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

Question

write a function named month_range that takes two days of a year named day_one and day_two (e.g. 65, 128, assuming the year has 365 days) as input and return an int list of its months. the size of this int list must be day_two - day_one + 1; be 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) and February(1,2,..,5)

I wrote the code but it 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)
  then 1
  else    
    1 + aux(sum, (hd numbers + hd numbers_tail)::(tl numbers_tail))
end
in
  aux(day, month_days)
end
in
  if (day1>day2)
  then []
  else what_month(day1) @ what_month(day2)
end

Answer 1

Well as per your previous question, you have a function what_month, which will return the month number of a given day of the year.

You could pretty simple iterate from day_one through day_two, calling your what_month function each time.

Now putting it all in a resulting list, could be done by concatenating the result of what_month with a recursive call to your function with the index incremented by one, concatenating with the empty list when your index reach day_two.