[plt-scheme] addition to pregexp

I like this feature.

Instead of introducing a new name, how about generalizing
`[p]regexp-replace[*]' to accept either a string or a function as its
last argument?

Matthew

At Thu, 16 Mar 2006 20:59:45 -0500, Jon Rafkind wrote:
> Can the following function be added to pregexp.ss or string.ss( or 
> whatever the best regexp libary in mzscheme is )?
> 
> I wrote this using pregexp, though.
> 
> (pregexp-replace% regexp str func)
> 
> Which works exactly like pregexp-replace* except the replacement string 
> for each match is the result of (func match). This is handy to do things 
> like uppercase the matched pattern and other such things. One other 
> language I know of( ruby ) has this and I find it pretty useful. I 
> thought mzscheme would like it as well.
> 
> Heres my attempt at its implementation:
> 
> (require (lib "list.ss"))
> (require (lib "string.ss"))
> (require (lib "pregexp.ss"))
> 
> ;; return a list of pairs, each pair equal to the start and end of a match
> (define (pregexp-match-positions* regexp str)
>   (let loop ((start 0)
> 	     (matches '()))
>     (if (>= start (string-length str))
>       (reverse matches)
>       (let ((match (pregexp-match-positions regexp str start)))
> 	(if (not match)
> 	  (reverse matches)
> 	  (loop 
> 	    (if (eq? (caar match)
> 		     (cdar match))
> 	      (add1 (cdar match))
> 	      (cdar match))
> 	    (cons (car match) matches)))))))
> 
> ;; replace all matches of `regexp' in `str' with the result of `func' applied 
> to
> ;; each match
> (define (pregexp-replace% regexp str func)
>   (let ((matches (pregexp-match-positions* regexp str))
>         (last-position 0))
>     (string-append
>       (apply string-append
>              (map (lambda (match)
>                     (let ((start (car match))
>                           (end (cdr match)))
>                       (let ((result (string-append
>                                       (substring str last-position start)
>                                       (func (substring str start end)))))
>                         (set! last-position end)
>                         result)))
>                   matches))
>       (substring str last-position)))) 
> 
> (define (string-assert str1 str2)
>   (unless (string=? str1 str2)
>       (printf "~a != ~a\n" str1 str2)))
> 
> (string-assert (pregexp-replace% "xyz" "hello" (lambda (x) x)) "hello")
> (string-assert (pregexp-replace% "e" "hello" (lambda (x) x)) "hello")
> (string-assert (pregexp-replace% "l*" "hello" (lambda (x) 
> 						(string-upcase x)))
> 	       "heLLo")
> 
> (string-assert (pregexp-replace% 
> 		 "[A-Z]+_?" "SOME_STRING"
> 		 (lambda (x)
> 		   (string-append (substring x 0 1)
> 				  (string-downcase
> 				    (substring
> 				      (pregexp-replace "_" x "") 1)))))
> 	       "SomeString")
> 
> 
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