Excerpts from Brandon Allbery's message of Fri Apr 20 19:31:54 -0400 2012:
> > So, it would be pretty interesting if we could have an ST s style
> > mechanism, where the data structure is not allowed to escape.
> > But I wonder if this would be too cumbersome for anyone to use.
> Isn't this what monadic regions are for?
That's right! But we have a hard enough time convincing people it's
worth it, just for file handles.