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Are type variables in GADT heads meaningful?

Is there a difference between the two GADT ads?

data A ab where ... data A :: * -> * -> * where ...
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syntax haskell gadt
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There is no difference. You might think that you do not need to mention type variables in the header to use different names for them in constructor signatures, for example:

 data A :: * -> * -> * where AN :: Num x => x -> b -> A xb AS :: IsString s => s -> b -> A sb

However, as the GHC User Guide says ...

Unlike a Haskell-98 type data type declaration, a variable of type (s) in the data Set a where header has no scope.

... and therefore this also works:

 data A ab where AN :: Num x => x -> b -> A xb AS :: IsString s => s -> b -> A sb
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