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
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
1599
1600
1601
1602
1603
1604
1605
1606
1607
1608
1609
1610
1611
1612
1613
1614
1615
1616
1617
1618
1619
1620
1621
1622
1623
1624
1625
1626
1627
1628
1629
1630
1631
1632
1633
1634
1635
1636
1637
1638
1639
1640
1641
1642
1643
1644
1645
1646
1647
1648
1649
1650
1651
1652
1653
1654
1655
1656
1657
1658
1659
1660
1661
1662
1663
1664
1665
1666
1667
1668
1669
1670
1671
1672
1673
1674
1675
1676
1677
1678
1679
1680
1681
1682
1683
1684
1685
1686
1687
1688
1689
1690
1691
1692
1693
1694
1695
1696
1697
1698
1699
1700
1701
1702
1703
1704
1705
1706
1707
1708
1709
1710
1711
1712
1713
1714
1715
1716
1717
1718
1719
1720
1721
1722
1723
1724
1725
1726
1727
1728
1729
1730
1731
1732
1733
1734
1735
1736
1737
1738
1739
1740
1741
1742
1743
1744
1745
1746
1747
1748
1749
1750
1751
1752
1753
1754
1755
1756
1757
1758
1759
1760
1761
1762
1763
1764
1765
1766
1767
1768
1769
1770
1771
1772
1773
1774
1775
1776
1777
1778
1779
1780
1781
1782
1783
1784
1785
1786
1787
1788
1789
1790
1791
1792
1793
1794
1795
1796
1797
1798
1799
1800
1801
1802
1803
1804
1805
| | @c -*-texinfo-*-
@c This is part of the GNU Emacs Lisp Reference Manual.
@c Copyright (C) 1990--1995, 1998--1999, 2001--2020 Free Software
@c Foundation, Inc.
@c See the file elisp.texi for copying conditions.
@node Sequences Arrays Vectors
@chapter Sequences, Arrays, and Vectors
@cindex sequence
The @dfn{sequence} type is the union of two other Lisp types: lists
and arrays. In other words, any list is a sequence, and any array is
a sequence. The common property that all sequences have is that each
is an ordered collection of elements.
An @dfn{array} is a fixed-length object with a slot for each of its
elements. All the elements are accessible in constant time. The four
types of arrays are strings, vectors, char-tables and bool-vectors.
A list is a sequence of elements, but it is not a single primitive
object; it is made of cons cells, one cell per element. Finding the
@var{n}th element requires looking through @var{n} cons cells, so
elements farther from the beginning of the list take longer to access.
But it is possible to add elements to the list, or remove elements.
The following diagram shows the relationship between these types:
@example
@group
_____________________________________________
| |
| Sequence |
| ______ ________________________________ |
| | | | | |
| | List | | Array | |
| | | | ________ ________ | |
| |______| | | | | | | |
| | | Vector | | String | | |
| | |________| |________| | |
| | ____________ _____________ | |
| | | | | | | |
| | | Char-table | | Bool-vector | | |
| | |____________| |_____________| | |
| |________________________________| |
|_____________________________________________|
@end group
@end example
@menu
* Sequence Functions:: Functions that accept any kind of sequence.
* Arrays:: Characteristics of arrays in Emacs Lisp.
* Array Functions:: Functions specifically for arrays.
* Vectors:: Special characteristics of Emacs Lisp vectors.
* Vector Functions:: Functions specifically for vectors.
* Char-Tables:: How to work with char-tables.
* Bool-Vectors:: How to work with bool-vectors.
* Rings:: Managing a fixed-size ring of objects.
@end menu
@node Sequence Functions
@section Sequences
This section describes functions that accept any kind of sequence.
@defun sequencep object
This function returns @code{t} if @var{object} is a list, vector,
string, bool-vector, or char-table, @code{nil} otherwise. See also
@code{seqp} below.
@end defun
@defun length sequence
@cindex string length
@cindex list length
@cindex vector length
@cindex sequence length
@cindex bool-vector length
@cindex char-table length
@anchor{Definition of length}
This function returns the number of elements in @var{sequence}. The
function signals the @code{wrong-type-argument} error if the argument
is not a sequence or is a dotted list; it signals the
@code{circular-list} error if the argument is a circular list. For a
char-table, the value returned is always one more than the maximum
Emacs character code.
@xref{Definition of safe-length}, for the related function @code{safe-length}.
@example
@group
(length '(1 2 3))
@result{} 3
@end group
@group
(length ())
@result{} 0
@end group
@group
(length "foobar")
@result{} 6
@end group
@group
(length [1 2 3])
@result{} 3
@end group
@group
(length (make-bool-vector 5 nil))
@result{} 5
@end group
@end example
@end defun
@noindent
See also @code{string-bytes}, in @ref{Text Representations}.
