Re: [bug #22022] hashx-set! and -ref

[Gregory Marton]

> What do you think?

I didn't read that part of the spec, so I was confused, and I'll grant that 
the cases may be out of scope.

Moreover, I think the hash specification is problematic.
   (a) the representation seems to wish to hide the current size of the
       hash vector, or at least that would be sensible, but it is exposed
       in the printout and as an argument to the hash-function supplied to
       hashx.  The point at which the hash is resized is unpredictable from
       the user's point of view.  This is three flavors of rep exposure.

   (b) if, as the doc says, "it's imperative that just one set is then used
       consistently, or results will be unpredictable", then it makes sense
       to enforce this.  A common way to enforce it is to ask for the hash
       function just once, at creation time.  By requiring it everywhere,
       we force the user to expose a representation, the hash function and
       equality predicate, between one part of their program and another.

   (c) the assoc requirement is a rep exposure of a third sort -- it exposes
       the fact that buckets are alists.  There is no reason for the user to
       know this, and there is no reason it should be so.  If a future
       implementation wants to do something else, say hash with another
       hash, they will have to emulate assoc-ability to make this API work.
       Moreover, this forces the user to write the assoc function on top of
       their equality predicate, which is neither fast (it's Scheme instead
       of C) nor DRY (Don't Repeat Yourself -- a principle of not
       duplicating code).

If the current set of decisions seems self-consistent and useful to the 
community, then I guess I'd submit an enhancement request, for a new set of 
fast functions:
   (make-hashf-table one-arg-hash-function equality-predicate [size])
   (hashf-set! hashf-table 'key value)
   (hashf-ref hashf-table 'key [default])
   (hashf-remove! hashf-table 'key)
   (hashf-size hashf-table) ===> the number of keys stored
   ... [clear get-handle create-handle for-each for-each-handle map->list

"f" for the functions it stores.

Thanks,
Grem

--
------ __@   Gregory A. Marton                http://csail.mit.edu/~gremio/
--- _`\<,_                                                                .
-- (*)/ (*)             Contents may have settled out of court.
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