Fixing long-time (pre-GIT) bug. The object (nil) was stupidly used to

represent empty optional output clauses, distinguishing them from
missing clauses. This creates an ambiguity, so that an @(output)
block which puts out a single empty line is treated as empty.
Present but empty clauses are now represented by t.

* match.c (do_output_line): Check for t and bail.
(do_output): Check for t instead of (nil) and bail.

* parser.y (o_elems_opt2): Nonterminal deleted.
(out_clauses_opt): Empty case generates nil.
(req_parts_opt): o_elems_opt2 replaced by o_elems_opt.
(repeat_rep_helper): Function now keeps track of which
clauses were specified. For those that were specified, but
empty, it substitutes t.

* tests/008/empty-clauses.expected: New file.

* tests/008/empty-clauses.txr: New file.

1 files changed, 4 insertions, 1 deletions

diff --git a/match.c b/match.c
index e8fc7f65..5dda9602 100644
--- a/match.c
+++ b/match.c
@@ -1559,6 +1559,9 @@ static val extract_bindings(val bindings, val output_spec)
 
 static void do_output_line(val bindings, val specline, val filter, val out)
 {
+  if (specline == t)
+    return;
+
   for (; specline; specline = rest(specline)) {
     val elem = first(specline);
 
@@ -1689,7 +1692,7 @@ static void do_output_line(val bindings, val specline, val filter, val out)
 
 static void do_output(val bindings, val specs, val filter, val out)
 {
-  if (equal(specs, null_list))
+  if (specs == t)
     return;
 
   for (; specs; specs = cdr(specs)) {