If you need to compute the width of a string on display, you should use
@code{string-width} (@pxref{Size of Displayed Text}), not @code{length},
since @code{length} only counts the number of characters, but does not
account for the display width of each character.
@defun elt sequence index
@anchor{Definition of elt}
@cindex elements of sequences
This function returns the element of @var{sequence} indexed by
@var{index}. Legitimate values of @var{index} are integers ranging
from 0 up to one less than the length of @var{sequence}. If
@var{sequence} is a list, out-of-range values behave as for
@code{nth}. @xref{Definition of nth}. Otherwise, out-of-range values
trigger an @code{args-out-of-range} error.
@example
@group
(elt [1 2 3 4] 2)
@result{} 3
@end group
@group
(elt '(1 2 3 4) 2)
@result{} 3
@end group
@group
;; @r{We use @code{string} to show clearly which character @code{elt} returns.}
(string (elt "1234" 2))
@result{} "3"
@end group
@group
(elt [1 2 3 4] 4)
@error{} Args out of range: [1 2 3 4], 4
@end group
@group
(elt [1 2 3 4] -1)
@error{} Args out of range: [1 2 3 4], -1
@end group
@end example
This function generalizes @code{aref} (@pxref{Array Functions}) and
@code{nth} (@pxref{Definition of nth}).
@end defun
@defun copy-sequence seqr
@cindex copying sequences
This function returns a copy of @var{seqr}, which should be either a
sequence or a record. The copy is the same type of object as the
original, and it has the same elements in the same order. However, if
@var{seqr} is empty, like a string or a vector of zero length, the
value returned by this function might not be a copy, but an empty
object of the same type and identical to @var{seqr}.
Storing a new element into the copy does not affect the original
@var{seqr}, and vice versa. However, the elements of the copy
are not copies; they are identical (@code{eq}) to the elements
of the original. Therefore, changes made within these elements, as
found via the copy, are also visible in the original.
If the argument is a string with text properties, the property list in
the copy is itself a copy, not shared with the original's property
list. However, the actual values of the properties are shared.
@xref{Text Properties}.
This function does not work for dotted lists. Trying to copy a
circular list may cause an infinite loop.
See also @code{append} in @ref{Building Lists}, @code{concat} in
@ref{Creating Strings}, and @code{vconcat} in @ref{Vector Functions},
for other ways to copy sequences.
@example
@group
(setq bar (list 1 2))
@result{} (1 2)
@end group
@group
(setq x (vector 'foo bar))
@result{} [foo (1 2)]
@end group
@group
(setq y (copy-sequence x))
@result{} [foo (1 2)]
@end group
@group
(eq x y)
@result{} nil
@end group
@group
(equal x y)
@result{} t
@end group
@group
(eq (elt x 1) (elt y 1))
@result{} t
@end group
@group
;; @r{Replacing an element of one sequence.}
(aset x 0 'quux)
x @result{} [quux (1 2)]
y @result{} [foo (1 2)]
@end group
@group
;; @r{Modifying the inside of a shared element.}
(setcar (aref x 1) 69)
x @result{} [quux (69 2)]
y @result{} [foo (69 2)]
@end group
@end example
@end defun
@defun reverse sequence
@cindex string reverse
@cindex list reverse
@cindex vector reverse
@cindex sequence reverse
This function creates a new sequence whose elements are the elements
of @var{sequence}, but in reverse order. The original argument @var{sequence}
is @emph{not} altered. Note that char-tables cannot be reversed.
@example
@group
(setq x '(1 2 3 4))
@result{} (1 2 3 4)
@end group
@group
(reverse x)
@result{} (4 3 2 1)
x
@result{} (1 2 3 4)
@end group
@group
(setq x [1 2 3 4])
@result{} [1 2 3 4]
@end group
@group
(reverse x)
@result{} [4 3 2 1]
x
@result{} [1 2 3 4]
@end group
@group
(setq x "xyzzy")
@result{} "xyzzy"
@end group
@group
(reverse x)
@result{} "yzzyx"
x
@result{} "xyzzy"
@end group
@end example
@end defun
@defun nreverse sequence
@cindex reversing a string
@cindex reversing a list
@cindex reversing a vector
This function reverses the order of the elements of @var{sequence}.
Unlike @code{reverse} the original @var{sequence} may be modified.
