Larry wrote:

>  : Can I write that as:
>  : 
>  :   sub factorial (Int $n:) {
>  :     return 1 when 0;
>  :     return $n * factorial $n;
>  :   }
>  
>  As it stands right now, no.  Ordinary subs do not allow invocants.
>  Arguably, it'd be more consistent if ordinary subs always topicalized
>  their first argument.  (But blocks have to be handled differently
>  since they expect to see the outer binding of $_ unless the block itself
>  rebinds $_.)  On the other hand, it'd probably work if you threw a
>  "multi" in front of the "sub".
>  
>  Can anyone think of a good reason not to topicalize the first arg
>  of ordinary subs these days?

Only that methods no longer topicalize their invocant...they now invocantize it.

Also it's not a good general solution. I can easily imagine situations where 
you want the second argument, or the last arg, to be the topic.

I still think it would be better to allow people to explicitly say what they mean:

     sub factorial (Int $n is topic) {
         return 1 when 0;
         return $n * factorial $n;
     }

Damian