Path: utzoo!mnetor!uunet!mcvax!botter!klipper!victor
From: victor@cs.vu.nl (L. Victor Allis)
Newsgroups: comp.lang.pascal
Subject: Re: Conformable Arrays
Message-ID: <964@klipper.cs.vu.nl>
Date: 21 Dec 87 00:12:07 GMT
References: <1472@cartan.Berkeley.EDU>
Reply-To: victor@cs.vu.nl (Victor Allis)
Organization: VU Informatica, Amsterdam
Lines: 44

In article <1472@cartan.Berkeley.EDU> naparst@cartan.Berkeley.EDU (Harold Naparst) writes:
>I don't quite understand conformable array parameters.
>
>  1)  How do you pass part of an array, like in fortran ?
>  2)  Probably most importantly, are conformable arrays standard ?  Cooper
>      says something about Level 1 and Level 2 Pascal.  What finally happened ?

1) It is not possible to pass parts of array's in Pascal, not even using
   conformant array paramaters.

   In Pascal one has to specify exactly on what type of parameter the
   function or procedure is going to work. Sometimes you want to perform
   the same operations on similar, but different typed variables.
   Suppose you use at least two different real array's. You want to know
   the average of the elements in the array's. It would be boring to
   write two similar functions to perform this actions.
   This is the place where conformant array parameters come in:

   function Average(SomeArray : array[Lower..Upper: integer] of real): real;
   var i : integer;
       Sum : real;
   begin
     Sum := 0.0;
     for i := Lower to Upper do
       Sum := Sum + SomeArray[i];
     Average := Sum / (Upper - Lower + 1)
   end;

   This function can be called with each actual parameter which is a
   real arry, with index a subrange of integer, instead of only one type
   of array.
   This is the only place in Pascal where structure-equivalence is
   important instead of name-equivalence.

2) In fact it is called level 0 Pascal (no conformant array parameters)
   and level 1 Pascal (with conformant array parameters).
   Both levels are defined in the Pascal ISO-standard. I can recommend
   the Pascal User Manual and Report by Jensen and Wirth. This book will
   answer all your questions.

Victor Allis.
Vrije Universiteit of Amsterdam.
The Netherlands.