Examples of using polymorphic datatypes ML

	datatype 'a option = NONE | SOME of 'a
	datatype 'a mylist = EMPTY | Cons of 'a * 'a mylist
	datatype ('a,'b) tree =
	Node of 'a * ('a,'b) tree * ('a,'b) tree
	| Leaf of 'b
	val sometree = Node( 1, Leaf(2), Node(3, Leaf(4),Leaf(5)) );
	(* output of program
	- use "polymorphic.sml";
	[opening polymorphic.sml]
	datatype 'a option = NONE | SOME of 'a
	datatype 'a mylist = Cons of 'a * 'a mylist | EMPTY
	datatype ('a,'b) tree = Leaf of 'b | Node of 'a * ('a,'b) tree * ('a,'b) tree
	val sometree = Node (1,Leaf 2,Node (3,Leaf #,Leaf #)) : (int,int) tree
	val it = () : unit
	*)

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