For example:
@example
@group
(setq x (list 'a 'b 'c))
@result{} (a b c)
@end group
@group
x
@result{} (a b c)
(nreverse x)
@result{} (c b a)
@end group
@group
;; @r{The cons cell that was first is now last.}
x
@result{} (a)
@end group
@end example
To avoid confusion, we usually store the result of @code{nreverse}
back in the same variable which held the original list:
@example
(setq x (nreverse x))
@end example
Here is the @code{nreverse} of our favorite example, @code{(a b c)},
presented graphically:
@smallexample
@group
@r{Original list head:} @r{Reversed list:}
------------- ------------- ------------
| car | cdr | | car | cdr | | car | cdr |
| a | nil |<-- | b | o |<-- | c | o |
| | | | | | | | | | | | |
------------- | --------- | - | -------- | -
| | | |
------------- ------------
@end group
@end smallexample
For the vector, it is even simpler because you don't need setq:
@example
(setq x (copy-sequence [1 2 3 4]))
@result{} [1 2 3 4]
(nreverse x)
@result{} [4 3 2 1]
x
@result{} [4 3 2 1]
@end example
Note that unlike @code{reverse}, this function doesn't work with strings.
Although you can alter string data by using @code{aset}, it is strongly
encouraged to treat strings as immutable even when they are mutable.
@end defun
@defun sort sequence predicate
@cindex stable sort
@cindex sorting lists
@cindex sorting vectors
This function sorts @var{sequence} stably. Note that this function doesn't work
for all sequences; it may be used only for lists and vectors. If @var{sequence}
is a list, it is modified destructively. This functions returns the sorted
@var{sequence} and compares elements using @var{predicate}. A stable sort is
one in which elements with equal sort keys maintain their relative order before
and after the sort. Stability is important when successive sorts are used to
order elements according to different criteria.
The argument @var{predicate} must be a function that accepts two
arguments. It is called with two elements of @var{sequence}. To get an
increasing order sort, the @var{predicate} should return non-@code{nil} if the
first element is ``less'' than the second, or @code{nil} if not.
The comparison function @var{predicate} must give reliable results for
any given pair of arguments, at least within a single call to
@code{sort}. It must be @dfn{antisymmetric}; that is, if @var{a} is
less than @var{b}, @var{b} must not be less than @var{a}. It must be
@dfn{transitive}---that is, if @var{a} is less than @var{b}, and @var{b}
is less than @var{c}, then @var{a} must be less than @var{c}. If you
use a comparison function which does not meet these requirements, the
result of @code{sort} is unpredictable.
The destructive aspect of @code{sort} for lists is that it rearranges the
cons cells forming @var{sequence} by changing @sc{cdr}s. A nondestructive
sort function would create new cons cells to store the elements in their
sorted order. If you wish to make a sorted copy without destroying the
original, copy it first with @code{copy-sequence} and then sort.
Sorting does not change the @sc{car}s of the cons cells in @var{sequence};
the cons cell that originally contained the element @code{a} in
@var{sequence} still has @code{a} in its @sc{car} after sorting, but it now
appears in a different position in the list due to the change of
@sc{cdr}s. For example:
@example
@group
(setq nums (list 1 3 2 6 5 4 0))
@result{} (1 3 2 6 5 4 0)
@end group
@group
(sort nums #'<)
@result{} (0 1 2 3 4 5 6)
@end group
@group
nums
@result{} (1 2 3 4 5 6)
@end group
@end example
@noindent
@strong{Warning}: Note that the list in @code{nums} no longer contains
0; this is the same cons cell that it was before, but it is no longer
the first one in the list. Don't assume a variable that formerly held
the argument now holds the entire sorted list! Instead, save the result
of @code{sort} and use that. Most often we store the result back into
the variable that held the original list:
@example
(setq nums (sort nums #'<))
@end example
For the better understanding of what stable sort is, consider the following
vector example. After sorting, all items whose @code{car} is 8 are grouped
at the beginning of @code{vector}, but their relative order is preserved.
All items whose @code{car} is 9 are grouped at the end of @code{vector},
but their relative order is also preserved:
@example
@group
(setq
vector
(vector '(8 . "xxx") '(9 . "aaa") '(8 . "bbb") '(9 . "zzz")
'(9 . "ppp") '(8 . "ttt") '(8 . "eee") '(9 . "fff")))
@result{} [(8 . "xxx") (9 . "aaa") (8 . "bbb") (9 . "zzz")
(9 . "ppp") (8 . "ttt") (8 . "eee") (9 . "fff")]
@end group
@group
(sort vector (lambda (x y) (< (car x) (car y))))
@result{} [(8 . "xxx") (8 . "bbb") (8 . "ttt") (8 . "eee")
(9 . "aaa") (9 . "zzz") (9 . "ppp") (9 . "fff")]
@end group
@end example
@xref{Sorting}, for more functions that perform sorting.
See @code{documentation} in @ref{Accessing Documentation}, for a
useful example of @code{sort}.
@end defun
@cindex sequence functions in seq
@cindex seq library
@cindex sequences, generalized
The @file{seq.el} library provides the following additional sequence
manipulation macros and functions, prefixed with @code{seq-}. To use
them, you must first load the @file{seq} library.
All functions defined in this library are free of side-effects;
i.e., they do not modify any sequence (list, vector, or string) that
you pass as an argument. Unless otherwise stated, the result is a
sequence of the same type as the input. For those functions that take
a predicate, this should be a function of one argument.
