[Haskell-cafe] beginner's problam with a monad

[Julien Oster]

Dan Doel wrote:

> Thus, unfortunately, you won't be able to implement the general bind
> operator. To do so, you'd need to have Tracker use a list that can
> store values of heterogeneous types, which is an entire library unto
> itself (HList).

Telling me that it just won't work was one of the best answers you could
give me, because now I know that I can stop trying (well, I think I will
have a look at HList. If it's easy enough...)

Now if anyone could enlighten me about the "instance Monad Tracker a"
instead of "instance Monad Tracker" part, everything will be clear!

Thanks a lot,
Julien