File: bwb_exp.c

package info (click to toggle)
bwbasic 2.20pl2-11
  • links: PTS
  • area: main
  • in suites: buster, jessie, jessie-kfreebsd, stretch, wheezy
  • size: 1,236 kB
  • sloc: ansic: 21,001; makefile: 80
file content (1490 lines) | stat: -rw-r--r-- 37,040 bytes parent folder | download | duplicates (10)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
/****************************************************************

        bwb_exp.c       Expression Parser
                        for Bywater BASIC Interpreter

                        Copyright (c) 1993, Ted A. Campbell
                        Bywater Software

                        email: tcamp@delphi.com

        Copyright and Permissions Information:

        All U.S. and international rights are claimed by the author,
        Ted A. Campbell.

	This software is released under the terms of the GNU General
	Public License (GPL), which is distributed with this software
	in the file "COPYING".  The GPL specifies the terms under
	which users may copy and use the software in this distribution.

	A separate license is available for commercial distribution,
	for information on which you should contact the author.

****************************************************************/

/*---------------------------------------------------------------*/
/* NOTE: Modifications marked "JBV" were made by Jon B. Volkoff, */
/* 11/1995 (eidetics@cerf.net).                                  */
/*---------------------------------------------------------------*/

#include <stdio.h>
#include <ctype.h>
#include <math.h>

#include "bwbasic.h"
#include "bwb_mes.h"

/***************************************************************

        FUNCTION:	bwb_exp()

        DESCRIPTION:	This is the function by which the expression
			parser is called.

***************************************************************/

#if ANSI_C
struct exp_ese *
bwb_exp( char *expression, int assignment, int *position )
#else
struct exp_ese *
bwb_exp( expression, assignment, position )
   char *expression;
   int assignment;
   int *position;
#endif
   {
   struct exp_ese *rval;			/* return value */
   int entry_level, main_loop, err_condition;
   char *e;                                     /* pointer to current string */
   int r;                                       /* return value from functions */
   register int c;                              /* quick counter */
#if OLD_WAY
   int adv_loop;
#endif

#if INTENSIVE_DEBUG
   sprintf( bwb_ebuf, "entered bwb_exp(): expression <%s> assignment <%d> level <%d>",
      & ( expression[ *position ] ), assignment, CURTASK expsc );
   bwb_debug( bwb_ebuf );
#endif

   /* save the entry level of the expression stack in order to
      check it at the end of this function */

   entry_level = CURTASK expsc;
   err_condition = FALSE;

   /* advance past whitespace or beginning of line segment */

#if MULTISEG_LINES
   if ( expression[ *position ] == ':' )
      {
      ++( *position );
      }
#endif
   adv_ws( expression, position );
#if MULTISEG_LINES
   if ( expression[ *position ] == ':' )
      {
      ++( *position );
      adv_ws( expression, position );
      }
#endif

   /* increment the expression stack counter to get a new level */

   inc_esc();

   /* check to be sure there is a legitimate expression
      and set initial parameters for the main loop */

   if ( is_eol( expression, position ) == TRUE )
      {
      main_loop = FALSE;    /* break out of loop */
      }
   else
      {
      main_loop = TRUE;
      CURTASK exps[ CURTASK expsc ].pos_adv = 0;
      }

#if OLDWAY
   adv_loop = TRUE;
   while( adv_loop == TRUE )
      {
      switch( expression[ *position ] )
         {
         case ' ':                           /* whitespace */
         case '\t':
            ++(*position);
            break;
         case '\0':                          /* end of string */
         case '\r':
         case '\n':
            main_loop = adv_loop = FALSE;    /* break out of loop */
            break;
         default:
            adv_loop = FALSE;
            main_loop = TRUE;
            CURTASK exps[ CURTASK expsc ].pos_adv = 0;
            break;
         }
      }
#endif

   /* main parsing loop */

   while ( main_loop == TRUE )
      {

      /* set variable <e> to the start of the expression */

      e = &( expression[ *position ] );

#if INTENSIVE_DEBUG
      sprintf( bwb_ebuf, "in bwb_exp(): main loop, level <%d> element <%s> ",
         CURTASK expsc, e );
      bwb_debug( bwb_ebuf );
#endif

      /* detect the operation required at this level */

      CURTASK exps[ CURTASK expsc ].operation = exp_findop( e );

#if INTENSIVE_DEBUG
      sprintf( bwb_ebuf, "in bwb_exp(): exp_findop() returned <%d>",
         CURTASK exps[ CURTASK expsc ].operation );
      bwb_debug( bwb_ebuf );
#endif

