State of the monad libraries

[Ross Paterson]

On Wed, Sep 22, 2004 at 12:22:08PM +0200, Sven Panne wrote:
> I'm a little bit confused about the various bits and pieces of monad
> libraries currently in the HEAD:
> 
>    fptools/libraries/mtl
>    fptools/libraries/monads/Monad/...
>    fptools/libraries/monads/Unstable/...
> 
> Only the first one is being built by the fptools build system, the last
> two have a kind of home-grown build system. What's the relationship
> between these libraries and what are the future plans?

The mtl package is Andy Gill's original Monad Transformer library, widely
used but unmaintained since April 2001.  Only Control.Monad.State has
Haddock documentation.

The monads package is maintained by Iavor Diatchki, but has few users
(just one?).  Unstable.Control.Monad.* is a fork of the MTL, with a
slightly changed interface.  Monad.* is another version, aiming to be
Haskell 98 compatible.

There's a consensus that the proper place in the module namespace for
a monad transformer library is Control.Monad.*, but no other plans.
I don't see anything happening until either
- Iavor sells his fork to the MTL users and we ditch the mtl package, or
- one of the MTL users starts maintaining the mtl package.