pgen.c revision 114900298ea26e5e25edd5d05f24648dcd5ea95b 
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
13extern int Py_DebugFlag;
14extern int Py_IgnoreEnvironmentFlag; /* needed by Py_GETENV */
15
16
17/* PART ONE -- CONSTRUCT NFA -- Cf. Algorithm 3.2 from [Aho&Ullman 77] */
18
19typedef struct _nfaarc {
20	int	ar_label;
21	int	ar_arrow;
22} nfaarc;
23
24typedef struct _nfastate {
25	int	st_narcs;
26	nfaarc	*st_arc;
27} nfastate;
28
29typedef 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 */
38static void compile_rhs(labellist *ll,
39			nfa *nf, node *n, int *pa, int *pb);
40static void compile_alt(labellist *ll,
41			nfa *nf, node *n, int *pa, int *pb);
42static void compile_item(labellist *ll,
43			 nfa *nf, node *n, int *pa, int *pb);
44static void compile_atom(labellist *ll,
45			 nfa *nf, node *n, int *pa, int *pb);
46
47static int
48addnfastate(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
62static void
63addnfaarc(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
78static nfa *
79newnfa(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
95typedef struct _nfagrammar {
96	int		gr_nnfas;
97	nfa		**gr_nfa;
98	labellist	gr_ll;
99} nfagrammar;
100
101/* Forward */
102static void compile_rule(nfagrammar *gr, node *n);
103
104static nfagrammar *
105newnfagrammar(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
120static nfa *
121addnfa(nfagrammar *gr, char *name)
122{
123	nfa *nf;
124
125	nf = newnfa(name);
126	gr->gr_nfa = (nfa **)PyObject_REALLOC(gr->gr_nfa,
127				      sizeof(nfa) * (gr->gr_nnfas + 1));
128	if (gr->gr_nfa == NULL)
129		Py_FatalError("out of mem");
130	gr->gr_nfa[gr->gr_nnfas++] = nf;
131	addlabel(&gr->gr_ll, NAME, nf->nf_name);
132	return nf;
133}
134
135#ifdef Py_DEBUG
136
137static char REQNFMT[] = "metacompile: less than %d children\n";
138
139#define REQN(i, count) \
140 	if (i < count) { \
141		fprintf(stderr, REQNFMT, count); \
142		Py_FatalError("REQN"); \
143	} else
144
145#else
146#define REQN(i, count)	/* empty */
147#endif
148
149static nfagrammar *
150metacompile(node *n)
151{
152	nfagrammar *gr;
153	int i;
154
155	if (Py_DebugFlag)
156		printf("Compiling (meta-) parse tree into NFA grammar\n");
157	gr = newnfagrammar();
158	REQ(n, MSTART);
159	i = n->n_nchildren - 1; /* Last child is ENDMARKER */
160	n = n->n_child;
161	for (; --i >= 0; n++) {
162		if (n->n_type != NEWLINE)
163			compile_rule(gr, n);
164	}
165	return gr;
166}
167
168static void
169compile_rule(nfagrammar *gr, node *n)
170{
171	nfa *nf;
172
173	REQ(n, RULE);
174	REQN(n->n_nchildren, 4);
175	n = n->n_child;
176	REQ(n, NAME);
177	nf = addnfa(gr, n->n_str);
178	n++;
179	REQ(n, COLON);
180	n++;
181	REQ(n, RHS);
182	compile_rhs(&gr->gr_ll, nf, n, &nf->nf_start, &nf->nf_finish);
183	n++;
184	REQ(n, NEWLINE);
185}
186
187static void
188compile_rhs(labellist *ll, nfa *nf, node *n, int *pa, int *pb)
