2007-02-07 Paolo Bonzini <bonzini@gnu.org>

[bison.git] / src / symtab.c

diff --git a/src/symtab.c b/src/symtab.c
index 8cbfc54f6c64d446306fa7e21bfe6cf725fd058f..8910f09c4ee0e4744f848b1aad4ec655c24e5dfe 100644 (file)
--- a/src/symtab.c
+++ b/src/symtab.c
@@ -1,7 +1,7 @@
 /* Symbol table manager for Bison.
 
 /* Symbol table manager for Bison.
 

-   Copyright (C) 1984, 1989, 2000, 2001, 2002, 2004, 2005 Free Software
-   Foundation, Inc.
+   Copyright (C) 1984, 1989, 2000, 2001, 2002, 2004, 2005, 2006, 2007 Free
+   Software Foundation, Inc.

 
    This file is part of Bison, the GNU Compiler Compiler.
 
 
    This file is part of Bison, the GNU Compiler Compiler.
 


@@ -20,7 +20,7 @@
    the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
    Boston, MA 02110-1301, USA.  */
 
    the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
    Boston, MA 02110-1301, USA.  */
 

-
+#include <config.h>

 #include "system.h"
 
 #include <hash.h>
 #include "system.h"
 
 #include <hash.h>


@@ -41,6 +41,15 @@ symbol *accept = NULL;
 symbol *startsymbol = NULL;
 location startsymbol_location;
 
 symbol *startsymbol = NULL;
 location startsymbol_location;
 

+/*---------------------------------------.
+| Default %destructor's and %printer's.  |
+`---------------------------------------*/
+
+static code_props default_tagged_destructor = CODE_PROPS_NONE_INIT;
+static code_props default_tagless_destructor = CODE_PROPS_NONE_INIT;
+static code_props default_tagged_printer = CODE_PROPS_NONE_INIT;
+static code_props default_tagless_printer = CODE_PROPS_NONE_INIT;
+

 /*---------------------------------.
 | Create a new symbol, named TAG.  |
 `---------------------------------*/
 /*---------------------------------.
 | Create a new symbol, named TAG.  |
 `---------------------------------*/


@@ -55,8 +64,8 @@ symbol_new (uniqstr tag, location loc)
   res->location = loc;
 
   res->type_name = NULL;
   res->location = loc;
 
   res->type_name = NULL;

-  res->destructor = NULL;
-  res->printer = NULL;
+  code_props_none_init (&res->destructor);
+  code_props_none_init (&res->printer);

 
   res->number = NUMBER_UNDEFINED;
   res->prec = 0;
 
   res->number = NUMBER_UNDEFINED;
   res->prec = 0;


@@ -65,6 +74,7 @@ symbol_new (uniqstr tag, location loc)
 
   res->alias = NULL;
   res->class = unknown_sym;
 
   res->alias = NULL;
   res->class = unknown_sym;

+  res->declared = false;

 
   if (nsyms == SYMBOL_NUMBER_MAXIMUM)
     fatal (_("too many symbols in input grammar (limit is %d)"),
 
   if (nsyms == SYMBOL_NUMBER_MAXIMUM)
     fatal (_("too many symbols in input grammar (limit is %d)"),


@@ -73,6 +83,23 @@ symbol_new (uniqstr tag, location loc)
   return res;
 }
 
   return res;
 }
 

+/*----------------------------------------.
+| Create a new semantic type, named TAG.  |
+`----------------------------------------*/
+
+static semantic_type *
+semantic_type_new (uniqstr tag)
+{
+  semantic_type *res = xmalloc (sizeof *res);
+
+  uniqstr_assert (tag);
+  res->tag = tag;
+  code_props_none_init (&res->destructor);
+  code_props_none_init (&res->printer);
+
+  return res;
+}
+

 
 /*-----------------.
 | Print a symbol.  |
 
 /*-----------------.
 | Print a symbol.  |


@@ -82,16 +109,26 @@ symbol_new (uniqstr tag, location loc)
   if (s->Attr)                                         \
     fprintf (f, " %s { %s }", #Attr, s->Attr)
 
   if (s->Attr)                                         \
     fprintf (f, " %s { %s }", #Attr, s->Attr)
 

