Here is the same for-tree macro processing TXR Lisp's built-in search tree type. That does not use structs, but built in node and tree types. The left, right a

Here is the same for-tree macro processing TXR Lisp's built-in search tree type. That does not use structs, but built in node and tree types. The left, right and key fields of a node object are accessed with like-named functions. We must call tree-root on a tree object to get to the encapsulated root node: 1> (for-tree n (tree-root #T(() 1 2 3 4 5 6 7 8)) (left n) (right n) (prinl (key n))) 1 2 3 4 5 6 7 8 How about a tree of integers. Let's say the root integer is 1, and to go left is to multiply by 2, and to go right is to multiply by 2 and mask in a 1. And let's say the depth caps out at the value 16: 2> (for-tree n 1 (if (< n 8) (* 2 n)) (if (< n 8) (+ 1 (* 2 n))) (prinl n)) 8 4 9 2 10 5 11 1 12 6 13 3 14 7 15 nil Let's see that in binary: 3> (for-tree n 1 (if (< n 8) (* 2 n)) (if (< n 8) (+ 1 (* 2 n))) (format t "~b\n" n)) 1000 100 1001 10 1010 101 1011 1 1100 110 1101 11 1110 111 1111 nil Let's right-align digits to see different patterns in it: 2> (for-tree n 1 (if (< n 8) (* 2 n)) (if (< n 8) (+ 1 (* 2 n))) (format t "~6b\n" n)) 1000 100 1001 10 1010 101 1011 1 1100 110 1101 11 1110 111 1111 nil Nah, left-aligned wins.