## Summary currently it isn't possible to change the visibility of a quantified type in a class method a class method with `forall tv ->` will introduce a new `tv` visibly quantified type variable named `tv` even if the class definition contains a `tv` type variable shadowing the existing one and making the method be ambigously typed ## Steps to reproduce ```haskell class Bits b where bitSize :: forall b -> Int ``` ## Expected behavior actually it is somewhat unclear, a `forall tv.` also introduces a new variable shadowing the one from the class head but in a constructor the types from the data declaration aren't in scope so you could use `forall tv ->` if it weren't explicitly disallowed. Basically there should be a way to define a method which works the same as ```haskell class Bits b where bitSize :: forall a -> a ~ b => Int ``` without introducing a new variable, also in the future assuming `foreach tv.` and `foreach tv ->` are introduced we probably should be able to control how a class variable is quantified in each method ## Environment * GHC version used: The Glorious Glasgow Haskell Compilation System, version 9.10.1 Optional: * Operating System: Linux * System Architecture: x86_64