Mercurial > cpython-lru_cache-weakref
annotate Parser/parser.c @ 4566:6403c94de50d legacy-trunk
Added safeguard against failure in __del__.
| author | Guido van Rossum <guido@python.org> |
|---|---|
| date | Wed, 27 Nov 1996 19:39:58 +0000 |
| parents | 65d2d8e67da3 |
| children | 4567e158d20c |
| rev | line source |
|---|---|
| 145 | 1 /*********************************************************** |
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2 Copyright 1991-1995 by Stichting Mathematisch Centrum, Amsterdam, |
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3 The Netherlands. |
| 145 | 4 |
| 5 All Rights Reserved | |
| 6 | |
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7 Permission to use, copy, modify, and distribute this software and its |
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8 documentation for any purpose and without fee is hereby granted, |
| 145 | 9 provided that the above copyright notice appear in all copies and that |
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10 both that copyright notice and this permission notice appear in |
| 145 | 11 supporting documentation, and that the names of Stichting Mathematisch |
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12 Centrum or CWI or Corporation for National Research Initiatives or |
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13 CNRI not be used in advertising or publicity pertaining to |
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14 distribution of the software without specific, written prior |
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15 permission. |
| 145 | 16 |
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17 While CWI is the initial source for this software, a modified version |
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18 is made available by the Corporation for National Research Initiatives |
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19 (CNRI) at the Internet address ftp://ftp.python.org. |
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20 |
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21 STICHTING MATHEMATISCH CENTRUM AND CNRI DISCLAIM ALL WARRANTIES WITH |
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22 REGARD TO THIS SOFTWARE, INCLUDING ALL IMPLIED WARRANTIES OF |
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23 MERCHANTABILITY AND FITNESS, IN NO EVENT SHALL STICHTING MATHEMATISCH |
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24 CENTRUM OR CNRI BE LIABLE FOR ANY SPECIAL, INDIRECT OR CONSEQUENTIAL |
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25 DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR |
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26 PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER |
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27 TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR |
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28 PERFORMANCE OF THIS SOFTWARE. |
| 145 | 29 |
| 30 ******************************************************************/ | |
| 31 | |
| 6 | 32 /* Parser implementation */ |
| 33 | |
| 34 /* For a description, see the comments at end of this file */ | |
| 35 | |
| 36 /* XXX To do: error recovery */ | |
| 37 | |
| 86 | 38 #include "pgenheaders.h" |
| 6 | 39 #include "assert.h" |
| 40 #include "token.h" | |
| 41 #include "grammar.h" | |
| 42 #include "node.h" | |
| 43 #include "parser.h" | |
| 44 #include "errcode.h" | |
| 45 | |
| 46 | |
| 47 #ifdef DEBUG | |
| 86 | 48 extern int debugging; |
| 6 | 49 #define D(x) if (!debugging); else x |
| 50 #else | |
| 51 #define D(x) | |
| 52 #endif | |
| 53 | |
| 54 | |
| 55 /* STACK DATA TYPE */ | |
| 56 | |
