: clear-but
	(... x1 x2 ... xN N -- x1 x2 ... xN)
	(removes all but the top N things from the stack)
	depth 1 - over -
	(... x1 x2 ... xN N Ntrash)
	dup 0 > if
		(... x1 x2 ... xN N Ntrash)
		swap 1 + swap
		1 swap 1 for
			pop
			(... t x1 x2 ... xN N+1)
			dup rotate pop
			(... x1 x2 ... xN N+1)
		loop
		(x1 x2 ... xN N+1)
	else
		(x1 x2 ... xN N Ntrash)
		pop
	then
	(x1 x2 ... xN num)
	pop
;