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