[Israel.pm] Perl and Debugging question

[Shlomi Fish]

Hi Peter!

On Monday 14 May 2007, Peter Gordon wrote:
> If you have a look it dumpvar.pl, you will find my name there. Once upon
> a time, during the birth pangs of Perl 5,  I did bang my head against
> it.
>
> I agree with you that the debugger is a Real Mess (tm) and hopefully in
> Perl 6 it will be a lot nicer.

Wait for Perl 6 which will be a whole new ball game just for a better 
debugger? Get real. At the moment, as far as I know, Pugs and Parrot don't 
have any debuggers at all.

It is possible to write a better debugger for perl 5 see Devel::ebug for 
instance:

http://search.cpan.org/dist/Devel-ebug/

And you can always refactor the existing debugger into shape if the need 
arises.

Regards,

	Shlomi Fish

>
> Another way would be make an opaque object so that the values don't get
> dumped down.
>
> Peter
>
> On Mon, 2007-05-14 at 09:30 +0300, Gaal Yahas wrote:
> > I disagree on both counts. :-)
> >
> > Simplicity isn't one of the best descriptions of the debugger code.
> > (By which I mean
> > the actual debugger, perl5db.pl.) I mean sure, you could tweak around
> > lines: 2434
> > 654
> > 5547
> >
> > But you'd still have to bang your head against dumpvar.pl.
> >
> > And how to make the interface for it? Just hardcode some arbitrary
> > limit? Yet another config option? What happens when your members are
> > actually tied scalars that when read do some expensive operation like
> > compute a value or read from the network? Maybe you want to skip those
> > fields too... How?
> >
> > If what guides you is a sense that debuggability features don't seem
> > clean to leave in production code, I hear you, but consider that they
> > would be implemented in a separate unit of modularity (a Role, in the
> > case of Perl 6) and have declarative, thus uncluttering,
> > configuration. Incidentally, in Perl 6 Roles can be composed at
> > runtime, so your production program has absolutely no trace of this
> > filterable dumpage, until you drop into the debugger and add it to a
> > particular instance. Then you also have a consistent interface to mess
> > around with its properties.
> >
> > On 5/14/07, Peter Gordon <peter at pg-consultants.com> wrote:
> > > It might be simpler and more consistent to add an option to the
> > > debugger itself.
> > >
> > > On Sun, 2007-05-13 at 21:50 +0300, Gaal Yahas wrote:
> > > > On 5/13/07, Peter Gordon <peter at pg-consultants.com> wrote:
> > > > > On this occasion, one of the elements is a string a few megabytes
> > > > > long, and I don't really want to dump the whole string.
> > > > >
> > > > > What would be the nicest way to suppress printing of this
> > > > > particular element.
> > > > >
> > > > > I could print each element in turn, but that is inelegant.
> > > >
> > > > I'm afraid I don't have an elegant solution to offer. (A related
> > > > problem that does
> > > > have debugger support is deeply recursive structures. Saying "x 3
> > > > $that" limits to
> > > > depth 3 print.)
> > > >
> > > > What you might do -- and I'm not saying this is significantly
> > > > different from printing each element in turn -- is add a to_debug
> > > > method to the object. This copies the object but only leaves a digest
> > > > version of the long string, say with the first 100 characters.
> > > >
> > > > Not that I've searched CPAN for prior art, but you might want to make
> > > > this into a reusable module. (With Moose.pm or Perl 6, it would more
> > > > properly be a Role.) Something like:
> > > >
> > > > package MyModuleWithLongMember;
> > > >
> > > > use Debug::Dump::Digest qw(long_memb1 huge_memb2);
> > > >
> > > > And then in the debugger:
> > > >
> > > > x $self->to_debug;
> > >
> > > _______________________________________________
> > > Perl mailing list
> > > Perl at perl.org.il
> > > http://perl.org.il/mailman/listinfo/perl
>
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Shlomi Fish      shlomif at iglu.org.il
Homepage:        http://www.shlomifish.org/

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