How to use validatecommand?

[Frank]

Hello,

I'm trying to use the validatecommand of entry. The following code
throws an error. How do I use it correctly?

Thanks,
Frank


(defun foo ()
  (with-ltk ()
    (let ((e (make-instance 'entry :text "hello world!"
				   :validate "focusin"
				   :validatecommand (lambda ()
						      (format t
"validating...")))))
      (pack e))))
(foo)

#|
invalid command name "1"
invalid command name "1"
    while executing
"1"
	(in -validatecommand validation command executed by .wc)
|#