First the script, script.pl :

#!/usr/bin/perl

use strict;
use warnings;

use lib '.';

use Bozo;

print go_bozo();
[download]

Then there's of course the "Bozo.pm" module :

use strict;
use warnings;

# module Bozo

use Exporter;
my @EXPORT=qw( go_bozo);

sub go_bozo {
    return "BOZO!\n"
}

1;
[download]

OK, so THIS work exactly as I'd expect it to work. Now, the stuff that's driving me nuts, let's change the script and add an additional module :

#!/usr/bin/perl

use strict;
use warnings;

use lib '.';

use Foo;

print Foo->Foo();
[download]

Then the module Foo.pm (please be patient):

#!/usr/bin/perl

use strict;
use warnings;

package Foo;

use lib '.';
use Bozo;

sub Foo {
    return go_bozo()
}

1;
[download]

Fine, it still works! Now is coming whant I don't understand, just changing the script a little:

#!/usr/bin/perl

use strict;
use warnings;

use lib '.';

use Bozo;
use Foo;

print go_bozo();

print Foo->Foo();
[download]

And now it doesn't work anymore : Undefined subroutine &Foo::go_bozo called at Foo.pm line 13. I understand what's wrong : i'm useing Bozo.pm twice, and that's certainly evil (well actually I don't se why, but never mind...). But why doesn't it give an error such as importing twice the same module at Foo.pm line 10 then ?