emacs-24.0.92 and backquote

emacs-24.0.92 and backquote

[Nelson H. F. Beebe]

In testing emacs-24.0.92, I discovered that some venerable code that
has worked from Fall 1994 through emacs-23.* versions now fails to
load in emacs-24.0.92.  I get this error:

Loading /u/sy/beebe/emacs/ltxmenu.el (source)...
setq: Invalid function: (\` ("LaTeX main menu" ((\,
    internal-x-LaTeX-menu-startup)) ((\, internal-x-LaTeX-menu-accents))
    ((\, internal-x-LaTeX-menu-insertion)) ((\,
    internal-x-LaTeX-menu-begin-end)) ((\,
    internal-x-LaTeX-menu-begin-end-1)) ((\,
    internal-x-LaTeX-menu-begin-end-2)) ((\,
    internal-x-LaTeX-menu-begin-end-3)) ((\,
    internal-x-LaTeX-menu-begin-end-4)) ((\,
    internal-x-LaTeX-menu-checking)) ...))

The code in ltxmenu.el (available at

	http://www.math.utah.edu/pub/emacs/ltxmenu.el

) has this function:

(setq internal-x-LaTeX-menu-of-menus
      (`("LaTeX main menu"		;this menu title is never displayed
	(, internal-x-LaTeX-menu-startup)
	(, internal-x-LaTeX-menu-accents)
...
	(, internal-x-LaTeX-menu-miscellaneous)
	)))

I dug around in the emacs-24 source code, and in lread.c, found the
function load_warn_old_style_backquotes().  However, I cannot find any
indication in ChangeLog files or the *.texi files that the syntax of
backquote has changed, so I don't know what ``old-style backquotes''
is supposed to mean.

As new versions of emacs have appeared, it has been rare to require
modification of my existing Emacs Lisp code (70K lines or so).

Can any of you offer suggestions as to what is expected here, or have
I possibly exposed a bug in the new emacs-24 code?

Our university's winter term break begins next week, and that is
usually the time that we make newer versions of software and hardware
the default ones, so I would like to get this resolved soon.

-------------------------------------------------------------------------------
- Nelson H. F. Beebe                    Tel: +1 801 581 5254                  -
- University of Utah                    FAX: +1 801 581 4148                  -
- Department of Mathematics, 110 LCB    Internet e-mail: beebe@math.utah.edu  -
- 155 S 1400 E RM 233                       beebe@acm.org  beebe@computer.org -
- Salt Lake City, UT 84112-0090, USA    URL: http://www.math.utah.edu/~beebe/ -
-------------------------------------------------------------------------------

Re: emacs-24.0.92 and backquote

[Paul Eggert]

On 12/10/11 16:00, Nelson H. F. Beebe wrote:
> Can any of you offer suggestions as to what is expected here, or have
> I possibly exposed a bug in the new emacs-24 code?

In Emacs Lisp one used to write (` EXPR) rather than `EXPR.  The
latter is the normal style in other Lisps, and was adopted by Emacs as
the "new-style backquotes" around Emacs 20, but the old style was
still supported for a while (and still is, to some extent).
Bug#6490 <http://debbugs.gnu.org/cgi/bugreport.cgi?bug=6490> contains
more info about this.  Old-style backquotes apparently stopped working
to some extent in Emacs 20 and were marked officially obsolete in
Emacs 22.1, and are scheduled to be removed in Emacs 25.

The info about the old syntax was removed from the documentation in
March 2009 in bzr 95128
<http://bzr.savannah.gnu.org/lh/emacs/trunk/revision/95128>.
Emacs 24 still accepts this old syntax, so perhaps it should still be
documented?  Here's the text that was removed:

   In old Emacs versions, before version 19.29, @samp{`} used a
   different syntax which required an extra level of parentheses
   around the entire backquote construct.  Likewise, each @samp{,} or
   @samp{,@@} substitution required an extra level of parentheses
   surrounding both the @samp{,} or @samp{,@@} and the following
   expression.  The old syntax required whitespace between the
   @samp{`}, @samp{,} or @samp{,@@} and the following expression.

   This syntax is still accepted, for compatibility with old Emacs
   versions, but support for it will be removed in the future.


Anyway, to get back to your example, it uses the syntax (`(EXPR)) that
was formerly invalid, but was silently accepted as if it were the
old-style (` (EXPR)), i.e., the new-style `(EXPR).  I think support
for this invalid usage was removed around bzr 100605
<http://bzr.savannah.gnu.org/lh/emacs/trunk/revision/100605>, dated
June of this year, and that's what is causing your problem.

The simplest fix for your example is to change it to use the old syntax:

--- ltxmenu.el	2004-07-28 16:58:31.000000000 -0700
+++ ltxmenu-fix.el	2011-12-10 18:16:56.652363670 -0800
@@ -533,7 +533,7 @@
 ;;; of its components have been defined above.
 
