p7.scm

(define once
    (let ((called #f))
        (lambda (f)
            (lambda args
                (cond
                    ((not called)
                        (set! called #t)
                        (apply f args))
                    (else args))))))

(define p (once (lambda (x) (* x x))))

(print (p 7))
(print (p 8))
(print (p 9))