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From: sfk@otter.hpl.hp.com (Steve Knight)
Newsgroups: comp.lang.prolog
Subject: Re: Garbage collecting names in Prolog
Message-ID: <1600027@otter.hpl.hp.com>
Date: 10 Apr 91 11:26:52 GMT
References: <1991Apr5.143158.7857@swift.cs.tcd.ie>
Organization: Hewlett-Packard Laboratories, Bristol, UK.
Lines: 17

This is an interesting question.  The Poplog Prolog system, which is the
one I normally use, collects all inaccessible atoms.  Atoms are 
accessible either from the "dictionary" or from the currently executing
context (or because they reside in the constant portion of the process.)

The "dictionary" is a mapping from functor/arity -> location.  This
mapping is not garbage-collectable, since that would be an error in
an incrementally compiled system, but names can be "cancelled".  This
gives the user the ability to deliver their application without 
the predicate names being present.  

However, this feature is only used by confident & competent programmers 
since some predicates, such as call, require parts of the dictionary 
to be present.  Consequently, the Poplog Prolog module system allows you 
to cancel the dictionary on a structured and controlled basis.

Steve