         cnt: uint,
-                         f: |&mut PrettyEncoder<'a>| -> EncodeResult) -> EncodeResult {
+    fn emit_enum_variant<F>(&mut self,
+                            name: &str,
+                            _id: uint,
+                            cnt: uint,
+                            f: F)
+                            -> EncodeResult where
+        F: FnOnce(&mut PrettyEncoder<'a>) -> EncodeResult,
+    {
         if cnt == 0 {
             escape_str(self.writer, name)
         } else {
@@ -697,9 +715,9 @@ impl<'a> ::Encoder<io::IoError> for PrettyEncoder<'a> {
         }
     }
 
-    fn emit_enum_variant_arg(&mut self,
-                             idx: uint,
-                             f: |&mut PrettyEncoder<'a>| -> EncodeResult) -> EncodeResult {
+    fn emit_enum_variant_arg<F>(&mut self, idx: uint, f: F) -> EncodeResult where
+        F: FnOnce(&mut PrettyEncoder<'a>) -> EncodeResult,
+    {
         if idx != 0 {
             try!(write!(self.writer, ",\n"));
         }
@@ -707,26 +725,29 @@ impl<'a> ::Encoder<io::IoError> for PrettyEncoder<'a> {
         f(self)
     }
 
-    fn emit_enum_struct_variant(&mut self,
-                                name: &str,
-                                id: uint,
-                                cnt: uint,
-                                f: |&mut PrettyEncoder<'a>| -> EncodeResult) -> EncodeResult {
+    fn emit_enum_struct_variant<F>(&mut self,
+                                   name: &str,
+                                   id: uint,
+                                   cnt: uint,
+                                   f: F) -> EncodeResult where
+        F: FnOnce(&mut PrettyEncoder<'a>) -> EncodeResult,
+    {
         self.emit_enum_variant(name, id, cnt, f)
     }
 
-    fn emit_enum_struct_variant_field(&mut self,
-                                      _: &str,
-                                      idx: uint,
-                                      f: |&mut PrettyEncoder<'a>| -> EncodeResult) -> EncodeResult {
+    fn emit_enum_struct_variant_field<F>(&mut self,
+                                         _: &str,
+                                         idx: uint,
+                                         f: F) -> EncodeResult where
+        F: FnOnce(&mut PrettyEncoder<'a>) -> EncodeResult,
+    {
         self.emit_enum_variant_arg(idx, f)
     }
 
 
-    fn emit_struct(&mut self,
-                   _: &str,
-                   len: uint,
-                   f: |&mut PrettyEncoder<'a>| -> EncodeResult) -> EncodeResult {
+    fn emit_struct<F>(&mut self, _: &str, len: uint, f: F) -> EncodeResult where
+        F: FnOnce(&mut PrettyEncoder<'a>) -> EncodeResult,
+    {
         if len == 0 {
             write!(self.writer, "{{}}")
         } else {
@@ -740,10 +761,9 @@ impl<'a> ::Encoder<io::IoError> for PrettyEncoder<'a> {
         }
     }
 
-    fn emit_struct_field(&mut self,
-                         name: &str,
-                         idx: uint,
-                         f: |&mut PrettyEncoder<'a>| -> EncodeResult) -> EncodeResult {
+    fn emit_struct_field<F>(&mut self, name: &str, idx: uint, f: F) -> EncodeResult where
+        F: FnOnce(&mut PrettyEncoder<'a>) -> EncodeResult,
+    {
         if idx == 0 {
             try!(write!(self.writer, "\n"));
         } else {
@@ -755,40 +775,43 @@ impl<'a> ::Encoder<io::IoError> for PrettyEncoder<'a> {
         f(self)
     }
 
-    fn emit_tuple(&mut self,
-                  len: uint,
-                  f: |&mut PrettyEncoder<'a>| -> EncodeResult) -> EncodeResult {
+    fn emit_tuple<F>(&mut self, len: uint, f: F) -> EncodeResult where
+        F: FnOnce(&mut PrettyEncoder<'a>) -> EncodeResult,
+    {
         self.emit_seq(len, f)
     }
-    fn emit_tuple_arg(&mut self,
-                      idx: uint,
-                      f: |&mut PrettyEncoder<'a>| -> EncodeResult) -> EncodeResult {
+    fn emit_tuple_arg<F>(&mut self, idx: uint, f: F) -> EncodeResult where
+        F: FnOnce(&mut PrettyEncoder<'a>) -> EncodeResult,
+    {
         self.emit_seq_elt(idx, f)
     }
 
