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From: =?utf-8?Q?Yannick_Duch=C3=AAne_=28Hibou57?=
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Date: Tue, 31 Jan 2012 23:08:44 +0100
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Date: 2012-01-31T23:08:44+01:00
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Le Tue, 31 Jan 2012 13:33:41 +0100, Georg Bauhaus  =

<rm.dash-bauhaus@futureapps.de> a =C3=A9crit:

> On 31.01.12 11:22, Dmitry A. Kazakov wrote:
>> On Tue, 31 Jan 2012 10:35:35 +0100, Georg Bauhaus wrote:
>>
>>> On 31.01.12 09:54, Dmitry A. Kazakov wrote:
>>>> On Tue, 31 Jan 2012 00:11:43 +0100, Yannick Duch=C3=AAne (Hibou57) =
wrote:
>>>>
>>>>>      function Parsed (S : String) return Parsed_Type
>>>>>         with Post =3D>
>>>>>           (if S'Length not in Image_Length_Type then
>>>>>               Parsed'Result.Status =3D Format_Error);
>>>>>            -- There may be other failure conditions.
>>>>>
>>>>>
>>>>> Is such a post=E2=80=91condition a good or bad practice in your hu=
mble or
>>>>> authoritative opinion ?
>>>>
>>>> I would say it would be a bad practice. The reason is that IMO the
>>>> postcondition must be complete, it must tell all truth or nothing. =
 =

>>>> Your
>>>> prostcondition is a partial truth, it does not describe all cases w=
hen
>>>> Status is mandated to be Format_Error.
>>>
>>> One way to express a "hints only" postcondition is
>>>
>>>    with Post =3D> True or  -- yes, mathniks, just FTR:
>>>      (if ... then ...
>>>
>>> The idea is that the partial truth, in the shape of a
>>> formal note, can later lead to an improved program
>>> structure.
>>
>> Apply your idea to the case statement:
>>
>> case Char is
>>    when 'A' =3D> Put_Line ("Got A");
>> end case;
>
> I was only picking up the idea that a case statement's completeness
> is decidable and postconditions aren't. Nor need they be. Yet, incompl=
ete
> information ("lies") can add value to the "about" part of the
> annotated thing. Until the formalists succeed in making the
> program better ("correct" WRT a set of decidable hypotheses),
> that's something.

You both got it. I was exactly hesitating between Dmitry's comment and  =

yours and had both in mind.

-- =

=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