XML CO538 Anonymous Questions and Answers Keyword Index

This page provides a keyword index to questions and answers. Clicking on a keyword will take you to a page containing all questions and answers for that keyword, grouped by year.

To submit a question, use the anonymous questions page. You may find the keyword index and/or top-level index useful for locating past questions and answers.

Keyword reference for multiplex

Question 82 (2000):

I am attempting to plex together multiple channels into one. Each channel uses a tagged protocol, STATUS, that I have defined. I have found a working solution:

  PROC plex ([]CHAN OF STATUS in, CHAN OF STATUS out)
    WHILE TRUE
      ALT i = 0 FOR SIZE in
        in[i] ? CASE
          INT v:
          sitting; v
            out ! sitting; v
          thinking;
            out ! thinking
          ...  same for all the other variants

However, I am not happy with this, since I am just switching based on what's in the protocol, and just outputting it in every case. What I want to be able to do is something like:

  PROC plex ([]CHAN OF STATUS in, CHAN OF STATUS out)
    WHILE TRUE
      ALT i = 0 FOR SIZE in
        STATUS s:
        in[i] ? s
          out ! s
  :

All my attempts at this have failed, usually resulting in:

    Error-oc-myq7.occ(117)- Name STATUS is not a TYPE.

Can you point me at the right syntax for this? Thanks.

Answer 82:

Your question is a very good one. I'm afraid that occam2.1 has no syntax to express your perfectly reasonable request! This problem occurs when writing many standard components for handling variant (CASE) protocols - buffers, message routers as well as multiplexors and de-mutiplexors. The proposed, but so far unimplemented, occam3 language enabled the declaration of UNION data-types, that would mostly solve this problem. The draft occam3 language specification can be found on:

    http://wotug.ukc.ac.uk/parallel/occam/documentation/

for those interested (1.4 MBytes postscript). Summer or group project anyone?

Keywords: q7 , multiplex