3 files changed, 61 insertions, 2 deletions

diff --git a/eval.c b/eval.c
index b04b15a2..b4233e42 100644
--- a/eval.c
+++ b/eval.c
@@ -6073,7 +6073,8 @@ void eval_init(void)
   reg_fun(intern(lit("copy-list"), user_package), func_n1(copy_list));
   reg_fun(intern(lit("nreverse"), user_package), func_n1(nreverse));
   reg_fun(intern(lit("reverse"), user_package), func_n1(reverse));
-  reg_fun(intern(lit("ldiff"), user_package), func_n2(ldiff));
+  reg_fun(intern(lit("ldiff"), user_package),
+          func_n2(if3(opt_compat && opt_compat <= 190, ldiff_old, ldiff)));
   reg_fun(intern(lit("last"), user_package), func_n2o(last, 1));
   reg_fun(intern(lit("butlast"), user_package), func_n2o(butlast, 1));
   reg_fun(intern(lit("nthlast"), user_package), func_n2(nthlast));
diff --git a/lib.c b/lib.c
index 7c201e90..673a1a4c 100644
--- a/lib.c
+++ b/lib.c
@@ -1447,7 +1447,62 @@ val lazy_appendl(val lists)
   return lazy_appendv(args);
 }
 
-val ldiff(val list1, val list2)
+val ldiff(val seq1_in, val seq2)
+{
+  val seq1 = seq1_in;
+  list_collect_decl (out, ptail);
+
+loop:
+  if (seq1 == seq2)
+    return out;
+
+  {
+    seq_info_t si1 = seq_info(seq1);
+    seq_info_t si2 = seq_info(seq2);
+
+    switch (SEQ_KIND_PAIR(si1.kind, si2.kind)) {
+    case SEQ_KIND_PAIR(SEQ_NIL, SEQ_NIL):
+    case SEQ_KIND_PAIR(SEQ_NIL, SEQ_LISTLIKE):
+    case SEQ_KIND_PAIR(SEQ_NIL, SEQ_VECLIKE):
+    case SEQ_KIND_PAIR(SEQ_NIL, SEQ_HASHLIKE):
+    case SEQ_KIND_PAIR(SEQ_NIL, SEQ_NOTSEQ):
+      break;
+    case SEQ_KIND_PAIR(SEQ_LISTLIKE, SEQ_NIL):
+    case SEQ_KIND_PAIR(SEQ_VECLIKE, SEQ_NIL):
+    case SEQ_KIND_PAIR(SEQ_HASHLIKE, SEQ_NIL):
+    case SEQ_KIND_PAIR(SEQ_NOTSEQ, SEQ_NIL):
+      return seq1;
+    case SEQ_KIND_PAIR(SEQ_LISTLIKE, SEQ_LISTLIKE):
+      ptail = list_collect(ptail, car(si1.obj));
+      seq1 = cdr(si1.obj);
+      goto loop;
+    case SEQ_KIND_PAIR(SEQ_LISTLIKE, SEQ_VECLIKE):
+    case SEQ_KIND_PAIR(SEQ_LISTLIKE, SEQ_HASHLIKE):
+    case SEQ_KIND_PAIR(SEQ_LISTLIKE, SEQ_NOTSEQ):
+      ptail = list_collect(ptail, car(si1.obj));
+      seq1 = cdr(si1.obj);
+      goto loop;
+    case SEQ_KIND_PAIR(SEQ_VECLIKE, SEQ_VECLIKE):
+      if (equal(seq1, seq2) || zerop(length(seq1)))
+        break;
+      ptail = list_collect(ptail, ref(seq1, zero));
+      seq1 = sub(seq1, one, t);
+      goto loop;
+    case SEQ_KIND_PAIR(SEQ_HASHLIKE, SEQ_HASHLIKE):
+    case SEQ_KIND_PAIR(SEQ_NOTSEQ, SEQ_NOTSEQ):
+      if (!equal(seq1, seq2))
+        ptail = list_collect_append(ptail, seq1);
+      break;
+    default:
+      ptail = list_collect_append(ptail, seq1);
+      break;
+    }
+  }
+
+  return make_like(out, seq1_in);
+}
+
+val ldiff_old(val list1, val list2)
 {
   val list_orig = list1;
   list_collect_decl (out, ptail);
diff --git a/lib.h b/lib.h
index ca72f970..f5e4194f 100644
--- a/lib.h
+++ b/lib.h
@@ -359,6 +359,8 @@ typedef struct seq_info {
 
 extern const seq_kind_t seq_kind_tab[MAXTYPE+1];
 
+#define SEQ_KIND_PAIR(A, B) ((A) << 3 | (B))
+
 INLINE cnum tag(val obj) { return coerce(cnum, obj) & TAG_MASK; }
 INLINE int is_ptr(val obj) { return obj && tag(obj) == TAG_PTR; }
 INLINE int is_num(val obj) { return tag(obj) == TAG_NUM; }
@@ -566,6 +568,7 @@ val replace_list(val list, val items, val from, val to);
 val lazy_appendl(val lists);
 val lazy_appendv(struct args *lists);
 val ldiff(val list1, val list2);
+val ldiff_old(val list1, val list2);
 val flatten(val list);
 val lazy_flatten(val list);
 val flatcar(val list);