I want to use a module M from another module X, only if the calling program P currently uses it.

I have the following test case that works, but X asumes that P uses M:

P.pl:

#!perl

use strict;
use warnings;

use M;
use X;

hello("world");
bye();

[download]

M.pm:

package M;

require Exporter;
@ISA = (Exporter);
@EXPORT = qw(hello);

use warnings;
use strict;

sub hello {
  print "Hello @_!\n";
}

[download]

X.pm:

package X;

require Exporter;
@ISA = (Exporter);
@EXPORT = qw(bye);

use warnings;
use strict;

sub bye {
  M::hello("again"); # if exists M:hello();
  print "That's all, folks!\n";
}

[download]

What should be checked in X to recognize that M is loaded and available? If it's not, do nothing!

BTW, in real life, M could be any CPAN's module.

In reply to Use a module only if it is in use by vitoco

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