mirror of https://github.com/python/cpython
410 lines
8.4 KiB
C
410 lines
8.4 KiB
C
/***********************************************************
|
|
Copyright (c) 2000, BeOpen.com.
|
|
Copyright (c) 1995-2000, Corporation for National Research Initiatives.
|
|
Copyright (c) 1990-1995, Stichting Mathematisch Centrum.
|
|
All rights reserved.
|
|
|
|
See the file "Misc/COPYRIGHT" for information on usage and
|
|
redistribution of this file, and for a DISCLAIMER OF ALL WARRANTIES.
|
|
******************************************************************/
|
|
|
|
/* Parser implementation */
|
|
|
|
/* For a description, see the comments at end of this file */
|
|
|
|
/* XXX To do: error recovery */
|
|
|
|
#include "pgenheaders.h"
|
|
#include "assert.h"
|
|
#include "token.h"
|
|
#include "grammar.h"
|
|
#include "node.h"
|
|
#include "parser.h"
|
|
#include "errcode.h"
|
|
|
|
|
|
#ifdef Py_DEBUG
|
|
extern int Py_DebugFlag;
|
|
#define D(x) if (!Py_DebugFlag); else x
|
|
#else
|
|
#define D(x)
|
|
#endif
|
|
|
|
|
|
/* STACK DATA TYPE */
|
|
|
|
static void s_reset(stack *);
|
|
|
|
static void
|
|
s_reset(s)
|
|
stack *s;
|
|
{
|
|
s->s_top = &s->s_base[MAXSTACK];
|
|
}
|
|
|
|
#define s_empty(s) ((s)->s_top == &(s)->s_base[MAXSTACK])
|
|
|
|
static int s_push(stack *, dfa *, node *);
|
|
|
|
static int
|
|
s_push(s, d, parent)
|
|
register stack *s;
|
|
dfa *d;
|
|
node *parent;
|
|
{
|
|
register stackentry *top;
|
|
if (s->s_top == s->s_base) {
|
|
fprintf(stderr, "s_push: parser stack overflow\n");
|
|
return -1;
|
|
}
|
|
top = --s->s_top;
|
|
top->s_dfa = d;
|
|
top->s_parent = parent;
|
|
top->s_state = 0;
|
|
return 0;
|
|
}
|
|
|
|
#ifdef Py_DEBUG
|
|
|
|
static void s_pop(stack *);
|
|
|
|
static void
|
|
s_pop(s)
|
|
register stack *s;
|
|
{
|
|
if (s_empty(s))
|
|
Py_FatalError("s_pop: parser stack underflow -- FATAL");
|
|
s->s_top++;
|
|
}
|
|
|
|
#else /* !Py_DEBUG */
|
|
|
|
#define s_pop(s) (s)->s_top++
|
|
|
|
#endif
|
|
|
|
|
|
/* PARSER CREATION */
|
|
|
|
parser_state *
|
|
PyParser_New(g, start)
|
|
grammar *g;
|
|
int start;
|
|
{
|
|
parser_state *ps;
|
|
|
|
if (!g->g_accel)
|
|
PyGrammar_AddAccelerators(g);
|
|
ps = PyMem_NEW(parser_state, 1);
|
|
if (ps == NULL)
|
|
return NULL;
|
|
ps->p_grammar = g;
|
|
ps->p_tree = PyNode_New(start);
|
|
if (ps->p_tree == NULL) {
|
|
PyMem_DEL(ps);
|
|
return NULL;
|
|
}
|
|
s_reset(&ps->p_stack);
|
|
(void) s_push(&ps->p_stack, PyGrammar_FindDFA(g, start), ps->p_tree);
|
|
return ps;
|
|
}
|
|
|
|
void
|
|
PyParser_Delete(ps)
|
|
parser_state *ps;
|
|
{
|
|
/* NB If you want to save the parse tree,
|
|
you must set p_tree to NULL before calling delparser! */
|
|
PyNode_Free(ps->p_tree);
|
|
PyMem_DEL(ps);
|
|
}
|
|
|
|
|
|
/* PARSER STACK OPERATIONS */
|
|
|
|
static int shift(stack *, int, char *, int, int);
|
|
|
|
static int
|
|
shift(s, type, str, newstate, lineno)
|
|
register stack *s;
|
|
int type;
|
|
char *str;
|
|
int newstate;
|
|
int lineno;
|
|
{
|
|
int err;
|
|
assert(!s_empty(s));
|
|
err = PyNode_AddChild(s->s_top->s_parent, type, str, lineno);
|
|
if (err)
|
|
return err;
|
|
s->s_top->s_state = newstate;
|
|
return 0;
|
|
}
|
|
|
|
static int push(stack *, int, dfa *, int, int);
|
|
|
|
static int
|
|