The @file{seq.el} library can be extended to work with additional
types of sequential data-structures. For that purpose, all functions
are defined using @code{cl-defgeneric}. @xref{Generic Functions}, for
more details about using @code{cl-defgeneric} for adding extensions.
@defun seq-elt sequence index
This function returns the element of @var{sequence} at the specified
@var{index}, which is an integer whose valid value range is zero to
one less than the length of @var{sequence}. For out-of-range values
on built-in sequence types, @code{seq-elt} behaves like @code{elt}.
For the details, see @ref{Definition of elt}.
@example
@group
(seq-elt [1 2 3 4] 2)
@result{} 3
@end group
@end example
@code{seq-elt} returns places settable using @code{setf}
(@pxref{Setting Generalized Variables}).
@example
@group
(setq vec [1 2 3 4])
(setf (seq-elt vec 2) 5)
vec
@result{} [1 2 5 4]
@end group
@end example
@end defun
@defun seq-length sequence
This function returns the number of elements in @var{sequence}. For
built-in sequence types, @code{seq-length} behaves like @code{length}.
@xref{Definition of length}.
@end defun
@defun seqp object
This function returns non-@code{nil} if @var{object} is a sequence
(a list or array), or any additional type of sequence defined via
@file{seq.el} generic functions. This is an extensible variant of
@code{sequencep}.
@example
@group
(seqp [1 2])
@result{} t
@end group
@group
(seqp 2)
@result{} nil
@end group
@end example
@end defun
@defun seq-drop sequence n
This function returns all but the first @var{n} (an integer)
elements of @var{sequence}. If @var{n} is negative or zero,
the result is @var{sequence}.
@example
@group
(seq-drop [1 2 3 4 5 6] 3)
@result{} [4 5 6]
@end group
@group
(seq-drop "hello world" -4)
@result{} "hello world"
@end group
@end example
@end defun
@defun seq-take sequence n
This function returns the first @var{n} (an integer) elements of
@var{sequence}. If @var{n} is negative or zero, the result
is @code{nil}.
@example
@group
(seq-take '(1 2 3 4) 3)
@result{} (1 2 3)
@end group
@group
(seq-take [1 2 3 4] 0)
@result{} []
@end group
@end example
@end defun
@defun seq-take-while predicate sequence
This function returns the members of @var{sequence} in order,
stopping before the first one for which @var{predicate} returns @code{nil}.
@example
@group
(seq-take-while (lambda (elt) (> elt 0)) '(1 2 3 -1 -2))
@result{} (1 2 3)
@end group
@group
(seq-take-while (lambda (elt) (> elt 0)) [-1 4 6])
@result{} []
@end group
@end example
@end defun
@defun seq-drop-while predicate sequence
This function returns the members of @var{sequence} in order,
starting from the first one for which @var{predicate} returns @code{nil}.
@example
@group
(seq-drop-while (lambda (elt) (> elt 0)) '(1 2 3 -1 -2))
@result{} (-1 -2)
@end group
@group
(seq-drop-while (lambda (elt) (< elt 0)) [1 4 6])
@result{} [1 4 6]
@end group
@end example
@end defun
@defun seq-do function sequence
This function applies @var{function} to each element of
@var{sequence} in turn (presumably for side effects), and returns
@var{sequence}.
@end defun
@defun seq-map function sequence
This function returns the result of applying @var{function} to each
element of @var{sequence}. The returned value is a list.
@example
@group
(seq-map #'1+ '(2 4 6))
@result{} (3 5 7)
@end group
@group
(seq-map #'symbol-name [foo bar])
@result{} ("foo" "bar")
@end group
@end example
@end defun
@defun seq-map-indexed function sequence
This function returns the result of applying @var{function} to each
element of @var{sequence} and its index within @var{seq}. The
returned value is a list.
@example
@group
(seq-map-indexed (lambda (elt idx)
(list idx elt))
'(a b c))
@result{} ((0 a) (b 1) (c 2))
@end group
@end example
@end defun
@defun seq-mapn function &rest sequences
This function returns the result of applying @var{function} to each
element of @var{sequences}. The arity (@pxref{What Is a Function,
subr-arity}) of @var{function} must match the number of sequences.
Mapping stops at the end of the shortest sequence, and the returned
value is a list.
@example
@group
(seq-mapn #'+ '(2 4 6) '(20 40 60))
@result{} (22 44 66)
@end group
@group
(seq-mapn #'concat '("moskito" "bite") ["bee" "sting"])
@result{} ("moskitobee" "bitesting")
@end group
@end example
@end defun
@defun seq-filter predicate sequence
@cindex filtering sequences
This function returns a list of all the elements in @var{sequence}
for which @var{predicate} returns non-@code{nil}.
