Towers of Hanoi with Lisp: Lisp, Firefox 2.0

by: angelIIIPosted on 2008-03-25 at 09:33:05ID: 21203483

>I have been trying to understand Lisp for a few days now and I can definitely find better uses of my time in more productive languages.

learning Lisp is not necessarily about "to use it later in real-life", but "understanding how things work".
such courses are there to "format" your brain in a way to get you "thinking the true developer way".

I "had to go through" lisp also, and had not only the pleasure of doing hanoi, but also Dr Eliza with lisp.
although lisp will "waste" your time at syntax level with all those brackets, it's capabilities in pure methodology are, AFAIK, still unreached...

by: jvilla1983Posted on 2008-03-25 at 09:41:41ID: 21203590

Ok.. Well.. Yeah your right. I guess its just so weird looking at it and its like .. ok? where do I go from here? We were only given a 3 hour class on it.

I guess I'm not looking for a straight answer, I just need a direction to go from here. I know that we recursively call hanoi from the first block and send it back through with n - 1 as we send one of the smaller rings from the first to the third tower. I know that much.. but as far as what to add to that is boggling my mind. Also, I have no idea what the function atomize is doing, or even why its there for that matter.

I'm thinking that in the first block of hanoi that I need to take atomize all of the lists but normally in other languages though, the recursive statement will be reached before we would be able to call it.. IE.. the area where there is missing code.

by: angelIIIPosted on 2008-03-25 at 13:30:50ID: 21205826

>. I know that we recursively call hanoi from the first block and send it back through with n - 1 as we send one of the smaller rings from the first to the third tower. I know that much.
yes, that's it: recursive function/thinking :)

>I'm thinking that in the first block of hanoi that I need to take atomize all of the lists but normally in other languages though, the recursive statement will be reached before we would be able to call it.. IE.. the area where there is missing code.
in a recursive function, you have 2 parts:
* a return of the function, based on the "quit" condition
-> in the case of the hanoi towers, that is when you have only 1 block on the leftmost tower to get that to the rightmost tower
-> can be done freely, no "blocking condition"
* the general case (level=n), which can be "reduced" to the situation of the case of a lower complexity (n-1).
-> this will continue more and more until n=0, the base condition.
-> in hanoi, you have 1 small block (b1) on top of a larger block (b2). to move that from left to rightmost (t1, t2, t3), you do the following steps:
1) move b1 from t1 to t2
2) move b2 from t1 to t3
3) move b1 from t2 to t3
now, you moved the "combined" block from t1 to t3

done.
for level n=3 blocks, you know you can move b1+b2 to t2 (or t3) -> using complexity n-1 = 2. you can then move b3 to t3, and again move blocks b1+b2 (with complexity n-1) to t3.
cqfd

by: jvilla1983Posted on 2008-03-25 at 13:42:22ID: 21205938

I actually figured this out and I got the program to work in its sorting..

unfortunately, my output has each print on another line.. is there a way that I can put everything all on one line?

(defun hanoi(n t1 t2 t3)
 
  (if (> n 0)
 
      (progn
 
       (hanoi (- n 1) t1 t3 t2)
 
         ;ok.. This is where we start...
 
         ;We are already operating recursively.. from this point..
 
       'myoutput
 
       (print("move 1 disc from"))
 
       (print t1)
 
       (print "to")
 
       (print t2)
 
       (hanoi (- n 1) t3 t2 t1)
 
       )
 
    )
 
)

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Select all Open in new window

by: angelIIIPosted on 2008-03-25 at 14:01:22ID: 21206155

please check the format function:
http://www.n-a-n-o.com/lisp/cmucl-tutorials/LISP-tutorial-8.html

by: jvilla1983Posted on 2008-03-25 at 14:04:30ID: 21206186

See, the thing is that we arent allowed to use any other functions than the ones on the list. I tried using this already and even went so far as to try it with the (print function.. unfortunately print only takes 2 parameters.. what I was thinking is that I might be able to copy each as a part of a list into a variable and then print the output of the variable.. which might be the solution, but I dont quite know where to start on that.

by: angelIIIPosted on 2008-03-25 at 14:15:36ID: 21206291

which list? the pdf file attached is about a C assignment :)

by: jvilla1983Posted on 2008-03-27 at 08:31:41ID: 31442702

Not quite the answer that I was looking for, but its in the general direction. I figured this out on my own, so everything is ok in that manner. This would be good for someone that is wanting to know the implementation of the Hanoi towers.

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Towers of Hanoi with Lisp

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