parser.c

   1 #include <malloc.h>
   2 #include <math.h>
   3 #include <stdio.h>
   4 #include <stdlib.h>
   5
   6 #include "debug.h"
   7
   8 #include "parser.h"
   9
  10 /* global variables */
  11
  12 double answer = 0;
  13
  14 #define STORAGE_SIZE 10
  15 double storage[STORAGE_SIZE] = {0};
  16
  17 /* compare codes */
  18
  19 int codecmp (char *ref, char *str)
  20 {
  21     int sig;
  22
  23     while (*ref != '\0') {
  24         if (*ref == '\t') {
  25              sig = (*str == '.') ? -1 : ((*str >= '0') && (*str <= '9'));
  26         } else {
  27             sig = *str - *ref;
  28         }
  29         if (sig != 0) {
  30             return (sig > 0) ? 1 : -1;
  31         }
  32         str++;
  33         ref++;
  34     }
  35
  36     return 0;
  37 }
  38
  39 /* allocate new element */
  40
  41 element_t *newelement (func_t function, int nbops, int prio)
  42 {
  43     element_t *new = (element_t *) calloc (1, sizeof (element_t));
  44     if (new == NULL) {
  45         VERBOSE (ERROR, fprintf (stderr, "can't allocate memory\n"));
  46         return NULL;
  47     }
  48     if (nbops) {
  49         new->ops = (element_t **) calloc (nbops, sizeof (element_t *));
  50         if (new->ops == NULL) {
  51             free (new);
  52             VERBOSE (ERROR, fprintf (stderr, "can't allocate memory\n"));
  53             return NULL;
  54         }
  55     }
  56     new->func = function;
  57     new->nbops = nbops;
  58     new->prio = prio;
  59
  60     return new;
  61 }
  62
  63 /* desallocate element */
  64
  65 void delelement (element_t *root)
  66 {
  67     if ((root != NULL) && (root != ERROR_OP)) {
  68         int i;
  69         for (i = 0; i < root->nbops; i++) {
  70             if ((root->ops[i] != NULL) && (root->ops[i] != ERROR_OP)) {
  71                 delelement (root->ops[i]);
  72             }
  73         }
  74         if (root->nbops) {
  75             free (root->ops);
  76         }
  77         free (root);
  78     }
  79 }
  80
  81 /* duplicate element */
  82
  83 element_t *dupelement (element_t *root)
  84 {
  85     element_t *tmp = NULL;
  86     int i;
  87
  88     if ((root == NULL) || (root == ERROR_OP)) {
  89         return root;
  90     }
  91     tmp = newelement (root->func, root->nbops, root->prio);
  92     if (tmp == NULL) {
  93         return ERROR_OP;
  94     }
  95     tmp->value = root->value;
  96     for (i = 0; i < root->nbops; i++) {
  97         tmp->ops[i] = dupelement (root->ops[i]);
  98         if (tmp->ops[i] == ERROR_OP) {
  99             delelement (tmp);
 100             return ERROR_OP;
 101         }
 102     }
 103     return tmp;
 104 }
 105
 106 /* functions */
 107
 108 #define NB_OPERATORS 14
 109 keyword_t operators[NB_OPERATORS] = {
 110     { "+\t", Add, 2, 1, 1},
 111     { "-\t", Sub, 2, 1, 1},
 112     { "*",   Mul, 2, 1, 2},
 113     { "/",   Div, 2, 1, 2},
 114     { "%",   Mod, 2, 1, 3},
 115     { "^",   Pow, 2, 1, 4},
 116     { "==",  Equal, 2, 2, -1},
 117     { "!=",  Diff, 2, 2, -1},
 118     { ">=",  Ge, 2, 2, -1},
 119     { "<=",  Le, 2, 2, -1},
 120     { ">",   Gt, 2, 1, -1},
 121     { "<",   Lt, 2, 1, -1},
 122     { "&",   And, 2, 1, -2},
 123     { "|",   Or, 2, 1, -2}
 124 };
 125
 126 #define NB_FUNCTIONS 17
 127 keyword_t functions[NB_FUNCTIONS] = {
 128     { "sqrt", Sqr, 1, 4, 5},
 129     { "pow",  Pow, 2, 3, 5},
 130     { "cos",  Cos, 1, 3, 5},
 131     { "sin",  Sin, 1, 3, 5},
 132     { "atan", Atan, 1, 4, 5},
 133     { "exp",  Exp, 1, 3, 5},
 134     { "log",  Log, 1, 3, 5},
 135     { "sto",  Store, 2, 3, 5},
 136     { "rcl",  Recall, 1, 3, 5},
 137     { "inc",  Inc, 1, 3, 5},
 138     { "dec",  Dec, 1, 3, 5},
 139     { "disp", Disp, 0, 4, 9},
 140     { "quit", Quit, 0, 4, 9},
 141     { "help", Help, 0, 4, 9},
