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From: =?utf-8?Q?Yannick_Duch=C3=AAne_=28Hibou57?=
 =?utf-8?Q?=29?=
 <yannick_duchene@yahoo.fr>
Newsgroups: comp.lang.ada
Subject: Weird behavior with modular type
Date: Tue, 07 Feb 2012 18:24:57 +0100
Organization: Ada @ Home
Message-ID: <op.v9bjzvhzule2fv@douda-yannick>
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Date: 2012-02-07T18:24:57+01:00
List-Id: <comp.lang.ada>

Hi all,

I expect the test to be shortened enough.


The following compiles and run without an error:


    with Ada.Text_IO;
    procedure Bug is

       type Modular_Type is mod 256;
       subtype Index_Type is Natural range 1 .. 3;

       E : Modular_Type :=3D 255;
       I : Index_Type :=3D 3;
       B : Boolean;

    begin
       B :=3D E < 10 ** I;
       Ada.Text_IO.Put_Line (Boolean'Image (B));
    end Bug;


It prints "FALSE"

Now, the following, with added =E2=80=9CNatural'Pos (...)=E2=80=9D, did =
not even compile:


    with Ada.Text_IO;
    procedure Bug is

       type Modular_Type is mod 256;
       subtype Index_Type is Natural range 1 .. 3;

       E : Modular_Type :=3D 255;
       I : Index_Type :=3D 3;
       B : Boolean;

    begin
       B :=3D E < Natural'Pos (10 ** I);
       Ada.Text_IO.Put_Line (Boolean'Image (B));
    end Bug;


That's counter intuitive. I would expect the first to behave as the  =

second, with either a failure to compile or range error at run=E2=80=91t=
ime.

Someone remember a pointer to the most relevant part in the RM? I may be=
 a  =

bit tired, could not find it.

Seems in the first case, the left=E2=80=91side of =E2=80=9CE < 10 ** I=E2=
=80=9D has a modulo  =

applied, or else, I see no way to explain the result, "FALSE". But why  =

would this modulo be applied with a subtype of Natural and not with an  =

Universal_Integer?

I don't like it (and must be idiot in some way, don't you think?).


-- =

=E2=80=9CSyntactic sugar causes cancer of the semi-colons.=E2=80=9D [1]
=E2=80=9CStructured Programming supports the law of the excluded muddle.=
=E2=80=9D [1]
[1]: Epigrams on Programming =E2=80=94 Alan J. =E2=80=94 P. Yale Univers=
ity