class Regexp::Parser

def parse_token(token)
  case token.type
  when :anchor;                     anchor(token)
  when :assertion, :group;          group(token)
  when :backref;                    backref(token)
  when :conditional;                conditional(token)
  when :escape;                     escape(token)
  when :free_space;                 free_space(token)
  when :keep;                       keep(token)
  when :literal;                    literal(token)
  when :meta;                       meta(token)
  when :posixclass, :nonposixclass; posixclass(token)
  when :property, :nonproperty;     property(token)
  when :quantifier;                 quantifier(token)
  when :set;                        set(token)
  when :type;                       type(token)
  else
    raise UnknownTokenTypeError.new(token.type, token)
  end
  close_completed_character_set_range
end