Finding this issue made me LOL

pro.sml

fun get_nth (words : string list, n : int) =
  if n = 1
  then (hd words)
  else get_nth((tl words), n - 1)
 
fun date_to_string(date : int*int*int) =
  let
    val months = ["January", "February", "March", "April", "June",
    "July", "August", "September", "October", "November", "December"]
    val month = get_nth(months, #2 date)
  in
    month ^ " " ^ Int.toString(#3 date) ^ ", " ^ Int.toString(#1 date)
  end

(* Find the error...*)
(* - date_to_string((2013, 6, 1)) = "June 1, 2013" *)
(* val it = false : bool *)
(* - date_to_string((2013, 6, 1)); *)
(* val it = "July 1, 2013" : string *)