-    fn emit_tuple_struct(&mut self,
-                         _: &str,
-                         len: uint,
-                         f: |&mut PrettyEncoder<'a>| -> EncodeResult) -> EncodeResult {
+    fn emit_tuple_struct<F>(&mut self, _: &str, len: uint, f: F) -> EncodeResult where
+        F: FnOnce(&mut PrettyEncoder<'a>) -> EncodeResult,
+    {
         self.emit_seq(len, f)
     }
-    fn emit_tuple_struct_arg(&mut self,
-                             idx: uint,
-                             f: |&mut PrettyEncoder<'a>| -> EncodeResult) -> EncodeResult {
+    fn emit_tuple_struct_arg<F>(&mut self, idx: uint, f: F) -> EncodeResult where
+        F: FnOnce(&mut PrettyEncoder<'a>) -> EncodeResult,
+    {
         self.emit_seq_elt(idx, f)
     }
 
-    fn emit_option(&mut self, f: |&mut PrettyEncoder<'a>| -> EncodeResult) -> EncodeResult {
+    fn emit_option<F>(&mut self, f: F) -> EncodeResult where
+        F: FnOnce(&mut PrettyEncoder<'a>) -> EncodeResult,
+    {
         f(self)
     }
     fn emit_option_none(&mut self) -> EncodeResult { self.emit_nil() }
-    fn emit_option_some(&mut self, f: |&mut PrettyEncoder<'a>| -> EncodeResult) -> EncodeResult {
+    fn emit_option_some<F>(&mut self, f: F) -> EncodeResult where
+        F: FnOnce(&mut PrettyEncoder<'a>) -> EncodeResult,
+    {
         f(self)
     }
 
-    fn emit_seq(&mut self,
-                len: uint,
-                f: |&mut PrettyEncoder<'a>| -> EncodeResult) -> EncodeResult {
+    fn emit_seq<F>(&mut self, len: uint, f: F) -> EncodeResult where
+        F: FnOnce(&mut PrettyEncoder<'a>) -> EncodeResult,
+    {
         if len == 0 {
             write!(self.writer, "[]")
         } else {
@@ -802,9 +825,9 @@ impl<'a> ::Encoder<io::IoError> for PrettyEncoder<'a> {
         }
     }
 
-    fn emit_seq_elt(&mut self,
-                    idx: uint,
-                    f: |&mut PrettyEncoder<'a>| -> EncodeResult) -> EncodeResult {
+    fn emit_seq_elt<F>(&mut self, idx: uint, f: F) -> EncodeResult where
+        F: FnOnce(&mut PrettyEncoder<'a>) -> EncodeResult,
+    {
         if idx == 0 {
             try!(write!(self.writer, "\n"));
         } else {
@@ -814,9 +837,9 @@ impl<'a> ::Encoder<io::IoError> for PrettyEncoder<'a> {
         f(self)
     }
 
-    fn emit_map(&mut self,
-                len: uint,
-                f: |&mut PrettyEncoder<'a>| -> EncodeResult) -> EncodeResult {
+    fn emit_map<F>(&mut self, len: uint, f: F) -> EncodeResult where
+        F: FnOnce(&mut PrettyEncoder<'a>) -> EncodeResult,
+    {
         if len == 0 {
             write!(self.writer, "{{}}")
         } else {
@@ -830,9 +853,9 @@ impl<'a> ::Encoder<io::IoError> for PrettyEncoder<'a> {
         }
     }
 
-    fn emit_map_elt_key(&mut self,
-                        idx: uint,
-                        f: |&mut PrettyEncoder<'a>| -> EncodeResult) -> EncodeResult {
+    fn emit_map_elt_key<F>(&mut self, idx: uint, mut f: F) -> EncodeResult where
+        F: FnMut(&mut PrettyEncoder<'a>) -> EncodeResult,
+    {
         if idx == 0 {
             try!(write!(self.writer, "\n"));
         } else {
@@ -855,9 +878,9 @@ impl<'a> ::Encoder<io::IoError> for PrettyEncoder<'a> {
         Ok(())
     }
 
