sub define_definer {
  my ($name, $handler) = @_;
  *{$name} = sub {
    my ($name, $value) = @_;
    $data{$name} = $value;
    &$handler($name, $value);
  }
}
define_definer 'define_function', \&create_function;
define_definer 'define_code', sub {
  my ($name, $value) = @_;
  eval $value;
};