189{
190	int i;
191	int a, b;
192
193	REQ(n, RHS);
194	i = n->n_nchildren;
195	REQN(i, 1);
196	n = n->n_child;
197	REQ(n, ALT);
198	compile_alt(ll, nf, n, pa, pb);
199	if (--i <= 0)
200		return;
201	n++;
202	a = *pa;
203	b = *pb;
204	*pa = addnfastate(nf);
205	*pb = addnfastate(nf);
206	addnfaarc(nf, *pa, a, EMPTY);
207	addnfaarc(nf, b, *pb, EMPTY);
208	for (; --i >= 0; n++) {
209		REQ(n, VBAR);
210		REQN(i, 1);
211		--i;
212		n++;
213		REQ(n, ALT);
214		compile_alt(ll, nf, n, &a, &b);
215		addnfaarc(nf, *pa, a, EMPTY);
216		addnfaarc(nf, b, *pb, EMPTY);
217	}
218}
219
220static void
221compile_alt(labellist *ll, nfa *nf, node *n, int *pa, int *pb)
222{
223	int i;
224	int a, b;
225
226	REQ(n, ALT);
227	i = n->n_nchildren;
228	REQN(i, 1);
229	n = n->n_child;
230	REQ(n, ITEM);
231	compile_item(ll, nf, n, pa, pb);
232	--i;
233	n++;
234	for (; --i >= 0; n++) {
235		REQ(n, ITEM);
236		compile_item(ll, nf, n, &a, &b);
237		addnfaarc(nf, *pb, a, EMPTY);
238		*pb = b;
239	}
240}
241
242static void
243compile_item(labellist *ll, nfa *nf, node *n, int *pa, int *pb)
244{
245	int i;
246	int a, b;
247
248	REQ(n, ITEM);
249	i = n->n_nchildren;
250	REQN(i, 1);
251	n = n->n_child;
252	if (n->n_type == LSQB) {
253		REQN(i, 3);
254		n++;
255		REQ(n, RHS);
256		*pa = addnfastate(nf);
257		*pb = addnfastate(nf);
258		addnfaarc(nf, *pa, *pb, EMPTY);
259		compile_rhs(ll, nf, n, &a, &b);
260		addnfaarc(nf, *pa, a, EMPTY);
261		addnfaarc(nf, b, *pb, EMPTY);
262		REQN(i, 1);
263		n++;
264		REQ(n, RSQB);
265	}
266	else {
267		compile_atom(ll, nf, n, pa, pb);
268		if (--i <= 0)
269			return;
270		n++;
271		addnfaarc(nf, *pb, *pa, EMPTY);
272		if (n->n_type == STAR)
273			*pb = *pa;
274		else
275			REQ(n, PLUS);
276	}
277}
278
279static void
280compile_atom(labellist *ll, nfa *nf, node *n, int *pa, int *pb)
281{
282	int i;
283
284	REQ(n, ATOM);
285	i = n->n_nchildren;
286	REQN(i, 1);
287	n = n->n_child;
288	if (n->n_type == LPAR) {
289		REQN(i, 3);
290		n++;
291		REQ(n, RHS);
292		compile_rhs(ll, nf, n, pa, pb);
293		n++;
294		REQ(n, RPAR);
295	}
296	else if (n->n_type == NAME || n->n_type == STRING) {
297		*pa = addnfastate(nf);
298		*pb = addnfastate(nf);
299		addnfaarc(nf, *pa, *pb, addlabel(ll, n->n_type, n->n_str));
300	}
301	else
302		REQ(n, NAME);
303}
304
305static void
306dumpstate(labellist *ll, nfa *nf, int istate)
307{
308	nfastate *st;
309	int i;
310	nfaarc *ar;
311
312	printf("%c%2d%c",
313		istate == nf->nf_start ? '*' : ' ',
314		istate,
315		istate == nf->nf_finish ? '.' : ' ');
316	st = &nf->nf_state[istate];
317	ar = st->st_arc;
318	for (i = 0; i < st->st_narcs; i++) {
319		if (i > 0)
320			printf("\n    ");
321		printf("-> %2d  %s", ar->ar_arrow,
322			PyGrammar_LabelRepr(&ll->ll_label[ar->ar_label]));
323		ar++;
324	}
325	printf("\n");
326}
327
328static void
329dumpnfa(labellist *ll, nfa *nf)
330{
331	int i;