      /* perform actions specific to the operation */

      switch( CURTASK exps[ CURTASK expsc ].operation )
         {
         case OP_ERROR:
            main_loop = FALSE;
            err_condition = TRUE;
            break;

	 case OP_TERMINATE:                /* terminate at THEN, ELSE, TO */
#if INTENSIVE_DEBUG
	    bwb_debug( "in bwb_exp(): Found OP_TERMINATE" );
#endif
         case OP_STRJOIN:                  /* string join or tab */
         case OP_STRTAB:
	    main_loop = FALSE;
	    err_condition = FALSE;
	    dec_esc();
	    break;

	 case OP_ADD:                      /* in the case of any numerical operation, */
         case OP_SUBTRACT:
         case OP_MULTIPLY:
         case OP_DIVIDE:
         case OP_MODULUS:
         case OP_EXPONENT:
         case OP_INTDIVISION:
         case OP_GREATERTHAN:
         case OP_LESSTHAN:
         case OP_GTEQ:
         case OP_LTEQ:
         case OP_NOTEQUAL:
         case OP_NOT:
         case OP_AND:
         case OP_OR:
         case OP_XOR:
         case OP_IMPLIES:
         case OP_EQUIV:
         case OP_NEGATION: /* JBV */

#if INTENSIVE_DEBUG
            sprintf( bwb_ebuf, "in bwb_exp(): operator detected." );
            bwb_debug( bwb_ebuf );
#endif

            CURTASK exps[ CURTASK expsc ].pos_adv = -1;             /* set to strange number */

            /* cycle through operator table to find match */

            for ( c = 0; c < N_OPERATORS; ++c )
               {
               if ( exp_ops[ c ].operation == CURTASK exps[ CURTASK expsc ].operation )
                  {
                  CURTASK exps[ CURTASK expsc ].pos_adv = strlen( exp_ops[ c ].symbol );
                  }
               }

            if ( CURTASK exps[ CURTASK expsc ].pos_adv == -1 )      /* was a match found? */
               {
               CURTASK exps[ CURTASK expsc ].pos_adv = 0;           /* no -- set to 0 */
               }
            break;                         /* and move on */

         case OP_EQUALS:

#if INTENSIVE_DEBUG
            sprintf( bwb_ebuf, "in bwb_exp(): equal sign detected." );
            bwb_debug( bwb_ebuf );
#endif

            if ( assignment == TRUE )
               {
               CURTASK exps[ CURTASK expsc ].operation = OP_ASSIGN;
               }
            CURTASK exps[ CURTASK expsc ].pos_adv = 1;
            break;

         case PARENTHESIS:
            r = exp_paren( e );
            break;

	 case CONST_STRING:
            r = exp_strconst( e );
            break;

	 case CONST_NUMERICAL:
            r = exp_numconst( e );
#if INTENSIVE_DEBUG
            sprintf( bwb_ebuf, "in bwb_exp(): return from exp_numconst(), r = <%d>",
               r );
            bwb_debug( bwb_ebuf );
#endif
            break;

         case FUNCTION:

#if INTENSIVE_DEBUG
            sprintf( bwb_ebuf, "in bwb_exp(): calling exp_function(), expression <%s>",
               e );
            bwb_debug( bwb_ebuf );
#endif

            r = exp_function( e );
            break;

         case OP_USERFNC:

#if INTENSIVE_DEBUG
            sprintf( bwb_ebuf, "in bwb_exp(): calling exp_ufnc(), expression <%s>",
               e );
            bwb_debug( bwb_ebuf );
#endif

	    r = exp_ufnc( e );

#if INTENSIVE_DEBUG
	    sprintf( bwb_ebuf, "in bwb_exp(): return from exp_ufnc(), buffer <%s>",
	       &( expression[ *position ] ) );
	    bwb_debug( bwb_ebuf );
#endif

            break;

         case VARIABLE:
            r = exp_variable( e );
            break;

	 default:
            err_condition = TRUE;
            main_loop = FALSE;
#if PROG_ERRORS
            sprintf( bwb_ebuf, "in bwb_exp.c:bwb_exp(): unidentified operation (%d).",
               CURTASK exps[ CURTASK expsc ].operation );
            bwb_error( bwb_ebuf );
#else
            bwb_error( err_syntax );
#endif
            break;
         }

      /* increment *position counter based on previous actions */

      *position += CURTASK exps[ CURTASK expsc ].pos_adv;
      CURTASK exps[ CURTASK expsc ].pos_adv = 0;            /* reset advance counter */

#if INTENSIVE_DEBUG
      sprintf( bwb_ebuf, "in bwb_exp(): advanced position; r <%d> err_c <%d>",
         r, err_condition );
      bwb_debug( bwb_ebuf );
#endif

#if INTENSIVE_DEBUG
      if ( CURTASK exps[ CURTASK expsc ].operation == OP_EQUALS )
         {
         sprintf( bwb_ebuf, "in bwb_exp(): with OP_EQUALS: finished case" );
         bwb_debug( bwb_ebuf );
         }
#endif

