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From: kasper@pukeko.cosc.canterbury.ac.nz (Kasper Osterbye)
Newsgroups: comp.lang.beta
Subject: Re: THIS and COMPONENTs
Date: 26 Jul 1996 00:14:14 GMT
Organization: University of Canterbury
Lines: 66
Distribution: world
Message-ID: <KASPER.96Jul26121414@pukeko.cosc.canterbury.ac.nz>
References: <4t0s10$jrs@gjallar.daimi.aau.dk>
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In-reply-to: "S\xren Brandt"'s message of 22 Jul 1996 21:32:16 GMT

In article <4t0s10$jrs@gjallar.daimi.aau.dk> "S\xren Brandt" <sbrandt@daimi.aau.dk> writes:

> Kasper Osterbye wrote:
> > 
> > Hi,
> > 
> > Is there a way to obtain a referece to the currently executing
> > co-routine?
> 
> Yes. The systemenv pattern (in basicsystemenv.bet) contains
> the following declaration:
> 
>    theActive: ^|sysHead; 
> 
> which is exactly what you are asking for.

No, it is not.  I am not using the systems library, I am controlling
the scheduling of the co-routines myself (which might be the wrong
approach, but was what I wanted to do - to make the simulation
scheduler directly).  I believe that there is no such mechanism (to
obtain the currently executing co-routine), which is why the basic
system library has a variable "theActive" (in my scheduler I called it
currentEntity).

The BETA S.fork is now S[]->fork because it is not possible to write
it as:
System: 
(# ...
   fork :
   (# do ...
         this(system)[] -> Scheduler.queue
   #)
#)

(Or whatever the scheduler is called).

Because Scheduler.queue will expect something qualified as
"^|System[]" but this(system)[] is an item, not a component.

Therefore fork is implemented to recieve a co-routine reference,
which avoids the problem of "casting" between items and components.

I would like to do "this(|System)[]" or similar.

But I hope there is a way anyway, it would look better. 

In the "objinterface" library I have found the following two
procedures. What I lack is the third which could have been named
"objectToComponent"

isComponent: BooleanValue
  (* Exits true if obj is a component. *)
  (# obj: ^Object;
  enter obj[]
  <<SLOT isComponentBody:dopart>>
  #);

componentToObject: 
  (* Exits the item part of the object entered *)
  (# comp: ^|Object;
     obj: ^Object;
  enter comp[]
  do <<SLOT componentToObjectBody:descriptor>>
  exit obj[]
  #);