+#define SYMBOL_CODE_PRINT(Attr)                         \
+  if (s->Attr.code)                                     \
+    fprintf (f, " %s { %s }", #Attr, s->Attr.code)
+

 void
 symbol_print (symbol *s, FILE *f)
 {
 void
 symbol_print (symbol *s, FILE *f)
 {

-  fprintf (f, "\"%s\"", s->tag);
-  SYMBOL_ATTR_PRINT (type_name);
-  SYMBOL_ATTR_PRINT (destructor);
-  SYMBOL_ATTR_PRINT (printer);
+  if (s)
+    {
+      fprintf (f, "\"%s\"", s->tag);
+      SYMBOL_ATTR_PRINT (type_name);
+      SYMBOL_CODE_PRINT (destructor);
+      SYMBOL_CODE_PRINT (printer);
+    }
+  else
+    fprintf (f, "<NULL>");

 }
 
 #undef SYMBOL_ATTR_PRINT
 }
 
 #undef SYMBOL_ATTR_PRINT

+#undef SYMBOL_CODE_PRINT

 
 /*------------------------------------------------------------------.
 | Complain that S's WHAT is redeclared at SECOND, and was first set |
 
 /*------------------------------------------------------------------.
 | Complain that S's WHAT is redeclared at SECOND, and was first set |


@@ -99,10 +136,19 @@ symbol_print (symbol *s, FILE *f)
 `------------------------------------------------------------------*/
 
 static void
 `------------------------------------------------------------------*/
 
 static void

-redeclaration (symbol* s, const char *what, location first, location second)
+symbol_redeclaration (symbol *s, const char *what, location first,
+                      location second)

 {
   complain_at (second, _("%s redeclaration for %s"), what, s->tag);
 {
   complain_at (second, _("%s redeclaration for %s"), what, s->tag);

-  complain_at (first, _("first declaration"));
+  complain_at (first, _("previous declaration"));
+}
+
+static void
+semantic_type_redeclaration (semantic_type *s, const char *what, location first,
+                             location second)
+{
+  complain_at (second, _("%s redeclaration for <%s>"), what, s->tag);
+  complain_at (first, _("previous declaration"));

 }
 
 
 }
 
 


@@ -117,7 +163,7 @@ symbol_type_set (symbol *sym, uniqstr type_name, location loc)
   if (type_name)
     {
       if (sym->type_name)
   if (type_name)
     {
       if (sym->type_name)

-       redeclaration (sym, "%type", sym->type_location, loc);
+       symbol_redeclaration (sym, "%type", sym->type_location, loc);

       uniqstr_assert (type_name);
       sym->type_name = type_name;
       sym->type_location = loc;
       uniqstr_assert (type_name);
       sym->type_name = type_name;
       sym->type_location = loc;


@@ -125,39 +171,116 @@ symbol_type_set (symbol *sym, uniqstr type_name, location loc)
 }
 
 
 }
 
 

-/*------------------------------------------------------------------.
-| Set the DESTRUCTOR associated with SYM.  Do nothing if passed 0.  |
-`------------------------------------------------------------------*/
+/*-----------------------------------------.
+| Set the DESTRUCTOR associated with SYM.  |
+`-----------------------------------------*/
+
+void
+symbol_destructor_set (symbol *sym, code_props const *destructor)
+{
+  if (sym->destructor.code)
+    symbol_redeclaration (sym, "%destructor", sym->destructor.location,
+                          destructor->location);
+  sym->destructor = *destructor;
+}
+
+/*------------------------------------------.
+| Set the DESTRUCTOR associated with TYPE.  |
+`------------------------------------------*/

 
 void
 
 void

-symbol_destructor_set (symbol *sym, const char *destructor, location loc)
+semantic_type_destructor_set (semantic_type *type,
+                              code_props const *destructor)