      /* check for end of string */

      if ( is_eol( expression, position ) == TRUE )
         {
         main_loop = FALSE;    /* break out of loop */         
         }

#if OLDWAY
      adv_loop = TRUE;
      while( adv_loop == TRUE )
         {
         switch( expression[ *position ] )
            {
            case ' ':                           /* whitespace */
            case '\t':
               ++(*position);
               break;
            case '\0':                          /* end of string */
            case '\r':
            case '\n':
            case ':':
               main_loop = adv_loop = FALSE;    /* break out of loop */
               break;
            default:
               adv_loop = FALSE;
               break;
            }
         }
#endif

      /* get a new stack level before looping */

      if ( main_loop == TRUE )
         {
         r = inc_esc();
#if INTENSIVE_DEBUG
         sprintf( bwb_ebuf, "in bwb_exp(): increment esc, r <%d>, err_c <%d>",
            r, err_condition );
         bwb_debug( bwb_ebuf );
#endif
         }

      /* check for error return */

      if ( r == OP_ERROR )
         {
#if INTENSIVE_DEBUG
         sprintf( bwb_ebuf, "in bwb_exp(): found r == OP_ERROR." );
         bwb_debug( bwb_ebuf );
#endif
         main_loop = FALSE;
         err_condition = TRUE;
         }
      else
         {
         r = TRUE;
         }

      }                                 /* end of main parsing loop */

#if INTENSIVE_DEBUG
   sprintf( bwb_ebuf, "in bwb_exp(): breakout from main parsing loop, r <%d> err_c <%d>",
      r, err_condition );
   bwb_debug( bwb_ebuf );
#endif

   /* check error condition */

   if ( err_condition == TRUE )
      {

#if INTENSIVE_DEBUG
      sprintf( bwb_ebuf, "error detected in expression parser" );
      bwb_debug( bwb_ebuf );
#endif

      /* decrement the expression stack counter until it matches entry_level */

      while( CURTASK expsc > entry_level )
         {
         dec_esc();
         }

#if PROG_ERRORS
      bwb_error( "in bwb_exp():  Error detected in parsing expression" );
#else
      bwb_error( err_syntax );
#endif
      }

   /* no error; normal exit from function */

   else
      {

      /* are any more operations needed? if we are still at entry level,
         then they are not */

      /* try operations */

      exp_operation( entry_level );

      /* see what is on top of the stack */

      if ( CURTASK expsc > ( entry_level + 1 ))
         {
         switch( CURTASK exps[ CURTASK expsc ].operation )
            {
            case OP_STRJOIN:
               if ( CURTASK expsc != ( entry_level + 2 ))
                  {
#if PROG_ERRORS
                  sprintf( bwb_ebuf, "in bwb_exp(): OP_STRJOIN in wrong position." );
                  bwb_error( bwb_ebuf );
#else
                  bwb_error( err_syntax );
#endif
                  }
               break;
            default:
#if PROG_ERRORS
               sprintf( bwb_ebuf, "in bwb_exp(): incomplete expression." );
               bwb_error( bwb_ebuf );
#else
               bwb_error( err_syntax );
#endif
               break;
            }

         /* decrement the expression stack counter */

#if INTENSIVE_DEBUG
         sprintf( bwb_ebuf, "in bwb_exp(): before dec_esc type is <%c>",
            CURTASK exps[ CURTASK expsc ].type );
         bwb_debug( bwb_ebuf );
#endif

         dec_esc();

         }

      /* assign rvar to the variable for the current level */

      rval = &( CURTASK exps[ CURTASK expsc ] );

      /* decrement the expression stack counter */

      dec_esc();

      /* check the current level before exit */

      if ( entry_level != CURTASK expsc )
         {
#if PROG_ERRORS
         sprintf( bwb_ebuf, "in bwb_exp(): exit stack level (%d) does not match entry stack level (%d)",
            CURTASK expsc, entry_level );
         bwb_error( bwb_ebuf );
#else
         bwb_error( err_overflow );
#endif
         }

      }

   /* return a pointer to the last stack level */

   return rval;

   }

/***************************************************************

	FUNCTION:       exp_findop()

	DESCRIPTION:    This function reads the expression to find
			what operation is required at its stack level.

