Question

*****In SML/NJ******

1. Write a function count_list with type

int list -> int

that returns the number of items in a list. An item that is repeated is counted each time it appears in the list.

2. Write an ML function sum_list with type

int list -> int

that returns the sum of all the elements within a list

3. Write a function countdown with the type

int -> int list

that returns a list of numbers from its argument down to 1.

countdown (5) = [5, 4, 3, 2, 1]
countdown (10) = [10, 9, 8, 7, 6, 5, 4, 3, 2, 1]

4. Write a function countup with type

int * int -> int list

that takes two arguments (start and finish) and returns a list with all the numbers between start and finish.

countup (1, 10) = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

countup (2, 7) = [2, 3, 4, 5, 6, 7]

5. Write a function find_last with type

int list -> int

that returns the last element in a list:

findlast [1, 3, 5, 7, 9] = 9

findlast [2, 3, 4, 5] = 5

Answer 1

IF YOU HAVE ANY DOUBTS COMMENT BELOW I WILL BE THERE TO HELP YOU

ANSWER:

EXPLANATION:

Answer 1:

If the exclusiveness of the elements in the list is not to be taken into consideration then

(length ( list 1 2 3 4 1))

ELSE

(define (count-unique-elements lst unique-elems count)
(cond ((null? lst) count)
((member (car lst) unique-elems)
(count-unique-elements (cdr lst) unique-elems count))
(else
(count-unique-elements (cdr lst)
(cons (car lst) unique-elems)
(+ 1 count)))))

(count-unique-elements '(1 2 3 4 5 1 2 3 4 5) '() 0)

Answer 2:

(define (sum-of-elements L)

(apply + L))

(sum-of-elements '(10 9 8 7 6 5 4 3 2 1))

HOPE IT HELPS YOU

RATE THUMBSUP PLEASE