Slurpy nullary vs nonslurpy nullary

[Autrijus Tang]

After getting Life and Mandel to run on Pugs yesterday (see
http://svn.perl.org/perl6/pugs/trunk/examples/ ), today I've
made this version of Quicksort to run:

    use v6;

    multi sub quicksort ( ) { () }

    multi sub quicksort ( *$x, [EMAIL PROTECTED] ) {
        my @pre  = @xs.grep{ $_ < $x };
        my @post = @xs.grep{ $_ >= $x };
        (@pre.quicksort, $x, @post.quicksort);
    }

    (1, 5, 2, 4, 3).quicksort.say;

Note the use of @xs.grep{} above.  Pugs currently has two multisub
named "grep":

    * List as invocant, takes a Code arg
    * Takes two args: Code and List

It sort of makes sense to me.  Please correct me if it's wrong. :)

But anyway.  The real problem is the multisub dispatcher initially
complained about the () signature, saying that it is "non-slurpy"
and may not take a list, even though the list eventually flattens
into an empty list; so I modified the definition to make () explicitly
slurpy.

However, that feels wrong, as I'd like to distinguish from a slurpy
nullnary (something that can take a list, as long as it's empty) and a
non-slurpy nullary (something that takes no arguments whatsoever).

I have been wondering whether something like 

    quicksort( *[] ) 

Can mean a slurpy nullnary, but I failed to find relevant text in
Synopses, so here I am. :-)

(PS. Yes, I understand that I can use array unpacking and have
quicksort always take a single array argument, but I'd still like to
inquire about slurpy nullary...)

Thanks,
/Autrijus/

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