1 /* Parser generator */
2
3 /* For a description, see the comments at end of this file */
4
5 #include "Python.h"
6 #include "pgenheaders.h"
7 #include "token.h"
8 #include "node.h"
9 #include "grammar.h"
10 #include "metagrammar.h"
11 #include "pgen.h"
12
13 extern int Py_DebugFlag;
14 extern int Py_IgnoreEnvironmentFlag; /* needed by Py_GETENV */
15
16
17 /* PART ONE -- CONSTRUCT NFA -- Cf. Algorithm 3.2 from [Aho&Ullman 77] */
18
19 typedef struct _nfaarc {
20 int ar_label;
21 int ar_arrow;
22 } nfaarc;
23
24 typedef struct _nfastate {
25 int st_narcs;
26 nfaarc *st_arc;
27 } nfastate;
28
29 typedef struct _nfa {
30 int nf_type;
31 char *nf_name;
32 int nf_nstates;
33 nfastate *nf_state;
34 int nf_start, nf_finish;
35 } nfa;
36
37 /* Forward */
38 static void compile_rhs(labellist *ll,
39 nfa *nf, node *n, int *pa, int *pb);
40 static void compile_alt(labellist *ll,
41 nfa *nf, node *n, int *pa, int *pb);
42 static void compile_item(labellist *ll,
43 nfa *nf, node *n, int *pa, int *pb);
44 static void compile_atom(labellist *ll,
45 nfa *nf, node *n, int *pa, int *pb);
46
47 static int
addnfastate(nfa * nf)48 addnfastate(nfa *nf)
49 {
50 nfastate *st;
51
52 nf->nf_state = (nfastate *)PyObject_REALLOC(nf->nf_state,
53 sizeof(nfastate) * (nf->nf_nstates + 1));
54 if (nf->nf_state == NULL)
55 Py_FatalError("out of mem");
56 st = &nf->nf_state[nf->nf_nstates++];
57 st->st_narcs = 0;
58 st->st_arc = NULL;
59 return st - nf->nf_state;
60 }
61
62 static void
addnfaarc(nfa * nf,int from,int to,int lbl)63 addnfaarc(nfa *nf, int from, int to, int lbl)
64 {
65 nfastate *st;
66 nfaarc *ar;
67
68 st = &nf->nf_state[from];
69 st->st_arc = (nfaarc *)PyObject_REALLOC(st->st_arc,
70 sizeof(nfaarc) * (st->st_narcs + 1));
71 if (st->st_arc == NULL)
72 Py_FatalError("out of mem");
73 ar = &st->st_arc[st->st_narcs++];
74 ar->ar_label = lbl;
75 ar->ar_arrow = to;
76 }
77
78 static nfa *
newnfa(char * name)79 newnfa(char *name)
80 {
81 nfa *nf;
82 static int type = NT_OFFSET; /* All types will be disjunct */
83
84 nf = (nfa *)PyObject_MALLOC(sizeof(nfa));
85 if (nf == NULL)
86 Py_FatalError("no mem for new nfa");
87 nf->nf_type = type++;
88 nf->nf_name = name; /* XXX strdup(name) ??? */
89 nf->nf_nstates = 0;
90 nf->nf_state = NULL;
91 nf->nf_start = nf->nf_finish = -1;
92 return nf;
93 }
94
95 typedef struct _nfagrammar {
96 int gr_nnfas;
97 nfa **gr_nfa;
98 labellist gr_ll;
99 } nfagrammar;
100
101 /* Forward */
102 static void compile_rule(nfagrammar *gr, node *n);
103
104 static nfagrammar *
newnfagrammar(void)105 newnfagrammar(void)
106 {
107 nfagrammar *gr;
108
109 gr = (nfagrammar *)PyObject_MALLOC(sizeof(nfagrammar));
110 if (gr == NULL)
111 Py_FatalError("no mem for new nfa grammar");
112 gr->gr_nnfas = 0;
113 gr->gr_nfa = NULL;
114 gr->gr_ll.ll_nlabels = 0;
115 gr->gr_ll.ll_label = NULL;
116 addlabel(&gr->gr_ll, ENDMARKER, "EMPTY");
117 return gr;
118 }
119
120 static void
freenfagrammar(nfagrammar * gr)121 freenfagrammar(nfagrammar *gr)
122 {
123 int i;
