Introduce element categories and move resolver towards being more compositional.

dart/frog/leg/scanner/token.dart

 // Copyright (c) 2011, 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.
 
 final int EOF_TOKEN = 0;
 
 final int KEYWORD_TOKEN = $k;
 final int IDENTIFIER_TOKEN = $a;
 final int DOUBLE_TOKEN = $d;
 final int INT_TOKEN = $i;
@@ skipping 180 matching lines @@
   bool hasNext() => index < end;
   int next() => string.charCodeAt(index++);
 }
 
 class BeginGroupToken extends StringToken {
   Token endGroup;
   BeginGroupToken(PrecedenceInfo info, String value, int charOffset)
     : super(info, value, charOffset);
 }
 
+bool isUserDefinableOperator(String value) {
+  return
+    (value === '==') ||
+    (value === '~') ||
+    (value === 'negate') ||
+    (value === '[]') ||
+    (value === '[]=') ||
+    (value === '*') ||
+    (value === '/') ||
+    (value === '%') ||
+    (value === '~/') ||
+    (value === '+') ||
+    (value === '-') ||
+    (value === '<<') ||
+    (value === '>>>') ||
+    (value === '>>') ||
+    (value === '>=') ||
+    (value === '>') ||
+    (value === '<=') ||
+    (value === '<') ||
+    (value === '&') ||
+    (value === '^') ||
+    (value === '|');
+}
+
 class PrecedenceInfo {
   final SourceString value;
   final int precedence;
   final int kind;
 
   const PrecedenceInfo(this.value, this.precedence, this.kind);
 
   toString() => 'PrecedenceInfo($value, $precedence, $kind)';
 }
 
@@ skipping 188 matching lines @@
 final PrecedenceInfo STRING_INTERPOLATION_INFO =
   const PrecedenceInfo(const SourceString('\${'), 0,
                        STRING_INTERPOLATION_TOKEN);
 
 final PrecedenceInfo HEXADECIMAL_INFO =
   const PrecedenceInfo(const SourceString('hexadecimal'), 0, HEXADECIMAL_TOKEN);
 
 // For reporting lexical errors.
 final PrecedenceInfo ERROR_INFO =
   const PrecedenceInfo(const SourceString('?'), 0, UNKNOWN_TOKEN);