Another twist is to use the 'on interator which binds its first argument to each successive element and implicitly binds 'index to the index of that element.
arc> (on c "arc" (prn index ":" c))
0:a
1:r
2:c
nil
(def ugh (str)
(let x 5
(on c str
(let v (trunc (/ 12 (+ index 1)))
(if (is c #\A)
(++ x v)
(-- x v))))
x))
