reader.c

bison 2.0 主要可以用来做语法分析用的

| The previous action turns out the be a mid-rule action.  Attach it |
| to the current rule, i.e., create a dummy symbol, attach it this   |
| mid-rule action, and append this dummy nonterminal to the current  |
| rule.                                                              |
`-------------------------------------------------------------------*/

void
grammar_midrule_action (void)
{
  /* Since the action was written out with this rule's number, we must
     give the new rule this number by inserting the new rule before
     it.  */

  /* Make a DUMMY nonterminal, whose location is that of the midrule
     action.  Create the MIDRULE.  */
  location dummy_location = current_rule->action_location;
  symbol *dummy = dummy_symbol_get (dummy_location);
  symbol_list *midrule = symbol_list_new (dummy, dummy_location);

  /* Make a new rule, whose body is empty, before the current one, so
     that the action just read can belong to it.  */
  ++nrules;
  ++nritems;
  /* Attach its location and actions to that of the DUMMY.  */
  midrule->location = dummy_location;
  midrule->action = current_rule->action;
  midrule->action_location = dummy_location;
  current_rule->action = NULL;

  if (previous_rule_end)
    previous_rule_end->next = midrule;
  else
    grammar = midrule;

  /* End the dummy's rule.  */
  previous_rule_end = symbol_list_new (NULL, dummy_location);
  previous_rule_end->next = current_rule;

  midrule->next = previous_rule_end;

  /* Insert the dummy nonterminal replacing the midrule action into
     the current rule.  */
  grammar_current_rule_symbol_append (dummy, dummy_location);
}

/* Set the precedence symbol of the current rule to PRECSYM. */

void
grammar_current_rule_prec_set (symbol *precsym, location loc)
{
  if (current_rule->ruleprec)
    complain_at (loc, _("only one %s allowed per rule"), "%prec");
  current_rule->ruleprec = precsym;
}

/* Attach dynamic precedence DPREC to the current rule. */

void
grammar_current_rule_dprec_set (int dprec, location loc)
{
  if (! glr_parser)
    warn_at (loc, _("%s affects only GLR parsers"), "%dprec");
  if (dprec <= 0)
    complain_at (loc, _("%s must be followed by positive number"), "%dprec");
  else if (current_rule->dprec != 0)
    complain_at (loc, _("only one %s allowed per rule"), "%dprec");
  current_rule->dprec = dprec;
}

/* Attach a merge function NAME with argument type TYPE to current
   rule. */

void
grammar_current_rule_merge_set (uniqstr name, location loc)
{
  if (! glr_parser)
    warn_at (loc, _("%s affects only GLR parsers"), "%merge");
  if (current_rule->merger != 0)
    complain_at (loc, _("only one %s allowed per rule"), "%merge");
  current_rule->merger =
    get_merge_function (name, current_rule->sym->type_name, loc);
}

/* Attach SYM to the current rule.  If needed, move the previous
   action as a mid-rule action.  */

void
grammar_current_rule_symbol_append (symbol *sym, location loc)
{
  if (current_rule->action)
    grammar_midrule_action ();
  ++nritems;
  grammar_symbol_append (sym, loc);
}

/* Attach an ACTION to the current rule.  If needed, move the previous
   action as a mid-rule action.  */

void
grammar_current_rule_action_append (const char *action, location loc)
{
  if (current_rule->action)
    grammar_midrule_action ();
  current_rule->action = action;
  current_rule->action_location = loc;
}


/*---------------------------------------------------------------.
| Convert the rules into the representation using RRHS, RLHS and |
| RITEM.                                                         |
`---------------------------------------------------------------*/

static void
packgram (void)
{
  unsigned int itemno = 0;
  rule_number ruleno = 0;
  symbol_list *p = grammar;

  ritem = xnmalloc (nritems, sizeof *ritem);
  rules = xnmalloc (nrules, sizeof *rules);

  while (p)
    {
      symbol *ruleprec = p->ruleprec;
      rules[ruleno].user_number = ruleno;
      rules[ruleno].number = ruleno;
      rules[ruleno].lhs = p->sym;
      rules[ruleno].rhs = ritem + itemno;
      rules[ruleno].prec = NULL;
      rules[ruleno].dprec = p->dprec;
      rules[ruleno].merger = p->merger;
      rules[ruleno].precsym = NULL;
      rules[ruleno].location = p->location;
      rules[ruleno].useful = true;
      rules[ruleno].action = p->action;
      rules[ruleno].action_location = p->action_location;

