]> git.saurik.com Git - bison.git/blobdiff - data/yacc.c
maint: update TODO.
[bison.git] / data / yacc.c
index d1715367db6fba1feb4363f6a23fbc3ac82e0f8f..1866a66acef45b0da5ca52568a3f913f9866233a 100644 (file)
@@ -1,11 +1,11 @@
                                                              -*- C -*-
 # Yacc compatible skeleton for Bison
 
-# Copyright (C) 1984, 1989, 1990, 2000, 2001, 2002, 2003, 2004, 2005,
-# 2006, 2007, 2008, 2009, 2010 Free Software Foundation, Inc.
+# Copyright (C) 1984, 1989-1990, 2000-2012 Free Software Foundation,
+# Inc.
 
 m4_pushdef([b4_copyright_years],
-           [1984, 1989, 1990, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010])
+           [1984, 1989-1990, 2000-2012])
 
 # This program is free software: you can redistribute it and/or modify
 # it under the terms of the GNU General Public License as published by
@@ -31,13 +31,26 @@ m4_case(b4_percent_define_get([[api.push-pull]]),
         [push], [m4_define([b4_pull_flag], [[0]])])
 
 # Handle BISON_USE_PUSH_FOR_PULL for the test suite.  So that push parsing
-# tests function as written, don't let BISON_USE_PUSH_FOR_PULL modify Bison's
-# behavior at all when push parsing is already requested.
+# tests function as written, do not let BISON_USE_PUSH_FOR_PULL modify the
+# behavior of Bison at all when push parsing is already requested.
 b4_define_flag_if([use_push_for_pull])
 b4_use_push_for_pull_if([
   b4_push_if([m4_define([b4_use_push_for_pull_flag], [[0]])],
              [m4_define([b4_push_flag], [[1]])])])
 
+# Check the value of %define parse.lac and friends, where LAC stands for
+# lookahead correction.
+b4_percent_define_default([[parse.lac]], [[none]])
+b4_percent_define_default([[parse.lac.es-capacity-initial]], [[20]])
+b4_percent_define_default([[parse.lac.memory-trace]], [[failures]])
+b4_percent_define_check_values([[[[parse.lac]], [[full]], [[none]]]],
+                               [[[[parse.lac.memory-trace]],
+                                 [[failures]], [[full]]]])
+b4_define_flag_if([lac])
+m4_define([b4_lac_flag],
+          [m4_if(b4_percent_define_get([[parse.lac]]),
+                 [none], [[0]], [[1]])])
+
 m4_include(b4_pkgdatadir/[c.m4])
 
 ## ---------------- ##
@@ -63,8 +76,8 @@ m4_define([b4_pure_flag],
 # Expand IF-TRUE, if %pure-parser and %parse-param, IF-FALSE otherwise.
 m4_define([b4_yacc_pure_if],
 [b4_pure_if([m4_ifset([b4_parse_param],
-                     [$1], [$2])],
-           [$2])])
+                      [$1], [$2])],
+            [$2])])
 
 
 # b4_yyerror_args
@@ -104,7 +117,7 @@ m4_define([b4_int_type],
 
        m4_eval([0 <= $1]),                [1], [unsigned int],
 
-                                              [int])])
+                                               [int])])
 
 
 ## ----------------- ##
@@ -207,7 +220,11 @@ m4_define([b4_declare_parser_state_variables], [b4_pure_if([[
     /* The locations where the error started and ended.  */
     YYLTYPE yyerror_range[3];]])[
 
-    YYSIZE_T yystacksize;]])
+    YYSIZE_T yystacksize;]b4_lac_if([[
+
+    yytype_int16 yyesa@{]b4_percent_define_get([[parse.lac.es-capacity-initial]])[@};
+    yytype_int16 *yyes;
+    YYSIZE_T yyes_capacity;]])])
 
 
 ## --------------------------------------------------------- ##
@@ -218,7 +235,7 @@ m4_define([b4_declare_parser_state_variables], [b4_pure_if([[
 m4_changecom()
 m4_divert_push(0)dnl
 @output(b4_parser_file_name@)@
-b4_copyright([Implementation for Bison's Yacc-like parsers in C])[
+b4_copyright([Bison implementation for Yacc-like parsers in C])[
 
 /* C LALR(1) parser skeleton written by Richard Stallman, by
    simplifying the original so-called "semantic" parser.  */
@@ -401,10 +418,10 @@ typedef short int yytype_int16;
 }
 #endif
 
-#if ! defined yyoverflow || YYERROR_VERBOSE
+#if ]b4_lac_if([[1]], [[! defined yyoverflow || YYERROR_VERBOSE]])[
 
-]b4_push_if([],
-[[/* The parser invokes alloca or malloc; define the necessary symbols.  */
+/* The parser invokes alloca or malloc; define the necessary symbols.  */]dnl
+b4_push_if([], [b4_lac_if([], [[
 
 # ifdef YYSTACK_USE_ALLOCA
 #  if YYSTACK_USE_ALLOCA
@@ -427,10 +444,9 @@ typedef short int yytype_int16;
 #    endif
 #   endif
 #  endif
-# endif
+# endif]])])[
 
-]])dnl
-[# ifdef YYSTACK_ALLOC
+# ifdef YYSTACK_ALLOC
    /* Pacify GCC's `empty if-body' warning.  */
 #  define YYSTACK_FREE(Ptr) do { /* empty */; } while (YYID (0))
 #  ifndef YYSTACK_ALLOC_MAXIMUM
@@ -448,7 +464,7 @@ typedef short int yytype_int16;
 #  endif
 #  if (defined __cplusplus && ! defined EXIT_SUCCESS \
        && ! ((defined YYMALLOC || defined malloc) \
-            && (defined YYFREE || defined free)))
+             && (defined YYFREE || defined free)))
 #   include <stdlib.h> /* INFRINGES ON USER NAME SPACE */
 #   ifndef EXIT_SUCCESS
 #    define EXIT_SUCCESS 0
@@ -466,14 +482,15 @@ void *malloc (YYSIZE_T); /* INFRINGES ON USER NAME SPACE */
 void free (void *); /* INFRINGES ON USER NAME SPACE */
 #   endif
 #  endif
-# endif
-#endif /* ! defined yyoverflow || YYERROR_VERBOSE */
+# endif]b4_lac_if([[
+# define YYCOPY_NEEDED 1]])[
+#endif]b4_lac_if([], [[ /* ! defined yyoverflow || YYERROR_VERBOSE */]])[
 
 
 #if (! defined yyoverflow \
      && (! defined __cplusplus \
-        || (]b4_locations_if([[defined YYLTYPE_IS_TRIVIAL && YYLTYPE_IS_TRIVIAL \
-            && ]])[defined YYSTYPE_IS_TRIVIAL && YYSTYPE_IS_TRIVIAL)))
+         || (]b4_locations_if([[defined YYLTYPE_IS_TRIVIAL && YYLTYPE_IS_TRIVIAL \
+             && ]])[defined YYSTYPE_IS_TRIVIAL && YYSTYPE_IS_TRIVIAL)))
 
