use strict;
use warnings;

# ABSTRACTION
package My::Lesson;
	
	sub new{
		my $class = shift;
		return bless { steps => [] }, $class;
	}
	
	sub add_step{
		my $self = shift;
		push @{ $self->{ steps }}, @_;
	}



# INCARNATION
package My::Lesson::Example;
	our @ISA = ( 'My::Lesson' );
	sub new{
		my $class = shift;
		my $self = $class->SUPER::new;
		$self->add_step('one','two');
		
		return $self;
	}

# USAGE
# Please note that this is only an example of usage. The real one will be done by an object of the Perl::Teacher class, like in
#
# $teacher->current_lesson( My::Lesson::Example->new )
#
# or something similar
package main;

my $lesson = My::Lesson::Example->new;


##</code><code>##

# INCARNATION
package My::Lesson::Example;

	require Exporter;
	our @ISA = qw( Exporter );
	our @EXPORT = qw( @steps );
	
	my @steps = ( 'three', 'four' );


# ABSTRACTION
package My::Lesson;

	use Module::Load 'autoload';
	# or CPAN Module::Runtime
	
	sub new{
		my $class = shift;
		my %opts = @_;
		
		# here must be some logic to load the appropriate incarnation module.
		# paying attention to the @steps array (?)
		#
		# autoload from Module::Load should be the right tool (not tested)
		# autoload $opts{lesson};
		warn "autoloading $opts{lesson}";
		
		return bless { steps => [ @steps ] }, $class;
	}
	
# USAGE	
package main;

my $lesson = My::Lesson->new( lesson => 'My::Lesson::Example' );


##</code><code>##

# ABSTRACTION
package My::Lesson;

	use Module::Load 'autoload';
	
	sub new{
		my $class = shift;
		my %opts = @_;
		
		if ( $class->isa( 'My::Lesson' ) ){
			return bless { steps => [] }, $class;
		}
		elsif ( $class->isa( 'Exporter' ) ){
			# autoload $opts{lesson};
			warn "autoloading $opts{lesson}";
			return bless { steps => [ @steps ] }, $class;
		}
		else{
			die "incarnation method not recognized for class [$class]!";
		}		
	}