Re: [Caml-list] "super-compaction" of values

[Markus Mottl <markus@mail4.ai.univie.ac.at>]

On Wed, 01 Aug 2001, John R Harrison wrote:
> About 5 years ago I became very enthusiastic about using hash-consing in
> the HOL Light prover to share common subterms of theorems. I was
> convinced it would cut space usage dramatically.

Well, it's actually not so much space savings that I am interested in,
but mostly exploiting (sub-)program equivalences to speed up expensive
computations.

> I ended up writing a naive implementation, without making stuff
> garbage-collectible, but only using it for structures I knew were
> persistent. To my chagrin, it turned out that Malcolm was absolutely
> right. Space usage actually went *up*, presumably because the hashing
> datastructures were large enough to overwhelm the small amount of
> sharing.

I can well imagine this. In my case it's not "real" programming languages
that I have to deal with, but rather quite confined ones, and there are
likely to be hundreds of not-so-large programs that mostly differ by a
few subtrees only (= lots of opportunities for sharing). It seems worth
a try...

Regards,
Markus Mottl

-- 
Markus Mottl                                             markus@oefai.at
Austrian Research Institute
for Artificial Intelligence                  http://www.oefai.at/~markus
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