[Haskell-beginners] :kind (->) - What do the question marks imply?

[Amitava Shee]

Hello Haskell gurus,

I am trying to understand "kind"

Prelude> :k Maybe
Maybe :: * -> *
Prelude> :k (->)
(->) :: ?? -> ? -> *

What are the question marks? Why are they different from *? How is this
related to rank-2 polymorphism?

Thanks in advance,

Regards,
Amitava Shee
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