How to remove nested parentheses in LISP

Question

How can I remove nested parentheses recursively in Common LISP Such as

  (unnest \'(a b c (d e) ((f) g))) => (a b c d e f g)
  (unnest \'(a b))                    


        

Answer 1

(defun flatten (l)
  (cond ((null l) nil)
        ((atom (car l)) (cons (car l) (flatten (cdr l))))
        (t (append (flatten (car l)) (flatten (cdr l))))))