compat: Improve 'string-any' and 'string-every'.

* gash/compat.scm [mes] (string-every): Add optional 'start' and
'end' arguments.
[mes] (string-any): Likewise.

gash/compat.scm

@@ -148,11 +148,23 @@
   (define (string-for-each proc str)
     (for-each proc (string->list str)))
 
-  (define (string-every pred str)
-    ((@ (srfi srfi-1) every) (char-pred pred) (string->list str)))
+  (define* (string-every pred str #:optional (start 0)
+                         (end (string-length str)))
+    (let ((pred (char-pred pred)))
+      (let loop ((k start))
+        (if (= k end)
+            #t
+            (and (pred (string-ref str k))
+                 (loop (+ k 1)))))))
 
-  (define (string-any pred str)
-    ((@ (srfi srfi-1) any) (char-pred pred) (string->list str)))
+  (define* (string-any pred str #:optional (start 0)
+                       (end (string-length str)))
+    (let ((pred (char-pred pred)))
+      (let loop ((k start))
+        (and (< k end)
+             (if (pred (string-ref str k))
+                 #t
+                 (loop (+ k 1)))))))
 
   (define the-eof-object (integer->char -1))