 {
 {

-  if (destructor)
+  if (type->destructor.code)
+    semantic_type_redeclaration (type, "%destructor",
+                                 type->destructor.location,
+                                 destructor->location);
+  type->destructor = *destructor;
+}
+
+/*---------------------------------------.
+| Get the computed %destructor for SYM.  |
+`---------------------------------------*/
+
+code_props const *
+symbol_destructor_get (symbol const *sym)
+{
+  /* Per-symbol %destructor.  */
+  if (sym->destructor.code)
+    return &sym->destructor;
+
+  /* Per-type %destructor.  */
+  if (sym->type_name)

     {
     {

-      if (sym->destructor)
-       redeclaration (sym, "%destructor", sym->destructor_location, loc);
-      sym->destructor = destructor;
-      sym->destructor_location = loc;
+      code_props const *destructor =
+        &semantic_type_get (sym->type_name)->destructor;
+      if (destructor->code)
+        return destructor;

     }
     }

+
+  /* Apply default %destructor's only to user-defined symbols.  */
+  if (sym->tag[0] == '$' || sym == errtoken)
+    return &code_props_none;
+
+  if (sym->type_name)
+    return &default_tagged_destructor;
+  return &default_tagless_destructor;

 }
 
 }
 

+/*--------------------------------------.
+| Set the PRINTER associated with SYM.  |
+`--------------------------------------*/

 
 

-/*---------------------------------------------------------------.
-| Set the PRINTER associated with SYM.  Do nothing if passed 0.  |
-`---------------------------------------------------------------*/
+void
+symbol_printer_set (symbol *sym, code_props const *printer)
+{
+  if (sym->printer.code)
+    symbol_redeclaration (sym, "%printer",
+                          sym->printer.location, printer->location);
+  sym->printer = *printer;
+}
+
+/*---------------------------------------.
+| Set the PRINTER associated with TYPE.  |
+`---------------------------------------*/

 
 void
 
 void

-symbol_printer_set (symbol *sym, const char *printer, location loc)
+semantic_type_printer_set (semantic_type *type, code_props const *printer)
+{
+  if (type->printer.code)
+    semantic_type_redeclaration (type, "%printer",
+                                 type->printer.location, printer->location);
+  type->printer = *printer;
+}
+
+/*------------------------------------.
+| Get the computed %printer for SYM.  |
+`------------------------------------*/
+
+code_props const *
+symbol_printer_get (symbol const *sym)

 {
 {

-  if (printer)
+  /* Per-symbol %printer.  */
+  if (sym->printer.code)
+    return &sym->printer;
+
+  /* Per-type %printer.  */
+  if (sym->type_name)

     {
     {

-      if (sym->printer)
-       redeclaration (sym, "%printer", sym->destructor_location, loc);
-      sym->printer = printer;
-      sym->printer_location = loc;
+      code_props const *printer = &semantic_type_get (sym->type_name)->printer;
+      if (printer->code)
+        return printer;

     }
     }

-}

 
 

+  /* Apply the default %printer only to user-defined symbols.  */
+  if (sym->tag[0] == '$' || sym == errtoken)
+    return &code_props_none;
+
+  if (sym->type_name)
+    return &default_tagged_printer;
+  return &default_tagless_printer;
+}

 
 /*-----------------------------------------------------------------.
 | Set the PRECEDENCE associated with SYM.  Does nothing if invoked |
 
 /*-----------------------------------------------------------------.
 | Set the PRECEDENCE associated with SYM.  Does nothing if invoked |


@@ -170,14 +293,15 @@ symbol_precedence_set (symbol *sym, int prec, assoc a, location loc)
   if (a != undef_assoc)
     {
       if (sym->prec != 0)
   if (a != undef_assoc)
     {
       if (sym->prec != 0)

-       redeclaration (sym, assoc_to_string (a), sym->prec_location, loc);
+       symbol_redeclaration (sym, assoc_to_string (a), sym->prec_location,
+                              loc);

       sym->prec = prec;
       sym->assoc = a;
       sym->prec_location = loc;
     }
 
   /* Only terminals have a precedence. */
       sym->prec = prec;
       sym->assoc = a;
       sym->prec_location = loc;
     }
 
