#!/usr/bin/perl -w
use strict;

my @input = (1,2,3,4,5,6,7,8);

print swap_pairs(@input); # prints: 21436587

sub swap_pairs
{
   my @swapped_pairs;
   while ( my ($x,$y) = splice(@_,0,2) )
   {
      push @swapped_pairs,($y,$x);
   }
   return @swapped_pairs;
}