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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Subject: Re: Unary operator after binary operator: legal or not? => Compiler
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Date: Fri, 3 Aug 2007 09:51:59 +0200
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Date: 2007-08-03T09:48:00+02:00
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On Thu, 2 Aug 2007 20:44:49 GMT, Charles Lindsey wrote:

> In <wccy7gwa7sh.fsf@shell01.TheWorld.com> Robert A Duff <bobduff@shell01.TheWorld.com> writes:
> 
>>But don't you think:
> 
>>    X * -3
> 
>>ought to be legal (no user-defined operators in sight)?
> 
> Interestingly, that example works in ALGOL 68, which generally speaking is
> as pernickety a language as you are likely to get.
> 
> --x works too. Essentially, all the monadic operators have a higher
> preference than the dyadic ones.

The Ada's rule is not about precedence it is about association. Unary minus
does not associate with itself in Ada. This was a deliberate decision.

> The only case where this turns out to be a little odd is
> 
>    -2^2
>
> which is to be contrasted with the effect of
>    x-2^2

No problem, if you wanted -2**2 |= -(2**2), but 2**-2 |= 2**(-2), you would
just extend the precedence model, see

http://www.dmitry-kazakov.de/ada/components.htm#Parsers_etc

(chapter 8.2.2)

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de