Path: utzoo!mnetor!uunet!husc6!sri-unix!quintus!ok
From: ok@quintus.UUCP (Richard A. O'Keefe)
Newsgroups: comp.lang.misc
Subject: Re: Var scoping in Wirth-type languages (was: Poor Algorithms)
Message-ID: <758@cresswell.quintus.UUCP>
Date: 11 Mar 88 09:25:30 GMT
References: <3821@ihlpf.ATT.COM> <2791@enea.se> <3949@ihlpf.ATT.COM> <4760@sigi.Colorado.EDU>
Organization: Quintus Computer Systems, Mountain View, CA
Lines: 27

In article <3949@ihlpf.ATT.COM>, nevin1@ihlpf (00704a-Liber) writes:
> If some vars are declared 'globally' (at the topmost level), it is very
> inefficient to access those variables in a procedure declared more than 1
> or 2 levels deep.  There is a way to implement scoping that alleviates this
> inefficiency, however.

Can you say "display"?  I knew you could.
You don't even need a full display.  Just retain a pointer to each level of
the display you actually need.  E.g.
	
program main(..); var x;
    procedure one(...); var y;
	procedure two(...); var z;
	    procedure three(...);
		begin {use x and y but not z}
		end;

-->
	    procedure three(...);
		var one_ptr: ^frame of one;
		begin
		    one_ptr := self^.parent^.parent;
		    {use global^.x and one_ptr^.y}
		end;

Any Pascal compiler which searches the static chain on every non-local
variable reference is a toy.