 /* A type that is properly aligned for any stack member.  */
 union yyalloc
@@ -496,6 +513,27 @@ union yyalloc
      ((N) * (sizeof (yytype_int16) + sizeof (YYSTYPE)) \
       + YYSTACK_GAP_MAXIMUM)])[
 
+# define YYCOPY_NEEDED 1
+
+/* Relocate STACK from its old location to the new one.  The
+   local variables YYSIZE and YYSTACKSIZE give the old and new number of
+   elements in the stack, and YYPTR gives the new location of the
+   stack.  Advance YYPTR to a properly aligned location for the next
+   stack.  */
+# define YYSTACK_RELOCATE(Stack_alloc, Stack)                           \
+    do                                                                  \
+      {                                                                 \
+        YYSIZE_T yynewbytes;                                            \
+        YYCOPY (&yyptr->Stack_alloc, Stack, yysize);                    \
+        Stack = &yyptr->Stack_alloc;                                    \
+        yynewbytes = yystacksize * sizeof (*Stack) + YYSTACK_GAP_MAXIMUM; \
+        yyptr += yynewbytes / sizeof (*yyptr);                          \
+      }                                                                 \
+    while (YYID (0))
+
+#endif
+
+#if defined YYCOPY_NEEDED && YYCOPY_NEEDED
 /* Copy COUNT objects from FROM to TO.  The source and destination do
    not overlap.  */
 # ifndef YYCOPY
@@ -503,34 +541,17 @@ union yyalloc
 #   define YYCOPY(To, From, Count) \
       __builtin_memcpy (To, From, (Count) * sizeof (*(From)))
 #  else
-#   define YYCOPY(To, From, Count)             \
-      do                                       \
-       {                                       \
-         YYSIZE_T yyi;                         \
-         for (yyi = 0; yyi < (Count); yyi++)   \
-           (To)[yyi] = (From)[yyi];            \
-       }                                       \
+#   define YYCOPY(To, From, Count)              \
+      do                                        \
+        {                                       \
+          YYSIZE_T yyi;                         \
+          for (yyi = 0; yyi < (Count); yyi++)   \
+            (To)[yyi] = (From)[yyi];            \
+        }                                       \
       while (YYID (0))
 #  endif
 # endif
-
-/* Relocate STACK from its old location to the new one.  The
-   local variables YYSIZE and YYSTACKSIZE give the old and new number of
-   elements in the stack, and YYPTR gives the new location of the
-   stack.  Advance YYPTR to a properly aligned location for the next
-   stack.  */
-# define YYSTACK_RELOCATE(Stack_alloc, Stack)                          \
-    do                                                                 \
-      {                                                                        \
-       YYSIZE_T yynewbytes;                                            \
-       YYCOPY (&yyptr->Stack_alloc, Stack, yysize);                    \
-       Stack = &yyptr->Stack_alloc;                                    \
-       yynewbytes = yystacksize * sizeof (*Stack) + YYSTACK_GAP_MAXIMUM; \
-       yyptr += yynewbytes / sizeof (*yyptr);                          \
-      }                                                                        \
-    while (YYID (0))
-
-#endif
+#endif /* !YYCOPY_NEEDED */
 
 /* YYFINAL -- State number of the termination state.  */
 #define YYFINAL  ]b4_final_state_number[
@@ -551,7 +572,7 @@ union yyalloc
 #define YYUNDEFTOK  ]b4_undef_token_number[
 #define YYMAXUTOK   ]b4_user_token_number_max[
 
-#define YYTRANSLATE(YYX)                                               \
+#define YYTRANSLATE(YYX)                                                \
   ((unsigned int) (YYX) <= YYMAXUTOK ? yytranslate[YYX] : YYUNDEFTOK)
 
 /* YYTRANSLATE[TOKEN-NUM] -- Symbol number corresponding to TOKEN-NUM
@@ -596,14 +617,14 @@ static const ]b4_int_type_for([b4_toknum])[ yytoknum[] =
 
 ]b4_parser_tables_define[
 
-#define yyerrok                (yyerrstatus = 0)
-#define yyclearin      (yychar = YYEMPTY)
-#define YYEMPTY                (-2)
-#define YYEOF          0
+#define yyerrok         (yyerrstatus = 0)
+#define yyclearin       (yychar = YYEMPTY)
+#define YYEMPTY         (-2)
+#define YYEOF           0
 
-#define YYACCEPT       goto yyacceptlab
-#define YYABORT                goto yyabortlab
-#define YYERROR                goto yyerrorlab
+#define YYACCEPT        goto yyacceptlab
+#define YYABORT         goto yyabortlab
+#define YYERROR         goto yyerrorlab
 
 
 /* Like YYERROR except do call yyerror.  This remains here temporarily
@@ -613,7 +634,7 @@ static const ]b4_int_type_for([b4_toknum])[ yytoknum[] =
    in Bison 2.4.2's NEWS entry, where a plan to phase it out is
    discussed.  */
 
-#define YYFAIL         goto yyerrlab
+#define YYFAIL          goto yyerrlab
 #if defined YYFAIL
   /* This is here to suppress warnings from the GCC cpp's
      -Wunused-macros.  Normally we don't worry about that warning, but
@@ -623,25 +644,26 @@ static const ]b4_int_type_for([b4_toknum])[ yytoknum[] =
 
 #define YYRECOVERING()  (!!yyerrstatus)
 
-#define YYBACKUP(Token, Value)                                 \
-do                                                             \
-  if (yychar == YYEMPTY && yylen == 1)                         \
-    {                                                          \
-      yychar = (Token);                                                \
-      yylval = (Value);                                                \
-      YYPOPSTACK (1);                                          \
-      goto yybackup;                                           \
-    }                                                          \
-  else                                                         \
-    {                                                          \
+#define YYBACKUP(Token, Value)                                  \
+do                                                              \
+  if (yychar == YYEMPTY && yylen == 1)                          \
+    {                                                           \
+      yychar = (Token);                                         \
+      yylval = (Value);                                         \
+      YYPOPSTACK (1);                                           \]b4_lac_if([[
+      YY_LAC_DISCARD ("YYBACKUP");                              \]])[
+      goto yybackup;                                            \
+    }                                                           \
+  else                                                          \
+    {                                                           \
       yyerror (]b4_yyerror_args[YY_("syntax error: cannot back up")); \
-      YYERROR;                                                 \
-    }                                                          \
+      YYERROR;                                                  \
+    }                                                           \
 while (YYID (0))
 
 
-#define YYTERROR       1
-#define YYERRCODE      256
+#define YYTERROR        1
+#define YYERRCODE       256
 