***************************************************************/

#if ANSI_C
int
exp_findop( char *expression )
#else
int
exp_findop( expression )
   char *expression;
#endif
   {
   register int c;                              /* character counter */
   int carry_on;                                /* boolean: control while loop */
   int rval;                                    /* return value */
   char cbuf[ MAXSTRINGSIZE + 1 ];              /* capitalized expression */
   char nbuf[ MAXSTRINGSIZE + 1 ];              /* non-capitalized expression */
   int position;                                /* position in the expression */
   int adv_loop;                                /* control loop to build expression */

#if INTENSIVE_DEBUG
   sprintf( bwb_ebuf, "in exp_findop(): received <%s>", expression );
   bwb_debug( bwb_ebuf );
#endif

   /* set return value to OP_NULL initially */

   rval = OP_NULL;

   /* assign local pointer to expression to begin reading */

   position = 0;

   /* advance to the first significant character */

   adv_ws( expression, &position );

#if INTENSIVE_DEBUG
   sprintf( bwb_ebuf, "in exp_findop(): expression after advance <%s>",
      &( expression[ position ] ) );
   bwb_debug( bwb_ebuf );
#endif

   /* we now have the first significant character and can begin parsing */

   /* check the first character for an indication of a parenthetical
      expression, a string constant, or a numerical constant that begins
      with a digit (numerical constants beginning with a plus or minus
      sign or hex/octal/binary constants will have to be detected by
      exp_isnc() */

   carry_on = TRUE;
   switch ( expression[ position ] )
      {
      case '\"':                /* this should indicate a string constant */
         rval = CONST_STRING;
         break;
      case '(':                 /* this will indicate a simple parenthetical expression */
         rval = PARENTHESIS;
         break;

#if MULTISEG_LINES
      case ':':                 /* terminate processing */
#endif
      case ')':			/* end of argument list? */
         rval = OP_TERMINATE;
         break;

      case '0':                 /* these will indicate a numerical constant */
      case '1':
      case '2':
      case '3':
      case '4':
      case '5':
      case '6':
      case '7':
      case '8':
      case '9':
      case '.':
      case '&':                 /* designator for hex or octal constant */
         rval = CONST_NUMERICAL;
         break;
      }

#if INTENSIVE_DEBUG
   sprintf( bwb_ebuf, "in exp_findop(): rval pos 1 is <%d>", rval );
   bwb_debug( bwb_ebuf );
#endif

   /* String constants, numerical constants, open parentheses, and
      the plus and minus operators have been checked at this point;
      but if the return value is still OP_NULL, other possibilities
      must be checked, namely, other operators, function names, and
      variable names.  The function adv_element cannot be used here
      because it will stop, e.g., with certain operators and not
      include them in the returned element. */

   /* get a character string to be interpreted */

   adv_loop = TRUE;
   cbuf[ 0 ] = '\0';
   nbuf[ 0 ] = '\0';
   c = 0;
   while ( adv_loop == TRUE )
      {

#if INTENSIVE_DEBUG
      sprintf( bwb_ebuf, "in exp_findop() loop position <%d> char 0x%x",
	 c, expression[ position ] );
      bwb_debug( bwb_ebuf );
#endif

      switch( expression[ position ] )
	 {
	 case ' ':              /* whitespace */
	 case '\t':
	 case '\r':             /* end of line */
	 case '\n':
	 case '\0':             /* end of string */
	 case '(':              /* parenthesis terminating function name */
	    adv_loop = FALSE;
	    break;
	 default:
	    nbuf[ c ] = cbuf[ c ] = expression[ position ];
	    ++c;
	    nbuf[ c ] = cbuf[ c ] = '\0';
	    ++position;
	    break;
	 }

      if ( c >= MAXSTRINGSIZE )
	 {
	 adv_loop = FALSE;
	 }

      }
   bwb_strtoupper( cbuf );

#if INTENSIVE_DEBUG
   sprintf( bwb_ebuf, "in exp_findop(): cbuf element is <%s>", cbuf );
   bwb_debug( bwb_ebuf );
#endif

   /* check for numerical constant */

   if ( rval == OP_NULL )
      {
      rval = exp_isnc( cbuf );
      }

   /* check for other operators */

   if ( rval == OP_NULL )
      {
      rval = exp_isop( cbuf );
      }

   /* check for user-defined function */

   if ( rval == OP_NULL )
      {
      rval = exp_isufn( nbuf );
      }

   /* check for function name */

   if ( rval == OP_NULL )
      {
      rval = exp_isfn( nbuf );
      }

   /* check for a BASIC command, esp. to catch THEN or ELSE */

   if ( rval == OP_NULL )
      {
      rval = exp_iscmd( cbuf );
      }

   /* last: check for variable name, and assign it if there
      is not already one */

   if ( rval == OP_NULL )
      {
      rval = exp_isvn( nbuf );
      }

   /* return the value assigned (or OP_ERROR if none assigned) */

   if ( rval == OP_NULL )
      {
      return OP_ERROR;
      }
   else
      {
      return rval;
      }

   }

/***************************************************************

	FUNCTION:       exp_isnc()

	DESCRIPTION:    This function reads the expression to find
			if a numerical constant is present at this
			point.

