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Date: Wed, 01 Feb 2012 11:51:12 +0100
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Date: 2012-02-01T11:51:12+01:00
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Le Wed, 01 Feb 2012 11:37:31 +0100, <stefan-lucks@see-the.signature> a  =

=C3=A9crit:

> On Wed, 1 Feb 2012, Dmitry A. Kazakov wrote:
>
>> But that seems not bad enough. To make the disaster complete, it shou=
ld
>> become undefined as well. Right?
>
> This doesn't need to be a disaster.
>
> 1. For the purpose of proving program correctness, you don't necessari=
ly
> need complete postconditions. As a trivial example, consider

Will read the remaining of your post later, but for now, I agree with yo=
u.  =

Post conditions are not even necessarily a matter of correctness, this m=
ay  =

also be a matter of completing a behavior description. At least here, no=
  =

exception is raised, and it may deals with input from the outside world,=
  =

which can hardly be proved to be always correct.

In the area of correctness however, there is another signature I did not=
  =

quote before, which may talk better to Dmitry. Here is:

    function Image (Instance : Instance_Type) return Image_Type
       with Post =3D>
         (Parsed (Image'Result).Status =3D Parsed) and
         (Parsed (Image'Result).Instance =3D Instance);
       -- Result can always be successfully parsed and the resulting
       -- instance is always equal to the one whose image is returned.

The postcondition for Image, also talks about Parsed behavior. So you ha=
ve  =

an option to ensure correctness, providing a given image was produced by=
  =

the Image function.


-- =

=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