 (setq internal-x-LaTeX-menu-of-menus
-      (`("LaTeX main menu"		;this menu title is never displayed
+      (` ("LaTeX main menu"		;this menu title is never displayed
 	(, internal-x-LaTeX-menu-startup)
 	(, internal-x-LaTeX-menu-accents)
 	(, internal-x-LaTeX-menu-insertion)

But that will stop working in Emacs 25.
Instead, I'd change to the new syntax:

--- ltxmenu.el	2004-07-28 16:58:31.000000000 -0700
+++ ltxmenu-fix.el	2011-12-10 18:18:28.883204171 -0800
@@ -533,22 +533,22 @@
 ;;; of its components have been defined above.
 
 (setq internal-x-LaTeX-menu-of-menus
-      (`("LaTeX main menu"		;this menu title is never displayed
-	(, internal-x-LaTeX-menu-startup)
-	(, internal-x-LaTeX-menu-accents)
-	(, internal-x-LaTeX-menu-insertion)
-	(, internal-x-LaTeX-menu-begin-end)
-	(, internal-x-LaTeX-menu-begin-end-1)
-	(, internal-x-LaTeX-menu-begin-end-2)
-	(, internal-x-LaTeX-menu-begin-end-3)
-	(, internal-x-LaTeX-menu-begin-end-4)
-	(, internal-x-LaTeX-menu-checking)
-	(, internal-x-LaTeX-menu-comment)
-	(, internal-x-LaTeX-menu-cross-reference)
-	(, internal-x-LaTeX-menu-font)
-	(, internal-x-LaTeX-menu-index)
-	(, internal-x-LaTeX-menu-miscellaneous)
-	)))
+      `("LaTeX main menu"		;this menu title is never displayed
+	,internal-x-LaTeX-menu-startup
+	,internal-x-LaTeX-menu-accents
+	,internal-x-LaTeX-menu-insertion
+	,internal-x-LaTeX-menu-begin-end
+	,internal-x-LaTeX-menu-begin-end-1
+	,internal-x-LaTeX-menu-begin-end-2
+	,internal-x-LaTeX-menu-begin-end-3
+	,internal-x-LaTeX-menu-begin-end-4
+	,internal-x-LaTeX-menu-checking
+	,internal-x-LaTeX-menu-comment
+	,internal-x-LaTeX-menu-cross-reference
+	,internal-x-LaTeX-menu-font
+	,internal-x-LaTeX-menu-index
+	,internal-x-LaTeX-menu-miscellaneous
+	))
 
 ;;; NB: All internal-x-LaTeX-xxx commands that are called from the
 ;;; menus MUST call (interactive) (so commandp is true).

Re: emacs-24.0.92 and backquote

[Jambunathan K]

Paul Eggert <eggert@cs.ucla.edu> writes:

> On 12/10/11 16:00, Nelson H. F. Beebe wrote:
>> Can any of you offer suggestions as to what is expected here, or have
>> I possibly exposed a bug in the new emacs-24 code?
>
> In Emacs Lisp one used to write (` EXPR) rather than `EXPR.  The
> latter is the normal style in other Lisps, and was adopted by Emacs as
> the "new-style backquotes" around Emacs 20, but the old style was
> still supported for a while (and still is, to some extent).
> Bug#6490 <http://debbugs.gnu.org/cgi/bugreport.cgi?bug=6490> contains
> more info about this.  Old-style backquotes apparently stopped working
> to some extent in Emacs 20 and were marked officially obsolete in
> Emacs 22.1, and are scheduled to be removed in Emacs 25.
>
> The info about the old syntax was removed from the documentation in
> March 2009 in bzr 95128
> <http://bzr.savannah.gnu.org/lh/emacs/trunk/revision/95128>.
> Emacs 24 still accepts this old syntax, so perhaps it should still be
> documented?  Here's the text that was removed:
>
>    In old Emacs versions, before version 19.29, @samp{`} used a
>    different syntax which required an extra level of parentheses
>    around the entire backquote construct.  Likewise, each @samp{,} or
>    @samp{,@@} substitution required an extra level of parentheses
>    surrounding both the @samp{,} or @samp{,@@} and the following
>    expression.  The old syntax required whitespace between the
>    @samp{`}, @samp{,} or @samp{,@@} and the following expression.
>
>    This syntax is still accepted, for compatibility with old Emacs
>    versions, but support for it will be removed in the future.
>
>
> Anyway, to get back to your example, it uses the syntax (`(EXPR)) that
> was formerly invalid, but was silently accepted as if it were the
> old-style (` (EXPR)), i.e., the new-style `(EXPR).  I think support
> for this invalid usage was removed around bzr 100605
> <http://bzr.savannah.gnu.org/lh/emacs/trunk/revision/100605>, dated
> June of this year, and that's what is causing your problem.

The NEWS has the following entry:

,---- Incompatible Lisp Changes in Emacs 24.1
| ** A backquote not followed by a space is now always treated as new-style.
`----

Wondering what a "new-style" means!

