Not entirely tested but I assume this is working... need tests lol

gib-gab-gob/game.scm

@@ -5,6 +5,7 @@
   #:use-module (goblins actor-lib sealers)
   #:use-module (goblins actor-lib selfish-spawn)
   #:use-module (ice-9 match)
+  #:use-module (srfi srfi-1)
   #:use-module (ice-9 rdelim)
   #:export (^ggg-controller))
 
@@ -62,3 +63,21 @@
           (array->list x))
      (format #t "\n"))
    board))
+
+(define (board-winner? board mark)
+  (define idxs (iota ggg-size))
+  (define (row-winner? y)
+    (apply eq? mark (map (lambda (x) (board-ref board (list x y))) idxs)))
+  (define (col-winner? x)
+    (apply eq? mark (map (lambda (y) (board-ref board (list x y))) idxs)))
+  (define (diag-winner?)
+    (or
+     (apply eq? mark (map (lambda (x) (board-ref board (list x x))) idxs))
+     (apply eq? mark (map (lambda (x) (board-ref board (list x x))) idxs))))
+
+  (any (lambda (x) (eq? #t x))
+       (cons
+        (diag-winner?)
+        (append
+         (map row-winner? idxs)
+         (map col-winner? idxs)))))