 
 /* YYLLOC_DEFAULT -- Set CURRENT to span from RHS[1] to RHS[N].
@@ -650,22 +672,22 @@ while (YYID (0))
 
 #define YYRHSLOC(Rhs, K) ((Rhs)[K])
 #ifndef YYLLOC_DEFAULT
-# define YYLLOC_DEFAULT(Current, Rhs, N)                               \
-    do                                                                 \
+# define YYLLOC_DEFAULT(Current, Rhs, N)                                \
+    do                                                                  \
       if (YYID (N))                                                    \
-       {                                                               \
-         (Current).first_line   = YYRHSLOC (Rhs, 1).first_line;        \
-         (Current).first_column = YYRHSLOC (Rhs, 1).first_column;      \
-         (Current).last_line    = YYRHSLOC (Rhs, N).last_line;         \
-         (Current).last_column  = YYRHSLOC (Rhs, N).last_column;       \
-       }                                                               \
-      else                                                             \
-       {                                                               \
-         (Current).first_line   = (Current).last_line   =              \
-           YYRHSLOC (Rhs, 0).last_line;                                \
-         (Current).first_column = (Current).last_column =              \
-           YYRHSLOC (Rhs, 0).last_column;                              \
-       }                                                               \
+        {                                                               \
+          (Current).first_line   = YYRHSLOC (Rhs, 1).first_line;        \
+          (Current).first_column = YYRHSLOC (Rhs, 1).first_column;      \
+          (Current).last_line    = YYRHSLOC (Rhs, N).last_line;         \
+          (Current).last_column  = YYRHSLOC (Rhs, N).last_column;       \
+        }                                                               \
+      else                                                              \
+        {                                                               \
+          (Current).first_line   = (Current).last_line   =              \
+            YYRHSLOC (Rhs, 0).last_line;                                \
+          (Current).first_column = (Current).last_column =              \
+            YYRHSLOC (Rhs, 0).last_column;                              \
+        }                                                               \
     while (YYID (0))
 #endif]b4_locations_if([[
 
@@ -676,10 +698,10 @@ while (YYID (0))
 
 #ifndef YY_LOCATION_PRINT
 # if defined YYLTYPE_IS_TRIVIAL && YYLTYPE_IS_TRIVIAL
-#  define YY_LOCATION_PRINT(File, Loc)                 \
-     fprintf (File, "%d.%d-%d.%d",                     \
-             (Loc).first_line, (Loc).first_column,     \
-             (Loc).last_line,  (Loc).last_column)
+#  define YY_LOCATION_PRINT(File, Loc)                  \
+     fprintf (File, "%d.%d-%d.%d",                      \
+              (Loc).first_line, (Loc).first_column,     \
+              (Loc).last_line,  (Loc).last_column)
 # else
 #  define YY_LOCATION_PRINT(File, Loc) ((void) 0)
 # endif
@@ -709,21 +731,21 @@ while (YYID (0))
 #  define YYFPRINTF fprintf
 # endif
 
-# define YYDPRINTF(Args)                       \
-do {                                           \
-  if (yydebug)                                 \
-    YYFPRINTF Args;                            \
+# define YYDPRINTF(Args)                        \
+do {                                            \
+  if (yydebug)                                  \
+    YYFPRINTF Args;                             \
 } while (YYID (0))
 
-# define YY_SYMBOL_PRINT(Title, Type, Value, Location)                   \
-do {                                                                     \
-  if (yydebug)                                                           \
-    {                                                                    \
-      YYFPRINTF (stderr, "%s ", Title);                                          \
-      yy_symbol_print (stderr,                                           \
-                 Type, Value]b4_locations_if([, Location])[]b4_user_args[); \
-      YYFPRINTF (stderr, "\n");                                                  \
-    }                                                                    \
+# define YY_SYMBOL_PRINT(Title, Type, Value, Location)                    \
+do {                                                                      \
+  if (yydebug)                                                            \
+    {                                                                     \
+      YYFPRINTF (stderr, "%s ", Title);                                   \
+      yy_symbol_print (stderr,                                            \
+                  Type, Value]b4_locations_if([, Location])[]b4_user_args[); \
+      YYFPRINTF (stderr, "\n");                                           \
+    }                                                                     \
 } while (YYID (0))
 
 ]b4_yy_symbol_print_generate([b4_c_function_def])[
@@ -734,8 +756,8 @@ do {                                                                          \
 `------------------------------------------------------------------*/
 
 ]b4_c_function_def([yy_stack_print], [static void],
-                  [[yytype_int16 *yybottom], [yybottom]],
-                  [[yytype_int16 *yytop],    [yytop]])[
+                   [[yytype_int16 *yybottom], [yybottom]],
+                   [[yytype_int16 *yytop],    [yytop]])[
 {
   YYFPRINTF (stderr, "Stack now");
   for (; yybottom <= yytop; yybottom++)
@@ -746,10 +768,10 @@ do {                                                                        \
   YYFPRINTF (stderr, "\n");
 }
 
-# define YY_STACK_PRINT(Bottom, Top)                           \
-do {                                                           \
-  if (yydebug)                                                 \
-    yy_stack_print ((Bottom), (Top));                          \
+# define YY_STACK_PRINT(Bottom, Top)                            \
+do {                                                            \
+  if (yydebug)                                                  \
+    yy_stack_print ((Bottom), (Top));                           \
 } while (YYID (0))
 
 
@@ -782,9 +804,9 @@ do {                                                                \
     }
 }
 
-# define YY_REDUCE_PRINT(Rule)         \
-do {                                   \
-  if (yydebug)                         \
+# define YY_REDUCE_PRINT(Rule)          \
+do {                                    \
+  if (yydebug)                          \
     yy_reduce_print (yyssp, yyvsp, ]b4_locations_if([yylsp, ])[Rule]b4_user_args[); \
 } while (YYID (0))
 
@@ -800,7 +822,7 @@ int yydebug;
 
 
 /* YYINITDEPTH -- initial size of the parser's stacks.  */
-#ifndef        YYINITDEPTH
+#ifndef YYINITDEPTH
 # define YYINITDEPTH ]b4_stack_depth_init[
 #endif
 
@@ -813,9 +835,244 @@ int yydebug;
 
