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Task/Generate-Chess960-starting-position/Racket/generate-chess960-starting-position.rkt

@@ -0,0 +1,32 @@
+#lang racket
+(define white (match-lambda ['P #\♙] ['R #\♖] ['B #\♗] ['N #\♘] ['Q #\♕] ['K #\♔]))
+(define black (match-lambda ['P #\♟] ['R #\♜] ['B #\♝] ['N #\♞] ['Q #\♛] ['K #\♚]))
+
+(define (piece->unicode piece colour)
+  (match colour ('w white) ('b black)) piece)
+
+(define (find/set!-random-slot vec val k (f values))
+  (define r (f (random k)))
+  (cond
+    [(vector-ref vec r)
+     (find/set!-random-slot vec val k f)]
+    [else
+     (vector-set! vec r val)
+     r]))
+
+(define (chess960-start-position)
+  (define v (make-vector 8 #f))
+  ;; Kings and Rooks
+  (let ((k (find/set!-random-slot v (white 'K) 6 add1)))
+    (find/set!-random-slot v (white 'R) k)
+    (find/set!-random-slot v (white 'R) (- 7 k) (curry + k 1)))
+  ;; Bishops -- so far only three squares allocated, so there is at least one of each colour left
+  (find/set!-random-slot v (white 'B) 4 (curry * 2))
+  (find/set!-random-slot v (white 'B) 4 (compose add1 (curry * 2)))
+  ;; Everyone else
+  (find/set!-random-slot v (white 'Q) 8)
+  (find/set!-random-slot v (white 'N) 8)
+  (find/set!-random-slot v (white 'N) 8)
+  (list->string (vector->list v)))
+
+(chess960-start-position)