Non type-variable argument in the constraint error, while using with infix

Unfortunately I have been facing a strange error. It happens while using infix with data constructor.

I am new to Haskell. Can any one help me in this regard ?

Prelude> data L a = Cons a (L a) | Emp deriving Show
Prelude> 10 `Cons` Emp
Cons 10 Emp
Prelude> 10 `Cons` 10 `Cons` Emp

<interactive>:43:1: error:
    • Non type-variable argument in the constraint: Num (L a)
      (Use FlexibleContexts to permit this)
    • When checking the inferred type
        it :: forall a. (Num a, Num (L a)) => L (L a)
Prelude> 10 `Cons` (10 `Cons` Emp) 
Cons 10 (Cons 10 Emp)
Prelude> 10 `Cons` 10 `Cons` Emp

<interactive>:45:1: error:
    • Non type-variable argument in the constraint: Num (L a)
      (Use FlexibleContexts to permit this)
    • When checking the inferred type
        it :: forall a. (Num a, Num (L a)) => L (L a)
Prelude> data L a = Emp | Cons a (L a)  deriving Show
Prelude> 10 `Cons` 10 `Cons` Emp

<interactive>:47:1: error:
    • Non type-variable argument in the constraint: Num (L a)
      (Use FlexibleContexts to permit this)
    • When checking the inferred type
        it :: forall a. (Num a, Num (L a)) => L (L a)
Prelude> 

You can define the data constructor to be right-associative,

infixr 5 `Cons`

data L a = Cons a (L a) | Emp deriving Show

Then it will work as you expected.

main = print $ (21::Int) `Cons` 42 `Cons` Emp

-- => Cons 21 (Cons 42 Emp)