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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Subject: Re: Disabling string evaluation in a logging system
Newsgroups: comp.lang.ada
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Date: Tue, 18 May 2010 14:54:49 +0200
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Date: 2010-05-18T14:54:49+02:00
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On Tue, 18 May 2010 14:10:15 +0200, Georg Bauhaus wrote:

> On 18.05.10 12:26, Dmitry A. Kazakov wrote:
> 
>> BTW, it could be a statement, e.g. conditional call:
>> 
>>    <procedure/entry-call> when <condition>;
> 
> Wouldn't conditional expression work this way?
> 
>    Proc ((if Condition then This else That));

Yes, if we wanted to introduce a full-blown lazy evaluation in Ada. But
then I wished a better, lighter syntax and cleaner semantics.

procedure Write (Where : in out Log; Message : lazy String);

BTW, another case for lazy evaluation is controlling side effects and
evaluation order. E.g.

   function Read (From : access Stream) return Byte;
   function Read (From : access Stream) return Byte;
   function "&" (Left : Byte_Array; Right : lazy Byte) return Byte_Array;

then:

   X : Byte_Array := Read (S) & Read (S); -- This is unambiguous

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