 142     { "!",    Not, 1, 1, 6},
 143     { "cond", Cond, 3, 4, 5},
 144     { "whl",  While, 2, 3, 5}
 145 };
 146
 147 #define NB_CONSTANTS 3
 148 keyword_t constants[NB_CONSTANTS] = {
 149     { "ans", Ans, 0, 3, 5},
 150     { "e",   E, 0, 1, 5},
 151     { "pi",  Pi, 0, 2, 5}
 152 };
 153
 154 /* subparser function */
 155
 156 element_t *subparser (element_t **proot, char **pstr, func_t func, int nbops, int prio)
 157 {
 158     element_t *new = newelement (func, nbops, prio);
 159     if (new == NULL) {
 160         return ERROR_OP;
 161     }
 162     new->ops[0] = *proot;
 163     new->ops[1] = parser (*pstr, pstr, new->prio);
 164     if ((new->ops[1] == NULL) || ((new->ops[1] != ERROR_OP) && (new->ops[1]->prio == 9))) {
 165         delelement (new->ops[1]);
 166         new->ops[1] = ERROR_OP;
 167     }
 168     if (new->ops[1] == ERROR_OP) {
 169         delelement (new);
 170         *proot = NULL;
 171         return ERROR_OP;
 172     }
 173     *proot = newelement (Val, 1, 5);
 174     if (*proot == NULL) {
 175         delelement (new);
 176         return ERROR_OP;
 177     }
 178     (*proot)->ops[0] = new;
 179
 180     return *proot;
 181 }
 182
 183 /* parser function */
 184
 185 element_t *parser (char *str, char **next, int prio)
 186 {
 187     element_t *root = NULL;
 188     int i;
 189
 190     VERBOSE (DEBUG, fprintf (stdout, "Starting parsing\n"));
 191
 192     /* main loop */
 193     while (*str != '\0') {
 194         int found = 0;
 195         element_t *new = NULL;
 196         VERBOSE (INFO, fprintf (stdout, "Processing: %s\n", str));
 197
 198         /* skip spaces and tabs */
 199
 200         if ((*str == ' ') || (*str == '\t')) {
 201             str++;
 202             continue;
 203         }
 204
 205         /* check for open brace */
 206
 207         if (*str == '{') {
 208             VERBOSE (DEBUG, fprintf (stdout, "start processing brace\n"));
 209             if (root != NULL) {
 210                 delelement (root);
 211                 return ERROR_OP;
 212             }
 213             element_t **prog = NULL;
 214             new = newelement (Prog, 0, 5);
 215             if (new == NULL) {
 216                 delelement (root);
 217                 return ERROR_OP;
 218             }
 219             root = new;
 220             prog = &root;
 221
 222             do {
 223                 new = parser (str + 1, &str, 0);
 224                 if ((new == NULL) || ((new != ERROR_OP) && (new->prio == 9))) {
 225                     delelement (new);
 226                     new = ERROR_OP;
 227                 }
 228                 if (new == ERROR_OP) {
 229                     delelement (root);
 230                     return ERROR_OP;
 231                 }
 232                 element_t *newprog = newelement (Prog, (*prog)->nbops + 1, 5);
 233                 for (i = 0; i < (*prog)->nbops; i++) {
 234                     newprog->ops[i] = (*prog)->ops[i];
 235                     (*prog)->ops[i] = NULL;
 236                 }
 237                 newprog->ops[(*prog)->nbops] = new;
 238                 delelement (*prog);
 239                 (*prog) = newprog;
 240             } while (*str == ',');
 241
 242             if (*str != '}') {
 243                 delelement (root);
 244                 return ERROR_OP;
 245             }
 246             str++;
 247             VERBOSE (DEBUG, fprintf (stdout, "stop processing brace\n"));
 248             continue;
 249         }
 250
 251         /* check for open bracket */
 252
 253         if (*str == '(') {
 254             VERBOSE (DEBUG, fprintf (stdout, "start processing bracket\n"));
 255             if (root) {
 256                 do {
 257                     found = 0;
 258                     new = parser (str + 1, &str, 0);
