Ben Franksen wrote:
...and the Unimo paper[1] explains how to easily write a 'correct' ListT. BTW, Unimo is an extreme case of the monad laws holding only w.r.t. the 'right' equality, i.e. in the laws m == m' is to be understood as observe_monad m == observe_monad m' (and even this '==' is of course /not/ the Eq class method but a semantic equality.) [1] http://web.cecs.pdx.edu/~cklin/papers/unimo-143.pdf
Are you sure? Maybe I am missing something, but I don't see any claim that the Unimo ListT satisfies the laws any more than the old mtl ListT. It looks to me like Unimo is just an attempt to provide an easier way to create, use, and understand monads, not a change in their semantics. ListT-Done-Right could also be defined via the Unimo framework, and then it would satisfy the monad laws. Thanks, Yitz