124 for (i = 0; i < gr->gr_nnfas; i++) {
125 PyObject_FREE(gr->gr_nfa[i]->nf_state);
126 }
127 PyObject_FREE(gr->gr_nfa);
128 PyObject_FREE(gr);
129 }
130
131 static nfa *
addnfa(nfagrammar * gr,char * name)132 addnfa(nfagrammar *gr, char *name)
133 {
134 nfa *nf;
135
136 nf = newnfa(name);
137 gr->gr_nfa = (nfa **)PyObject_REALLOC(gr->gr_nfa,
138 sizeof(nfa*) * (gr->gr_nnfas + 1));
139 if (gr->gr_nfa == NULL)
140 Py_FatalError("out of mem");
141 gr->gr_nfa[gr->gr_nnfas++] = nf;
142 addlabel(&gr->gr_ll, NAME, nf->nf_name);
143 return nf;
144 }
145
146 #ifdef Py_DEBUG
147
148 static char REQNFMT[] = "metacompile: less than %d children\n";
149
150 #define REQN(i, count) do { \
151 if (i < count) { \
152 fprintf(stderr, REQNFMT, count); \
153 Py_FatalError("REQN"); \
154 } \
155 } while (0)
156
157 #else
158 #define REQN(i, count) /* empty */
159 #endif
160
161 static nfagrammar *
metacompile(node * n)162 metacompile(node *n)
163 {
164 nfagrammar *gr;
165 int i;
166
167 if (Py_DebugFlag)
168 printf("Compiling (meta-) parse tree into NFA grammar\n");
169 gr = newnfagrammar();
170 REQ(n, MSTART);
171 i = n->n_nchildren - 1; /* Last child is ENDMARKER */
172 n = n->n_child;
173 for (; --i >= 0; n++) {
174 if (n->n_type != NEWLINE)
175 compile_rule(gr, n);
176 }
177 return gr;
178 }
179
180 static void
compile_rule(nfagrammar * gr,node * n)181 compile_rule(nfagrammar *gr, node *n)
182 {
183 nfa *nf;
184
185 REQ(n, RULE);
186 REQN(n->n_nchildren, 4);
187 n = n->n_child;
188 REQ(n, NAME);
189 nf = addnfa(gr, n->n_str);
190 n++;
191 REQ(n, COLON);
192 n++;
193 REQ(n, RHS);
194 compile_rhs(&gr->gr_ll, nf, n, &nf->nf_start, &nf->nf_finish);
195 n++;
196 REQ(n, NEWLINE);
197 }
198
199 static void
compile_rhs(labellist * ll,nfa * nf,node * n,int * pa,int * pb)200 compile_rhs(labellist *ll, nfa *nf, node *n, int *pa, int *pb)
201 {
202 int i;
203 int a, b;
204
205 REQ(n, RHS);
206 i = n->n_nchildren;
207 REQN(i, 1);
208 n = n->n_child;
209 REQ(n, ALT);
210 compile_alt(ll, nf, n, pa, pb);
211 if (--i <= 0)
212 return;
213 n++;
214 a = *pa;
215 b = *pb;
216 *pa = addnfastate(nf);
217 *pb = addnfastate(nf);
218 addnfaarc(nf, *pa, a, EMPTY);
219 addnfaarc(nf, b, *pb, EMPTY);
220 for (; --i >= 0; n++) {
221 REQ(n, VBAR);
222 REQN(i, 1);
223 --i;
224 n++;
225 REQ(n, ALT);
226 compile_alt(ll, nf, n, &a, &b);
227 addnfaarc(nf, *pa, a, EMPTY);
228 addnfaarc(nf, b, *pb, EMPTY);
229 }
230 }
231
232 static void
compile_alt(labellist * ll,nfa * nf,node * n,int * pa,int * pb)233 compile_alt(labellist *ll, nfa *nf, node *n, int *pa, int *pb)
234 {
235 int i;
236 int a, b;
237
238 REQ(n, ALT);
239 i = n->n_nchildren;
240 REQN(i, 1);
241 n = n->n_child;
242 REQ(n, ITEM);
243 compile_item(ll, nf, n, pa, pb);
244 --i;
245 n++;
246 for (; --i >= 0; n++) {
247 REQ(n, ITEM);
248 compile_item(ll, nf, n, &a, &b);
249 addnfaarc(nf, *pb, a, EMPTY);
250 *pb = b;
251 }
252 }
253
254 static void
compile_item(labellist * ll,nfa * nf,node * n,int * pa,int * pb)255 compile_item(labellist *ll, nfa *nf, node *n, int *pa, int *pb)
