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From: Robert A Duff <bobduff@shell01.TheWorld.com>
Newsgroups: comp.lang.ada
Subject: Re: Silly and stupid post-condition or not ?
Date: Mon, 06 Feb 2012 09:39:14 -0500
Organization: The World Public Access UNIX, Brookline, MA
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Date: 2012-02-06T09:39:14-05:00
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"Yannick Duchêne (Hibou57)" <yannick_duchene@yahoo.fr> writes:

> Seems nice, but given this…
>
>    subtype Image_Type is String
>       with Static_Predicate => Image_Type'Length in Length_Type;
>
>    function Image (Instance : Instance_Type) return Image_Type
>       with Post =>
>         (Parsed (Image'Result).Status = Parsed) and
>         (Parsed (Image'Result).Instance = Instance);
>       -- Result can always be successfully parsed and the resulting
>       -- instance is always equal to the one whose image is returned.
>
> …how do I move Image's Post predicate to an Image_Type's dynamic
> predicate  ? I could not figure the syntax nor if it's at least possible.

Not possible.  Predicates can only express a property of a single
thing, but here you're trying to express a relationship
between two things (parameter and result).

- Bob