Now solved [was RE: Problem with backtracking monad transformer]

Andrew Bromage wrote:

...

You may have meant to stack the monad transformers in a different order.

I finally understand. This was exactly my problem. I had to discard my state monad, and use a state monad transformer on the simple backtracking monad (not the backtracking monad transformer on the state monad). Now it works fine (of course). Thanks for the help. cheers, Simon