enEven :: Integer -> Even Integer Integer
genEven = anaEven (\x -> if x <= 0 then Nothing else Just (x, pred x)) (\x -> (x, pred x))

genEven :: Integer -> Even Integer Integer
genEven = anaEven (\x -> if x <= 0 then Nothing else Just (x, pred x)) (\x -> (x, pred x))
genEven = anaEven (\x -> if x <= 0 then Nothing else Just (x, pred x)) (\x -> (x, pred x))