[cap-talk] Petnames versus E-order with ocaps

[Charles Landau]

David-Sarah Hopwood wrote:
> Karp, Alan H wrote:
>> E-order guarantees the following property.  If Alice sends a
>> message to Carol, and then Alice sends a message to Bob containing
>> a reference to Carol,
> 
> You mean "the same reference to Carol".
> 
>> and Bob uses that reference to send a message to Carol, Carol will
>> receive the message from Bob after she receives the message from
>> Alice. (Did I get that right, MarkM?)
> 
> To avoid mistakes I suggest explicitly labelling the references, like
> this:
> 
> If alice sends a message to carol on reference C, and then alice
> sends a message to bob containing C, and bob uses C to send a message
> to carol, carol will receive the message from bob after she receives
> the message from alice.
> 
> (I prefer using lowercase names for subjects.)

Your usage of terms here leads to confusion. Permit me to recast this
scenario in the precise terms used in MarkM's thesis. In that view, all
references to an object are equivalent.

If alice sends a message to bob containing C (and bob is in a different
vat), then what bob receives is not C but a different reference C' to a
different object with the different property that messages to C' are
delivered (to carol) after certain other messages.

You can choose to view C and C' as facets of a composite object, but
please do not confuse composite objects with objects.

>> A petname is a one-to-one mapping between an object reference and a
>> name binding.
> 
> That's a bit imprecise. I use the following definitions:
> 
> Petname: an identifier that is bound in a petnamespace.
> 
> Petnamespace: a one-to-one mapping between petnames and subjects.
> 
> Petname binding: a binding in a petnamespace -- that is, an ordered
> pair (petname, subject).
> 
> Note that the mapping is not to a reference, it is to a subject.

In MarkM's terms, there is a one-to-one relation between references and
objects (aka subjects), so it makes just as much sense to say the
mapping is to a reference.

> (I think it is clearer to say "subject" than "object" here, but I 
> suppose that's a matter of taste.)

>> If Bob has a reference to Carol that he calls foo, a reference to 
>> Carol that Bob receives from Alice will also be denoted foo.

No, because bob receives a different reference from alice.

> If "foo" is the petname for carol in a given petnamespace, then any
> reference to carol will map back to "foo". I don't think this is a
> problem, since there is no suggestion that petnames should replace
> lambda names as the only way to denote references.

I think we are all operating with different notions of the hypothetical 
petname system.