256 {
257 int i;
258 int a, b;
259
260 REQ(n, ITEM);
261 i = n->n_nchildren;
262 REQN(i, 1);
263 n = n->n_child;
264 if (n->n_type == LSQB) {
265 REQN(i, 3);
266 n++;
267 REQ(n, RHS);
268 *pa = addnfastate(nf);
269 *pb = addnfastate(nf);
270 addnfaarc(nf, *pa, *pb, EMPTY);
271 compile_rhs(ll, nf, n, &a, &b);
272 addnfaarc(nf, *pa, a, EMPTY);
273 addnfaarc(nf, b, *pb, EMPTY);
274 REQN(i, 1);
275 n++;
276 REQ(n, RSQB);
277 }
278 else {
279 compile_atom(ll, nf, n, pa, pb);
280 if (--i <= 0)
281 return;
282 n++;
283 addnfaarc(nf, *pb, *pa, EMPTY);
284 if (n->n_type == STAR)
285 *pb = *pa;
286 else
287 REQ(n, PLUS);
288 }
289 }
290
291 static void
compile_atom(labellist * ll,nfa * nf,node * n,int * pa,int * pb)292 compile_atom(labellist *ll, nfa *nf, node *n, int *pa, int *pb)
293 {
294 int i;
295
296 REQ(n, ATOM);
297 i = n->n_nchildren;
298 (void)i; /* Don't warn about set but unused */
299 REQN(i, 1);
300 n = n->n_child;
301 if (n->n_type == LPAR) {
302 REQN(i, 3);
303 n++;
304 REQ(n, RHS);
305 compile_rhs(ll, nf, n, pa, pb);
306 n++;
307 REQ(n, RPAR);
308 }
309 else if (n->n_type == NAME || n->n_type == STRING) {
310 *pa = addnfastate(nf);
311 *pb = addnfastate(nf);
312 addnfaarc(nf, *pa, *pb, addlabel(ll, n->n_type, n->n_str));
313 }
314 else
315 REQ(n, NAME);
316 }
317
318 static void
dumpstate(labellist * ll,nfa * nf,int istate)319 dumpstate(labellist *ll, nfa *nf, int istate)
320 {
321 nfastate *st;
322 int i;
323 nfaarc *ar;
324
325 printf("%c%2d%c",
326 istate == nf->nf_start ? '*' : ' ',
327 istate,
328 istate == nf->nf_finish ? '.' : ' ');
329 st = &nf->nf_state[istate];
330 ar = st->st_arc;
331 for (i = 0; i < st->st_narcs; i++) {
332 if (i > 0)
333 printf("\n ");
334 printf("-> %2d %s", ar->ar_arrow,
335 PyGrammar_LabelRepr(&ll->ll_label[ar->ar_label]));
336 ar++;
337 }
338 printf("\n");
339 }
340
341 static void
dumpnfa(labellist * ll,nfa * nf)342 dumpnfa(labellist *ll, nfa *nf)
343 {
344 int i;
345
346 printf("NFA '%s' has %d states; start %d, finish %d\n",
347 nf->nf_name, nf->nf_nstates, nf->nf_start, nf->nf_finish);
348 for (i = 0; i < nf->nf_nstates; i++)
349 dumpstate(ll, nf, i);
350 }
351
352
353 /* PART TWO -- CONSTRUCT DFA -- Algorithm 3.1 from [Aho&Ullman 77] */
354
355 static void
addclosure(bitset ss,nfa * nf,int istate)356 addclosure(bitset ss, nfa *nf, int istate)
357 {
358 if (addbit(ss, istate)) {
359 nfastate *st = &nf->nf_state[istate];
360 nfaarc *ar = st->st_arc;
361 int i;
362
363 for (i = st->st_narcs; --i >= 0; ) {
364 if (ar->ar_label == EMPTY)
365 addclosure(ss, nf, ar->ar_arrow);
366 ar++;
367 }
368 }
369 }
370
371 typedef struct _ss_arc {
372 bitset sa_bitset;
373 int sa_arrow;
374 int sa_label;
375 } ss_arc;
376
377 typedef struct _ss_state {
378 bitset ss_ss;
379 int ss_narcs;
380 struct _ss_arc *ss_arc;
381 int ss_deleted;
382 int ss_finish;
383 int ss_rename;
384 } ss_state;
385
386 typedef struct _ss_dfa {
387 int sd_nstates;
388 ss_state *sd_state;
389 } ss_dfa;
390
391 /* Forward */
