Guido van Rossum | f70e43a | 1991-02-19 12:39:46 +0000 | [diff] [blame] | 1 | /*********************************************************** |
| 2 | Copyright 1991 by Stichting Mathematisch Centrum, Amsterdam, The |
| 3 | Netherlands. |
| 4 | |
| 5 | All Rights Reserved |
| 6 | |
| 7 | Permission to use, copy, modify, and distribute this software and its |
| 8 | documentation for any purpose and without fee is hereby granted, |
| 9 | provided that the above copyright notice appear in all copies and that |
| 10 | both that copyright notice and this permission notice appear in |
| 11 | supporting documentation, and that the names of Stichting Mathematisch |
| 12 | Centrum or CWI not be used in advertising or publicity pertaining to |
| 13 | distribution of the software without specific, written prior permission. |
| 14 | |
| 15 | STICHTING MATHEMATISCH CENTRUM DISCLAIMS ALL WARRANTIES WITH REGARD TO |
| 16 | THIS SOFTWARE, INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND |
| 17 | FITNESS, IN NO EVENT SHALL STICHTING MATHEMATISCH CENTRUM BE LIABLE |
| 18 | FOR ANY SPECIAL, INDIRECT OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES |
| 19 | WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN |
| 20 | ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT |
| 21 | OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. |
| 22 | |
| 23 | ******************************************************************/ |
| 24 | |
Guido van Rossum | 85a5fbb | 1990-10-14 12:07:46 +0000 | [diff] [blame] | 25 | /* Parser implementation */ |
| 26 | |
| 27 | /* For a description, see the comments at end of this file */ |
| 28 | |
| 29 | /* XXX To do: error recovery */ |
| 30 | |
Guido van Rossum | 3f5da24 | 1990-12-20 15:06:42 +0000 | [diff] [blame] | 31 | #include "pgenheaders.h" |
Guido van Rossum | 85a5fbb | 1990-10-14 12:07:46 +0000 | [diff] [blame] | 32 | #include "assert.h" |
Guido van Rossum | 85a5fbb | 1990-10-14 12:07:46 +0000 | [diff] [blame] | 33 | #include "token.h" |
| 34 | #include "grammar.h" |
| 35 | #include "node.h" |
| 36 | #include "parser.h" |
| 37 | #include "errcode.h" |
| 38 | |
Guido van Rossum | 85a5fbb | 1990-10-14 12:07:46 +0000 | [diff] [blame] | 39 | |
| 40 | #ifdef DEBUG |
Guido van Rossum | 3f5da24 | 1990-12-20 15:06:42 +0000 | [diff] [blame] | 41 | extern int debugging; |
Guido van Rossum | 85a5fbb | 1990-10-14 12:07:46 +0000 | [diff] [blame] | 42 | #define D(x) if (!debugging); else x |
| 43 | #else |
| 44 | #define D(x) |
| 45 | #endif |
| 46 | |
| 47 | |
| 48 | /* STACK DATA TYPE */ |
| 49 | |
| 50 | static void s_reset PROTO((stack *)); |
| 51 | |
| 52 | static void |
| 53 | s_reset(s) |
| 54 | stack *s; |
| 55 | { |
| 56 | s->s_top = &s->s_base[MAXSTACK]; |
| 57 | } |
| 58 | |
| 59 | #define s_empty(s) ((s)->s_top == &(s)->s_base[MAXSTACK]) |
| 60 | |
| 61 | static int s_push PROTO((stack *, dfa *, node *)); |
| 62 | |
| 63 | static int |
| 64 | s_push(s, d, parent) |
| 65 | register stack *s; |
| 66 | dfa *d; |
| 67 | node *parent; |
| 68 | { |
| 69 | register stackentry *top; |
| 70 | if (s->s_top == s->s_base) { |
