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From: dewar@cs.nyu.edu (Robert Dewar)
Newsgroups: comp.lang.ada
Subject: Re: Conformance problem in VAX Ada?
Date: 16 Dec 1994 08:49:00 -0500
Organization: Courant Institute of Mathematical Sciences
Message-ID: <3cs5sc$mar@gnat.cs.nyu.edu>
References: <00988B51.1523CFA0.69@gtewd.mtv.gtegsc.com>
 <3chsku$1abb@watnews1.watson.ibm.com>
NNTP-Posting-Host: gnat.cs.nyu.edu
Date: 1994-12-16T08:49:00-05:00
List-Id: <comp.lang.ada>

I certainly agree that this is a compiler problem (failure to diagnose
different default expressions as conformance problem). Here is the GNAT
output:

     1. with Text_IO;
     2. procedure Test is
     3.
     4.    procedure Error (I  : in Integer := Integer'First);
     5.
     6.    procedure Error (I  : in Integer := Integer'Last) is
                     |
        >>> not fully conformant with declaration at line 4
        >>> default expression for "I" does not match

     7.    begin
     8.       Text_IO.Put_Line (Integer'Image (I));
     9.    end Error;
    10.
    11. begin
    12.    Error;
    13. end Test;

THe checking of default expressions is tricky, because they don't have
to be identical (for instance X.A can match A, and things get worse in
9X where "+(a,b) can match a+b. On the other hand 3 does not match 1+2,
so if your compiler folds 1+2 to 3 (which you can expect given that 1+2
is static), it had better make sure this does not happen at a point that
will result in false conformance.

Still this particular case seems pretty straightforward, and would suggest
that the compiler(s) involved are taking some shortcuts on conformance
analysis.