This code doesn't work:

test :: Eq a => a -> Bool test a = f a where (f) = \a -> (==) a a

-- during after type inference/checking Error: Context for Prelude.Eq needed in left hand pattern at 8:5.

Removing the brackets makes it work. I suspect the problem is in the type checker, but perhaps the parser should be removing the brackets from the AST before this point.