TEST 18

matricola: ______________________________

nome (solo se non si ricorda la matricola): __________________________________

• What is a closure? Why are closures necessary?
  

•  Define a Scheme function F that takes as input a predicate P? on natural numbers and returns a predicate on lists of numbers that returns #t on a list ls if and only if  P? is true on all the elements of ls.             Example: ((F odd?) (list 3 5 7) ) --> #t

(define (F P?)
  (lambda (ls)
    (or (null? ls)
        (and (P? (car ls))
             ((F P?) (cdr ls))))))

• Describe the Environment at the end of the evaluation of the following Scheme expression:

                                      (let ((a 5))
                                          ( (lambda (y) (+ a 5) )  a )  )