functional programming - how to get an int list of months by giving two days of a year? -

write function named month_range takes 2 days of year named day_one , day_two (e.g. 65, 128, assuming year has 365 days) input , return int list of months. size of int list must day_two - day_one + 1; aware, if day_one>day_two, size of list = 0

example : month_range(25,36) should return [1,1,1,1,1,1,1,2,2,2,2,2]january(25,26,27,..,31) , february(1,2,..,5)

i wrote code doesn't work :

 fun month_range (day1:int,day2:int) =  let    val month_days= [31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31];  fun what_month(day :int) =    let      fun aux(sum :int,  numbers: int list) = let   val numbers_tail = tl numbers in   if sum <= (hd numbers)   1   else         1 + aux(sum, (hd numbers + hd numbers_tail)::(tl numbers_tail)) end in   aux(day, month_days) end in   if (day1>day2)   []   else what_month(day1) @ what_month(day2) end 

well per previous question, have function what_month, return month number of given day of year.

you pretty simple iterate day_one through day_two, calling what_month function each time.

now putting in resulting list, done concatenating result of what_month recursive call function index incremented one, concatenating empty list when index reach day_two.