First Examle

Started a little late. Anyway, when you move from sequential to concurrent/interactional computation the structure of a conversation becomes larger. The call-return pattern:

A->B: ask a question
B->A: return an answer

is a good pattern for sequential computation (well I will explain) but may not be so for a call back pattern:

A->B: passes a handle
B->A: calls that handle
A->B: says OK

which may be done as a single conversation. This simplest form of extending call-return pattern can be extended to an unbounded callback pattern which may be useful for e.g. updates for auction:

A->B: passes a handle
B->A: calls that handle
A->B: says OK
B->A: invokes that handle
.....

which may be done as many times as needed, all in a single conversation: here B is a server and each callback from B is an update of a bidding price.

Well a real auction may be abstracted in a slightly more complex pattern. In my next post --- perhaps a day or two later --- we shall present a little more complex example including those by Gary.