There isn't. GHC will infer kind `Type -> Type` for `MyType2`. You can check that in `ghci` with `:kind MyType` and `:kind MyType2`. There's also third way to write it by adding a standalone kind signature:
```
{-# LANGUAGE StandalondKindSignatures, GADTs #-}
type MyType3 :: Type -> Type
data MyType3 a where
MkT3 :: Int -> MyType3 Int
```
A polykinded version would look like this:
```
{-# LANGUAGE PolyKinds #-}
type MyType4 :: forall a -> Type
data MyType4 a where
MkT3 :: MyType4 Int
```
in `ghci` the kind of `MyType4` is:
```
:kind MyType4
MyType4 :: forall k. forall (a :: k) -> Type
```
Best regards,
Marcin
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‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
On Thursday, June 10th, 2021 at 13:15, Velichko Lefterov
I tried to understand DataKinds and GADTs...Is there a difference between:
data MyType :: Type -> Type where
MyTypeConstructor :: Int -> MyType Int
data MyType2 a where
MyTypeConstructor2 :: Int -> MyType2 Int