attempt.sml

(* functions *)

 fun number_before_reaching_sum (sum : int, xs : int list) =
     let fun sum_aux (limit, ys, acc, count) =
	     if acc >= limit
	     then count - 1
	     else
		 sum_aux (limit, tl ys, acc + hd ys, count + 1);
     in
	 sum_aux(sum, xs, 0, 0)
     end
 
   

 fun what_month (day : int) =
     let val months = [31,28,31,30,31,30,31,31,30,31,30,31]
     in
	1 + number_before_reaching_sum (day, months)
     end
 

fun month_range (day1 : int, day2 : int) =
    if day1 > day2 then []
    else
	let
	    fun what_month (day : int) =
		if day > day2 then 0
		else
		    let val months = [31,28,31,30,31,30,31,31,30,31,30,31]
		    in
			1 + number_before_reaching_sum (day, months)
		    end;
	in
	    what_month (day1) :: what_month (day1 + 1)
	end

(* tests and error message *)

val number_before_reaching_sum = fn : int * int list -> int
val what_month = fn : int -> int
homework-week-1.sml:93.6-93.48 Error: operator and operand don't agree [tycon mismatch]
  operator domain: int * int list
  operand:         int * int
  in expression:
    what_month day1 :: what_month (day1 + 1)
val it = () : unit
homework-week1-test.sml:22.14-22.25 Error: unbound variable or constructor: month_range
val it = () : unit