I'll take a stab at a minimal implementation. The goal would certainly be for users to be able to simply delete their `shrink` function. If they were previously using the default (shrink _ = []), they'd then get shrinking for free. For those looking for more motivation, take a look at how boilerplate shrink implementations end up being in practice. Further, care must be given to respect any implicit constraints during shrinking, that are respected during generation. For example, when generating with `choose 10 20`, you must never shrink to a value below 10. This would all be taken care of using the proposed method.