/* Parser implementation */ | |
/* For a description, see the comments at end of this file */ | |
/* XXX To do: error recovery */ | |
#include "Python.h" | |
#include "pgenheaders.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(stack *s) | |
{ | |
s->s_top = &s->s_base[MAXSTACK]; | |
} | |
#define s_empty(s) ((s)->s_top == &(s)->s_base[MAXSTACK]) | |
static int | |
s_push(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 E_NOMEM; | |
} | |
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(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(grammar *g, int start) | |
{ | |
parser_state *ps; | |
if (!g->g_accel) | |
PyGrammar_AddAccelerators(g); | |
ps = (parser_state *)PyMem_MALLOC(sizeof(parser_state)); | |
if (ps == NULL) | |
return NULL; | |
ps->p_grammar = g; | |
#ifdef PY_PARSER_REQUIRES_FUTURE_KEYWORD | |
ps->p_flags = 0; | |
#endif | |
ps->p_tree = PyNode_New(start); | |
if (ps->p_tree == NULL) { | |
PyMem_FREE(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(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_FREE(ps); | |
} | |
/* PARSER STACK OPERATIONS */ | |
static int | |
shift(register stack *s, int type, char *str, int newstate, int lineno, int col_offset) | |
{ | |
int err; | |
assert(!s_empty(s)); | |
err = PyNode_AddChild(s->s_top->s_parent, type, str, lineno, col_offset); | |
if (err) | |
return err; | |
s->s_top->s_state = newstate; | |
return 0; | |
} | |
static int | |
push(register stack *s, int type, dfa *d, int newstate, int lineno, int col_offset) | |
{ | |
int err; | |
register node *n; | |
n = s->s_top->s_parent; | |
assert(!s_empty(s)); | |
err = PyNode_AddChild(n, type, (char *)NULL, lineno, col_offset); | |
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(parser_state *ps, int type, char *str) | |
{ | |
grammar *g = ps->p_grammar; | |
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) | |
continue; | |
#ifdef PY_PARSER_REQUIRES_FUTURE_KEYWORD | |
if (ps->p_flags & CO_FUTURE_PRINT_FUNCTION && | |
s[0] == 'p' && strcmp(s, "print") == 0) { | |
break; /* no longer a keyword */ | |
} | |
#endif | |
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; | |
} | |
#ifdef PY_PARSER_REQUIRES_FUTURE_KEYWORD | |
static void | |
future_hack(parser_state *ps) | |
{ | |
node *n = ps->p_stack.s_top->s_parent; | |
node *ch, *cch; | |
int i; | |
/* from __future__ import ..., must have at least 4 children */ | |
n = CHILD(n, 0); | |
if (NCH(n) < 4) | |
return; | |
ch = CHILD(n, 0); | |
if (STR(ch) == NULL || strcmp(STR(ch), "from") != 0) | |
return; | |
ch = CHILD(n, 1); | |
if (NCH(ch) == 1 && STR(CHILD(ch, 0)) && | |
strcmp(STR(CHILD(ch, 0)), "__future__") != 0) | |
return; | |
ch = CHILD(n, 3); | |
/* ch can be a star, a parenthesis or import_as_names */ | |
if (TYPE(ch) == STAR) | |
return; | |
if (TYPE(ch) == LPAR) | |
ch = CHILD(n, 4); | |
for (i = 0; i < NCH(ch); i += 2) { | |
cch = CHILD(ch, i); | |
if (NCH(cch) >= 1 && TYPE(CHILD(cch, 0)) == NAME) { | |
char *str_ch = STR(CHILD(cch, 0)); | |
if (strcmp(str_ch, FUTURE_WITH_STATEMENT) == 0) { | |
ps->p_flags |= CO_FUTURE_WITH_STATEMENT; | |
} else if (strcmp(str_ch, FUTURE_PRINT_FUNCTION) == 0) { | |
ps->p_flags |= CO_FUTURE_PRINT_FUNCTION; | |
} else if (strcmp(str_ch, FUTURE_UNICODE_LITERALS) == 0) { | |
ps->p_flags |= CO_FUTURE_UNICODE_LITERALS; | |
} | |
} | |
} | |
} | |
#endif /* future keyword */ | |
int | |
PyParser_AddToken(register parser_state *ps, register int type, char *str, | |
int lineno, int col_offset, int *expected_ret) | |
{ | |
register int ilabel; | |
int err; | |
D(printf("Token %s/'%s' ... ", _PyParser_TokenNames[type], str)); | |
/* Find out which label this token is */ | |
ilabel = classify(ps, 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, col_offset)) > 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, col_offset)) > 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(" DFA '%s', state %d: " | |
"Direct pop.\n", | |
d->d_name, | |
ps->p_stack.s_top->s_state)); | |
#ifdef PY_PARSER_REQUIRES_FUTURE_KEYWORD | |
if (d->d_name[0] == 'i' && | |
strcmp(d->d_name, | |
"import_stmt") == 0) | |
future_hack(ps); | |
#endif | |
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) { | |
#ifdef PY_PARSER_REQUIRES_FUTURE_KEYWORD | |
if (d->d_name[0] == 'i' && | |
strcmp(d->d_name, "import_stmt") == 0) | |
future_hack(ps); | |
#endif | |
/* 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")); | |
if (expected_ret) { | |
if (s->s_lower == s->s_upper - 1) { | |
/* Only one possible expected token */ | |
*expected_ret = ps->p_grammar-> | |
g_ll.ll_label[s->s_lower].lb_type; | |
} | |
else | |
*expected_ret = -1; | |
} | |
return E_SYNTAX; | |
} | |
} | |
#ifdef Py_DEBUG | |
/* DEBUG OUTPUT */ | |
void | |
dumptree(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(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(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))) | |
*/ |