Guido van Rossum | f70e43a | 1991-02-19 12:39:46 +0000 | [diff] [blame] | 1 | /*********************************************************** |
Guido van Rossum | b9f8d6e | 1995-01-04 19:08:09 +0000 | [diff] [blame] | 2 | Copyright 1991-1995 by Stichting Mathematisch Centrum, Amsterdam, |
| 3 | The Netherlands. |
Guido van Rossum | f70e43a | 1991-02-19 12:39:46 +0000 | [diff] [blame] | 4 | |
| 5 | All Rights Reserved |
| 6 | |
Guido van Rossum | d266eb4 | 1996-10-25 14:44:06 +0000 | [diff] [blame] | 7 | Permission to use, copy, modify, and distribute this software and its |
| 8 | documentation for any purpose and without fee is hereby granted, |
Guido van Rossum | f70e43a | 1991-02-19 12:39:46 +0000 | [diff] [blame] | 9 | provided that the above copyright notice appear in all copies and that |
Guido van Rossum | d266eb4 | 1996-10-25 14:44:06 +0000 | [diff] [blame] | 10 | both that copyright notice and this permission notice appear in |
Guido van Rossum | f70e43a | 1991-02-19 12:39:46 +0000 | [diff] [blame] | 11 | supporting documentation, and that the names of Stichting Mathematisch |
Guido van Rossum | d266eb4 | 1996-10-25 14:44:06 +0000 | [diff] [blame] | 12 | Centrum or CWI or Corporation for National Research Initiatives or |
| 13 | CNRI not be used in advertising or publicity pertaining to |
| 14 | distribution of the software without specific, written prior |
| 15 | permission. |
Guido van Rossum | f70e43a | 1991-02-19 12:39:46 +0000 | [diff] [blame] | 16 | |
Guido van Rossum | d266eb4 | 1996-10-25 14:44:06 +0000 | [diff] [blame] | 17 | While CWI is the initial source for this software, a modified version |
| 18 | is made available by the Corporation for National Research Initiatives |
| 19 | (CNRI) at the Internet address ftp://ftp.python.org. |
| 20 | |
| 21 | STICHTING MATHEMATISCH CENTRUM AND CNRI DISCLAIM ALL WARRANTIES WITH |
| 22 | REGARD TO THIS SOFTWARE, INCLUDING ALL IMPLIED WARRANTIES OF |
| 23 | MERCHANTABILITY AND FITNESS, IN NO EVENT SHALL STICHTING MATHEMATISCH |
| 24 | CENTRUM OR CNRI BE LIABLE FOR ANY SPECIAL, INDIRECT OR CONSEQUENTIAL |
| 25 | DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR |
| 26 | PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER |
| 27 | TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR |
| 28 | PERFORMANCE OF THIS SOFTWARE. |
Guido van Rossum | f70e43a | 1991-02-19 12:39:46 +0000 | [diff] [blame] | 29 | |
| 30 | ******************************************************************/ |
| 31 | |
Guido van Rossum | 85a5fbb | 1990-10-14 12:07:46 +0000 | [diff] [blame] | 32 | /* Parser implementation */ |
| 33 | |
| 34 | /* For a description, see the comments at end of this file */ |
| 35 | |
| 36 | /* XXX To do: error recovery */ |
| 37 | |
Guido van Rossum | 3f5da24 | 1990-12-20 15:06:42 +0000 | [diff] [blame] | 38 | #include "pgenheaders.h" |
Guido van Rossum | 85a5fbb | 1990-10-14 12:07:46 +0000 | [diff] [blame] | 39 | #include "assert.h" |
Guido van Rossum | 85a5fbb | 1990-10-14 12:07:46 +0000 | [diff] [blame] | 40 | #include "token.h" |
| 41 | #include "grammar.h" |
| 42 | #include "node.h" |
| 43 | #include "parser.h" |
| 44 | #include "errcode.h" |
| 45 | |
Guido van Rossum | 85a5fbb | 1990-10-14 12:07:46 +0000 | [diff] [blame] | 46 | |
| 47 | #ifdef DEBUG |
Guido van Rossum | 3f5da24 | 1990-12-20 15:06:42 +0000 | [diff] [blame] | 48 | extern int debugging; |
Guido van Rossum | 85a5fbb | 1990-10-14 12:07:46 +0000 | [diff] [blame] | 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 | { |
Guido van Rossum | 588633d | 1994-12-30 15:46:02 +0000 | [diff] [blame] | 96 | if (s_empty(s)) |
| 97 | fatal("s_pop: parser stack underflow -- FATAL"); |
Guido van Rossum | 85a5fbb | 1990-10-14 12:07:46 +0000 | [diff] [blame] | 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; |
Guido van Rossum | 3f5da24 | 1990-12-20 15:06:42 +0000 | [diff] [blame] | 123 | ps->p_tree = newtree(start); |
Guido van Rossum | 85a5fbb | 1990-10-14 12:07:46 +0000 | [diff] [blame] | 124 | if (ps->p_tree == NULL) { |
