Path: utzoo!attcan!uunet!cs.utexas.edu!yale!cmcl2!phri!marob!cowan
From: cowan@marob.masa.com (John Cowan)
Newsgroups: comp.lang.lisp
Subject: Re: STRUCTUREP
Message-ID: <27133D6E.715C@marob.masa.com>
Date: 10 Oct 90 15:25:33 GMT
References: <753@forsight.Jpl.Nasa.Gov>
Organization: The Logical Language Group, Inc.
Lines: 16

In article <753@forsight.Jpl.Nasa.Gov> gat@robotics.Jpl.Nasa.Gov (Erann Gat) writes:
>Is there any way in Common Lisp to test if an object is a structure?  There
>doesn't seem to be a structurep function.

No, there isn't, and that's intentional.  Some of the Common Lisp standard
types, notably STREAM, READTABLE, RANDOM-STATE, PATHNAME, and PACKAGE
may be implemented using the structure mechanism, but this fact is hidden
from the user.  A STRUCTUREP function would be unable to discriminate
between these implementation-defined structures and user-defined ones.

There's very little you can say about a structure qua structure, anyway.
The names of the {access, constructor} functions aren't deducible from the
outside, given that the default names can be overridden at DEFSTRUCT time.
-- 
cowan@marob.masa.com			(aka ...!hombre!marob!cowan)
			e'osai ko sarji la lojban