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From: buschman@tubsibr.uucp (Andreas Buschmann)
Newsgroups: comp.lang.modula3
Subject: LOCATION
Message-ID: <9104151354.AA01507@pollux>
Date: 15 Apr 91 13:54:25 GMT
Reply-To: buschman@tubsibr.uucp
Lines: 68
To: kalsow (Bill Kalsow)
Cc: m3

Hi!
> >       For my interpreter I created a procedureal operator LOCATION:
> >  
> >  	LOCATION (VAR x: Any) : REF Any
> >  
> >       How is this supposed to go in the new standard?
> 
> I don't understand.  Are you proposing that LOCATION be added to the
> language?  If so, you should post a full explanation of the proposal
> and its impact.  For instance, it appears to me that LOCATION would
> place great constraints on the possible allocator/collector implementations.
> Since I can use LOCATION to create a REF to an arbirary field in an
> arbitrary record, the collector cannot assume that type tags are near by?
> 
>   - Bill Kalsow

no, I am not sure about proposing this to be added to the language. At
this moment it is a local hack of mine, which doesn't interfere with
my heap storage implementation (I am using bitmaps to keep track of
which storage is still in use). What I want to know is: how do I get
the same effect, with legal actions defined in Modula3.

						Tschuess
							Andreas

A C example of what I want to do:

typedef struct node {
	struct node *next;
	int info;
} NODE;

#define NO_NODE ((NODE*) 0)


insert (NODE **list; NODE *new_node)
{
	NODE **ptr;

	for (ptr = list; 
	     *ptr != NO_NODE && (*ptr) -> info < new_node -> info; 
	     ptr = &((*ptr) -> next));

	new_node -> next = *ptr;
	*ptr = new_node;
}

in Algol68 this would be:

MODE NODE = STRUCT (
	REF NODE next;
	INT info
);

REF NODE no node = NIL;

PROC insert (REF REF NODE list; REF NODE new node) =
BEGIN
  REF REF NODE ptr;

  ptr := list;
  WHILE (ptr <> no node | info OF ptr < info OF new node | false)  DO
    ptr := next OF ptr
  OD;

  next OF new node := ptr;
  REF NODE ptr := new node
END