It is written in C. The only real reason C was used was performance concerns, real or imagined. I can post a diff of the changes - it isn't that many lines.
> That's too bad (I mean, its good for performance, but unfortunate one of
> the use cases doesn't exist). However, the treap functions may still be of
> general use. Let me know if there is any interest. They are documented
> and tested. They fill a gap between alists (persistent, linear lookup) and
> hash tables (ephemeral, constant lookup) by being persistent while
> providing average case logarithmic lookup.
Is it written in C or Elisp? If it's Elisp, then we definitely would
welcome it into GNU ELPA (there is already an avl-tree implementation in
Emacs itself at lisp/emacs-lisp/avl-tree.el, but the more the merrier).
If it's written C, I'll let others decide whether we want to include it.
Stefan