Re: functional hash operations

[prj@po.cwru.edu (Paul Jarc)]

Thien-Thi Nguyen <ttn@giblet.glug.org> wrote:
>    From: prj@po.cwru.edu (Paul Jarc)
>    Date: Mon, 30 Dec 2002 18:29:38 -0500
>
>    "make a copy of this hash which also has this additional entry", etc.
>    It would also be nice to make such copies share as much memory as
>    possible with the original hash.
>
> check out (ice-9 hcons).

I don't see how that will help me here.  I want something like:
(define (hash-add table key val)
  (let ((new-table (list->vector (vector->list table)))
        (index (hash key (vector-length table))))
    (vector-set! new-table index `((,key . ,val) . ,(vector-ref table index)))
    new-table))

This shares the keys, the values, the association pairs, and the list
pairs between the two tables.  (BTW, is there a better way to copy a
vector?)

Actually, I'm already writing my own constructors now, and it's easy
enough to reimplement the accessors too; I could avoid the built-in
hash functions altogether (other than hash itself).  As long as I'm at
it, I might as well create the new tables with more appropriate sizes
when they become full.  Is there any convenient way to compute a good
table size, given the number of entries?


paul


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