Re: [Haskell-cafe] What is MonadPlus good for?

Josef Svenningsson wrote:

You claimed that monad transformers break the mzero-is-right-identity-for-bind law because they can be applied to IO. I say, it's not the monad transformers fault. They cannot possibly be expected to repair the law if they are given a faulty monad.

Doesn't that argue for allowing proven and unproven Monads in Haskell? Using the Curry-Howard correspondance, wouldn't it make sense to provide (proof) terms in a Monad's signature that are witnesses for the monad laws? One could then have signature-only Monads (ie a rather weak requirement) and signature+laws Monads (much stronger). Jacques