class Query
    prechigh
        left OPERATOR_NOT
        left OPERATOR_AND
        left OPERATOR_OR
      preclow
    rule
        target: expression
                | /* none */ { result = 0 }

          expression: TERM_WITHOUT_QUOTES                                       { result = {:DEFAULT_COLUMN => val[0]} }
          |     TERM_WITH_QUOTES                                                { result = {:DEFAULT_COLUMN => val[0]} }
          |     TERM_WITHOUT_QUOTES COLON TERM_WITHOUT_QUOTES                   { result = {val[0] => val[2]} }
          |     TERM_WITHOUT_QUOTES COLON TERM_WITH_QUOTES                      { result = {val[0] => val[2]} }
          |     expression OPERATOR_OR expression                               { result = {:OPERATOR_OR => [val[0], val[2]]} }
          |     expression OPERATOR_AND expression                              { result = {:OPERATOR_AND => [val[0], val[2]]} }
          |     OPERATOR_NOT expression                                         { result = {:OPERATOR_NOT => val[1]} }
          |     L_BRACKET expression R_BRACKET                                  { result = val[1] }
          |     expression expression                                           { result = {:OPERATOR_OR => [val[0], val[1]]} }
end

---- header
  require_relative 'lexer'

---- inner
  def parse(input)
    scan_str(input)
  end