[Koha-devel] Re: FAQ: Why am I prompted to save a .pl file? was: Problems adding a biblio...

[MJ Ray]

Rick Welykochy <rick at praxis.com.au> wrote:
> The "perldoc -f die" entry does not mention Carp. [...]

That's strange.  It does in perl 5.8.8:
  "See also exit(), warn(), and the Carp module."

> Carp provides better formatting of message sent via die: [...]
> Carp does not provide exception catching. That has to be implemented
> by the application writer.
>
> Carp does not provide the functionality I have demonstrated at
>     http://praxis.com.au/demo_error.pl/showio
> which intercepts an IO error, and displays detailed information to
> the browser in addition to notifying the sysadmin.

And what does that script do when it intercepts it?  It displays a
better-formatted system error, dumping lots of internal data!  Using a
Carp is more general and would reveal less about the internals by
default.

Also, what happens if your script contains an error outside the
eval{}? Sod's law says that some errors would occur outside the eval{}
anyway. Putting a use Carp at the top handles the whole script.  Only
a perl core problem would derail that and that's beyond our powers.

If we can recover gracefully from a resource failure, we should test
for it and handle it in the code, as usual, not get into the
half-hidden couplings of throwing and catching exceptions.  (Look up
about exceptions and coupling in programming/software engineering
texts and journals if you've not noticed this problem.  I expect
someone has posted something with a title like "Exceptions considered
harmful" on the web by now.)

If the exception is a programming error, how do you handle that?  If
it's in a module, it would be far better if the module routine
returned an error code instead of die()ing.  If it's in the main code,
there's not much we can do better than output a bug report.  Our
current error output (the server's default 500) can be improved.

I feel that die()ing, whether on our own request or forced by perl,
should only be handled to produce saner output for a bug report, which
is what Carp does.  die()ing shouldn't be a part of normal operation.

Hope that explains,
-- 
MJ Ray - see/vidu http://mjr.towers.org.uk/email.html
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