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From: wf@dcs.gla.ac.uk (Bill Findlay)
Subject: Re: Type mess in Ada standard library
Date: 1999/07/22
Message-ID: <wf-2207991837250001@wyre.dcs.gla.ac.uk>#1/1
X-Deja-AN: 504090237
References: <7n1uu4$so8$1@pegasus.csx.cam.ac.uk> <7n32tt$cio$1@nnrp1.deja.com>
 <7n41v3$j6$1@pegasus.csx.cam.ac.uk>
Organization: The University of Glasgow
Newsgroups: comp.lang.ada
Date: 1999-07-22T00:00:00+00:00
List-Id: <comp.lang.ada>

In article <7n41v3$j6$1@pegasus.csx.cam.ac.uk>,
mgk25@cl.cam.ac.uk (Markus Kuhn) wrote:

> 
> Would it at the same time also be possible to add anonymous arrays?
> 
>   typ'Array(0..255,0..255)  -- anonymous 64k 2D array of typ
>   typ'Array(<>,<>,<>)       -- any 3D array of typ
> 
> or something like that, which wherever they are used lead to identical
> types iff the parameters are identical.

This is beginning to look somewhat like (BS/ISO) Standard Pascal
conformant array parameters!

When I posted on Pascal's type relations I restrained myself
from a presentation of the relationship of "conformability"
between an array type and a conformant array schema.

Essentially, conformant array parameters provide anonymous
array parameter types, with syntax that smuggles the array
'first and 'last attributes into Pascal.

They were motivated by the problem of binding to libraries of
array-intensive routines (especially, NAG) in the context
of Pascal's lack of unconstrained array types; but they also
greatly alleviated the difficulty of writing reusable string
handling subprograms in Standard Pascal.
(I.e. they made it possible to write reusable string handling!)

Example:

procedure sayHello (name : packed array [low..high : Integer] of Char);
  var i : Integer;
begin
   write('Hello: ');
  for i := low to high do
    write(name[i]);
end;
...
sayHello('Bill');
sayHello('sailor');

Excuse any Ada-isms in the syntax - it's a long time since I last
wrote Pascal code.  8-)

The introduction of conformant array parameters was the only
bit of new language design that the authors of BS Standard Pascal
indulged in; but we did so at the specific request of Niklaus Wirth
and Tony Hoare, so we felt ourselves righteously justified!

-- 
Bill Findlay
Department of Computing Science
The University of Glasgow