src/state.h

   1 /* Type definitions for nondeterministic finite state machine for Bison.
   2
   3    Copyright (C) 1984, 1989, 2000, 2001, 2002, 2003, 2004, 2007 Free
   4    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
  24 /* These type definitions are used to represent a nondeterministic
  25    finite state machine that parses the specified grammar.  This
  26    information is generated by the function generate_states in the
  27    file LR0.
  28
  29    Each state of the machine is described by a set of items --
  30    particular positions in particular rules -- that are the possible
  31    places where parsing could continue when the machine is in this
  32    state.  These symbols at these items are the allowable inputs that
  33    can follow now.
  34
  35    A core represents one state.  States are numbered in the NUMBER
  36    field.  When generate_states is finished, the starting state is
  37    state 0 and NSTATES is the number of states.  (FIXME: This sentence
  38    is no longer true: A transition to a state whose state number is
  39    NSTATES indicates termination.)  All the cores are chained together
  40    and FIRST_STATE points to the first one (state 0).
  41
  42    For each state there is a particular symbol which must have been
  43    the last thing accepted to reach that state.  It is the
  44    ACCESSING_SYMBOL of the core.
  45
  46    Each core contains a vector of NITEMS items which are the indices
  47    in the RITEM vector of the items that are selected in this state.
  48
  49    The two types of actions are shifts/gotos (push the lookahead token
  50    and read another/goto to the state designated by a nterm) and
  51    reductions (combine the last n things on the stack via a rule,
  52    replace them with the symbol that the rule derives, and leave the
  53    lookahead token alone).  When the states are generated, these
  54    actions are represented in two other lists.
  55
  56    Each transition structure describes the possible transitions out
  57    of one state, the state whose number is in the number field.  Each
  58    contains a vector of numbers of the states that transitions can go
  59    to.  The accessing_symbol fields of those states' cores say what
  60    kind of input leads to them.
  61
  62    A transition to state zero should be ignored: conflict resolution
  63    deletes transitions by having them point to zero.
  64
  65    Each reductions structure describes the possible reductions at the
  66    state whose number is in the number field.  rules is an array of
  67    num rules.  lookahead_tokens is an array of bitsets, one per rule.
  68
  69    Conflict resolution can decide that certain tokens in certain
  70    states should explicitly be errors (for implementing %nonassoc).
  71    For each state, the tokens that are errors for this reason are
  72    recorded in an errs structure, which holds the token numbers.
  73
  74    There is at least one goto transition present in state zero.  It
  75    leads to a next-to-final state whose accessing_symbol is the
  76    grammar's start symbol.  The next-to-final state has one shift to
  77    the final state, whose accessing_symbol is zero (end of input).
  78    The final state has one shift, which goes to the termination state.
  79    The reason for the extra state at the end is to placate the
  80    parser's strategy of making all decisions one token ahead of its
  81    actions.  */
  82
  83 #ifndef STATE_H_
  84 # define STATE_H_
  85
  86 # include <bitset.h>
  87
  88 # include "gram.h"
  89 # include "symtab.h"
  90
  91
  92 /*-------------------.
  93 | Numbering states.  |
  94 `-------------------*/
  95
  96 typedef int state_number;
  97 # define STATE_NUMBER_MAXIMUM INT_MAX
  98
  99 /* Be ready to map a state_number to an int.  */
 100 static inline int
 101 state_number_as_int (state_number s)
 102 {
 103   return s;
 104 }
 105
 106
 107 typedef struct state state;
 108
 109 /*--------------.
