def_or is a good name, short and quite obvious. Many computer languages use "def" as a shortcut for "define" or "defined". So, no surprises here.

dor_call, on the other hand, is not so obvious, you have cut away too much. What the heck is "dor"? A mis-spelled door? And what would be a door-call? "Don't make me think!" def_or_call is longer, but also clearer.

So, now that I have def_or_call(), my code will very soon look very ugly and my fingers will bleed from the many keystrokes that I need:

# Perl >= 5.10
my $pid=fork() // die "Can't fork: $!";

# Perl < 5.9 manually
my $pid=fork(); defined($pid) or die "Can't fork: $!";
#                                      123456789012345
# 15 extra characters

# Perl < 5.9 + your module
my $pid=def_or_call(fork(),sub { die "Can't fork: $!" });
#                                      123456789012345678
# 18 extra characters -- oops!
# And you should never forget to wrap die in a sub ...

# Perl < 5.9 + your module with defined_or_die
# (remember to check if arguments are ALWAYS evaluated left-to-right!)
# (or find a better solution ...)
my $pid=def_or_die(fork(),"Can't fork: $!");
#                                      12345
# just 5 extra characters - 10 less than manually
# and no wrapper needed
[download]

So, I think you should really provide def(ined)_or_die and def(ined)_or_warn. Sure, it is more work than the other functions. You should really look into the Carp sources to see how they cope with the problems your module will also have. Like I said, I'm very sure that you can use Carp for the line number problem. You could load it at runtime, inside def_or_die()/def_or_warn(). Something like this:

sub def_or_die
{
    my ($v,$msg)=@_;
    return def_or_call($v,sub {
        require Carp;
        die Carp::some_magic_helper_function($msg);
    });
}
[download]

And I think you should also provide their Carp equivalents, for the same reasons. You could export them on demand only, and load Carp at runtime. Something like this:

sub def_or_carp
{
    my ($v,$msg)=@_;
    return def_or_call($v,sub {
        require Carp;
        Carp::please_ignore_these_wrappers();
        Carp::carp($msg);
    });
}
[download]

Support for CGI::Carp would look about like this:

sub def_or_carp
{
    my ($v,$msg)=@_;
    return def_or_call($v,sub {
        if (exists $INC{'CGI/Carp.pm'}) {
            # CGI::Carp loaded
            CGI::Carp::please_ignore_these_wrappers();
            CGI::Carp::carp($msg);
        } else {
            require Carp;
            Carp::please_ignore_these_wrappers();
            Carp::carp($msg);
        }
    });
}
[download]

Alexander