Check whether a type is an instance of Show in Haskell?

Question

Suppose I have a simple data type in Haskell for storing a value:

data V a = V a

I want to make V an instance of Show, regardless of a\'s t

Answer 1

Even if you could do this, it would be a bad design. I would recommend adding a Show constraint to a:

instance Show a => Show (V a) where ...

If you want to store members in a container data type that are not an instance of Show, then you should create a new data type fore them.