diff --git a/src/libstd/char.rs b/src/libstd/char.rs
index 8f0870af513..101ea67cf59 100644
--- a/src/libstd/char.rs
+++ b/src/libstd/char.rs
@@ -12,12 +12,11 @@
 
 use container::Container;
 use option::{None, Option, Some};
-use str;
-use str::{StrSlice, OwnedStr};
-use u32;
-use uint;
+use str::StrSlice;
 use unicode::{derived_property, general_category};
 
+#[cfg(test)] use str::OwnedStr;
+
 #[cfg(not(test))] use cmp::{Eq, Ord};
 #[cfg(not(test))] use num::Zero;
 
@@ -202,21 +201,21 @@ pub fn from_digit(num: uint, radix: uint) -> Option<char> {
 /// - chars in [0x100,0xffff] get 4-digit escapes: `\\uNNNN`
 /// - chars above 0x10000 get 8-digit escapes: `\\UNNNNNNNN`
 ///
-pub fn escape_unicode(c: char) -> ~str {
-    let s = u32::to_str_radix(c as u32, 16u);
-    let (c, pad) = cond!(
-        (c <= '\xff')   { ('x', 2u) }
-        (c <= '\uffff') { ('u', 4u) }
-        _               { ('U', 8u) }
+pub fn escape_unicode(c: char, f: &fn(char)) {
+    // avoid calling str::to_str_radix because we don't really need to allocate
+    // here.
+    f('\\');
+    let pad = cond!(
+        (c <= '\xff')   { f('x'); 2 }
+        (c <= '\uffff') { f('u'); 4 }
+        _               { f('U'); 8 }
     );
-    assert!(s.len() <= pad);
-    let mut out = ~"\\";
-    out.push_str(str::from_char(c));
-    for uint::range(s.len(), pad) |_| {
-        out.push_str("0");
+    for int::range_step(4 * (pad - 1), -1, -4) |offset| {
+        match ((c as u32) >> offset) & 0xf {
+            i @ 0 .. 9 => { f('0' + i as char); }
+            i => { f('a' + (i - 10) as char); }
+        }
     }
-    out.push_str(s);
-    out
 }
 
 ///
@@ -231,16 +230,16 @@ pub fn escape_unicode(c: char) -> ~str {
 /// - Any other chars in the range [0x20,0x7e] are not escaped.
 /// - Any other chars are given hex unicode escapes; see `escape_unicode`.
 ///
-pub fn escape_default(c: char) -> ~str {
+pub fn escape_default(c: char, f: &fn(char)) {
     match c {
-        '\t' => ~"\\t",
-        '\r' => ~"\\r",
-        '\n' => ~"\\n",
-        '\\' => ~"\\\\",
-        '\'' => ~"\\'",
-        '"'  => ~"\\\"",
-        '\x20' .. '\x7e' => str::from_char(c),
-        _ => c.escape_unicode(),
+        '\t' => { f('\\'); f('t'); }
+        '\r' => { f('\\'); f('r'); }
+        '\n' => { f('\\'); f('n'); }
+        '\\' => { f('\\'); f('\\'); }
+        '\'' => { f('\\'); f('\''); }
+        '"'  => { f('\\'); f('"'); }
+        '\x20' .. '\x7e' => { f(c); }
+        _ => c.escape_unicode(f),
     }
 }
 
@@ -274,8 +273,8 @@ pub trait Char {
     fn is_digit_radix(&self, radix: uint) -> bool;
     fn to_digit(&self, radix: uint) -> Option<uint>;
     fn from_digit(num: uint, radix: uint) -> Option<char>;
-    fn escape_unicode(&self) -> ~str;
-    fn escape_default(&self) -> ~str;
+    fn escape_unicode(&self, f: &fn(char));
+    fn escape_default(&self, f: &fn(char));
     fn len_utf8_bytes(&self) -> uint;
 }
 
@@ -302,9 +301,9 @@ impl Char for char {
 
     fn from_digit(num: uint, radix: uint) -> Option<char> { from_digit(num, radix) }
 
-    fn escape_unicode(&self) -> ~str { escape_unicode(*self) }
+    fn escape_unicode(&self, f: &fn(char)) { escape_unicode(*self, f) }
 
-    fn escape_default(&self) -> ~str { escape_default(*self) }
+    fn escape_default(&self, f: &fn(char)) { escape_default(*self, f) }
 
     fn len_utf8_bytes(&self) -> uint { len_utf8_bytes(*self) }
 }
@@ -392,27 +391,37 @@ fn test_is_digit() {
 