| 71 | fprintf(stderr, "s_push: parser stack overflow\n"); |
| 72 | return -1; |
| 73 | } |
| 74 | top = --s->s_top; |
| 75 | top->s_dfa = d; |
| 76 | top->s_parent = parent; |
| 77 | top->s_state = 0; |
| 78 | return 0; |
| 79 | } |
| 80 | |
| 81 | #ifdef DEBUG |
| 82 | |
| 83 | static void s_pop PROTO((stack *)); |
| 84 | |
| 85 | static void |
| 86 | s_pop(s) |
| 87 | register stack *s; |
| 88 | { |
| 89 | if (s_empty(s)) { |
| 90 | fprintf(stderr, "s_pop: parser stack underflow -- FATAL\n"); |
| 91 | abort(); |
| 92 | } |
| 93 | s->s_top++; |
| 94 | } |
| 95 | |
| 96 | #else /* !DEBUG */ |
| 97 | |
| 98 | #define s_pop(s) (s)->s_top++ |
| 99 | |
| 100 | #endif |
| 101 | |
| 102 | |
| 103 | /* PARSER CREATION */ |
| 104 | |
| 105 | parser_state * |
| 106 | newparser(g, start) |
| 107 | grammar *g; |
| 108 | int start; |
| 109 | { |
| 110 | parser_state *ps; |
| 111 | |
| 112 | if (!g->g_accel) |
| 113 | addaccelerators(g); |
| 114 | ps = NEW(parser_state, 1); |
| 115 | if (ps == NULL) |
| 116 | return NULL; |
| 117 | ps->p_grammar = g; |
Guido van Rossum | 3f5da24 | 1990-12-20 15:06:42 +0000 | [diff] [blame] | 118 | ps->p_tree = newtree(start); |
Guido van Rossum | 85a5fbb | 1990-10-14 12:07:46 +0000 | [diff] [blame] | 119 | if (ps->p_tree == NULL) { |
Guido van Rossum | 85a5fbb | 1990-10-14 12:07:46 +0000 | [diff] [blame] | 120 | DEL(ps); |
| 121 | return NULL; |
| 122 | } |
| 123 | s_reset(&ps->p_stack); |
| 124 | (void) s_push(&ps->p_stack, finddfa(g, start), ps->p_tree); |
| 125 | return ps; |
| 126 | } |
| 127 | |
| 128 | void |
| 129 | delparser(ps) |
| 130 | parser_state *ps; |
| 131 | { |
Guido van Rossum | 99f02d4 | 1990-11-18 17:38:42 +0000 | [diff] [blame] | 132 | /* NB If you want to save the parse tree, |
| 133 | you must set p_tree to NULL before calling delparser! */ |
Guido van Rossum | 3f5da24 | 1990-12-20 15:06:42 +0000 | [diff] [blame] | 134 | freetree(ps->p_tree); |
Guido van Rossum | 85a5fbb | 1990-10-14 12:07:46 +0000 | [diff] [blame] | 135 | DEL(ps); |
| 136 | } |
| 137 | |
| 138 | |
| 139 | /* PARSER STACK OPERATIONS */ |
| 140 | |
Guido van Rossum | 3f5da24 | 1990-12-20 15:06:42 +0000 | [diff] [blame] | 141 | static int shift PROTO((stack *, int, char *, int, int)); |
Guido van Rossum | 85a5fbb | 1990-10-14 12:07:46 +0000 | [diff] [blame] | 142 | |
| 143 | static int |
Guido van Rossum | 3f5da24 | 1990-12-20 15:06:42 +0000 | [diff] [blame] | 144 | shift(s, type, str, newstate, lineno) |
Guido van Rossum | 85a5fbb | 1990-10-14 12:07:46 +0000 | [diff] [blame] | 145 | register stack *s; |
| 146 | int type; |
| 147 | char *str; |
| 148 | int newstate; |
Guido van Rossum | 3f5da24 | 1990-12-20 15:06:42 +0000 | [diff] [blame] | 149 | int lineno; |
Guido van Rossum | 85a5fbb | 1990-10-14 12:07:46 +0000 | [diff] [blame] | 150 | { |
| 151 | assert(!s_empty(s)); |
Guido van Rossum | 3f5da24 | 1990-12-20 15:06:42 +0000 | [diff] [blame] | 152 | if (addchild(s->s_top->s_parent, type, str, lineno) == NULL) { |
Guido van Rossum | 85a5fbb | 1990-10-14 12:07:46 +0000 | [diff] [blame] | 153 | fprintf(stderr, "shift: no mem in addchild\n"); |
| 154 | return -1; |
