On Mon, 2008-10-13 at 13:37 -0700, Daryoush Mehrtash wrote:
Question 1: Why are there lazy and strict modules of some monads? (e.g. Control.Monad.State)
Because both are useful, for different purposes. (For the same reason that it's helpful, in general, to have both eager and lazy evaluation in the same language --- sometimes one version is more efficient, sometimes the other one is).
Question 2: If I define a new monad (say XYZ), does it have to be as Control.Monad.XYZ module?
No. Haskell has neither a requirement nor a convention that monads go in Control.Monad. Control.Monad.* is simply the home of the MTL library, which contains a number of exceptionally useful monads; new monads that aren't as exceptionally general-purpose as MTL probably shouldn't go there, to reduce clutter. jcc