sub first(&@) {
   my $cb = shift(@_);
   for (@_) {
      my $i = ref eq 'CODE' ? $_->() : $$_;
      my $rv;
      $rv = $cb->() for $i;
      return $i if $rv;
   }
   return;
}

my $theme = first { defined }
   \$global_config->{modes}{$current_mode}{theme},
   \$theme_config->{current_theme},
   \&ask_user,
   \'none';