Path: utzoo!attcan!uunet!ncc!alberta!steph
From: steph@alberta.UUCP (Stephanie Miller)
Newsgroups: comp.lang.lisp
Subject: Re: Problems with Lisp Packages
Summary: packages can be a pain!
Keywords: Packages, Constants
Message-ID: <2075@pembina.UUCP>
Date: 24 Feb 89 15:36:10 GMT
References: <117@bosco.dit.upm.es>
Organization: U. of Alberta, Edmonton, AB
Lines: 44

In article <117@bosco.dit.upm.es>, ibm@bosco.dit.upm.es (Ignacio Bellido Montes) writes:
> 
>  ...
> 	I use a Hewlett-Packard 9000-350 with Lucid Common Lisp II. I made a
> group of functions which made things like:
> 
> 	(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.
> ===========================================================================
> Ignacio Bellido Fernandez-Montes,

   I use Lucid common lisp and had exactly the same problem when starting
to use packages. There are three ways I can think of to fix the problem
(and I use them all in various places).
  
1) Any global constants like YES or No can be exported from the main
package you run things from (user hopefully). Then for each package you
set up, let it "use" the user package (I'm not sure how your common lisp
works, but ours lets you have a keyword parameter :use on the in-papackage
command). This will make all uses of that constant be the one in the user
package.
 
2) If you are starting from the same top level package each time, you can 
just prepend user:: on each constant you are testing - this only works if
all you input comes from the same package originally.
 
3) You can use find-symbol to find that symbol in the current package, and
then compare it (that only works if you have interned all possible constants
you will get into the package already).
 
4) You can explode the constant's name, strip off the package name (ends with :)and implode the rest to get the basic constant and then compare that.
I have routines that do that - let me know if you want them.
 
  Actually thats 4 ways!
 
   - Stephanie Miller
     steph@alberta.uucp