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Subject: Re: and then... (a curiosity)
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From: Ray Blaak <rAYblaaK@STRIPCAPStelus.net>
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Date: Mon, 01 Sep 2008 17:56:11 GMT
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Date: 2008-09-01T17:56:11+00:00
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Martin Krischik <krischik@users.sourceforge.net> writes:
> Actually it is good example - for both:
> 
> 1) Log to both Disk and Network and return true if at least one was
> successful:
> 
> Log_To_Network (Message) or Log_To_Disk (Message)
> 
> 2) Log to Network and if that fails log to Disk and return true if at
> least one was successful:
> 
> Log_To_Network (Message) or else Log_To_Disk (Message)
> 
> And it shows nicely the why there are two: The programmer can decide
> which behaviour he / she wants.

My problem is not with the theoretical elegance as such, but rather that "or"
vs "or else" is not immediately clear to me.

As a multi-language programmer, I am really really used to thinking of boolean
or as "if one is true we don't care about the other". This instinct is
reenforced both from the current popular languages as well as from formal
proof styles in programming methodology.

So, I don't like relying the execution of both disjuncts. Sure, I could use
"or else" consistently, but I like thinking of boolean or as good old regular
boolean or.

So, my preference for the first log example (do both, return success of at
least one is:

  declare
    Network_Logged : Boolean := Log_To_Network(Message);
    Disked_Logged : Boolean := Log_To_Disk(Message); 
  begin
    return Network_Logged or Disked_Logged;
  end;

-- 
Cheers,                                        The Rhythm is around me,
                                               The Rhythm has control.
Ray Blaak                                      The Rhythm is inside me,
rAYblaaK@STRIPCAPStelus.net                    The Rhythm has my soul.