From 4a1612ff9b968fe446bc4dd20460bfaccabeb3b3 Mon Sep 17 00:00:00 2001
From: Roberto Ierusalimschy <roberto@inf.puc-rio.br>
Date: Wed, 7 Mar 2018 12:55:38 -0300
Subject: new experimental syntax using reserved word 'undef'

---
 lparser.c | 29 ++++++++++++++++++-----------
 1 file changed, 18 insertions(+), 11 deletions(-)

(limited to 'lparser.c')

diff --git a/lparser.c b/lparser.c
index da27c472..9bf5485e 100644
--- a/lparser.c
+++ b/lparser.c
@@ -1,5 +1,5 @@
 /*
-** $Id: lparser.c,v 2.177 2018/02/09 15:16:06 roberto Exp roberto $
+** $Id: lparser.c,v 2.178 2018/02/17 19:20:00 roberto Exp roberto $
 ** Lua Parser
 ** See Copyright Notice in lua.h
 */
@@ -65,13 +65,6 @@ static void statement (LexState *ls);
 static void expr (LexState *ls, expdesc *v);
 
 
-/* semantic error */
-static l_noret semerror (LexState *ls, const char *msg) {
-  ls->t.token = 0;  /* remove "near <token>" from final message */
-  luaX_syntaxerror(ls, msg);
-}
-
-
 static l_noret error_expected (LexState *ls, int token) {
   luaX_syntaxerror(ls,
       luaO_pushfstring(ls->L, "%s expected", luaX_token2str(ls, token)));
@@ -347,7 +340,7 @@ static void closegoto (LexState *ls, int g, Labeldesc *label) {
     const char *msg = luaO_pushfstring(ls->L,
       "<goto %s> at line %d jumps into the scope of local '%s'",
       getstr(gt->name), gt->line, getstr(vname));
-    semerror(ls, msg);
+    luaK_semerror(ls, msg);
   }
   luaK_patchgoto(fs, gt->pc, label->pc, 1);
   /* remove goto from pending list */
@@ -477,7 +470,7 @@ static void fixbreaks (FuncState *fs, BlockCnt *bl) {
 static l_noret undefgoto (LexState *ls, Labeldesc *gt) {
   const char *msg = "no visible label '%s' for <goto> at line %d";
   msg = luaO_pushfstring(ls->L, msg, getstr(gt->name), gt->line);
-  semerror(ls, msg);
+  luaK_semerror(ls, msg);
 }
 
 
@@ -900,6 +893,11 @@ static void primaryexp (LexState *ls, expdesc *v) {
       singlevar(ls, v);
       return;
     }
+    case TK_UNDEF: {
+      luaX_next(ls);
+      init_exp(v, VUNDEF, 0);
+      return;
+    }
     default: {
       luaX_syntaxerror(ls, "unexpected symbol");
     }
@@ -1185,6 +1183,10 @@ static void assignment (LexState *ls, struct LHS_assign *lh, int nvars) {
   else {  /* assignment -> '=' explist */
     int nexps;
     checknext(ls, '=');
+    if (nvars == 1 && testnext(ls, TK_UNDEF)) {
+      luaK_codeundef(ls->fs, &lh->v);
+      return;
+    }
     nexps = explist(ls, &e);
     if (nexps != nvars)
       adjust_assign(ls, nvars, nexps, &e);
@@ -1237,7 +1239,7 @@ static void checkrepeated (FuncState *fs, Labellist *ll, TString *label) {
       const char *msg = luaO_pushfstring(fs->ls->L,
                           "label '%s' already defined on line %d",
                           getstr(label), ll->arr[i].line);
-      semerror(fs->ls, msg);
+      luaK_semerror(fs->ls, msg);
     }
   }
 }
@@ -1650,6 +1652,11 @@ static void statement (LexState *ls) {
       luaX_next(ls);  /* skip LOCAL */
       if (testnext(ls, TK_FUNCTION))  /* local function? */
         localfunc(ls);
+      else if (testnext(ls, TK_UNDEF))
+        (void)0;  /* ignore */
+      /* old versions may need to declare 'local undef'
+         when using 'undef' with no environment; so this
+         version accepts (and ignores) these declarations */
       else
         localstat(ls);
       break;
-- 
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