***************************************************************/

#if ANSI_C
int
exp_isnc( char *expression )
#else
int
exp_isnc( expression )
   char *expression;
#endif
   {
   char tbuf[ MAXVARNAMESIZE + 1 ]; /* JBV */

   switch( expression[ 0 ] )
      {
      case '0':                 /* these will indicate a numerical constant */
      case '1':
      case '2':
      case '3':
      case '4':
      case '5':
      case '6':
      case '7':
      case '8':
      case '9':
      case '&':                 /* indicator for hex or octal constant */
         return CONST_NUMERICAL;
      case '+':
      case '-':

         /* if the previous stack level was a numerical value or a string,
            then this is certainly not one; return OP_NULL here
            and let the next function call to exp_isop() determine
            the (plus or minus) operator */

         if (  ( CURTASK exps[ CURTASK expsc - 1 ].operation == NUMBER )
            || ( CURTASK exps[ CURTASK expsc - 1 ].operation == VARIABLE )
            || ( CURTASK exps[ CURTASK expsc - 1 ].operation == CONST_STRING ) )
            {

#if INTENSIVE_DEBUG
            sprintf( bwb_ebuf, "in exp_isnc(): previous function is a number or string" );
            bwb_debug( bwb_ebuf );
#endif

            return OP_NULL;
            }

         /* similarly, if the previous stack level was a variable
            with a numerical value (not a string), then this level
            must be an operator, not a numerical constant */

         if ( ( CURTASK exps[ CURTASK expsc - 1 ].operation == VARIABLE )
            && ( CURTASK exps[ CURTASK expsc - 1 ].type != STRING ))
            {
            return OP_NULL;
            }

         /*--------------------------------------------------------*/
         /* Check for unary minus sign added by JBV.               */
         /* Could be prefixing a parenthetical expression or a     */
         /* variable name.                                         */
         /* But parentheses won't show up in expression (cbuf), so */
         /* just check for expression and variable name lengths.   */
         /*--------------------------------------------------------*/
         if (expression[0] == '-')
         {
             if (strlen(expression) == 1) return OP_NEGATION;
             exp_getvfname(&expression[1], tbuf);
             if (strlen(tbuf) != 0) return OP_NEGATION;
         }

         /* failing these tests, the argument must be a numerical
            constant preceded by a plus or minus sign */

         return CONST_NUMERICAL;

      default:
         return OP_NULL;
      }

   }

/***************************************************************

	FUNCTION:       exp_isop()

	DESCRIPTION:    This function reads the expression to find
			if a logical or mathematical operation is
			required at this point.

        This function presupposes that a numerical constant with
        affixed plus or minus sign has been ruled out.

***************************************************************/

#if ANSI_C
int
exp_isop( char *expression )
#else
int
exp_isop( expression )
   char *expression;
#endif
   {
   register int c;                              /* counter */

#if INTENSIVE_DEBUG
   sprintf( bwb_ebuf, "in exp_isop(): expression is <%s>", expression );
   bwb_debug( bwb_ebuf );
#endif

   /* compare the initial characters of the string with the table
      of operators */

   for ( c = 0; c < N_OPERATORS; ++c )
      {
      if ( strncmp( expression, exp_ops[ c ].symbol,
         (size_t) strlen( exp_ops[ c ].symbol ) ) == 0 )
         {

#if INTENSIVE_DEBUG
         sprintf( bwb_ebuf, "in exp_isop(): match <%s>, number <%d>.",
            exp_ops[ c ].symbol, c );
         bwb_debug( bwb_ebuf );
#endif

         return exp_ops[ c ].operation;
         }
      }

   /* search failed; return OP_NULL */

   return OP_NULL;

   }

/***************************************************************

	FUNCTION:       exp_iscmd()

	DESCRIPTION:    This function reads the expression to find
			if a BASIC command name is present; if so,
			it returns OP_TERMINATE to terminate expression
			parsing.  This is critical, for example, in
			parsing a conditional following IF where THEN,
			ELSE, and other BASIC commands may follow.

***************************************************************/

#if ANSI_C
int
exp_iscmd( char *expression )
#else
int
exp_iscmd( expression )
   char *expression;
#endif
   {
   register int n;

#if INTENSIVE_DEBUG
   sprintf( bwb_ebuf, "in exp_iscmd(): expression received <%s>",
      expression );
   bwb_debug( bwb_ebuf );
#endif

   /* first check for THEN or ELSE statements */

   if ( strcmp( expression, CMD_THEN ) == 0 )
      {
#if INTENSIVE_DEBUG
      sprintf( bwb_ebuf, "in exp_iscmd(): match found, <%s>",
	 expression );
      bwb_debug( bwb_ebuf );
#endif
      return OP_TERMINATE;
      }

