src/gram.h

   1 /* Data definitions for internal representation of Bison's input.
   2
   3    Copyright (C) 1984, 1986, 1989, 1992, 2001, 2002, 2003, 2004
   4    Free Software Foundation, Inc.
   5
   6    This file is part of Bison, the GNU Compiler Compiler.
   7
   8    Bison is free software; you can redistribute it and/or modify
   9    it under the terms of the GNU General Public License as published by
  10    the Free Software Foundation; either version 2, or (at your option)
  11    any later version.
  12
  13    Bison is distributed in the hope that it will be useful,
  14    but WITHOUT ANY WARRANTY; without even the implied warranty of
  15    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  16    GNU General Public License for more details.
  17
  18    You should have received a copy of the GNU General Public License
  19    along with Bison; see the file COPYING.  If not, write to
  20    the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
  21    Boston, MA 02110-1301, USA.  */
  22
  23 #ifndef GRAM_H_
  24 # define GRAM_H_
  25
  26 /* Representation of the grammar rules:
  27
  28    NTOKENS is the number of tokens, and NVARS is the number of
  29    variables (nonterminals).  NSYMS is the total number, ntokens +
  30    nvars.
  31
  32    Each symbol (either token or variable) receives a symbol number.
  33    Numbers 0 to NTOKENS - 1 are for tokens, and NTOKENS to NSYMS - 1
  34    are for variables.  Symbol number zero is the end-of-input token.
  35    This token is counted in ntokens.  The true number of token values
  36    assigned is NTOKENS reduced by one for each alias declaration.
  37
  38    The rules receive rule numbers 1 to NRULES in the order they are
  39    written.  More precisely Bison augments the grammar with the
  40    initial rule, `$accept: START-SYMBOL $end', which is numbered 1,
  41    all the user rules are 2, 3 etc.  Each time a rule number is
  42    presented to the user, we subtract 1, so *displayed* rule numbers
  43    are 0, 1, 2...
  44
  45    Internally, we cannot use the number 0 for a rule because for
  46    instance RITEM stores both symbol (the RHS) and rule numbers: the
  47    symbols are shorts >= 0, and rule number are stored negative.
  48    Therefore 0 cannot be used, since it would be both the rule number
  49    0, and the token $end).
  50
  51    Actions are accessed via the rule number.
  52
  53    The rules themselves are described by several arrays: amongst which
  54    RITEM, and RULES.
  55
  56    RULES is an array of rules, whose members are:
  57
  58    RULES[R].lhs -- the symbol of the left hand side of rule R.
  59
  60    RULES[R].rhs -- the index in RITEM of the beginning of the portion
  61    for rule R.
  62
  63    RULES[R].prec -- the symbol providing the precedence level of R.
  64
  65    RULES[R].precsym -- the symbol attached (via %prec) to give its
  66    precedence to R.  Of course, if set, it is equal to `prec', but we
  67    need to distinguish one from the other when reducing: a symbol used
  68    in a %prec is not useless.
  69
  70    RULES[R].assoc -- the associativity of R.
  71
  72    RULES[R].dprec -- the dynamic precedence level of R (for GLR
  73    parsing).
  74
  75    RULES[R].merger -- index of merging function for R (for GLR
  76    parsing).
  77
  78    RULES[R].line -- the line where R was defined.
  79
  80    RULES[R].useful -- true iff the rule is used (i.e., false if thrown
  81    away by reduce).
  82
  83    The right hand side is stored as symbol numbers in a portion of
  84    RITEM.
  85
  86    The length of the portion is one greater than the number of symbols
  87    in the rule's right hand side.  The last element in the portion
  88    contains minus R, which identifies it as the end of a portion and
  89    says which rule it is for.
  90
  91    The portions of RITEM come in order of increasing rule number.
  92    NRITEMS is the total length of RITEM.  Each element of RITEM is
  93    called an "item" and its index in RITEM is an item number.
  94
  95    Item numbers are used in the finite state machine to represent
  96    places that parsing can get to.
  97
  98    SYMBOLS[I]->prec records the precedence level of each symbol.
  99
 100    Precedence levels are assigned in increasing order starting with 1
 101    so that numerically higher precedence values mean tighter binding
 102    as they ought to.  Zero as a symbol or rule's precedence means none
 103    is assigned.
 104
 105    Associativities are recorded similarly in SYMBOLS[I]->assoc.  */
 106
 107 # include "location.h"
 108 # include "symtab.h"
 109
 110 # define ISTOKEN(i)     ((i) < ntokens)
 111 # define ISVAR(i)       ((i) >= ntokens)
 112
 113 extern int nsyms;
 114 extern int ntokens;
 115 extern int nvars;
 116
 117 typedef int item_number;
 118 extern item_number *ritem;
 119 extern unsigned int nritems;
 120
 121 /* There is weird relationship between OT1H item_number and OTOH
 122    symbol_number and rule_number: we store the latter in
 123    item_number.  symbol_number values are stored as-is, while
 124    the negation of (rule_number + 1) is stored.