      p = p->next;
      while (p && p->sym)
	{
	  /* item_number = symbol_number.
	     But the former needs to contain more: negative rule numbers. */
	  ritem[itemno++] = symbol_number_as_item_number (p->sym->number);
	  /* A rule gets by default the precedence and associativity
	     of the last token in it.  */
	  if (p->sym->class == token_sym && default_prec)
	    rules[ruleno].prec = p->sym;
	  if (p)
	    p = p->next;
	}

      /* If this rule has a %prec,
         the specified symbol's precedence replaces the default.  */
      if (ruleprec)
	{
	  rules[ruleno].precsym = ruleprec;
	  rules[ruleno].prec = ruleprec;
	}
      ritem[itemno++] = rule_number_as_item_number (ruleno);
      ++ruleno;

      if (p)
	p = p->next;
    }

  if (itemno != nritems)
    abort ();

  if (trace_flag & trace_sets)
    ritem_print (stderr);
}

/*------------------------------------------------------------------.
| Read in the grammar specification and record it in the format     |
| described in gram.h.  All actions are copied into ACTION_OBSTACK, |
| in each case forming the body of a C function (YYACTION) which    |
| contains a switch statement to decide which action to execute.    |
`------------------------------------------------------------------*/

void
reader (void)
{
  /* Initialize the symbol table.  */
  symbols_new ();

  /* Construct the accept symbol. */
  accept = symbol_get ("$accept", empty_location);
  accept->class = nterm_sym;
  accept->number = nvars++;

  /* Construct the error token */
  errtoken = symbol_get ("error", empty_location);
  errtoken->class = token_sym;
  errtoken->number = ntokens++;

  /* Construct a token that represents all undefined literal tokens.
     It is always token number 2.  */
  undeftoken = symbol_get ("$undefined", empty_location);
  undeftoken->class = token_sym;
  undeftoken->number = ntokens++;

  /* Initialize the obstacks. */
  obstack_init (&pre_prologue_obstack);
  obstack_init (&post_prologue_obstack);

  finput = xfopen (grammar_file, "r");
  gram_in = finput;

  gram__flex_debug = trace_flag & trace_scan;
  gram_debug = trace_flag & trace_parse;
  scanner_initialize ();
  gram_parse ();

  /* If something went wrong during the parsing, don't try to
     continue.  */
  if (complaint_issued)
    return;

  /* Grammar has been read.  Do some checking */
  if (nrules == 0)
    fatal (_("no rules in the input grammar"));

  /* Report any undefined symbols and consider them nonterminals.  */
  symbols_check_defined ();

  /* If the user did not define her ENDTOKEN, do it now. */
  if (!endtoken)
    {
      endtoken = symbol_get ("$end", empty_location);
      endtoken->class = token_sym;
      endtoken->number = 0;
      /* Value specified by POSIX.  */
      endtoken->user_token_number = 0;
    }

  /* Insert the initial rule, which line is that of the first rule
     (not that of the start symbol):

     accept: %start EOF.  */
  {
    symbol_list *p = symbol_list_new (accept, empty_location);
    p->location = grammar->location;
    p->next = symbol_list_new (startsymbol, empty_location);
    p->next->next = symbol_list_new (endtoken, empty_location);
    p->next->next->next = symbol_list_new (NULL, empty_location);
    p->next->next->next->next = grammar;
    nrules += 1;
    nritems += 3;
    grammar = p;
  }

  if (! (nsyms <= SYMBOL_NUMBER_MAXIMUM && nsyms == ntokens + nvars))
    abort ();

  xfclose (finput);

  /* Assign the symbols their symbol numbers.  Write #defines for the
     token symbols into FDEFINES if requested.  */
  symbols_pack ();

  /* Convert the grammar into the format described in gram.h.  */
  packgram ();

  /* The grammar as a symbol_list is no longer needed. */
  LIST_FREE (symbol_list, grammar);
}