push(s, type, d, newstate, lineno)
|
|
register stack *s;
|
|
int type;
|
|
dfa *d;
|
|
int newstate;
|
|
int lineno;
|
|
{
|
|
int err;
|
|
register node *n;
|
|
n = s->s_top->s_parent;
|
|
assert(!s_empty(s));
|
|
err = PyNode_AddChild(n, type, (char *)NULL, lineno);
|
|
if (err)
|
|
return err;
|
|
s->s_top->s_state = newstate;
|
|
return s_push(s, d, CHILD(n, NCH(n)-1));
|
|
}
|
|
|
|
|
|
/* PARSER PROPER */
|
|
|
|
static int classify(grammar *, int, char *);
|
|
|
|
static int
|
|
classify(g, type, str)
|
|
grammar *g;
|
|
register int type;
|
|
char *str;
|
|
{
|
|
register int n = g->g_ll.ll_nlabels;
|
|
|
|
if (type == NAME) {
|
|
register char *s = str;
|
|
register label *l = g->g_ll.ll_label;
|
|
register int i;
|
|
for (i = n; i > 0; i--, l++) {
|
|
if (l->lb_type == NAME && l->lb_str != NULL &&
|
|
l->lb_str[0] == s[0] &&
|
|
strcmp(l->lb_str, s) == 0) {
|
|
D(printf("It's a keyword\n"));
|
|
return n - i;
|
|
}
|
|
}
|
|
}
|
|
|
|
{
|
|
register label *l = g->g_ll.ll_label;
|
|
register int i;
|
|
for (i = n; i > 0; i--, l++) {
|
|
if (l->lb_type == type && l->lb_str == NULL) {
|
|
D(printf("It's a token we know\n"));
|
|
return n - i;
|
|
}
|
|
}
|
|
}
|
|
|
|
D(printf("Illegal token\n"));
|
|
return -1;
|
|
}
|
|
|
|
int
|
|
PyParser_AddToken(ps, type, str, lineno)
|
|
register parser_state *ps;
|
|
register int type;
|
|
char *str;
|
|
int lineno;
|
|
{
|
|
register int ilabel;
|
|
int err;
|
|
|
|
D(printf("Token %s/'%s' ... ", _PyParser_TokenNames[type], str));
|
|
|
|
/* Find out which label this token is */
|
|
ilabel = classify(ps->p_grammar, type, str);
|
|
if (ilabel < 0)
|
|
return E_SYNTAX;
|
|
|
|
/* Loop until the token is shifted or an error occurred */
|
|
for (;;) {
|
|
/* Fetch the current dfa and state */
|
|
register dfa *d = ps->p_stack.s_top->s_dfa;
|
|
register state *s = &d->d_state[ps->p_stack.s_top->s_state];
|
|
|
|
D(printf(" DFA '%s', state %d:",
|
|
d->d_name, ps->p_stack.s_top->s_state));
|
|
|
|
/* Check accelerator */
|
|
if (s->s_lower <= ilabel && ilabel < s->s_upper) {
|
|
register int x = s->s_accel[ilabel - s->s_lower];
|
|
if (x != -1) {
|
|
if (x & (1<<7)) {
|
|
/* Push non-terminal */
|
|
int nt = (x >> 8) + NT_OFFSET;
|
|
int arrow = x & ((1<<7)-1);
|
|
dfa *d1 = PyGrammar_FindDFA(
|
|
ps->p_grammar, nt);
|
|
if ((err = push(&ps->p_stack, nt, d1,
|
|
arrow, lineno)) > 0) {
|
|
D(printf(" MemError: push\n"));
|
|
return err;
|
|
}
|
|
D(printf(" Push ...\n"));
|
|
continue;
|
|
}
|
|
|
|
/* Shift the token */
|
|
if ((err = shift(&ps->p_stack, type, str,
|
|
x, lineno)) > 0) {
|
|
D(printf(" MemError: shift.\n"));
|
|
return err;
|
|
}
|
|
D(printf(" Shift.\n"));
|
|
/* Pop while we are in an accept-only state */
|
|
while (s = &d->d_state
|
|
[ps->p_stack.s_top->s_state],
|
|
s->s_accept && s->s_narcs == 1) {
|
|
D(printf(" Direct pop.\n"));
|
|
s_pop(&ps->p_stack);
|
|
if (s_empty(&ps->p_stack)) {
|
|
D(printf(" ACCEPT.\n"));
|
|
return E_DONE;
|
|
}
|
|
d = ps->p_stack.s_top->s_dfa;
|
|
}
|
|
return E_OK;
|
|
}
|
|
}
|
|
|
|
if (s->s_accept) {
|
|
/* Pop this dfa and try again */
|
|
s_pop(&ps->p_stack);
|
|
D(printf(" Pop ...\n"));
|
|
if (s_empty(&ps->p_stack)) {
|
|
D(printf(" Error: bottom of stack.\n"));
|
|
return E_SYNTAX;
