Representing A Tree in Clojure

Question

What would be an idiomatic way to represent a tree in Clojure? E.g.:

     A
    / \\
   B   C
  /\\    \\
 D  E    F

Performance is not imp

Answer 1

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)))