src/state.h

   1 /* Type definitions for nondeterministic finite state machine for bison,
   2    Copyright 1984, 1989, 2000, 2001 Free Software Foundation, Inc.
   3
   4    This file is part of Bison, the GNU Compiler Compiler.
   5
   6    Bison is free software; you can redistribute it and/or modify
   7    it under the terms of the GNU General Public License as published by
   8    the Free Software Foundation; either version 2, or (at your option)
   9    any later version.
  10
  11    Bison is distributed in the hope that it will be useful,
  12    but WITHOUT ANY WARRANTY; without even the implied warranty of
  13    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14    GNU General Public License for more details.
  15
  16    You should have received a copy of the GNU General Public License
  17    along with Bison; see the file COPYING.  If not, write to
  18    the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
  19    Boston, MA 02111-1307, USA.  */
  20
  21
  22 /* These type definitions are used to represent a nondeterministic
  23    finite state machine that parses the specified grammar.  This
  24    information is generated by the function generate_states in the
  25    file LR0.
  26
  27    Each state of the machine is described by a set of items --
  28    particular positions in particular rules -- that are the possible
  29    places where parsing could continue when the machine is in this
  30    state.  These symbols at these items are the allowable inputs that
  31    can follow now.
  32
  33    A core represents one state.  States are numbered in the NUMBER
  34    field.  When generate_states is finished, the starting state is
  35    state 0 and NSTATES is the number of states.  (FIXME: This sentence
  36    is no longer true: A transition to a state whose state number is
  37    NSTATES indicates termination.)  All the cores are chained together
  38    and FIRST_STATE points to the first one (state 0).
  39
  40    For each state there is a particular symbol which must have been
  41    the last thing accepted to reach that state.  It is the
  42    ACCESSING_SYMBOL of the core.
  43
  44    Each core contains a vector of NITEMS items which are the indices
  45    in the RITEMS vector of the items that are selected in this state.
  46
  47    The two types of transitions are shifts (push the lookahead token
  48    and read another) and reductions (combine the last n things on the
  49    stack via a rule, replace them with the symbol that the rule
  50    derives, and leave the lookahead token alone).  When the states are
  51    generated, these transitions are represented in two other lists.
  52
  53    Each shifts structure describes the possible shift transitions out
  54    of one state, the state whose number is in the number field.  The
  55    shifts structures are linked through next and first_shift points to
  56    them.  Each contains a vector of numbers of the states that shift
  57    transitions can go to.  The accessing_symbol fields of those
  58    states' cores say what kind of input leads to them.
  59
  60    A shift to state zero should be ignored.  Conflict resolution
  61    deletes shifts by changing them to zero.
  62
  63    Each reductions structure describes the possible reductions at the
  64    state whose number is in the number field.  The data is a list of
  65    nreds rules, represented by their rule numbers.  first_reduction
  66    points to the list of these structures.
  67
  68    Conflict resolution can decide that certain tokens in certain
  69    states should explicitly be errors (for implementing %nonassoc).
  70    For each state, the tokens that are errors for this reason are
  71    recorded in an errs structure, which has the state number in its
  72    number field.  The rest of the errs structure is full of token
  73    numbers.
  74
  75    There is at least one shift transition present in state zero.  It
  76    leads to a next-to-final state whose accessing_symbol is the
  77    grammar's start symbol.  The next-to-final state has one shift to
  78    the final state, whose accessing_symbol is zero (end of input).
  79    The final state has one shift, which goes to the termination state
  80    (whose number is nstates-1).  The reason for the extra state at the
  81    end is to placate the parser's strategy of making all decisions one
  82    token ahead of its actions.  */
  83
  84 #ifndef STATE_H_
  85 # define STATE_H_
  86
  87 # include "bitsetv.h"
  88
  89
  90 /*-------------------.
  91 | Numbering states.  |
  92 `-------------------*/
  93
  94 typedef short state_number_t;
  95 # define STATE_NUMBER_MAX ((state_number_t) SHRT_MAX)
  96
  97 /* Be ready to map a state_number_t to an int.  */
  98 # define state_number_as_int(Tok) ((int) (Tok))
  99
 100 /*---------.