@example
@group
(seq-filter (lambda (elt) (> elt 0)) [1 -1 3 -3 5])
@result{} (1 3 5)
@end group
@group
(seq-filter (lambda (elt) (> elt 0)) '(-1 -3 -5))
@result{} nil
@end group
@end example
@end defun
@defun seq-remove predicate sequence
@cindex removing from sequences
This function returns a list of all the elements in @var{sequence}
for which @var{predicate} returns @code{nil}.
@example
@group
(seq-remove (lambda (elt) (> elt 0)) [1 -1 3 -3 5])
@result{} (-1 -3)
@end group
@group
(seq-remove (lambda (elt) (< elt 0)) '(-1 -3 -5))
@result{} nil
@end group
@end example
@end defun
@defun seq-reduce function sequence initial-value
@cindex reducing sequences
This function returns the result of calling @var{function} with
@var{initial-value} and the first element of @var{sequence}, then calling
@var{function} with that result and the second element of @var{sequence},
then with that result and the third element of @var{sequence}, etc.
@var{function} should be a function of two arguments. If
@var{sequence} is empty, this returns @var{initial-value} without
calling @var{function}.
@example
@group
(seq-reduce #'+ [1 2 3 4] 0)
@result{} 10
@end group
@group
(seq-reduce #'+ '(1 2 3 4) 5)
@result{} 15
@end group
@group
(seq-reduce #'+ '() 3)
@result{} 3
@end group
@end example
@end defun
@defun seq-some predicate sequence
This function returns the first non-@code{nil} value returned by
applying @var{predicate} to each element of @var{sequence} in turn.
@example
@group
(seq-some #'numberp ["abc" 1 nil])
@result{} t
@end group
@group
(seq-some #'numberp ["abc" "def"])
@result{} nil
@end group
@group
(seq-some #'null ["abc" 1 nil])
@result{} t
@end group
@group
(seq-some #'1+ [2 4 6])
@result{} 3
@end group
@end example
@end defun
@defun seq-find predicate sequence &optional default
This function returns the first element in @var{sequence} for which
@var{predicate} returns non-@code{nil}. If no element matches
@var{predicate}, the function returns @var{default}.
Note that this function has an ambiguity if the found element is
identical to @var{default}, as in that case it cannot be known whether
an element was found or not.
@example
@group
(seq-find #'numberp ["abc" 1 nil])
@result{} 1
@end group
@group
(seq-find #'numberp ["abc" "def"])
@result{} nil
@end group
@end example
@end defun
@defun seq-every-p predicate sequence
This function returns non-@code{nil} if applying @var{predicate}
to every element of @var{sequence} returns non-@code{nil}.
@example
@group
(seq-every-p #'numberp [2 4 6])
@result{} t
@end group
@group
(seq-every-p #'numberp [2 4 "6"])
@result{} nil
@end group
@end example
@end defun
@defun seq-empty-p sequence
This function returns non-@code{nil} if @var{sequence} is empty.
@example
@group
(seq-empty-p "not empty")
@result{} nil
@end group
@group
(seq-empty-p "")
@result{} t
@end group
@end example
@end defun
@defun seq-count predicate sequence
This function returns the number of elements in @var{sequence} for which
@var{predicate} returns non-@code{nil}.
@example
(seq-count (lambda (elt) (> elt 0)) [-1 2 0 3 -2])
@result{} 2
@end example
@end defun
@cindex sorting sequences
@defun seq-sort function sequence
This function returns a copy of @var{sequence} that is sorted
according to @var{function}, a function of two arguments that returns
non-@code{nil} if the first argument should sort before the second.
@end defun
@defun seq-sort-by function predicate sequence
This function is similar to @code{seq-sort}, but the elements of
@var{sequence} are transformed by applying @var{function} on them
before being sorted. @var{function} is a function of one argument.
@example
(seq-sort-by #'seq-length #'> ["a" "ab" "abc"])
@result{} ["abc" "ab" "a"]
@end example
@end defun
@defun seq-contains-p sequence elt &optional function
This function returns non-@code{nil} if at least one element in
@var{sequence} is equal to @var{elt}. If the optional argument
@var{function} is non-@code{nil}, it is a function of two arguments to
use instead of the default @code{equal}.
@example
@group
(seq-contains '(symbol1 symbol2) 'symbol1)
@result{} symbol1
@end group
@group
(seq-contains '(symbol1 symbol2) 'symbol3)
@result{} nil
@end group
@end example
@end defun
@defun seq-set-equal-p sequence1 sequence2 &optional testfn
This function checks whether @var{sequence1} and @var{sequence2}
contain the same elements, regardless of the order. If the optional
argument @var{testfn} is non-@code{nil}, it is a function of two
arguments to use instead of the default @code{equal}.