#if STRUCT_CMDS
   if ( strcmp( expression, CMD_TO ) == 0 )
      {
#if INTENSIVE_DEBUG
      sprintf( bwb_ebuf, "in exp_iscmd(): match found, <%s>",
	 expression );
      bwb_debug( bwb_ebuf );
#endif
      return OP_TERMINATE;
      }
#endif

   if ( strcmp( expression, CMD_ELSE ) == 0 )
      {
#if INTENSIVE_DEBUG
      sprintf( bwb_ebuf, "in exp_iscmd(): match found, <%s>",
	 expression );
      bwb_debug( bwb_ebuf );
#endif
      return OP_TERMINATE;
      }

   /* run through the command table and search for a match */

   for ( n = 0; n < COMMANDS; ++n )
      {
      if ( strcmp( expression, bwb_cmdtable[ n ].name ) == 0 )
         {
#if INTENSIVE_DEBUG
         sprintf( bwb_ebuf, "in exp_iscmd(): match found, <%s>",
            expression );
         bwb_debug( bwb_ebuf );
#endif
         return OP_TERMINATE;
         }
#if INTENSIVE_DEBUG
      else
         {
         sprintf( bwb_ebuf, "in exp_iscmd(): No match, <%s> and <%s>; returns %d",
            expression, bwb_cmdtable[ n ].name,
            strcmp( expression, bwb_cmdtable[ n ].name ) );
         bwb_debug( bwb_ebuf );
         }
#endif
      }

   /* search failed, return NULL */

   return OP_NULL;

   }

/***************************************************************

        FUNCTION:   	exp_isufn()

        DESCRIPTION:  	This function reads the expression to find
        		if a user-defined function name is present
			at this point.

***************************************************************/

#if ANSI_C
int
exp_isufn( char *expression )
#else
int
exp_isufn( expression )
   char *expression;
#endif
   {
   struct fslte *f;
   char tbuf[ MAXVARNAMESIZE + 1 ];

   exp_getvfname( expression, tbuf );

   for ( f = CURTASK fslt_start.next; f != &CURTASK fslt_end; f = f->next )
      {
      if ( strcmp( f->name, tbuf ) == 0 )
         {
#if INTENSIVE_DEBUG
         sprintf( bwb_ebuf, "in exp_isufn(): found user function <%s>",
            tbuf );
         bwb_debug( bwb_ebuf );
#endif

         /* a user function name was found: but is it the local variable
            name for the user function? If so, return OP_NULL and the
            name will be read as a variable */

         if ( var_islocal( tbuf ) != NULL )
            {
            return OP_NULL;
            }
         else
            {

#if INTENSIVE_DEBUG
            sprintf( bwb_ebuf, "in exp_isufn(): found function <%s> not a local variable, EXEC level <%d>",
               tbuf, CURTASK exsc );
            bwb_debug( bwb_ebuf );
            getchar();
#endif

            return OP_USERFNC;
            }
         }
      }

   return OP_NULL;

   }

/***************************************************************

	FUNCTION:       exp_isfn()

	DESCRIPTION:    This function reads the expression to find
			if a function name is present at this point.

***************************************************************/

#if ANSI_C
int
exp_isfn( char *expression )
#else
int
exp_isfn( expression )
   char *expression;
#endif
   {

   /* Block out the call to exp_getvfname() if exp_isvn() is called
      after exp_isfn() */

   exp_getvfname( expression, CURTASK exps[ CURTASK expsc ].string );

#if INTENSIVE_DEBUG
   sprintf( bwb_ebuf, "in exp_isfn(): search for function <%s>",
      expression );
   bwb_debug( bwb_ebuf );
#endif

   if ( fnc_find( CURTASK exps[ CURTASK expsc ].string ) == NULL )
      {
#if INTENSIVE_DEBUG
      sprintf( bwb_ebuf, "in exp_isfn(): failed to find function <%s>",
         expression );
      bwb_debug( bwb_ebuf );
#endif
      return OP_NULL;
      }
   else
      {
#if INTENSIVE_DEBUG
      sprintf( bwb_ebuf, "in exp_isfn(): found function <%s>",
         expression );
      bwb_debug( bwb_ebuf );
#endif
      return FUNCTION;
      }

   }

/***************************************************************

	FUNCTION:       exp_isvn()

	DESCRIPTION:    This function reads the expression to find
			if a variable name at this point.

