#
# @newlist = semijoin($expr, $itemcount, @list);
#
# $expr      - A string to be used in a join() call.
# $itemcount - The number of items in a list to be joined.
#              It may be negative.
# @list      - The list
#
# Create a new list by performing a join on I<$itemcount> elements at 
+a
# time on the original list. Any leftover elements from the end of the
# list become the last item of the new list, unless I<$itemcount> is
# negative, in which case the first item of the new list is made from 
+the
# leftover elements from the front of the list.
#
sub semijoin
{
    my($jstr, $itemcount, @oldlist) = @_;
    my(@newlist);

    return @oldlist if ($itemcount <= 1 and $itemcount >= -1);

    if ($itemcount > 0)
    {
        push @newlist, join $jstr, splice(@oldlist, 0, $itemcount)
            while @oldlist;
    }
    else
    {
        $itemcount = -$itemcount;
        unshift @newlist, join $jstr, splice(@oldlist, -$itemcount, $i
+temcount)
            while $itemcount <= @oldlist;
        unshift @newlist, join $jstr, splice( @oldlist, 0, $itemcount)
            if @oldlist;
    }

    return @newlist;
}
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