occam: out ! 0 :: "" semantics

[Oyvind Teig <Oyvind.Teig@xxxxxxxxxxxx>]

-- In a "ByteStream.PROTOCOL.Tokenizer" I've written to marshal
-- bytes on the socket stream I/O, I came upon this problem of
-- what to do when a counted array has zero bytes "to send" off.
-- In SPoC it seems to do a synchronization and an OUTPUT/INPUT
-- pair of len zero in the case, and no memcpy.

-- Obviously we can't send zero bytes over a network, but inside
-- the SPoC runtime system it's ok to say "here is your zero bytes"
-- as long as both parts adher to the same protocol.
--
-- What does KRoC do?

PROTOCOL Envelope IS INT :: []BYTE:

PROC Producer (CHAN OF Envelope out)
  out ! 0 :: ""
:
PROC Consumer (CHAN OF Envelope in)
  INT len:
  [100]BYTE data:
  in ? len :: data
:

CHAN OF Envelope chan:
PAR
  Producer(chan)
  Consumer(chan)

-- 
Oyvind
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