cpython/Parser/pgen.c at pythoncapi · pythoncapi/cpython · GitHub

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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 void

freenfagrammar(nfagrammar *gr)

{

for (int i = 0; i < gr->gr_nnfas; i++) {

PyObject_FREE(gr->gr_nfa[i]->nf_state);

}

PyObject_FREE(gr->gr_nfa);

PyObject_FREE(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 const char REQNFMT[] = "metacompile: less than %d children\n";

#define REQN(i, count) do { \

if (i < count) { \

fprintf(stderr, REQNFMT, count); \

Py_FatalError("REQN"); \

} \

} while (0)

#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;

(void)i; /* Don't warn about set but unused */

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, const 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);

for (int i = 0; i < xx_nstates; i++) {

for (int j = 0; j < xx_state[i].ss_narcs; j++)

delbitset(xx_state[i].ss_arc[j].sa_bitset);

PyObject_FREE(xx_state[i].ss_arc);

}

PyObject_FREE(xx_state);

}

static void

printssdfa(int xx_nstates, ss_state *xx_state, int nbits,

labellist *ll, const 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);

freenfagrammar(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)

cpython/Parser/pgen.c at pythoncapi · pythoncapi/cpython · GitHub

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