   /* Only terminals have a precedence. */

-  symbol_class_set (sym, token_sym, loc);
+  symbol_class_set (sym, token_sym, loc, false);

 }
 
 
 }
 
 


@@ -186,10 +310,13 @@ symbol_precedence_set (symbol *sym, int prec, assoc a, location loc)
 `------------------------------------*/
 
 void
 `------------------------------------*/
 
 void

-symbol_class_set (symbol *sym, symbol_class class, location loc)
+symbol_class_set (symbol *sym, symbol_class class, location loc, bool declaring)

 {
   if (sym->class != unknown_sym && sym->class != class)
 {
   if (sym->class != unknown_sym && sym->class != class)

-    complain_at (loc, _("symbol %s redefined"), sym->tag);
+    {
+      complain_at (loc, _("symbol %s redefined"), sym->tag);
+      sym->declared = false;
+    }

 
   if (class == nterm_sym && sym->class != nterm_sym)
     sym->number = nvars++;
 
   if (class == nterm_sym && sym->class != nterm_sym)
     sym->number = nvars++;


@@ -197,6 +324,13 @@ symbol_class_set (symbol *sym, symbol_class class, location loc)
     sym->number = ntokens++;
 
   sym->class = class;
     sym->number = ntokens++;
 
   sym->class = class;

+
+  if (declaring)
+    {
+      if (sym->declared)
+       warn_at (loc, _("symbol %s redeclared"), sym->tag);
+      sym->declared = true;
+    }

 }
 
 
 }
 
 


@@ -207,14 +341,19 @@ symbol_class_set (symbol *sym, symbol_class class, location loc)
 void
 symbol_user_token_number_set (symbol *sym, int user_token_number, location loc)
 {
 void
 symbol_user_token_number_set (symbol *sym, int user_token_number, location loc)
 {

-  if (sym->class != token_sym)
-    abort ();
+  int *user_token_numberp;
+
+  aver (sym->class == token_sym);

 
 

-  if (sym->user_token_number != USER_NUMBER_UNDEFINED
-      && sym->user_token_number != user_token_number)
+  if (sym->user_token_number != USER_NUMBER_ALIAS)
+    user_token_numberp = &sym->user_token_number;
+  else
+    user_token_numberp = &sym->alias->user_token_number;
+  if (*user_token_numberp != USER_NUMBER_UNDEFINED
+      && *user_token_numberp != user_token_number)

     complain_at (loc, _("redefining user token number of %s"), sym->tag);
 
     complain_at (loc, _("redefining user token number of %s"), sym->tag);
 

-  sym->user_token_number = user_token_number;
+  *user_token_numberp = user_token_number;

   /* User defined $end token? */
   if (user_token_number == 0)
     {
   /* User defined $end token? */
   if (user_token_number == 0)
     {


@@ -276,13 +415,7 @@ symbol_make_alias (symbol *sym, symbol *symval, location loc)
       sym->user_token_number = USER_NUMBER_ALIAS;
       symval->alias = sym;
       sym->alias = symval;
       sym->user_token_number = USER_NUMBER_ALIAS;
       symval->alias = sym;
       sym->alias = symval;

-      /* sym and symval combined are only one symbol.  */
-      nsyms--;
-      ntokens--;
-      if (ntokens != sym->number && ntokens != symval->number)
-       abort ();
-      sym->number = symval->number =
-       (symval->number < sym->number) ? symval->number : sym->number;
+      symval->number = sym->number;

       symbol_type_set (symval, sym->type_name, loc);
     }
 }
       symbol_type_set (symval, sym->type_name, loc);
     }
 }


@@ -312,22 +445,20 @@ symbol_check_alias_consistency (symbol *this)
     }
 
 
     }
 
 

-  if (orig->destructor || alias->destructor)
+  if (orig->destructor.code || alias->destructor.code)