 #ifndef YYMAXDEPTH
 # define YYMAXDEPTH ]b4_stack_depth_max[
+#endif]b4_lac_if([[
+
+/* Given a state stack such that *YYBOTTOM is its bottom, such that
+   *YYTOP is either its top or is YYTOP_EMPTY to indicate an empty
+   stack, and such that *YYCAPACITY is the maximum number of elements it
+   can hold without a reallocation, make sure there is enough room to
+   store YYADD more elements.  If not, allocate a new stack using
+   YYSTACK_ALLOC, copy the existing elements, and adjust *YYBOTTOM,
+   *YYTOP, and *YYCAPACITY to reflect the new capacity and memory
+   location.  If *YYBOTTOM != YYBOTTOM_NO_FREE, then free the old stack
+   using YYSTACK_FREE.  Return 0 if successful or if no reallocation is
+   required.  Return 1 if memory is exhausted.  */
+static int
+yy_lac_stack_realloc (YYSIZE_T *yycapacity, YYSIZE_T yyadd,
+#if YYDEBUG
+                      char const *yydebug_prefix,
+                      char const *yydebug_suffix,
 #endif
+                      yytype_int16 **yybottom,
+                      yytype_int16 *yybottom_no_free,
+                      yytype_int16 **yytop, yytype_int16 *yytop_empty)
+{
+  YYSIZE_T yysize_old =
+    *yytop == yytop_empty ? 0 : *yytop - *yybottom + 1;
+  YYSIZE_T yysize_new = yysize_old + yyadd;
+  if (*yycapacity < yysize_new)
+    {
+      YYSIZE_T yyalloc = 2 * yysize_new;
+      yytype_int16 *yybottom_new;
+      /* Use YYMAXDEPTH for maximum stack size given that the stack
+         should never need to grow larger than the main state stack
+         needs to grow without LAC.  */
+      if (YYMAXDEPTH < yysize_new)
+        {
+          YYDPRINTF ((stderr, "%smax size exceeded%s", yydebug_prefix,
+                      yydebug_suffix));
+          return 1;
+        }
+      if (YYMAXDEPTH < yyalloc)
+        yyalloc = YYMAXDEPTH;
+      yybottom_new =
+        (yytype_int16*) YYSTACK_ALLOC (yyalloc * sizeof *yybottom_new);
+      if (!yybottom_new)
+        {
+          YYDPRINTF ((stderr, "%srealloc failed%s", yydebug_prefix,
+                      yydebug_suffix));
+          return 1;
+        }
+      if (*yytop != yytop_empty)
+        {
+          YYCOPY (yybottom_new, *yybottom, yysize_old);
+          *yytop = yybottom_new + (yysize_old - 1);
+        }
+      if (*yybottom != yybottom_no_free)
+        YYSTACK_FREE (*yybottom);
+      *yybottom = yybottom_new;
+      *yycapacity = yyalloc;]m4_if(b4_percent_define_get([[parse.lac.memory-trace]]),
+                                   [full], [[
+      YYDPRINTF ((stderr, "%srealloc to %lu%s", yydebug_prefix,
+                  (unsigned long int) yyalloc, yydebug_suffix));]])[
+    }
+  return 0;
+}
+
+/* Establish the initial context for the current lookahead if no initial
+   context is currently established.
+
+   We define a context as a snapshot of the parser stacks.  We define
+   the initial context for a lookahead as the context in which the
+   parser initially examines that lookahead in order to select a
+   syntactic action.  Thus, if the lookahead eventually proves
+   syntactically unacceptable (possibly in a later context reached via a
+   series of reductions), the initial context can be used to determine
+   the exact set of tokens that would be syntactically acceptable in the
+   lookahead's place.  Moreover, it is the context after which any
+   further semantic actions would be erroneous because they would be
+   determined by a syntactically unacceptable token.
+
+   YY_LAC_ESTABLISH should be invoked when a reduction is about to be
+   performed in an inconsistent state (which, for the purposes of LAC,
+   includes consistent states that don't know they're consistent because
+   their default reductions have been disabled).  Iff there is a
+   lookahead token, it should also be invoked before reporting a syntax
+   error.  This latter case is for the sake of the debugging output.
+
+   For parse.lac=full, the implementation of YY_LAC_ESTABLISH is as
+   follows.  If no initial context is currently established for the
+   current lookahead, then check if that lookahead can eventually be
+   shifted if syntactic actions continue from the current context.
+   Report a syntax error if it cannot.  */
+#define YY_LAC_ESTABLISH                                         \
+do {                                                             \
+  if (!yy_lac_established)                                       \
+    {                                                            \
+      YYDPRINTF ((stderr,                                        \
+                  "LAC: initial context established for %s\n",   \
+                  yytname[yytoken]));                            \
+      yy_lac_established = 1;                                    \
+      {                                                          \
+        int yy_lac_status =                                      \
+          yy_lac (yyesa, &yyes, &yyes_capacity, yyssp, yytoken); \
+        if (yy_lac_status == 2)                                  \
+          goto yyexhaustedlab;                                   \
+        if (yy_lac_status == 1)                                  \
+          goto yyerrlab;                                         \
+      }                                                          \
+    }                                                            \
+} while (YYID (0))
+
+/* Discard any previous initial lookahead context because of Event,
+   which may be a lookahead change or an invalidation of the currently
+   established initial context for the current lookahead.
+
+   The most common example of a lookahead change is a shift.  An example
+   of both cases is syntax error recovery.  That is, a syntax error
+   occurs when the lookahead is syntactically erroneous for the
+   currently established initial context, so error recovery manipulates
+   the parser stacks to try to find a new initial context in which the
+   current lookahead is syntactically acceptable.  If it fails to find
+   such a context, it discards the lookahead.  */
+#if YYDEBUG
+# define YY_LAC_DISCARD(Event)                                           \
+do {                                                                     \
+  if (yy_lac_established)                                                \
+    {                                                                    \
+      if (yydebug)                                                       \
+        YYFPRINTF (stderr, "LAC: initial context discarded due to "      \
+                   Event "\n");                                          \
+      yy_lac_established = 0;                                            \
+    }                                                                    \
+} while (YYID (0))
+#else
+# define YY_LAC_DISCARD(Event) yy_lac_established = 0
+#endif
+
+/* Given the stack whose top is *YYSSP, return 0 iff YYTOKEN can
+   eventually (after perhaps some reductions) be shifted, return 1 if
+   not, or return 2 if memory is exhausted.  As preconditions and
+   postconditions: *YYES_CAPACITY is the allocated size of the array to
+   which *YYES points, and either *YYES = YYESA or *YYES points to an
+   array allocated with YYSTACK_ALLOC.  yy_lac may overwrite the
+   contents of either array, alter *YYES and *YYES_CAPACITY, and free
+   any old *YYES other than YYESA.  */
+static int
+yy_lac (yytype_int16 *yyesa, yytype_int16 **yyes,
+        YYSIZE_T *yyes_capacity, yytype_int16 *yyssp, int yytoken)
+{
+  yytype_int16 *yyes_prev = yyssp;
+  yytype_int16 *yyesp = yyes_prev;
+  YYDPRINTF ((stderr, "LAC: checking lookahead %s:", yytname[yytoken]));
+  if (yytoken == YYUNDEFTOK)
+    {
+      YYDPRINTF ((stderr, " Always Err\n"));
+      return 1;
+    }
+  while (1)
+    {
+      int yyrule = yypact[*yyesp];
+      if (yypact_value_is_default (yyrule)
+          || (yyrule += yytoken) < 0 || YYLAST < yyrule
+          || yycheck[yyrule] != yytoken)
+        {
+          yyrule = yydefact[*yyesp];
+          if (yyrule == 0)
+            {
+              YYDPRINTF ((stderr, " Err\n"));
+              return 1;
+            }
+        }
+      else
+        {
+          yyrule = yytable[yyrule];
+          if (yytable_value_is_error (yyrule))
+            {
+              YYDPRINTF ((stderr, " Err\n"));
+              return 1;
+            }
+          if (0 < yyrule)
+            {
+              YYDPRINTF ((stderr, " S%d\n", yyrule));
+              return 0;
+            }
+          yyrule = -yyrule;
+        }
+      {
+        YYSIZE_T yylen = yyr2[yyrule];
+        YYDPRINTF ((stderr, " R%d", yyrule - 1));
+        if (yyesp != yyes_prev)
+          {
+            YYSIZE_T yysize = yyesp - *yyes + 1;
+            if (yylen < yysize)
+              {
+                yyesp -= yylen;
+                yylen = 0;
+              }
+            else
+              {
+                yylen -= yysize;
+                yyesp = yyes_prev;
+              }
+          }
+        if (yylen)
+          yyesp = yyes_prev -= yylen;
+      }
+      {
+        int yystate;
+        {
+          int yylhs = yyr1[yyrule] - YYNTOKENS;
+          yystate = yypgoto[yylhs] + *yyesp;
+          if (yystate < 0 || YYLAST < yystate
+              || yycheck[yystate] != *yyesp)
+            yystate = yydefgoto[yylhs];
+          else
+            yystate = yytable[yystate];
+        }
+        if (yyesp == yyes_prev)
+          {
+            yyesp = *yyes;
+            *yyesp = yystate;
+          }
+        else
+          {
+            if (yy_lac_stack_realloc (yyes_capacity, 1,
+#if YYDEBUG
+                                      " (", ")",
+#endif
+                                      yyes, yyesa, &yyesp, yyes_prev))
+              {
+                YYDPRINTF ((stderr, "\n"));
+                return 2;
+              }
+            *++yyesp = yystate;
+          }
+        YYDPRINTF ((stderr, " G%d", yystate));
+      }
+    }
+}]])[
 
