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Principles of Programming Languages Exam of 2014.07.25 Notes Total available time: 2h. You may use any written material you need. You cannot use computers or phones during the exam. GIVEN NAME _______________________ SURNAME _______________________ SIGNATURE _______________________ Scheme Exercise 1.1 (4 points) Define a procedure (called vecstrings) that accepts two parameters: a vector V and a list L of strings. vecstrings is used to put every string s in L in V , depending on its length: s is placed at position V[|s|], while strings too long are discarded. If more than one strings have the same length, they are collected in a list. Example: (define ex '("hi" "there" "have" "an" "interesting" "day")) (define v1 (make-vector 7 #f)) (vecstrings v1 ex) is the vector #(#f #f (“an” “hi”) “day” “have” “there” #f) (define (vecstrings V strls) (let ((top (- (vector-length V) 1))) (for-each (lambda (s) (let ((sl (string-length s))) (when (<= sl top) (vector-set! V sl (let ((old (vector-ref V sl))) (cond ((string? old) (list s old)) ((list? old) (cons s old)) (else s))))))) strls) V)) Exercise 1.2 (6 points) Define the procedure make-vecstring, which is a variant of vecstrings returning a closure over V . Such closure has one parameter that must be a string s and works like vecstrings, by putting s in V . When the closure is called with the parameter 'return, it must return the current value of V . Example: (define my-v (make-vecstring v1)) ; the definition of v1 is in Ex. 1.1 (my-v "another") (my-v "member") (my-v "no") (my-v 'return) is the vector #(#f #f (“no” “an” “hi”) “day” “have” “there” “member”) (define (make-vecstring V) (let ((top (- (vector-length V) 1))) (lambda (s) (if (eq? s 'return) V (let ((sl (string-length s))) (when (<= sl top) (vector-set! V sl (let ((old…