'`foreach` in Haskell

This code type-checks:

type T :: Type -> foreach (r :: Type) -> Type -> Type
data T k r a

type T' :: Type -> Type
type T' a = T a Identity a

Why is it that the compiler requires a type of kind Type -> Type (ie., Identity) here? It fails to type-check if you replace Identity with say Int.
What is foreach keyword, and how does one use it in Haskell?

haskell dependent-type

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