Generalize MonadIO to MonadBase

[wren ng thornton]

Bas van Dijk wrote:
> To be honest I also never used a stack of monad transformers that had
> another base monad than IO. So I also don't see myself using it.
> 
> However I can imagine other people will use it or are already using it
> (users of MonadLib for example) and I'm interested in their use-cases
> and experiences.

I've used ST as a base monad a number of times. I rarely (if ever) use 
IO as part of a transformer stack because it has no coherent semantics 
and is best kept on its own. ST however gives access to mutable 
references and is very useful for a number of applications. ...Not that 
I've found the lack of liftST burdensome...

-- 
Live well,
~wren