332
333	printf("NFA '%s' has %d states; start %d, finish %d\n",
334		nf->nf_name, nf->nf_nstates, nf->nf_start, nf->nf_finish);
335	for (i = 0; i < nf->nf_nstates; i++)
336		dumpstate(ll, nf, i);
337}
338
339
340/* PART TWO -- CONSTRUCT DFA -- Algorithm 3.1 from [Aho&Ullman 77] */
341
342static void
343addclosure(bitset ss, nfa *nf, int istate)
344{
345	if (addbit(ss, istate)) {
346		nfastate *st = &nf->nf_state[istate];
347		nfaarc *ar = st->st_arc;
348		int i;
349
350		for (i = st->st_narcs; --i >= 0; ) {
351			if (ar->ar_label == EMPTY)
352				addclosure(ss, nf, ar->ar_arrow);
353			ar++;
354		}
355	}
356}
357
358typedef struct _ss_arc {
359	bitset	sa_bitset;
360	int	sa_arrow;
361	int	sa_label;
362} ss_arc;
363
364typedef struct _ss_state {
365	bitset	ss_ss;
366	int	ss_narcs;
367	struct _ss_arc	*ss_arc;
368	int	ss_deleted;
369	int	ss_finish;
370	int	ss_rename;
371} ss_state;
372
373typedef struct _ss_dfa {
374	int	sd_nstates;
375	ss_state *sd_state;
376} ss_dfa;
377
378/* Forward */
379static void printssdfa(int xx_nstates, ss_state *xx_state, int nbits,
380		       labellist *ll, char *msg);
381static void simplify(int xx_nstates, ss_state *xx_state);
382static void convert(dfa *d, int xx_nstates, ss_state *xx_state);
383
384static void
385makedfa(nfagrammar *gr, nfa *nf, dfa *d)
386{
387	int nbits = nf->nf_nstates;
388	bitset ss;
389	int xx_nstates;
390	ss_state *xx_state, *yy;
391	ss_arc *zz;
392	int istate, jstate, iarc, jarc, ibit;
393	nfastate *st;
394	nfaarc *ar;
395
396	ss = newbitset(nbits);
397	addclosure(ss, nf, nf->nf_start);
398	xx_state = (ss_state *)PyObject_MALLOC(sizeof(ss_state));
399	if (xx_state == NULL)
400		Py_FatalError("no mem for xx_state in makedfa");
401	xx_nstates = 1;
402	yy = &xx_state[0];
403	yy->ss_ss = ss;
404	yy->ss_narcs = 0;
405	yy->ss_arc = NULL;
406	yy->ss_deleted = 0;
407	yy->ss_finish = testbit(ss, nf->nf_finish);
408	if (yy->ss_finish)
409		printf("Error: nonterminal '%s' may produce empty.\n",
410			nf->nf_name);
411
412	/* This algorithm is from a book written before
413	   the invention of structured programming... */
414
415	/* For each unmarked state... */
416	for (istate = 0; istate < xx_nstates; ++istate) {
417		size_t size;
418		yy = &xx_state[istate];
419		ss = yy->ss_ss;
420		/* For all its states... */
421		for (ibit = 0; ibit < nf->nf_nstates; ++ibit) {
422			if (!testbit(ss, ibit))
423				continue;
424			st = &nf->nf_state[ibit];
425			/* For all non-empty arcs from this state... */
426			for (iarc = 0; iarc < st->st_narcs; iarc++) {
427				ar = &st->st_arc[iarc];
428				if (ar->ar_label == EMPTY)
429					continue;
430				/* Look up in list of arcs from this state */
431				for (jarc = 0; jarc < yy->ss_narcs; ++jarc) {
432					zz = &yy->ss_arc[jarc];
433					if (ar->ar_label == zz->sa_label)
434						goto found;
435				}
436				/* Add new arc for this state */