@example
@group
(seq-set-equal-p '(a b c) '(c b a))
@result{} t
@end group
@group
(seq-set-equal-p '(a b c) '(c b))
@result{} nil
@end group
@group
(seq-set-equal-p '("a" "b" "c") '("c" "b" "a"))
@result{} t
@end group
@group
(seq-set-equal-p '("a" "b" "c") '("c" "b" "a") #'eq)
@result{} nil
@end group
@end example
@end defun
@defun seq-position sequence elt &optional function
This function returns the index of the first element in
@var{sequence} that is equal to @var{elt}. If the optional argument
@var{function} is non-@code{nil}, it is a function of two arguments to
use instead of the default @code{equal}.
@example
@group
(seq-position '(a b c) 'b)
@result{} 1
@end group
@group
(seq-position '(a b c) 'd)
@result{} nil
@end group
@end example
@end defun
@defun seq-uniq sequence &optional function
This function returns a list of the elements of @var{sequence} with
duplicates removed. If the optional argument @var{function} is non-@code{nil},
it is a function of two arguments to use instead of the default @code{equal}.
@example
@group
(seq-uniq '(1 2 2 1 3))
@result{} (1 2 3)
@end group
@group
(seq-uniq '(1 2 2.0 1.0) #'=)
@result{} (1 2)
@end group
@end example
@end defun
@defun seq-subseq sequence start &optional end
@cindex sub-sequence
This function returns a subset of @var{sequence} from @var{start}
to @var{end}, both integers (@var{end} defaults to the last element).
If @var{start} or @var{end} is negative, it counts from the end of
@var{sequence}.
@example
@group
(seq-subseq '(1 2 3 4 5) 1)
@result{} (2 3 4 5)
@end group
@group
(seq-subseq '[1 2 3 4 5] 1 3)
@result{} [2 3]
@end group
@group
(seq-subseq '[1 2 3 4 5] -3 -1)
@result{} [3 4]
@end group
@end example
@end defun
@defun seq-concatenate type &rest sequences
This function returns a sequence of type @var{type} made of the
concatenation of @var{sequences}. @var{type} may be: @code{vector},
@code{list} or @code{string}.
@example
@group
(seq-concatenate 'list '(1 2) '(3 4) [5 6])
@result{} (1 2 3 4 5 6)
@end group
@group
(seq-concatenate 'string "Hello " "world")
@result{} "Hello world"
@end group
@end example
@end defun
@defun seq-mapcat function sequence &optional type
This function returns the result of applying @code{seq-concatenate}
to the result of applying @var{function} to each element of
@var{sequence}. The result is a sequence of type @var{type}, or a
list if @var{type} is @code{nil}.
@example
@group
(seq-mapcat #'seq-reverse '((3 2 1) (6 5 4)))
@result{} (1 2 3 4 5 6)
@end group
@end example
@end defun
@defun seq-partition sequence n
This function returns a list of the elements of @var{sequence}
grouped into sub-sequences of length @var{n}. The last sequence may
contain less elements than @var{n}. @var{n} must be an integer. If
@var{n} is a negative integer or 0, the return value is @code{nil}.
@example
@group
(seq-partition '(0 1 2 3 4 5 6 7) 3)
@result{} ((0 1 2) (3 4 5) (6 7))
@end group
@end example
@end defun
@defun seq-intersection sequence1 sequence2 &optional function
@cindex sequences, intersection of
@cindex intersection of sequences
This function returns a list of the elements that appear both in
@var{sequence1} and @var{sequence2}. If the optional argument
@var{function} is non-@code{nil}, it is a function of two arguments to
use to compare elements instead of the default @code{equal}.
@example
@group
(seq-intersection [2 3 4 5] [1 3 5 6 7])
@result{} (3 5)
@end group
@end example
@end defun
@defun seq-difference sequence1 sequence2 &optional function
This function returns a list of the elements that appear in
@var{sequence1} but not in @var{sequence2}. If the optional argument
@var{function} is non-@code{nil}, it is a function of two arguments to
use to compare elements instead of the default @code{equal}.
@example
@group
(seq-difference '(2 3 4 5) [1 3 5 6 7])
@result{} (2 4)
@end group
@end example
@end defun
@defun seq-group-by function sequence
This function separates the elements of @var{sequence} into an alist
whose keys are the result of applying @var{function} to each element
of @var{sequence}. Keys are compared using @code{equal}.
@example
@group
(seq-group-by #'integerp '(1 2.1 3 2 3.2))
@result{} ((t 1 3 2) (nil 2.1 3.2))
@end group
@group
(seq-group-by #'car '((a 1) (b 2) (a 3) (c 4)))
@result{} ((b (b 2)) (a (a 1) (a 3)) (c (c 4)))
@end group
@end example
@end defun
@defun seq-into sequence type
@cindex convert sequence to another type
@cindex list to vector
@cindex vector to list
@cindex string to vector
This function converts the sequence @var{sequence} into a sequence
of type @var{type}. @var{type} can be one of the following symbols:
@code{vector}, @code{string} or @code{list}.
