From: Mark Thom <markjordanthom@gmail.com>
Date: Thu, 7 Apr 2022 04:53:48 +0000 (-0600)
Subject: detect immediately cyclic lists (#1384)
X-Git-Tag: v0.9.1~71
X-Git-Url: https://git.sagredo.dev/?a=commitdiff_plain;h=4a6ffb6b9ee24d0357af2e09e116ca32fd7faf76;p=scryer-prolog.git

detect immediately cyclic lists (#1384)
---

diff --git a/src/heap_iter.rs b/src/heap_iter.rs
index 21a65dbd..8c40d56a 100644
--- a/src/heap_iter.rs
+++ b/src/heap_iter.rs
@@ -167,7 +167,12 @@ impl<'a> StackfulPreOrderHeapIter<'a> {
                    self.push_if_unmarked(vh);
 
                    self.stack.push(IterStackLoc::iterable_heap_loc(vh + 1));
-                   forward_if_referent_marked(&mut self.heap, vh + 1);
+
+                   if self.heap[vh + 1].get_mark_bit() {
+                       self.heap[vh + 1].set_forwarding_bit(true);
+                   } else {
+                       forward_if_referent_marked(&mut self.heap, vh + 1);
+                   }
 
                    self.stack.push(IterStackLoc::mark_heap_loc(vh));
                    forward_if_referent_marked(&mut self.heap, vh);