use 5.010;

my @numbers = qw(1 3 5 6 7 8);

sub reduce (&@)
{
	my ($code, $first, @rest) = @_;
	return $first unless @rest;
	
	return $code->(
		$first,
		reduce($code, @rest),
	);
}

sub sum
{
	return reduce { $_[0] + $_[1] } @_;
}

say sum @numbers;