-\f
 
 #if YYERROR_VERBOSE
 
@@ -872,27 +1129,27 @@ yytnamerr (char *yyres, const char *yystr)
       char const *yyp = yystr;
 
       for (;;)
-       switch (*++yyp)
-         {
-         case '\'':
-         case ',':
-           goto do_not_strip_quotes;
-
-         case '\\':
-           if (*++yyp != '\\')
-             goto do_not_strip_quotes;
-           /* Fall through.  */
-         default:
-           if (yyres)
-             yyres[yyn] = *yyp;
-           yyn++;
-           break;
-
-         case '"':
-           if (yyres)
-             yyres[yyn] = '\0';
-           return yyn;
-         }
+        switch (*++yyp)
+          {
+          case '\'':
+          case ',':
+            goto do_not_strip_quotes;
+
+          case '\\':
+            if (*++yyp != '\\')
+              goto do_not_strip_quotes;
+            /* Fall through.  */
+          default:
+            if (yyres)
+              yyres[yyn] = *yyp;
+            yyn++;
+            break;
+
+          case '"':
+            if (yyres)
+              yyres[yyn] = '\0';
+            return yyn;
+          }
     do_not_strip_quotes: ;
     }
 
@@ -904,22 +1161,19 @@ yytnamerr (char *yyres, const char *yystr)
 # endif
 
 /* Copy into *YYMSG, which is of size *YYMSG_ALLOC, an error message
-   about the unexpected token YYTOKEN while in state YYSTATE.
-
-   Return 0 if *YYMSG was successfully written.  Return 1 if an ordinary
-   "syntax error" message will suffice instead.  Return 2 if *YYMSG is
-   not large enough to hold the message.  In the last case, also set
-   *YYMSG_ALLOC to either (a) the required number of bytes or (b) zero
-   if the required number of bytes is too large to store.  */
+   about the unexpected token YYTOKEN for the state stack whose top is
+   YYSSP.]b4_lac_if([[  In order to see if a particular token T is a
+   valid looakhead, invoke yy_lac (YYESA, YYES, YYES_CAPACITY, YYSSP, T).]])[
+
+   Return 0 if *YYMSG was successfully written.  Return 1 if *YYMSG is
+   not large enough to hold the message.  In that case, also set
+   *YYMSG_ALLOC to the required number of bytes.  Return 2 if the
+   required number of bytes is too large to store]b4_lac_if([[ or if
+   yy_lac returned 2]])[.  */
 static int
 yysyntax_error (YYSIZE_T *yymsg_alloc, char **yymsg,
-                int yystate, int yytoken)
-{
-  int yyn = yypact[yystate];
-
-  if (! (YYPACT_NINF < yyn && yyn <= YYLAST))
-    return 1;
-  else
+                ]b4_lac_if([[yytype_int16 *yyesa, yytype_int16 **yyes,
+                YYSIZE_T *yyes_capacity, ]])[yytype_int16 *yyssp, int yytoken)
 {
   YYSIZE_T yysize0 = yytnamerr (0, yytname[yytoken]);
   YYSIZE_T yysize = yysize0;
@@ -929,26 +1183,74 @@ yysyntax_error (YYSIZE_T *yymsg_alloc, char **yymsg,
   const char *yyformat = 0;
   /* Arguments of yyformat. */
   char const *yyarg[YYERROR_VERBOSE_ARGS_MAXIMUM];
+  /* Number of reported tokens (one for the "unexpected", one per
+     "expected"). */
+  int yycount = 0;
 
