Scanner can include comments in the token stream.

lib/compiler/implementation/scanner/parser.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.
 
 /**
  * An event generating parser of Dart programs. This parser expects
  * all tokens in a linked list (aka a token stream).
  *
  * The class [Scanner] is used to generate a token stream. See the
  * file scanner.dart.
@@ skipping 260 matching lines @@
     token = parseIdentifier(token);
     if (optional('extends', token)) {
       token = parseType(token.next);
     } else {
       listener.handleNoType(token);
     }
     listener.endTypeVariable(token);
     return token;
   }
 
+  /**
+   * Returns true if the stringValue of the [token] is [value].
+   */
   bool optional(String value, Token token) => value === token.stringValue;
 
   bool notEofOrValue(String value, Token token) {
     return token.kind !== EOF_TOKEN && value !== token.stringValue;
   }
 
   Token parseType(Token token) {
     Token begin = token;
     if (isIdentifier(token)) {
       token = parseIdentifier(token);
@@ skipping 981 matching lines @@
     while (token.kind === STRING_TOKEN) {
       token = parseSingleLiteralString(token);
       count++;
     }
     if (count > 1) {
       listener.handleStringJuxtaposition(count);
     }
     return token;
   }
 
+  /**
+   * Only called when [:token.kind === STRING_TOKEN:].
+   */
   Token parseSingleLiteralString(Token token) {
     listener.beginLiteralString(token);
+    // Parsing the prefix, for instance 'x of 'x${id}y${id}z'
     token = token.next;
     int interpolationCount = 0;
-    while (optional('\${', token)) {
-      token = token.next;
-      token = parseExpression(token);
-      token = expect('}', token);
+    var kind = token.kind;
+    while (kind != EOF_TOKEN) {
+      if (kind === STRING_INTERPOLATION_TOKEN) {
+        // Parsing ${expression}.
+        token = token.next;
+        token = parseExpression(token);
+        token = expect('}', token);
+      } else if (kind === STRING_INTERPOLATION_IDENTIFIER_TOKEN) {
+        // Parsing $identifier.
+        token = token.next;
+        token = parseExpression(token);
+      } else {
+        break;
+      }
+      ++interpolationCount;
+      // Parsing the infix/suffix, for instance y and z' of 'x${id}y${id}z'

[ahe, 2012/06/25 10:55:52]

Very nice.

       token = parseStringPart(token);
-      ++interpolationCount;
+      kind = token.kind;
     }
     listener.endLiteralString(interpolationCount);
     return token;
   }
 
   Token parseLiteralBool(Token token) {
     listener.handleLiteralBool(token);
     return token.next;
   }
 
@@ skipping 370 matching lines @@
     }
     listener.handleContinueStatement(hasTarget, continueKeyword, token);
     return expectSemicolon(token);
   }
 
   Token parseEmptyStatement(Token token) {
     listener.handleEmptyStatement(token);
     return expectSemicolon(token);
   }
 }