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From: Gallagher@cs.umass.edu (Kevin Gallagher)
Newsgroups: comp.lang.lisp
Subject: Re: stupid package question
Message-ID: <26205@dime.cs.umass.edu>
Date: 7 Feb 91 01:54:46 GMT
References: <6026@rex.cs.tulane.edu>
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Reply-To: Gallagher@cs.umass.edu
Organization: Computer Science, University of Massachusetts, Amherst, MA
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    > Is there a correct way to do the following in a file?

    > 1)  make a package, P
    > 2)  load a system into this package
    > 3)  set some parameters of the system (symbols in the package)

The best thing to do is to create a separate file (in package "P") to
do the third step.  This is the cleanest and least likely to cause
you problems later on.

If you only have a few variables that you want to set you can do
something like:

  ;; This is exactly the same as (SETF P::*PARAMETER-ONE* 35)
  ;; except that package P need not need not exist when this
  ;; form is read.
  (setf (symbol-value (intern "*PARAMETER-ONE*" "P")) 35)

It's a bit ugly, and, generally, you should avoid using intern
unless you *really* need it.  This is the sort of situation where
you need it.

Also, not all lisps allow a package name as the second argument to
intern, they require the actual package.  In those cases you must do:

  (setf (symbol-value (intern "*PARAMETER-ONE*" (find-package "P")))
        35)

Which is even more opaque.

Kevin Gallagher