I have a data type looking like this:

data Foo e a where                                                                                                                            
   Foo :: e →  Foo e a    

I would like to instantiate it to make it equivalent to:

data Bar a where                                                                                                                              
   A :: String    →  Bar Int
   B :: Maybe a     →  Bar a

How can I do that? With a functional dependency?

I probably need to change the definition of Foo.