🚀 go-pugleaf

>In article <1992Dec17.185017.17766@cs.uoregon.edu> debray@majestix.cs.uoregon.edu (Saumya K. Debray) writes:
>
>Fernando Pereira writes:
>> Nonetheless, the efficiency reasons that led to Prolog's
>> unification not having the check are pretty compelling, so I do not advocate
>> adding it to Prolog in all cases. 
>
>While I believe this statement, it would be interesting to actually see some
>numbers (preferably for programs other than nrev) showing how much more
>expensive unification becomes with the occurs check. ...
>
That's a topic we are interested in, too. Often, people
working on the sound omission of the occur check write that carrying
out sound unification always is prohibited for efficiency reasons.
But has anybody investigated this systematically? 

In order to support the efficiency argument for omitting the occur
check, we carried out some small experiments with SEPIA-Prolog.
We ran the reverse-program on a list of about 1000 terms.  
The result was astonishing (at least to us): 
performance degrades only about 10-20 percent when using sound
unification. Here, it was necessary to work on (moderately) large terms in
order to note a difference at all. 

Maybe our observation is not true in general, and the result is due to
the clever implementation of SEPIA. Does someone know about 
the SEPIA-Implementation? 
Are there any better examples supporting the effciency argument?

	P. Baumgartner
--
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Peter Baumgartner                      | peter@infko.uni-koblenz.de
Universitaet Koblenz,                  |
Institut fuer Informatik               | Voice: +49 261 9119-426
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