> 
> > let rec range a b =
> >   if a > b then []
> >   else a :: range (a+1) b
> >   ;;
> > 
> > let list = range 1 1000000;;
> > 
> > Printf.printf "length = %d\n" (List.length list);;
> > 
> > Can you tell me why this function isn't tail recursive, and 
> > share any useful tips on how to tell whether a function is or 
> > is not tail recursive?
> 
> The recursive call to range is not the result for its 
> caller.  Instead, the result of recursive call is 
> an argument to the cons (the :: operator).
> 
> -- Paul

Hence, here is a tail-recursive range function.

let rec do_range a b r =
  if a > b then r
  else do_range a (b-1) (b::r) (* tail-rec call *)
  ;;

let range a b = do_range a b []
;;

--Luc

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