Edward Kmett
You may want to review the thread here:
http://www.haskell.org/pipermail/libraries/2009-November/012833.html
The gist of it is, I would recommend sticking with MTL for right now, but confining yourself to the portions of it that transformers + monads-fd export (i.e. using StateT s Identity instead of State, or avoiding the use of the State constructors and instances on State) until transformers is done being refactored and monads-fd + transformers becomes more or less mtl compatible and the mtl shim = monads-fd + transformers shim is introduced in a future haskell platform. At that point in time you should be able to remove mtl and just reference monads-fd (and/or monads-tf) + transformers. This has the benefit of not fragmenting the user base, letting you link against the large quantities of code that is built on the haskell platform (i.e. HTTP, etc), and provides an upgrade path to bring the code written for use with transformers and the code written for use with mtl into alignment so they can all link some day in the relatively near future without cabal flipping its lid.
Of course, adding support for monadLib, which doesn't conflict with any of this is a completely concern.
In its highest level "not fragmenting the user base" means going back to C++ and Windows. So this doesn't appear like a valid argument to me. I'll choose the package with the highest quality, not the one, which most people use. Fragmenting Hackage is bad. But on the other hand I don't see why I should stick with the inconvenient mtl. Open source software is all about choice, and as long as the mtl fails to provide the same flexibility and convenience, I won't use it. Combined with the fact that fixing it would break existing packages, it appears like I won't go back to the mtl ever. MonadLib does conflict with the mtl, because it uses the same function and type names almost everywhere with only a few minor differences. But that's seldomly a problem in actual applications. Greets, Ertugrul -- nightmare = unsafePerformIO (getWrongWife >>= sex) http://ertes.de/