'nullable' ('checkaux') uses tag from 'verifyrule'

When checking whether a rule is nullable, 'checkaux' reuses tag
previously set by 'verifyrule'.

5 files changed, 75 insertions, 13 deletions

diff --git a/lpcode.c b/lpcode.c
index f3b8ae3..2a4e642 100644
--- a/lpcode.c
+++ b/lpcode.c
@@ -139,7 +139,12 @@ int checkaux (TTree *tree, int pred) {
       if (checkaux(sib2(tree), pred)) return 1;
       /* else return checkaux(sib1(tree), pred); */
       tree = sib1(tree); goto tailcall;
-    case TCapture: case TGrammar: case TRule: case TXInfo:
+    case TRule:
+      assert(tree->cap == RLNULL || tree->cap == RLNONNULL);
+      if (pred == PEnullable)
+        return (tree->cap == RLNULL);
+    /* else */ /* FALLTHROUGH */
+    case TCapture: case TGrammar: case TXInfo:
       /* return checkaux(sib1(tree), pred); */
       tree = sib1(tree); goto tailcall;
     case TCall:  /* return checkaux(sib2(tree), pred); */
diff --git a/lpprint.c b/lpprint.c
index 42824cc..0150750 100644
--- a/lpprint.c
+++ b/lpprint.c
@@ -278,10 +278,16 @@ static void printktable (lua_State *L, int idx) {
 /* }====================================================== */
 
 
-static int lp_printtree (lua_State *L) {
+static Pattern * getp (lua_State *L, int compile) {
   Pattern *p = (Pattern *)luaL_checkudata(L, 1, PATTERN_T);
-  if (lua_toboolean(L, 2))
+  if (compile && p->code == NULL)  /* not compiled yet? */
     prepcompile(L, p, 1);
+  return p;
+}
+
+
+static int lp_printtree (lua_State *L) {
+  Pattern *p = getp(L, lua_toboolean(L, 2));
   printktable(L, 1);
   printtree(p->tree, 0);
   return 0;
@@ -289,17 +295,24 @@ static int lp_printtree (lua_State *L) {
 
 
 static int lp_printcode (lua_State *L) {
-  Pattern *p = (Pattern *)luaL_checkudata(L, 1, PATTERN_T);
+  Pattern *p = getp(L, 1);
   printktable(L, 1);
-  if (p->code == NULL)  /* not compiled yet? */
-    prepcompile(L, p, 1);
   printpatt(p->code);
   return 0;
 }
 
+
+static int lp_nullable (lua_State *L) {
+  Pattern *p = getp(L, 0);
+  lua_pushboolean(L, nullable(p->tree));
+  return 1;
+}
+
+
 static struct luaL_Reg debugreg[] = {
   {"ptree", lp_printtree},
   {"pcode", lp_printcode},
+  {"nullable", lp_nullable},
   {NULL, NULL}
 };
 
diff --git a/lptree.c b/lptree.c
index 835595c..568b64f 100644
--- a/lptree.c
+++ b/lptree.c
@@ -1016,13 +1016,6 @@ static int collectrules (lua_State *L, int arg, int *totalsize) {
 }
 
 
-/* Status of a Rule */
-#define RLNOTVISITED    0       /* rule not visited yet */
-#define RLBEINGVISITED  1       /* rule is being visited */
-#define RLNULL          2       /* rule was visited and is nullable */
-#define RLNONNULL       3       /* rule was visited and is not nullable */
-
-
 static void buildgrammar (lua_State *L, TTree *grammar, int frule, int n) {
   int i;
   TTree *nd = sib1(grammar);  /* auxiliary pointer to traverse the tree */
diff --git a/lptree.h b/lptree.h
index 4c0951d..875ae4f 100644
--- a/lptree.h
+++ b/lptree.h
@@ -63,6 +63,13 @@ typedef struct TTree {
 } TTree;
 
 
+/* Status of a Rule */
+#define RLNOTVISITED    0       /* rule not visited yet */
+#define RLBEINGVISITED  1       /* rule is being visited */
+#define RLNULL          2       /* rule was visited and is nullable */
+#define RLNONNULL       3       /* rule was visited and is not nullable */
+
+
 /* access to charset */
 #define treebuffer(t)      ((t)->u.set.bitmap)
 
diff --git a/test.lua b/test.lua
index 3241408..a81c8b8 100755
--- a/test.lua
+++ b/test.lua
@@ -1662,6 +1662,50 @@ errmsg("x <- 'a'  x <- 'b'", 'already defined')
 errmsg("'a' -", "near '-'")
 
 
+if m.nullable then
+  print "testing nullable predicate"
+
+
+  local bg = re.compile[[
+    A31 <- A30 A30
+    A30 <- A29 A29
+    A29 <- A28 A28
+    A28 <- A27 A27
+    A27 <- A26 A26
+    A26 <- A25 A25
+    A25 <- A24 A24
+    A24 <- A23 A23
+    A23 <- A22 A22
+    A22 <- A21 A21
+    A21 <- A20 A20
+    A20 <- A19 A19
+    A19 <- A18 A18
+    A18 <- A17 A17
+    A17 <- A16 A16
+    A16 <- A15 A15
+    A15 <- A14 A14
+    A14 <- A13 A13
+    A13 <- A12 A12
+    A12 <- A11 A11
+    A11 <- A10 A10
+    A10 <- A9 A9
+    A9 <- A8 A8
+    A8 <- A7 A7
+    A7 <- A6 A6
+    A6 <- A5 A5
+    A5 <- A4 A4
+    A4 <- A3 A3
+    A3 <- A2 A2
+    A2 <- A1 A1
+    A1 <- ""
+  ]]
+
+  assert(bg:nullable())
+  assert((bg * bg):nullable())
+  assert(not (bg * bg * "a"):nullable())
+  assert(m.P(-1):nullable())
+end
+
 print"OK"