From 9ec47b693f9618bfd29347226157dc2f8a655ff8 Mon Sep 17 00:00:00 2001
From: Kaz Kylheku <kaz@kylheku.com>
Date: Sun, 22 Aug 2021 11:18:19 -0700
Subject: iter-begin: allow iterator argument.

* lib.c (seq_iter_init_with_info): Allow the iterated object
to be an iterator, in which case a copy of the iterator is
set up.

* txr.1: Documented.
---
 lib.c |  5 +++++
 txr.1 | 11 +++++++++++
 2 files changed, 16 insertions(+)

diff --git a/lib.c b/lib.c
index 628ed06e..6175497f 100644
--- a/lib.c
+++ b/lib.c
@@ -987,6 +987,11 @@ void seq_iter_init_with_info(val self, seq_iter_t *it,
         }
       }
     }
+    if (it->inf.obj->co.cls == seq_iter_cls)
+    {
+      *it = *coerce(struct seq_iter *, it->inf.obj->co.handle);
+      break;
+    }
     if (it->inf.obj->co.cls == tree_iter_cls)
     {
       it->ui.iter = if3(support_rewind,
diff --git a/txr.1 b/txr.1
index 8b0f53a3..61354add 100644
--- a/txr.1
+++ b/txr.1
@@ -35605,6 +35605,17 @@ itself as the iterator. Likewise if
 .meta seq
 is a number.
 
+If
+.meta seq
+is an iterator produced by
+.code iter-begin
+then an iterator similar to that iterator is returned, which can continue
+iterating the same sequence. The iterator may be
+.meta seq
+itself or share state with
+.metn seq ,
+and thus may not be relied on to produce an independent, parallel iteration.
+
 If
 .meta seq
 is a structure which supports the
-- 
cgit v1.2.3