> The simplest fix for your example is to change it to use the old syntax:
>
> --- ltxmenu.el	2004-07-28 16:58:31.000000000 -0700
> +++ ltxmenu-fix.el	2011-12-10 18:16:56.652363670 -0800
> @@ -533,7 +533,7 @@
>  ;;; of its components have been defined above.
>  
>  (setq internal-x-LaTeX-menu-of-menus
> -      (`("LaTeX main menu"		;this menu title is never displayed
> +      (` ("LaTeX main menu"		;this menu title is never displayed
>  	(, internal-x-LaTeX-menu-startup)
>  	(, internal-x-LaTeX-menu-accents)
>  	(, internal-x-LaTeX-menu-insertion)
>
> But that will stop working in Emacs 25.
> Instead, I'd change to the new syntax:
>
> --- ltxmenu.el	2004-07-28 16:58:31.000000000 -0700
> +++ ltxmenu-fix.el	2011-12-10 18:18:28.883204171 -0800
> @@ -533,22 +533,22 @@
>  ;;; of its components have been defined above.
>  
>  (setq internal-x-LaTeX-menu-of-menus
> -      (`("LaTeX main menu"		;this menu title is never displayed
> -	(, internal-x-LaTeX-menu-startup)
> -	(, internal-x-LaTeX-menu-accents)
> -	(, internal-x-LaTeX-menu-insertion)
> -	(, internal-x-LaTeX-menu-begin-end)
> -	(, internal-x-LaTeX-menu-begin-end-1)
> -	(, internal-x-LaTeX-menu-begin-end-2)
> -	(, internal-x-LaTeX-menu-begin-end-3)
> -	(, internal-x-LaTeX-menu-begin-end-4)
> -	(, internal-x-LaTeX-menu-checking)
> -	(, internal-x-LaTeX-menu-comment)
> -	(, internal-x-LaTeX-menu-cross-reference)
> -	(, internal-x-LaTeX-menu-font)
> -	(, internal-x-LaTeX-menu-index)
> -	(, internal-x-LaTeX-menu-miscellaneous)
> -	)))
> +      `("LaTeX main menu"		;this menu title is never displayed
> +	,internal-x-LaTeX-menu-startup
> +	,internal-x-LaTeX-menu-accents
> +	,internal-x-LaTeX-menu-insertion
> +	,internal-x-LaTeX-menu-begin-end
> +	,internal-x-LaTeX-menu-begin-end-1
> +	,internal-x-LaTeX-menu-begin-end-2
> +	,internal-x-LaTeX-menu-begin-end-3
> +	,internal-x-LaTeX-menu-begin-end-4
> +	,internal-x-LaTeX-menu-checking
> +	,internal-x-LaTeX-menu-comment
> +	,internal-x-LaTeX-menu-cross-reference
> +	,internal-x-LaTeX-menu-font
> +	,internal-x-LaTeX-menu-index
> +	,internal-x-LaTeX-menu-miscellaneous
> +	))
>  
>  ;;; NB: All internal-x-LaTeX-xxx commands that are called from the
>  ;;; menus MUST call (interactive) (so commandp is true).
>
>
>

-- 

Re: emacs-24.0.92 and backquote

[Nelson H. F. Beebe]

Many thanks to Paul Eggert for the fine detective work in tracing the
gradual disappearance of the `old-style backquote' and its
reappearance in a `new-style backquote' form with one level of outer
parentheses stripped in the evolution of emacs-20 to emacs-24.

I've spent part of today revising ltxmenu.el, and moved the old and
new versions of the backquoted menu definition into separate files
that are loaded according to the value of emacs-version, so as not to
break the code on any currently-installed version of emacs (I have
many such, on more than two dozen flavors of Unix).

The new files are available here:

	http://www.math.utah.edu/pub/emacs/ltxaccnt.el
	http://www.math.utah.edu/pub/emacs/ltxmenu.el
	http://www.math.utah.edu/pub/emacs/ltxmenu-23.el
	http://www.math.utah.edu/pub/emacs/ltxmenu-24.el

There are corresponding .sig files for each, as well as signed
checksum files for the entire directory.

-------------------------------------------------------------------------------
- Nelson H. F. Beebe                    Tel: +1 801 581 5254                  -
- University of Utah                    FAX: +1 801 581 4148                  -
- Department of Mathematics, 110 LCB    Internet e-mail: beebe@math.utah.edu  -
- 155 S 1400 E RM 233                       beebe@acm.org  beebe@computer.org -
- Salt Lake City, UT 84112-0090, USA    URL: http://www.math.utah.edu/~beebe/ -
-------------------------------------------------------------------------------

Re: emacs-24.0.92 and backquote

[Stefan Monnier]

> I've spent part of today revising ltxmenu.el, and moved the old and
> new versions of the backquoted menu definition into separate files
> that are loaded according to the value of emacs-version, so as not to
> break the code on any currently-installed version of emacs (I have
> many such, on more than two dozen flavors of Unix).

The "new"-style works at least since Emacs-19.34 (the oldest version
I have here installed), so I have a hard time imagining you have an
Emacs around that's still running and yet doesn't support the
"new"-style of backquotes.


        Stefan