| 155 | } |
| 156 | s->s_top->s_state = newstate; |
| 157 | return 0; |
| 158 | } |
| 159 | |
Guido van Rossum | 3f5da24 | 1990-12-20 15:06:42 +0000 | [diff] [blame] | 160 | static int push PROTO((stack *, int, dfa *, int, int)); |
Guido van Rossum | 85a5fbb | 1990-10-14 12:07:46 +0000 | [diff] [blame] | 161 | |
| 162 | static int |
Guido van Rossum | 3f5da24 | 1990-12-20 15:06:42 +0000 | [diff] [blame] | 163 | push(s, type, d, newstate, lineno) |
Guido van Rossum | 85a5fbb | 1990-10-14 12:07:46 +0000 | [diff] [blame] | 164 | register stack *s; |
| 165 | int type; |
| 166 | dfa *d; |
| 167 | int newstate; |
Guido van Rossum | 3f5da24 | 1990-12-20 15:06:42 +0000 | [diff] [blame] | 168 | int lineno; |
Guido van Rossum | 85a5fbb | 1990-10-14 12:07:46 +0000 | [diff] [blame] | 169 | { |
| 170 | register node *n; |
| 171 | n = s->s_top->s_parent; |
| 172 | assert(!s_empty(s)); |
Guido van Rossum | 3f5da24 | 1990-12-20 15:06:42 +0000 | [diff] [blame] | 173 | if (addchild(n, type, (char *)NULL, lineno) == NULL) { |
Guido van Rossum | 85a5fbb | 1990-10-14 12:07:46 +0000 | [diff] [blame] | 174 | fprintf(stderr, "push: no mem in addchild\n"); |
| 175 | return -1; |
| 176 | } |
| 177 | s->s_top->s_state = newstate; |
| 178 | return s_push(s, d, CHILD(n, NCH(n)-1)); |
| 179 | } |
| 180 | |
| 181 | |
| 182 | /* PARSER PROPER */ |
| 183 | |
| 184 | static int classify PROTO((grammar *, int, char *)); |
| 185 | |
| 186 | static int |
| 187 | classify(g, type, str) |
| 188 | grammar *g; |
| 189 | register int type; |
| 190 | char *str; |
| 191 | { |
| 192 | register int n = g->g_ll.ll_nlabels; |
| 193 | |
| 194 | if (type == NAME) { |
| 195 | register char *s = str; |
| 196 | register label *l = g->g_ll.ll_label; |
| 197 | register int i; |
| 198 | for (i = n; i > 0; i--, l++) { |
| 199 | if (l->lb_type == NAME && l->lb_str != NULL && |
| 200 | l->lb_str[0] == s[0] && |
| 201 | strcmp(l->lb_str, s) == 0) { |
| 202 | D(printf("It's a keyword\n")); |
| 203 | return n - i; |
| 204 | } |
| 205 | } |
| 206 | } |
| 207 | |
| 208 | { |
| 209 | register label *l = g->g_ll.ll_label; |
| 210 | register int i; |
| 211 | for (i = n; i > 0; i--, l++) { |
| 212 | if (l->lb_type == type && l->lb_str == NULL) { |
| 213 | D(printf("It's a token we know\n")); |
| 214 | return n - i; |
| 215 | } |
| 216 | } |
| 217 | } |
| 218 | |
| 219 | D(printf("Illegal token\n")); |
| 220 | return -1; |
| 221 | } |
| 222 | |
| 223 | int |
Guido van Rossum | 3f5da24 | 1990-12-20 15:06:42 +0000 | [diff] [blame] | 224 | addtoken(ps, type, str, lineno) |
Guido van Rossum | 85a5fbb | 1990-10-14 12:07:46 +0000 | [diff] [blame] | 225 | register parser_state *ps; |
| 226 | register int type; |
| 227 | char *str; |
Guido van Rossum | 3f5da24 | 1990-12-20 15:06:42 +0000 | [diff] [blame] | 228 | int lineno; |
Guido van Rossum | 85a5fbb | 1990-10-14 12:07:46 +0000 | [diff] [blame] | 229 | { |
| 230 | register int ilabel; |
| 231 | |
| 232 | D(printf("Token %s/'%s' ... ", tok_name[type], str)); |
| 233 | |
| 234 | /* Find out which label this token is */ |
| 235 | ilabel = classify(ps->p_grammar, type, str); |
