anchor.diff:    /// function is declared.
     Callable getFunction(String name) {
       var index = _functionIndices[name];
  -    if (index != null) _functions[index][name];
  +    if (index != null) return _functions[index][name];
   
       index = _functionIndex(name);
       if (index == null) return null;
  
positive.code:   /// declared.
    Callable getMixin(String name) {
      var index = _mixinIndices[name];
      if (index != null) _mixins[index][name];
  
      index = _mixinIndex(name);
      if (index == null) return null;
  
negative.code:   /// variable is declared.
    Value getVariable(String name) {
      var index = _variableIndices[name];
      if (index != null) return _variables[index][name];
  
      index = _variableIndex(name);
      if (index == null) return null;
  