Merge branch 'master' of ssh://github.com/mthom/scryer-prolog

src/heap_iter.rs

@@ -86,17 +86,23 @@ impl<'a> EagerStackfulPreOrderHeapIter<'a> {
                     let arity = cell_as_atom_cell!(self.heap[s]).get_arity();
 
                     for idx in (s + 1 .. s + arity + 1).rev() {
+			if self.heap[idx].get_mark_bit() != self.mark_phase {
                             self.iter_stack.push(self.heap[idx]);
                             self.heap[idx].set_mark_bit(self.mark_phase);
 			}
                     }
+                }
                 (HeapCellValueTag::Lis, l) => {
+		    if self.heap[l+1].get_mark_bit() != self.mark_phase {
 			self.iter_stack.push(self.heap[l+1]);
-                    self.iter_stack.push(self.heap[l]);
-
-                    self.heap[l].set_mark_bit(self.mark_phase);
 			self.heap[l+1].set_mark_bit(self.mark_phase);
 		    }
+
+		    if self.heap[l].get_mark_bit() != self.mark_phase {
+			self.iter_stack.push(self.heap[l]);
+			self.heap[l].set_mark_bit(self.mark_phase);
+		    }
+                }
                 (HeapCellValueTag::AttrVar | HeapCellValueTag::Var, h) => {
                     let var_value = self.heap[h];
                     self.heap[h].set_mark_bit(self.mark_phase);

src/tests/term_variables.pl

@@ -45,7 +45,7 @@ test("term_variables#2097", (
 
 test("term_variables#2100", (
     termt2(T), term_variables(T,Vs),
-    T = [[T|_B]|_A], Vs == [_A,_B]
+    T = [[T|A]|B], Vs == [A,B]
 )).
 
 test("term_variables#2101", (