What do you mean by "similar functionality"? Without using mutable
state, you won't be able to retain the defnode-style interface. But
obviously a twenty-questions program like this is easy to implement in
a purely functional way:
(defn ask [questions node]
(let [data (questions node)]
(assert data)
(if (string? data)
(println "The answer is" data)
(let [[question yes-node no-node] data]
(println question)
(print ">> ")
(flush)
(recur questions (if (= (read) 'yes) yes-node no-node))))))
(def sample-questions
{:people ["Is the person a man?" :male :female]
:male ["Is he living?" :liveman :deadman]
:deadman ["Was he American?" :us :them]
:us ["Is he on a coin?" :coin :cidence]
:coin ["Is the coin a penny?" :penny :coins]
:penny "Abraham Lincoln"})
(ask sample-questions :people)
-Per
On Tue, Apr 13, 2010 at 11:29 PM, Aravindh Johendran
<ajohend...@gmail.com> wrote:
> Is there a way to write this in clojure without java's hashmaps or
> clojure's atom/ref/var-binding/etc? The program doesn't have to be an
> exact translation. I just want similar functionality.
>
> ----------------------------------------------------------------------------------------------
> From chapter 6 of On Lisp - Figure 6.5
>
> (defvar *nodes* (make-hash-table))
>
> (defun defnode (name conts &optional yes no)
> (setf (gethash name *nodes*)
> (if yes
> #’(lambda ()
> (format t "~A~%>> " conts)
> (case (read)
> (yes (funcall (gethash yes *nodes*)))
> (t (funcall (gethash no *nodes*)))))
> #’(lambda () conts))))
>
> (defnode ’people "Is the person a man?" ’male ’female)
> (defnode ’male "Is he living?" ’liveman ’deadman)
> (defnode ’deadman "Was he American?" ’us ’them)
> (defnode ’us "Is he on a coin?" ’coin ’cidence)
> (defnode ’coin "Is the coin a penny?" ’penny ’coins)
> (defnode ’penny ’lincoln)
>
> (funcall (gethash ’people *nodes*))
> -----------------------------------------------------------------------------------------
>
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