Symboling dotted list

This is homework :) please don't tell my teacher.
I have a problem adding symbol as a first element over a dotted list,
actually tree.

(add-symbol :foo 1)
1

(add-symbol :foo '(1 . 2))
(foo  1 . 2)

(add-symbol :foo '(1 (2 3 . 4) 5))
(foo 1 (foo 2 3 . 4) 5)

The solution for regular list is easy with dolist or loop/colect but
how to loop the dotted list.

thanks
bobi

Slobodan Blazeski < XXXX@XXXXX.COM > writes:


Have a look at:
 http://www.**--****.com/ 
 http://www.**--****.com/ 

So you have trees.  It looks like the nodes of these trees have no
label, only a list of children, and for some strange reason, this can
be a dotted-list.

(defun make-tree     (children) children)
(defun tree-children (tree)     tree)
(defun leafp         (tree)     (atom tree))

(defun add-symbol (keyword-designating-the-symbol-name-why-is-it-so-I-wonder tree)
  (add-symbol-1 (intern (string keyword-designating-the-symbol-name-why-is-it-so-I-wonder))
                tree))

(defun add-symbol-1 (symbol tree)
  (if (leafp tree)
      tree ; no change on a leaf.
      (make-tree (cons symbol (map-dotted-list (lambda (subtree) (add-symbol-1 symbol subtree))
                                               (tree-children tree))))))

To process a dotted list, the difference is that instead of getting
NIL when you reach the end of the list, you get a atom.  So you only
have to chance one test to the normal list processing:

(defun map-dotted-list (fun dotted-list)
  (cond
    ((null dotted-list) ; it wasn't a dotted list
       '())
    ((atom dotted-list) ; this is the last item of the dotted list.
       (funcall fun dotted-list))
    (t ; this is a cons cell:
       (cons (funcall fun (car dotted-list)) (map-dotted-list fun (cdr dotted-list))))))



-- 
__Pascal Bourguignon__

On May 3, 1:55m,  XXXX@XXXXX.COM  (Pascal J. Bourguignon)


> (defun tree-children (tree) tr>e)
> (defun leafp (tree) (at>m >ree))
>
> (defun add-symbol (keyword-designating-the-symbol-name-why-is-it-so-I-won>er tree)
> (add-symbol-1 (intern (string keyword-designating-the-symbol-name-why-is-it-so->-wonder))
> > gt;tree))
>
> (defun add-symb>l-1 (symbol tree)
>>(if (leafp tree)
> tree > no change on a leaf.
> (make-tree (cons symbol (map-dotted-list (lambda (subtree) (add->ymbol-1 symbol subtree))
> gt;> tree-children tree))))))
>
> To process a dotte> list, the difference is that instead of getting
> NIL when you reach >he end of the list, you get a atom. o you only
> have >o >hance one test to the normal list processin>:
>
> (>efun map-dotted-list (fun dotted-list)
> (cond
>> ((nu>l dotted-list) ; it wasn't a dotted list
> ())
> ((ato> dotted-list) ; this is the last>item of the dotted list.
> > funcall fun dotted-list))
> (t ; this is a cons cell:
> cons (funcal> f>n (ca> dotted-list)) (map-dotted-list fun (cdr dotted-list))))))
>
> --
> __Pascal Bourguignon__

Many thanks. Great code and great read.

bobi