Guido van Rossum | 85a5fbb | 1990-10-14 12:07:46 +0000 | [diff] [blame] | 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 | { |
Guido van Rossum | 99f02d4 | 1990-11-18 17:38:42 +0000 | [diff] [blame] | 137 | /* NB If you want to save the parse tree, |
| 138 | you must set p_tree to NULL before calling delparser! */ |
Guido van Rossum | 3f5da24 | 1990-12-20 15:06:42 +0000 | [diff] [blame] | 139 | freetree(ps->p_tree); |
Guido van Rossum | 85a5fbb | 1990-10-14 12:07:46 +0000 | [diff] [blame] | 140 | DEL(ps); |
| 141 | } |
| 142 | |
| 143 | |
| 144 | /* PARSER STACK OPERATIONS */ |
| 145 | |
Guido van Rossum | 3f5da24 | 1990-12-20 15:06:42 +0000 | [diff] [blame] | 146 | static int shift PROTO((stack *, int, char *, int, int)); |
Guido van Rossum | 85a5fbb | 1990-10-14 12:07:46 +0000 | [diff] [blame] | 147 | |
| 148 | static int |
Guido van Rossum | 3f5da24 | 1990-12-20 15:06:42 +0000 | [diff] [blame] | 149 | shift(s, type, str, newstate, lineno) |
Guido van Rossum | 85a5fbb | 1990-10-14 12:07:46 +0000 | [diff] [blame] | 150 | register stack *s; |
| 151 | int type; |
| 152 | char *str; |
| 153 | int newstate; |
Guido van Rossum | 3f5da24 | 1990-12-20 15:06:42 +0000 | [diff] [blame] | 154 | int lineno; |
Guido van Rossum | 85a5fbb | 1990-10-14 12:07:46 +0000 | [diff] [blame] | 155 | { |
| 156 | assert(!s_empty(s)); |
Guido van Rossum | 3f5da24 | 1990-12-20 15:06:42 +0000 | [diff] [blame] | 157 | if (addchild(s->s_top->s_parent, type, str, lineno) == NULL) { |
Guido van Rossum | 85a5fbb | 1990-10-14 12:07:46 +0000 | [diff] [blame] | 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 | |
Guido van Rossum | 3f5da24 | 1990-12-20 15:06:42 +0000 | [diff] [blame] | 165 | static int push PROTO((stack *, int, dfa *, int, int)); |
Guido van Rossum | 85a5fbb | 1990-10-14 12:07:46 +0000 | [diff] [blame] | 166 | |
| 167 | static int |
Guido van Rossum | 3f5da24 | 1990-12-20 15:06:42 +0000 | [diff] [blame] | 168 | push(s, type, d, newstate, lineno) |
Guido van Rossum | 85a5fbb | 1990-10-14 12:07:46 +0000 | [diff] [blame] | 169 | register stack *s; |
| 170 | int type; |
| 171 | dfa *d; |
| 172 | int newstate; |
Guido van Rossum | 3f5da24 | 1990-12-20 15:06:42 +0000 | [diff] [blame] | 173 | int lineno; |
Guido van Rossum | 85a5fbb | 1990-10-14 12:07:46 +0000 | [diff] [blame] | 174 | { |
| 175 | register node *n; |
| 176 | n = s->s_top->s_parent; |
| 177 | assert(!s_empty(s)); |
Guido van Rossum | 3f5da24 | 1990-12-20 15:06:42 +0000 | [diff] [blame] | 178 | if (addchild(n, type, (char *)NULL, lineno) == NULL) { |
Guido van Rossum | 85a5fbb | 1990-10-14 12:07:46 +0000 | [diff] [blame] | 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 |
Guido van Rossum | 3f5da24 | 1990-12-20 15:06:42 +0000 | [diff] [blame] | 229 | addtoken(ps, type, str, lineno) |
Guido van Rossum | 85a5fbb | 1990-10-14 12:07:46 +0000 | [diff] [blame] | 230 | register parser_state *ps; |
| 231 | register int type; |
| 232 | char *str; |
Guido van Rossum | 3f5da24 | 1990-12-20 15:06:42 +0000 | [diff] [blame] | 233 | int lineno; |
Guido van Rossum | 85a5fbb | 1990-10-14 12:07:46 +0000 | [diff] [blame] | 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); |
Guido van Rossum | 3f5da24 | 1990-12-20 15:06:42 +0000 | [diff] [blame] | 262 | if (push(&ps->p_stack, nt, d1, |
| 263 | arrow, lineno) < 0) { |
Guido van Rossum | 85a5fbb | 1990-10-14 12:07:46 +0000 | [diff] [blame] | 264 | D(printf(" MemError: push.\n")); |
| 265 | return E_NOMEM; |
| 266 | } |
| 267 | D(printf(" Push ...\n")); |
| 268 | continue; |
| 269 | } |
| 270 | |
| 271 | /* Shift the token */ |
Guido van Rossum | 3f5da24 | 1990-12-20 15:06:42 +0000 | [diff] [blame] | 272 | if (shift(&ps->p_stack, type, str, |
| 273 | x, lineno) < 0) { |
Guido van Rossum | 85a5fbb | 1990-10-14 12:07:46 +0000 | [diff] [blame] | 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); |
Guido van Rossum | cf7448b | 1992-09-03 20:46:37 +0000 | [diff] [blame] | 328 | l.lb_str = STR(n); |
Guido van Rossum | 85a5fbb | 1990-10-14 12:07:46 +0000 | [diff] [blame] | 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 | */ |