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- (define-module (shuffling)
- #:export (fisher-yates-shuffle)
- #:use-module (rnrs base)
- #:use-module ((guile) #:select (lambda* λ record-constructor))
- #:use-module ((random-number-generator) #:select (make-random-integer-generator))
- #:pure)
- (define fisher-yates-shuffle
- (lambda* (lst #:key (rng (make-random-integer-generator #:seed 12345)))
- "Shuffle the given list LST using the optional keyword argument
- provided random number generator RNG. If no random number generator is
- given, a predetermined one will be used."
- (let ([lst-as-vec (list->vector lst)])
- (let loop ([result '()]
- [elements-to-pick (vector-length lst-as-vec)])
- (cond
- [(zero? elements-to-pick) result]
- [else
- (let* ([rand-int (rng elements-to-pick)]
- [val (vector-ref lst-as-vec rand-int)])
- (vector-set! lst-as-vec
- rand-int
- (vector-ref lst-as-vec
- (- elements-to-pick 1)))
- (loop
- (cons val result)
- (- elements-to-pick 1)))])))))
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