anchor.diff:  
   expressionStatement
       : expression ';'                                    # unconditionalStatement
  +    | variableDeclaration ';'                           # variableDeclarationStatement
       | expression IF expression ';'                      # conditionalIfStatement
       | expression UNLESS expression ';'                  # conditionalUnlessStatement
       // | expression WHILE expression ';'                   # repeatedStatement
  
positive.code: ////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
  // TOKENS
  
  UNLESS  : 'unless';
  IF      : 'if';
  ELSE    : 'else';
  
negative.code: ////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
  // EXPRESSIONS
  
  variableDeclaration
      : DEF ( VariableName | ConstantName ) (':' ObjectOrClassName)? ('=' expression)?
      ;
  
  expression
      : expression '*' expression                         # multiplicationExpression
      | expression '+' expression                         # additionExpression
  