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
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