Hi Iavor,
It is not clear to me what is the right thing to do here (although I agree that the transformer and the monad should be consistent). In 'monadLib' at first I was very careful to make things as lazy as possible, but then I noticed that this was a source of memory leaks, that a user of the library could not really avoid. So now I have started making things stricter,
Lack of laziness is also a serious problem that a user cannot avoid. In my case, I have to completely rewrite StateT, otherwise it is totally unusable. This is definitely a bug. If you make State strict, I am sure it would break many existing programs. (It would certainly break many of mine.) I doubt that very much existing code is relying on the accidental strictness in StateT. Strictness is a problem throughout the Haskell libraries. There was a recent discussion about Data.Map, for example. Right now, there seems to be a need for at least two different versions of every single container and monad in the library, depending on strictness. It would be great if someone could come up with a nicer and more general approach. (And if not - it would be nice of all of those different versions would be added already.) If we are forced to choose one or the other, I would definitely vote for the lazy version. Otherwise, what have we accomplished by using Haskell? Regards, Yitz