Initial revision

1 files changed, 729 insertions, 0 deletions

diff --git a/Parser/pgen.c b/Parser/pgen.c
new file mode 100644
index 0000000..34d9b71
--- /dev/null
+++ b/Parser/pgen.c
@@ -0,0 +1,729 @@
+/* Parser generator */
+
+/* For a description, see the comments at end of this file */
+
+#include <stdio.h>
+#include "assert.h"
+
+#include "PROTO.h"
+#include "malloc.h"
+#include "token.h"
+#include "node.h"
+#include "grammar.h"
+#include "metagrammar.h"
+#include "pgen.h"
+
+extern int debugging;
+
+
+/* PART ONE -- CONSTRUCT NFA -- Cf. Algorithm 3.2 from [Aho&Ullman 77] */
+
+typedef struct _nfaarc {
+	int	ar_label;
+	int	ar_arrow;
+} nfaarc;
+
+typedef struct _nfastate {
+	int	st_narcs;
+	nfaarc	*st_arc;
+} nfastate;
+
+typedef struct _nfa {
+	int		nf_type;
+	char		*nf_name;
+	int		nf_nstates;
+	nfastate	*nf_state;
+	int		nf_start, nf_finish;
+} nfa;
+
+static int
+addnfastate(nf)
+	nfa *nf;
+{
+	nfastate *st;
+	
+	RESIZE(nf->nf_state, nfastate, nf->nf_nstates + 1);
+	if (nf->nf_state == NULL)
+		fatal("out of mem");
+	st = &nf->nf_state[nf->nf_nstates++];
+	st->st_narcs = 0;
+	st->st_arc = NULL;
+	return st - nf->nf_state;
+}
+
+static void
+addnfaarc(nf, from, to, lbl)
+	nfa *nf;
+	int from, to, lbl;
+{
+	nfastate *st;
+	nfaarc *ar;
+	
+	st = &nf->nf_state[from];
+	RESIZE(st->st_arc, nfaarc, st->st_narcs + 1);
+	if (st->st_arc == NULL)
+		fatal("out of mem");
+	ar = &st->st_arc[st->st_narcs++];
+	ar->ar_label = lbl;
+	ar->ar_arrow = to;
+}
+
+static nfa *
+newnfa(name)
+	char *name;
+{
+	nfa *nf;
+	static type = NT_OFFSET; /* All types will be disjunct */
+	
+	nf = NEW(nfa, 1);
+	if (nf == NULL)
+		fatal("no mem for new nfa");
+	nf->nf_type = type++;
+	nf->nf_name = name; /* XXX strdup(name) ??? */
+	nf->nf_nstates = 0;
+	nf->nf_state = NULL;
+	nf->nf_start = nf->nf_finish = -1;
+	return nf;
+}
+
+typedef struct _nfagrammar {
+	int		gr_nnfas;
+	nfa		**gr_nfa;
+	labellist	gr_ll;
+} nfagrammar;
+
+static nfagrammar *
+newnfagrammar()
+{
+	nfagrammar *gr;
+	
+	gr = NEW(nfagrammar, 1);
+	if (gr == NULL)
+		fatal("no mem for new nfa grammar");
+	gr->gr_nnfas = 0;
+	gr->gr_nfa = NULL;
+	gr->gr_ll.ll_nlabels = 0;
+	gr->gr_ll.ll_label = NULL;
+	addlabel(&gr->gr_ll, ENDMARKER, "EMPTY");
+	return gr;
+}
+
+static nfa *
+addnfa(gr, name)
+	nfagrammar *gr;
+	char *name;
+{
+	nfa *nf;
+	
+	nf = newnfa(name);
+	RESIZE(gr->gr_nfa, nfa *, gr->gr_nnfas + 1);
+	if (gr->gr_nfa == NULL)
+		fatal("out of mem");
+	gr->gr_nfa[gr->gr_nnfas++] = nf;
+	addlabel(&gr->gr_ll, NAME, nf->nf_name);
+	return nf;
+}
+
+#ifdef DEBUG
+
+static char REQNFMT[] = "metacompile: less than %d children\n";
+
+#define REQN(i, count) \
+ 	if (i < count) { \
+		fprintf(stderr, REQNFMT, count); \
+		abort(); \
+	} else
+
+#else
+#define REQN(i, count)	/* empty */