 110 | Transitions.  |
 111 `--------------*/
 112
 113 typedef struct
 114 {
 115   int num;
 116   state *states[1];
 117 } transitions;
 118
 119
 120 /* What is the symbol labelling the transition to
 121    TRANSITIONS->states[Num]?  Can be a token (amongst which the error
 122    token), or non terminals in case of gotos.  */
 123
 124 #define TRANSITION_SYMBOL(Transitions, Num) \
 125   (Transitions->states[Num]->accessing_symbol)
 126
 127 /* Is the TRANSITIONS->states[Num] a shift? (as opposed to gotos).  */
 128
 129 #define TRANSITION_IS_SHIFT(Transitions, Num) \
 130   (ISTOKEN (TRANSITION_SYMBOL (Transitions, Num)))
 131
 132 /* Is the TRANSITIONS->states[Num] a goto?. */
 133
 134 #define TRANSITION_IS_GOTO(Transitions, Num) \
 135   (!TRANSITION_IS_SHIFT (Transitions, Num))
 136
 137 /* Is the TRANSITIONS->states[Num] labelled by the error token?  */
 138
 139 #define TRANSITION_IS_ERROR(Transitions, Num) \
 140   (TRANSITION_SYMBOL (Transitions, Num) == errtoken->number)
 141
 142 /* When resolving a SR conflicts, if the reduction wins, the shift is
 143    disabled.  */
 144
 145 #define TRANSITION_DISABLE(Transitions, Num) \
 146   (Transitions->states[Num] = NULL)
 147
 148 #define TRANSITION_IS_DISABLED(Transitions, Num) \
 149   (Transitions->states[Num] == NULL)
 150
 151
 152 /* Iterate over each transition over a token (shifts).  */
 153 #define FOR_EACH_SHIFT(Transitions, Iter)                       \
 154   for (Iter = 0;                                                \
 155        Iter < Transitions->num                                  \
 156          && (TRANSITION_IS_DISABLED (Transitions, Iter)         \
 157              || TRANSITION_IS_SHIFT (Transitions, Iter));       \
 158        ++Iter)                                                  \
 159     if (!TRANSITION_IS_DISABLED (Transitions, Iter))
 160
 161
 162 /* Return the state such SHIFTS contain a shift/goto to it on SYM.
 163    Abort if none found.  */
 164 struct state *transitions_to (transitions *shifts, symbol_number sym);
 165
 166
 167 /*-------.
 168 | Errs.  |
 169 `-------*/
 170
 171 typedef struct
 172 {
 173   int num;
 174   symbol *symbols[1];
 175 } errs;
 176
 177 errs *errs_new (int num, symbol **tokens);
 178
 179
 180 /*-------------.
 181 | Reductions.  |
 182 `-------------*/
 183
 184 typedef struct
 185 {
 186   int num;
 187   bitset *lookahead_tokens;
 188   rule *rules[1];
 189 } reductions;
 190
 191
 192
 193 /*---------.
 194 | states.  |
 195 `---------*/
 196
 197 struct state
 198 {
 199   state_number number;
 200   symbol_number accessing_symbol;
 201   transitions *transitions;
 202   reductions *reductions;
 203   errs *errs;
 204
 205   /* If non-zero, then no lookahead sets on reduce actions are needed to
 206      decide what to do in state S.  */
 207   char consistent;
 208
 209   /* If some conflicts were solved thanks to precedence/associativity,
 210      a human readable description of the resolution.  */
 211   const char *solved_conflicts;
 212
 213   /* Its items.  Must be last, since ITEMS can be arbitrarily large.
 214      */
 215   size_t nitems;
 216   item_number items[1];
 217 };
 218
 219 extern state_number nstates;
 220 extern state *final_state;
 221
 222 /* Create a new state with ACCESSING_SYMBOL for those items.  */
 223 state *state_new (symbol_number accessing_symbol,
 224                   size_t core_size, item_number *core);
 225
 226 /* Set the transitions of STATE.  */
 227 void state_transitions_set (state *s, int num, state **trans);
 228
 229 /* Set the reductions of STATE.  */
 230 void state_reductions_set (state *s, int num, rule **reds);
 231
 232 int state_reduction_find (state *s, rule *r);
 233
 234 /* Set the errs of STATE.  */
 235 void state_errs_set (state *s, int num, symbol **errors);
 236
 237 /* Print on OUT all the lookahead tokens such that this STATE wants to
 238    reduce R.  */
 239 void state_rule_lookahead_tokens_print (state *s, rule *r, FILE *out);
 240
 241 /* Create/destroy the states hash table.  */
 242 void state_hash_new (void);
 243 void state_hash_free (void);
 244
 245 /* Find the state associated to the CORE, and return it.  If it does
 246    not exist yet, return NULL.  */
 247 state *state_hash_lookup (size_t core_size, item_number *core);
 248
 249 /* Insert STATE in the state hash table.  */
 250 void state_hash_insert (state *s);
 251
 252 /* Remove unreachable states, renumber remaining states, update NSTATES, and
 253    write to OLD_TO_NEW a mapping of old state numbers to new state numbers such
 254    that the old value of NSTATES is written as the new state number for removed
 255    states.  The size of OLD_TO_NEW must be the old value of NSTATES.  */
 256 void state_remove_unreachable_states (state_number old_to_new[]);
 257
 258 /* All the states, indexed by the state number.  */
 259 extern state **states;
 260
 261 /* Free all the states.  */
 262 void states_free (void);
 263
 264 #endif /* !STATE_H_ */