guile: Use char-sets for char-pred arguments.

* lib/guile.scm (%string-trim, string-split): Use char-sets for char-pred.
* test/test-string.scm: Add string-index test using char-sets.

lib/guile.scm

@@ -2222,6 +2222,7 @@
   (define (string-split str char-pred)
     (let ((char-pred (match char-pred
                        ((? char? a) (lambda (b) (char=? a b)))
+                       ((? char-set? cs) (lambda (c) (char-set-contains? cs c)))
                        ((? procedure?) char-pred))))
       (call-with-input-string str
         (lambda (port)
@@ -2286,6 +2287,7 @@
     (let ((char-pred
            (match char-pred
              ((? char?) (lambda (c) (char=? c char-pred)))
+             ((? char-set? cs) (lambda (c) (char-set-contains? cs c)))
              ((? procedure?) char-pred))))
       (let lp ((i 0)
                (sl (string->list (substring s start end))))

test/test-strings.scm

@@ -49,13 +49,16 @@
 ;;            "ululululul")
 
 (with-additional-imports
-    ((only (guile) string-index string-rindex
+    ((only (guile) char-set:lower-case
+           string-index string-rindex
            string-prefix? string-prefix-ci?
            string-suffix? string-suffix-ci?))
 
   (test-call "2" (lambda (str c) (string-index str c)) "fox" #\x)
   (test-call "2" (lambda (str c) (string-index str c)) "fox"
              (lambda (c) (char=? c #\x)))
+  (test-call "0" (lambda (str) (string-index str char-set:lower-case))
+             "fox")
   (test-call "2" (lambda (str c start) (string-index str c start)) "fox" #\x 1)
   (test-call "1" (lambda (str c start end) (string-index str c start end))
              "fox" #\o 0 2)