(*----------------------------------------------------------------*)
(* Sum of a real list, using hd() and tl() *)
(*----------------------------------------------------------------*)
fun sum (L: real list) =
   if null(L) then 
      0.0
   else
      hd(L) + sum(tl(L));


(*----------------------------------------------------------------*)
(* Sum of a real list, using patterns *)
(*----------------------------------------------------------------*)
fun sump (nil) = 
       0.0
|   sump (Head::Tail: real list) = 
       Head + sump(Tail);


(*----------------------------------------------------------------*)
(* Calculate the mean of a list of real numbers *)
(*----------------------------------------------------------------*)
fun mean (L: real list) = 
   sump(L) / real(length(L));



(*----------------------------------------------------------------*)
(* Calculate the mean of a list of real numbers *)
(*----------------------------------------------------------------*)
fun factorial (n) = 
   if n=1 then 
      1
   else 
      n * factorial(n-1);