-    fn emit_map_elt_val(&mut self,
-                        _idx: uint,
-                        f: |&mut PrettyEncoder<'a>| -> EncodeResult) -> EncodeResult {
+    fn emit_map_elt_val<F>(&mut self, _idx: uint, f: F) -> EncodeResult where
+        F: FnOnce(&mut PrettyEncoder<'a>) -> EncodeResult,
+    {
         try!(write!(self.writer, ": "));
         f(self)
     }
@@ -2052,17 +2075,16 @@ impl ::Decoder<DecoderError> for Decoder {
         expect!(self.pop(), String)
     }
 
-    fn read_enum<T>(&mut self,
-                    name: &str,
-                    f: |&mut Decoder| -> DecodeResult<T>) -> DecodeResult<T> {
+    fn read_enum<T, F>(&mut self, name: &str, f: F) -> DecodeResult<T> where
+        F: FnOnce(&mut Decoder) -> DecodeResult<T>,
+    {
         debug!("read_enum({})", name);
         f(self)
     }
 
-    fn read_enum_variant<T>(&mut self,
-                            names: &[&str],
-                            f: |&mut Decoder, uint| -> DecodeResult<T>)
-                            -> DecodeResult<T> {
+    fn read_enum_variant<T, F>(&mut self, names: &[&str], f: F) -> DecodeResult<T> where
+        F: FnOnce(&mut Decoder, uint) -> DecodeResult<T>,
+    {
         debug!("read_enum_variant(names={})", names);
         let name = match self.pop() {
             Json::String(s) => s,
@@ -2103,46 +2125,48 @@ impl ::Decoder<DecoderError> for Decoder {
         f(self, idx)
     }
 
-    fn read_enum_variant_arg<T>(&mut self, idx: uint, f: |&mut Decoder| -> DecodeResult<T>)
-                                -> DecodeResult<T> {
+    fn read_enum_variant_arg<T, F>(&mut self, idx: uint, f: F) -> DecodeResult<T> where
+        F: FnOnce(&mut Decoder) -> DecodeResult<T>,
+    {
         debug!("read_enum_variant_arg(idx={})", idx);
         f(self)
     }
 
-    fn read_enum_struct_variant<T>(&mut self,
-                                   names: &[&str],
-                                   f: |&mut Decoder, uint| -> DecodeResult<T>)
-                                   -> DecodeResult<T> {
+    fn read_enum_struct_variant<T, F>(&mut self, names: &[&str], f: F) -> DecodeResult<T> where
+        F: FnOnce(&mut Decoder, uint) -> DecodeResult<T>,
+    {
         debug!("read_enum_struct_variant(names={})", names);
         self.read_enum_variant(names, f)
     }
 
 
-    fn read_enum_struct_variant_field<T>(&mut self,
+    fn read_enum_struct_variant_field<T, F>(&mut self,
                                          name: &str,
                                          idx: uint,
-                                         f: |&mut Decoder| -> DecodeResult<T>)
-                                         -> DecodeResult<T> {
+                                         f: F)
+                                         -> DecodeResult<T> where
+        F: FnOnce(&mut Decoder) -> DecodeResult<T>,
+    {
         debug!("read_enum_struct_variant_field(name={}, idx={})", name, idx);
         self.read_enum_variant_arg(idx, f)
     }
 
-    fn read_struct<T>(&mut self,
-                      name: &str,
-                      len: uint,
-                      f: |&mut Decoder| -> DecodeResult<T>)
-                      -> DecodeResult<T> {
+    fn read_struct<T, F>(&mut self, name: &str, len: uint, f: F) -> DecodeResult<T> where
+        F: FnOnce(&mut Decoder) -> DecodeResult<T>,
+    {
         debug!("read_struct(name={}, len={})", name, len);
         let value = try!(f(self));
         self.pop();
         Ok(value)
     }
 
-    fn read_struct_field<T>(&mut self,
-                            name: &str,
-                            idx: uint,
-                            f: |&mut Decoder| -> DecodeResult<T>)
-                            -> DecodeResult<T> {
+    fn read_struct_field<T, F>(&mut self,
+                               name: &str,
+                               idx: uint,
+                               f: F)
+                               -> DecodeResult<T> where
+        F: FnOnce(&mut Decoder) -> DecodeResult<T>,
+    {
         debug!("read_struct_field(name={}, idx={})", name, idx);
         let mut obj = try!(expect!(self.pop(), Object));
 
