Allow function as replacement argument to String.replaceAll.

runtime/lib/string_base.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 /**
  * [_StringBase] contains common methods used by concrete String
  * implementations, e.g., _OneByteString.
  */
 class _StringBase {
 
@@ skipping 192 matching lines @@
     int startIndex = 0;
     Iterator iterator = pattern.allMatches(this).iterator();
     if (iterator.hasNext) {
       Match match = iterator.next();
       buffer.add(this.substring(startIndex, match.start)).add(replacement);
       startIndex = match.end;
     }
     return buffer.add(this.substring(startIndex)).toString();
   }
 
-  String replaceAll(Pattern pattern, String replacement) {
+  String replaceAll(Pattern pattern, var replacement) {
     if (pattern is! Pattern) {
       throw new ArgumentError("${pattern} is not a Pattern");
     }
+    if (replacement is Function) {
+      StringBuffer buffer = new StringBuffer();
+      int startIndex = 0;
+      for (Match match in pattern.allMatches(this)) {
+        if (match.start > startIndex) {
+          buffer.add(this.substring(startIndex, match.start));
+        }
+        buffer.add(replacement(match).toString());
+        startIndex = match.end;
+      }
+      if (startIndex < this.length) {
+        buffer.add(this.substring(startIndex));
+      }
+      return buffer.toString();
+    }
     if (replacement is! String) {
-      throw new ArgumentError("${replacement} is not a String");
+      throw new ArgumentError(
+          "${replacement} is not a String or Match->String function");
     }
     StringBuffer buffer = new StringBuffer();
     int startIndex = 0;
     for (Match match in pattern.allMatches(this)) {
       buffer.add(this.substring(startIndex, match.start)).add(replacement);
       startIndex = match.end;
     }
     return buffer.add(this.substring(startIndex)).toString();
   }
 
@@ skipping 249 matching lines @@
     for (int g in groups) {
       result.add(group(g));
     }
     return result;
   }
 
   final int start;
   final String str;
   final String pattern;
 }