392 static void printssdfa(int xx_nstates, ss_state *xx_state, int nbits,
393 labellist *ll, char *msg);
394 static void simplify(int xx_nstates, ss_state *xx_state);
395 static void convert(dfa *d, int xx_nstates, ss_state *xx_state);
396
397 static void
makedfa(nfagrammar * gr,nfa * nf,dfa * d)398 makedfa(nfagrammar *gr, nfa *nf, dfa *d)
399 {
400 int nbits = nf->nf_nstates;
401 bitset ss;
402 int xx_nstates;
403 ss_state *xx_state, *yy;
404 ss_arc *zz;
405 int istate, jstate, iarc, jarc, ibit;
406 nfastate *st;
407 nfaarc *ar;
408 int i, j;
409
410 ss = newbitset(nbits);
411 addclosure(ss, nf, nf->nf_start);
412 xx_state = (ss_state *)PyObject_MALLOC(sizeof(ss_state));
413 if (xx_state == NULL)
414 Py_FatalError("no mem for xx_state in makedfa");
415 xx_nstates = 1;
416 yy = &xx_state[0];
417 yy->ss_ss = ss;
418 yy->ss_narcs = 0;
419 yy->ss_arc = NULL;
420 yy->ss_deleted = 0;
421 yy->ss_finish = testbit(ss, nf->nf_finish);
422 if (yy->ss_finish)
423 printf("Error: nonterminal '%s' may produce empty.\n",
424 nf->nf_name);
425
426 /* This algorithm is from a book written before
427 the invention of structured programming... */
428
429 /* For each unmarked state... */
430 for (istate = 0; istate < xx_nstates; ++istate) {
431 size_t size;
432 yy = &xx_state[istate];
433 ss = yy->ss_ss;
434 /* For all its states... */
435 for (ibit = 0; ibit < nf->nf_nstates; ++ibit) {
436 if (!testbit(ss, ibit))
437 continue;
438 st = &nf->nf_state[ibit];
439 /* For all non-empty arcs from this state... */
440 for (iarc = 0; iarc < st->st_narcs; iarc++) {
441 ar = &st->st_arc[iarc];
442 if (ar->ar_label == EMPTY)
443 continue;
444 /* Look up in list of arcs from this state */
445 for (jarc = 0; jarc < yy->ss_narcs; ++jarc) {
446 zz = &yy->ss_arc[jarc];
447 if (ar->ar_label == zz->sa_label)
448 goto found;
449 }
450 /* Add new arc for this state */
451 size = sizeof(ss_arc) * (yy->ss_narcs + 1);
452 yy->ss_arc = (ss_arc *)PyObject_REALLOC(
453 yy->ss_arc, size);
454 if (yy->ss_arc == NULL)
455 Py_FatalError("out of mem");
456 zz = &yy->ss_arc[yy->ss_narcs++];
457 zz->sa_label = ar->ar_label;
458 zz->sa_bitset = newbitset(nbits);
459 zz->sa_arrow = -1;
460 found: ;
461 /* Add destination */
462 addclosure(zz->sa_bitset, nf, ar->ar_arrow);
463 }
464 }
465 /* Now look up all the arrow states */
466 for (jarc = 0; jarc < xx_state[istate].ss_narcs; jarc++) {
467 zz = &xx_state[istate].ss_arc[jarc];
468 for (jstate = 0; jstate < xx_nstates; jstate++) {
469 if (samebitset(zz->sa_bitset,
470 xx_state[jstate].ss_ss, nbits)) {
471 zz->sa_arrow = jstate;
472 goto done;
473 }
474 }
475 size = sizeof(ss_state) * (xx_nstates + 1);
476 xx_state = (ss_state *)PyObject_REALLOC(xx_state,
477 size);
478 if (xx_state == NULL)
479 Py_FatalError("out of mem");
480 zz->sa_arrow = xx_nstates;
481 yy = &xx_state[xx_nstates++];
482 yy->ss_ss = zz->sa_bitset;
483 yy->ss_narcs = 0;
484 yy->ss_arc = NULL;
485 yy->ss_deleted = 0;
486 yy->ss_finish = testbit(yy->ss_ss, nf->nf_finish);
487 done: ;
488 }
489 }
490
