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Re: elisp's cl package. Don't understand the notice about eval-when-comp


From: Michael Ekstrand
Subject: Re: elisp's cl package. Don't understand the notice about eval-when-compile
Date: Tue, 24 Mar 2009 23:42:47 -0500
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/23.0.91 (gnu/linux)

Xah Lee <address@hidden> writes:
> in emacs lisp's CL package documentation “(info "(cl)Overview")”, it
> has this passage:
>
>    *Please note:* the "CL" functions are not standard parts of the
> Emacs Lisp name space, so it is legitimate for users to define them
> with other, conflicting meanings.  To avoid conflicting with those
> user
> activities, we have a policy that packages installed in Emacs must not
> load "CL" at run time.  (It is ok for them to load "CL" at compile
> time
> only, with `eval-when-compile', and use the macros it provides.)  If
> you are writing packages that you plan to distribute and invite
> widespread use for, you might want to observe the same rule.
>
> I don't quite understand it.
>
> If i distribute a package xyz.el, which calls
>
> (eval-when-compile (require 'cl))
>
> And, this package does not require users to byte-compile it. Then,
> how's the eval-when-compile solve the name conflict problem?
>
> does it imply that if you distribute a package using cl, it must be
> byte compiled eventually?

No, it just implies that if you distribute a package using cl, and you
want to be nice to your users, you will follow the guideline (only use
macros and put the require in eval-when-compile) and include a warning
or notice with the package that loading it directly from source will
import the cl package.  If this bothers them then they can byte compile
it.

Most substantial third-party packages for Emacs that I have come across
have an installation mechanism, frequently via some form of Makefile,
which performs byte-compilation, so it isn't an issue there.

- Michael

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