From 33383583acc82aa80516267d0ec7f9fa93d33bde Mon Sep 17 00:00:00 2001
From: Avril <flanchan@cumallover.me>
Date: Sun, 19 Apr 2020 21:46:50 +0100
Subject: [PATCH] shuffle

---
 cl-rng.lisp | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/cl-rng.lisp b/cl-rng.lisp
index ab766e4..ca55ec7 100644
--- a/cl-rng.lisp
+++ b/cl-rng.lisp
@@ -26,3 +26,15 @@
 
 (export 'weighted)
 
+(defun shuffle! (sequence &key (provider *default-randomness-provider*))
+  (if (listp sequence)
+      (loop for i from (1- (length sequence)) above 0 do
+	   (rotatef (nth i sequence)
+		    (nth (funcall provider :limit i :transform #'floor) sequence)))
+      (loop for i from (1- (length sequence)) above 0 do
+	   (rotatef (aref sequence i)
+		    (aref sequence (funcall provider :limit i :transform #'floor)))))
+  sequence)
+
+(export 'shuffle!)
+