 259                     if ((new == NULL) || ((new != ERROR_OP) && (new->prio == 9))) {
 260                         delelement (new);
 261                         new = ERROR_OP;
 262                     }
 263                     if ((new == NULL) || (new == ERROR_OP)) {
 264                         delelement (root);
 265                         return ERROR_OP;
 266                     }
 267                     for (i = 0; i < root->nbops; i++) {
 268                         if (root->ops[i] == NULL) {
 269                             root->ops[i] = new;
 270                             found = 1;
 271                             break;
 272                         }
 273                     }
 274                     if (!found) {
 275                         delelement (new);
 276                         delelement (root);
 277                         return ERROR_OP;
 278                     }
 279                 } while (*str == ',');
 280             } else {
 281                 root = newelement (Val, 1, 5);
 282                 if (root == NULL) {
 283                     return ERROR_OP;
 284                 }
 285                 new = parser (str + 1, &str, 0);
 286                 if ((new == NULL) || ((new != ERROR_OP) && (new->prio == 9))) {
 287                     delelement (new);
 288                     new = ERROR_OP;
 289                 }
 290                 if ((new == NULL) || (new == ERROR_OP) || (*str == ',')) {
 291                     delelement (new);
 292                     delelement (root);
 293                     return ERROR_OP;
 294                 }
 295                 root->ops[0] = new;
 296             }
 297             if (*str != ')') {
 298                 delelement (root);
 299                 return ERROR_OP;
 300             }
 301             str++;
 302             VERBOSE (DEBUG, fprintf (stdout, "stop processing bracket\n"));
 303             continue;
 304         }
 305
 306         /* check for closing bracket, closing brace or koma */
 307
 308         if ((*str == ')') || (*str == '}') || (*str == ',')) {
 309             if (prio == -9) {
 310                 delelement (root);
 311                 return ERROR_OP;
 312             }
 313             if (next != NULL) {
 314                 *next = str;
 315             }
 316             return root;
 317         }
 318
 319         /* look for operators */
 320
 321         for (i = 0; i < NB_OPERATORS; i++) {
 322             keyword_t *operator = operators + i;
 323             if (codecmp (operator->keyword, str) == 0) {
 324                 VERBOSE (DEBUG, fprintf (stdout, "start processing operator\n"));
 325                 if (root) {
 326                     if ((prio) && (prio > operator->prio)) {
 327                         VERBOSE (DEBUG, fprintf (stdout, "stop because operator priority\n"));
 328                         *next = str;
 329                         return root;
 330                     }
 331                     str += operator->offset;
 332                     VERBOSE (INFO, fprintf (stdout, "Oper: %d\n", operator->func));
 333                     if (subparser (&root, &str, operator->func, operator->nbops, operator->prio) == ERROR_OP) {
 334                         delelement (root);
 335                         return ERROR_OP;
 336                     }
 337                 } else if (*str == '-') {
 338                     new = newelement (Sig, 1, 9);
 339                     if (new == NULL) {
 340                         return ERROR_OP;
 341                     }
 342                     root = new;
 343                 } else {
 344                     return ERROR_OP;
 345                 }
 346                 found = 1;
 347                 VERBOSE (DEBUG, fprintf (stdout, "stop processing operator\n"));
 348                 break;
 349             }