     {
     {

-      if (orig->destructor)
-       symbol_destructor_set (alias, orig->destructor,
-                              orig->destructor_location);
+      if (orig->destructor.code)
+       symbol_destructor_set (alias, &orig->destructor);

       else
       else

-       symbol_destructor_set (orig, alias->destructor,
-                              alias->destructor_location);
+       symbol_destructor_set (orig, &alias->destructor);

     }
 
     }
 

-  if (orig->printer || alias->printer)
+  if (orig->printer.code || alias->printer.code)

     {
     {

-      if (orig->printer)
-       symbol_printer_set (alias, orig->printer, orig->printer_location);
+      if (orig->printer.code)
+       symbol_printer_set (alias, &orig->printer);

       else
       else

-       symbol_printer_set (orig, alias->printer, alias->printer_location);
+       symbol_printer_set (orig, &alias->printer);

     }
 
   if (alias->prec || orig->prec)
     }
 
   if (alias->prec || orig->prec)


@@ -373,8 +504,7 @@ symbol_pack (symbol *this)
            this->number = this->alias->number = 0;
          else
            {
            this->number = this->alias->number = 0;
          else
            {

-             if (this->alias->number == NUMBER_UNDEFINED)
-               abort ();
+             aver (this->alias->number != NUMBER_UNDEFINED);

              this->number = this->alias->number;
            }
        }
              this->number = this->alias->number;
            }
        }


@@ -383,10 +513,7 @@ symbol_pack (symbol *this)
        return true;
     }
   else /* this->class == token_sym */
        return true;
     }
   else /* this->class == token_sym */

-    {
-      if (this->number == NUMBER_UNDEFINED)
-       abort ();
-    }
+    aver (this->number != NUMBER_UNDEFINED);

 
   symbols[this->number] = this;
   return true;
 
   symbols[this->number] = this;
   return true;


@@ -432,14 +559,15 @@ symbol_translation_processor (void *this, void *null ATTRIBUTE_UNUSED)
 }
 
 
 }
 
 

-/*----------------------.
-| A symbol hash table.  |
-`----------------------*/
+/*---------------------------------------.
+| Symbol and semantic type hash tables.  |
+`---------------------------------------*/

 
 

-/* Initial capacity of symbols hash table.  */
+/* Initial capacity of symbol and semantic type hash table.  */

 #define HT_INITIAL_CAPACITY 257
 
 static struct hash_table *symbol_table = NULL;
 #define HT_INITIAL_CAPACITY 257
 
 static struct hash_table *symbol_table = NULL;

+static struct hash_table *semantic_type_table = NULL;

 
 static inline bool
 hash_compare_symbol (const symbol *m1, const symbol *m2)
 
 static inline bool
 hash_compare_symbol (const symbol *m1, const symbol *m2)


@@ -448,12 +576,25 @@ hash_compare_symbol (const symbol *m1, const symbol *m2)
   return UNIQSTR_EQ (m1->tag, m2->tag);
 }
 
   return UNIQSTR_EQ (m1->tag, m2->tag);
 }
 

+static inline bool
+hash_compare_semantic_type (const semantic_type *m1, const semantic_type *m2)
+{
+  /* Since names are unique, we can compare the pointers themselves.  */
+  return UNIQSTR_EQ (m1->tag, m2->tag);
+}
+

 static bool
 hash_symbol_comparator (void const *m1, void const *m2)
 {
   return hash_compare_symbol (m1, m2);
 }
 
 static bool
 hash_symbol_comparator (void const *m1, void const *m2)
 {
   return hash_compare_symbol (m1, m2);
 }
 

+static bool
+hash_semantic_type_comparator (void const *m1, void const *m2)
+{
+  return hash_compare_semantic_type (m1, m2);
+}
+

 static inline size_t
 hash_symbol (const symbol *m, size_t tablesize)
 {
 static inline size_t
 hash_symbol (const symbol *m, size_t tablesize)
 {