491 if (Py_DebugFlag)
492 printssdfa(xx_nstates, xx_state, nbits, &gr->gr_ll,
493 "before minimizing");
494
495 simplify(xx_nstates, xx_state);
496
497 if (Py_DebugFlag)
498 printssdfa(xx_nstates, xx_state, nbits, &gr->gr_ll,
499 "after minimizing");
500
501 convert(d, xx_nstates, xx_state);
502
503 for (i = 0; i < xx_nstates; i++) {
504 for (j = 0; j < xx_state[i].ss_narcs; j++)
505 delbitset(xx_state[i].ss_arc[j].sa_bitset);
506 PyObject_FREE(xx_state[i].ss_arc);
507 }
508 PyObject_FREE(xx_state);
509 }
510
511 static void
printssdfa(int xx_nstates,ss_state * xx_state,int nbits,labellist * ll,char * msg)512 printssdfa(int xx_nstates, ss_state *xx_state, int nbits,
513 labellist *ll, char *msg)
514 {
515 int i, ibit, iarc;
516 ss_state *yy;
517 ss_arc *zz;
518
519 printf("Subset DFA %s\n", msg);
520 for (i = 0; i < xx_nstates; i++) {
521 yy = &xx_state[i];
522 if (yy->ss_deleted)
523 continue;
524 printf(" Subset %d", i);
525 if (yy->ss_finish)
526 printf(" (finish)");
527 printf(" { ");
528 for (ibit = 0; ibit < nbits; ibit++) {
529 if (testbit(yy->ss_ss, ibit))
530 printf("%d ", ibit);
531 }
532 printf("}\n");
533 for (iarc = 0; iarc < yy->ss_narcs; iarc++) {
534 zz = &yy->ss_arc[iarc];
535 printf(" Arc to state %d, label %s\n",
536 zz->sa_arrow,
537 PyGrammar_LabelRepr(
538 &ll->ll_label[zz->sa_label]));
539 }
540 }
541 }
542
543
544 /* PART THREE -- SIMPLIFY DFA */
545
546 /* Simplify the DFA by repeatedly eliminating states that are
547 equivalent to another oner. This is NOT Algorithm 3.3 from
548 [Aho&Ullman 77]. It does not always finds the minimal DFA,
549 but it does usually make a much smaller one... (For an example
550 of sub-optimal behavior, try S: x a b+ | y a b+.)
551 */
552
553 static int
samestate(ss_state * s1,ss_state * s2)554 samestate(ss_state *s1, ss_state *s2)
555 {
556 int i;
557
558 if (s1->ss_narcs != s2->ss_narcs || s1->ss_finish != s2->ss_finish)
559 return 0;
560 for (i = 0; i < s1->ss_narcs; i++) {
561 if (s1->ss_arc[i].sa_arrow != s2->ss_arc[i].sa_arrow ||
562 s1->ss_arc[i].sa_label != s2->ss_arc[i].sa_label)
563 return 0;
564 }
565 return 1;
566 }
567
568 static void
renamestates(int xx_nstates,ss_state * xx_state,int from,int to)569 renamestates(int xx_nstates, ss_state *xx_state, int from, int to)
570 {
571 int i, j;
572
573 if (Py_DebugFlag)
574 printf("Rename state %d to %d.\n", from, to);
575 for (i = 0; i < xx_nstates; i++) {
576 if (xx_state[i].ss_deleted)
577 continue;
578 for (j = 0; j < xx_state[i].ss_narcs; j++) {
579 if (xx_state[i].ss_arc[j].sa_arrow == from)
580 xx_state[i].ss_arc[j].sa_arrow = to;
581 }
582 }
583 }
584
585 static void
simplify(int xx_nstates,ss_state * xx_state)586 simplify(int xx_nstates, ss_state *xx_state)
587 {
588 int changes;
589 int i, j;
590
591 do {
592 changes = 0;
593 for (i = 1; i < xx_nstates; i++) {
594 if (xx_state[i].ss_deleted)
595 continue;
596 for (j = 0; j < i; j++) {
597 if (xx_state[j].ss_deleted)
598 continue;
599 if (samestate(&xx_state[i], &xx_state[j])) {
