Newsgroups: comp.lang.scheme
Path: cantaloupe.srv.cs.cmu.edu!das-news2.harvard.edu!news2.near.net!MathWorks.Com!europa.eng.gtefsd.com!howland.reston.ans.net!pipex!uunet!rosevax!reddwarf!grante
From: grante@reddwarf.rosemount.com (Grant Edwards)
Subject: Re: Property list question
Message-ID: <1994Oct17.141723.8070@rosevax.rosemount.com>
Sender: news@rosevax.rosemount.com (Rosevax USENET News auto-admin account)
Nntp-Posting-Host: reddwarf
Organization: Fisher-Rosemount, Rosemount Inc.
X-Newsreader: TIN [version 1.2 PL2]
References: <1994Oct14.225950.28456@rosevax.rosemount.com>
Date: Mon, 17 Oct 1994 14:17:23 GMT
Lines: 35

Grant Edwards (grante@reddwarf.rosemount.com) wrote:

: In Dybvig's book "The Scheme Programming Language" section 5-7
: describes property lists and the getprop and putprop procedures.
: These are listed as extensions (which I assume are provided by Chez
: Scheme - since the foreword states the examples were done using Chez
: Scheme).

: The book states that property lists belong to "symbols."  The text is
: quite explicit that the argument must be a symbol, and all examples
: are shown with quoted symbols.

: Do the properties in fact belong to the symbol and not to the object
: to which the symbol is bound?

Thanks to everybody who lent me a clue.

What I hadn't realized was that a propertie list doesn't "belong to" a
symbol in the sense that an object (like a list or vector) contains
information.  Rather the property list is assocated with the specified
key symbol in an annonymous, global database.

Part of my confusion stems from my expectation that a database like
that would be a first-class object.  The implementation of Scheme that
I use (STk) provides hash-tables as first-class objects.  These hash
tables provide the exact same functionality as putprop getprop.  I
couldn't figure out which Scheme object corresponded to a hash-table
object and thus contained the property lists to with which
putprop/getprop were referring.

--
Grant Edwards                                 |Yow!  Now KEN and BARBIE are
Rosemount Inc.                                |PERMANENTLY ADDICTED to
                                              |MIND-ALTERING DRUGS..
grante@rosemount.com                          |
