While this will probably work, it ends up with the same problem from the original idea: you have to maintain a repository of new functions which may be overlooked.

You could skip the repository, and so something like

  if ( -f "$attr.sub" ) {
      # load and eval "$attr.sub"
      goto &$attr;
  }
[download]

I used a registry so that you could stage the debugging of new functions. If that isn't an issue for you, then don't use a registry. I've used a registry for something like this in years past, and have found it useful, but YMMV.