Simple monads

[Christian Maeder]

>>The portable parts of Control.Monad.State (that are sufficient for most
>>cases) should be in an extra module (maybe called Control.Monad.StateTypes).
>>In addition further non-overloaded names for put, get, gets and modify would
>>be needed (maybe putState, getState, etc.)
> 
> I fear, this would complicate the module structure too much. 

I only suggest to split a (comparatively large) module 
Control.Monad.State into two modules. I think that is rather 
appropriate. (I'm willing to supply these modules.)

I've already extracted a portable part, because I wanted to try out the 
nhc98 tracer.

Christian