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From: Phil Clayton <phil.clayton@lineone.net>
Newsgroups: comp.lang.ada
Subject: Re: Gnat GPL 2010 available soon (conditional expressions)
Date: Mon, 5 Jul 2010 07:24:28 -0700 (PDT)
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Date: 2010-07-05T07:24:28-07:00
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On Jul 5, 11:26=A0am, Georg Bauhaus <rm.dash-bauh...@futureapps.de>
wrote:
> On 05.07.10 03:27, Phil Clayton wrote:
>
> > On Jun 30, 4:21 am, Britt Snodgrass <britt.snodgr...@gmail.com> wrote:
> > For formal verification tools, conditional expressions could be
> > useful. =A0For example, there are two paths through
>
> > =A0 if C then
> > =A0 =A0 Y :=3D A;
> > =A0 else
> > =A0 =A0 Y :=3D B;
> > =A0 end if;
>
> > but only one path through
>
> > =A0 Y :=3D (if C then A else B);
>
> Any advantage over a function---which in SPARK case will
> be a pure function, IIRC?
>
> =A0 Y :=3D Find_Y (Depends =3D> C);

Not much advantage over a function, only that you don't have the
overheads of introducing the new function and ensuring its
specification has sufficient information.  I wasn't really considering
the possibility of introducing new functions as a general
alternative.  For example, I would rather see certain conditional
expressions inline and not tucked away inside functions, for
readability.

(Correct, SPARK does not allow functions to have side effects.)


> > In my view, condition expressions are a step in the right direction...
> > but I'm the sort of person who wants to write an array aggregate like
>
> > =A0 (for I in 1 .. 5 =3D> (for J in 1 .. 7 =3D> (if I =3D J then 1.0 el=
se
> > 0.0)))
>
> What kind of name would you pick for the thing?

I suppose I'd call it a 'tabulation'..

Phil