@@ -2165,12 +2189,11 @@ impl ::Decoder<DecoderError> for Decoder {
         Ok(value)
     }
 
-    fn read_tuple<T>(&mut self,
-                     tuple_len: uint,
-                     f: |&mut Decoder| -> DecodeResult<T>)
-                     -> DecodeResult<T> {
+    fn read_tuple<T, F>(&mut self, tuple_len: uint, f: F) -> DecodeResult<T> where
+        F: FnOnce(&mut Decoder) -> DecodeResult<T>,
+    {
         debug!("read_tuple()");
-        self.read_seq(|d, len| {
+        self.read_seq(move |d, len| {
             if len == tuple_len {
                 f(d)
             } else {
@@ -2179,31 +2202,37 @@ impl ::Decoder<DecoderError> for Decoder {
         })
     }
 
-    fn read_tuple_arg<T>(&mut self,
-                         idx: uint,
-                         f: |&mut Decoder| -> DecodeResult<T>) -> DecodeResult<T> {
+    fn read_tuple_arg<T, F>(&mut self, idx: uint, f: F) -> DecodeResult<T> where
+        F: FnOnce(&mut Decoder) -> DecodeResult<T>,
+    {
         debug!("read_tuple_arg(idx={})", idx);
         self.read_seq_elt(idx, f)
     }
 
-    fn read_tuple_struct<T>(&mut self,
-                            name: &str,
-                            len: uint,
-                            f: |&mut Decoder| -> DecodeResult<T>)
-                            -> DecodeResult<T> {
+    fn read_tuple_struct<T, F>(&mut self,
+                               name: &str,
+                               len: uint,
+                               f: F)
+                               -> DecodeResult<T> where
+        F: FnOnce(&mut Decoder) -> DecodeResult<T>,
+    {
         debug!("read_tuple_struct(name={})", name);
         self.read_tuple(len, f)
     }
 
-    fn read_tuple_struct_arg<T>(&mut self,
-                                idx: uint,
-                                f: |&mut Decoder| -> DecodeResult<T>)
-                                -> DecodeResult<T> {
+    fn read_tuple_struct_arg<T, F>(&mut self,
+                                   idx: uint,
+                                   f: F)
+                                   -> DecodeResult<T> where
+        F: FnOnce(&mut Decoder) -> DecodeResult<T>,
+    {
         debug!("read_tuple_struct_arg(idx={})", idx);
         self.read_tuple_arg(idx, f)
     }
 
-    fn read_option<T>(&mut self, f: |&mut Decoder, bool| -> DecodeResult<T>) -> DecodeResult<T> {
+    fn read_option<T, F>(&mut self, f: F) -> DecodeResult<T> where
+        F: FnOnce(&mut Decoder, bool) -> DecodeResult<T>,
+    {
         debug!("read_option()");
         match self.pop() {
             Json::Null => f(self, false),
@@ -2211,7 +2240,9 @@ impl ::Decoder<DecoderError> for Decoder {
         }
     }
 
-    fn read_seq<T>(&mut self, f: |&mut Decoder, uint| -> DecodeResult<T>) -> DecodeResult<T> {
+    fn read_seq<T, F>(&mut self, f: F) -> DecodeResult<T> where
+        F: FnOnce(&mut Decoder, uint) -> DecodeResult<T>,
+    {
         debug!("read_seq()");
         let array = try!(expect!(self.pop(), Array));
         let len = array.len();
@@ -2221,14 +2252,16 @@ impl ::Decoder<DecoderError> for Decoder {
         f(self, len)
     }
 
-    fn read_seq_elt<T>(&mut self,
-                       idx: uint,
-                       f: |&mut Decoder| -> DecodeResult<T>) -> DecodeResult<T> {
+    fn read_seq_elt<T, F>(&mut self, idx: uint, f: F) -> DecodeResult<T> where
+        F: FnOnce(&mut Decoder) -> DecodeResult<T>,
+    {
         debug!("read_seq_elt(idx={})", idx);
         f(self)
     }
 
