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From: Florian Weimer <fw@deneb.enyo.de>
Newsgroups: comp.lang.ada
Subject: Re: Operator visibility question
Date: 03 Jun 2001 18:34:26 +0200
Organization: Enyo's not your organization
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Date: 2001-06-03T18:34:26+02:00
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rod@praxis-cs.co.uk (Rod Chapman) writes:

> The SPARK Examiner rejects the declaration of C with the message:
> 
>    9     C : constant Boolean := (A + 2) < B; -- Is "<" visible here?
>                                          ^
> ***        Semantic Error    :309: Operator not visible for these types.

This error message seems to be correct.

> On the other hand, GNAT 3.13 accepts the code with no errors.  Can anyone
> explain which is right, and (more importantly) why?

If one argument of a comparison operator is a universal integer,
a universal real, a string, or an aggregate, then the visibility
check is not performed.  I guess the bug is in somehwere in
Sem_Ch4.Find_Comparison_Types.Try_One_Interp, but I'm not sure, and
it's probably due to the way GNAT deals with operators for universal
types.