;; PROGRAMMING  SET 3

;; Finite Functions or key-value pairs

;; empty list

(define empty-list '())

;; insert

(define insert







;; look-up   --- you may use assq

(define lookup
  (lambda (x l)











(define list1 '((a 10) (b 44) (c (_a1 -> _a2)) (d int)))
(define list2 (insert 'a 9 (insert 'b 43 (insert 'c '(_a2 -> _a3) (insert 'd 'bool empty-list)))))

(define test1 (lookup 'a list1))  ;; Answer > 10
(define test2 (lookup 'c list1))  ;; Answer > (_a1 -> _a2)
(define test3 (lookup 'd list1))  ;; Answer > int
(define test4 (lookup 'a list2))  ;; Answer > 9
(define test5 (lookup 'c list2))  ;; Answer > (_a2 -> _a3)
(define test6 (lookup 'd list2))  ;; Answer > bool
(define test7 (lookup 'f list2))  ;; Answer > ERROR: lookup "no valid entry"
(define test8 (lookup 'f '()))    ;; Answer > ERROR: lookup "no valid entry"