SPUG: re:humble print statement for debugging

Kristi Anderson kanderson at nwadmin.com
Mon Mar 22 13:18:01 CST 2004


Hi all,

I've just recently added perl to the list of languages of which I know just enough to be dangerous.  One thing I've noticed about all of them is that you can almost always easily figure out how to use print or show or display or printf or cout, but to learn the debugger of each is considerably more time consuming.

Kristi

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Today's Topics:

   1. Fwd: Re: SPUG: Last night's meeting (Marc M. Adkins)
   2. Re: Fwd: Re: SPUG: Last night's meeting (Michael R. Wolf)


----------------------------------------------------------------------

Message: 1
Date: Thu, 18 Mar 2004 17:10:56 -0500
From: "Marc M. Adkins" <Perl at Doorways.org>
Subject: Fwd: Re: SPUG: Last night's meeting
To: Seattle Perl Users Group <spug-list at pm.org>
Message-ID: <200403181710.56598.Perl at Doorways.org>
Content-Type: text/plain;  charset="iso-8859-1"

>> Condemn all debug print statements now!
>
> IMHO, the humble print statement has a significant advantage over
> any interactive-debugging based strategy, which is simply that it
> will still be there if/when the program breaks again, and it can
> easily be re-activated to deliver its benefits again.
>
> AFAIK, there's no way to preserve the activities of an
> interactive debugging session, and replay them at a future time.

I have a (Filter::Util::Call) filter that I've been using for a number of
years to turn trace statements embedded in comments on and off.  I can turn
on individual trace statements or blocks of trace statements by keyword or by
subroutine with only a few keystrokes.

	use Trace	qw(KEYWORD);

	#!#	warn "Trace statement off\n";
	#*#	warn "Trace statemetn on\n";
	#!#	warn "Trace statement w/keyword on\n";	#[KEYWORD]
	#!#	warn "Trace statement w/keyword off\n";	#[WRONGWORD]

	sub	function
	{
	  #!#	warn "Trace statement off\n";
	  #$#	warn "All remaining trace statements in routine on\n";
	  #!#	warn "Trace statement on\n";
	}

Since it's a filter, when they're off they're just comments and so there is
_no_ run-time cost.  I can leave them in the code forever.
It's remarkable how few lines of code this is (even w/o Filter::Simple) and
how powerful it is in practice.

And yet...I hesitate sometimes to mention it in 'polite' company because
 there seems to be a subtle prejudice in favor of debuggers of infinite power
 among "real" programmers.  Hummph. [sic]  I get a lot of mileage from the
 humble print statement.

mma


------------------------------

Message: 2
Date: Fri, 19 Mar 2004 00:01:08 -0800
From: "Michael R. Wolf" <MichaelRWolf at att.net>
Subject: Re: Fwd: Re: SPUG: Last night's meeting
To: spug-list at mail.pm.org
Message-ID: <uu10luuyj.fsf at att.net>
Content-Type: text/plain; charset=us-ascii

"Marc M. Adkins" <Perl at doorways.org> writes:

[...]

> And yet...I hesitate sometimes to mention it in 'polite' company because

We're not *that* 'polite' -- I prefer to think we're respectfully
courteous, yet not quite tame -- but thanks for the compliment. :-)

[...]

>  humble print statement.

The debugger of infinate power?




-- 
Michael R. Wolf
    All mammals learn by playing!
        MichaelRWolf at att.net



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