(**********************************************************************************
 ****************** Assignment 5 **************************************************
 **********************************************************************************)
(* Configure printing *)
Control.Print.printDepth := 100;   

(****************** Datatypes *****************************************************)

(* n-ary tree *)
datatype 'a n_tree = Leaf of 'a
				   | N_branch of 'a n_tree list
(* n-ary itree *)
datatype 'a labeled_n_tree = L_Leaf of 'a
				   | L_N_branch of 'a * 'a labeled_n_tree list

(* lazy list *)
datatype 'a seq = Nil | Cons of 'a * (unit -> 'a seq)

(****************** Auxiliary functions ******************************************) 
(* Take from sequence *)
val rec take =
       fn (seq, 0)        => [ ]
        | (Nil, n)        => raise Subscript
        | (Cons(h, t), n) => h::take(t(), n-1);

(* Even numbers sequence builder *)
val rec evens_from = 
      fn (n) => Cons(n, fn() => evens_from(n + 2));

(* Add sequences *)
val rec add_seqs = 
   fn (Cons(h, t), Cons (h', t')) => Cons(h + h', fn() => add_seqs(t(), t'()))
    | _                           => Nil;