%pages = (
  list_products => \&list_products,
  view_product  => \&view_product,
  edit_product  => \&edit_product,
  save_product  => \&save_product,
  default       => \&start,
);

if ($pages{$page}) {
  $pages{$page}->();
} else {
  $pages{default}->();
}
sub list_products {
  print '...';
}