sub Value_eq {
        my ($target_value) = @_;
        sub { $_[0] eq $target_value ? 0 : undef }
    }
    
    sub Negative {
        sub { $_[0] < 0 ? 0 : undef }
    }

##</code><code>##

    package Base;
    
    multimethod new => (Value_eq('Base'))           => sub {...}    
    multimethod new => (Value_eq('Base'), Negative) => sub {...}
    multimethod new => (Value_eq('Base'), '#')      => sub {...}
    
    package Der;
    use base 'Base';
    
    multimethod new => (Value_eq('Der'))      => sub {...}  
    multimethod new => (Value_eq('Der'), '$') => sub {...}  
    # etc.

##</code><code>##

  
    sub This::Class {
        my $target_value = caller;
        sub { $_[0] eq $target_value ? 0 : undef }
    }

##</code><code>##

    package Base;
    
    multimethod new => (This::Class)           => sub {...} 
    multimethod new => (This::Class, Negative) => sub {...}
    multimethod new => (This::Class, '#')      => sub {...}
    
    package Der;
    use base 'Base';
    
    multimethod new => (This::Class)      => sub {...}  
    multimethod new => (This::Class, '$') => sub {...}  
    # etc.