-    fn read_map<T>(&mut self, f: |&mut Decoder, uint| -> DecodeResult<T>) -> DecodeResult<T> {
+    fn read_map<T, F>(&mut self, f: F) -> DecodeResult<T> where
+        F: FnOnce(&mut Decoder, uint) -> DecodeResult<T>,
+    {
         debug!("read_map()");
         let obj = try!(expect!(self.pop(), Object));
         let len = obj.len();
@@ -2239,14 +2272,16 @@ impl ::Decoder<DecoderError> for Decoder {
         f(self, len)
     }
 
-    fn read_map_elt_key<T>(&mut self, idx: uint, f: |&mut Decoder| -> DecodeResult<T>)
-                           -> DecodeResult<T> {
+    fn read_map_elt_key<T, F>(&mut self, idx: uint, f: F) -> DecodeResult<T> where
+       F: FnOnce(&mut Decoder) -> DecodeResult<T>,
+    {
         debug!("read_map_elt_key(idx={})", idx);
         f(self)
     }
 
-    fn read_map_elt_val<T>(&mut self, idx: uint, f: |&mut Decoder| -> DecodeResult<T>)
-                           -> DecodeResult<T> {
+    fn read_map_elt_val<T, F>(&mut self, idx: uint, f: F) -> DecodeResult<T> where
+       F: FnOnce(&mut Decoder) -> DecodeResult<T>,
+    {
         debug!("read_map_elt_val(idx={})", idx);
         f(self)
     }
diff --git a/src/libserialize/lib.rs b/src/libserialize/lib.rs
index 9711d5c7209b..390b3976562f 100644
--- a/src/libserialize/lib.rs
+++ b/src/libserialize/lib.rs
@@ -24,6 +24,7 @@ Core encoding and decoding interfaces.
        html_playground_url = "http://play.rust-lang.org/")]
 #![allow(unknown_features)]
 #![feature(macro_rules, default_type_params, phase, slicing_syntax, globs)]
+#![feature(unboxed_closures)]
 
 // test harness access
 #[cfg(test)]
diff --git a/src/libserialize/serialize.rs b/src/libserialize/serialize.rs
index 7539a6dc3486..98bd2f6bc930 100644
--- a/src/libserialize/serialize.rs
+++ b/src/libserialize/serialize.rs
@@ -39,58 +39,61 @@ pub trait Encoder<E> {
     fn emit_str(&mut self, v: &str) -> Result<(), E>;
 
     // Compound types:
-    fn emit_enum(&mut self, name: &str, f: |&mut Self| -> Result<(), E>) -> Result<(), E>;
+    fn emit_enum<F>(&mut self, name: &str, f: F) -> Result<(), E> where
+        F: FnOnce(&mut Self) -> Result<(), E>;
 
-    fn emit_enum_variant(&mut self,
-                         v_name: &str,
-                         v_id: uint,
-                         len: uint,
-                         f: |&mut Self| -> Result<(), E>) -> Result<(), E>;
-    fn emit_enum_variant_arg(&mut self,
-                             a_idx: uint,
-                             f: |&mut Self| -> Result<(), E>) -> Result<(), E>;
+    fn emit_enum_variant<F>(&mut self, v_name: &str,
+                            v_id: uint,
+                            len: uint,
+                            f: F) -> Result<(), E> where
+        F: FnOnce(&mut Self) -> Result<(), E>;
+    fn emit_enum_variant_arg<F>(&mut self, a_idx: uint, f: F) -> Result<(), E> where
+        F: FnOnce(&mut Self) -> Result<(), E>;
 
-    fn emit_enum_struct_variant(&mut self,
-                                v_name: &str,
-                                v_id: uint,
-                                len: uint,
-                                f: |&mut Self| -> Result<(), E>) -> Result<(), E>;
-    fn emit_enum_struct_variant_field(&mut self,
-                                      f_name: &str,
-                                      f_idx: uint,
-                                      f: |&mut Self| -> Result<(), E>) -> Result<(), E>;
+    fn emit_enum_struct_variant<F>(&mut self, v_name: &str,
+                                   v_id: uint,
+                                   len: uint,
+                                   f: F) -> Result<(), E> where
+        F: FnOnce(&mut Self) -> Result<(), E>;
+    fn emit_enum_struct_variant_field<F>(&mut self,
+                                         f_name: &str,
+                                         f_idx: uint,
+                                         f: F) -> Result<(), E> where
+        F: FnOnce(&mut Self) -> Result<(), E>;
 
