New function string-replace-substring in (ice-9 string-fun)

By A. Wingo in
https://lists.gnu.org/archive/html/guile-devel/2014-03/msg00058.html.

* module/ice-9/string-fun.scm (string-replace-substring): As stated.
* doc/ref/api-data.texi: Document the new function.
* test-suite/tests/strings.test: Test.

doc/ref/api-data.texi

@@ -4227,6 +4227,22 @@ a predicate, if it is a character, it is tested for equality and if it
 is a character set, it is tested for membership.
 @end deffn
 
+The following additional functions are available in the module @code{(ice-9 string-fun)}. They can be used with:
+
+@example
+(use-modules (ice-9 string-fun))
+@end example
+
+@deffn {Scheme Procedure} string-replace-substring str substring replacement
+Return a new string where every instance of @var{substring} in string
+@var{str} has been replaced by @var{replacement}. For example:
+
+@lisp
+(string-replace-substring "a ring of strings" "ring" "rut")
+@result{} "a rut of struts"
+@end lisp
+@end deffn
+
 @node Representing Strings as Bytes
 @subsubsection Representing Strings as Bytes
 

module/ice-9/string-fun.scm

@@ -25,13 +25,17 @@
 	   separate-fields-discarding-char separate-fields-after-char
 	   separate-fields-before-char string-prefix-predicate string-prefix=?
 	   sans-surrounding-whitespace sans-trailing-whitespace
-	   sans-leading-whitespace sans-final-newline has-trailing-newline?))
+	   sans-leading-whitespace sans-final-newline has-trailing-newline?
+           string-replace-substring))
 
 ;;;;
 ;;;
 ;;; Various string funcitons, particularly those that take
 ;;; advantage of the "shared substring" capability.
+;;; FIXME Document these functions in Miscellaneous String Operations::
+;;; in doc/ref/api-data.texi.
 ;;;
+
 
 ;;; {String Fun: Dividing Strings Into Fields}
 ;;; 
@@ -278,3 +282,34 @@
 ;;;         (fail parts)
 ;;;         (apply return parts))))
 
+
+
+;;; {String Fun: string-replace-substring}
+;;;
+
+;; string-replace-substring By A. Wingo in
+;; https://lists.gnu.org/archive/html/guile-devel/2014-03/msg00058.html
+;; also in string-replace-substring guix:guix/utils.scm.
+
+(define (string-replace-substring str substring replacement)
+  "Return a new string where every instance of @var{substring} in string
+   @var{str} has been replaced by @var{replacement}. For example:
+
+   @lisp
+   (string-replace-substring \"a ring of strings\" \"ring\" \"rut\")
+   @result{} \"a rut of struts\"
+   @end lisp
+   "
+  (let ((sublen (string-length substring)))
+    (with-output-to-string
+      (lambda ()
+        (let lp ((start 0))
+          (cond
+           ((string-contains str substring start)
+            => (lambda (end)
+                 (display (substring/shared str start end))
+                 (display replacement)
+                 (lp (+ end sublen))))
+           (else
+            (display (substring/shared str start)))))))))
+

test-suite/tests/strings.test

@@ -20,7 +20,8 @@
 
 (define-module (test-strings)
   #:use-module ((system base compile) #:select (compile))
-  #:use-module (test-suite lib))
+  #:use-module (test-suite lib)
+  #:use-module (ice-9 string-fun))
 
 (define exception:read-only-string
   (cons 'misc-error "^string is read-only"))
@@ -693,3 +694,9 @@
       (string-upcase! (substring/shared str2 1 4))
       (and (string=? str1 "foofoofoo")
 	   (string=? str2 "oFOOf")))))
+
+(with-test-prefix "miscellaneous string functions"
+
+  (pass-if "string-replace-substring"
+    (string=? (string-replace-substring "a ring of strings" "ring" "rut")
+              "a rut of struts")))