Christopher Browne <[EMAIL PROTECTED]> writes:
> I have come to understand how Guile handles hashing; Rob Browning
> was looking, in .../scm/prefs.scm for a "hash-for-each."
>
> I have some code in transit that handles this; that will also fairly
> substantively change the QIF code that I'm now actively fiddling with
> again.
>
> ;;; Less-than-well-tested:
> (define (hash-for-each fun table)
> (array-for-each
> (lambda (sublst)
> (if sublst
> (for-each fun sublst)))
> table))
I've finally gotten around to looking at this, and are you sure it's
correct? It seems to assume that hashes will always be founded on
vectors of empty lists, and I don't think that's guaranteed. In fact
I've always started my hashes with no values. For example, I believe
this is a functionally acceptable guile hash:
(define some-hash (make-vector 5))
(hashq-set! some-hash 'a 1)
(hashq-set! some-hash 'b 2)
(hashq-set! some-hash 'c 3)
which ends up being
guile> some-hash
#(#<unspecified> ((c . 3) . #<unspecified>) #<unspecified> ((b . 2)
. #<unspecified>) ((a . 1) . #<unspecified>))
and works just fine.
This ambiguity was why I didn't bother with hash-for-each before. I
couldn't find in the docs a clear what defines a legitimate hash, so
it wasn't completely clear how to traverse it "correctly", and I
didn't really have to have hashes at the time. I do seem to recall
that I asked about this on the guile list and there was a big debate
about what would be the optimal solution.
However, as a "good enough" solution, and presuming that we really
need hashes (we probably do), you could modify your code as indicated
below, and I think it'll work in all the likely cases:
(define (hash-for-each thunk hashtable)
(array-for-each
(lambda (bucket)
(if (pair? bucket)
;; Can't use for-each here since a bucket doesn't have to be
;; a proper list. (make-vector 17) is a functional hash table.
(let loop ((remaining-items bucket))
(if (pair? remaining-items)
(begin
(thunk (car remaining-items))
(loop (cdr remaining-items)))))))
hashtable))
--
Rob Browning <[EMAIL PROTECTED]> PGP=E80E0D04F521A094 532B97F5D64E3930
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