437				size = sizeof(ss_arc) * (yy->ss_narcs + 1);
438				yy->ss_arc = (ss_arc *)PyObject_REALLOC(
439                                                            yy->ss_arc, size);
440				if (yy->ss_arc == NULL)
441					Py_FatalError("out of mem");
442				zz = &yy->ss_arc[yy->ss_narcs++];
443				zz->sa_label = ar->ar_label;
444				zz->sa_bitset = newbitset(nbits);
445				zz->sa_arrow = -1;
446			 found:	;
447				/* Add destination */
448				addclosure(zz->sa_bitset, nf, ar->ar_arrow);
449			}
450		}
451		/* Now look up all the arrow states */
452		for (jarc = 0; jarc < xx_state[istate].ss_narcs; jarc++) {
453			zz = &xx_state[istate].ss_arc[jarc];
454			for (jstate = 0; jstate < xx_nstates; jstate++) {
455				if (samebitset(zz->sa_bitset,
456					xx_state[jstate].ss_ss, nbits)) {
457					zz->sa_arrow = jstate;
458					goto done;
459				}
460			}
461			size = sizeof(ss_state) * (xx_nstates + 1);
462			xx_state = (ss_state *)PyObject_REALLOC(xx_state,
463                                                                    size);
464			if (xx_state == NULL)
465				Py_FatalError("out of mem");
466			zz->sa_arrow = xx_nstates;
467			yy = &xx_state[xx_nstates++];
468			yy->ss_ss = zz->sa_bitset;
469			yy->ss_narcs = 0;
470			yy->ss_arc = NULL;
471			yy->ss_deleted = 0;
472			yy->ss_finish = testbit(yy->ss_ss, nf->nf_finish);
473		 done:	;
474		}
475	}
476
477	if (Py_DebugFlag)
478		printssdfa(xx_nstates, xx_state, nbits, &gr->gr_ll,
479						"before minimizing");
480
481	simplify(xx_nstates, xx_state);
482
483	if (Py_DebugFlag)
484		printssdfa(xx_nstates, xx_state, nbits, &gr->gr_ll,
485						"after minimizing");
486
487	convert(d, xx_nstates, xx_state);
488
489	/* XXX cleanup */
490}
491
492static void
493printssdfa(int xx_nstates, ss_state *xx_state, int nbits,
494	   labellist *ll, char *msg)
495{
496	int i, ibit, iarc;
497	ss_state *yy;
498	ss_arc *zz;
499
500	printf("Subset DFA %s\n", msg);
501	for (i = 0; i < xx_nstates; i++) {
502		yy = &xx_state[i];
503		if (yy->ss_deleted)
504			continue;
505		printf(" Subset %d", i);
506		if (yy->ss_finish)
507			printf(" (finish)");
508		printf(" { ");
509		for (ibit = 0; ibit < nbits; ibit++) {
510			if (testbit(yy->ss_ss, ibit))
511				printf("%d ", ibit);
512		}
513		printf("}\n");
514		for (iarc = 0; iarc < yy->ss_narcs; iarc++) {
515			zz = &yy->ss_arc[iarc];
516			printf("  Arc to state %d, label %s\n",
517				zz->sa_arrow,
518				PyGrammar_LabelRepr(
519					&ll->ll_label[zz->sa_label]));
520		}
521	}
522}
523
524
525/* PART THREE -- SIMPLIFY DFA */
526
527/* Simplify the DFA by repeatedly eliminating states that are
528   equivalent to another oner.  This is NOT Algorithm 3.3 from
529   [Aho&Ullman 77].  It does not always finds the minimal DFA,
530   but it does usually make a much smaller one...  (For an example
531   of sub-optimal behavior, try S: x a b+ | y a b+.)
