Log Message:
Import mtl-2.2.0.1 as devel/hs-mtl,
packaged for wip by pho.

Monad classes using functional dependencies, with instances for
various monad transformers, inspired by the paper Functional
Programming with Overloading and Higher-Order Polymorphism, by Mark P
Jones, in Advanced School of Functional Programming, 1995
(http://web.cecs.pdx.edu/~mpj/pubs/springschool.html).