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#------------------------------------------------------------
# Return an iterator of all possible combinations (of all
...
    my ($by, $next) = (0, 1);

    return sub {

        # We're done after we've returned a list of all symbols
        return () if @position == @list;

        if ( $next ) {
            # We finished all combos of size $by, now do $by+1
            $by++;

            # If new size is larger than list, we're done!
            return () if $by > @list;

            # Start with leftmost $by symbols (except last,
...
        return @list[ @position ];
    }
}