[haskell] the One Big Monad problem

[Christopher Jeris]

A while ago someone mentioned the problem of several monads tending to
coalesce into one big monad, and alluded to a solution to this problem
called "monad transformers".  I am struggling with this now in some code
that I am trying to sketch out.  Could someone give a quick explanation of
how to keep several monads (say, a simulation-state monad and IO, which is
what I have now) separated ?

Sorry to keep asking basic questions, I need that "haskell-newbies" list!

thanks & peace,
Chris Jeris