+  /* There are many possibilities here to consider:
+     - Assume YYFAIL is not used.  It's too flawed to consider.  See
+       <http://lists.gnu.org/archive/html/bison-patches/2009-12/msg00024.html>
+       for details.  YYERROR is fine as it does not invoke this
+       function.
+     - If this state is a consistent state with a default action, then
+       the only way this function was invoked is if the default action
+       is an error action.  In that case, don't check for expected
+       tokens because there are none.
+     - The only way there can be no lookahead present (in yychar) is if
+       this state is a consistent state with a default action.  Thus,
+       detecting the absence of a lookahead is sufficient to determine
+       that there is no unexpected or expected token to report.  In that
+       case, just report a simple "syntax error".
+     - Don't assume there isn't a lookahead just because this state is a
+       consistent state with a default action.  There might have been a
+       previous inconsistent state, consistent state with a non-default
+       action, or user semantic action that manipulated yychar.]b4_lac_if([[
+       In the first two cases, it might appear that the current syntax
+       error should have been detected in the previous state when yy_lac
+       was invoked.  However, at that time, there might have been a
+       different syntax error that discarded a different initial context
+       during error recovery, leaving behind the current lookahead.]], [[
+     - Of course, the expected token list depends on states to have
+       correct lookahead information, and it depends on the parser not
+       to perform extra reductions after fetching a lookahead from the
+       scanner and before detecting a syntax error.  Thus, state merging
+       (from LALR or IELR) and default reductions corrupt the expected
+       token list.  However, the list is correct for canonical LR with
+       one exception: it will still contain any token that will not be
+       accepted due to an error action in a later state.]])[
+  */
+  if (yytoken != YYEMPTY)
+    {
+      int yyn = yypact[*yyssp];]b4_lac_if([[
+      YYDPRINTF ((stderr, "Constructing syntax error message\n"));]])[
+      yyarg[yycount++] = yytname[yytoken];
+      if (!yypact_value_is_default (yyn))
+        {]b4_lac_if([], [[
           /* Start YYX at -YYN if negative to avoid negative indexes in
              YYCHECK.  In other words, skip the first -YYN actions for
              this state because they are default actions.  */
           int yyxbegin = yyn < 0 ? -yyn : 0;
-
           /* Stay within bounds of both yycheck and yytname.  */
           int yychecklim = YYLAST - yyn + 1;
-          int yyxend = yychecklim < YYNTOKENS ? yychecklim : YYNTOKENS;
-  /* Number of reported tokens (one for the "unexpected", one per
-     "expected"). */
-  int yycount = 0;
-          int yyx;
+          int yyxend = yychecklim < YYNTOKENS ? yychecklim : YYNTOKENS;]])[
+          int yyx;]b4_lac_if([[
 
-  yyarg[yycount++] = yytname[yytoken];
+          for (yyx = 0; yyx < YYNTOKENS; ++yyx)
+            if (yyx != YYTERROR && yyx != YYUNDEFTOK)
+              {
+                {
+                  int yy_lac_status = yy_lac (yyesa, yyes, yyes_capacity,
+                                              yyssp, yyx);
+                  if (yy_lac_status == 2)
+                    return 2;
+                  if (yy_lac_status == 1)
+                    continue;
+                }]], [[
 
           for (yyx = yyxbegin; yyx < yyxend; ++yyx)
             if (yycheck[yyx + yyn] == yyx && yyx != YYTERROR
                 && !yytable_value_is_error (yytable[yyx + yyn]))
-              {
+              {]])[
                 if (yycount == YYERROR_VERBOSE_ARGS_MAXIMUM)
                   {
                     yycount = 1;
@@ -957,36 +1259,36 @@ yysyntax_error (YYSIZE_T *yymsg_alloc, char **yymsg,
                   }
                 yyarg[yycount++] = yytname[yyx];
                 yysize1 = yysize + yytnamerr (0, yytname[yyx]);
-                if (! (yysize <= yysize1 && yysize1 <= YYSTACK_ALLOC_MAXIMUM))
-                  {
-                    /* Overflow.  */
-                    *yymsg_alloc = 0;
-                    return 2;
-                  }
+                if (! (yysize <= yysize1
+                       && yysize1 <= YYSTACK_ALLOC_MAXIMUM))
+                  return 2;
                 yysize = yysize1;
               }
+        }]b4_lac_if([[
+# if YYDEBUG
+      else if (yydebug)
+        YYFPRINTF (stderr, "No expected tokens.\n");
+# endif]])[
+    }
 
   switch (yycount)
     {
-#define YYCASE_(N, S)                       \
+# define YYCASE_(N, S)                      \
       case N:                               \
         yyformat = S;                       \
       break
+      YYCASE_(0, YY_("syntax error"));
       YYCASE_(1, YY_("syntax error, unexpected %s"));
       YYCASE_(2, YY_("syntax error, unexpected %s, expecting %s"));
       YYCASE_(3, YY_("syntax error, unexpected %s, expecting %s or %s"));
       YYCASE_(4, YY_("syntax error, unexpected %s, expecting %s or %s or %s"));
       YYCASE_(5, YY_("syntax error, unexpected %s, expecting %s or %s or %s or %s"));
-#undef YYCASE_
+# undef YYCASE_
     }
 
   yysize1 = yysize + yystrlen (yyformat);
   if (! (yysize <= yysize1 && yysize1 <= YYSTACK_ALLOC_MAXIMUM))
-    {
-      /* Overflow.  */
-      *yymsg_alloc = 0;
-      return 2;
-    }
+    return 2;
   yysize = yysize1;
 
   if (*yymsg_alloc < yysize)
@@ -995,7 +1297,7 @@ yysyntax_error (YYSIZE_T *yymsg_alloc, char **yymsg,
       if (! (yysize <= *yymsg_alloc
              && *yymsg_alloc <= YYSTACK_ALLOC_MAXIMUM))
         *yymsg_alloc = YYSTACK_ALLOC_MAXIMUM;
-      return 2;
+      return 1;
     }
 
   /* Avoid sprintf, as that infringes on the user's name space.
@@ -1018,9 +1320,7 @@ yysyntax_error (YYSIZE_T *yymsg_alloc, char **yymsg,
   }
   return 0;
 }
-}
 #endif /* YYERROR_VERBOSE */
-\f
 
 ]b4_yydestruct_generate([b4_c_function_def])b4_push_if([], [[
 
@@ -1105,7 +1405,9 @@ b4_c_function_def([[yyparse]], [[int]], b4_parse_param)[
      stack still needs to be freed.  */
   if (!yyps->yynew && yyps->yyss != yyps->yyssa)
     YYSTACK_FREE (yyps->yyss);
-#endif
+#endif]b4_lac_if([[
+  if (!yyps->yynew && yyps->yyes != yyps->yyesa)
+    YYSTACK_FREE (yyps->yyes);]])[
   free (yyps);]b4_pure_if([], [[
   yypstate_allocated = 0;]])[
 }
@@ -1123,7 +1425,10 @@ b4_c_function_def([[yyparse]], [[int]], b4_parse_param)[
 #define yyls yyps->yyls
 #define yylsp yyps->yylsp
 #define yyerror_range yyps->yyerror_range]])[
-#define yystacksize yyps->yystacksize
+#define yystacksize yyps->yystacksize]b4_lac_if([[
+#define yyesa yyps->yyesa
+#define yyes yyps->yyes
+#define yyes_capacity yyps->yyes_capacity]])[
 
