On 22 Sep 2024, at 14:56, Marc Nieper-Wißkirchen <xxxxxx@gmail.com> wrote:

> (Apart from this, some implementations GC symbols, others do not, so even if SRFI 254 allowed symbols as weak keys, you wouldn't see the same behaviour everywhere.)

Implementations which don’t GC symbols are broken and vulnerable to DDoS attacks by memory exhaustion the moment you expose an SXML or JSON parser to the internet using one. See e.g. my issue on Gambit: <https://github.com/gambit/gambit/issues/675>

R7RS Large will probably make weaknesses in collection like this implementation-specified, so conforming impls will have to document if they can’t collect symbols.

>>   This needs a stronger definition of what has ‘location’ and what not than R7RS small provides. Also stronger than R6RS’s, to my knowledge.
>
> What does not have a location is not important for SRFI 254.

If you are going to ban keys that don’t have locations, it’s very important.

> What is important is that there are enough types that have a location, and this is in RnRS (see the listed types above).

But RnRS’s definition of this is not strong enough and you should make it stronger instead of depending on it.

Daphne