saving compositions or not

saving compositions or not

[Stefan Monnier]

I've been using my silly "lambda hack" (posted on gnu.emacs.sources
a little while back) and have noticed that it has an unintended
consequence: because it uses compositions (to turn the `lambda'
keyword into a lambda letter from the greek alphabet) it ends up
modifying the file if the file is saved in emacs-mule format (which
is the format naturally chosen by Emacs for those files it seems).
That is, the composition itself is saved, so the file still works,
but it unexpectedly still appears with a lambda-char rather than
a lambda-keyword if you load it in `emacs -q --no-site-file'.

Up until here, I could consider it a feature, except that it means
that the file will look odd in a non-Emacs editor (because it
uses the emacs-mule coding-system rather than plain ASCII)
and (more importantly) that `cvs diff' will show that the file has
changed, replacing the lambda keyword with a lambda char composition.

How could I change my hack such that the composition is *not* saved
(i.e. is kept as a display-only trick which has no impact whatsoever on
the saved buffer) ?


	Stefan

Re: saving compositions or not

[Kenichi Handa]

In article <200208280043.g7S0hIA32094@rum.cs.yale.edu>, "Stefan Monnier" <monnier+gnu/emacs@rum.cs.yale.edu> writes:
> I've been using my silly "lambda hack" (posted on gnu.emacs.sources
> a little while back) and have noticed that it has an unintended
> consequence: because it uses compositions (to turn the `lambda'
> keyword into a lambda letter from the greek alphabet) it ends up
> modifying the file if the file is saved in emacs-mule format (which
> is the format naturally chosen by Emacs for those files it seems).

If your file doesn't contain any non-ascii chars except in
compositions, I don't know why emacs-mule is naturally
chosen.  Or, do you actually inserts non-ASCII chars of
several charsets?

> That is, the composition itself is saved, so the file still works,
> but it unexpectedly still appears with a lambda-char rather than
> a lambda-keyword if you load it in `emacs -q --no-site-file'.

> Up until here, I could consider it a feature, except that it means
> that the file will look odd in a non-Emacs editor (because it
> uses the emacs-mule coding-system rather than plain ASCII)
> and (more importantly) that `cvs diff' will show that the file has
> changed, replacing the lambda keyword with a lambda char composition.

> How could I change my hack such that the composition is *not* saved
> (i.e. is kept as a display-only trick which has no impact whatsoever on
> the saved buffer) ?

Currently, the coding system emacs-mule is hardcoded to
handle composition.  But, many coding systems
(e.g. iso-latin-*, utf-8) doesn't handle composition.  So,
using one of them will solve your problem.

But, if you really inserts non-ASCII chars of many charsets
in your file, and thus non of above is useless, you can use
iso-latin-X-with-esc.

You can also make a coding system something like this and
use it.

(make-coding-system
 'iso-2022-7bit-no-composition 2 ?J
 "Like iso-2022-7bit bug doesn't preserve information of compositions."
 '((ascii t) nil nil nil
   short ascii-eol ascii-cntl seven)
 '((safe-charsets . t)))

---
Ken'ichi HANDA
handa@etl.go.jp