BEGIN {
    package Err;

    require Exporter;
    our @ISA = qw(Exporter);
    our @EXPORT = qw(err);

    use overload q("") => sub { my $e = shift; "ERROR $e->[0]: $e->[1]" };

    sub new { my $class = shift; bless $_[0], $class }

    sub err { __PACKAGE__->new([@_]) }
}

package main;
BEGIN { Err->import }
use Carp::Always;

sub f {
    g();
}

sub g {
    die err(403, "Permission denied");
}

f();