***************************************************************/

#if ANSI_C
int
exp_isvn( char *expression )
#else
int
exp_isvn( expression )
   char *expression;
#endif
   {

   /* Block out the call to exp_getvfname() if exp_isfn() is called
      after exp_isvn() */

   /* exp_getvfname( expression, CURTASK exps[ CURTASK expsc ].string ); */

   /* rule out null name */

   if ( strlen( CURTASK exps[ CURTASK expsc ].string ) == 0 )
      {
      return OP_NULL;
      }

#if INTENSIVE_DEBUG
   sprintf( bwb_ebuf, "in exp_isvn(): search for variable <%s>",
      CURTASK exps[ CURTASK expsc ].string );
   bwb_debug( bwb_ebuf );
#endif

   if ( var_find( CURTASK exps[ CURTASK expsc ].string ) == NULL )
      {
#if INTENSIVE_DEBUG
      sprintf( bwb_ebuf, "in exp_isvn(): failed to find variable <%s>",
         expression );
      bwb_debug( bwb_ebuf );
#endif
      return OP_NULL;
      }
   else
      {
#if INTENSIVE_DEBUG
      sprintf( bwb_ebuf, "in exp_isvn(): found variable <%s>",
         CURTASK exps[ CURTASK expsc ].string );
      bwb_debug( bwb_ebuf );
#endif
      return VARIABLE;
      }

   }

/***************************************************************

	FUNCTION:       exp_getvfname()

	DESCRIPTION:    This function reads the expression to find
			a variable or function name at this point.

***************************************************************/

#if ANSI_C
int
exp_getvfname( char *source, char *destination )
#else
int
exp_getvfname( source, destination )
   char *source;
   char *destination;
#endif
   {
   int s_pos, d_pos;                    /* source, destination positions */

#if INTENSIVE_DEBUG
   sprintf( bwb_ebuf, "in exp_getvfname(): source buffer <%s>", source );
   bwb_debug( bwb_ebuf );
#endif

   s_pos = d_pos = 0;
   destination[ 0 ] = '\0';
   while( source[ s_pos ] != '\0' )
      {

      /* all alphabetical characters are acceptable */

      if ( isalpha( source[ s_pos ] ) != 0 )

         {
         destination[ d_pos ] = source[ s_pos ];

         ++d_pos;
         ++s_pos;
         destination[ d_pos ] = '\0';
         }

      /* numerical characters are acceptable but not in the first position */

      else if (( isdigit( source[ s_pos ] ) != 0 ) && ( d_pos != 0 ))
         {
         destination[ d_pos ] = source[ s_pos ];
         ++d_pos;
         ++s_pos;
         destination[ d_pos ] = '\0';
         }

      /* other characters will have to be tried on their own merits */

      else
         {
         switch( source[ s_pos ] )
            {

            case '.':                           /* tolerated non-alphabetical characters */
            case '_':
               destination[ d_pos ] = source[ s_pos ];
               ++d_pos;
               ++s_pos;
               destination[ d_pos ] = '\0';
               break;

	    case STRING:                        /* terminating characters */
	    case '#':                           /* Microsoft-type double precision */
	    case '!':                           /* Microsoft-type single precision */

	       destination[ d_pos ] = source[ s_pos ];
               ++d_pos;
               ++s_pos;
               destination[ d_pos ] = '\0';

               return TRUE;

            case '(':				/* begin function/sub name */
               return TRUE;

            default:                            /* anything else is non-tolerated */
               return FALSE;
            }
         }
      }

#if INTENSIVE_DEBUG
   sprintf( bwb_ebuf, "in exp_getvfname(): found name <%s>", destination );
   bwb_debug( bwb_ebuf );
#endif

   return TRUE;                         /* exit after coming to the end */

   }

/***************************************************************

	FUNCTION:       exp_validarg()

	DESCRIPTION:    This function reads the expression to
			determine whether it is a valid argument (to be
			read recursively by bwb_exp() and passed to a
			function.

***************************************************************/

#if ANSI_C
int
exp_validarg( char *expression )
#else
int
exp_validarg( expression )
   char *expression;
#endif
   {
   register int c;

#if INTENSIVE_DEBUG
   sprintf( bwb_ebuf, "in exp_validarg(): expression <%s>.",
      expression );
   bwb_debug( bwb_ebuf );
#endif

   c = 0;
   while ( TRUE )
      {
      switch( expression[ c ] )
         {
         case ' ':
         case '\t':
            ++c;
            break;
         case '\0':
            return FALSE;
         default:
            return TRUE;
         }
      }

   }

/***************************************************************

        FUNCTION:   	exp_getnval()

	DESCRIPTION:    This function returns the numerical value
			contain in the expression-stack element
			pointed to by 'e'.