 
 /*---------------.
@@ -1155,7 +1460,8 @@ b4_c_function_def([[yyparse]], [[int]], b4_parse_param)[
   YYLTYPE yypushed_loc = yylloc;]])
 ])],
   [b4_declare_parser_state_variables
-])[
+])b4_lac_if([[
+  int yy_lac_established = 0;]])[
   int yyn;
   int yyresult;
   /* Lookahead token as an internal (translated) token number.  */
@@ -1188,7 +1494,12 @@ b4_c_function_def([[yyparse]], [[int]], b4_parse_param)[
   yyss = yyssa;
   yyvs = yyvsa;]b4_locations_if([[
   yyls = yylsa;]])[
-  yystacksize = YYINITDEPTH;
+  yystacksize = YYINITDEPTH;]b4_lac_if([[
+
+  yyes = yyesa;
+  yyes_capacity = sizeof yyesa / sizeof *yyes;
+  if (YYMAXDEPTH < yyes_capacity)
+    yyes_capacity = YYMAXDEPTH;]])[
 
   YYDPRINTF ((stderr, "Starting parse\n"));
 
@@ -1241,26 +1552,26 @@ m4_ifdef([b4_at_dollar_used], [[  yylsp[0] = yylloc;
 
 #ifdef yyoverflow
       {
-       /* Give user a chance to reallocate the stack.  Use copies of
-          these so that the &'s don't force the real ones into
-          memory.  */
-       YYSTYPE *yyvs1 = yyvs;
-       yytype_int16 *yyss1 = yyss;]b4_locations_if([
-       YYLTYPE *yyls1 = yyls;])[
-
-       /* Each stack pointer address is followed by the size of the
-          data in use in that stack, in bytes.  This used to be a
-          conditional around just the two extra args, but that might
-          be undefined if yyoverflow is a macro.  */
-       yyoverflow (YY_("memory exhausted"),
-                   &yyss1, yysize * sizeof (*yyssp),
-                   &yyvs1, yysize * sizeof (*yyvsp),]b4_locations_if([
-                   &yyls1, yysize * sizeof (*yylsp),])[
-                   &yystacksize);
+        /* Give user a chance to reallocate the stack.  Use copies of
+           these so that the &'s don't force the real ones into
+           memory.  */
+        YYSTYPE *yyvs1 = yyvs;
+        yytype_int16 *yyss1 = yyss;]b4_locations_if([
+        YYLTYPE *yyls1 = yyls;])[
+
+        /* Each stack pointer address is followed by the size of the
+           data in use in that stack, in bytes.  This used to be a
+           conditional around just the two extra args, but that might
+           be undefined if yyoverflow is a macro.  */
+        yyoverflow (YY_("memory exhausted"),
+                    &yyss1, yysize * sizeof (*yyssp),
+                    &yyvs1, yysize * sizeof (*yyvsp),]b4_locations_if([
+                    &yyls1, yysize * sizeof (*yylsp),])[
+                    &yystacksize);
 ]b4_locations_if([
-       yyls = yyls1;])[
-       yyss = yyss1;
-       yyvs = yyvs1;
+        yyls = yyls1;])[
+        yyss = yyss1;
+        yyvs = yyvs1;
       }
 #else /* no yyoverflow */
 # ifndef YYSTACK_RELOCATE
@@ -1268,23 +1579,23 @@ m4_ifdef([b4_at_dollar_used], [[  yylsp[0] = yylloc;
 # else
       /* Extend the stack our own way.  */
       if (YYMAXDEPTH <= yystacksize)
-       goto yyexhaustedlab;
+        goto yyexhaustedlab;
       yystacksize *= 2;
       if (YYMAXDEPTH < yystacksize)
-       yystacksize = YYMAXDEPTH;
+        yystacksize = YYMAXDEPTH;
 
       {
-       yytype_int16 *yyss1 = yyss;
-       union yyalloc *yyptr =
-         (union yyalloc *) YYSTACK_ALLOC (YYSTACK_BYTES (yystacksize));
-       if (! yyptr)
-         goto yyexhaustedlab;
-       YYSTACK_RELOCATE (yyss_alloc, yyss);
-       YYSTACK_RELOCATE (yyvs_alloc, yyvs);]b4_locations_if([
-       YYSTACK_RELOCATE (yyls_alloc, yyls);])[
+        yytype_int16 *yyss1 = yyss;
+        union yyalloc *yyptr =
+          (union yyalloc *) YYSTACK_ALLOC (YYSTACK_BYTES (yystacksize));
+        if (! yyptr)
+          goto yyexhaustedlab;
+        YYSTACK_RELOCATE (yyss_alloc, yyss);
+        YYSTACK_RELOCATE (yyvs_alloc, yyvs);]b4_locations_if([
+        YYSTACK_RELOCATE (yyls_alloc, yyls);])[
 #  undef YYSTACK_RELOCATE
-       if (yyss1 != yyssa)
-         YYSTACK_FREE (yyss1);
+        if (yyss1 != yyssa)
+          YYSTACK_FREE (yyss1);
       }
 # endif
 #endif /* no yyoverflow */
@@ -1294,10 +1605,10 @@ m4_ifdef([b4_at_dollar_used], [[  yylsp[0] = yylloc;
       yylsp = yyls + yysize - 1;])[
 
       YYDPRINTF ((stderr, "Stack size increased to %lu\n",
-                 (unsigned long int) yystacksize));
+                  (unsigned long int) yystacksize));
 
       if (yyss + yystacksize - 1 <= yyssp)
-       YYABORT;
+        YYABORT;
     }
 
   YYDPRINTF ((stderr, "Entering state %d\n", yystate));
@@ -1362,13 +1673,18 @@ yyread_pushed_token:]])[
   /* If the proper action on seeing token YYTOKEN is to reduce or to
      detect an error, take that action.  */
   yyn += yytoken;
-  if (yyn < 0 || YYLAST < yyn || yycheck[yyn] != yytoken)
-    goto yydefault;
+  if (yyn < 0 || YYLAST < yyn || yycheck[yyn] != yytoken)]b4_lac_if([[
+    {
+      YY_LAC_ESTABLISH;
+      goto yydefault;
+    }]], [[
+    goto yydefault;]])[
   yyn = yytable[yyn];
   if (yyn <= 0)
     {
       if (yytable_value_is_error (yyn))
-       goto yyerrlab;
+        goto yyerrlab;]b4_lac_if([[
+      YY_LAC_ESTABLISH;]])[
       yyn = -yyn;
       goto yyreduce;
     }
@@ -1382,7 +1698,8 @@ yyread_pushed_token:]])[
   YY_SYMBOL_PRINT ("Shifting", yytoken, &yylval, &yylloc);
 
