Trying to create a datatype/constructor given just its constructor as a string, something like:

mkConstr :: String -> Constr
parseData :: (Data a) => String -> a

***without knowing in advance anything about the datatype apart from the string contents***

So, not something like:

parseData "Just 3" :: [Maybe]

but simply:

parseData "Just 3"

(This is linked to the other post: the goal is to be able to deserialize xml without needing to know in advance the data type we are deserializing)