Representing A Tree in Clojure

Question

'(A (B (D) (E)) (C (F)))

There's a scary way of doing it using just cons:

(defn mktree 
  ([label l r] (cons label (cons l r))) 
  ([leaf] (cons leaf (cons nil nil))))
(defn getlabel [t] (first t))
(defn getchildren [t] (rest t))
(defn getleft [t] (first (getchildren t)))
(defn getright [t] (rest (getchildren t)))

Note that children isn't a list; it's a pair. If your trees aren't just binary, you could make it a list. use nil when there's no left or right child, of course.

Otherwise, see this answer.

The tree in your picture:

(mktree 'A (mktree 'B (mktree 'D) (mktree 'E)) (mktree 'C nil (mktree 'F)))

Trees underly just about everything in Clojure because they lend themselves so nicely to structural sharing in persistent data structure. Maps and Vectors are actually trees with a high branching factor to give them bounded lookup and insert time. So the shortest answer I can give (though it's not really that useful) is that I really recommend Purely functional data structures by Chris Okasaki for a real answer to this question. Also Rich Hickey's video on Clojure data structures on blip.tv

(set 'A 'B 'C)