Replacing substrings in strings

Replacing substrings in strings

[Sebastian Tennant]

Hi Guilers,

I needed to replace two consecutive spaces in strings with '  ' so
I came up with this:

 (define (replace-substring s t u)
   "Return string S with all occurrences of string T replaced by string U."
   (let ((rv ""))
     (let loop ((r s)) ; r for 'remaining'
       (let ((a 0) (b 0))
         (set! a (string-contains r t)) ;match-start index
         (if a
             (begin
               (set! b (+ a (string-length t))) ;match-end index
               ;; concatenate that which precedes match-start and u to rv
               (set! rv (string-append rv (substring r 0 a) u)) 
               (loop (substring r b))) ;repeat on that which follows match-end
           (set! rv (string-append rv r)))))
     rv))

 (replace-string "Hello.  How are you?" "  " "  ")
 => "Hello.  How are you?"

It works, but seems like a lot of work to achieve something pretty
banal.

At first I thought Richard Todd's (string transform) module in guile-lib
would be able to help, but it works on single characters rather than
substrings.

Are there any there other string libraries I don't know about that could
be used to achieve this?  Or is there a better algorithm for that
matter?  Silly question - of course there is!

Regards,

Seb
-- 
Emacs' AlsaPlayer - Music Without Jolts
Lightweight, full-featured and mindful of your idyllic happiness.
http://home.gna.org/eap

Re: Replacing substrings in strings

[Linas Vepstas]

2009/4/14 Sebastian Tennant <sebyte@smolny.plus.com>:
> Hi Guilers,
>
> I needed to replace two consecutive spaces in strings with ' &nbsp;' so

Most programming languages use regex, and so does guile:

http://www.gnu.org/software/guile/manual/html_node/Regular-Expressions.html

--linas

Re: Replacing substrings in strings

[Sebastian Tennant]

Quoth Linas Vepstas <linasvepstas@gmail.com>:
> 2009/4/14 Sebastian Tennant <sebyte@smolny.plus.com>:
>> I needed to replace two consecutive spaces in strings with ' &nbsp;' so
>
> Most programming languages use regex, and so does guile:

Of course it can be done using regexps, I'm just a little surprised
there isn't already a replace-substring function knocking around.

Seb
-- 
Emacs' AlsaPlayer - Music Without Jolts
Lightweight, full-featured and mindful of your idyllic happiness.
http://home.gna.org/eap

Re: Replacing substrings in strings

[Ludovic Courtès]

Hello,

I would probably use, e.g., `regexp-substitute/global' as Linas
suggested.  Otherwise, you could try using SRFI-13 as well if it's
enough (consecutive spaces are coalesced here):

  (string-join (string-tokenize "hello, world.") " ")
  => "hello, world."

Thanks,
Ludo'.

Re: Replacing substrings in strings

[Sebastian Tennant]

Quoth ludo@gnu.org (Ludovic Courtès):
> Otherwise, you could try using SRFI-13 as well if it's enough
> (consecutive spaces are coalesced here):
>
>   (string-join (string-tokenize "hello, world.") " ")
>   => "hello, world."

I need to only replace two consecutive spaces.  Also string-tokenize (in
guile-1.8) doesn't like unicode strings...  I have my answer - regexps,
although sledgehammers and nuts come to mind.

I remember reading that work is currently underway to implement wide
string handling in Guile.  Any idea when it might make it into a stable
release?

Seb
-- 
Emacs' AlsaPlayer - Music Without Jolts
Lightweight, full-featured and mindful of your idyllic happiness.
http://home.gna.org/eap

Re: Replacing substrings in strings

[Ludovic Courtès]

Sebastian Tennant <sebyte@smolny.plus.com> writes:

> I remember reading that work is currently underway to implement wide
> string handling in Guile.  Any idea when it might make it into a stable
> release?

Mike Gran is working on it.  It won't be released before the next stable
series (2.x), which isn't precisely scheduled.  :-)

Thanks,
Ludo'.

Re: Replacing substrings in strings

[Neil Jerram]

Sebastian Tennant <sebyte@smolny.plus.com> writes:

> Quoth Linas Vepstas <linasvepstas@gmail.com>:
>> 2009/4/14 Sebastian Tennant <sebyte@smolny.plus.com>:
>>> I needed to replace two consecutive spaces in strings with ' &nbsp;' so
>>
>> Most programming languages use regex, and so does guile:
>
> Of course it can be done using regexps, I'm just a little surprised
> there isn't already a replace-substring function knocking around.

There is, and I guess it's what Linas had in mind:
regexp-substitute/global (from (ice-9 regex)).

For example:

  ;; Replace forward slashes by backward ones.
  (set! path (regexp-substitute/global #f "/" path 'pre "\\" 'post))

Regards,
        Neil