One way to do it is to write a class and overload '+' (untested):

package Coord;
use overload '+' => \&add;

sub new {
    my ($class, $x, $y) = @_;
    return bless { x => $x, y => $y}, $class;
}

sub add {
   my ($self, $other) = @_;
   return Coord->new($self->{x} + $other->{x}, 
       $self->{y} + $other->{y});
}
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Of course this code is missing all kinds of sanity checks. You might even consider to bless an array ref instead of a hash ref, but then it's much harder to extend.