Re: Fwd: Re: Inadequate documentation of silly characters on screen.

[Alan Mackenzie]

Hi, Stefan,

On Thu, Nov 19, 2009 at 09:08:29AM -0500, Stefan Monnier wrote:

> >> If you give us more context (i.e. more of the real code where the
> >> problem show up), maybe we can tell you how to avoid it.

> > OK.  I have my own routine to display regexps.  As a first step, I
> > translate \n -> ñ, (and \t, \r, \f similarly).  This is how:

> >     (defun translate-rnt (regexp)
> >       "REGEXP is a string.  Translate any \t \n \r and \f characters
> >     to wierd non-ASCII printable characters: \t to Î (206, \xCE), \n
> >     to ñ (241, \xF1), \r to ® (174, \xAE) and \f to £ (163, \xA3).
> >     The original string is modified."
> >       (let (ch pos)
> >         (while (setq pos (string-match "[\t\n\r\f]" regexp))
> >           (setq ch (aref regexp pos))
> >           (aset regexp pos                        ; <===================
> >                 (cond ((eq ch ?\t) ?Î)
> >                       ((eq ch ?\n) ?ñ)
> >                       ((eq ch ?\r) ?®)
> >                       (t           ?£))))
> >         regexp))

> Each one of those `aset' (when performed according to your wishes) would
> change the byte-size of the string, so it would internally require
> copying the whole string each time: aset on (multibyte) strings is very
> inefficient (compared to what most people expect, not necessarily
> compared to other operations).  I'd recommend you use higher-level
> operations since they'll work just as well and are less susceptible to
> such problems:

>   (replace-regexp-in-string "[\t\n\r\f]"
>                             (lambda (s)
>                               (or (cdr (assoc s '(("\t" . "Î")
>                                                   ("\n" . "ñ")
>                                                   ("\r" . "®"))))
>                                   "£"))
>                             regexp)

That works 100%.  Even in Emacs 23 ;-).  Thanks!

>         Stefan

-- 
Alan Mackenzie (Nuremberg, Germany).