@@ -461,12 +602,24 @@ hash_symbol (const symbol *m, size_t tablesize)
   return ((uintptr_t) m->tag) % tablesize;
 }
 
   return ((uintptr_t) m->tag) % tablesize;
 }
 

+static inline size_t
+hash_semantic_type (const semantic_type *m, size_t tablesize)
+{
+  /* Since names are unique, we can hash the pointer itself.  */
+  return ((uintptr_t) m->tag) % tablesize;
+}
+

 static size_t
 hash_symbol_hasher (void const *m, size_t tablesize)
 {
   return hash_symbol (m, tablesize);
 }
 
 static size_t
 hash_symbol_hasher (void const *m, size_t tablesize)
 {
   return hash_symbol (m, tablesize);
 }
 

+static size_t
+hash_semantic_type_hasher (void const *m, size_t tablesize)
+{
+  return hash_semantic_type (m, tablesize);
+}

 
 /*-------------------------------.
 | Create the symbol hash table.  |
 
 /*-------------------------------.
 | Create the symbol hash table.  |


@@ -480,6 +633,11 @@ symbols_new (void)
                                  hash_symbol_hasher,
                                  hash_symbol_comparator,
                                  free);
                                  hash_symbol_hasher,
                                  hash_symbol_comparator,
                                  free);

+  semantic_type_table = hash_initialize (HT_INITIAL_CAPACITY,
+                                        NULL,
+                                        hash_semantic_type_hasher,
+                                        hash_semantic_type_comparator,
+                                        free);

 }
 
 
 }
 
 


@@ -489,12 +647,11 @@ symbols_new (void)
 `----------------------------------------------------------------*/
 
 symbol *
 `----------------------------------------------------------------*/
 
 symbol *

-symbol_get (const char *key, location loc)
+symbol_from_uniqstr (const uniqstr key, location loc)

 {
   symbol probe;
   symbol *entry;
 
 {
   symbol probe;
   symbol *entry;
 

-  key = uniqstr_new (key);

   probe.tag = key;
   entry = hash_lookup (symbol_table, &probe);
 
   probe.tag = key;
   entry = hash_lookup (symbol_table, &probe);
 


@@ -508,6 +665,54 @@ symbol_get (const char *key, location loc)
 }
 
 
 }
 
 

+/*-----------------------------------------------------------------------.
+| Find the semantic type named KEY, and return it.  If it does not exist |
+| yet, create it.                                                        |
+`-----------------------------------------------------------------------*/
+
+semantic_type *
+semantic_type_from_uniqstr (const uniqstr key)
+{
+  semantic_type probe;
+  semantic_type *entry;
+
+  probe.tag = key;
+  entry = hash_lookup (semantic_type_table, &probe);
+
+  if (!entry)
+    {
+      /* First insertion in the hash. */
+      entry = semantic_type_new (key);
+      hash_insert (semantic_type_table, entry);
+    }
+  return entry;
+}
+
+
+/*----------------------------------------------------------------.
+| Find the symbol named KEY, and return it.  If it does not exist |
+| yet, create it.                                                 |
+`----------------------------------------------------------------*/
+
+symbol *
+symbol_get (const char *key, location loc)
+{
+  return symbol_from_uniqstr (uniqstr_new (key), loc);
+}
+
+
+/*-----------------------------------------------------------------------.
+| Find the semantic type named KEY, and return it.  If it does not exist |
+| yet, create it.                                                        |
+`-----------------------------------------------------------------------*/
+
+semantic_type *
+semantic_type_get (const char *key)
+{
+  return semantic_type_from_uniqstr (uniqstr_new (key));
+}
+
+

 /*------------------------------------------------------------------.
 | Generate a dummy nonterminal, whose name cannot conflict with the |
 | user's names.                                                     |
 /*------------------------------------------------------------------.
 | Generate a dummy nonterminal, whose name cannot conflict with the |
 | user's names.                                                     |


@@ -522,13 +727,18 @@ dummy_symbol_get (location loc)
 
   symbol *sym;
 
 
   symbol *sym;
 

