> That's an interesting idea. It appears to use the same idea as ShowS, but
> more generally with lists and not just strings.

The difference-list approach to solving the appending problem is classic.
There's a variant for unification-based logic languages as well. Both are
functional takes on the imperative approach of keeping a tail pointer.
Dons just took the time to package it up for us all :)

If you're planning on releasing the code, I'd suggest a different spelling
of (.+.) though. The (.X.) pattern for a family of operators is pretty
common, so it's good to avoid it for modules that want to be used in
combination with many others. YMMV and all that.