The simple answer is don't do that! Modules calling each other or calling themselves are usually a sign of bad design.


Putting aside the validity of your design, let's first find the cause of the problem. Keep in mind that

use Module LIST;

[download]

is the same as

require Module;
Module->import LIST if Module->can('import');

[download]

while we look, line by line, at the code Perl executes:

test1.pl:2     use strict;
test1.pl:4     use lib qq{/usr/web/wonko/test/lib/SYS};
test1.pl:5     use lib qq{/usr/web/wonko/test/lib/AB};
test1.pl:7     require SYS_mail;

   Start executing SYS_mail.pm

SYS_mail.pm:1  package SYS_mail;
SYS_mail.pm:3  use lib qq{/usr/web/wonko/test/lib/AB};
SYS_mail.pm:5  require AB_prod;

   Start executing AB_prod.pm

AB_prod.pm:1   package AB_prod;
AB_prod.pm:3   use lib qq{/usr/web/wonko/test/lib/SYS};
AB_prod.pm:5   require SYS_mail;

   Does nothing. Already required

AB_prod.pm:5   SYS_mail->import(qw ( send_mail ))
                  if SYS_mail->can('import');

   ERROR!!

[download]

The error is that we haven't yet executed

use vars qw(@ISA @EXPORT_OK);
use Exporter();
@ISA = qw(Exporter);
@EXPORT_OK = qw( send_notice );

[download]

in SYS_mail.pm, so SYS_mail has no import function, so send_mail doesn't get imported into AB_prod. Similar errors occur at later points in the program.


And now the fix:

To fix this problem (aside from the obvious one of not including yourself directly or indirectly), change your modules to the following:

/usr/web/wonko/test/AB/AB_prod.pm
#--------------------------------------------------------------------
package AB_prod;

use lib qq{/usr/web/wonko/test/lib/SYS};

use strict;
use warnings;

BEGIN {
   our @ISA = qw( Exporter );
   our @EXPORT_OK = qw( send_notice );
   require Exporter;
}

use SYS_mail qw ( send_mail );

sub send_notice
{
   print qq{Hello from AB_prod::send_notice\n};

   send_mail();
}
1;
#--------------------------------------------------------------------

[download]
/usr/web/wonko/test/lib/SYS/SYS_mail.pm
#--------------------------------------------------------------------
package SYS_mail;

use lib qq{/usr/web/wonko/test/lib/AB};

use strict;
use warnings;

BEGIN {
   our @ISA = qw( Exporter );
   our @EXPORT_OK = qw( send_mail );
   require Exporter;
}

use AB_prod qw( send_notice );

sub send_mail
{
   print qq{Hello from SYS_mail::send_mail\n};
}
1;
#--------------------------------------------------------------------

[download]


Tested:

use strict;
use warnings;

use SYS_mail qw( send_mail );
use AB_prod qw( send_notice );

send_notice();

__END__
output
======
Hello from AB_prod::send_notice
Hello from SYS_mail::send_mail

[download]

I also tested it with the two use statements inverted. It gave the same output.


Update: It doesn't matter that sub send_mail { ... } hasn't been reached at the point Exporter->import('send_mail') is called, so I removed the stub functions I added just below the BEGIN in SYS_mail. Same idea for AB_prod.

In reply to Re: Namespace and use confusion. "Undefined subroutine errors" by ikegami
in thread Namespace and use confusion. "Undefined subroutine errors" by Wonko the sane

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.