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

sub map2 (&@) {
    my $code = shift;
    if(@_ % 2) {
        require Carp;
        Carp::croak('Odd number of values in list');
    }

	local ($a, $b);
	my @r;

	push @r, $code->() while ($a, $b) = splice @_, 0, 2;
	@r;
}

my %hash = qw/A B C D E F G H/;

# let's remove the multiple calls to print() and
# make the use of a map justifiable, shall we?
print map2 sub { "key $a => value $b\n" }, %hash;