src/gram.h

   1 /* Data definitions for internal representation of bison's input,
   2    Copyright (C) 1984, 1986, 1989, 1992, 2001, 2002
   3    Free Software Foundation, Inc.
   4
   5    This file is part of Bison, the GNU Compiler Compiler.
   6
   7    Bison is free software; you can redistribute it and/or modify
   8    it under the terms of the GNU General Public License as published by
   9    the Free Software Foundation; either version 2, or (at your option)
  10    any later version.
  11
  12    Bison is distributed in the hope that it will be useful,
  13    but WITHOUT ANY WARRANTY; without even the implied warranty of
  14    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15    GNU General Public License for more details.
  16
  17    You should have received a copy of the GNU General Public License
  18    along with Bison; see the file COPYING.  If not, write to
  19    the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
  20    Boston, MA 02111-1307, USA.  */
  21
  22 #ifndef GRAM_H_
  23 # define GRAM_H_
  24
  25 /* Representation of the grammar rules:
  26
  27    NTOKENS is the number of tokens, and NVARS is the number of
  28    variables (nonterminals).  NSYMS is the total number, ntokens +
  29    nvars.
  30
  31    Each symbol (either token or variable) receives a symbol number.
  32    Numbers 0 to NTOKENS - 1 are for tokens, and NTOKENS to NSYMS - 1
  33    are for variables.  Symbol number zero is the end-of-input token.
  34    This token is counted in ntokens.  The true number of token values
  35    assigned is NTOKENS reduced by one for each alias declaration.
  36
  37    The rules receive rule numbers 1 to NRULES in the order they are
  38    written.  More precisely Bison augments the grammar with the
  39    initial rule, `$axiom: START-SYMBOL EOF', which is numbered 1, all
  40    the user rules are 2, 3 etc.  Each time a rule number is presented
  41    to the user, we subtract 1, so *displayed* rule numbers are 0, 1,
  42    2...
  43
  44    Internally, we cannot use the number 0 for a rule because for
  45    instance RITEM stores both symbol (the RHS) and rule numbers: the
  46    symbols are shorts >= 0, and rule number are stored negative.
  47    Therefore 0 cannot be used, since it would be both the rule number
  48    0, and the token EOF).
  49
  50    Actions and guards are accessed via the rule number.
  51
  52    The rules themselves are described by several arrays: amongst which
  53    RITEM, and RULES.
  54
  55    RULES is an array of struct rule_s, which members are:
  56
  57    RULES[R].lhs -- the symbol of the left hand side of rule R.
  58
  59    RULES[R].rhs -- the index in RITEM of the beginning of the portion
  60    for rule R.
  61
  62    RULES[R].prec -- the symbol providing the precedence level of R.
  63
  64    RULES[R].precsym -- the symbol attached (via %prec) to give its
  65    precedence to R.  Of course, if set, it is equal to `prec', but we
  66    need to distinguish one from the other when reducing: a symbol used
  67    in a %prec is not useless.
  68
  69    RULES[R].assoc -- the associativity of R.
  70
  71    RULES[R].line -- the line where R was defined.
  72
  73    RULES[R].useful -- TRUE iff the rule is used (i.e., FALSE if thrown
  74    away by reduce).
  75
  76    The right hand side is stored as symbol numbers in a portion of
  77    RITEM.
  78
  79    The length of the portion is one greater than the number of symbols
  80    in the rule's right hand side.  The last element in the portion
  81    contains minus R, which identifies it as the end of a portion and
  82    says which rule it is for.
  83
  84    The portions of RITEM come in order of increasing rule number and
  85    are followed by an element which is zero to mark the end.  nitems
  86    is the total length of ritem, not counting the final zero.  Each
  87    element of RITEM is called an "item" and its index in RITEM is an
  88    item number.
  89
  90    Item numbers are used in the finite state machine to represent
  91    places that parsing can get to.
  92
  93    SYMBOLS[I]->prec records the precedence level of each symbol.
  94
  95    Precedence levels are assigned in increasing order starting with 1
  96    so that numerically higher precedence values mean tighter binding
  97    as they ought to.  Zero as a symbol or rule's precedence means none
  98    is assigned.
  99
 100    Associativities are recorded similarly in SYMBOLS[I]->assoc.  */
 101
 102 #include "symtab.h"
 103
 104 #define ISTOKEN(s)      ((s) < ntokens)
 105 #define ISVAR(s)        ((s) >= ntokens)
 106
 107 extern int nitems;
 108 extern int nrules;
 109 extern int nsyms;
 110 extern int ntokens;
 111 extern int nvars;
 112
 113 extern short *ritem;
 114 extern int nritems;
 115
 116 extern int start_symbol;
 117
 118 typedef struct rule_s
 119 {
 120   /* The number of the rule in the source.  It is usually the index in
 121      RULES too, except if there are useless rules.  */
 122   short user_number;
 123
 124   /* The index in RULES.  Usually the rule number in the source,
 125      except if some rules are useless.  */
 126   short number;
 127
 128   symbol_t *lhs;
 129   short *rhs;
 130
 131   /* This symbol provides both the associativity, and the precedence. */
 132   symbol_t *prec;
 133
 134   /* This symbol was attached to the rule via %prec. */
 135   symbol_t *precsym;
 136
 137   short line;
 138   bool useful;
 139
 140   const char *action;
 141   short action_line;
 142
 143   const char *guard;
 144   short guard_line;
 145 } rule_t;
 146
 147 extern struct rule_s *rules;
 148
 149 /* Table of the symbols, indexed by the symbol number. */
 150 extern symbol_t **symbols;
 151
 152 /* token translation table: indexed by a token number as returned by
 153    the user's yylex routine, it yields the internal token number used
 154    by the parser and throughout bison.  */
 155
 156 extern short *token_translations;
 157 extern int max_user_token_number;
 158
 159 /* SEMANTIC_PARSER is nonzero if the input file says to use the hairy
 160    parser that provides for semantic error recovery.  If it is zero,
 161    the yacc-compatible simplified parser is used.  */
 162
 163 extern int semantic_parser;
 164
 165 /* PURE_PARSER is nonzero if should generate a parser that is all pure
 166    and reentrant.  */
 167
 168 extern int pure_parser;
 169
 170 /* ERROR_TOKEN_NUMBER is the token number of the error token.  */
 171
 172 extern int error_token_number;
 173
 174 /* Report the length of the RHS. */
 175 int rule_rhs_length PARAMS ((rule_t *rule));
 176
 177 /* Dump RITEM for traces. */
 178 void ritem_print PARAMS ((FILE *out));
 179
 180 /* Return the size of the longest rule RHS.  */
 181 size_t ritem_longest_rhs PARAMS ((void));
 182
 183 #endif /* !GRAM_H_ */