+#endif
+
+static nfagrammar *
+metacompile(n)
+	node *n;
+{
+	nfagrammar *gr;
+	int i;
+	
+	printf("Compiling (meta-) parse tree into NFA grammar\n");
+	gr = newnfagrammar();
+	REQ(n, MSTART);
+	i = n->n_nchildren - 1; /* Last child is ENDMARKER */
+	n = n->n_child;
+	for (; --i >= 0; n++) {
+		if (n->n_type != NEWLINE)
+			compile_rule(gr, n);
+	}
+	return gr;
+}
+
+static
+compile_rule(gr, n)
+	nfagrammar *gr;
+	node *n;
+{
+	nfa *nf;
+	
+	REQ(n, RULE);
+	REQN(n->n_nchildren, 4);
+	n = n->n_child;
+	REQ(n, NAME);
+	nf = addnfa(gr, n->n_str);
+	n++;
+	REQ(n, COLON);
+	n++;
+	REQ(n, RHS);
+	compile_rhs(&gr->gr_ll, nf, n, &nf->nf_start, &nf->nf_finish);
+	n++;
+	REQ(n, NEWLINE);
+}
+
+static
+compile_rhs(ll, nf, n, pa, pb)
+	labellist *ll;
+	nfa *nf;
+	node *n;
+	int *pa, *pb;
+{
+	int i;
+	int a, b;
+	
+	REQ(n, RHS);
+	i = n->n_nchildren;
+	REQN(i, 1);
+	n = n->n_child;
+	REQ(n, ALT);
+	compile_alt(ll, nf, n, pa, pb);
+	if (--i <= 0)
+		return;
+	n++;
+	a = *pa;
+	b = *pb;
+	*pa = addnfastate(nf);
+	*pb = addnfastate(nf);
+	addnfaarc(nf, *pa, a, EMPTY);
+	addnfaarc(nf, b, *pb, EMPTY);
+	for (; --i >= 0; n++) {
+		REQ(n, VBAR);
+		REQN(i, 1);
+		--i;
+		n++;
+		REQ(n, ALT);
+		compile_alt(ll, nf, n, &a, &b);
+		addnfaarc(nf, *pa, a, EMPTY);
+		addnfaarc(nf, b, *pb, EMPTY);
+	}
+}
+
+static
+compile_alt(ll, nf, n, pa, pb)
+	labellist *ll;
+	nfa *nf;
+	node *n;
+	int *pa, *pb;
+{
+	int i;
+	int a, b;
+	
+	REQ(n, ALT);
+	i = n->n_nchildren;
+	REQN(i, 1);
+	n = n->n_child;
+	REQ(n, ITEM);
+	compile_item(ll, nf, n, pa, pb);
+	--i;
+	n++;
+	for (; --i >= 0; n++) {
+		if (n->n_type == COMMA) { /* XXX Temporary */
+			REQN(i, 1);
+			--i;
+			n++;
+		}
+		REQ(n, ITEM);
+		compile_item(ll, nf, n, &a, &b);
+		addnfaarc(nf, *pb, a, EMPTY);
+		*pb = b;
+	}
+}
+
+static
+compile_item(ll, nf, n, pa, pb)
+	labellist *ll;
+	nfa *nf;
+	node *n;
+	int *pa, *pb;
+{
+	int i;
+	int a, b;
+	
+	REQ(n, ITEM);
+	i = n->n_nchildren;
+	REQN(i, 1);
+	n = n->n_child;
+	if (n->n_type == LSQB) {
+		REQN(i, 3);
+		n++;
+		REQ(n, RHS);
+		*pa = addnfastate(nf);
+		*pb = addnfastate(nf);
+		addnfaarc(nf, *pa, *pb, EMPTY);
+		compile_rhs(ll, nf, n, &a, &b);
+		addnfaarc(nf, *pa, a, EMPTY);
+		addnfaarc(nf, b, *pb, EMPTY);
+		REQN(i, 1);
+		n++;
+		REQ(n, RSQB);
+	}
+	else {
+		compile_atom(ll, nf, n, pa, pb);
+		if (--i <= 0)
+			return;
+		n++;
+		addnfaarc(nf, *pb, *pa, EMPTY);
+		if (n->n_type == STAR)
+			*pb = *pa;
+		else
+			REQ(n, PLUS);
+	}
+}
+
+static
+compile_atom(ll, nf, n, pa, pb)
+	labellist *ll;
+	nfa *nf;
+	node *n;
+	int *pa, *pb;
+{
+	int i;
+	
+	REQ(n, ATOM);
+	i = n->n_nchildren;
+	REQN(i, 1);
+	n = n->n_child;
+	if (n->n_type == LPAR) {
+		REQN(i, 3);
+		n++;
+		REQ(n, RHS);
+		compile_rhs(ll, nf, n, pa, pb);
+		n++;
+		REQ(n, RPAR);
+	}
