Dan Grossman wrote:

> It enforces that you don't confuse your reads and writes, but *not* that 
> you don't use a file after you close it.  A monadic approach (where each 
> operation would return a "new" file) or linearity appears necessary for 
> the latter.

	Okay, good point.  However, that raises the interesting question of 
whether there is a nice positive specification of the class of 
"protocols" that are expressible in the presence of effects, rather than 
a negative characterization -- all those that can be broken by aliasing, 
nontermination, etc.