Re: Car and cdr (Re: Python syntax in Lisp and Scheme)

From: Pascal Bourguignon (spam_at_thalassa.informatimago.com)
Date: 10/13/03 

Date: 13 Oct 2003 18:39:38 +0200

Pascal Costanza <costanza@web.de> writes:
> >>>"left" and "right" - referring to 'subtrees'?
> >>
> >>Sure, why not?
> >>
> >>(defun left (tree)
> >> (car tree))
> >>
> >>(defun right (tree)
> >> (cdr tree))
> >>
> >>;-)
> > Wrong:
> > (defun left (tree) (car (car tree)))
> > (defun right (tree) (cdr (car tree)))
> > (defun label (tree) (cdr tree))
>
> I see your point, but "wrong" is a bit strong here:

This was a rhetorical "wrong" :-)
 
> (defvar *tree-labels* (make-hash-table))
>
> (defun label (tree) (gethash tree *tree-labels*))

While this kind of technique may be helpful (or even save our "life"
sometimes), I don't like it because of the loose coupling and possible
inconsistency between the various data structures... I think it can
only be justified by low-level optimization reasons. 

-- 
__Pascal_Bourguignon__
http://www.informatimago.com/
Do not adjust your mind, there is a fault in reality.

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