+	else if (n->n_type == NAME || n->n_type == STRING) {
+		*pa = addnfastate(nf);
+		*pb = addnfastate(nf);
+		addnfaarc(nf, *pa, *pb, addlabel(ll, n->n_type, n->n_str));
+	}
+	else
+		REQ(n, NAME);
+}
+
+static void
+dumpstate(ll, nf, istate)
+	labellist *ll;
+	nfa *nf;
+	int istate;
+{
+	nfastate *st;
+	int i;
+	nfaarc *ar;
+	
+	printf("%c%2d%c",
+		istate == nf->nf_start ? '*' : ' ',
+		istate,
+		istate == nf->nf_finish ? '.' : ' ');
+	st = &nf->nf_state[istate];
+	ar = st->st_arc;
+	for (i = 0; i < st->st_narcs; i++) {
+		if (i > 0)
+			printf("\n    ");
+		printf("-> %2d  %s", ar->ar_arrow,
+			labelrepr(&ll->ll_label[ar->ar_label]));
+		ar++;
+	}
+	printf("\n");
+}
+
+static void
+dumpnfa(ll, nf)
+	labellist *ll;
+	nfa *nf;
+{
+	int i;
+	
+	printf("NFA '%s' has %d states; start %d, finish %d\n",
+		nf->nf_name, nf->nf_nstates, nf->nf_start, nf->nf_finish);
+	for (i = 0; i < nf->nf_nstates; i++)
+		dumpstate(ll, nf, i);
+}
+
+
+/* PART TWO -- CONSTRUCT DFA -- Algorithm 3.1 from [Aho&Ullman 77] */
+
+static int
+addclosure(ss, nf, istate)
+	bitset ss;
+	nfa *nf;
+	int istate;
+{
+	if (addbit(ss, istate)) {
+		nfastate *st = &nf->nf_state[istate];
+		nfaarc *ar = st->st_arc;
+		int i;
+		
+		for (i = st->st_narcs; --i >= 0; ) {
+			if (ar->ar_label == EMPTY)
+				addclosure(ss, nf, ar->ar_arrow);
+			ar++;
+		}
+	}
+}
+
+typedef struct _ss_arc {
+	bitset	sa_bitset;
+	int	sa_arrow;
+	int	sa_label;
+} ss_arc;
+
+typedef struct _ss_state {
+	bitset	ss_ss;
+	int	ss_narcs;
+	ss_arc	*ss_arc;
+	int	ss_deleted;
+	int	ss_finish;
+	int	ss_rename;
+} ss_state;
+
+typedef struct _ss_dfa {
+	int	sd_nstates;
+	ss_state *sd_state;
+} ss_dfa;
+
+static
+makedfa(gr, nf, d)
+	nfagrammar *gr;
+	nfa *nf;
+	dfa *d;
+{
+	int nbits = nf->nf_nstates;
+	bitset ss;
+	int xx_nstates;
+	ss_state *xx_state, *yy;
+	ss_arc *zz;
+	int istate, jstate, iarc, jarc, ibit;
+	nfastate *st;
+	nfaarc *ar;
+	
+	ss = newbitset(nbits);
+	addclosure(ss, nf, nf->nf_start);
+	xx_state = NEW(ss_state, 1);
+	if (xx_state == NULL)
+		fatal("no mem for xx_state in makedfa");
+	xx_nstates = 1;
+	yy = &xx_state[0];
+	yy->ss_ss = ss;
+	yy->ss_narcs = 0;
+	yy->ss_arc = NULL;
+	yy->ss_deleted = 0;
+	yy->ss_finish = testbit(ss, nf->nf_finish);
+	if (yy->ss_finish)
+		printf("Error: nonterminal '%s' may produce empty.\n",
+			nf->nf_name);
+	
+	/* This algorithm is from a book written before
+	   the invention of structured programming... */
+
+	/* For each unmarked state... */
+	for (istate = 0; istate < xx_nstates; ++istate) {
+		yy = &xx_state[istate];
+		ss = yy->ss_ss;
+		/* For all its states... */
+		for (ibit = 0; ibit < nf->nf_nstates; ++ibit) {
+			if (!testbit(ss, ibit))
+				continue;
+			st = &nf->nf_state[ibit];
+			/* For all non-empty arcs from this state... */
