* lib.c (sel): Accept a function in place of the index list.

* txr.1: Documented.

3 files changed, 23 insertions, 2 deletions

diff --git a/ChangeLog b/ChangeLog
index 80681bd7..720e9371 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+2014-11-20  Kaz Kylheku  <kaz@kylheku.com>
+
+	* lib.c (sel): Accept a function in place of the index list.
+
+	* txr.1: Documented.
+
 2014-11-17  Kaz Kylheku  <kaz@kylheku.com>
 
 	* lib.c (split_str): If the separator string is empty,
diff --git a/lib.c b/lib.c
index 796a126c..c4e6395f 100644
--- a/lib.c
+++ b/lib.c
@@ -6209,7 +6209,9 @@ val sel(val seq_in, val where_in)
 {
   list_collect_decl (out, ptail);
   val seq = nullify(seq_in);
-  val where = nullify(where_in);
+  val where = if3(functionp(where_in),
+                  funcall1(where_in, seq),
+                  nullify(where_in));
 
   switch (type(seq)) {
   case NIL:
diff --git a/txr.1 b/txr.1
index 74e542f4..7b4d85fe 100644
--- a/txr.1
+++ b/txr.1
@@ -13312,7 +13312,7 @@ that element is added to a list. Finally, the list is returned.
 
 .coNP Function @ select
 .synb
-.mets (select < object << index-list )
+.mets (select < object >> { index-list <> | function })
 .syne
 .desc
 
@@ -13327,6 +13327,19 @@ the indices in
 .metn index-list .
 
 If
+.meta function
+is given instead of
+.metn index-list ,
+then
+.meta function
+is invoked with
+.meta object
+as its argument. The return value is then taken as
+if it were the
+.meta index-list
+argument .
+
+If
 .meta object
 is a sequence, then
 .meta index-list