   /* Discard the shifted token.  */
-  yychar = YYEMPTY;
+  yychar = YYEMPTY;]b4_lac_if([[
+  YY_LAC_DISCARD ("shift");]])[
 
   yystate = yyn;
   *++yyvsp = yylval;
@@ -1420,12 +1737,22 @@ yyreduce:
 ]b4_locations_if(
 [[  /* Default location.  */
   YYLLOC_DEFAULT (yyloc, (yylsp - yylen), yylen);]])[
-  YY_REDUCE_PRINT (yyn);
+  YY_REDUCE_PRINT (yyn);]b4_lac_if([[
+  {
+    int yychar_backup = yychar;
+    switch (yyn)
+      {
+        ]b4_user_actions[
+        default: break;
+      }
+    if (yychar_backup != yychar)
+      YY_LAC_DISCARD ("yychar change");
+  }]], [[
   switch (yyn)
     {
       ]b4_user_actions[
       default: break;
-    }
+    }]])[
   /* User semantic actions sometimes alter yychar, and that requires
      that yytoken be updated with the new translation.  We take the
      approach of translating immediately before every use of yytoken.
@@ -1467,7 +1794,7 @@ yyreduce:
 yyerrlab:
   /* Make sure we have latest lookahead translation.  See comments at
      user semantic actions for why this is necessary.  */
-  yytoken = YYTRANSLATE (yychar);
+  yytoken = yychar == YYEMPTY ? YYEMPTY : YYTRANSLATE (yychar);
 
   /* If not already recovering from an error, report this error.  */
   if (!yyerrstatus)
@@ -1476,14 +1803,18 @@ yyerrlab:
 #if ! YYERROR_VERBOSE
       yyerror (]b4_yyerror_args[YY_("syntax error"));
 #else
-# define YYSYNTAX_ERROR yysyntax_error (&yymsg_alloc, &yymsg, yystate, \
-                                        yytoken)
+# define YYSYNTAX_ERROR yysyntax_error (&yymsg_alloc, &yymsg, \]b4_lac_if([[
+                                        yyesa, &yyes, &yyes_capacity, \]])[
+                                        yyssp, yytoken)
       {
         char const *yymsgp = YY_("syntax error");
-        int yysyntax_error_status = YYSYNTAX_ERROR;
+        int yysyntax_error_status;]b4_lac_if([[
+        if (yychar != YYEMPTY)
+          YY_LAC_ESTABLISH;]])[
+        yysyntax_error_status = YYSYNTAX_ERROR;
         if (yysyntax_error_status == 0)
           yymsgp = yymsg;
-        else if (yysyntax_error_status == 2 && 0 < yymsg_alloc)
+        else if (yysyntax_error_status == 1)
           {
             if (yymsg != yymsgbuf)
               YYSTACK_FREE (yymsg);
@@ -1492,6 +1823,7 @@ yyerrlab:
               {
                 yymsg = yymsgbuf;
                 yymsg_alloc = sizeof yymsgbuf;
+                yysyntax_error_status = 2;
               }
             else
               {
@@ -1512,20 +1844,20 @@ yyerrlab:
   if (yyerrstatus == 3)
     {
       /* If just tried and failed to reuse lookahead token after an
-        error, discard it.  */
+         error, discard it.  */
 
       if (yychar <= YYEOF)
-       {
-         /* Return failure if at end of input.  */
-         if (yychar == YYEOF)
-           YYABORT;
-       }
+        {
+          /* Return failure if at end of input.  */
+          if (yychar == YYEOF)
+            YYABORT;
+        }
       else
-       {
-         yydestruct ("Error: discarding",
-                     yytoken, &yylval]b4_locations_if([, &yylloc])[]b4_user_args[);
-         yychar = YYEMPTY;
-       }
+        {
+          yydestruct ("Error: discarding",
+                      yytoken, &yylval]b4_locations_if([, &yylloc])[]b4_user_args[);
+          yychar = YYEMPTY;
+        }
     }
 
   /* Else will try to reuse lookahead token after shifting the error
@@ -1558,33 +1890,37 @@ yyerrorlab:
 | yyerrlab1 -- common code for both syntax error and YYERROR.  |
 `-------------------------------------------------------------*/
 yyerrlab1:
-  yyerrstatus = 3;     /* Each real token shifted decrements this.  */
+  yyerrstatus = 3;      /* Each real token shifted decrements this.  */
 
   for (;;)
     {
       yyn = yypact[yystate];
       if (!yypact_value_is_default (yyn))
-       {
-         yyn += YYTERROR;
-         if (0 <= yyn && yyn <= YYLAST && yycheck[yyn] == YYTERROR)
-           {
-             yyn = yytable[yyn];
-             if (0 < yyn)
-               break;
-           }
-       }
+        {
+          yyn += YYTERROR;
+          if (0 <= yyn && yyn <= YYLAST && yycheck[yyn] == YYTERROR)
+            {
+              yyn = yytable[yyn];
+              if (0 < yyn)
+                break;
+            }
+        }
 
       /* Pop the current state because it cannot handle the error token.  */
       if (yyssp == yyss)
-       YYABORT;
+        YYABORT;
 
 ]b4_locations_if([[      yyerror_range[1] = *yylsp;]])[
       yydestruct ("Error: popping",
-                 yystos[yystate], yyvsp]b4_locations_if([, yylsp])[]b4_user_args[);
+                  yystos[yystate], yyvsp]b4_locations_if([, yylsp])[]b4_user_args[);
       YYPOPSTACK (1);
       yystate = *yyssp;
       YY_STACK_PRINT (yyss, yyssp);
-    }
+    }]b4_lac_if([[
+
+  /* If the stack popping above didn't lose the initial context for the
+     current lookahead token, the shift below will for sure.  */
+  YY_LAC_DISCARD ("error recovery");]])[
 
   *++yyvsp = yylval;
 ]b4_locations_if([[
@@ -1615,7 +1951,7 @@ yyabortlab:
   yyresult = 1;
   goto yyreturn;
 
-#if !defined(yyoverflow) || YYERROR_VERBOSE
+#if ]b4_lac_if([[1]], [[!defined(yyoverflow) || YYERROR_VERBOSE]])[
 /*-------------------------------------------------.
 | yyexhaustedlab -- memory exhaustion comes here.  |
 `-------------------------------------------------*/
@@ -1641,13 +1977,15 @@ yyreturn:
   while (yyssp != yyss)
     {
       yydestruct ("Cleanup: popping",
-                 yystos[*yyssp], yyvsp]b4_locations_if([, yylsp])[]b4_user_args[);
+                  yystos[*yyssp], yyvsp]b4_locations_if([, yylsp])[]b4_user_args[);
       YYPOPSTACK (1);
     }
 #ifndef yyoverflow
   if (yyss != yyssa)
     YYSTACK_FREE (yyss);
-#endif]b4_push_if([[
+#endif]b4_lac_if([[
+  if (yyes != yyesa)
+    YYSTACK_FREE (yyes);]])b4_push_if([[
   yyps->yynew = 1;
 
 yypushreturn:]])[
@@ -1662,7 +2000,7 @@ yypushreturn:]])[
 ]b4_epilogue[]dnl
 b4_defines_if(
 [@output(b4_spec_defines_file@)@
-b4_copyright([Interface for Bison's Yacc-like parsers in C])dnl
+b4_copyright([Bison interface for Yacc-like parsers in C])dnl
 
 b4_percent_code_get([[requires]])[]dnl