From 25acd90a481357942cd3a7f3add6b8b996345305 Mon Sep 17 00:00:00 2001
From: "Sven M. Hallberg" <pesco@khjk.org>
Date: Sun, 1 Nov 2015 17:49:53 +0100
Subject: [PATCH] allow h_sequence(NULL) as parser for the empty sequence

---
 src/parsers/sequence.c | 43 +++++++++++++++++++++++-------------------
 src/t_parser.c         |  2 ++
 2 files changed, 26 insertions(+), 19 deletions(-)

diff --git a/src/parsers/sequence.c b/src/parsers/sequence.c
index 6377589..55c0c88 100644
--- a/src/parsers/sequence.c
+++ b/src/parsers/sequence.c
@@ -117,28 +117,33 @@ HParser* h_sequence__v(HParser* p, va_list ap) {
 }
 
 HParser* h_sequence__mv(HAllocator* mm__, HParser *p, va_list ap_) {
-  va_list ap;
-  size_t len = 0;
-  const HParser *arg;
-
-  assert(p != NULL);
-  va_copy(ap, ap_);
-  do {
-    len++;
-    arg = va_arg(ap, HParser *);
-  } while (arg);
-  va_end(ap);
   HSequence *s = h_new(HSequence, 1);
-  s->p_array = h_new(HParser *, len);
+  s->len = 0;
 
-  va_copy(ap, ap_);
-  s->p_array[0] = p;
-  for (size_t i = 1; i < len; i++) {
-    s->p_array[i] = va_arg(ap, HParser *);
-  } while (arg);
-  va_end(ap);
+  if(p) {
+    // non-empty sequence
+    const HParser *arg;
+    size_t len = 0;
+    va_list ap;
+
+    va_copy(ap, ap_);
+    do {
+      len++;
+      arg = va_arg(ap, HParser *);
+    } while (arg);
+    va_end(ap);
+    s->p_array = h_new(HParser *, len);
+
+    va_copy(ap, ap_);
+    s->p_array[0] = p;
+    for (size_t i = 1; i < len; i++) {
+      s->p_array[i] = va_arg(ap, HParser *);
+    } while (arg);
+    va_end(ap);
+
+    s->len = len;
+  }
 
-  s->len = len;
   return h_new_parser(mm__, &sequence_vt, s);
 }
 
diff --git a/src/t_parser.c b/src/t_parser.c
index c42eca9..331d262 100644
--- a/src/t_parser.c
+++ b/src/t_parser.c
@@ -241,6 +241,7 @@ static void test_nothing_p(gconstpointer backend) {
 static void test_sequence(gconstpointer backend) {
   const HParser *sequence_1 = h_sequence(h_ch('a'), h_ch('b'), NULL);
   const HParser *sequence_2 = h_sequence(h_ch('a'), h_whitespace(h_ch('b')), NULL);
+  const HParser *sequence_3 = h_sequence(NULL, NULL);   // second NULL is to silence GCC
 
   g_check_parse_match(sequence_1, (HParserBackend)GPOINTER_TO_INT(backend), "ab", 2, "(u0x61 u0x62)");
   g_check_parse_failed(sequence_1, (HParserBackend)GPOINTER_TO_INT(backend), "a", 1);
@@ -248,6 +249,7 @@ static void test_sequence(gconstpointer backend) {
   g_check_parse_match(sequence_2, (HParserBackend)GPOINTER_TO_INT(backend), "ab", 2, "(u0x61 u0x62)");
   g_check_parse_match(sequence_2, (HParserBackend)GPOINTER_TO_INT(backend), "a b", 3, "(u0x61 u0x62)");
   g_check_parse_match(sequence_2, (HParserBackend)GPOINTER_TO_INT(backend), "a  b", 4, "(u0x61 u0x62)");  
+  g_check_parse_match(sequence_3, (HParserBackend)GPOINTER_TO_INT(backend), "", 0, "()");
 }
 
 static void test_choice(gconstpointer backend) {