#!/usr/bin/perl -w
use strict; # enforces decleration of variables

sub changeL{
	# $listRef is assigned the first element of the argument
	# list, which is a reference to the list containing BAB
	my $listRef = $_[0];
	$listRef->[0] = "ABA";
}

# list with one element
my @list = ("BAB");

# makes a reference to the list
my $listR = \@list;

# print first element of the list
print "$list[0]\n";

# call the subroutine changeL
changeL($listR);

# print first element of the list
print "$list[0]\n";