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From: "Randy Brukardt" <randy@rrsoftware.com>
Newsgroups: comp.lang.ada
Subject: Re: Redefining "in" "operator"
Date: Mon, 5 Feb 2018 18:48:24 -0600
Organization: JSA Research & Innovation
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Date: 2018-02-05T18:48:24-06:00
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"Jeffrey R. Carter" <spam.jrcarter.not@spam.not.acm.org> wrote in message 
news:p5a1bq$f3v$1@dont-email.me...
> On 02/05/2018 05:26 PM, Alejandro R. Mosteo wrote:
>>
>> Are there special reasons not to allow something like that? I think "in" 
>> is not an operator in the Ada RM sense but now I'm curious why the 
>> special treatment.
>
> The right side of "[not] in" is a subtype. Ada does not allow operators to 
> have operands that are subtypes.

Well, Ada 2012 also allows it to be a (set) of expressions as well. But your 
basic point applies: there aren't any function parameters that are subtypes 
or that are sets of expressions. One could imagine allowing a pair of 
expressions, but that's just "=" (and "in" in fact uses user-defined "=" 
when necessary).

                                 Randy.