loaded.pm

package if::loaded;
use Module::Runtime qw(module_notional_filename use_module);

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

    my %args = map { $_ => [] } qw(try else args);
    my $arg = 'try';
    for (@_) {
        if (/\A-(.*)\z/) {
            die "Invalid option '$_'\n"
                unless exists $args{$1};
            $arg = $1;
            next;
        }
        push $args{$arg}, $_
    }
    die "Need at least one module" unless @{$args{try}};
    die "Only one fallback module allowed" if @{$args{else}} > 1;

    for my $module (@{$args{try}}) {
        if ($INC{module_notional_filename($module)}) {
            if (my $m = $module->can($method)) {
                @_ = ($module, @{$args{args}});
                goto &$m;
            }
            return;
        }
    }

    my $module = $args{else}[0] or die "no modules loaded and no -else\n";
    if (my $m = use_module($module)->can($method)) {
        @_ = ($module, @{$args{args}});
        goto &$m;
    }
}

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

1;