Re: Bug in regexp-substitute/global

[Jim Blandy <jimb AT red-bean dot com>]

> Old (correct, IMO) behaviour:
> 
> (regexp-substitute/global #f "x" "string" 'pre "y" 'post)
> =>  "string"   ;; no substitutions applied
> 
> 
> New (in CVS), buggy behaviour:
> =>  ""        ;; empty string?  what gives!?!?
> 
> If a (any!) substitution is made, then the result is correct.

Yes; the old code got some border cases wrong, and I rewrote it.
I even wrote a bunch of test cases, but forgot this one.

1999-09-16  Jim Blandy  <jimb@savonarola.red-bean.com>

	* regex.scm (regexp-substitute/global): Handle the end of the
	match list and an empty match list identically.  (Thanks to Greg
	Badros.)

I think this patch makes a more consistent general structure, in that
you only handle the tail in one place.  (I also flipped the sense of
the if, but that's just cosmetic.)

Index: regex.scm
===================================================================
RCS file: /egcs/carton/guile-home/cvsfiles/guile/guile-core/ice-9/regex.scm,v
retrieving revision 1.4
diff -c -c -b -F'^(' -r1.4 regex.scm
*** regex.scm	1999/09/11 17:38:31	1.4
--- regex.scm	1999/09/16 14:36:21
***************
*** 166,172 ****
        ;; Walk the set of non-overlapping, maximal matches.
        (let next-match ((matches (list-matches regexp string))
  		       (start 0))
! 	(if (pair? matches)
  	    (let ((m (car matches)))
  
  	      ;; Process all of the items for this match.  Don't use
--- 166,173 ----
        ;; Walk the set of non-overlapping, maximal matches.
        (let next-match ((matches (list-matches regexp string))
  		       (start 0))
! 	(if (null? matches)
! 	    (display (make-shared-substring string start) port)
  	    (let ((m (car matches)))
  
  	      ;; Process all of the items for this match.  Don't use
***************
*** 184,194 ****
  		     (make-shared-substring string start (match:start m))
  		     port))
  		   ((eq? item 'post)
! 		    (if (pair? (cdr matches))
! 			(next-match (cdr matches) (match:end m))
! 			(display
! 			 (make-shared-substring string (match:end m))
! 			 port)))
  		   (else (error 'wrong-type-arg item))))
  
  		(if (pair? items)
--- 185,191 ----
  		     (make-shared-substring string start (match:start m))
  		     port))
  		   ((eq? item 'post)
! 		    (next-match (cdr matches) (match:end m)))
  		   (else (error 'wrong-type-arg item))))
  
  		(if (pair? items)