From 4e3e4e1ccc60331ff8ff4c1c139e9da3c95e2272 Mon Sep 17 00:00:00 2001
From: Kaz Kylheku <kaz@kylheku.com>
Date: Mon, 24 Aug 2015 06:37:19 -0700
Subject: New function: shuffle.

* eval.c (eval_init): Register shuffle as intrinsic.

* lib.c (shuffle): New function.

* lib.h (shuffle): Declared.
---
 lib.c | 43 +++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 43 insertions(+)

(limited to 'lib.c')

diff --git a/lib.c b/lib.c
index a39c7a09..27b77808 100644
--- a/lib.c
+++ b/lib.c
@@ -6166,6 +6166,49 @@ val sort(val seq_in, val lessfun, val keyfun)
   return seq;
 }
 
+val shuffle(val seq)
+{
+  switch (type(seq)) {
+  case NIL:
+    return nil;
+  case CONS:
+  case LCONS:
+    if (cdr(seq))
+    {
+      val v = shuffle(vector_list(seq));
+      val i, l;
+
+      for (l = seq, i = zero; l; i = succ(i), l = cdr(l))
+        rplaca(l, ref(v, i));
+    }
+    return seq;
+  case LIT:
+    uw_throwf(error_s, lit("shuffle: ~s is a literal"), seq, nao);
+  case STR:
+  case LSTR:
+  case VEC:
+    {
+      val rs = random_state;
+      val n = length(seq);
+      val i;
+
+      if (n == zero || n == one)
+        return seq;
+
+      for (i = pred(n); ge(i, one); i = pred(i)) {
+        val j = random(rs, succ(i));
+        val t = ref(seq, i);
+        refset(seq, i, ref(seq, j));
+        refset(seq, j, t);
+      }
+
+      return seq;
+    }
+  default:
+    type_mismatch(lit("shuffle: ~s is not a sequence"), seq, nao);
+  }
+}
+
 static val multi_sort_less(val funcs_cons, val llist, val rlist)
 {
   cons_bind (funcs, key_funcs, funcs_cons);
-- 
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