That's great! Is that described in the documentation? I can't seem to find it.

good catch! It is only mentioned at the end of the install section: http://ciel-lang.org/#/install?id=use-in-the-repl-and-in-new...

This feature is based on generic-cl, a high quality library. To be franc, I didn't test much the integration with generic-cl, it's on the todo list. When I started out, I was carving for a library like this. Now, I don't feel the need anymore.