# infix operators: ==, or, and
# grouping: ()
# terminals : \w+
#
# term := (expr)             {print '[' .  $expr . ']'}
#         | \w+              {print $word}
# expr := term /and/ term    {print 'and,' . $term1 . ',' . $term2}
#         | term /or/ term   {print 'or,' . $term1 . ',' . $term2}
#         | term /==/ term   {print '==,' . $term1 . ',' . $term2}