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

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