Re: SCM_BOOL_F == 0 and BDW-GC

[Ludovic Courtès]

Hello,

Neil Jerram <address@hidden> writes:

> address@hidden (Ludovic Courtès) writes:

[...]

>> Instead what's really needed is a special pointer-to-reclaimed-object
>> value that can be distinguished from valid Scheme values since that
>> value ends up in the car or cdr of weak pairs in hash table buckets.  As
>> such, SCM_PACK (NULL) was a good choice until now.
>
> Here I'm confused again.  I thought we now had no choice about the
> pointer-to-reclaimed-object value, because BDW-GC always uses NULL.

True.  So, what I meant is that ((SCM) NULL) must be distinguishable
from valid Scheme values.

>> SCM_UNDEFINED == 0 would work fine because SCM_UNDEFINED is not a valid
>> Scheme value, but it wouldn't change the implementation.
>
> I'm afraid I don't understand "but it wouldn't change the
> implementation".

Ugly stuff like ‘scm_fixup_weak_alist ()’ would still be needed.

> SCM_UNDEFINED == 0 is sounding promising...

Yeah.  Sorry for the false hope about SCM_BOOL_F == 0.

Thanks,
Ludo’.