#!/usr/local/bin/perl

use warnings;
use strict;

my @in = qw/2 3 5 polka dot bikini/;

#  Help the helper code help us
init( \@in );

foreach (0 .. scalar @in -1)
{
  printf " Current: %s\n    Next: %s\nPrevious: %s\n"
    , map { defined $_ ? $_ : 'undefined' }
        #
        #  Let something else fetch the values (in forward direction only)
        get( $_ )
        #
        #  Do it yourself
        #sub { move_fore(); ( current() , next_() , prev() ); }->()
    ;


  print "\n";
}

#  Helper code
{ my ($old , $cursor , $size , $array);

  sub init
  { $array = shift;
    $size = scalar @{$array} or die "empty array\n";
    $old = $cursor = 0;
  }

  sub get
  { $cursor = shift;
    die "no index given\n" unless defined $cursor;
    move_fore();
    return ( current() , next_() , prev() );
  }

  sub current
  { return $array->[$old];
  }
  sub prev
  { return ($old -1) >= 0 ?  $array->[ $old -1 ] : undef;
  }
  sub next_
  { return ($old +1) < $size ? $array->[ $old +1 ] : undef;
  }

  sub move_fore { $old = $cursor++; }
  sub move_back { $old = --$cursor; }
}