/Parser/parser.c
http://unladen-swallow.googlecode.com/ · C · 436 lines · 315 code · 54 blank · 67 comment · 98 complexity · 1da01b7fe4e60020e3d010c25c46a177 MD5 · raw file
- /* 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)))
- */