data Nat : Type where
     Z : Nat
     S : Nat -> Nat

namespace Stream
    public export
    data Stream : Type -> Type where
         Cons : $a -> Inf (Stream $a) -> Stream $a

ones : Stream Integer
ones = Cons 1 ones

countFrom : Integer -> Stream Integer
countFrom $x = Cons x (countFrom (prim__add_Integer 1 x))

data List : Type -> Type where
     Nil : List $a
     Cons : $a -> List $a -> List $ a

take : Nat -> Stream $a -> List $a
take Z $xs = Nil
take (S $k) (Cons $x $xs) = Cons x (take k xs)

every2nd : Nat -> Stream $a -> List $a
every2nd Z $xs = Nil
every2nd (S $k) (Cons _ (Cons $x $xs)) = Cons x (every2nd k xs)