Idiomatic string rotation in Clojure

Question

How to idiomatically rotate a string in Clojure for the Burrows-Wheeler transform?

I came up with this, which uses (cycle "string"), but feels a bit imperative:

(let [s (str "^" "banana" "|")
      l (count s)
      c (cycle s)
      m (map #(take l (drop % c)) (range l))]
  (apply map str m))
=> ("^banana|" "banana|^" "anana|^b" "nana|^ba" "ana|^ban" "na|^bana" "a|^banan" "|^banana")

I'm not sure if this qualifies as code golf. Is there a cleaner way to do this?

Answer 1

I would do:

(defn bwrot [s]
  (let [s (str "^" s "|")]
    (for [i (range (count s))]
      (str (subs s i) (subs s 0 i)))))

or:

(defn bwrot [s]
  (let [n (+ 2 (count s))
        s (str "^" s "|^" s "|")]
    (for [i (range n)]
      (subs s i (+ i n)))))

The second one should allocate less (one string instead of three per iteration).