sub make_estimator {
  return sub {0} unless @_; # You might want to die?
  my @points = @_;
  return sub {
    my $weight_total;
    my $weighted_sum;
    foreach my $point (@points) {
      my $dist_squared = 0;
      foreach my $coord (0..$#_) {
        $dist_squared += ($point->[$coord] - $_[$coord])**2;
      }
      if (0 == $dist_squared) {
        return $point->[-1];
      }
      else {
        my $weight = 1/$dist_squared;
        $weight_total += $weight;
        $weighted_sum += $weight * $point->[-1];
      }
    }
    return $weighted_sum/$weight_total;
  };
}

my $estimator = make_estimator(
  [3, 4],
  [4, 5],
);

print $estimator->(3.5);