anchor.diff:      | ifStat
       | whileStat
       | caseStat
  -    | ID
  +    | expr 
       | NL
       ;
   
  
positive.code: 
  fragment
  ESC : '\'\'' ;
  
negative.code: expr
      : expr '(' exprList ')'
      | expr ('\''|'.\''|'.^'|'^') expr
      | ('+'|'-'|'~') expr
      | expr ('*'|'.*'|'/'|'./'|'\\'|'.\\') expr
      | expr ('+'|'-') expr
      | expr ':' expr
  