|
|
}
|
|
continue;
|
|
}
|
|
|
|
/* Stuck, report syntax error */
|
|
D(printf(" Error.\n"));
|
|
return E_SYNTAX;
|
|
}
|
|
}
|
|
|
|
|
|
#ifdef Py_DEBUG
|
|
|
|
/* DEBUG OUTPUT */
|
|
|
|
void
|
|
dumptree(g, n)
|
|
grammar *g;
|
|
node *n;
|
|
{
|
|
int i;
|
|
|
|
if (n == NULL)
|
|
printf("NIL");
|
|
else {
|
|
label l;
|
|
l.lb_type = TYPE(n);
|
|
l.lb_str = STR(n);
|
|
printf("%s", PyGrammar_LabelRepr(&l));
|
|
if (ISNONTERMINAL(TYPE(n))) {
|
|
printf("(");
|
|
for (i = 0; i < NCH(n); i++) {
|
|
if (i > 0)
|
|
printf(",");
|
|
dumptree(g, CHILD(n, i));
|
|
}
|
|
printf(")");
|
|
}
|
|
}
|
|
}
|
|
|
|
void
|
|
showtree(g, n)
|
|
grammar *g;
|
|
node *n;
|
|
{
|
|
int i;
|
|
|
|
if (n == NULL)
|
|
return;
|
|
if (ISNONTERMINAL(TYPE(n))) {
|
|
for (i = 0; i < NCH(n); i++)
|
|
showtree(g, CHILD(n, i));
|
|
}
|
|
else if (ISTERMINAL(TYPE(n))) {
|
|
printf("%s", _PyParser_TokenNames[TYPE(n)]);
|
|
if (TYPE(n) == NUMBER || TYPE(n) == NAME)
|
|
printf("(%s)", STR(n));
|
|
printf(" ");
|
|
}
|
|
else
|
|
printf("? ");
|
|
}
|
|
|
|
void
|
|
printtree(ps)
|
|
parser_state *ps;
|
|
{
|
|
if (Py_DebugFlag) {
|
|
printf("Parse tree:\n");
|
|
dumptree(ps->p_grammar, ps->p_tree);
|
|
printf("\n");
|
|
printf("Tokens:\n");
|
|
showtree(ps->p_grammar, ps->p_tree);
|
|
printf("\n");
|
|
}
|
|
printf("Listing:\n");
|
|
PyNode_ListTree(ps->p_tree);
|
|
printf("\n");
|
|
}
|
|
|
|
#endif /* Py_DEBUG */
|
|
|
|
/*
|
|
|
|
Description
|
|
-----------
|
|
|
|
The parser's interface is different than usual: the function addtoken()
|
|
must be called for each token in the input. This makes it possible to
|
|
turn it into an incremental parsing system later. The parsing system
|
|
constructs a parse tree as it goes.
|
|
|
|
A parsing rule is represented as a Deterministic Finite-state Automaton
|
|
(DFA). A node in a DFA represents a state of the parser; an arc represents
|
|
a transition. Transitions are either labeled with terminal symbols or
|
|
with non-terminals. When the parser decides to follow an arc labeled
|
|
with a non-terminal, it is invoked recursively with the DFA representing
|
|
the parsing rule for that as its initial state; when that DFA accepts,
|
|
the parser that invoked it continues. The parse tree constructed by the
|
|
recursively called parser is inserted as a child in the current parse tree.
|
|
|
|
The DFA's can be constructed automatically from a more conventional
|
|
language description. An extended LL(1) grammar (ELL(1)) is suitable.
|
|
Certain restrictions make the parser's life easier: rules that can produce
|
|
the empty string should be outlawed (there are other ways to put loops
|
|
or optional parts in the language). To avoid the need to construct
|
|
FIRST sets, we can require that all but the last alternative of a rule
|
|
(really: arc going out of a DFA's state) must begin with a terminal
|
|
symbol.
|
|
|
|
As an example, consider this grammar:
|
|
|
|
expr: term (OP term)*
|
|
term: CONSTANT | '(' expr ')'
|
|
|
|
The DFA corresponding to the rule for expr is:
|
|
|
|
------->.---term-->.------->
|
|
^ |
|
|
| |
|
|
\----OP----/
|
|
|
|
The parse tree generated for the input a+b is:
|
|
|
|
(expr: (term: (NAME: a)), (OP: +), (term: (NAME: b)))
|
|
|
|
*/
|