| 57 static void s_reset PROTO((stack *)); | |
| 58 | |
| 59 static void | |
| 60 s_reset(s) | |
| 61 stack *s; | |
| 62 { | |
| 63 s->s_top = &s->s_base[MAXSTACK]; | |
| 64 } | |
| 65 | |
| 66 #define s_empty(s) ((s)->s_top == &(s)->s_base[MAXSTACK]) | |
| 67 | |
| 68 static int s_push PROTO((stack *, dfa *, node *)); | |
| 69 | |
| 70 static int | |
| 71 s_push(s, d, parent) | |
| 72 register stack *s; | |
| 73 dfa *d; | |
| 74 node *parent; | |
| 75 { | |
| 76 register stackentry *top; | |
| 77 if (s->s_top == s->s_base) { | |
| 78 fprintf(stderr, "s_push: parser stack overflow\n"); | |
| 79 return -1; | |
| 80 } | |
| 81 top = --s->s_top; | |
| 82 top->s_dfa = d; | |
| 83 top->s_parent = parent; | |
| 84 top->s_state = 0; | |
| 85 return 0; | |
| 86 } | |
| 87 | |
| 88 #ifdef DEBUG | |
| 89 | |
| 90 static void s_pop PROTO((stack *)); | |
| 91 | |
| 92 static void | |
| 93 s_pop(s) | |
| 94 register stack *s; | |
| 95 { | |
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96 if (s_empty(s)) |
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97 fatal("s_pop: parser stack underflow -- FATAL"); |
| 6 | 98 s->s_top++; |
| 99 } | |
| 100 | |
| 101 #else /* !DEBUG */ | |
| 102 | |
| 103 #define s_pop(s) (s)->s_top++ | |
| 104 | |
| 105 #endif | |
| 106 | |
| 107 | |
| 108 /* PARSER CREATION */ | |
| 109 | |
| 110 parser_state * | |
| 111 newparser(g, start) | |
| 112 grammar *g; | |
| 113 int start; | |
| 114 { | |
| 115 parser_state *ps; | |
| 116 | |
| 117 if (!g->g_accel) | |
| 118 addaccelerators(g); | |
| 119 ps = NEW(parser_state, 1); | |
| 120 if (ps == NULL) | |
| 121 return NULL; | |
| 122 ps->p_grammar = g; | |
| 86 | 123 ps->p_tree = newtree(start); |
| 6 | 124 if (ps->p_tree == NULL) { |
| 125 DEL(ps); | |
| 126 return NULL; | |
| 127 } | |
| 128 s_reset(&ps->p_stack); | |
| 129 (void) s_push(&ps->p_stack, finddfa(g, start), ps->p_tree); | |
| 130 return ps; | |
| 131 } | |
| 132 | |
| 133 void | |
| 134 delparser(ps) | |
| 135 parser_state *ps; | |
| 136 { | |
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137 /* NB If you want to save the parse tree, |
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138 you must set p_tree to NULL before calling delparser! */ |
| 86 | 139 freetree(ps->p_tree); |
| 6 | 140 DEL(ps); |
| 141 } | |
| 142 | |
| 143 | |
| 144 /* PARSER STACK OPERATIONS */ | |
| 145 | |
| 86 | 146 static int shift PROTO((stack *, int, char *, int, int)); |
| 6 | 147 |
| 148 static int | |
| 86 | 149 shift(s, type, str, newstate, lineno) |
| 6 | 150 register stack *s; |
| 151 int type; | |
| 152 char *str; | |
| 153 int newstate; | |
| 86 | 154 int lineno; |
| 6 | 155 { |
| 156 assert(!s_empty(s)); | |
| 86 | 157 if (addchild(s->s_top->s_parent, type, str, lineno) == NULL) { |
| 6 | 158 fprintf(stderr, "shift: no mem in addchild\n"); |
| 159 return -1; | |
| 160 } | |
| 161 s->s_top->s_state = newstate; | |
| 162 return 0; | |
| 163 } | |
| 164 | |
| 86 | 165 static int push PROTO((stack *, int, dfa *, int, int)); |
| 6 | 166 |
| 167 static int | |
| 86 | 168 push(s, type, d, newstate, lineno) |
| 6 | 169 register stack *s; |
| 170 int type; | |
| 171 dfa *d; | |
| 172 int newstate; | |
| 86 | 173 int lineno; |
| 6 | 174 { |
| 175 register node *n; | |
| 176 n = s->s_top->s_parent; | |
| 177 assert(!s_empty(s)); | |
| 86 | 178 if (addchild(n, type, (char *)NULL, lineno) == NULL) { |
| 6 | 179 fprintf(stderr, "push: no mem in addchild\n"); |
| 180 return -1; | |
| 181 } | |
| 182 s->s_top->s_state = newstate; | |
| 183 return s_push(s, d, CHILD(n, NCH(n)-1)); | |
| 184 } | |
| 185 | |
| 186 | |
| 187 /* PARSER PROPER */ | |
| 188 | |
| 189 static int classify PROTO((grammar *, int, char *)); | |
| 190 | |
