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