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From: RLS@psu.edu    (Robert L. Spooner, AD3K)
Subject: Re: Help with Exceptions!
Date: 1996/05/09
Message-ID: <4mt0um$dgu@hearst.cac.psu.edu>#1/1
X-Deja-AN: 153895473
references: <4mmimq$s4r@hatathli.csulb.edu> <318F353D.4531@mtm.syr.ge.com>
 <4mqio5$a8b@news.sanders.lockheed.com>
organization: Applied Research Laboratory, The Pennsylvania State Universitiy
reply-to: RLS19@psuvm.psu.edu
newsgroups: comp.lang.ada
Date: 1996-05-09T00:00:00+00:00
List-Id: <comp.lang.ada>


In <4mqio5$a8b@news.sanders.lockheed.com>, John Cupak <jcupak@isd99.sanders.lockheed.com> writes:
>Well, I just *have* to put in my $0.02 worth....
>
>In some cases, you *do* want to re-execute the same statement. For example,
>if you query the user for a number, and you get something else: 
>
>function Response (Prompt : in String) return Integer is
>   Line : String(1..80);
>   Size : Natural;
>begin
>   Try_Again: loop
>      Error_Handler: begin
>         Put(Prompt);                         -- Ask user for input
>         Get_Line(Line,Size);                 -- Get user input
>         return Integer'Value(Line(1..Size)); -- Raise exception if bad input
>      exception
>          when others =>
>             Put_Line("""" & Line(1..Size) & """ is not a valid value.");
>             -- Stay in Try_Again loop
>      end Error_Handler;
>   end loop Try_Again;
>end Response;
>
>I trust my Ada83 code is correct, as I didn't compile it for this response.
>
>Hope this helps!

Another way to reexecute a statement is to have the function call itself from the 
exception handler, after outputting an error message.  Once the user enters valid 
input, the function willrecursively return with the proper value.  For user input 
from a keyboard, any performance differences between the loop and the recursive function 
call will be negligible.

function Response (Prompt : String) return integer is

   line : ...
   Size : ...

begin
   Put (Prompt);
   Get_Line (...;
   return ...
exception
   when others =>
      Put_Line (...;  -- error message
      return Response(Prompt);
end Response;

>-- 
>John J. Cupak, Jr., CCP     Internet       : jcupak@isd99.sanders.lockheed.com
>Lockheed Sanders, Inc.      Lockheed LAN   : jcupak@mailgw.sanders.lockheed.com
>95 Canal Street/MER15-2403  Lockheed DECNet: NHQVAX::CUPAK 
>Nashua, NH 03061-0868       Work Telephone : 603 885-2142 FAX: 603 885-1480
>

Bob

Robert L. Spooner             Applied Research Laboratory
(814) 863-4120                             PO Box 30
RLS19@PSUVM.PSU.EDU      State College, PA 16804-0030