anchor.diff:  
   primary_expr :
        literal
  -  |  lparen FILLER? expr FILLER? rparen
  +  |  t_lparen FILLER? expr FILLER? t_rparen
     |  matrix
     |  cell_array
     |  access
  
positive.code:   ;
  
  paren_access :
       cell_access (FILLER? lparen FILLER? (arg_list FILLER?)? rparen)?
    ;
  
  cell_access :
       name (FILLER? lcurly FILLER? arg_list FILLER? rcurly)*
    |  {inParens()}? name FILLER? AT FILLER? name
    |  {!inParens()}? name AT name //TODO-AC: fix error message for name AT FILLER name case
    ;
  
negative.code:   ;
  
  matrix :
       t_lsquare optional_row_list t_rsquare
    ;
  
  cell_array :
       t_lcurly optional_row_list t_rcurly
    ;
  
  optional_row_list :
  