On Fri 13 Sep 2013 21:41, Mark H Weaver <m...@netris.org> writes:
> Here's an implementation that does this benchmark about 80 times faster
> on my machine: (20 milliseconds vs 1.69 seconds)
>
> (define* (string-replace-substring s substr replacement
> #:optional
> (start 0)
> (end (string-length s)))
> (let ((substr-length (string-length substr)))
> (if (zero? substr-length)
> (error "string-replace-substring: empty substr")
> (let loop ((start start)
> (pieces (list (substring s 0 start))))
> (let ((idx (string-contains s substr start end)))
> (if idx
> (loop (+ idx substr-length)
> (cons* replacement
> (substring s start idx)
> pieces))
> (string-concatenate-reverse (cons (substring s start)
> pieces))))))))
Inspired to code-golf a bit, here's one that's even faster :)
(define (string-replace-substring s substring replacement)
"Replace every instance of substring in s by replacement."
(let ((sublen (string-length substring)))
(with-output-to-string
(lambda ()
(let lp ((start 0))
(cond
((string-contains s substring start)
=> (lambda (end)
(display (substring/shared s start end))
(display replacement)
(lp (+ end sublen))))
(else
(display (substring/shared s start)))))))))
Just marginally so, though.
Andy
--
http://wingolog.org/
