Re: [Caml-list] Scoped Bound Resource Management just for C++?

[Florian Weimer <fw@deneb.enyo.de>]

* Andreas Rossberg:

>> If you have coroutines or threads with communication among them, you
>> can always turn type-enforced region-based handles into open handles
>> with an explicit close operation.
>
> I still don't know what you are talking about. Why should a suitable
> type system not be able to make such an operation ill-typed?

It's a general problem.  Once you've got message passing, you've got
mutable state and the ability to escape regions.  Basically, you do
something like this:

  val resource = openResource params
  fun loop()
    (case receiveMailbox () of
       READ count => (read resource count; sendMailbox ACK; loop ())
       WRITE buffer => (write resource buffer; sendMailbox ACK; loop ())
       CLOSE => ())
  end
  val _ = loop ()
  val _ = close resource

>> Like array bounds checking, integer division or other partial
>> functions. 8-)
>
> Right. But these are examples of collateral damage of useful features,
> while the one under discussion is just the damage, with no new
> expressiveness to justify it. ;)

It's not about expressiveness, it's about making writing correct (that
is, resource-aware) code easier.