gistfile1.lisp

user> (defn assoc-with
  "Associates a value in a nested associative structure, where ks is a
  sequence of keys and v is the new value and returns a new nested structure."
  [m [fn & fns] v]
  (let [val (or (fn m) [])]
    (if fns
      (replace {val (assoc-with val fns v)} m)
      (replace {val v} m))))
#'user/assoc-with
user> (assoc-with [1 2 [[3 4 5]]] [last first last] 6)
[1 2 [[3 4 6]]]
user> (defn update-with
  "'Updates' a value in a nested associative structure, where fns is a
  sequence of fns and f is a function that will take the old value
  and any supplied args and return the new value, and returns a new
  nested structure."
  ([m [fn & fns] f & args]
     (let [val (or (fn m) [])]
       (if fns
	 (replace {val (apply update-with val fns f args)} m)
	 (replace {val (apply f val args)} m)))))
#'user/update-with
user> (update-with [1 2 [[3 4 5]]] [last first] conj 6)
[1 2 [[3 4 5 6]]]