cwr.p6

use v6;
use Test;

sub combinations_with_replacement(@iterable, $r)  {
    gather {
        cwr(@iterable, [], $r);
    }
}
sub cwr(@iterable, @state, $r) {
    my $place = @state.elems;
    @state.push(Nil);
    for @iterable {
        @state[$place] = $_;
        if $r > 1 {
            cwr(@iterable, @state, $r-1);
            @state.pop;
        } else {
            take @state;
        }
    }
}
say combinations_with_replacement(('a','b','c'), 2)[^1];
say combinations_with_replacement(('a','b','c'), 2)[^2];
say combinations_with_replacement(('a','b','c'), 2)[^3];