From 6794da515963d17a0cff8acc96ffa285995f14c7 Mon Sep 17 00:00:00 2001
From: Justin Ethier <justin.ethier@gmail.com>
Date: Thu, 7 Jul 2016 23:24:39 -0400
Subject: [PATCH] WIP - equalp with checks for circular lists

---
 runtime.c | 37 +++++++++++++++++++++++++++++++++++++
 1 file changed, 37 insertions(+)

diff --git a/runtime.c b/runtime.c
index 427a5372..4f7c97d6 100644
--- a/runtime.c
+++ b/runtime.c
@@ -876,8 +876,18 @@ object memqp(void *data, object x, list l)
   return boolean_f;
 }
 
+/**
+ */
 object equalp(object x, object y)
 {
+  object slow_lis = x, fast_lis;
+  int second_cycle = 0;
+
+//  if (Cyc_is_pair(x) == boolean_t &&
+//      Cyc_is_pair(cdr(x)) == boolean_t){
+//    fast_lis = cdr(x);
+//  }
+
   for (;; x = cdr(x), y = cdr(y)) {
     if (equal(x, y))
       return boolean_t;
@@ -885,8 +895,35 @@ object equalp(object x, object y)
         (x == NULL) || (y == NULL) ||
         type_of(x) != pair_tag || type_of(y) != pair_tag)
       return boolean_f;
+
+    // Both objects are lists at this point, compare cars
     if (boolean_f == equalp(car(x), car(y)))
       return boolean_f;
+
+//    // If there is no cycle, keep checking equality
+//    if (fast_lis == NULL ||
+//        Cyc_is_pair(fast_lis) == boolean_f ||
+//        cdr(fast_lis) == NULL ||
+//        Cyc_is_pair(cdr(fast_lis)) == boolean_f ||
+//        cddr(fast_lis) == NULL){
+//      continue;
+//    }
+//
+//    // If there is a cycle, handle it
+//    if (slow_lis == fast_lis) {
+//      // if this is y, both lists have cycles and are equal, return #t
+//      if (second_cycle)
+//        return boolean_t;
+//      // if this is x, keep going and check for a cycle in y
+//      second_cycle = 1;
+//      slow_lis = y;
+//      if (Cyc_is_pair(y) == boolean_t) {
+//        fast_lis = cdr(y);
+//      }
+//      continue;
+//    }
+//    slow_lis = cdr(slow_lis);
+//    fast_lis = cddr(fast_lis);
   }
 }