Path: utzoo!utgpu!news-server.csri.toronto.edu!bonnie.concordia.ca!uunet!mcsun!ukc!edcastle!aiai!jeff
From: jeff@aiai.ed.ac.uk (Jeff Dalton)
Newsgroups: comp.lang.lisp
Subject: Re: Question about INTERN
Message-ID: <4091@skye.ed.ac.uk>
Date: 11 Feb 91 17:29:53 GMT
References: <1991Jan29.055536.1523@magnus.ircc.ohio-state.edu> <5783@idunno.Princeton.EDU> <4037@skye.ed.ac.uk> <5821@idunno.Princeton.EDU>
Reply-To: jeff@aiai.UUCP (Jeff Dalton)
Organization: AIAI, University of Edinburgh, Scotland
Lines: 31

In article <5821@idunno.Princeton.EDU> eliot@phoenix.Princeton.EDU (Eliot Handelman) writes:
>In article <4037@skye.ed.ac.uk> jeff@aiai.UUCP (Jeff Dalton) writes:
>;In article <5783@idunno.Princeton.EDU> eliot@phoenix.Princeton.EDU (Eliot Handelman) writes:
>;>Common Lisp says that (TYPE-OF any-house) might return T.
>;
>;Actually, according to CLtL II, page 66, TYPE-OF never returns T.
>
>Yes, I'm wrong, but anyhow CLtL II isn't Common Lisp (or so I've
>been led to believe from some recent discussion on the common lisp
>mailing list, for as Steele says in the preface, "In no way  does this
>book constitute a definitive description of the *forthcoming* ANSI
>standards" (pg xii, my asterisks)).

You're right that CLtL II isn't Common Lisp, as the preface says.  But
CLtL I is as close to definitive as we can get at present, and it also
says TYPE-OF returns the appropriate type for a defstruct.  Moreover,
CLtL II is the best source we have for what X3J13 intends as well as
to what implementations that have tried to follow X3J13 may have done.
I don't think the X3J13 draft is yet sufficiently solid to take over
as the main definition of CL, and so when we have to cite some source
CLtL II is about as good as it gets at present.

The main cases where it's best not to follow CLtL II too closely are
when something appears to be an artifact of the language used in CLtL
II and so not necessarily a reliable account of the language.

However, you are certainly right is steering programmers away from
TYPE-OF.  Barmar has a good suggestion, namely to use (TYPEP x type)
rather than (EQ (TYPE-OF x) type).

-- jeff