| 236 | if (ilabel < 0) |
| 237 | return E_SYNTAX; |
| 238 | |
| 239 | /* Loop until the token is shifted or an error occurred */ |
| 240 | for (;;) { |
| 241 | /* Fetch the current dfa and state */ |
| 242 | register dfa *d = ps->p_stack.s_top->s_dfa; |
| 243 | register state *s = &d->d_state[ps->p_stack.s_top->s_state]; |
| 244 | |
| 245 | D(printf(" DFA '%s', state %d:", |
| 246 | d->d_name, ps->p_stack.s_top->s_state)); |
| 247 | |
| 248 | /* Check accelerator */ |
| 249 | if (s->s_lower <= ilabel && ilabel < s->s_upper) { |
| 250 | register int x = s->s_accel[ilabel - s->s_lower]; |
| 251 | if (x != -1) { |
| 252 | if (x & (1<<7)) { |
| 253 | /* Push non-terminal */ |
| 254 | int nt = (x >> 8) + NT_OFFSET; |
| 255 | int arrow = x & ((1<<7)-1); |
| 256 | dfa *d1 = finddfa(ps->p_grammar, nt); |
Guido van Rossum | 3f5da24 | 1990-12-20 15:06:42 +0000 | [diff] [blame] | 257 | if (push(&ps->p_stack, nt, d1, |
| 258 | arrow, lineno) < 0) { |
Guido van Rossum | 85a5fbb | 1990-10-14 12:07:46 +0000 | [diff] [blame] | 259 | D(printf(" MemError: push.\n")); |
| 260 | return E_NOMEM; |
| 261 | } |
| 262 | D(printf(" Push ...\n")); |
| 263 | continue; |
| 264 | } |
| 265 | |
| 266 | /* Shift the token */ |
Guido van Rossum | 3f5da24 | 1990-12-20 15:06:42 +0000 | [diff] [blame] | 267 | if (shift(&ps->p_stack, type, str, |
| 268 | x, lineno) < 0) { |
Guido van Rossum | 85a5fbb | 1990-10-14 12:07:46 +0000 | [diff] [blame] | 269 | D(printf(" MemError: shift.\n")); |
| 270 | return E_NOMEM; |
| 271 | } |
| 272 | D(printf(" Shift.\n")); |
| 273 | /* Pop while we are in an accept-only state */ |
| 274 | while (s = &d->d_state |
| 275 | [ps->p_stack.s_top->s_state], |
| 276 | s->s_accept && s->s_narcs == 1) { |
| 277 | D(printf(" Direct pop.\n")); |
| 278 | s_pop(&ps->p_stack); |
| 279 | if (s_empty(&ps->p_stack)) { |
| 280 | D(printf(" ACCEPT.\n")); |
| 281 | return E_DONE; |
| 282 | } |
| 283 | d = ps->p_stack.s_top->s_dfa; |
| 284 | } |
| 285 | return E_OK; |
| 286 | } |
| 287 | } |
| 288 | |
| 289 | if (s->s_accept) { |
| 290 | /* Pop this dfa and try again */ |
| 291 | s_pop(&ps->p_stack); |
| 292 | D(printf(" Pop ...\n")); |
| 293 | if (s_empty(&ps->p_stack)) { |
| 294 | D(printf(" Error: bottom of stack.\n")); |
| 295 | return E_SYNTAX; |
| 296 | } |
| 297 | continue; |
| 298 | } |
| 299 | |
| 300 | /* Stuck, report syntax error */ |
| 301 | D(printf(" Error.\n")); |
| 302 | return E_SYNTAX; |
| 303 | } |
| 304 | } |
| 305 | |
| 306 | |
| 307 | #ifdef DEBUG |
| 308 | |
| 309 | /* DEBUG OUTPUT */ |
| 310 | |
| 311 | void |
| 312 | dumptree(g, n) |
| 313 | grammar *g; |
| 314 | node *n; |
| 315 | { |
| 316 | int i; |
| 317 | |
| 318 | if (n == NULL) |
| 319 | printf("NIL"); |
| 320 | else { |
| 321 | label l; |
| 322 | l.lb_type = TYPE(n); |
| 323 | l.lb_str = TYPE(str); |
| 324 | printf("%s", labelrepr(&l)); |
| 325 | if (ISNONTERMINAL(TYPE(n))) { |
| 326 | printf("("); |
| 327 | for (i = 0; i < NCH(n); i++) { |
| 328 | if (i > 0) |
| 329 | printf(","); |
| 330 | dumptree(g, CHILD(n, i)); |
| 331 | } |
| 332 | printf(")"); |
| 333 | } |
| 334 | } |
| 335 | } |
| 336 | |
