Check if we are vacant and set after peer done.

gib-gab-gob/board.scm

@@ -2,6 +2,7 @@
   #:use-module (srfi srfi-1)
   #:export (make-board
             board-ref
+            board-assert-vacant
             board-choose!
             board-display
             board-winner?))
@@ -11,14 +12,13 @@
 (define (make-board)
   (make-array #f ggg-size ggg-size))
 
-(define (board-ref board x y)
-  (array-ref board y x))
+(define (board-assert-vacant x y)
+  (define ref (board-ref board x y))
+  (if ref (error "That space is already occupied with:" ref) ref))
 
 (define (board-choose! board val x y)
-  (define ref (board-ref board x y))
-  (if ref
-      (error "That space is already occupied with:" ref)
-      (array-set! board val y x)))
+  (board-assert-vacant)
+  (array-set! board val y x))
 
 (define (board-display board)
   (array-slice-for-each-in-order

gib-gab-gob/game.scm

@@ -31,12 +31,14 @@
    ;; TODO: These need to go somewhere else so the peer can't move or init for us!
    [(try-transition) 'playing]
    [(initialize!)
-    (on (<- peer 'try-transition) (lambda (status) (format #t "Peer's status: ~a\n" status)) #:promise? #t)]
+    (on (<- peer 'try-transition) (λ (status) (format #t "Peer's status: ~a\n" status)) #:promise? #t)]
    [(my-turn! x y)
     (if my-turn?
         (begin
-          (board-choose! board mark x y)
-          (set! my-turn? (not my-turn?))
-          (display)
-          (<- peer 'peer-turn! x y))
+          (board-assert-vacant board x y)
+          (on (<- peer 'peer-turn! x y)
+              (λ (_)
+                (board-choose! board mark x y)
+                (set! my-turn? (not my-turn?))
+                (display))))
         (error "It's not my turn."))]))