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Date: Mon, 5 Dec 2016 10:42:56 -0800 (PST)
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Subject: Re: Ada 2012 Constraints (WRT an Ada IR)
From: Shark8 <onewingedshark@gmail.com>
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Xref: news.eternal-september.org comp.lang.ada:32617
Date: 2016-12-05T10:42:56-08:00
List-Id: <comp.lang.ada>

On Monday, December 5, 2016 at 4:09:42 AM UTC-7, Simon Wright wrote:
>
> [...]
> > Things called in Ada pre- and post-conditions if evaluated during
> > run-time are merely subprogram bodies booby-trapped with unanticipated
> > exceptions. Bad thing.
> 
> Just as bad a thing as Constraint_Error.
> 
> To me, there's no practical difference, at any rate from a black box
> point of view, between a language-defined exception and an assertion (or
> condifion) failure; just a matter of who defines what is out of the
> envelope for the program.


And now we come back full-circle to the topic of the thread:

    Subtype P0 is Integer range 1..Integer'Last;
    Subtype P3 is Integer with
      Static_Predicate  => P3 in 1..Integer'Last,
      Predicate_Failure => raise Constraint_Error; 

are conceptually the same thing (although in Ada they are implemented differently such that turning off assertions makes P3 not raise Constraint_Error).

Since these are conceptually the same, they should have similar representations in an IR, preferably the same representation with a flag/discriminant on the constraint indicating whether or not turning assertions off impacts the condition-check.