purely functional data structures chapter 2.1 and chapter 2.2

chapter_2.el

;; Put the cursor over progn and hit C-M-x
(progn
  (defun exersize_2_1 ()
    (defun suffixes (list)
      (if (not list)
          nil
        (cons list (suffixes (cdr list)))
        ))

    (defun printer (list)
      (insert (format "%s" list)))

    )


  (defun exersize_2_2 ()
    (setq empty-tree '(nil nil nil) )

    (defun tree-is-empty (tree)
      (or
      (equal tree '(nil empty-tree empty-tree))
      (equal tree '(nil nil nil))
      )
    )

    (defun tree-insert (element tree)
      (let ((tree-node (car tree))
            (left-tree (nth 1 tree))
            (right-tree (nth 2 tree)))
        (cond ((tree-is-empty tree) (list element empty-tree empty-tree)) 
              ((eql tree-node element) tree )
              ((< element tree-node)
                (list tree-node (tree-insert element left-tree) right-tree))
              ((> element tree-node)
                (list tree-node left-tree (tree-insert element right-tree)))
              )
        )
      )

    (defun tree-build-from-list-helper (list tree)
      (if (not list)
            tree
            (tree-build-from-list-helper
            (cdr list)
            (tree-insert (car list) tree)))
      )

    (defun tree-build-from-list (list)
      (tree-build-from-list-helper list empty-tree)
      )

    (defun tree-member (element tree)
      (let ((tree-node (car tree))
            (left-tree (nth 1 tree))
            (right-tree (nth 2 tree)))
        (cond ((tree-is-empty tree) ( nil ))
              ((eql tree-node element) ( t ) )
              ((< element tree-node)
              (tree-member element left-tree))
              ((> element tree-node)
              (tree-member element right-tree))
              )
        )
      )

    (defun printer (tree)
      (insert
      (apply 'format (cons "root: %s\nleft-tree: %s\nright-tree: %s\n" tree)))
      )
  )

  (defun setup-board ()
    (switch-to-buffer-other-window "HAHA")
    (erase-buffer)
    (switch-to-buffer-other-window "chapter_2.el")

    (defun run-exersize (list fun printer)
      (switch-to-buffer-other-window "HAHA")
      (printer (funcall fun list))
      (insert "\n\n")
      (switch-to-buffer-other-window "chapter_2.el"))

    )

  (setup-board)

  (exersize_2_1)
  (run-exersize '(5 4 2 1) 'suffixes 'printer)

  (exersize_2_2)
  (setq tree-from-list (tree-build-from-list '(8 5 4 1 40)))
  (run-exersize tree-from-list 'identity 'printer)
)