 350         }
 351         if (found) {
 352             continue;
 353         }
 354
 355         /* look for functions */
 356
 357         for (i = 0; i < NB_FUNCTIONS; i++) {
 358             keyword_t *function = functions + i;
 359             if (codecmp (function->keyword, str) == 0) {
 360                 VERBOSE (DEBUG, fprintf (stdout, "start processing function\n"));
 361                 if (root == NULL) {
 362                     VERBOSE (INFO, fprintf (stdout, "Func: %d\n", function->func));
 363                     new = newelement (function->func, function->nbops, function->prio);
 364                     if (new == NULL) {
 365                         return ERROR_OP;
 366                     }
 367                     root = new;
 368                 } else {
 369                     delelement (root);
 370                     return ERROR_OP;
 371                 }
 372                 str += function->offset;
 373                 found = 1;
 374                 VERBOSE (DEBUG, fprintf (stdout, "stop processing function\n"));
 375                 break;
 376             }
 377         }
 378         if (found) {
 379             continue;
 380         }
 381
 382         /* look for constant */
 383
 384         for (i = 0; i < NB_CONSTANTS; i++) {
 385             keyword_t *constant = constants + i;
 386             if (codecmp (constant->keyword, str) == 0) {
 387                 VERBOSE (DEBUG, fprintf (stdout, "start processing constant\n"));
 388                 if (root == NULL) {
 389                     VERBOSE (INFO, fprintf (stdout, "Const: %d\n", constant->func));
 390                     new = newelement (constant->func, constant->nbops, constant->prio);
 391                     if (new == NULL) {
 392                         return ERROR_OP;
 393                     }
 394                     root = new;
 395                 } else {
 396                     delelement (root);
 397                     return ERROR_OP;
 398                 }
 399                 str += constant->offset;
 400                 found = 1;
 401                 VERBOSE (DEBUG, fprintf (stdout, "stop processing constant\n"));
 402                 break;
 403             }
 404         }
 405         if (found) {
 406             continue;
 407         }
 408
 409         /* look for number */
 410
 411         if (((*str >= '0') && (*str <= '9')) ||
 412             (*str == '.') || (*str == '+') || (*str == '-')) {
 413             VERBOSE (DEBUG, fprintf (stdout, "start processing value\n"));
 414             char *pt;
 415             double value = strtod (str, &pt);
 416             VERBOSE (INFO, fprintf (stdout, "Value: %f\n", value));
 417             if (str != pt) {
 418                 if ((root == NULL) || (root->prio == 6)) {
 419                     new = newelement (Val, 1, 5);
 420                     if (new == NULL) {
 421                         return ERROR_OP;
 422                     }
 423                     new->value = value;
 424                     if (root == NULL) {
 425                         root = new;
 426                     } else {
 427                         for (i = 0; i < root->nbops; i++) {
 428                             if (root->ops[i] == NULL) {
 429                                 root->ops[i] = new;
 430                                 found = 1;
 431                                 break;
 432                             }
 433                         }
 434                         if (!found) {
 435                             delelement (new);
 436                             delelement (root);
 437                             return ERROR_OP;
 438                         }
 439                     }
 440                     str = pt;
 441                 } else if ((*str == '+') || (*str == '-')) {
