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lang-hs
*a.k.a.Typeis the kind of types likeIntwhose values are "lifted", that is, that can be pending computations (thunks) or evenundefined. But Haskell also has types likeInt#which are actual "machine ints" that can't be thunks. And each possible in-memory representation has its own kind. This aspect of GHC is still evolving. downloads.haskell.org/~ghc/9.0.1/docs/html/users_guide/exts/…forall k. (* -> k) -> k." Forall k is universal k. And * is not constrained, although at least 1 person has written that * is not a wildcard either. What is the difference between * and forall k?kis a variable, you can instantiate it to any kind you like:*, or* -> *, or(* -> *) -> *, etc.*is one specific concrete kind. It doesn't stand as a placeholder to be instantiated by something else, it is the most basic kind; it is also calledType, now, but it always acted like a basic name likeType, not like a wildcard or operator as the*symbol might suggest.Boolis also zero arity (TrueandFalse, lifted to type-level with theDataKindsextension). Any enum-like type will similarly contain only zero-arity things.Typeis a much better name, since that describes what it means and what is unique about it: every type-level thing whose kind isTypecan be used as the type of things at the term level, while no type-level thing with a different kind can be used that way.