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Re: occam: out ! 0 :: "" semantics
> -- 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:
> BYTE data:
> in ? len :: data
> CHAN OF Envelope chan:
KRoC uses the code generator from the transputer compiler as the first
step of compiling - so KRoC does just what the transputer would do with
the above code.
Namely, Producer generates a *single* communication of the 0 (INT) and
Consumer inputs the len (INT) count, tests it for *greater* than zero and -
only if that tests TRUE - does it do a further input (of len bytes). Of
course, it also tests that len is <= 100, causing an error if that fails.