- bug in make-win-attr-getter fixed

- added window-exists? function

scheme/xlib/window.scm

@@ -52,6 +52,8 @@
 ;; window-exists? returns #t if the windows still exists (makes sense,
 ;; doesn't it :-)
 
+;; This version is easier and faster, but causes an X Protocol error,
+;; if the window does not exist.
 (define (window-exists? window)
   (and (integer? (window-Xwindow window)) ;; hasn't been destroyed by
 					  ;; destroy-window
@@ -59,6 +61,27 @@
 	   #t #f)))			  ;; the window does not
 					  ;; exists.
 
+; (define (window-exists? window)
+;   (let ((dpy (window-display window)))
+;     (letrec ((loop (lambda (w)
+; 		     (or (eq? w window)
+; 			 (any loop (window-children w))))))
+;       (any loop (map (lambda (i)
+; 		       (display-root-window dpy i))
+; 		     (iota (display-screen-count dpy)))))))
+
+;; Alternative version, seems to be slower
+; (define (window-exists? window)
+;   (let ((dpy (window-display window)))
+;     (let loop ((candidates (map (lambda (i)
+; 				  (display-root-window dpy i))
+; 				(iota (display-screen-count dpy)))))
+;       (cond
+;        ((null? candidates) #f)
+;        ((eq? (car candidates) window) #t)
+;        (else (loop (append (cdr candidates)
+; 			   (window-children (car candidates)))))))))
+
 ;; *** change-window-attributes **************************************
 
 ;; change-window-attributes takes an alist of set-window-attributes
@@ -156,7 +179,8 @@
 
 (define (make-win-attr-getter attribute)
   (lambda (window)
-    (cdr (assq attribute (get-window-attributes window)))))
+    (let ((attribs (get-window-attributes window)))
+      (and attribs (cdr (assq attribute attribs))))))
 
 (define window-x (make-win-attr-getter (window-attribute x)))
 (define window-y (make-win-attr-getter (window-attribute y)))