[Haskell-cafe] A use case for *real* existential types

[oleg at okmij.org]

> > I must say though that I'd rather prefer Adres solution because his
> > init
> > > init :: (forall a. Inotify a -> IO b) -> IO b
> > 
> > ensures that Inotify does not leak, and so can be disposed of at the
> > end. So his init enforces the region discipline and could, after a

> It's probably not easy to do this by accident, but I think "ensures" is
> too strong a word here.

Indeed. I should've been more precise and said that 'init' -- like
Exception.bracket or System.IO.withFile -- are a good step towards
ensuring the region discipline.  One may wish that true regions were
used for this project (as they have been for similar ones, like
usb-safe).