Re: compute ISBN-10, char-to-int?

[<tomas@tuxteam.de>]

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On Thu, Sep 05, 2019 at 03:32:55AM +0200, Emanuel Berg via Users list for the GNU Emacs text editor wrote:
> Another quality release from
> uXu and THE SECRET EMPIRE [...]

> Anyway, questions:
> 
> that `char-to-int' looks a bit strange...

[...]

> (defun char-to-int (c)
>   (string-to-number (char-to-string c) ))

It looks a bit roundabout, sure. But how would you do it without
making any assumptions about the underlying encoding?

If you have no scruples, and since chars in Emacs Lisp are simply
integers, and since encoding is almost-UTF-8 which is basically
ASCII, you could do

(defun char-to-int (c)
  (- c ?0))

but...

  - it's ugly
  - I don't know if that addresses your question

It would be faster, yes. But that will start to count once we
have ISBN-4294967296 or something. By then, you'll have a faster
computer, too ;-)

Cheers
-- t

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