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From: shang@corp.mot.com (David L. Shang)
Subject: Re: THIS and COMPONENTs
Reply-To: shang@corp.mot.com
Organization: MOTOROLA 
Date: Mon, 29 Jul 1996 15:00:24 GMT
Message-ID: <1996Jul29.150024.13027@schbbs.mot.com>
References: <4tadg9$smm@gjallar.daimi.aau.dk>
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In article <4tadg9$smm@gjallar.daimi.aau.dk> "S\xren Brandt"  
<sbrandt@daimi.aau.dk> writes:
> Ah, well. It seems that I misunderstood your request. Below is the requested
> "objectToComponent". Please ignore that objectToComponent exploits  
undocumented 
> low-level features of the compiler. If the entered object is not a component,
> "objectToComponent" will return NONE.
> 
>    INCLUDE '~beta/sysutils/v1.4/objinterface';
>    ---lib:attributes---
>    objectToComponent:
>      (# o: ^Object;
>         c: ^|Object;
>         ato: @addressToObject;
>      enter o[]
>      do (if o[]<>NONE then
>             (if (o[]->getGCField)//-6 then
>                 (if ((@@o->tos'%AdrGetLong')-24->tos'%AdrGetLong')
>                  //ComponentPTvalue then
>                     (@@c,(@@o->tos'%AdrGetLong')-24)->assignRef
>                 if);
>             if);
>         if);
>      exit c[]
>      #);

My question is, if the concept of function (method) and class are
unified into "pattern" in Beta, why cann't the expression "this(P)"
represent a functional pattern or the current activity? Why should a
low-level hack be used? 

Consider a multi-thread task model (not exactly in Beta):

	PCGame : Task:
	(# 
	   BallQueue : Queue (#...#);   // a class pattern
	   Consume : Thread; 		// predefine a procedure pattern
	   Produce : Thread 		// a procedure pattern
	   (# ...
	      enter (...)
	      do repeat
		 ( if BallQueue.Full then
		      (this(Produce), Consume)->Wait;
			// let this(Produce) wait for a wake signal
			// from the  Consume thread
		   CreateBall->BallQueue.Append;
		   Produce->Wake;
			// wake one of threads who are waiting for
			// the Produce thread's signal
		   (this(Produce), two_seconds)->Sleep
		 )
	   #)
	   Consume : Thread 		// a procedure pattern
	   (# ...
	      enter (...)
	      do repeat
		 ( if BallQueue.Empty then
		      (this(Consume), Produce)->Wait;
		   BallQueue.RemoveHead;
		   Consume->Wake;
		   (this(Consume), one_seconds)->Sleep
		 )
	   #)
	#)

Can I have the above Beta program? Note that "Wait", "Wake" and "Sleep"
are all procedure patterns defined in the class pattern "Task":

	Task
	(# 
	   ...	// waiting queues are defined here
	   Thread
	   (# ...
	      //protocols for threads
	   #)
	   Wait
	   (# who:	Thread;
	      for_whom: class of Thread;
			// "for_whom" is a class variable!
	      enter (who, for_whom)
	      do append "who" in the waiting "for-whom" queue;
	   #)
	   Wake
	   (# whose:	class of Thread;
	      enter (whose)
	      do wake up the first one in the "whose" queue, if any;
	   #)
	   Sleep ...
	#)


David Shang