 442                     if ((prio) && (prio > 1)) {
 443                         VERBOSE (DEBUG, fprintf (stdout, "stop because operator priority\n"));
 444                         *next = str;
 445                         return root;
 446                     }
 447                     if (subparser (&root, &str, Add, 2, 1) == ERROR_OP) {
 448                         delelement (root);
 449                         return ERROR_OP;
 450                     }
 451                 } else {
 452                     delelement (root);
 453                     return ERROR_OP;
 454                 }
 455                 found = 1;
 456             }
 457             VERBOSE (DEBUG, fprintf (stdout, "stop processing value\n"));
 458         }
 459
 460         /* error */
 461
 462         if (!found) {
 463             delelement (root);
 464             return ERROR_OP;
 465         }
 466
 467     }
 468
 469     if (next != NULL) {
 470         *next = str;
 471     }
 472
 473     return root;
 474 }
 475
 476 /* print element tree */
 477
 478 void print_element (element_t *root, int level)
 479 {
 480     char *func = NULL;
 481     int i;
 482
 483     if ((root == NULL) || (root == ERROR_OP)) {
 484         return;
 485     }
 486
 487     for (i = 0; i < level; i++) {
 488         fprintf (stdout, " ");
 489     }
 490
 491     switch (root->func) {
 492     case Val: func = "Value"; break;
 493     case Sig: func = "Sign"; break;
 494     case Add: func = "Addition"; break;
 495     case Sub: func = "Subtraction"; break;
 496     case Mul: func = "Multiplication"; break;
 497     case Div: func = "Division"; break;
 498     case Mod: func = "Modulo"; break;
 499     case Pow: func = "Power"; break;
 500     case Sqr: func = "Square Root"; break;
 501     case Cos: func = "Cosine"; break;
 502     case Sin: func = "Sine"; break;
 503     case Atan: func = "Arc Tangent"; break;
 504     case Log: func = "Logarithm"; break;
 505     case Exp: func = "Exponantial"; break;
 506     case Store: func = "Store"; break;
 507     case Recall: func = "Recall"; break;
 508     case Inc: func = "Increase"; break;
 509     case Dec: func = "Decrease"; break;
 510     case Disp: func = "Display"; break;
 511     case Quit: func = "Quit"; break;
 512     case Help: func = "Help"; break;
 513     case Ans: func = "Ans"; break;
 514     case Pi: func = "Pi"; break;
 515     case E: func = "E"; break;
 516     case Equal: func = "Equal"; break;
 517     case Diff: func = "Different"; break;
 518     case Ge: func = "Greater or equal"; break;
 519     case Le: func = "Lesser or equal"; break;
 520     case Gt: func = "Greater"; break;
 521     case Lt: func = "Lesser"; break;
 522     case And: func = "And"; break;
 523     case Or: func = "Or"; break;
 524     case Not: func = "Not"; break;
 525     case Cond: func = "Condition"; break;
 526     case While: func = "While"; break;
 527     case Prog: func = "Program"; break;
 528     }
 529
 530     fprintf (stdout, "Function: %s\n", func);
 531
 532     if ((root->func == Val) && (root->ops[0] == NULL)) {
 533         for (i = 0; i < level; i++) {
 534             fprintf (stdout, " ");
 535         }
 536         fprintf (stdout, "value: %f\n", root->value);
 537     } else {
 538         for (i = 0; i < root->nbops; i++) {
 539             print_element (root->ops[i], level + 1);
 540         }
 541     }
 542 }
 543
 544 /* storage functions */
 545
 546 double store (int index, double value)
 547 {
 548     if ((index > 0) && (index <= STORAGE_SIZE)) {
 549         storage[index - 1] = value;
 550     } else {
 551         VERBOSE (WARNING, fprintf (stdout, "invalid index (%d) [1, %d]\n", index, STORAGE_SIZE));
 552     }
 553     return value;
 554 }
 555
 556 double recall (int index)
 557 {
 558     if ((index > 0) && (index <= STORAGE_SIZE)) {
