gistfile1.txt

(defn zipper
  []
  [() ()])

(defn insert-at-cursor
  [zipper newchar]
  [(cons newchar (first zipper)) (second zipper)])

(defn get-at-cursor
  [zipper]
  (ffirst zipper))

(defn move-left
  [zipper]
  [(rest (first zipper)) (cons (ffirst zipper) (second zipper))])

(defn move-right
  [zipper]
  [(cons (first (second zipper)) (first zipper)) (rest (second zipper))])

(defn delete-at-cursor
  [zipper]
  [(rest (first zipper)) (second zipper)])

;; tests

(def z (zipper))
(def z (insert-at-cursor z "a"))
(def z (insert-at-cursor z "b"))
(def z (insert-at-cursor z "c"))
(def z (insert-at-cursor z "d"))

(get-at-cursor z)

(def z (move-left z))
(get-at-cursor z)

(def z (delete-at-cursor z))
(get-at-cursor z)

(def z (insert-at-cursor z "q"))
(get-at-cursor z)

(def z (move-right z))
(get-at-cursor z)

(def z (move-right z))
(get-at-cursor z)