+			for (iarc = 0; iarc < st->st_narcs; iarc++) {
+				ar = &st->st_arc[iarc];
+				if (ar->ar_label == EMPTY)
+					continue;
+				/* Look up in list of arcs from this state */
+				for (jarc = 0; jarc < yy->ss_narcs; ++jarc) {
+					zz = &yy->ss_arc[jarc];
+					if (ar->ar_label == zz->sa_label)
+						goto found;
+				}
+				/* Add new arc for this state */
+				RESIZE(yy->ss_arc, ss_arc, yy->ss_narcs + 1);
+				if (yy->ss_arc == NULL)
+					fatal("out of mem");
+				zz = &yy->ss_arc[yy->ss_narcs++];
+				zz->sa_label = ar->ar_label;
+				zz->sa_bitset = newbitset(nbits);
+				zz->sa_arrow = -1;
+			 found:	;
+				/* Add destination */
+				addclosure(zz->sa_bitset, nf, ar->ar_arrow);
+			}
+		}
+		/* Now look up all the arrow states */
+		for (jarc = 0; jarc < xx_state[istate].ss_narcs; jarc++) {
+			zz = &xx_state[istate].ss_arc[jarc];
+			for (jstate = 0; jstate < xx_nstates; jstate++) {
+				if (samebitset(zz->sa_bitset,
+					xx_state[jstate].ss_ss, nbits)) {
+					zz->sa_arrow = jstate;
+					goto done;
+				}
+			}
+			RESIZE(xx_state, ss_state, xx_nstates + 1);
+			if (xx_state == NULL)
+				fatal("out of mem");
+			zz->sa_arrow = xx_nstates;
+			yy = &xx_state[xx_nstates++];
+			yy->ss_ss = zz->sa_bitset;
+			yy->ss_narcs = 0;
+			yy->ss_arc = NULL;
+			yy->ss_deleted = 0;
+			yy->ss_finish = testbit(yy->ss_ss, nf->nf_finish);
+		 done:	;
+		}
+	}
+	
+	if (debugging)
+		printssdfa(xx_nstates, xx_state, nbits, &gr->gr_ll,
+						"before minimizing");
+	
+	simplify(xx_nstates, xx_state);
+	
+	if (debugging)
+		printssdfa(xx_nstates, xx_state, nbits, &gr->gr_ll,
+						"after minimizing");
+	
+	convert(d, xx_nstates, xx_state);
+	
+	/* XXX cleanup */
+}
+
+static
+printssdfa(xx_nstates, xx_state, nbits, ll, msg)
+	int xx_nstates;
+	ss_state *xx_state;
+	int nbits;
+	labellist *ll;
+	char *msg;
+{
+	int i, ibit, iarc;
+	ss_state *yy;
+	ss_arc *zz;
+	
+	printf("Subset DFA %s\n", msg);
+	for (i = 0; i < xx_nstates; i++) {
+		yy = &xx_state[i];
+		if (yy->ss_deleted)
+			continue;
+		printf(" Subset %d", i);
+		if (yy->ss_finish)
+			printf(" (finish)");
+		printf(" { ");
+		for (ibit = 0; ibit < nbits; ibit++) {
+			if (testbit(yy->ss_ss, ibit))
+				printf("%d ", ibit);
+		}
+		printf("}\n");
+		for (iarc = 0; iarc < yy->ss_narcs; iarc++) {
+			zz = &yy->ss_arc[iarc];
+			printf("  Arc to state %d, label %s\n",
+				zz->sa_arrow,
+				labelrepr(&ll->ll_label[zz->sa_label]));
+		}
+	}
+}
+
+
+/* PART THREE -- SIMPLIFY DFA */
+
+/* Simplify the DFA by repeatedly eliminating states that are
+   equivalent to another oner.  This is NOT Algorithm 3.3 from
+   [Aho&Ullman 77].  It does not always finds the minimal DFA,
+   but it does usually make a much smaller one...  (For an example
+   of sub-optimal behaviour, try S: x a b+ | y a b+.)
