Implement @(next nil).

* match.c (v_next): If argument to @(next) is nil, then
evaluate remaining query in context with no list of files,
and no data.

* txr.1: Documented @(next nil).

1 files changed, 12 insertions, 0 deletions

diff --git a/txr.1 b/txr.1
index 3ece5efb..3b1bf55b 100644
--- a/txr.1
+++ b/txr.1
@@ -3163,6 +3163,7 @@ and takes various arguments, according to these possibilities:
 .mets @(next :env)
 .mets @(next :list << expr )
 .mets @(next :string << expr )
+.mets @(next nil)
 .cble
 
 The lone
@@ -3306,6 +3307,17 @@ the list
 which is not an empty input stream, but a stream consisting of
 one empty line.
 
+The
+.code @(next nil)
+variant indicates that the following subquery is applied to empty data,
+and the list of data sources from the command line is considered empty.
+This directive is useful in front of \*(TX code which doesn't process data
+sources from the command line, but takes command line arguments.
+The
+.code @(next nil)
+incantation absolutely prevents \*(TX from trying to open the
+first command line argument as a data source.
+
 Note that the
 .code @(next)
 directive only redirect the source of input over the scope of subquery in which