Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!cwjcc!tut.cis.ohio-state.edu!rutgers!mit-eddie!mit-amt!sokolov
From: sokolov@mit-amt (Michael Sokolov)
Newsgroups: comp.lang.lisp
Subject: Re: Problems with Lisp Packages
Keywords: Packages, Constants
Message-ID: <3591@mit-amt>
Date: 26 Feb 89 20:12:47 GMT
References: <117@bosco.dit.upm.es>
Reply-To: sokolov@media-lab.media.mit.edu (Michael Sokolov)
Organization: MIT Media Lab, Cambridge MA
Lines: 27

In article <117@bosco.dit.upm.es> ibm@bosco.UUCP (Ignacio Bellido Montes) writes:
>	(DEFUN FOO (X)
>		(COND ((EQUAL (CAR X) 'YES) ... )
>		      ((EQUAL (CAR X) 'NO) ... )
>		      (T (PRINT 'ERROR)))
>	)
>
>	When the current package is the same where the function is defined,
>the function is well evaluated. But when I use the function from another
>package, using (PACKAGE-FOO::FOO), the predicate EQUAL fails.

	This can be very annoying. The problem is that there are two
different symbols: foo is defined differently in two packages. There
are a few things you can do. One is to use strings instead of symbols.
Another is to use keywords (symbols beginning with a ":", like :yes
and :no), which are ALL defined in the keyword package and are thus
shared by other packages. Finally, (kind of ugly) if you really insist
on doing what you describe, you can do the following (in package foo):

(in-package 'foo)
	(defun test (x)
	...
		(equal (find-symbol (car x) 'foo) 'yes)
	...)

Happy hacking!

-MS