+*/
+
+static int
+samestate(s1, s2)
+	ss_state *s1, *s2;
+{
+	int i;
+	
+	if (s1->ss_narcs != s2->ss_narcs || s1->ss_finish != s2->ss_finish)
+		return 0;
+	for (i = 0; i < s1->ss_narcs; i++) {
+		if (s1->ss_arc[i].sa_arrow != s2->ss_arc[i].sa_arrow ||
+			s1->ss_arc[i].sa_label != s2->ss_arc[i].sa_label)
+			return 0;
+	}
+	return 1;
+}
+
+static void
+renamestates(xx_nstates, xx_state, from, to)
+	int xx_nstates;
+	ss_state *xx_state;
+	int from, to;
+{
+	int i, j;
+	
+	if (debugging)
+		printf("Rename state %d to %d.\n", from, to);
+	for (i = 0; i < xx_nstates; i++) {
+		if (xx_state[i].ss_deleted)
+			continue;
+		for (j = 0; j < xx_state[i].ss_narcs; j++) {
+			if (xx_state[i].ss_arc[j].sa_arrow == from)
+				xx_state[i].ss_arc[j].sa_arrow = to;
+		}
+	}
+}
+
+static
+simplify(xx_nstates, xx_state)
+	int xx_nstates;
+	ss_state *xx_state;
+{
+	int changes;
+	int i, j, k;
+	
+	do {
+		changes = 0;
+		for (i = 1; i < xx_nstates; i++) {
+			if (xx_state[i].ss_deleted)
+				continue;
+			for (j = 0; j < i; j++) {
+				if (xx_state[j].ss_deleted)
+					continue;
+				if (samestate(&xx_state[i], &xx_state[j])) {
+					xx_state[i].ss_deleted++;
+					renamestates(xx_nstates, xx_state, i, j);
+					changes++;
+					break;
+				}
+			}
+		}
+	} while (changes);
+}
+
+
+/* PART FOUR -- GENERATE PARSING TABLES */
+
+/* Convert the DFA into a grammar that can be used by our parser */
+
+static
+convert(d, xx_nstates, xx_state)
+	dfa *d;
+	int xx_nstates;
+	ss_state *xx_state;
+{
+	int i, j;
+	ss_state *yy;
+	ss_arc *zz;
+	
+	for (i = 0; i < xx_nstates; i++) {
+		yy = &xx_state[i];
+		if (yy->ss_deleted)
+			continue;
+		yy->ss_rename = addstate(d);
+	}
+	
+	for (i = 0; i < xx_nstates; i++) {
+		yy = &xx_state[i];
+		if (yy->ss_deleted)
+			continue;
+		for (j = 0; j < yy->ss_narcs; j++) {
+			zz = &yy->ss_arc[j];
+			addarc(d, yy->ss_rename,
+				xx_state[zz->sa_arrow].ss_rename,
+				zz->sa_label);
+		}
+		if (yy->ss_finish)
+			addarc(d, yy->ss_rename, yy->ss_rename, 0);
+	}
+	
+	d->d_initial = 0;
+}
+
+
+/* PART FIVE -- GLUE IT ALL TOGETHER */
+
+static grammar *
+maketables(gr)
+	nfagrammar *gr;
+{
+	int i;
+	nfa *nf;
+	dfa *d;
+	grammar *g;
+	
+	if (gr->gr_nnfas == 0)
+		return NULL;
+	g = newgrammar(gr->gr_nfa[0]->nf_type);
+			/* XXX first rule must be start rule */
+	g->g_ll = gr->gr_ll;
+	
+	for (i = 0; i < gr->gr_nnfas; i++) {
+		nf = gr->gr_nfa[i];
+		if (debugging) {
+			printf("Dump of NFA for '%s' ...\n", nf->nf_name);
+			dumpnfa(&gr->gr_ll, nf);
+		}
+		printf("Making DFA for '%s' ...\n", nf->nf_name);
+		d = adddfa(g, nf->nf_type, nf->nf_name);
+		makedfa(gr, gr->gr_nfa[i], d);
+	}
+	
+	return g;
+}
+
+grammar *
+pgen(n)
+	node *n;
+{
+	nfagrammar *gr;
+	grammar *g;
+	
+	gr = metacompile(n);
+	g = maketables(gr);
+	translatelabels(g);
+	addfirstsets(g);
+	return g;
+}
+
+
+/*
+
+Description
+-----------
+
+Input is a grammar in extended BNF (using * for repetition, + for
+at-least-once repetition, [] for optional parts, | for alternatives and
+() for grouping).  This has already been parsed and turned into a parse
+tree.
+
+Each rule is considered as a regular expression in its own right.
+It is turned into a Non-deterministic Finite Automaton (NFA), which
+is then turned into a Deterministic Finite Automaton (DFA), which is then
+optimized to reduce the number of states.  See [Aho&Ullman 77] chapter 3,
+or similar compiler books (this technique is more often used for lexical
+analyzers).
+
+The DFA's are used by the parser as parsing tables in a special way
+that's probably unique.  Before they are usable, the FIRST sets of all
+non-terminals are computed.
+
+Reference
+---------
+
+[Aho&Ullman 77]
+	Aho&Ullman, Principles of Compiler Design, Addison-Wesley 1977
+	(first edition)
+
+*/