 559         return storage[index - 1];
 560     } else {
 561         VERBOSE (WARNING, fprintf (stdout, "invalid index (%d) [1, %d]\n", index, STORAGE_SIZE));
 562     }
 563     return 0;
 564 }
 565
 566 double increase (int index)
 567 {
 568     if ((index > 0) && (index <= STORAGE_SIZE)) {
 569         return storage[index - 1]++;
 570     } else {
 571         VERBOSE (WARNING, fprintf (stdout, "invalid index (%d) [1, %d]\n", index, STORAGE_SIZE));
 572     }
 573     return 0;
 574 }
 575
 576 double decrease (int index)
 577 {
 578     if ((index > 0) && (index <= STORAGE_SIZE)) {
 579         return storage[index - 1]--;
 580     } else {
 581         VERBOSE (WARNING, fprintf (stdout, "invalid index (%d) [1, %d]\n", index, STORAGE_SIZE));
 582     }
 583     return 0;
 584 }
 585
 586 void display (void)
 587 {
 588     int i;
 589     fprintf (stdout, "storage:");
 590     for (i = 0; i < STORAGE_SIZE; i++) {
 591         fprintf (stdout, " %g", storage[i]);
 592     }
 593     fprintf (stdout, "\n");
 594 }
 595
 596 /* While do function */
 597
 598 double while_do (element_t *cond, element_t *action)
 599 {
 600     double ret = 0;
 601     element_t *temp = NULL;
 602
 603     VERBOSE (DEBUG, fprintf (stdout, "starting while loop\n"));
 604     if (cond == NULL) {
 605         return ret;
 606     }
 607     while (1) {
 608         VERBOSE (DEBUG, fprintf (stdout, "loop...\n"));
 609
 610         temp = dupelement (cond);
 611         if (!evaluate_element (temp, 0)) {
 612             break;
 613         }
 614         if (action) {
 615             temp = dupelement (action);
 616             ret = evaluate_element (temp, 0);
 617         }
 618     }
 619
 620     VERBOSE (DEBUG, fprintf (stdout, "ending while loop\n"));
 621
 622     return ret;
 623 }
 624
 625 /* program function */
 626
 627 double program_do (element_t **prog, int nbcalls)
 628 {
 629     double ret = 0;
 630     int i;
 631     for (i = 0; i < nbcalls; i++) {
 632         ret = evaluate_element (prog[i], 0);
 633         prog[i] = NULL;
 634     }
 635     return ret;
 636 }
 637
 638 /* quit function */
 639
 640 void quit (void)
 641 {
 642     fprintf (stdout, "bye\n");
 643     exit (0);
 644 }
 645
 646 /* help message */
 647
 648 void help (void)
 649 {
 650     fprintf (stdout, "calc is a simple calculator\n\n");
 651     fprintf (stdout, "supported operators:");
 652     fprintf (stdout, " + - * / %% ^\n");
 653     fprintf (stdout, "camparison operators:");
 654     fprintf (stdout, " == != >= <= > <\n");
 655     fprintf (stdout, "logical operators:");
 656     fprintf (stdout, " & | !\n");
 657     fprintf (stdout, "supported functions:");
 658     fprintf (stdout, " pow sqrt cos sin atan log exp\n");
 659     fprintf (stdout, "storage functions:");
 660     fprintf (stdout, " sto rcl inc dec\n");
 661     fprintf (stdout, "conditional functions:");
 662     fprintf (stdout, " cond\n");
 663     fprintf (stdout, "miscellaneous functions:");
 664     fprintf (stdout, " quit help\n");
 665     fprintf (stdout, "supported constants:");
 666     fprintf (stdout, " e pi\n");
 667 }
 668
 669 /* evaluate element tree */
 670
 671 #define MASK_SUB 0x1
 672 #define MASK_DIV 0x2
 673
 674 double evaluate_element (element_t *root, char mask)
 675 {
 676     double op0 = 0, op1 = 0;
 677     char nextmask = mask;
 678
 679     if ((root == NULL) || (root == ERROR_OP)) {
 680         VERBOSE (WARNING, fprintf (stdout, "error while evaluating\n"));
 681         return 0;
 682     }
 683
 684     /* mask to manage sub operator sub and div */
 685     switch (root->func) {
 686     case Add:
 687         nextmask &= ~MASK_SUB;
 688         nextmask &= ~MASK_DIV;
 689         break;
 690     case Sub:
 691         nextmask |= MASK_SUB;
 692         nextmask &= ~MASK_DIV;
 693         break;
