sub activate {
  my $self = shift;
  eval {
    $self->prototype_enter;
    $self->app_enter;
    my $this_page = $self->dispatch;
    $this_page->control_enter;
    $this_page->respond_enter;
    my $next_page = $this_page->respond;
    $this_page->respond_leave;
    if ($this_page ne $next_page) {
      $this_page->control_leave;
      $next_page->control_enter;
    }
    $next_page->render_enter;
    $next_page->render;
    $next_page->render_leave;
    $next_page->control_leave;
    $self->app_leave;
    $self->prototype_leave;
  };
  $self->error($@) if $@;	# failed something, go to safe mode
}