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- To: JONL at MIT-MC
- Subject: Re: SXHASH
- From: George J. Carrette <GJC at MIT-MC>
- Date: Fri ,31 Oct 80 11:01:00 EDT
- Cc: ALAN at MIT-MC, GSB at MIT-MC, LISP-FORUM at MIT-MC, jerryb at MIT-AI
JONL, since you mentioned Macsyma, I'd like to point out that
since the HASH that one wants to use depends heavily on the EQUAL in
use, Macsyma uses its own definition of HASH, and uses SXHASH only
to get that HASH for SYMBOLS. Also, how fancy the hash wants to
be depends on what it is used for, and the relative expense
of the EQUAL algorithm for the objects in use.
In other words, I don't think any good programmer who knows and cares
about the various hashing methods etc., should depend on the behavior
of a built-in like SXHASH anyway. (Except insofar as the SXHASH is defined
to do some kind of class dispatching for hashing the sub-nodes of a node).
p.s. For writing ones own hash function it would be *nice* if
(CASEQ (TYPEP X)
(FOOBAR ...) )
turned into code which, well, I'm sure you can guess.