[Haskell] Re: Simple IO Regions

[Dominic Steinitz]

Simon Peyton-Jones <simonpj <at> microsoft.com> writes:

> 
> I really like the way you use a set of constraints
> 	(IN m1 ms, IN m2 ms, IN m3 ms) 
> to maintain the set of marks.  Previously I've thought of using a nested
> tuple type
> 	(m1, (m2, (m3 ())))
> to maintain the set, but that is far less convenient.  Very neat.
> 
> Why do you need the 
> 	instance IN () b
> ?

This makes me realise I understand this less than I thought. Can someone give 
an explanation of how the marks get built up?

Thanks, Dominic.