1 files changed, 83 insertions, 0 deletions
diff --git a/lib.c b/lib.c
index 78b50751..006036a9 100644
--- a/lib.c
+++ b/lib.c
@@ -2927,6 +2927,89 @@ val keep_if(val pred, val seq, val keyfun)
   return remove_if(notf(pred), seq, keyfun);
 }
 
+val separate(val pred, val seq_in, val keyfun_in)
+{
+  val self = lit("separate");
+  val keyfun = default_null_arg(keyfun_in);
+
+  switch (type(seq_in)) {
+  case NIL:
+    return nil;
+  case CONS:
+  case LCONS:
+  case COBJ:
+    {
+      list_collect_decl (yea, yptail);
+      list_collect_decl (nay, nptail);
+      val list = seq_in;
+      val lastdiff = list;
+      val was_yea = nil; /* Initialize to nil to silence compiler warning. */
+
+      gc_hint(list);
+
+      for (; list; list = cdr(list)) {
+        val elem = car(list);
+        val key = keyfun ? funcall1(keyfun, elem) : elem;
+        val is_yea = if3(funcall1(pred, key), t, nil);
+
+        if (list != seq_in && neq(is_yea, was_yea)) {
+          if (was_yea)
+            yptail = list_collect_nconc(yptail, ldiff(lastdiff, list));
+          else
+            nptail = list_collect_nconc(nptail, ldiff(lastdiff, list));
+
+          lastdiff = list;
+        }
+
+        was_yea = is_yea;
+      }
+
+      if (was_yea)
+        yptail = list_collect_nconc(yptail, lastdiff);
+      else
+        nptail = list_collect_nconc(nptail, lastdiff);
+
+      return cons(yea, cons(nay, nil));
+    }
+  case LIT:
+  case STR:
+  case LSTR:
+    {
+      val yea = mkustring(zero);
+      val nay = mkustring(zero);
+      val str = seq_in;
+      cnum len = c_fixnum(length_str(str), self), i;
+
+      for (i = 0; i < len; i++) {
+        val elem = chr_str(str, num_fast(i));
+        val key = keyfun ? funcall1(keyfun, elem) : elem;
+
+        string_extend(funcall1(pred, key) ? yea : nay, elem);
+      }
+
+      return cons(yea, cons(nay, nil));
+    }
+  case VEC:
+    {
+      val yea = vector(zero, nil);
+      val nay = vector(zero, nil);
+      val vec = seq_in;
+      cnum len = c_fixnum(length_vec(vec), self), i;
+
+      for (i = 0; i < len; i++) {
+        val elem = vecref(vec, num_fast(i));
+        val key = keyfun ? funcall1(keyfun, elem) : elem;
+
+        vec_push(funcall1(pred, key) ? yea : nay, elem);
+      }
+
+      return cons(yea, cons(nay, nil));
+    }
+  default:
+    uw_throwf(error_s, lit("~a: ~s isn't a sequence"), self, seq_in, nao);
+  }
+}
+
 static val rem_lazy_rec(val obj, val list, val env, val func);
 
 static val rem_lazy_func(val env, val lcons)