***************************************************************/

#if ANSI_C
bnumber
exp_getnval( struct exp_ese *e )
#else
bnumber
exp_getnval( e )
   struct exp_ese *e;
#endif
   {

   /* check for variable */

   if ( e->operation == VARIABLE )
      {
      switch( e->type )
         {
         case NUMBER:
            return (* var_findnval( e->xvar, e->array_pos ));
         default:
            bwb_error( err_mismatch );
            return (bnumber) 0.0;
         }
      }

   /* must be a numerical value */

   if ( e->operation != NUMBER )
      {
#if PROG_ERRORS
      sprintf( bwb_ebuf, "in exp_getnval(): operation <%d> is not a number",
         e->operation );
      bwb_error( bwb_ebuf );
#else
      bwb_error( err_syntax );
#endif
      return (bnumber) 0.0;
      }

   /* return specific values */

   switch( e->type )
      {
      case NUMBER:
         return e->nval;
      default:
#if PROG_ERRORS
         sprintf( bwb_ebuf, "in exp_getnval(): type is <%c>",
            e->type );
         bwb_error( bwb_ebuf );
#else
         bwb_error( err_syntax );
#endif
         return (bnumber) 0.0;
      }

   }

/***************************************************************

	FUNCTION:       exp_getsval()

	DESCRIPTION:    This function returns a pointer to the
			BASIC string structure pointed to by
			expression-stack element 'e'.

***************************************************************/

#if ANSI_C
bstring *
exp_getsval( struct exp_ese *e )
#else
bstring *
exp_getsval( e )
   struct exp_ese *e;
#endif
   {
   static bstring b;
#if TEST_BSTRING
   static int init = FALSE;

   if ( init == FALSE )
      {
      sprintf( b.name, "<exp_getsval() bstring>" );
      }
#endif

   b.rab = FALSE;

   /* return based on operation type */

   switch( e->operation )
      {
      case CONST_STRING:
      case OP_STRJOIN:
         return &( e->sval );
      case VARIABLE:
        switch( e->type )
            {
	    case STRING:
               return var_findsval( e->xvar, e->array_pos );
            case NUMBER:
               sprintf( bwb_ebuf, "%lf ", (double) exp_getnval( e ) );
               str_ctob( &b, bwb_ebuf );
               return &b;
            default:
#if PROG_ERRORS
               sprintf( bwb_ebuf, "in exp_getsval(): type <%c> inappropriate for NUMBER",
                  e->type );
               bwb_error( bwb_ebuf );
#else
               bwb_error( err_syntax );
#endif
               return NULL;
            }
	 break;

      case NUMBER:
        switch( e->type )
            {
	    case NUMBER:
               sprintf( bwb_ebuf, "%lf ", (double) exp_getnval( e ) );
               str_ctob( &b, bwb_ebuf );
               return &b;
            default:
#if PROG_ERRORS
               sprintf( bwb_ebuf, "in exp_getsval(): type <%c> inappropriate for NUMBER",
                  e->type );
               bwb_error( bwb_ebuf );
#else
               bwb_error( err_syntax );
#endif
               return NULL;
            }
	 break;
      default:
#if PROG_ERRORS
         sprintf( bwb_ebuf, "in exp_getsval(): operation <%d> inappropriate",
            e->operation );
         bwb_error( bwb_ebuf );
#else
         bwb_error( err_syntax );
#endif
         return NULL;
      }

   /* this point may not be reached */

   return NULL;

   }

/***************************************************************

	FUNCTION:       inc_esc()

	DESCRIPTION:    This function increments the expression
			stack counter.

***************************************************************/

#if ANSI_C
int
inc_esc( void )
#else
int
inc_esc()
#endif
   {

#if INTENSIVE_DEBUG
   sprintf( bwb_ebuf, "in inc_esc(): prev level <%d>",
      CURTASK expsc );
   bwb_debug ( bwb_ebuf );
#endif

   ++CURTASK expsc;
   if ( CURTASK expsc >= ESTACKSIZE )
      {
      --CURTASK expsc;
#if PROG_ERRORS
      sprintf( bwb_ebuf, "in inc_esc(): Maximum expression stack exceeded <%d>",
         CURTASK expsc );
      bwb_error( bwb_ebuf );
#else
      bwb_error( err_overflow );
#endif
      return OP_NULL;
      }

#if INTENSIVE_DEBUG
   sprintf( CURTASK exps[ CURTASK expsc ].string, "New Expression Stack Level %d", CURTASK expsc );
#endif

   CURTASK exps[ CURTASK expsc ].type = NUMBER;
   CURTASK exps[ CURTASK expsc ].operation = OP_NULL;
   CURTASK exps[ CURTASK expsc ].pos_adv = 0;

   return TRUE;
   }

/***************************************************************

	FUNCTION:       dec_esc()

	DESCRIPTION:    This function decrements the expression
			stack counter.

***************************************************************/

#if ANSI_C
int
dec_esc( void )
#else
int
dec_esc()
#endif
   {
   --CURTASK expsc;
   if ( CURTASK expsc < 0 )
      {
      CURTASK expsc = 0;
#if PROG_ERRORS
      sprintf( bwb_ebuf, "in dec_esc(): Expression stack counter < 0." );
      bwb_error( bwb_ebuf );
#else
      bwb_error( err_overflow );
#endif
      return OP_NULL;
      }

   return TRUE;
   }