Write a function number_before_reaching_sum that takes an int called sum, which you can assume is positive, and an int list, which you can assume contains all positive numbers, and returns an int. You should return an int n such that the rst n elements of the list add to less than sum, but the rst n + 1 elements of the list add to sum or more. A…

number_before_reaching_sum.sml

fun number_before_reaching_sum (sum : int, xs : int list) =
    if null xs then 0
    (*else if null (tl xs) then 1*)
    else if hd xs > sum then 0
    else
	let fun helper (i : int, partial_sum : int, tl_xs : int list) =
		if partial_sum < 0 then i
                else
		    helper(i + 1, partial_sum - hd tl_xs, tl tl_xs)
        in
	    helper(1, sum, xs)
        end