Perl 6 tee

# Based on Python's itertools.tee, takes a list and a count and returns
# count number of iterators, each of which will "contain" all elements
# of the input list, but without evaluating/flattening the input list
# until needed.
#
sub tee(@list, :$count = 2) {
        my @indices = 0...^$count;
        my @inputs = @indices.map({[]});
        my $maketee = -> $i {
                gather loop {
                        if @inputs[$i].elems == 0 {
                                # Being careful not to flatten @list...
                                last unless ?@list;
                                my $next = @list.shift;
                                # Push the next item onto all inputs
                                for @indices -> $k {
                                        @inputs[$k].push($next);
                                }
                        }
                        take @inputs[$i].shift;
                }
        }
        gather for @indices -> $i {
                take $maketee($i).item;
        }
}

# Can't get this to behave lazily, even though simpler examples:
#   ./perl6 -e 'sub a(@list) { @list.shift } ; say a(1...*)'
# seem to work fine.
my ($a,$b) = tee(1...*, :count(4));
say $a.WHAT;
for 0...* -> $i {
        say $a[$i];
        last if $i > 10;
}