Ein Stapel in Haskell

stapel

module Stapel (
	Stapel,
	empty,
	isEmpty,
	push,
	top,
	pop
	) where
	data Stapel a = E | S a (Stapel a) deriving(Eq,Show)
	empty = E
	isEmpty s = s==E
	push x s = S x s
	top E = error "empty"
	top (S x rs) = x
	pop E = error "empty"
	pop (S x rs) = rs