| 191 static int | |
| 192 classify(g, type, str) | |
| 193 grammar *g; | |
| 194 register int type; | |
| 195 char *str; | |
| 196 { | |
| 197 register int n = g->g_ll.ll_nlabels; | |
| 198 | |
| 199 if (type == NAME) { | |
| 200 register char *s = str; | |
| 201 register label *l = g->g_ll.ll_label; | |
| 202 register int i; | |
| 203 for (i = n; i > 0; i--, l++) { | |
| 204 if (l->lb_type == NAME && l->lb_str != NULL && | |
| 205 l->lb_str[0] == s[0] && | |
| 206 strcmp(l->lb_str, s) == 0) { | |
| 207 D(printf("It's a keyword\n")); | |
| 208 return n - i; | |
| 209 } | |
| 210 } | |
| 211 } | |
| 212 | |
| 213 { | |
| 214 register label *l = g->g_ll.ll_label; | |
| 215 register int i; | |
| 216 for (i = n; i > 0; i--, l++) { | |
| 217 if (l->lb_type == type && l->lb_str == NULL) { | |
| 218 D(printf("It's a token we know\n")); | |
| 219 return n - i; | |
| 220 } | |
| 221 } | |
| 222 } | |
| 223 | |
| 224 D(printf("Illegal token\n")); | |
| 225 return -1; | |
| 226 } | |
| 227 | |
| 228 int | |
| 86 | 229 addtoken(ps, type, str, lineno) |
| 6 | 230 register parser_state *ps; |
| 231 register int type; | |
| 232 char *str; | |
| 86 | 233 int lineno; |
| 6 | 234 { |
| 235 register int ilabel; | |
| 236 | |
| 237 D(printf("Token %s/'%s' ... ", tok_name[type], str)); | |
| 238 | |
| 239 /* Find out which label this token is */ | |
| 240 ilabel = classify(ps->p_grammar, type, str); | |
| 241 if (ilabel < 0) | |
| 242 return E_SYNTAX; | |
| 243 | |
| 244 /* Loop until the token is shifted or an error occurred */ | |
| 245 for (;;) { | |
| 246 /* Fetch the current dfa and state */ | |
| 247 register dfa *d = ps->p_stack.s_top->s_dfa; | |
| 248 register state *s = &d->d_state[ps->p_stack.s_top->s_state]; | |
| 249 | |
| 250 D(printf(" DFA '%s', state %d:", | |
| 251 d->d_name, ps->p_stack.s_top->s_state)); | |
| 252 | |
| 253 /* Check accelerator */ | |
| 254 if (s->s_lower <= ilabel && ilabel < s->s_upper) { | |
| 255 register int x = s->s_accel[ilabel - s->s_lower]; | |
| 256 if (x != -1) { | |
| 257 if (x & (1<<7)) { | |
| 258 /* Push non-terminal */ | |
| 259 int nt = (x >> 8) + NT_OFFSET; | |
| 260 int arrow = x & ((1<<7)-1); | |
| 261 dfa *d1 = finddfa(ps->p_grammar, nt); | |
| 86 | 262 if (push(&ps->p_stack, nt, d1, |
| 263 arrow, lineno) < 0) { | |
| 6 | 264 D(printf(" MemError: push.\n")); |
| 265 return E_NOMEM; | |
| 266 } | |
| 267 D(printf(" Push ...\n")); | |
| 268 continue; | |
| 269 } | |
| 270 | |
| 271 /* Shift the token */ | |
| 86 | 272 if (shift(&ps->p_stack, type, str, |
| 273 x, lineno) < 0) { | |
| 6 | 274 D(printf(" MemError: shift.\n")); |
| 275 return E_NOMEM; | |
| 276 } | |
| 277 D(printf(" Shift.\n")); | |
| 278 /* Pop while we are in an accept-only state */ | |
| 279 while (s = &d->d_state | |
| 280 [ps->p_stack.s_top->s_state], | |
| 281 s->s_accept && s->s_narcs == 1) { | |
| 282 D(printf(" Direct pop.\n")); | |
| 283 s_pop(&ps->p_stack); | |
| 284 if (s_empty(&ps->p_stack)) { | |
| 285 D(printf(" ACCEPT.\n")); | |
| 286 return E_DONE; | |
| 287 } | |
| 288 d = ps->p_stack.s_top->s_dfa; | |
| 289 } | |
| 290 return E_OK; | |
| 291 } | |
| 292 } | |
| 293 | |
| 294 if (s->s_accept) { | |
| 295 /* Pop this dfa and try again */ | |
| 296 s_pop(&ps->p_stack); | |
| 297 D(printf(" Pop ...\n")); | |
| 298 if (s_empty(&ps->p_stack)) { | |
| 299 D(printf(" Error: bottom of stack.\n")); | |
| 300 return E_SYNTAX; | |
| 301 } | |
| 302 continue; | |
| 303 } | |
| 304 | |
| 305 /* Stuck, report syntax error */ | |
| 306 D(printf(" Error.\n")); | |
| 307 return E_SYNTAX; | |
| 308 } | |
| 309 } | |
| 310 | |
| 311 | |
| 312 #ifdef DEBUG | |
| 313 | |
| 314 /* DEBUG OUTPUT */ | |
| 315 | |
| 316 void | |
| 317 dumptree(g, n) | |
