my $sum = sub { (map {splice @_, 0, 2, $_[0] + ($_[1] // 0)} @_)[-1] }->(@list);

##</code><code>##

my $sum = sub { (map {splice @_, 0, 2, $_[0] + ($_[1] // 0)} @_)[-1] }->(0, @list);

##</code><code>##

my $sum = reduce { $a + $b } 0, @list;