src/state.h

   1 /* Type definitions for nondeterministic finite state machine for Bison.
   2
   3    Copyright (C) 1984, 1989, 2000, 2001, 2002 Free Software
   4    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., 59 Temple Place - Suite 330,
  21    Boston, MA 02111-1307, 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 RITEMS 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.  The data is a list of
  67    nreds rules, represented by their rule numbers.  first_reduction
  68    points to the list of these structures.
  69
  70    Conflict resolution can decide that certain tokens in certain
  71    states should explicitly be errors (for implementing %nonassoc).
  72    For each state, the tokens that are errors for this reason are
  73    recorded in an errs structure, which holds the token numbers.
  74
  75    There is at least one goto 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    The reason for the extra state at the end is to placate the
  81    parser's strategy of making all decisions one token ahead of its
  82    actions.  */
  83
  84 #ifndef STATE_H_
  85 # define STATE_H_
  86
  87 # include <bitset.h>
  88
  89 # include "gram.h"
  90 # include "symtab.h"
  91
  92
  93 /*-------------------.
  94 | Numbering states.  |
  95 `-------------------*/
  96
  97 typedef short state_number;
  98 # define STATE_NUMBER_MAXIMUM SHRT_MAX
  99
 100 /* Be ready to map a state_number to an int.  */
 101 static inline int
 102 state_number_as_int (state_number s)
 103 {
 104   return s;
 105 }
 106
 107
 108 typedef struct state state;
 109
 110 /*--------------.
 111 | Transitions.  |
 112 `--------------*/
 113
 114 typedef struct
 115 {
 116   short num;
 117   state *states[1];
 118 } transitions;
 119
 120
 121 /* What is the symbol labelling the transition to
 122    TRANSITIONS->states[Num]?  Can be a token (amongst which the error
 123    token), or non terminals in case of gotos.  */
 124
 125 #define TRANSITION_SYMBOL(Transitions, Num) \
 126   (Transitions->states[Num]->accessing_symbol)
 127
 128 /* Is the TRANSITIONS->states[Num] a shift? (as opposed to gotos).  */
 129
 130 #define TRANSITION_IS_SHIFT(Transitions, Num) \
 131   (ISTOKEN (TRANSITION_SYMBOL (Transitions, Num)))
 132
 133 /* Is the TRANSITIONS->states[Num] a goto?. */
 134
 135 #define TRANSITION_IS_GOTO(Transitions, Num) \
 136   (!TRANSITION_IS_SHIFT (Transitions, Num))
 137
 138 /* Is the TRANSITIONS->states[Num] labelled by the error token?  */
 139
 140 #define TRANSITION_IS_ERROR(Transitions, Num) \
 141   (TRANSITION_SYMBOL (Transitions, Num) == errtoken->number)
 142
 143 /* When resolving a SR conflicts, if the reduction wins, the shift is
 144    disabled.  */
 145
 146 #define TRANSITION_DISABLE(Transitions, Num) \
 147   (Transitions->states[Num] = NULL)
 148
 149 #define TRANSITION_IS_DISABLED(Transitions, Num) \
 150   (Transitions->states[Num] == NULL)
 151
 152
 153 /* Iterate over each transition over a token (shifts).  */
 154 #define FOR_EACH_SHIFT(Transitions, Iter)                       \
 155   for (Iter = 0;                                                \
 156        Iter < Transitions->num                                  \
 157          && (TRANSITION_IS_DISABLED (Transitions, Iter)         \
 158              || TRANSITION_IS_SHIFT (Transitions, Iter));       \
 159        ++Iter)                                                  \
 160     if (!TRANSITION_IS_DISABLED (Transitions, Iter))
 161
 162
 163 /* Return the state such SHIFTS contain a shift/goto to it on S.
 164    Abort if none found.  */
 165 struct state *transitions_to (transitions *shifts, symbol_number s);
 166
 167
 168 /*-------.
 169 | Errs.  |
 170 `-------*/
 171
 172 typedef struct
 173 {
 174   short num;
 175   symbol *symbols[1];
 176 } errs;
 177
 178 errs *errs_new (int num, symbol **tokens);
 179
 180
 181 /*-------------.
 182 | Reductions.  |
 183 `-------------*/
 184
 185 typedef struct
 186 {
 187   short num;
 188   bitset *lookaheads;
 189   rule *rules[1];
 190 } reductions;
 191
 192
 193
 194 /*---------.
 195 | states.  |
 196 `---------*/
 197
 198 struct state
 199 {
 200   state_number number;
 201   symbol_number accessing_symbol;
 202   transitions *transitions;
 203   reductions *reductions;
 204   errs *errs;
 205
 206   /* Nonzero if no lookahead is needed to 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   unsigned short 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 lookaheads such that this STATE wants to
 238    reduce R.  */
 239 void state_rule_lookaheads_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 /* All the states, indexed by the state number.  */
 253 extern state **states;
 254
 255 /* Free all the states.  */
 256 void states_free (void);
 257 #endif /* !STATE_H_ */