| 318 grammar *g; | |
| 319 node *n; | |
| 320 { | |
| 321 int i; | |
| 322 | |
| 323 if (n == NULL) | |
| 324 printf("NIL"); | |
| 325 else { | |
| 326 label l; | |
| 327 l.lb_type = TYPE(n); | |
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328 l.lb_str = STR(n); |
| 6 | 329 printf("%s", labelrepr(&l)); |
| 330 if (ISNONTERMINAL(TYPE(n))) { | |
| 331 printf("("); | |
| 332 for (i = 0; i < NCH(n); i++) { | |
| 333 if (i > 0) | |
| 334 printf(","); | |
| 335 dumptree(g, CHILD(n, i)); | |
| 336 } | |
| 337 printf(")"); | |
| 338 } | |
| 339 } | |
| 340 } | |
| 341 | |
| 342 void | |
| 343 showtree(g, n) | |
| 344 grammar *g; | |
| 345 node *n; | |
| 346 { | |
| 347 int i; | |
| 348 | |
| 349 if (n == NULL) | |
| 350 return; | |
| 351 if (ISNONTERMINAL(TYPE(n))) { | |
| 352 for (i = 0; i < NCH(n); i++) | |
| 353 showtree(g, CHILD(n, i)); | |
| 354 } | |
| 355 else if (ISTERMINAL(TYPE(n))) { | |
| 356 printf("%s", tok_name[TYPE(n)]); | |
| 357 if (TYPE(n) == NUMBER || TYPE(n) == NAME) | |
| 358 printf("(%s)", STR(n)); | |
| 359 printf(" "); | |
| 360 } | |
| 361 else | |
| 362 printf("? "); | |
| 363 } | |
| 364 | |
| 365 void | |
| 366 printtree(ps) | |
| 367 parser_state *ps; | |
| 368 { | |
| 369 if (debugging) { | |
| 370 printf("Parse tree:\n"); | |
| 371 dumptree(ps->p_grammar, ps->p_tree); | |
| 372 printf("\n"); | |
| 373 printf("Tokens:\n"); | |
| 374 showtree(ps->p_grammar, ps->p_tree); | |
| 375 printf("\n"); | |
| 376 } | |
| 377 printf("Listing:\n"); | |
| 378 listtree(ps->p_tree); | |
| 379 printf("\n"); | |
| 380 } | |
| 381 | |
| 382 #endif /* DEBUG */ | |
| 383 | |
| 384 /* | |
| 385 | |
| 386 Description | |
| 387 ----------- | |
| 388 | |
| 389 The parser's interface is different than usual: the function addtoken() | |
| 390 must be called for each token in the input. This makes it possible to | |
| 391 turn it into an incremental parsing system later. The parsing system | |
| 392 constructs a parse tree as it goes. | |
| 393 | |
| 394 A parsing rule is represented as a Deterministic Finite-state Automaton | |
| 395 (DFA). A node in a DFA represents a state of the parser; an arc represents | |
| 396 a transition. Transitions are either labeled with terminal symbols or | |
| 397 with non-terminals. When the parser decides to follow an arc labeled | |
| 398 with a non-terminal, it is invoked recursively with the DFA representing | |
| 399 the parsing rule for that as its initial state; when that DFA accepts, | |
| 400 the parser that invoked it continues. The parse tree constructed by the | |
| 401 recursively called parser is inserted as a child in the current parse tree. | |
| 402 | |
| 403 The DFA's can be constructed automatically from a more conventional | |
| 404 language description. An extended LL(1) grammar (ELL(1)) is suitable. | |
| 405 Certain restrictions make the parser's life easier: rules that can produce | |
| 406 the empty string should be outlawed (there are other ways to put loops | |
| 407 or optional parts in the language). To avoid the need to construct | |
| 408 FIRST sets, we can require that all but the last alternative of a rule | |
| 409 (really: arc going out of a DFA's state) must begin with a terminal | |
| 410 symbol. | |
| 411 | |
| 412 As an example, consider this grammar: | |
| 413 | |
| 414 expr: term (OP term)* | |
| 415 term: CONSTANT | '(' expr ')' | |
| 416 | |
| 417 The DFA corresponding to the rule for expr is: | |
| 418 | |
| 419 ------->.---term-->.-------> | |
| 420 ^ | | |
| 421 | | | |
| 422 \----OP----/ | |
| 423 | |
| 424 The parse tree generated for the input a+b is: | |
| 425 | |
| 426 (expr: (term: (NAME: a)), (OP: +), (term: (NAME: b))) | |
| 427 | |
| 428 */ |