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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: Data_Error and Enumeration_IO
Date: Fri, 13 Jan 2012 09:33:31 +0100
Organization: cbb software GmbH
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Date: 2012-01-13T09:33:31+01:00
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On Thu, 12 Jan 2012 18:10:37 -0600, Randy Brukardt wrote:

> My recommendation is always to read the input into a string and then process 
> it there (using the string Gets that the language provides). The reason for 
> this is that it always a better error message in the failure case, because 
> you still have the string in hand. That way, you can avoid a generic message 
> that puzzles the user.

Another reason is that you can always return back in the string and
re-parse improperly matched parts of it.
 
> [Aside: For some reason, this reminds me of the first C compiler I used, way 
> back at the University of Wisconsin in 1978. It was a PDP-11 compiler for an 
> early version of Unix, and it essentially had two error messages: "lvalue 
> expected" for any compile-time mistake, and "bus error - core dumped" for 
> any run-time mistake. Debugging programs using that compiler were almost 
> completely trial-and-error - you would guess what the error might have been, 
> and try something else to see if it fixed it. The compiler, and the fact 
> that early PC compilers were very much like it, had a lot to do with our 
> creating Janus/Ada a couple of years later. And that is why we always had 
> runtime trace backs and verbose runtime messages from the very beginning...]

Early Turbo Parscal compilers had only one to say "error in expression." 

But it is still sometimes a problem in C++ that the error message
incomprehensible. Then I would use the same technique I did 25 years ago:
comment everything out until it compiles and then uncomment line by line
compiling it each time.

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