 101 | Shifts.  |
 102 `---------*/
 103
 104 typedef struct shifts
 105 {
 106   short nshifts;
 107   state_number_t shifts[1];
 108 } shifts;
 109
 110 shifts *shifts_new PARAMS ((int n));
 111
 112
 113 /* What is the symbol which is shifted by SHIFTS->shifts[Shift]?  Can
 114    be a token (amongst which the error token), or non terminals in
 115    case of gotos.  */
 116
 117 #define SHIFT_SYMBOL(Shifts, Shift) \
 118   (states[Shifts->shifts[Shift]]->accessing_symbol)
 119
 120 /* Is the SHIFTS->shifts[Shift] a real shift? (as opposed to gotos.) */
 121
 122 #define SHIFT_IS_SHIFT(Shifts, Shift) \
 123   (ISTOKEN (SHIFT_SYMBOL (Shifts, Shift)))
 124
 125 /* Is the SHIFTS->shifts[Shift] a goto?. */
 126
 127 #define SHIFT_IS_GOTO(Shifts, Shift) \
 128   (!SHIFT_IS_SHIFT (Shifts, Shift))
 129
 130 /* Is the SHIFTS->shifts[Shift] then handling of the error token?. */
 131
 132 #define SHIFT_IS_ERROR(Shifts, Shift) \
 133   (SHIFT_SYMBOL (Shifts, Shift) == errtoken->number)
 134
 135 /* When resolving a SR conflicts, if the reduction wins, the shift is
 136    disabled.  */
 137
 138 #define SHIFT_DISABLE(Shifts, Shift) \
 139   (Shifts->shifts[Shift] = 0)
 140
 141 #define SHIFT_IS_DISABLED(Shifts, Shift) \
 142   (Shifts->shifts[Shift] == 0)
 143
 144
 145 /*-------.
 146 | Errs.  |
 147 `-------*/
 148
 149 typedef struct errs
 150 {
 151   short nerrs;
 152   short errs[1];
 153 } errs;
 154
 155 errs *errs_new PARAMS ((int n));
 156 errs *errs_dup PARAMS ((errs *src));
 157
 158
 159 /*-------------.
 160 | Reductions.  |
 161 `-------------*/
 162
 163 typedef struct reductions
 164 {
 165   short nreds;
 166   short rules[1];
 167 } reductions;
 168
 169 reductions *reductions_new PARAMS ((int n));
 170
 171
 172 /*----------.
 173 | State_t.  |
 174 `----------*/
 175
 176 typedef struct state_s
 177 {
 178   struct state_s *next;
 179
 180   state_number_t number;
 181   symbol_number_t accessing_symbol;
 182   shifts     *shifts;
 183   reductions *reductions;
 184   errs       *errs;
 185
 186   /* Nonzero if no lookahead is needed to decide what to do in state S.  */
 187   char consistent;
 188
 189   /* Used in LALR, not LR(0). */
 190   int nlookaheads;
 191   bitsetv lookaheads;
 192   rule_t **lookaheads_rule;
 193
 194   /* If some conflicts were solved thanks to precedence/associativity,
 195      a human readable description of the resolution.  */
 196   const char *solved_conflicts;
 197
 198   /* Its items.  Must be last, since ITEMS can be arbitrarily large.
 199      */
 200   unsigned short nitems;
 201   item_number_t items[1];
 202 } state_t;
 203
 204 extern state_number_t nstates;
 205 extern state_t *final_state;
 206
 207 /* Create a new state with ACCESSING_SYMBOL for those items.  */
 208
 209 state_t *state_new PARAMS ((symbol_number_t accessing_symbol,
 210                             size_t core_size, item_number_t *core));
 211
 212 /* Print on OUT all the lookaheads such that this STATE wants to
 213    reduce this RULE.  */
 214
 215 void state_rule_lookaheads_print PARAMS ((state_t *state, rule_t *rule,
 216                                           FILE *out));
 217
 218 /* Create/destroy the states hash table.  */
 219 void state_hash_new PARAMS ((void));
 220 void state_hash_free PARAMS ((void));
 221
 222 /* Find the state associated to the CORE, and return it.  If it does
 223    not exist yet, return NULL.  */
 224 state_t *state_hash_lookup PARAMS ((size_t core_size, item_number_t *core));
 225
 226 /* Insert STATE in the state hash table.  */
 227 void state_hash_insert PARAMS ((state_t *state));
 228
 229 /* All the states, indexed by the state number.  */
 230 extern state_t **states;
 231
 232 /* Free all the states.  */
 233 void states_free PARAMS ((void));
 234 #endif /* !STATE_H_ */