replace-list: negatives in index-list follow convention.

The index-list replacement isn't following the convention that
negative index values reference from the end of the target
sequence. Let's fix that.

* lib.c (replace_list): Likewise.

* txr.1: Documentation updated.

2 files changed, 15 insertions, 5 deletions

diff --git a/lib.c b/lib.c
index 385101cb..01e18b03 100644
--- a/lib.c
+++ b/lib.c
@@ -1438,6 +1438,8 @@ val replace_list(val list, val items, val from, val to)
                 self, nao);
 
     while (iter && seq_peek(&item_iter, &item) && seq_peek(&wh_iter, &wh)) {
+      if (minusp(wh))
+        wh = plus(wh, len ? len : (len = length(list)));
       if (lt(wh, idx)) {
         seq_geti(&wh_iter);
         seq_geti(&item_iter);
diff --git a/txr.1 b/txr.1
index dd5eb172..7e85020f 100644
--- a/txr.1
+++ b/txr.1
@@ -27017,6 +27017,11 @@ and
 .meta index-list
 are of different lengths, then the shorter of the two determines
 the maximum number of elements which are overwritten.
+Whenever a negative value occurs in
+.meta index-list
+the length of
+.meta sequence
+is added to that value.
 Furthermore, similar restrictions apply on
 .meta index-list
 as under the
@@ -27030,7 +27035,8 @@ furthermore, if
 is a list, then
 .meta index-list
 must
-be monotonically increasing.
+be monotonically increasing, after consideration of the
+displacement of negative values.
 
 If
 .meta sequence
@@ -27067,11 +27073,13 @@ arguments are converted to single range object,
 whereas an
 .meta index-list
 is passed as-is.
-It is an error if a
-.code to
-argument is given, and
+It is an error if the
 .code from
-is a list; the situation is diagnosed. If either
+argument is a sequence, indicating an
+.metn index-list ,
+and a
+.code to
+argument is also given; the situation is diagnosed. If either
 .code from
 or
 .code to