I guess this is late fallout from my long ago refactor that changed the
argument order for the patch sequencing operators. This isn't covered by
unit tests since they only use FLs. And the type checker cannot flag this
error because apply is monadic and Trees aren't tagged with witnesses.
1 patch for repository /home/ben/src/darcs/sent:
Author: Ben Franksen <email@example.com>
Date: Wed Mar 6 11:40:28 CET 2019
* fix a (serious!) bug in instance Apply (RL p)