my $grammar = q~

   logic: expression eod

   expression: <leftop: term termop term>

   termop: /and/i | /xor/i | /or/i

   term: '(' <commit> expression ')' | condition

   condition: element comparison element

   element: '<' <commit> /-?\w+/ '>'
          | /\d+/

   comparison: /=[><]=/ <commit> <error: Unable to match comparison>
             | /=?[><]=?/
             | '='
             | '!='

   eod: /^\Z/

~;