 694     case Mul:
 695         nextmask &= ~MASK_DIV;
 696         break;
 697     case Div:
 698         nextmask |= MASK_DIV;
 699         break;
 700     default:
 701         nextmask = mask;
 702     }
 703
 704     switch (root->func) {
 705     case Val:
 706     case Sig:
 707         op0 = (root->ops[0]) ? evaluate_element (root->ops[0], nextmask) : root->value;
 708         break;
 709     case Add:
 710     case Sub:
 711     case Mul:
 712     case Div:
 713     case Mod:
 714     case Pow:
 715     case Store:
 716     case Equal:
 717     case Diff:
 718     case Ge:
 719     case Le:
 720     case Gt:
 721     case Lt:
 722     case And:
 723     case Or:
 724         if (root->ops[1]) {
 725             op1 = evaluate_element (root->ops[1], nextmask);
 726         } else if (root->func != Store) {
 727             VERBOSE (WARNING, fprintf (stdout, "error while evaluating (op[1])\n"));
 728             return 0;
 729         }
 730         /* fallthrough */
 731     case Sqr:
 732     case Cos:
 733     case Sin:
 734     case Atan:
 735     case Log:
 736     case Exp:
 737     case Recall:
 738     case Inc:
 739     case Dec:
 740     case Not:
 741     case Cond:
 742         if (root->ops[0]) {
 743             op0 = evaluate_element (root->ops[0], 0);
 744         } else {
 745             VERBOSE (WARNING, fprintf (stdout, "error while evaluating (op[0])\n"));
 746             return 0;
 747         }
 748         break;
 749     case Disp:
 750     case Quit:
 751     case Help:
 752     case Ans:
 753     case Pi:
 754     case E:
 755     case Prog:
 756         break;
 757     case While:
 758         if (root->ops[0] == NULL) {
 759             VERBOSE (WARNING, fprintf (stdout, "error while evaluating (op[0])\n"));
 760             return 0;
 761         }
 762         break;
 763     }
 764
 765     switch (root->func) {
 766     case Val: return op0;
 767     case Sig: return -op0;
 768     case Add: return ((mask & MASK_SUB) == 0) ? op0 + op1 : op0 - op1;
 769     case Sub: return ((mask & MASK_SUB) == 0) ? op0 - op1 : op0 + op1;
 770     case Mul: return ((mask & MASK_DIV) == 0) ? op0 * op1 : op0 / op1;
 771     case Div: return ((mask & MASK_DIV) == 0) ? op0 / op1 : op0 * op1;
 772     case Mod: return fmod (op0, op1);
 773     case Pow: return pow (op0, op1);
 774     case Sqr: return sqrt (op0);
 775     case Cos: return cos (op0);
 776     case Sin: return sin (op0);
 777     case Atan: return atan (op0);
 778     case Log: return log (op0);
 779     case Exp: return exp (op0);
 780     case Store: return store ((int)op0, (op1) ? op1 : answer);
 781     case Recall: return recall ((int)op0);
 782     case Inc: return increase ((int)op0);
 783     case Dec: return decrease ((int)op0);
 784     case Disp: display (); break;
 785     case Quit: quit (); break;
 786     case Help: help (); break;
 787     case Ans: return answer;
 788     case Pi: return M_PI;
 789     case E: return M_E;
 790     case Equal: return op0 == op1;
 791     case Diff: return op0 != op1;
 792     case Ge: return op0 >= op1;
 793     case Le: return op0 <= op1;
 794     case Gt: return op0 > op1;
 795     case Lt: return op0 < op1;
 796     case And: return (op0 != 0) && (op1 != 0);
 797     case Or: return (op0 != 0) || (op1 != 0);
 798     case Not: return (op0 == 0);
 799     case Cond:
 800         if ((op0) && (root->ops[1])) {
 801             return evaluate_element (root->ops[1], 0);
 802         } else if ((!op0) && (root->ops[2])) {
 803             return evaluate_element (root->ops[2], 0);
 804         } else {
 805             return 0;
 806         }
 807     case While: return while_do (root->ops[0], root->ops[1]);
 808     case Prog: return program_do (root->ops, root->nbops);
 809     }
 810
 811     return 0;
 812 }
 813
 814 /* vim: set ts=4 sw=4 et: */