> On 25 Feb 2020, at 21:56, Andy Wingo <wi...@igalia.com> wrote:
>
> On Thu 20 Feb 2020 17:19, Ludovic Courtès <l...@gnu.org> writes:
>
>> Of all the scm_tc7_ values listed in ‘scm.h’, the following are not
>> explicitly listed (so they go to the default case that hashes the first
>> word):
>
> Reformatting your list so I can check one by one :)
>
>> variable,
>> hashtable,
>> fluid,
>> dynamic_state,
>> frame,
>> atomic_box,
>> program,
>> vm_cont,
>> weak_set,
>> weak_table,
>> port
>
> No equal? implementation, so should hashq() instead.
>
>> bytevector,
>> array,
>> bitvector,
>
> These have equal? implementations, and what's more, a bitvector can
> equal? an array... I think we have another bug!
>
> ;; Project 2d array as 1d array (scm_tc7_array)
> (define x
> (make-shared-array #2b((#t #t #t)) (lambda (i) (list 0 i)) '(0 2)))
> ;; scm_tc7_bitvector
> (define y #*111)
>
> (equal? x y) ;; => #t
> (equal? (hash x #xffffffff) (hash y #xffffffff)) ;; => #f
>
> Similarly for 1-d scm_tc7_array versus regular vectors, bytevectors,
> etc.
>
> Fixing this will not be straightforward... I think basically 1d arrays
> need some special hashing logic so that e.g. vectors and 1d arrays hash
> to the same thing.
I cannot check at the moment but I think that use of make-shared-array is
special cased to return a bitvector because the shared array and the root
happen to be equivalent. So your x isn't a scm_tc7_array but a
scm_tc7_bitvector. The same is true for the other vector types. You can see
that if you make a shared array with bounds '(0 1) instead of '(0 2) for
example, or non-unit step or non-zero lower bound or anything that cannot be
represented as a root vector.
Now it is true that functionally a root vector and a 1d array with the same
bounds and the same elements are equivalent even if the array has non-unit
stride and so on, but we had that logic before were you could use the root
vector functions on arrays and it was an absolute mess. I think there should be
a logic to hash n-d arrays that extends to 1-d arrays so there's no need to
make special cases. All vectors can be treated as 1-d arrays so that should
work fine for those too.
Partially related, I have a series of patches on wip-vector-cleanup to make
sure that the various vector implementations don't depend on arrays (as they
still do on some cases) but rather the other way around, strictly. I haven't
posted about it b/c it changes a few interfaces and I haven't figured out the
deprecation route.
regards
>
>> stringbuf,
>> values,
>
> These are never exposed to Scheme, and never compared using equal?
> AFAIU. No need for special cases.
>
> Basically I think the tc7 case should default to hashq, and include
> special cases for the ones that have equal? implementations or which
> have read syntax.
>
> Sound right to you?
>
> Andy
>
>
>