-  sprintf (buf, "@%d", ++dummy_count);
+  sprintf (buf, "$@%d", ++dummy_count);

   sym = symbol_get (buf, loc);
   sym->class = nterm_sym;
   sym->number = nvars++;
   return sym;
 }
 
   sym = symbol_get (buf, loc);
   sym->class = nterm_sym;
   sym->number = nvars++;
   return sym;
 }
 

+bool
+symbol_is_dummy (const symbol *sym)
+{
+  return sym->tag[0] == '@' || (sym->tag[0] == '$' && sym->tag[1] == '@');
+}

 
 /*-------------------.
 | Free the symbols.  |
 
 /*-------------------.
 | Free the symbols.  |


@@ -538,6 +748,7 @@ void
 symbols_free (void)
 {
   hash_free (symbol_table);
 symbols_free (void)
 {
   hash_free (symbol_table);

+  hash_free (semantic_type_table);

   free (symbols);
 }
 
   free (symbols);
 }
 


@@ -629,11 +840,35 @@ symbols_token_translations_init (void)
 void
 symbols_pack (void)
 {
 void
 symbols_pack (void)
 {

-  symbols = xcalloc (nsyms, sizeof *symbols);
-

   symbols_do (symbol_check_alias_consistency_processor, NULL);
   symbols_do (symbol_check_alias_consistency_processor, NULL);

+
+  symbols = xcalloc (nsyms, sizeof *symbols);

   symbols_do (symbol_pack_processor, NULL);
 
   symbols_do (symbol_pack_processor, NULL);
 

+  /* Aliases leave empty slots in symbols, so remove them.  */
+  {
+    int writei;
+    int readi;
+    int nsyms_old = nsyms;
+    for (writei = 0, readi = 0; readi < nsyms_old; readi += 1)
+      {
+        if (symbols[readi] == NULL)
+          {
+            nsyms -= 1;
+            ntokens -= 1;
+          }
+        else
+          {
+            symbols[writei] = symbols[readi];
+            symbols[writei]->number = writei;
+            if (symbols[writei]->alias)
+              symbols[writei]->alias->number = writei;
+            writei += 1;
+          }
+      }
+  }
+  symbols = xnrealloc (symbols, nsyms, sizeof *symbols);
+

   symbols_token_translations_init ();
 
   if (startsymbol->class == unknown_sym)
   symbols_token_translations_init ();
 
   if (startsymbol->class == unknown_sym)


@@ -645,3 +880,61 @@ symbols_pack (void)
              _("the start symbol %s is a token"),
              startsymbol->tag);
 }
              _("the start symbol %s is a token"),
              startsymbol->tag);
 }

+
+
+/*--------------------------------------------------.
+| Set default tagged/tagless %destructor/%printer.  |
+`--------------------------------------------------*/
+
+void
+default_tagged_destructor_set (code_props const *destructor)
+{
+  if (default_tagged_destructor.code)
+    {
+      complain_at (destructor->location,
+                   _("redeclaration for default tagged %%destructor"));
+      complain_at (default_tagged_destructor.location,
+                  _("previous declaration"));
+    }
+  default_tagged_destructor = *destructor;
+}
+
+void
+default_tagless_destructor_set (code_props const *destructor)
+{
+  if (default_tagless_destructor.code)
+    {
+      complain_at (destructor->location,
+                   _("redeclaration for default tagless %%destructor"));
+      complain_at (default_tagless_destructor.location,
+                  _("previous declaration"));
+    }
+  default_tagless_destructor = *destructor;
+}
+
+void
+default_tagged_printer_set (code_props const *printer)
+{
+  if (default_tagged_printer.code)
+    {
+      complain_at (printer->location,
+                   _("redeclaration for default tagged %%printer"));
+      complain_at (default_tagged_printer.location,
+                  _("previous declaration"));
+    }
+  default_tagged_printer = *printer;
+}
+
+void
+default_tagless_printer_set (code_props const *printer)
+{
+  if (default_tagless_printer.code)
+    {
+      complain_at (printer->location,
+                   _("redeclaration for default tagless %%printer"));
+      complain_at (default_tagless_printer.location,
+                  _("previous declaration"));
+    }
+  default_tagless_printer = *printer;
+}
+