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cpython/Parser/pgen.c

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/* Parser generator */
/* For a description, see the comments at end of this file */
#include "Python.h"
#include "pgenheaders.h"
#include "token.h"
#include "node.h"
#include "grammar.h"
#include "metagrammar.h"
#include "pgen.h"
extern int Py_DebugFlag;
extern int Py_IgnoreEnvironmentFlag; /* needed by Py_GETENV */
/* 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;
/* Forward */
static void compile_rhs(labellist *ll,
nfa *nf, node *n, int *pa, int *pb);
static void compile_alt(labellist *ll,
nfa *nf, node *n, int *pa, int *pb);
static void compile_item(labellist *ll,
nfa *nf, node *n, int *pa, int *pb);
static void compile_atom(labellist *ll,
nfa *nf, node *n, int *pa, int *pb);
static int
addnfastate(nfa *nf)
{
nfastate *st;
nf->nf_state = (nfastate *)PyObject_REALLOC(nf->nf_state,
sizeof(nfastate) * (nf->nf_nstates + 1));
if (nf->nf_state == NULL)
Py_FatalError("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(nfa *nf, int from, int to, int lbl)
{
nfastate *st;
nfaarc *ar;
st = &nf->nf_state[from];
st->st_arc = (nfaarc *)PyObject_REALLOC(st->st_arc,
sizeof(nfaarc) * (st->st_narcs + 1));
if (st->st_arc == NULL)
Py_FatalError("out of mem");
ar = &st->st_arc[st->st_narcs++];
ar->ar_label = lbl;
ar->ar_arrow = to;
}
static nfa *
newnfa(char *name)
{
nfa *nf;
static int type = NT_OFFSET; /* All types will be disjunct */
nf = (nfa *)PyObject_MALLOC(sizeof(nfa));
if (nf == NULL)
Py_FatalError("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;
/* Forward */
static void compile_rule(nfagrammar *gr, node *n);
static nfagrammar *
newnfagrammar(void)
{
nfagrammar *gr;
gr = (nfagrammar *)PyObject_MALLOC(sizeof(nfagrammar));
if (gr == NULL)
Py_FatalError("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(nfagrammar *gr, char *name)
{
nfa *nf;
nf = newnfa(name);
gr->gr_nfa = (nfa **)PyObject_REALLOC(gr->gr_nfa,
sizeof(nfa*) * (gr->gr_nnfas + 1));
if (gr->gr_nfa == NULL)
Py_FatalError("out of mem");
gr->gr_nfa[gr->gr_nnfas++] = nf;
addlabel(&gr->gr_ll, NAME, nf->nf_name);
return nf;
}
#ifdef Py_DEBUG
static char REQNFMT[] = "metacompile: less than %d children\n";
#define REQN(i, count) \
if (i < count) { \
fprintf(stderr, REQNFMT, count); \
Py_FatalError("REQN"); \
} else
#else
#define REQN(i, count) /* empty */
#endif
static nfagrammar *
metacompile(node *n)
{
nfagrammar *gr;
int i;
if (Py_DebugFlag)
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 void
compile_rule(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 void
compile_rhs(labellist *ll, nfa *nf, node *n, int *pa, int *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 void
compile_alt(labellist *ll, nfa *nf, node *n, int *pa, int *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++) {
REQ(n, ITEM);
compile_item(ll, nf, n, &a, &b);
addnfaarc(nf, *pb, a, EMPTY);
*pb = b;
}
}
static void
compile_item(labellist *ll, nfa *nf, node *n, int *pa, int *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 void
compile_atom(labellist *ll, nfa *nf, node *n, int *pa, int *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(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,
PyGrammar_LabelRepr(&ll->ll_label[ar->ar_label]));
ar++;
}
printf("\n");
}
static void
dumpnfa(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 void
addclosure(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;
struct _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;
/* Forward */
static void printssdfa(int xx_nstates, ss_state *xx_state, int nbits,
labellist *ll, char *msg);
static void simplify(int xx_nstates, ss_state *xx_state);
static void convert(dfa *d, int xx_nstates, ss_state *xx_state);
static void
makedfa(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 = (ss_state *)PyObject_MALLOC(sizeof(ss_state));
if (xx_state == NULL)
Py_FatalError("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) {
size_t size;
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 */
size = sizeof(ss_arc) * (yy->ss_narcs + 1);
yy->ss_arc = (ss_arc *)PyObject_REALLOC(
yy->ss_arc, size);
if (yy->ss_arc == NULL)
Py_FatalError("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;
}
}
size = sizeof(ss_state) * (xx_nstates + 1);
xx_state = (ss_state *)PyObject_REALLOC(xx_state,
size);
if (xx_state == NULL)
Py_FatalError("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 (Py_DebugFlag)
printssdfa(xx_nstates, xx_state, nbits, &gr->gr_ll,
"before minimizing");
simplify(xx_nstates, xx_state);
if (Py_DebugFlag)
printssdfa(xx_nstates, xx_state, nbits, &gr->gr_ll,
"after minimizing");
convert(d, xx_nstates, xx_state);
/* XXX cleanup */
PyObject_FREE(xx_state);
}
static void
printssdfa(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,
PyGrammar_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 behavior, try S: x a b+ | y a b+.)
*/
static int
samestate(ss_state *s1, ss_state *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(int xx_nstates, ss_state *xx_state, int from, int to)
{
int i, j;
if (Py_DebugFlag)
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 void
simplify(int xx_nstates, ss_state *xx_state)
{
int changes;
int i, j;
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 void
convert(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(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 (Py_DebugFlag) {
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(node *n)
{
nfagrammar *gr;
grammar *g;
gr = metacompile(n);
g = maketables(gr);
translatelabels(g);
addfirstsets(g);
PyObject_FREE(gr);
return g;
}
grammar *
Py_pgen(node *n)
{
return pgen(n);
}
/*
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)
*/
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