documentation of difference between lazy and strict State monad

[Henning Thielemann]

On Wed, 21 Sep 2011, Edward Kmett wrote:

> I like the idea, and particularly the fact that the example covers the 
> distinction between strictness in the value, tuple or state. If nothing 
> else, I could bundle this up into a documentation patch for mtl, but the 
> example probably belongs in transformers with the data types, which Ross 
> still maintains. You may have better luck emailing him directly.

I am still not happy with the need to define a custom 'mapM' function, 
since this cannot be ported to other traversable structures easily. But 
maybe there is a theoretical problem, that I did not realize so far.