LN_CORE: Improve list->utf8string (15% better than 8a65b9a)

Author: mgorges

modules/ln_core/utf8string.scm

@@ -76,15 +76,17 @@ SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 (define (utf8string->list s) (map integer->utf8char (utf8string->unicode s)))
 
 (define (list->utf8string lst)
-  (define len 0)
-  (for-each (lambda (l) (set! len (fx+ len (string-length l)))) lst)
-  (let ((offset 0)
-        (result (make-string len)))
-    (for-each (lambda (s)
-      (for-each (lambda (c) (string-set! result offset c) (set! offset (fx+ offset 1))) (string->list s))
-    ) lst)
-    result
-  ))
+  (let* ((len (do ((i 0 (fx+ i (string-length (car lst))))
+                   (lst lst (cdr lst)))
+                  ((null? lst) i)))
+         (result (make-string len)))
+    (do ((lst lst (cdr lst))
+         (offset 0 (fx+ offset (string-length (car lst)))))
+        ((null? lst) result)
+       (do ((strlst (string->list (car lst)) (cdr strlst))
+            (offset2 offset (fx+ offset2 1)))
+           ((null? strlst) offset2)
+        (string-set! result offset2 (car strlst))))))
 
 (define (utf8substring s ofs len)
   (list->utf8string (sublist (utf8string->list s) ofs len)))