# Implement a simple stack in terms of a list.
#
# $Id: Stack.pm,v 1.4 2003/04/24 15:12:40 albertel Exp $
#
# Copyright Michigan State University Board of Trustees
#
# This file is part of the LearningOnline Network with CAPA (LON-CAPA).
#
# LON-CAPA is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2 of the License, or
# (at your option) any later version.
#
# LON-CAPA is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with LON-CAPA; if not, write to the Free Software
# Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
#
# /home/httpd/html/adm/gpl.txt
#
# http://www.lon-capa.org/
#
=pod
=head1 Stack
An object oriented implementation of a Stack data structure.
Stacks are first in last out data structures.
=head1 Member functions:
=cut
package Stack;
=pod
=head2 new
Creates a new instance of a stack.
my $stack = Stack->new();
=cut
sub new {
my $class = shift; # Class name.
my $self = []; # Create an empty list to represent the stack.
bless($self, $class); # Turn this into an object and..
return $self; # Return it.
}
=pod
=head2 push
takes an item and pushes it onto the back end of the stack.
my $stack = Stack->new();
$stack->push(something);
=cut
sub push {
my $self = shift; # Gets the list...
my $item = shift; # The item to push.
push(@$self,$item);
}
=pod
=head2 pop
Returns the item at the top of the stack: does a pop.
my object = Stack->new();
my $item = object->pop();
=cut
sub pop {
my $self = shift;
return pop(@$self);
}
=pod
=head 1
Returns the number of items on the stack.
=cut
sub Count {
my $self = shift;
my $elements = scalar(@$self);
return $elements;
}
1;
=pod
=head1 Internal implementation details
Stacks are implemented as lists. Thus a stack is a thinly disguised
list with push and pop wrappers. Since PERL is a dynamically typed
language, stacks can contain any data type ... including a
heterogenous collection of types.
=cut
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