On 10/14/07, Yitzchak Gale wrote:

Interesting. What do you mean by a "commutative monad"? It can't be a monad with some sort of additional commutative law, because the old ListT doesn't even satisfy the monad laws. Or does it in some sense?

If m is a commutative monad, then ListT m is a fully paid up monad, not just "in some sense". On a brief definition of commutative monads, and for some examples indicating how common they are, see SPJ's http://research.microsoft.com/~simonpj/papers/haskell-retrospective/HaskellR...

OK, do you propose that we keep it and change its name?

+1, dump the old one completely because you can't express what kind of thing the old ListT is in Haskell. I just want to make sure it gets a good epitaph. If someone answers SPJ's challenge #2 maybe it'll come back. -- Dan