1 /* Type definitions for nondeterministic finite state machine for Bison.
2
3 Copyright (C) 1984, 1989, 2000, 2001, 2002, 2003, 2004 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 RITEMS vector of the items that are selected in this state.
48
49 The two types of actions are shifts/gotos (push the look-ahead 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 look-ahead 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 int state_number;
98 # define STATE_NUMBER_MAXIMUM INT_MAX
99
100 /* Be ready to map a state_number to an int. */
101 static inline int
state_number_as_int(state_number s)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 int 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 SYM.
164 Abort if none found. */
165 struct state *transitions_to (transitions *shifts, symbol_number sym);
166
167
168 /*-------.
169 | Errs. |
170 `-------*/
171
172 typedef struct
173 {
174 int 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 int num;
188 bitset *look_ahead_tokens;
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 look-ahead 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 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 look-ahead tokens such that this STATE wants to
238 reduce R. */
239 void state_rule_look_ahead_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 /* 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_ */
258