 #[test]
 fn test_escape_default() {
-    assert_eq!('\n'.escape_default(), ~"\\n");
-    assert_eq!('\r'.escape_default(), ~"\\r");
-    assert_eq!('\''.escape_default(), ~"\\'");
-    assert_eq!('"'.escape_default(), ~"\\\"");
-    assert_eq!(' '.escape_default(), ~" ");
-    assert_eq!('a'.escape_default(), ~"a");
-    assert_eq!('~'.escape_default(), ~"~");
-    assert_eq!('\x00'.escape_default(), ~"\\x00");
-    assert_eq!('\x1f'.escape_default(), ~"\\x1f");
-    assert_eq!('\x7f'.escape_default(), ~"\\x7f");
-    assert_eq!('\xff'.escape_default(), ~"\\xff");
-    assert_eq!('\u011b'.escape_default(), ~"\\u011b");
-    assert_eq!('\U0001d4b6'.escape_default(), ~"\\U0001d4b6");
+    fn string(c: char) -> ~str {
+        let mut result = ~"";
+        do escape_default(c) |c| { result.push_char(c); }
+        return result;
+    }
+    assert_eq!(string('\n'), ~"\\n");
+    assert_eq!(string('\r'), ~"\\r");
+    assert_eq!(string('\''), ~"\\'");
+    assert_eq!(string('"'), ~"\\\"");
+    assert_eq!(string(' '), ~" ");
+    assert_eq!(string('a'), ~"a");
+    assert_eq!(string('~'), ~"~");
+    assert_eq!(string('\x00'), ~"\\x00");
+    assert_eq!(string('\x1f'), ~"\\x1f");
+    assert_eq!(string('\x7f'), ~"\\x7f");
+    assert_eq!(string('\xff'), ~"\\xff");
+    assert_eq!(string('\u011b'), ~"\\u011b");
+    assert_eq!(string('\U0001d4b6'), ~"\\U0001d4b6");
 }
 
 #[test]
 fn test_escape_unicode() {
-    assert_eq!('\x00'.escape_unicode(), ~"\\x00");
-    assert_eq!('\n'.escape_unicode(), ~"\\x0a");
-    assert_eq!(' '.escape_unicode(), ~"\\x20");
-    assert_eq!('a'.escape_unicode(), ~"\\x61");
-    assert_eq!('\u011b'.escape_unicode(), ~"\\u011b");
-    assert_eq!('\U0001d4b6'.escape_unicode(), ~"\\U0001d4b6");
+    fn string(c: char) -> ~str {
+        let mut result = ~"";
+        do escape_unicode(c) |c| { result.push_char(c); }
+        return result;
+    }
+    assert_eq!(string('\x00'), ~"\\x00");
+    assert_eq!(string('\n'), ~"\\x0a");
+    assert_eq!(string(' '), ~"\\x20");
+    assert_eq!(string('a'), ~"\\x61");
+    assert_eq!(string('\u011b'), ~"\\u011b");
+    assert_eq!(string('\U0001d4b6'), ~"\\U0001d4b6");
 }
diff --git a/src/libstd/repr.rs b/src/libstd/repr.rs
index f39b5a00ed0..a96949d84c9 100644
--- a/src/libstd/repr.rs
+++ b/src/libstd/repr.rs
@@ -57,9 +57,9 @@ impl EscapedCharWriter for @Writer {
             '"' => self.write_str("\\\""),
             '\x20'..'\x7e' => self.write_char(ch),
             _ => {
-                // FIXME #4423: This is inefficient because it requires a
-                // malloc.
-                self.write_str(char::escape_unicode(ch))
+                do char::escape_unicode(ch) |c| {
+                    self.write_char(c);
+                }
             }
         }
     }
diff --git a/src/libsyntax/parse/token.rs b/src/libsyntax/parse/token.rs
index 94147825da4..a50fa416832 100644
--- a/src/libsyntax/parse/token.rs
+++ b/src/libsyntax/parse/token.rs
@@ -16,7 +16,6 @@ use util::interner::StrInterner;
 use util::interner;
 
 use std::cast;
-use std::char;
 use std::cmp::Equiv;
 use std::local_data;
 use std::rand;
@@ -166,7 +165,12 @@ pub fn to_str(in: @ident_interner, t: &Token) -> ~str {
 
       /* Literals */
       LIT_INT(c, ast::ty_char) => {
-        ~"'" + char::escape_default(c as char) + "'"
+          let mut res = ~"'";
+          do (c as char).escape_default |c| {
+              res.push_char(c);
+          }
+          res.push_char('\'');
+          res
       }
       LIT_INT(i, t) => {
           i.to_str() + ast_util::int_ty_to_str(t)
diff --git a/src/libsyntax/print/pprust.rs b/src/libsyntax/print/pprust.rs
index 978561eaa67..5e685d85f95 100644
--- a/src/libsyntax/print/pprust.rs
+++ b/src/libsyntax/print/pprust.rs
@@ -27,7 +27,6 @@ use print::pp::{breaks, consistent, inconsistent, eof};
 use print::pp;
 use print::pprust;
 
-use std::char;
 use std::io;
 use std::u64;
 use std::uint;
@@ -2016,7 +2015,12 @@ pub fn print_literal(s: @ps, lit: @ast::lit) {
     match lit.node {
       ast::lit_str(st) => print_string(s, st),
       ast::lit_int(ch, ast::ty_char) => {
-        word(s.s, ~"'" + char::escape_default(ch as char) + "'");
+          let mut res = ~"'";
+          do (ch as char).escape_default |c| {
+              res.push_char(c);
+          }
+          res.push_char('\'');
+          word(s.s, res);
       }
       ast::lit_int(i, t) => {
         if i < 0_i64 {