Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!rice!news
From: wright@utopia.rice.edu (Andrew Wright)
Newsgroups: comp.lang.lisp
Subject: Re: Weak Reference in Common Lisp
Message-ID: <1990Aug20.223114.2683@rice.edu>
Date: 20 Aug 90 22:31:14 GMT
References: <5819@hplabsz.HPL.HP.COM> <44659@cornell.UUCP> <1990Aug18.190312.25603@rice.edu>
Sender: news@rice.edu (News)
Organization: Rice University, Houston
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In article <1990Aug18.190312.25603@rice.edu> I wrote:
>In article <44659@cornell.UUCP> murthy@algron.cs.cornell.edu (Chet Murthy) writes:
>>>In article <81084@aerospace.AERO.ORG> srt@aero.org (Scott "TCB" Turner) writes:
>>>>Is there a mechanism in Common Lisp (specifically AKCL) for weak
>>>>reference?  By weak reference I mean a reference that won't prevent
>>>>garbage collection if no other references exist.
>
>>I know that there is such a facility (weak pointers) in the SML-NJ
>>(Standard ML of New Jersey) system.
>
>I think Chet must be referring to "weak types" of standard ML.
>SML's weak types have nothing to do with what the original poster intended.

It seems that buried in the debugger source that comes with the
New Jersey implementation there is an abstraction that implements
weak pointers like the original poster was seeking, but this module
is not available to programmers.  So while I may have leapt too far
to the conclusion that Chet was thinking of weak types, weak pointers
are not really in the New Jersey implementation, and are definitely
not in the standard.

Andrew K. Wright        Computer Science, Rice University
wright@rice.edu         Houston Texas  77251-1892