looping over characters in a string in elisp?

looping over characters in a string in elisp?

[Roy Smith]

I'm probably being dense, but I can't figure out how to loop over each 
character in a string in elisp (I'm using emacs 20.5.1).  I know I can 
use mapchar to map a function to each character, but I'm looking for 
something that lets me do (essentially):

(while char in string
   (do stuff)
)

Re: looping over characters in a string in elisp?

[Jesper Harder]

Roy Smith <roy@panix.com> writes:

> I can't figure out how to loop over each character in a string in
> elisp (I'm using emacs 20.5.1).  I know I can use mapchar to map a
> function to each character, but I'm looking for something that lets me
> do (essentially):
>
> (while char in string
>    (do stuff))

Here's two different ways:

(require 'cl)
(setq str "Test!")

(dolist (char (append str nil))
  (print char))

(dotimes (i (length str))
  (print (aref str i)))

Re: looping over characters in a string in elisp?

[Kai Großjohann]

Roy Smith <roy@panix.com> writes:

> I'm probably being dense, but I can't figure out how to loop over each 
> character in a string in elisp (I'm using emacs 20.5.1).  I know I can 
> use mapchar to map a function to each character, but I'm looking for 
> something that lets me do (essentially):
>
> (while char in string
>    (do stuff)
> )

Why does it have to be a while loop?  Why is a map-like look not
enough?

(mapcar (lambda (c) (char-to-string c)) "foobar")

This calls the lambda expression on each character and collects the
results in a list.  You can throw the result away if you don't like
it...

-- 
Do not be ashamed of ambibibentism.

Re: looping over characters in a string in elisp?

[Ian Zimmerman]

>> (while char in string (do stuff) )

Kai> Why does it have to be a while loop?  Why is a map-like look not
Kai> enough?

Kai> (mapcar (lambda (c) (char-to-string c)) "foobar")

Kai> This calls the lambda expression on each character and collects
Kai> the results in a list.  You can throw the result away if you
Kai> don't like it...

I can remember the time(s) when I had forgotten enough about Emacs
Lisp that I wanted to ask this question.  I always checked myself in
time and found the answer, but I think this is (a little bit of)
evidence that TFM needs a simple improvement.

Just put "STRINGS ARE ARRAYS" in big fat font at the beginning of the
Strings section (which precedes the Sequences Arrays Vectors section).

-- 
Ian Zimmerman, Oakland, California, U.S.A. 
if (sizeof(signed) > sizeof(unsigned) + 4) { delete this; }
GPG: 433BA087  9C0F 194F 203A 63F7 B1B8  6E5A 8CA3 27DB 433B A087

Re: looping over characters in a string in elisp?

[Kai Großjohann]

Ian Zimmerman <itz@speakeasy.org> writes:

> Just put "STRINGS ARE ARRAYS" in big fat font at the beginning of the
> Strings section (which precedes the Sequences Arrays Vectors section).

8-)  Actually, the Strings and Characters node starts with

/----
|    A string in Emacs Lisp is an array that contains an ordered sequence
| of characters.
\----

Whee.  Not much that can be improved there, except for the big fat
font...
-- 
Ambibibentists unite!