Re: Unicode in strings

Stefan Monnier <monnier@iro.umontreal.ca> writes:

Anyway, the Emacs Lisp functions right-char (and, after testing, also
left-char, forward-char, and backward-char) support the notion of
character at least for some scripts.  That may be the result of an
interaction with the redisplay code that you mention later, but in
that case it's that code that knows about characters in Unicode.

>
Indeed, the concept is somewhat visible, but it's not really exposed in
the language.  I think what you're seeing is implemented elsewhere than
in `forward-char`, it's a part of the interactive loop which sees that
after `forward-char` you end up "in the middle" of a composition and it
moves the point further, based on information that mostly belongs to the
redisplay code.
>
Try `C-u 2 C-f` and I suspect you'll see that it doesn't always advance
by 2 characters but rather it advances by "2 code points + rounding up
to the next character boundary".

Confirmed.  So Emacs Lisp has a codepoint-oriented interface and then
needs to compensate for that elsewhere.  This does not indicate that a
codepoint-oriented interface is a good idea, rather the opposite.

- anton
--
'Anyone trying for "industrial quality" ISA should avoid undefined behavior.'
  Mitch Alsup, <c17fcd89-f024-40e7-a594-88a85ac10d20o@googlegroups.com>