-    fn emit_struct(&mut self,
-                   name: &str,
-                   len: uint,
-                   f: |&mut Self| -> Result<(), E>) -> Result<(), E>;
-    fn emit_struct_field(&mut self,
-                         f_name: &str,
-                         f_idx: uint,
-                         f: |&mut Self| -> Result<(), E>) -> Result<(), E>;
+    fn emit_struct<F>(&mut self, name: &str, len: uint, f: F) -> Result<(), E> where
+        F: FnOnce(&mut Self) -> Result<(), E>;
+    fn emit_struct_field<F>(&mut self, f_name: &str, f_idx: uint, f: F) -> Result<(), E> where
+        F: FnOnce(&mut Self) -> Result<(), E>;
 
-    fn emit_tuple(&mut self, len: uint, f: |&mut Self| -> Result<(), E>) -> Result<(), E>;
-    fn emit_tuple_arg(&mut self, idx: uint, f: |&mut Self| -> Result<(), E>) -> Result<(), E>;
+    fn emit_tuple<F>(&mut self, len: uint, f: F) -> Result<(), E> where
+        F: FnOnce(&mut Self) -> Result<(), E>;
+    fn emit_tuple_arg<F>(&mut self, idx: uint, f: F) -> Result<(), E> where
+        F: FnOnce(&mut Self) -> Result<(), E>;
 
-    fn emit_tuple_struct(&mut self,
-                         name: &str,
-                         len: uint,
-                         f: |&mut Self| -> Result<(), E>) -> Result<(), E>;
-    fn emit_tuple_struct_arg(&mut self,
-                             f_idx: uint,
-                             f: |&mut Self| -> Result<(), E>) -> Result<(), E>;
+    fn emit_tuple_struct<F>(&mut self, name: &str, len: uint, f: F) -> Result<(), E> where
+        F: FnOnce(&mut Self) -> Result<(), E>;
+    fn emit_tuple_struct_arg<F>(&mut self, f_idx: uint, f: F) -> Result<(), E> where
+        F: FnOnce(&mut Self) -> Result<(), E>;
 
     // Specialized types:
-    fn emit_option(&mut self, f: |&mut Self| -> Result<(), E>) -> Result<(), E>;
+    fn emit_option<F>(&mut self, f: F) -> Result<(), E> where
+        F: FnOnce(&mut Self) -> Result<(), E>;
     fn emit_option_none(&mut self) -> Result<(), E>;
-    fn emit_option_some(&mut self, f: |&mut Self| -> Result<(), E>) -> Result<(), E>;
+    fn emit_option_some<F>(&mut self, f: F) -> Result<(), E> where
+        F: FnOnce(&mut Self) -> Result<(), E>;
 
-    fn emit_seq(&mut self, len: uint, f: |this: &mut Self| -> Result<(), E>) -> Result<(), E>;
-    fn emit_seq_elt(&mut self, idx: uint, f: |this: &mut Self| -> Result<(), E>) -> Result<(), E>;
+    fn emit_seq<F>(&mut self, len: uint, f: F) -> Result<(), E> where
+        F: FnOnce(&mut Self) -> Result<(), E>;
+    fn emit_seq_elt<F>(&mut self, idx: uint, f: F) -> Result<(), E> where
+        F: FnOnce(&mut Self) -> Result<(), E>;
 
-    fn emit_map(&mut self, len: uint, f: |&mut Self| -> Result<(), E>) -> Result<(), E>;
-    fn emit_map_elt_key(&mut self, idx: uint, f: |&mut Self| -> Result<(), E>) -> Result<(), E>;
-    fn emit_map_elt_val(&mut self, idx: uint, f: |&mut Self| -> Result<(), E>) -> Result<(), E>;
+    fn emit_map<F>(&mut self, len: uint, f: F) -> Result<(), E> where
+        F: FnOnce(&mut Self) -> Result<(), E>;
+    fn emit_map_elt_key<F>(&mut self, idx: uint, f: F) -> Result<(), E> where
+        F: FnMut(&mut Self) -> Result<(), E>;
+    fn emit_map_elt_val<F>(&mut self, idx: uint, f: F) -> Result<(), E> where
+        F: FnOnce(&mut Self) -> Result<(), E>;
 }
 
 pub trait Decoder<E> {
@@ -113,57 +116,57 @@ pub trait Decoder<E> {
     fn read_str(&mut self) -> Result<String, E>;
 
