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From: alan@pdn.UUCP (Alan Lovejoy)
Newsgroups: comp.lang.modula2
Subject: Re: procedure parameters and TRANSFER
Message-ID: <1323@pdn.UUCP>
Date: Tue, 15-Sep-87 16:55:28 EDT
Article-I.D.: pdn.1323
Posted: Tue Sep 15 16:55:28 1987
Date-Received: Fri, 18-Sep-87 01:43:10 EDT
References: <1966@uvacs.CS.VIRGINIA.EDU>
Reply-To: alan@pdn.UUCP (0000-Alan Lovejoy)
Organization: Paradyne Corporation, Largo, Florida
Lines: 32
Keywords: OS, TRANSFER

In article <1966@uvacs.CS.VIRGINIA.EDU> rlc@uvacs.CS.VIRGINIA.EDU (Robert L. Chase) writes:
>In setting up coroutines in Modula2, the NEWPROCESS procedure
>requires that the PROC (coroutine) be a parameterless procedure.
>Can anyone assist me with why that is the case? What is the 
>underlying mechanism that requires this? 

The underlying mechanism that "requires this" is that a well-designed
language avoids complicating the life of a certain language and/or
compiler designer named Niklaus Wirth.

Specifically, the NEWPROCESS pseudo-procedure has the formal header
definition: PROCEDURE NEWPROCESS(p: PROC; workArea: ADDRESS;
				 workAreaSize: CARDINAL; process: ADDRESS);

and a parameter of type PROC has to be a parameterless procedure.  The
language has no facility for specifying a procedure with a generic 
argument profile, and to make a special case for NEWPROCESS means
more work for Niklaus Wirth as well as introducing an irregularity.

Personally, I think the NEWPROCESS procedure *should* be a special
case which allows procedures of any type, but its not my language.
An even better solution would be to change the semantics of NEWPROCESS
so that the PROCEDURE (MODULE) that invokes NEWPROCESS is the one that
gets instantiated as a process.  The formal definition would then be:
PROCEDURE NEWPROCESS(workArea: ADDRESS; size: CARDINAL; VAR process: ADDRESS).  
This makes it unnecessary to specify the source-proc, since it is now
known to be the caller.

Lacking such changes to the syntax of Modula-2, the simplest and least
elegant fix is to "pass" parameters via global variables. Ugh.

--alan@pdn