Detect cycles in rlcp_tree.

This will be required when the parser becomes
capable of creating object graphs with cycles.

* parser.c (parser_callgraph_circ_check): New function.

* parser.h (struct circ_stack): New struct.
(parser_callgraph_circ_check): Declared.

* parser.y (rlcp_tree_rec): New static function.
(rlcp_tree): Reduced to wrapper for rlcp_tree_rec.

1 files changed, 10 insertions, 0 deletions

diff --git a/parser.c b/parser.c
index 6d7801c8..5f458f1e 100644
--- a/parser.c
+++ b/parser.c
@@ -200,6 +200,16 @@ void prime_parser_post(parser_t *p, enum prime_parser prim)
     p->recent_tok.yy_char = 0;
 }
 
+int parser_callgraph_circ_check(struct circ_stack *rs, val obj)
+{
+  for (; rs; rs = rs->up) {
+    if (rs->obj == obj)
+      return 0;
+  }
+
+  return 1;
+}
+
 void open_txr_file(val spec_file, val *txr_lisp_p, val *name, val *stream)
 {
   enum { none, tl, txr } suffix;