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.

2 files changed, 24 insertions, 0 deletions

diff --git a/tests/008/empty-clauses.expected b/tests/008/empty-clauses.expected
new file mode 100644
index 00000000..b0cbdaf5
--- /dev/null
+++ b/tests/008/empty-clauses.expected
@@ -0,0 +1,6 @@
+
+b
+b
+fa
+b
+b
diff --git a/tests/008/empty-clauses.txr b/tests/008/empty-clauses.txr
new file mode 100644
index 00000000..486d42a2
--- /dev/null
+++ b/tests/008/empty-clauses.txr
@@ -0,0 +1,18 @@
+@(bind a ("a" "b"))
+@(output)
+@(repeat)
+@a
+@(first)
+
+@(end)
+@(repeat)
+@a
+@(first)
+@(end)
+@(repeat)
+@a
+@(first)
+f@a
+@(end)
+@(rep)@a@(first)@(end)
+@(end)