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From: jsa@alexandria.organon.com (Jon S Anthony)
Subject: Re: Building blocks (Was: Design By Contract)
Date: 1997/09/19
Message-ID: <JSA.97Sep19164111@alexandria.organon.com>#1/1
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References: <5v34m5$pl9$1@trumpet.uni-mannheim.de>
 <wihnDCAGPDI0IwlD@treetop.demon.co.uk> <34215E3D.77AE@gsfc.nasa.gov>
 <3421E190.49CC@chimu.com>
Organization: PSINet
Newsgroups: comp.lang.ada,comp.lang.eiffel
Date: 1997-09-19T00:00:00+00:00
List-Id: <comp.lang.ada>


In article <3421E190.49CC@chimu.com> "Mark L. Fussell" <mark.fussell@chimu.com> writes:

> is
>     -- The Eiffel version of the above
> local
>     attempts : INTEGER  -- FYI: initializes attempts to 0
> do
>     if attempts = 0 then
>         -- do main stuff
>     else
>         -- do nothing
>     end
> rescue
>     attempts := attempts + 1
>     retry
> end

> Most of the difference between the Eiffel and Ada approach is really
> "what it feels like" in the exception handler.

That sounds "right" to me.

>  Eiffel's exception handler give you a chance to retry the main body
> which can than do what ever it wants (within its contract), but in
> so doing returns you to thinking about how to satisfy the routine
> call.  The Ada (and many other languages) approach allows you to try
> to both recover from the exception and satisfy the routine call in
> one place.  This may lead you to forget to do one or both of these
> responsibilities.

Is the Eiffel approach really conceptually different from a recursive
"retry" (where the Eiffel retry is basically a structured goto the
beginning of the current invocation)?  For example,

procedure P (.... Attempts : Natural := 0) is
...
    if Attempts = 0 then
        -- do main stuff
    else
        -- do nothing
    end;
exception
    when others => -- (or more specific exception...)
        P(....Attempts+1)
        ...
end P;


/Jon
-- 
Jon Anthony
STL, Belmont, MA 02178, 617.484.3383 
"Nightmares - Ha!  The way my life's been going lately,
 Who'd notice?"  -- Londo Mollari