More Complex Macros

Let’s suppose you need a custom my-length command. This is a classic list-eating function that will count the length of a list. We’ll write it in the proper “tail call optimized” style (discussed in Chapter 14), where the recursive function call is in the tail position. Here’s the code:

(defun my-length (lst)
   (labels ((f (lst acc)
              (if lst
                (f (cdr lst) (1+ acc))
      (f lst 0)))

As you can see, this function has tons of repetitive ...

Get Land of Lisp now with the O’Reilly learning platform.

O’Reilly members experience live online training, plus books, videos, and digital content from nearly 200 publishers.