datatype IntList
	= CONS of int * (unit -> IntList)
	| NIL

fun filter p NIL = NIL
	| filter p (CONS (x,xf)) =
		if p x then CONS (x, fn() => filter p (xf()))
		else filter p (xf())

fun take (xq, 0) = nil
	| take (NIL, n) = nil
	| take (CONS (x,xf), n) = x :: take (xf(),n-1)

val N =
	let
		fun genN (a) = CONS(a+1, fn() => genN(a+1))
	in
		CONS(1, fn() => genN(1))
	end

fun printList (x::xs) = (print ((Int.toString x) ^ " "); printList xs)
	| printList nil = ()

fun pred(x) = IntListSet.numItems( IntListSet.addList(IntListSet.empty, map((fn x => (valOf(Int.fromString(x)) ))) (map((fn x => Char.toString(x))) (String.explode(Int.toString(x))) ) )) = 4

fun main () =
	let
		val result = filter pred  N
	in
		printList (take (result,10))
	end