class IRB::ExtendCommand::ShowDoc

def execute(*names)
  require 'rdoc/ri/driver'
  unless ShowDoc.const_defined?(:Ri)
    opts = RDoc::RI::Driver.process_args([])
    ShowDoc.const_set(:Ri, RDoc::RI::Driver.new(opts))
  end
  if names.empty?
    Ri.interactive
  else
    names.each do |name|
      begin
        Ri.display_name(name.to_s)
      rescue RDoc::RI::Error
        puts $!.message
      end
    end
  end
  nil
rescue LoadError, SystemExit
  warn "Can't display document because `rdoc` is not installed."
end