Re: Error: Symbol's value as variable is void

[Kevin Rodgers <ihs_4664@yahoo.com>]

Joe Corneli wrote:
 > I wrote some code that contains the following forms:
 >
 > (defvar nero-link-regexp "\\[\\([0-9]+\\)\\]"
 >   "Regular expression that tells nero what links look like.
 > The first parenthesized subexpression is the unique string
 > denoting the webpage to load, which will sought among the
 > references.")
 >
 > (defvar nero-font-lock-keywords
 >  (eval-when-compile
 >   (list `(,nero-link-regexp . font-lock-keyword-face)))
 >   "Font lock for `nero-mode'.
 > Currently, only numbered links are fontified.")
 >
 > These work fine for me, but another person using the code reports the
 > following error upon byte-compiling:
 >
 > Compiling file /stor/garray/src/nero.el at Fri Mar 25 08:21:48 2005
 > nero.el:295:33:Error: Symbol's value as variable is void: 
nero-link-regexp
 >
 >
 > I don't see any such error when I byte compile.  I'm just curious to
 > know if using `eval-when-compile' here is bad form, or what.  I think
 > I've seen it being used in other packages in a similar context, but I
 > don't understand it well enough to know whether I should be using it
 > here.

You don't get an error because you have nero.el[c] already loaded when
you byte compile it, but the other person doesn't.  It's more reliable
to byte compile .el files in an uncustomized emacs (i.e. invoked with -q
and perhaps --no-site-file).

 > Removing it did make the other user's error go away.  I told him to
 > create a bug report, but if its just the fault of my bad code, I'd
 > like to know.  More generally, as a point of style, when is it good to
 > use `eval-when-compile'?

Only when you need it.  But since the simpler form is equivalent for
your purposes (I assume), why use the more complex eval-when-compile and
backquote form?

(defvar nero-font-lock-keywords
   (list (cons nero-link-regexp 'font-lock-keyword-face))
   "Font lock for `nero-mode'.
Currently, only numbered links are fontified.")

-- 
Kevin Rodgers