     // Compound types:
-    fn read_enum<T>(&mut self, name: &str, f: |&mut Self| -> Result<T, E>) -> Result<T, E>;
+    fn read_enum<T, F>(&mut self, name: &str, f: F) -> Result<T, E> where
+        F: FnOnce(&mut Self) -> Result<T, E>;
 
-    fn read_enum_variant<T>(&mut self,
-                            names: &[&str],
-                            f: |&mut Self, uint| -> Result<T, E>)
-                            -> Result<T, E>;
-    fn read_enum_variant_arg<T>(&mut self,
-                                a_idx: uint,
-                                f: |&mut Self| -> Result<T, E>)
-                                -> Result<T, E>;
+    fn read_enum_variant<T, F>(&mut self, names: &[&str], f: F) -> Result<T, E> where
+        F: FnOnce(&mut Self, uint) -> Result<T, E>;
+    fn read_enum_variant_arg<T, F>(&mut self, a_idx: uint, f: F) -> Result<T, E> where
+        F: FnOnce(&mut Self) -> Result<T, E>;
 
-    fn read_enum_struct_variant<T>(&mut self,
-                                   names: &[&str],
-                                   f: |&mut Self, uint| -> Result<T, E>)
-                                   -> Result<T, E>;
-    fn read_enum_struct_variant_field<T>(&mut self,
-                                         &f_name: &str,
-                                         f_idx: uint,
-                                         f: |&mut Self| -> Result<T, E>)
-                                         -> Result<T, E>;
+    fn read_enum_struct_variant<T, F>(&mut self, names: &[&str], f: F) -> Result<T, E> where
+        F: FnOnce(&mut Self, uint) -> Result<T, E>;
+    fn read_enum_struct_variant_field<T, F>(&mut self,
+                                            &f_name: &str,
+                                            f_idx: uint,
+                                            f: F)
+                                            -> Result<T, E> where
+        F: FnOnce(&mut Self) -> Result<T, E>;
 
-    fn read_struct<T>(&mut self, s_name: &str, len: uint, f: |&mut Self| -> Result<T, E>)
-                      -> Result<T, E>;
-    fn read_struct_field<T>(&mut self,
-                            f_name: &str,
-                            f_idx: uint,
-                            f: |&mut Self| -> Result<T, E>)
-                            -> Result<T, E>;
+    fn read_struct<T, F>(&mut self, s_name: &str, len: uint, f: F) -> Result<T, E> where
+        F: FnOnce(&mut Self) -> Result<T, E>;
+    fn read_struct_field<T, F>(&mut self,
+                               f_name: &str,
+                               f_idx: uint,
+                               f: F)
+                               -> Result<T, E> where
+        F: FnOnce(&mut Self) -> Result<T, E>;
 
-    fn read_tuple<T>(&mut self, len: uint, f: |&mut Self| -> Result<T, E>) -> Result<T, E>;
-    fn read_tuple_arg<T>(&mut self, a_idx: uint, f: |&mut Self| -> Result<T, E>) -> Result<T, E>;
+    fn read_tuple<T, F>(&mut self, len: uint, f: F) -> Result<T, E> where
+        F: FnOnce(&mut Self) -> Result<T, E>;
+    fn read_tuple_arg<T, F>(&mut self, a_idx: uint, f: F) -> Result<T, E> where
+        F: FnOnce(&mut Self) -> Result<T, E>;
 
-    fn read_tuple_struct<T>(&mut self,
-                            s_name: &str,
-                            len: uint,
-                            f: |&mut Self| -> Result<T, E>)
-                            -> Result<T, E>;
-    fn read_tuple_struct_arg<T>(&mut self,
-                                a_idx: uint,
-                                f: |&mut Self| -> Result<T, E>)
-                                -> Result<T, E>;
+    fn read_tuple_struct<T, F>(&mut self, s_name: &str, len: uint, f: F) -> Result<T, E> where
+        F: FnOnce(&mut Self) -> Result<T, E>;
+    fn read_tuple_struct_arg<T, F>(&mut self, a_idx: uint, f: F) -> Result<T, E> where
+        F: FnOnce(&mut Self) -> Result<T, E>;
 
