Hi, I'm new to lisp and trying to get a feel for things in CL. To that
end, I'm trying to write a binary tree, but I can't figure out how to
do it the way I'd like. Given nodes in the form of (key left-child
right-child . data), I'd prefer to write something like
<code>
(defun insert (key data &optional (node *root*))
(progn
(if (null *root*)
(setf *root* (make-node key data)))
(destructuring-bind (k l r . d) node
(if (funcall test k key)
(setf node (make-node key data l r))
(insert key data (if (funcall cmp k key)
l
r))))))
</code>
for the insert function, but obviously this isn't working. As you can
see, in two places I'm trying to set the <i>place</i> of a variable
I'm passing into the function, but all I'm really doing is clobbering
the version in the local scope.
I guess what I'm kind of trying to do is a bit like passing around
handles (pointers to pointers) in c. Is there some nice way to do
something like this in CL?
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