package Module::Functional;
# functional

# the more complex operations and logic would happen here
sub clean_to_level { 
 my ($cleanliness_now, $target_cleanliness) = @_;
 
 while( $cleanliness_now < $target_cleanliness ){
   $cleanliness_now++;
 }

 return $cleanliness_now;
}

1;

package Module::OO;
use Module::Functional;
# oo version

# this package would in great part be an interface to the other package.

sub clean_to_level {
 my ($self,$target_cleanliness) = @_;
 $target_cleanliness ||= $self->default_target_cleanliness;
 
 return Module::Functional::clean_to_level(
   $self->cleanliness_now, 
   $target_cleanliness,
 ); 
}