Searches backwards within a deque.
rposition
is identical to position
, except the search proceeds backwards
from the end of the deque.
The index returned is always a non-negative integer, so that it can more easily be
compared to the indexes returned by position
.
(let st "It bears the mark of Polaris.")
(prn (position st "ar")) ; prints 5
(prn (position st "ar" 10)) ; prints 14
(prn (rposition st "ar")) ; prints 24
(prn (rposition st "ar" 10)) ; prints 5