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Date: Fri, 04 Jan 2002 12:16:45 -0500
From: Hyman Rosen <hyrosen@mail.com>
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Subject: Re: A case where Ada defaults to unsafe?
References: <3C34BF2C.6030500@mail.com> <3C35675D.276C2D81@canal-plus.fr>
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Ted Dennison wrote:

> In article <3C35675D.276C2D81@canal-plus.fr>, Thierry Lelegard says...
>>Maybe the actual question should be "why are there two distinct formats,
>>with and without short-circuit?"
> 
> Again, I wish people would read the rationale before saying stuff like this. It
> is exaplained there.


It is not. The rationale explains the need for short-circuit
forms. It does not explain the need for the commutative forms,
merely taking it as a given that those forms exist. (Section
3.10 of the Ada83 Rationale.)


> One issue is that you may indeed want the side effects of both expressions


Which will happen in an indeterminate order, so they had better
not affect each other. Shrug. It doesn't seem like much of a
reason to me.


> Another is that the compiler is not free to reorder your
> expressions for efficiency with the short-circuit forms


The compiler is always free to reorder expressions provided
the result is as if they were evaluated in the correct order.

> Another is that there are some circumstances where a
> short-circuit is going to be *slower* than a non-short

 > circuit calculation.

Then why wouldn't the compiler just use the more efficient way?