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From: ksh@ely.cl.cam.ac.uk (Kish Shen)
Newsgroups: comp.lang.prolog
Subject: Re: Arrays in Prolog
Message-ID: <1990Sep12.170553.14414@cl.cam.ac.uk>
Date: 12 Sep 90 17:05:53 GMT
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Reply-To: ksh@cl.cam.ac.uk (Kish Shen)
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Mats Carlsson said:

>trailing?  Value trailing seems to have a rather high price: the trail
>becomes twice as large, and there is extra work for each (normal)
>variable to reset.

Perhaps I am showing my ignorance, but can you not have a "special trail" to 
store the those trailing that need value trailing? This is what I am doing for
my own work with implementing dependent and-parallelism in Prolog -- I have a
special trail which  grows in the opposite direction to the normal
trail, towards
the normal trail. This means that you only pay for the cost of value
trailing for
those variables that need to use it. Am I missing something? 

Kish Shen
ksh@cl.cam.ac.uk
Computer Lab.,
University of Cambridge
U.K.