532*/
533
534static int
535samestate(ss_state *s1, ss_state *s2)
536{
537	int i;
538
539	if (s1->ss_narcs != s2->ss_narcs || s1->ss_finish != s2->ss_finish)
540		return 0;
541	for (i = 0; i < s1->ss_narcs; i++) {
542		if (s1->ss_arc[i].sa_arrow != s2->ss_arc[i].sa_arrow ||
543			s1->ss_arc[i].sa_label != s2->ss_arc[i].sa_label)
544			return 0;
545	}
546	return 1;
547}
548
549static void
550renamestates(int xx_nstates, ss_state *xx_state, int from, int to)
551{
552	int i, j;
553
554	if (Py_DebugFlag)
555		printf("Rename state %d to %d.\n", from, to);
556	for (i = 0; i < xx_nstates; i++) {
557		if (xx_state[i].ss_deleted)
558			continue;
559		for (j = 0; j < xx_state[i].ss_narcs; j++) {
560			if (xx_state[i].ss_arc[j].sa_arrow == from)
561				xx_state[i].ss_arc[j].sa_arrow = to;
562		}
563	}
564}
565
566static void
567simplify(int xx_nstates, ss_state *xx_state)
568{
569	int changes;
570	int i, j;
571
572	do {
573		changes = 0;
574		for (i = 1; i < xx_nstates; i++) {
575			if (xx_state[i].ss_deleted)
576				continue;
577			for (j = 0; j < i; j++) {
578				if (xx_state[j].ss_deleted)
579					continue;
580				if (samestate(&xx_state[i], &xx_state[j])) {
581					xx_state[i].ss_deleted++;
582					renamestates(xx_nstates, xx_state,
583						     i, j);
584					changes++;
585					break;
586				}
587			}
588		}
589	} while (changes);
590}
591
592
593/* PART FOUR -- GENERATE PARSING TABLES */
594
595/* Convert the DFA into a grammar that can be used by our parser */
596
597static void
598convert(dfa *d, int xx_nstates, ss_state *xx_state)
599{
600	int i, j;
601	ss_state *yy;
602	ss_arc *zz;
603
604	for (i = 0; i < xx_nstates; i++) {
605		yy = &xx_state[i];
606		if (yy->ss_deleted)
607			continue;
608		yy->ss_rename = addstate(d);
609	}
610
611	for (i = 0; i < xx_nstates; i++) {
612		yy = &xx_state[i];
613		if (yy->ss_deleted)
614			continue;
615		for (j = 0; j < yy->ss_narcs; j++) {
616			zz = &yy->ss_arc[j];
617			addarc(d, yy->ss_rename,
618				xx_state[zz->sa_arrow].ss_rename,
619				zz->sa_label);
620		}
621		if (yy->ss_finish)
622			addarc(d, yy->ss_rename, yy->ss_rename, 0);
623	}
624
625	d->d_initial = 0;
626}
627
628
629/* PART FIVE -- GLUE IT ALL TOGETHER */
630
631static grammar *
632maketables(nfagrammar *gr)
633{
634	int i;
635	nfa *nf;
636	dfa *d;
637	grammar *g;
638
639	if (gr->gr_nnfas == 0)
640		return NULL;
641	g = newgrammar(gr->gr_nfa[0]->nf_type);
642			/* XXX first rule must be start rule */
643	g->g_ll = gr->gr_ll;
644
645	for (i = 0; i < gr->gr_nnfas; i++) {
646		nf = gr->gr_nfa[i];
647		if (Py_DebugFlag) {
648			printf("Dump of NFA for '%s' ...\n", nf->nf_name);
649			dumpnfa(&gr->gr_ll, nf);
650			printf("Making DFA for '%s' ...\n", nf->nf_name);
651		}
652		d = adddfa(g, nf->nf_type, nf->nf_name);
653		makedfa(gr, gr->gr_nfa[i], d);
654	}
655
656	return g;
657}
658
659grammar *
660pgen(node *n)
661{
662	nfagrammar *gr;
663	grammar *g;
664
665	gr = metacompile(n);
666	g = maketables(gr);
667	translatelabels(g);
668	addfirstsets(g);
669	return g;
670}
671
672grammar *
673Py_pgen(node *n)
674{
675  return pgen(n);
676}
677
678/*
679
680Description
681-----------
682
683Input is a grammar in extended BNF (using * for repetition, + for
684at-least-once repetition, [] for optional parts, | for alternatives and
685() for grouping).  This has already been parsed and turned into a parse
686tree.
687
688Each rule is considered as a regular expression in its own right.
689It is turned into a Non-deterministic Finite Automaton (NFA), which
690is then turned into a Deterministic Finite Automaton (DFA), which is then
691optimized to reduce the number of states.  See [Aho&Ullman 77] chapter 3,
692or similar compiler books (this technique is more often used for lexical
693analyzers).
694
695The DFA's are used by the parser as parsing tables in a special way
696that's probably unique.  Before they are usable, the FIRST sets of all
697non-terminals are computed.
698
699Reference
700---------
701
702[Aho&Ullman 77]
703	Aho&Ullman, Principles of Compiler Design, Addison-Wesley 1977
704	(first edition)
705
706*/
707