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Postings from April 2002
On Fri, 2002-04-26 at 14:51, Jason Frisvold wrote:
> Hrm.. I'll run some tests with it and see what I find out... Sounds
> promising if it really is a preprocessor... So does it just do
> something along the lines of a cat <file> | grep -v <stuff> and then
> execute the output? (I realize that is simplifying it by a great deal)
>
> I'm just trying to wrap my head around this... The program (actually
> programs) that I've been writing runs anywhere from once every 5 minutes
> to once a night... I know I can make it faster by porting to C, but
> it's that much easier to do in perl. However, I don't want to waste
> cycles running through a preprocessor every time, or running through a
> debug routing every time when it's not needed...
>
> Hrm... more thought needed.. *grin*
>
> ---------------------------
> Jason H. Frisvold
> Senior ATM Engineer
> Engineering Dept.
> Penteledata
> CCNA Certified - CSCO10151622
> friz@corp.ptd.net
> ---------------------------
> "Imagination is more important than knowledge. Knowledge is limited.
> Imagination encircles the world." -- Albert Einstein [1879-1955]
It will run through the filter every time it is executed so a program
with a filter will be slower than a program without a filter. Filters
work by using BEGIN blocks and some really neat backend magic. Here is
an example filter (with new comments) I wrote based on your earlier
email. In fact, come to think of it, if you reverse the import and
unimport subs, reverse substitution (s//^#/), and remember to comment
out the debug code your production code will run a top speed and your
debug code will be a little slower instead of the other way around.
#name the module
package DEBUG;
#all of the magic comes from this module
use Filter::Util::Call;
#minor magic that makes warns and dies report as if the code
#were in the calling file
use Carp;
#unimport gets called when you say "no MODULENAME;"
#I am using it here for my main filter because I
#want to be able to say "no DEBUG;" instead of
#"use DEDEBUG;" or other negative name.
sub unimport {
#grab the args passed into the module (ignore)
my ($type, @other_args) = @_;
#this variable determines whether we are in
#a chunk of code that needs to be commented
my $in_debug = 0;
#filter_add sets up the filter. There are two
#ways to use it, I am using the closure method
#because I think closures rock. The anonymous
#subroutine I define here will be called until
#there is no more data is left in the file, an
#error occurs, or the filter_del sub is called
filter_add (sub {
#this command reads a line from the source
#and stores it in $_. $status is set to 0
#if there are no more lines, 1 for success
#or to a negative number for failure
my $status = filter_read;
#If we are in a #DEBUG ON block and the file
#ends then we have a problem; better to fail
#than to screw up the script
croak "unbalanced '#DEBUG'" if $status == 0 and $in_debug;
#if the line starts with #DEBUG ON then
#we need to start commenting out lines
if (/^\s*#DEBUG ON/) {
#warn the user that nesting #DEBUG ONs
#can be dangerous (bad things can happen
#if you combine "use DEBUG;", "no DEBUG;",
#and nested #DEBUG ONs). We increment
#$in_debug so that we know how deeply we
#are nested (there must be a matching
#number of #DEBUG OFFs).
carp "nested #DEBUG ON is dangerous" if ++$in_debug > 1;
}
#else if the line contains #DEBUG OFF then we need to stop
#commenting out lines. We decrement $in_debug for the
#same reason we incremented it above.
elsif (/^\s*#DEBUG OFF/) {
#if there are more #DEBUG OFFs than #DEBUG ONs
#then we have a serious problem.
croak "unbalanced '#DEBUG'" if --$in_debug < 0;
}
#else if we are currently in a debug block then prepend
#a comment character to the line
elsif ($in_debug) {
s/^/#/;
}
#return the status
return $status;
});
}
#the import subroutine gets called when you "use MODULENAME;".
#I am using it here to turn off the filter.
sub import {
filter_del();
}
#modules must return true.
1;
--
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