anchor.diff:  form:   ID
       |   ID '=' expr
       |   '...'
  +    |   '.'
       ;
   
   sublist : sub (',' sub)* ;
  
positive.code: */
  grammar R;
  
  prog:   (   expr (';'|NL)
          |   NL
          )*
          EOF
  
negative.code:     |   'NULL' '='
      |   'NULL' '=' expr
      |   '...'
      |   '.'
      |
      ;
  
  