@example
@group
(seq-into [1 2 3] 'list)
@result{} (1 2 3)
@end group
@group
(seq-into nil 'vector)
@result{} []
@end group
@group
(seq-into "hello" 'vector)
@result{} [104 101 108 108 111]
@end group
@end example
@end defun
@defun seq-min sequence
@cindex minimum value of sequence
@cindex sequence minimum
This function returns the smallest element of @var{sequence}. The
elements of @var{sequence} must be numbers or markers
(@pxref{Markers}).
@example
@group
(seq-min [3 1 2])
@result{} 1
@end group
@group
(seq-min "Hello")
@result{} 72
@end group
@end example
@end defun
@defun seq-max sequence
@cindex maximum value of sequence
@cindex sequence maximum
This function returns the largest element of @var{sequence}. The
elements of @var{sequence} must be numbers or markers.
@example
@group
(seq-max [1 3 2])
@result{} 3
@end group
@group
(seq-max "Hello")
@result{} 111
@end group
@end example
@end defun
@defmac seq-doseq (var sequence) body@dots{}
@cindex sequence iteration
@cindex iteration over vector or string
This macro is like @code{dolist} (@pxref{Iteration, dolist}), except
that @var{sequence} can be a list, vector or string. This is
primarily useful for side-effects.
@end defmac
@anchor{seq-let}
@defmac seq-let var-sequence val-sequence body@dots{}
@cindex sequence destructuring
This macro binds the variables defined in @var{var-sequence} to the
values that are the corresponding elements of @var{val-sequence}.
This is known as @dfn{destructuring binding}. The elements of
@var{var-sequence} can themselves include sequences, allowing for
nested destructuring.
The @var{var-sequence} sequence can also include the @code{&rest}
marker followed by a variable name to be bound to the rest of
@var{val-sequence}.
@example
@group
(seq-let [first second] [1 2 3 4]
(list first second))
@result{} (1 2)
@end group
@group
(seq-let (_ a _ b) '(1 2 3 4)
(list a b))
@result{} (2 4)
@end group
@group
(seq-let [a [b [c]]] [1 [2 [3]]]
(list a b c))
@result{} (1 2 3)
@end group
@group
(seq-let [a b &rest others] [1 2 3 4]
others)
@end group
@result{} [3 4]
@end example
The @code{pcase} patterns provide an alternative facility for
destructuring binding, see @ref{Destructuring with pcase Patterns}.
@end defmac
@defun seq-random-elt sequence
This function returns an element of @var{sequence} taken at random.
@example
@group
(seq-random-elt [1 2 3 4])
@result{} 3
(seq-random-elt [1 2 3 4])
@result{} 2
(seq-random-elt [1 2 3 4])
@result{} 4
(seq-random-elt [1 2 3 4])
@result{} 2
(seq-random-elt [1 2 3 4])
@result{} 1
@end group
@end example
If @var{sequence} is empty, this function signals an error.
@end defun
@node Arrays
@section Arrays
@cindex array
An @dfn{array} object has slots that hold a number of other Lisp
objects, called the elements of the array. Any element of an array
may be accessed in constant time. In contrast, the time to access an
element of a list is proportional to the position of that element in
the list.
Emacs defines four types of array, all one-dimensional:
@dfn{strings} (@pxref{String Type}), @dfn{vectors} (@pxref{Vector
Type}), @dfn{bool-vectors} (@pxref{Bool-Vector Type}), and
@dfn{char-tables} (@pxref{Char-Table Type}). Vectors and char-tables
can hold elements of any type, but strings can only hold characters,
and bool-vectors can only hold @code{t} and @code{nil}.
All four kinds of array share these characteristics:
@itemize @bullet
@item
The first element of an array has index zero, the second element has
index 1, and so on. This is called @dfn{zero-origin} indexing. For
example, an array of four elements has indices 0, 1, 2, @w{and 3}.
@item
The length of the array is fixed once you create it; you cannot
change the length of an existing array.
@item
For purposes of evaluation, the array is a constant---i.e.,
it evaluates to itself.
@item
The elements of an array may be referenced or changed with the functions
@code{aref} and @code{aset}, respectively (@pxref{Array Functions}).
@end itemize
When you create an array, other than a char-table, you must specify
its length. You cannot specify the length of a char-table, because that
is determined by the range of character codes.
In principle, if you want an array of text characters, you could use
either a string or a vector. In practice, we always choose strings for
such applications, for four reasons:
@itemize @bullet
@item
They occupy one-fourth the space of a vector of the same elements.
@item
Strings are printed in a way that shows the contents more clearly
as text.
