Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Posting-Version: version B 2.10.1 (Tek) 9/26/83; site tektronix.UUCP
Path: utzoo!watmath!clyde!burl!ulysses!mhuxl!houxm!hogpc!houti!ariel!vax135!cornell!uw-beaver!tektronix!robertd
From: robertd@tektronix.UUCP
Newsgroups: net.lang.pascal
Subject: Re: X3J9 (Pascal) loops
Message-ID: <3506@tektronix.UUCP>
Date: Thu, 30-Aug-84 14:31:53 EDT
Article-I.D.: tektroni.3506
Posted: Thu Aug 30 14:31:53 1984
Date-Received: Sat, 1-Sep-84 11:44:15 EDT
References: <2356@dartvax.UUCP>
Organization: Tektronix, Beaverton OR
Lines: 53

-------------
Just for the record, the ANSI/IEEE Joint Pascal Committee is X3J9. X3J11 is
the "C" committee.

Regarding the J&W User Manual suggestion that actual parameters passed to 'var'
formal parameters be "distinct", two points:

  First, the User Manual section was exactly that, not a definition of the
  language. As such, it includes style suggestions like this, which seems
  to be suggesting that "aliasing" of variables should be avoided.

  Second, such a restriction is not possible to enforce without examining
  the data flow of a program. Consider the following example:

    var
       x: integer;

    procedure twovars( var a, b: integer);
      begin
          { don't care }
      end;

    procedure sneaky( var p: integer);
      begin
        twovars( p, x);      { aliasing ! }
      end;

    begin
        sneaky( x);
    end;

  Here the passing of x as a var parameter to sneaky results in the call to
  twovars passing x as both actual parameters. It can certainly be argued that
  passing global variables as parameters opens the way for such aliasing, but
  I doubt anyone will seriously suggest prohibiting it. There are certainly
  programs that make use of passing (more) global variables as well as
  aliasing.

Regarding assignment to value parameters: This is practice that amounts
to style preference. I too have been bitten by forgeting to make a parameter
'var', but at the same time I have made use of such assignments. A value
parameter IS a local copy of the actual parameter. The best way to find this
problem (without changing the language and breaking a lot of existing programs)
is to either use a good cross-reference that shows assignments, or bug the
author of your compiler to (optionally!) provide a warning when a value
parameter is assigned a value.

                                              Bob Dietrich
                                              Tektronix, Inc.
                                              (503) 629-1727
{ucb or dec}vax!tektronix!robertd             uucp address
robertd@tektronix                             csnet address
robertd.tektronix@rand-relay                  arpa address