You may think it doesn't matter, because you could instantiate it to
anything after the fact, but it's possible that the result of the case
statement depends on the choice of instantiation for sy; consider if
sy had an additional constraint:

> Sealed (fromInteger) :: forall t. Num t => Sealed ((->) Integer)

Now the result of the case statement is the concrete implementation of
fromInteger for whatever type it gets instantiated at.