On 16 Jul 2021, at 19:17, Marc Nieper-Wißkirchen <xxxxxx@gmail.com> wrote:

> SRFI 125 allows hash tables to ignore the provided hash function when a predicate finer than `equal?' is used.

And if I want to use the hash function for something else? If the implementation of SRFI 125 is allowed to peek behind the curtains, why can’t the implementation of SRFI 128? (This isn’t an argument for removing that permission from SRFI 125, which I guess is a useful accommodation for Scheme implementations on runtimes which have pointer-based hash tables but no access to pointer values as numbers.)

> Indeed, for moving garbage collectors, there is not a stable efficient hash function for `eq?' that can be exposed to the user, so it is largely irrelevant what the hash function packaged by `make-eq-comparator' is.

Right, but for non-moving garbage collectors there’s no reason not to provide something better. Hence I suggested implementations should be *allowed* to do something better than use default-hash, which they currently aren’t.

Daphne