| 337 | void |
| 338 | showtree(g, n) |
| 339 | grammar *g; |
| 340 | node *n; |
| 341 | { |
| 342 | int i; |
| 343 | |
| 344 | if (n == NULL) |
| 345 | return; |
| 346 | if (ISNONTERMINAL(TYPE(n))) { |
| 347 | for (i = 0; i < NCH(n); i++) |
| 348 | showtree(g, CHILD(n, i)); |
| 349 | } |
| 350 | else if (ISTERMINAL(TYPE(n))) { |
| 351 | printf("%s", tok_name[TYPE(n)]); |
| 352 | if (TYPE(n) == NUMBER || TYPE(n) == NAME) |
| 353 | printf("(%s)", STR(n)); |
| 354 | printf(" "); |
| 355 | } |
| 356 | else |
| 357 | printf("? "); |
| 358 | } |
| 359 | |
| 360 | void |
| 361 | printtree(ps) |
| 362 | parser_state *ps; |
| 363 | { |
| 364 | if (debugging) { |
| 365 | printf("Parse tree:\n"); |
| 366 | dumptree(ps->p_grammar, ps->p_tree); |
| 367 | printf("\n"); |
| 368 | printf("Tokens:\n"); |
| 369 | showtree(ps->p_grammar, ps->p_tree); |
| 370 | printf("\n"); |
| 371 | } |
| 372 | printf("Listing:\n"); |
| 373 | listtree(ps->p_tree); |
| 374 | printf("\n"); |
| 375 | } |
| 376 | |
| 377 | #endif /* DEBUG */ |
| 378 | |
| 379 | /* |
| 380 | |
| 381 | Description |
| 382 | ----------- |
| 383 | |
| 384 | The parser's interface is different than usual: the function addtoken() |
| 385 | must be called for each token in the input. This makes it possible to |
| 386 | turn it into an incremental parsing system later. The parsing system |
| 387 | constructs a parse tree as it goes. |
| 388 | |
| 389 | A parsing rule is represented as a Deterministic Finite-state Automaton |
| 390 | (DFA). A node in a DFA represents a state of the parser; an arc represents |
| 391 | a transition. Transitions are either labeled with terminal symbols or |
| 392 | with non-terminals. When the parser decides to follow an arc labeled |
| 393 | with a non-terminal, it is invoked recursively with the DFA representing |
| 394 | the parsing rule for that as its initial state; when that DFA accepts, |
| 395 | the parser that invoked it continues. The parse tree constructed by the |
| 396 | recursively called parser is inserted as a child in the current parse tree. |
| 397 | |
| 398 | The DFA's can be constructed automatically from a more conventional |
| 399 | language description. An extended LL(1) grammar (ELL(1)) is suitable. |
| 400 | Certain restrictions make the parser's life easier: rules that can produce |
| 401 | the empty string should be outlawed (there are other ways to put loops |
| 402 | or optional parts in the language). To avoid the need to construct |
| 403 | FIRST sets, we can require that all but the last alternative of a rule |
| 404 | (really: arc going out of a DFA's state) must begin with a terminal |
| 405 | symbol. |
| 406 | |
| 407 | As an example, consider this grammar: |
| 408 | |
| 409 | expr: term (OP term)* |
| 410 | term: CONSTANT | '(' expr ')' |
| 411 | |
| 412 | The DFA corresponding to the rule for expr is: |
| 413 | |
| 414 | ------->.---term-->.-------> |
| 415 | ^ | |
| 416 | | | |
| 417 | \----OP----/ |
| 418 | |
| 419 | The parse tree generated for the input a+b is: |
| 420 | |
| 421 | (expr: (term: (NAME: a)), (OP: +), (term: (NAME: b))) |
| 422 | |
| 423 | */ |