| |
| /* 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 = PyMem_NEW(parser_state, 1); |
| 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_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(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(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 |
| /* Leaving this in as an example */ |
| if (!(ps->p_flags & CO_FUTURE_WITH_STATEMENT)) { |
| if (s[0] == 'w' && strcmp(s, "with") == 0) |
| break; /* not a keyword yet */ |
| else if (s[0] == 'a' && strcmp(s, "as") == 0) |
| break; /* not a keyword yet */ |
| } |
| #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 |
| /* Leaving this in as an example */ |
| static void |
| future_hack(parser_state *ps) |
| { |
| node *n = ps->p_stack.s_top->s_parent; |
| node *ch; |
| 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; |
| for (i = 3; i < NCH(n); i += 2) { |
| /* XXX: assume we don't have parentheses in import: |
| from __future__ import (x, y, z) |
| */ |
| ch = CHILD(n, i); |
| if (NCH(ch) == 1) |
| ch = CHILD(ch, 0); |
| if (NCH(ch) >= 1 && TYPE(CHILD(ch, 0)) == NAME && |
| strcmp(STR(CHILD(ch, 0)), "with_statement") == 0) { |
| ps->p_flags |= CO_FUTURE_WITH_STATEMENT; |
| break; |
| } |
| } |
| } |
| #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))) |
| |
| */ |