anchor.diff:            break;
           default: throw new ArgumentError('Unsupported token: $currToken');
         }
  -      
  +
         exprStack.add(currExpr);
       }
   
  
positive.code: 
    /// The string value of this token type.
    final String value;
    
    /// The priority of this token type.
    final int priority;
  
    /// Associativity of this token type. true = left.
    final bool leftAssociative;
    
    /// True, if this token is an operator.
    final bool operator;
    
    /// True, if this token is a function.
    final bool function;
    
    /**
     * Internal constructor for a [TokenType].
     * To retrieve a token type, directly access the static final fields
  
negative.code:       Expression currExpr, left, right;
  
        switch(currToken.type) {
          case TokenType.VAL:
            currExpr = new Number(double.parse(currToken.text));
            break;
          case TokenType.VAR:
  