600 xx_state[i].ss_deleted++;
601 renamestates(xx_nstates, xx_state,
602 i, j);
603 changes++;
604 break;
605 }
606 }
607 }
608 } while (changes);
609 }
610
611
612 /* PART FOUR -- GENERATE PARSING TABLES */
613
614 /* Convert the DFA into a grammar that can be used by our parser */
615
616 static void
convert(dfa * d,int xx_nstates,ss_state * xx_state)617 convert(dfa *d, int xx_nstates, ss_state *xx_state)
618 {
619 int i, j;
620 ss_state *yy;
621 ss_arc *zz;
622
623 for (i = 0; i < xx_nstates; i++) {
624 yy = &xx_state[i];
625 if (yy->ss_deleted)
626 continue;
627 yy->ss_rename = addstate(d);
628 }
629
630 for (i = 0; i < xx_nstates; i++) {
631 yy = &xx_state[i];
632 if (yy->ss_deleted)
633 continue;
634 for (j = 0; j < yy->ss_narcs; j++) {
635 zz = &yy->ss_arc[j];
636 addarc(d, yy->ss_rename,
637 xx_state[zz->sa_arrow].ss_rename,
638 zz->sa_label);
639 }
640 if (yy->ss_finish)
641 addarc(d, yy->ss_rename, yy->ss_rename, 0);
642 }
643
644 d->d_initial = 0;
645 }
646
647
648 /* PART FIVE -- GLUE IT ALL TOGETHER */
649
650 static grammar *
maketables(nfagrammar * gr)651 maketables(nfagrammar *gr)
652 {
653 int i;
654 nfa *nf;
655 dfa *d;
656 grammar *g;
657
658 if (gr->gr_nnfas == 0)
659 return NULL;
660 g = newgrammar(gr->gr_nfa[0]->nf_type);
661 /* XXX first rule must be start rule */
662 g->g_ll = gr->gr_ll;
663
664 for (i = 0; i < gr->gr_nnfas; i++) {
665 nf = gr->gr_nfa[i];
666 if (Py_DebugFlag) {
667 printf("Dump of NFA for '%s' ...\n", nf->nf_name);
668 dumpnfa(&gr->gr_ll, nf);
669 printf("Making DFA for '%s' ...\n", nf->nf_name);
670 }
671 d = adddfa(g, nf->nf_type, nf->nf_name);
672 makedfa(gr, gr->gr_nfa[i], d);
673 }
674
675 return g;
676 }
677
678 grammar *
pgen(node * n)679 pgen(node *n)
680 {
681 nfagrammar *gr;
682 grammar *g;
683
684 gr = metacompile(n);
685 g = maketables(gr);
686 translatelabels(g);
687 addfirstsets(g);
688 freenfagrammar(gr);
689 return g;
690 }
691
692 grammar *
Py_pgen(node * n)693 Py_pgen(node *n)
694 {
695 return pgen(n);
696 }
697
698 /*
699
700 Description
701 -----------
702
703 Input is a grammar in extended BNF (using * for repetition, + for
704 at-least-once repetition, [] for optional parts, | for alternatives and
705 () for grouping). This has already been parsed and turned into a parse
706 tree.
707
708 Each rule is considered as a regular expression in its own right.
709 It is turned into a Non-deterministic Finite Automaton (NFA), which
710 is then turned into a Deterministic Finite Automaton (DFA), which is then
711 optimized to reduce the number of states. See [Aho&Ullman 77] chapter 3,
712 or similar compiler books (this technique is more often used for lexical
713 analyzers).
714
715 The DFA's are used by the parser as parsing tables in a special way
716 that's probably unique. Before they are usable, the FIRST sets of all
717 non-terminals are computed.
718
719 Reference
720 ---------
721
722 [Aho&Ullman 77]
723 Aho&Ullman, Principles of Compiler Design, Addison-Wesley 1977
724 (first edition)
725
726 */
727