Не, причём здесь классы типов? Пользуем data:

data Maybe a = Just a | Nothing
data Either a b = Left a | Right b
data Rec f = In (f (Rec f))

Имеем:

*MyModule> :k Maybe 
Maybe :: * -> *
*MyModule> :k Either
Either :: * -> * -> *
*MyModule> :k Rec
Rec :: (* -> *) -> *

kind'ом обладают конструкторы типов.

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