anchor.diff:  
   // GRAMMAR OF A FOR STATEMENT
   
  -for_statement : 'for' for_init?';' expression?';' expression? code_block
  +for_statement
  + : 'for' for_init? ';' expression? ';' expression? code_block
    | 'for' ( for_init?';' expression?';' expression?) code_block
    ;
   for_init : variable_declaration | expression_list  ;
  
positive.code: 
  // GRAMMAR OF OPERATORS
  
  Operator : Operator_character+ ;
  fragment Operator_character : [/=\-+!*%<>&|^!.] ;
  binary_operator : Operator ;
  prefix_operator : Operator  ;
  postfix_operator : Operator  ;
  
negative.code: // GRAMMAR OF A CONSTANT DECLARATION
  
  constant_declaration : attributes? declaration_specifiers? 'let' pattern_initializer_list  ;
  pattern_initializer_list : pattern_initializer (',' pattern_initializer)* ;
  pattern_initializer : pattern initializer? ;
  initializer : '=' expression  ;
  
  