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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: Re: SPARK
Date: Sat, 15 May 2010 21:08:05 +0200
Organization: Ada At Home
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Date: 2010-05-15T21:08:05+02:00
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Oh, something interesting:


    procedure Limit
      (X     : in out Integer;
       Lower : in     Integer;
       Upper : in     Integer)
    --# pre    Lower < Upper;
    --# post  ((X~ < Lower) -> (X =3D Lower)) and
    --#       ((X~ > Upper) -> (X =3D Upper)) and
    --#       (X in Lower .. Upper);

    -- .....


       Limit (Local_Data, Lowest, Highest);
       --# assert Local_Data <=3D Highest;  -- (1)
       Part :=3D Local_Data - Lowest;
       Whole :=3D Highest - Lowest;
       --# assert Part >=3D 0;              -- (2)
       --# assert Local_Data <=3D Highest;  -- (3)

    -- .....


If (2) is removed, it can prove (1) and (3). If (2) is there, it fails t=
o  =

prove (3), while nothing changes Local_Data in the path from (1) to (3),=
  =

and so (3) should be as much provable as (1).

When (2) is there, it seems to forget about the previously proved  =

hypothesis (1) or about hypotheses which make (1) provable.

Will have to better understand how this =E2=80=9Cthing=E2=80=9D thinks.

-- =

There is even better than a pragma Assert: an --# assert