data Lam :: Type -> Type where
    LamVar :: String -> Lam a
    LamInt :: Int -> Lam Int
    LamNeg :: Lam Int -> Lam Int
    LamAdd :: Lam Int -> Lam Int -> Lam Int
    LamSub :: Lam Int -> Lam Int -> Lam Int
    LamMul :: Lam Int -> Lam Int -> Lam Int
    LamAbs :: String -> Lam b -> Lam (a -> b)
    LamApp :: Lam (a -> b) -> Lam a -> Lam b