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NAME

     diagnostics - Perl compiler pragma to force verbose warning
     diagnostics

     splain - standalone program to do the same thing



SYNOPSIS
     As a pragma:

         use diagnostics;
         use diagnostics -verbose;

         enable  diagnostics;
         disable diagnostics;

     Aa a program:

         perl program 2>diag.out
         splain [-v] [-p] diag.out




DESCRIPTION
     The `diagnostics' Pragma

     This module extends the terse diagnostics normally emitted
     by both the perl compiler and the perl interpreter,
     augmenting them with the more explicative and endearing
     descriptions found in the perldiag manpage.  Like the other
     pragmata, it affects the compilation phase of your program
     rather than merely the execution phase.

     To use in your program as a pragma, merely invoke

         use diagnostics;

     at the start (or near the start) of your program.  (Note
     that this does enable perl's -w flag.)  Your whole
     compilation will then be subject(ed :-) to the enhanced
     diagnostics.  These still go out STDERR.

     Due to the interaction between runtime and compiletime
     issues, and because it's probably not a very good idea
     anyway, you may not use `no diagnostics' to turn them off at
     compiletime.  However, you may control there behaviour at
     runtime using the disable() and enable() methods to turn
     them off and on respectively.

     The -verbose flag first prints out the the perldiag manpage
     introduction before any other diagnostics.  The
     $diagnostics::PRETTY variable can generate nicer escape
     sequences for pagers.

     Warnings dispatched from perl itself (or more accurately,
     those that match descriptions found in the perldiag manpage)
     are only displayed once (no duplicate descriptions).  User
     code generated warnings ala warn() are unaffected, allowing
     duplicate user messages to be displayed.

     The splain Program

     While apparently a whole nuther program, splain is actually
     nothing more than a link to the (executable) diagnostics.pm
     module, as well as a link to the diagnostics.pod
     documentation.  The -v flag is like the `use diagnostics
     -verbose' directive.  The -p flag is like the
     $diagnostics::PRETTY variable.  Since you're post-processing
     with splain, there's no sense in being able to enable() or
     disable() processing.

     Output from splain is directed to STDOUT, unlike the pragma.



EXAMPLES
     The following file is certain to trigger a few errors at
     both runtime and compiletime:

         use diagnostics;
         print NOWHERE "nothing\n";
         print STDERR "\n\tThis message should be unadorned.\n";
         warn "\tThis is a user warning";
         print "\nDIAGNOSTIC TESTER: Please enter a <CR> here: ";
         my $a, $b = scalar <STDIN>;
         print "\n";
         print $x/$y;

     If you prefer to run your program first and look at its
     problem afterwards, do this:

         perl -w test.pl 2>test.out
         ./splain < test.out

     Note that this is not in general possible in shells of more
     dubious heritage, as the theoretical

         (perl -w test.pl >/dev/tty) >& test.out
         ./splain < test.out

     Because you just moved the existing stdout to somewhere
     else.

     If you don't want to modify your source code, but still have
     on-the-fly warnings, do this:

         exec 3>&1; perl -w test.pl 2>&1 1>&3 3>&- | splain 1>&2 3>&-

     Nifty, eh?

     If you want to control warnings on the fly, do something
     like this.  Make sure you do the `use' first, or you won't
     be able to get at the enable() or disable() methods.

         use diagnostics; # checks entire compilation phase
             print "\ntime for 1st bogus diags: SQUAWKINGS\n";
             print BOGUS1 'nada';
             print "done with 1st bogus\n";

         disable diagnostics; # only turns off runtime warnings
             print "\ntime for 2nd bogus: (squelched)\n";
             print BOGUS2 'nada';
             print "done with 2nd bogus\n";

         enable diagnostics; # turns back on runtime warnings
             print "\ntime for 3rd bogus: SQUAWKINGS\n";
             print BOGUS3 'nada';
             print "done with 3rd bogus\n";

         disable diagnostics;
             print "\ntime for 4th bogus: (squelched)\n";
             print BOGUS4 'nada';
             print "done with 4th bogus\n";




INTERNALS
     Diagnostic messages derive from the perldiag.pod file when
     available at runtime.  Otherwise, they may be embedded in
     the file itself when the splain package is built.   See the
     Makefile for details.

     If an extant $SIG{__WARN__} handler is discovered, it will
     continue to be honored, but only after the
     diagnostics::splainthis() function (the module's
     $SIG{__WARN__} interceptor) has had its way with your
     warnings.

     There is a $diagnostics::DEBUG variable you may set if
     you're desperately curious what sorts of things are being
     intercepted.

         BEGIN { $diagnostics::DEBUG = 1 }




BUGS
     Not being able to say "no diagnostics" is annoying, but may
     not be insurmountable.

     The `-pretty' directive is called too late to affect
     matters.  You have to do this instead, and before you load
     the module.

         BEGIN { $diagnostics::PRETTY = 1 }

     I could start up faster by delaying compilation until it
     should be needed, but this gets a "panic: top_level" when
     using the pragma form in Perl 5.001e.

     While it's true that this documentation is somewhat
     subserious, if you use a program named splain, you should
     expect a bit of whimsy.



AUTHOR
     Tom Christiansen <tchrist@mox.perl.com>, 25 June 1995.









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