State of the monad libraries

[Sven Panne]

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?

Cheers,
    S.