module Regexp::Parser

def self.backref(token)
  case token.token
  when :name_ref
    @node << Backreference::Name.new(token)
  when :name_nest_ref
    @node << Backreference::NameNestLevel.new(token)
  when :name_call
    @node << Backreference::NameCall.new(token)
  when :number, :number_ref
    @node << Backreference::Number.new(token)
  when :number_rel_ref
    @node << Backreference::NumberRelative.new(token)
  when :number_nest_ref
    @node << Backreference::NumberNestLevel.new(token)
  when :number_call
    @node << Backreference::NumberCall.new(token)
  when :number_rel_call
    @node << Backreference::NumberCallRelative.new(token)
  else
    raise UnknownTokenError.new('Backreference', token)
  end
end