[Haskell-cafe] Monad proof

Hello, I was studying Monads and I was trying to think about new Monads I could define. So, a question poped into my mind: how is proof regarding the 3 Monad laws handled? I know that, aside from testing all the possible values (and there can be a lot of them), there's no general way to prove it. Nonetheless, I think that it would be insightful to see how people write those proofs for their monads -- specially for new user monads. Is there some article or some notes on proving that Monads are implemented correctly? []'s Rafael