on-lisp

I was reading the book On Lisp by Paul Graham. In Chapter 4, Utility Functions, he gives examples of small functions that operate on lists, which would be helpful while writing a larger program. One of them is flatten . Given a nested list at any arbitrary level as argument, flatten will remove all the nested elements and put them on the top level. Below is my attempt at implementing flatten: (defun flatten (lst) (labels ((rflatten (lst1 acc) (dolist (el lst1) (if (listp el) (rflatten el acc) (push el acc))) acc)) (reverse (rflatten lst nil)))) But the above function does not flatten lists

In On Lisp , p. 267, Paul Graham provides an implementation of continuation passing macros: (setq *cont* #'identity) (defmacro =lambda (parms &body body) `#'(lambda (*cont* ,@parms) ,@body)) (defmacro =defun (name parms &body body) (let ((f (intern (concatenate 'string "=" (symbol-name name))))) `(progn (defmacro ,name ,parms `(,',f *cont* ,,@parms)) (defun ,f (*cont* ,@parms) ,@body)))) (defmacro =bind (parms expr &body body) `(let ((*cont* #'(lambda ,parms ,@body))) ,expr)) (defmacro =values (&rest retvals) `(funcall *cont* ,@retvals)) The following code to traverse a tree t2 for each leaf