# if you don't want to waste a _lot_ of timing guessing
# at mistakes that Perl could have told you about
# always put these two lines at the top of your scripts
# even before any other use or package statements
use strict;
use warnings;

package Foo::Bar::MyFrobincator;

#full name is Foo::Bar::MyFrobincator::make_frobnicator
sub make_frobnicator {
   ...
}

# full name: $Foo::Bar::MyFrobnicator::current_frobnicator
our $current_frobnicator;

# Perl knows we mean to call 
# Foo::Bar::MyFrobincator::make_frobnicator()
# and that we want to assign the value to
# $Foo::Bar::MyFrobnicator::current_frobnicator

$current_frobnicator = make_frobnicator();

# change the active namespace to Foo::Baz
package Foo::Baz;

# fullname: Foo::Baz::bye
sub bye { print "bye-bye\n"; }

# Since the active namespace is now Foo::Baz
# Perl now thinks you mean Foo::Baz::make_frobnicator()
# which doesn't exist so you get an error
make_frobnicator();

# so we need to use those awful long names - ugh!

$Foo::Bar::MyFrobnicator::current_frobnicator
  = Foo::Bar::MyFrobincator::make_frobnicator()

# but we can use a short name here
# because bye is part of the Foo::Baz package
# so Perl knows we mean Foo::Baz::bye()
bye();