Re: Source filters in eval/require

If you prefix eval strings with

'delete $INC{"Foo"}; use Foo;'
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in your filter, then your filter will be re-loaded when the string is eval'd.

However, when I tried this -- using Filter::Simple as I thought that I could use it's separation of code and strings to my advantage -- it gets very confusing about what stage you are at. Everytime I thought I was close to having something work, another gotcha popped up.

So, I thought I pass the basic idea along and see if it give you better inspiration than I. :)

Update: dws pointed out that the above code wasn't responsible for my percieved partial success. The use Foo; will happen before the delete $INC{'Foo'}. The delete $INC{'Foo'} needs to delete $INC{'Foo.pm'} anyway.

The thing fooled me was a redundant piece of test code in the external file....D'oh.

Anyway, having re-examined it, I did get a little closer, but still way short of anything that could be called successful.

The filter

package Filter::Test;
use Filter::Simple;

FILTER_ONLY
    code => sub {
#        print'C: ', $_;
        s[eval\s*($Filter::Simple::placeholder)]['<<<<<1>>>>>' eval '<
+<<<<2>>>>>' . $1 ];
#        print'C: ', $_;
        $_;
    },
    quotelike => sub {
#        print 'Q: ', $_;
        $_ = uc $_;
        s['<<<<<1>>>>>'][delete \$INC{'Filter/Test.pm'};];
        s['<<<<<2>>>>>']["BEGIN{ require Filter::Test; Filter::Test::i
+mport}"];
#        print 'Q: ', $_;
        $_;
    },
;

print 'Filter::Test loaded';
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P:\test>296091
Filter::Test loaded
HELLO WORLD FROM main

P:\test>296091
Filter::Test loaded
HELLO WORLD FROM main
Filter::Test loaded
Use of uninitialized value in concatenation (.) or string at d:/Perl/l
+ib/Filter/Simple.pm line 156.
Use of uninitialized value in concatenation (.) or string at d:/Perl/l
+ib/Filter/Simple.pm line 156.
String found where operator expected at (eval 5) line 1, near "PRINT '
+JUST ANOTHER PERL HACKER'"
        (Do you need to predeclare PRINT?)

P:\test>

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As you can see, the Filter is being loaded twice, and the text within the evald string has bee uppercased (too much of it, but that's a detail :).

I did have the require half working at one point, by using eval 'use Filter::Test;' do{ local *ARGV = 'file'; <> };, but it starts getting very complicated when you start trying to filter an eval'd require file that contains evals that contains requires....

I can't wrap my brain around it any longer, but maybe it will inspire you, or convince you to try a different route, which might be an equally valid assist :)

Examine what is said, not who speaks.

"Efficiency is intelligent laziness." -David Dunham
"When I'm working on a problem, I never think about beauty. I think only how to solve the problem. But when I have finished, if the solution is not beautiful, I know it is wrong." -Richard Buckminster Fuller
If I understand your problem, I can solve it! Of course, the same can be said for you.

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Re: Re: Source filters in eval/require
by liz (Monsignor) on Oct 03, 2003 at 07:54 UTC

...I can't wrap my brain around it any longer...

That describes my feelings quite a bit before posting ;-)

...maybe it will inspire you, or convince you to try a different route, which might be an equally valid assist :)

I'm considering stealing Filter::Util::Call::filter_add and Filter::Util::Call::filter_del. Problem only is that I would need to steal these before they're getting loaded. ;-( Does anyone have any idea about that?

Liz

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