loaded.pm

package if::loaded;

sub work {
        my $method = shift() ? 'import' : 'unimport';
        my $module = shift;
        my $option = shift;
        my $alternative = shift;

        unless ($module && $alternative && $option eq '-else') {
                die "Usage: use if::loaded 'Some::Module', -else => 'Alternative::Module' [, \@args ]"
        }
        (my $file = "$module.pm") =~ s[::][/]g;
        unless ($INC{$file}) {
                $module = $alternative;
                ($file = "$module.pm") =~ s[::][/]g;
                require $file;
        }
        my $m = $module->can($method);
        if ($m) {
                unshift @_, $module;
                goto &$m;
        }
}

sub import { shift; unshift @_, 1; goto &work }
sub unimport { shift; unshift @_, 0; goto &work }

1;