Trying to build a tic tac toe without any state (in pure fp style)

Question

I am learning Clojure and trying to implement a simple tic-tac-toe (or morpion). But i am working hard in order to avoid any ref/atom/agent ...

I know I could do it easily in a console application, as it would not be event-driven, so that I would exactly know when to pass in a new board value. I mean

my board would be a vector of vectors ([[:circle 0 :cross][:any :circle :empty][:cross :none :none]] where only :circle and :cross values matter)
I would have a simple text-based method which takes a board and return a string

But, whenever I want to implement a graphical Panel, I wonder how can I do the same thing. For example :

I am creating an instance of javax.swing.JPanel (please don't care about the other methods that are used here) :

(defn make-board-panel
"Builds the board JPanel, whose state is given by board argument,
and turn-piece argument (must be either :circle or :cross, I mean the next
value to set in the board)."
[board turn-piece]
{:pre ['morpion.core/is-board? board, 'morpion.core/is-a-player-piece? turn-piece]}
  (proxy [JPanel MouseListener] []
    (paintComponent [g]
        (proxy-super paintComponent g)
        (paint-board-lines g)
        (paint-board board g)
    )
    (mouseClicked [e]
        (if (and (abs-coord-in-cell? (.getX e)) (abs-coord-in-cell? (.getY e)))
            (let [cell-x (abs-coord-to-rel (.getX e))
                    cell-y (abs-coord-to-rel (.getY e))]
                ;; Here I compute the new board value
            )  
            nil ;; Here I wish I could return the new board value to the caller of make-board-panel, but this seems impossible !
        ) 
    )
    (mouseEntered [e])
    (mouseExited [e])
    (mousePressed [e])
    (mouseReleased [e])
   )
)

But it seems that there are no way for me to fetch the new value of the board, from the mouseClicked event of the Panel : unless I introduce a state variable.

So is there a workaround :

Sources for my complete project :

(I've tried to improve thanks to Igrapenthin comment, but I am still failing.)

You could pass a callback-function as an additional parameter that will be called from inside the MouseListener with the new board value. — Leon Grapenthin, Aug 27 '13 at 14:26
Thanks for your idea : I am trying it right now. I did not think about this way (Clojure beginner :) ) — loloof64, Aug 27 '13 at 14:29
Are you sure you're using your preconditions right? It looks like all it's doing now is checking of the provided values are non-nil, but that you actually want to check that `board` is a board and `turn-piece` is a piece. — DaoWen, Aug 27 '13 at 19:12
You can't avoid state unless you want to replace your panel by a new one after each turn. — cgrand, Aug 27 '13 at 20:11
Yes, that what I planned to do. But for now, I still have some errors to fix. — loloof64, Aug 27 '13 at 21:17

score 2 · Accepted Answer · answered Aug 27 '13 at 16:08

2

(defn make-board-panel
 [board turn-piece output-fn]
 (proxy [JPanel MouseListener] []
   ;; ...
   (mouseClicked [e]
     (when (and (abs-coord-in-cell? (.getX e)) 
           (abs-coord-in-cell? (.getY e)))
       (let [cell-x (abs-coord-to-rel (.getX e))
             cell-y (abs-coord-to-rel (.getY e))]
          ;; Here I compute the new board value
          (output-fn new-board-value))))
    ;; ...
    ))

answered Aug 27 '13 at 16:08

Leon Grapenthin

9,246
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Yes, I've written something like that, but I am still facing a strange ArityException in my code (it does not point me to the problem, but it just says ArityException in : Symbol) – loloof64 Aug 27 '13 at 16:18
1

your error is certainly due to the quote (') before morpion.core/play-board – cgrand Aug 27 '13 at 20:14
Thanks, I quoted 'morpion.core/play-board because I thought I could fix the namespace problem that way. But it didn't. So I must try with require/use instead. – loloof64 Aug 27 '13 at 20:50
If the issue is one of recursive require (both namespaces require the other), either make a third that both can require, or use `resolve` to look up the namespace and function at runtime. – noisesmith Aug 28 '13 at 17:15

Trying to build a tic tac toe without any state (in pure fp style)

1 Answers1