     // Specialized types:
-    fn read_option<T>(&mut self, f: |&mut Self, bool| -> Result<T, E>) -> Result<T, E>;
+    fn read_option<T, F>(&mut self, f: F) -> Result<T, E> where
+        F: FnOnce(&mut Self, bool) -> Result<T, E>;
 
-    fn read_seq<T>(&mut self, f: |&mut Self, uint| -> Result<T, E>) -> Result<T, E>;
-    fn read_seq_elt<T>(&mut self, idx: uint, f: |&mut Self| -> Result<T, E>) -> Result<T, E>;
+    fn read_seq<T, F>(&mut self, f: F) -> Result<T, E> where
+        F: FnOnce(&mut Self, uint) -> Result<T, E>;
+    fn read_seq_elt<T, F>(&mut self, idx: uint, f: F) -> Result<T, E> where
+        F: FnOnce(&mut Self) -> Result<T, E>;
 
-    fn read_map<T>(&mut self, f: |&mut Self, uint| -> Result<T, E>) -> Result<T, E>;
-    fn read_map_elt_key<T>(&mut self, idx: uint, f: |&mut Self| -> Result<T, E>) -> Result<T, E>;
-    fn read_map_elt_val<T>(&mut self, idx: uint, f: |&mut Self| -> Result<T, E>) -> Result<T, E>;
+    fn read_map<T, F>(&mut self, f: F) -> Result<T, E> where
+        F: FnOnce(&mut Self, uint) -> Result<T, E>;
+    fn read_map_elt_key<T, F>(&mut self, idx: uint, f: F) -> Result<T, E> where
+        F: FnOnce(&mut Self) -> Result<T, E>;
+    fn read_map_elt_val<T, F>(&mut self, idx: uint, f: F) -> Result<T, E> where
+        F: FnOnce(&mut Self) -> Result<T, E>;
 
     // Failure
     fn error(&mut self, err: &str) -> E;
@@ -585,13 +588,14 @@ impl<E, D:Decoder<E>,T:Decodable<D, E>+Send+Sync> Decodable<D, E> for Arc<T> {
 // Helper routines
 
 pub trait EncoderHelpers<E> {
-    fn emit_from_vec<T>(&mut self,
-                        v: &[T],
-                        f: |&mut Self, v: &T| -> Result<(), E>) -> Result<(), E>;
+    fn emit_from_vec<T, F>(&mut self, v: &[T], f: F) -> Result<(), E> where
+        F: FnMut(&mut Self, &T) -> Result<(), E>;
 }
 
 impl<E, S:Encoder<E>> EncoderHelpers<E> for S {
-    fn emit_from_vec<T>(&mut self, v: &[T], f: |&mut S, &T| -> Result<(), E>) -> Result<(), E> {
+    fn emit_from_vec<T, F>(&mut self, v: &[T], mut f: F) -> Result<(), E> where
+        F: FnMut(&mut S, &T) -> Result<(), E>,
+    {
         self.emit_seq(v.len(), |this| {
             for (i, e) in v.iter().enumerate() {
                 try!(this.emit_seq_elt(i, |this| {
@@ -604,11 +608,14 @@ impl<E, S:Encoder<E>> EncoderHelpers<E> for S {
 }
 
 pub trait DecoderHelpers<E> {
-    fn read_to_vec<T>(&mut self, f: |&mut Self| -> Result<T, E>) -> Result<Vec<T>, E>;
+    fn read_to_vec<T, F>(&mut self, f: F) -> Result<Vec<T>, E> where
+        F: FnMut(&mut Self) -> Result<T, E>;
 }
 
 impl<E, D:Decoder<E>> DecoderHelpers<E> for D {
-    fn read_to_vec<T>(&mut self, f: |&mut D| -> Result<T, E>) -> Result<Vec<T>, E> {
+    fn read_to_vec<T, F>(&mut self, mut f: F) -> Result<Vec<T>, E> where F:
+        FnMut(&mut D) -> Result<T, E>,
+    {
         self.read_seq(|this, len| {
             let mut v = Vec::with_capacity(len);
             for i in range(0, len) {