(* --------------------------------------------------------- *)
(* -- Illustrating basic use of exceptions in ML.         -- *)
(* -- Author: Roni Khardon. Adopted by Alan G. Labouseur  -- *)
(* ----------------------------------------------------------*)

(* Handling overflow - a pre-defined exception *)

fun fac(0)=1
 |  fac(n) = n * fac(n-1)
;

(* this raises an overflow exception for fac(33); *)

fun silentfailfac(n) = 
     fac(n)
     handle overflow => 0
;

silentfailfac(8); (* ok *)
silentfailfac(33); (* Exception handled *)



(* Find index of element in a list, if not in list we raise our own exception *)

exception NotThere;

fun getIndex(x, []) = raise NotThere
 |  getIndex(x, h::t) = 
        if x=h then 
          1
        else 
          1 + getIndex(x,t);

(* Here we wrap the previous function, giving a printed result. *)
fun UgetIndex(x,L) = 
    let
       val a= getIndex(x,L) 
    in 
       (print "The value is in position "; 
        print(Int.toString(a));
        print "\n") 
    end
    handle NotThere =>
	  print("The element is not in the list\n")
;
   
(* Test cases *)   
val a = [1,2,3,4,5,6,7,8,9];
val b = getIndex(1,a);
val b = getIndex(5,a);
(* val b = getIndex(15,a); *)
val b = UgetIndex(1,a);
val b = UgetIndex(5,a);
val b = UgetIndex(15,a);