[Haskell-beginners] Haskell data generics

[Eduardo]

Hello everyone,

Here is what I am trying to do: using Data and Typeable generate a
representation of any datatype. After looking at some examples this was my
attempt: http://lpaste.net/132669. But I can't seem to understand how extQ
should work. For instance

https://github.com/faylang/fay/blob/master/src/Fay/Convert.hs#L54

https://github.com/lymar/hastache/blob/master/Text/Hastache/Context.hs#L321

All seem to use extQ to "choose" the right way to encode the values(I
imagine it's because of the cast inside extQ?).

So what am I missing here?