def parse(scanner, rules, scope = ParserScope.empty)
      pos = scanner.pos
      result = (child.parse(scanner, rules, scope) && true)
      scanner.pos = pos
      result
    end
def parse(scanner, rules, scope = ParserScope.empty)
      pos = scanner.pos
      result = (child.parse(scanner, rules, scope) && true)
      scanner.pos = pos
      result
    end
Succeed or fail like the decorated parser but do not consume any input
 and return +true+ on success.

 @param (see Match#parse)

 @return [Boolean] +true+ if the decorated parser succeeds