 125
 126    Therefore, a symbol_number must be a valid item_number, and we
 127    sometimes have to perform the converse transformation.  */
 128
 129 static inline item_number
 130 symbol_number_as_item_number (symbol_number sym)
 131 {
 132   return sym;
 133 }
 134
 135 static inline symbol_number
 136 item_number_as_symbol_number (item_number i)
 137 {
 138   return i;
 139 }
 140
 141 /* Rule numbers.  */
 142 typedef int rule_number;
 143 extern rule_number nrules;
 144
 145 static inline item_number
 146 rule_number_as_item_number (rule_number r)
 147 {
 148   return -1 - r;
 149 }
 150
 151 static inline rule_number
 152 item_number_as_rule_number (item_number i)
 153 {
 154   return -1 - i;
 155 }
 156
 157
 158 /*--------.
 159 | Rules.  |
 160 `--------*/
 161
 162 typedef struct
 163 {
 164   /* The number of the rule in the source.  It is usually the index in
 165      RULES too, except if there are useless rules.  */
 166   rule_number user_number;
 167
 168   /* The index in RULES.  Usually the rule number in the source,
 169      except if some rules are useless.  */
 170   rule_number number;
 171
 172   symbol *lhs;
 173   item_number *rhs;
 174
 175   /* This symbol provides both the associativity, and the precedence. */
 176   symbol *prec;
 177
 178   int dprec;
 179   int merger;
 180
 181   /* This symbol was attached to the rule via %prec. */
 182   symbol *precsym;
 183
 184   location location;
 185   bool useful;
 186
 187   const char *action;
 188   location action_location;
 189 } rule;
 190
 191 extern rule *rules;
 192
 193 /* A function that selects a rule.  */
 194 typedef bool (*rule_filter) (rule *);
 195
 196 /* Return true IFF the rule has a `number' smaller than NRULES.  */
 197 bool rule_useful_p (rule *r);
 198
 199 /* Return true IFF the rule has a `number' higher than NRULES.  */
 200 bool rule_useless_p (rule *r);
 201
 202 /* Return true IFF the rule is not flagged as useful *and* is useful.
 203    In other words, it was discarded because of conflicts.  */
 204 bool rule_never_reduced_p (rule *r);
 205
 206 /* Print this rule's number and lhs on OUT.  If a PREVIOUS_LHS was
 207    already displayed (by a previous call for another rule), avoid
 208    useless repetitions.  */
 209 void rule_lhs_print (rule *r, symbol *previous_lhs, FILE *out);
 210
 211 /* Return the length of the RHS.  */
 212 int rule_rhs_length (rule *r);
 213
 214 /* Print this rule's RHS on OUT.  */
 215 void rule_rhs_print (rule *r, FILE *out);
 216
 217 /* Print this rule on OUT.  */
 218 void rule_print (rule *r, FILE *out);
 219
 220
 221
 222
 223 /* Table of the symbols, indexed by the symbol number. */
 224 extern symbol **symbols;
 225
 226 /* TOKEN_TRANSLATION -- a table indexed by a token number as returned
 227    by the user's yylex routine, it yields the internal token number
 228    used by the parser and throughout bison.  */
 229 extern symbol_number *token_translations;
 230 extern int max_user_token_number;
 231
 232
 233
 234 /* Dump RITEM for traces. */
 235 void ritem_print (FILE *out);
 236
 237 /* Return the size of the longest rule RHS.  */
 238 size_t ritem_longest_rhs (void);
 239
 240 /* Print the grammar's rules numbers from BEGIN (inclusive) to END
 241    (exclusive) on OUT under TITLE.  */
 242 void grammar_rules_partial_print (FILE *out, const char *title,
 243                                   rule_filter filter);
 244
 245 /* Print the grammar's rules on OUT.  */
 246 void grammar_rules_print (FILE *out);
 247
 248 /* Dump the grammar. */
 249 void grammar_dump (FILE *out, const char *title);
 250
 251 /* Report on STDERR the rules that are not flagged USEFUL, using the
 252    MESSAGE (which can be `useless rule' when invoked after grammar
 253    reduction, or `never reduced' after conflicts were taken into
 254    account).  */
 255 void grammar_rules_never_reduced_report (const char *message);
 256
 257 /* Free the packed grammar. */
 258 void grammar_free (void);
 259
 260 #endif /* !GRAM_H_ */