@item
Strings can hold text properties. @xref{Text Properties}.
@item
Many of the specialized editing and I/O facilities of Emacs accept only
strings. For example, you cannot insert a vector of characters into a
buffer the way you can insert a string. @xref{Strings and Characters}.
@end itemize
By contrast, for an array of keyboard input characters (such as a key
sequence), a vector may be necessary, because many keyboard input
characters are outside the range that will fit in a string. @xref{Key
Sequence Input}.
@node Array Functions
@section Functions that Operate on Arrays
In this section, we describe the functions that accept all types of
arrays.
@defun arrayp object
This function returns @code{t} if @var{object} is an array (i.e., a
vector, a string, a bool-vector or a char-table).
@example
@group
(arrayp [a])
@result{} t
(arrayp "asdf")
@result{} t
(arrayp (syntax-table)) ;; @r{A char-table.}
@result{} t
@end group
@end example
@end defun
@defun aref arr index
@cindex array elements
This function returns the @var{index}th element of the array or record
@var{arr}. The first element is at index zero.
@example
@group
(setq primes [2 3 5 7 11 13])
@result{} [2 3 5 7 11 13]
(aref primes 4)
@result{} 11
@end group
@group
(aref "abcdefg" 1)
@result{} 98 ; @r{@samp{b} is @acronym{ASCII} code 98.}
@end group
@end example
See also the function @code{elt}, in @ref{Sequence Functions}.
@end defun
@defun aset array index object
This function sets the @var{index}th element of @var{array} to be
@var{object}. It returns @var{object}.
@example
@group
(setq w (vector 'foo 'bar 'baz))
@result{} [foo bar baz]
(aset w 0 'fu)
@result{} fu
w
@result{} [fu bar baz]
@end group
@group
;; @r{@code{copy-sequence} creates a mutable string.}
(setq x (copy-sequence "asdfasfd"))
@result{} "asdfasfd"
(aset x 3 ?Z)
@result{} 90
x
@result{} "asdZasfd"
@end group
@end example
The @var{array} should be mutable; that is, it should not be a constant,
such as the constants created via quoting or via self-evaluating forms.
@xref{Constants and Mutability}.
If @var{array} is a string and @var{object} is not a character, a
@code{wrong-type-argument} error results. The function converts a
unibyte string to multibyte if necessary to insert a character.
@end defun
@defun fillarray array object
This function fills the array @var{array} with @var{object}, so that
each element of @var{array} is @var{object}. It returns @var{array}.
@example
@group
(setq a (copy-sequence [a b c d e f g]))
@result{} [a b c d e f g]
(fillarray a 0)
@result{} [0 0 0 0 0 0 0]
a
@result{} [0 0 0 0 0 0 0]
@end group
@group
(setq s (copy-sequence "When in the course"))
@result{} "When in the course"
(fillarray s ?-)
@result{} "------------------"
@end group
@end example
If @var{array} is a string and @var{object} is not a character, a
@code{wrong-type-argument} error results.
@end defun
The general sequence functions @code{copy-sequence} and @code{length}
are often useful for objects known to be arrays. @xref{Sequence Functions}.
@node Vectors
@section Vectors
@cindex vector (type)
A @dfn{vector} is a general-purpose array whose elements can be any
Lisp objects. (By contrast, the elements of a string can only be
characters. @xref{Strings and Characters}.) Vectors are used in
Emacs for many purposes: as key sequences (@pxref{Key Sequences}), as
symbol-lookup tables (@pxref{Creating Symbols}), as part of the
representation of a byte-compiled function (@pxref{Byte Compilation}),
and more.
Like other arrays, vectors use zero-origin indexing: the first
element has index 0.
Vectors are printed with square brackets surrounding the elements.
Thus, a vector whose elements are the symbols @code{a}, @code{b} and
@code{a} is printed as @code{[a b a]}. You can write vectors in the
same way in Lisp input.
A vector, like a string or a number, is considered a constant for
evaluation: the result of evaluating it is the same vector. This does
not evaluate or even examine the elements of the vector.
@xref{Self-Evaluating Forms}. Vectors written with square brackets
are constants and should not be modified via @code{aset} or other
destructive operations. @xref{Constants and Mutability}.
Here are examples illustrating these principles:
@example
@group
(setq avector [1 two '(three) "four" [five]])
@result{} [1 two '(three) "four" [five]]
(eval avector)
@result{} [1 two '(three) "four" [five]]
(eq avector (eval avector))
@result{} t
@end group
@end example
@node Vector Functions
@section Functions for Vectors
Here are some functions that relate to vectors:
@defun vectorp object
This function returns @code{t} if @var{object} is a vector.
@example
@group
(vectorp [a])
@result{} t
(vectorp "asdf")
@result{} nil
@end group
@end example
@end defun
@defun vector &rest objects
This function creates and returns a vector whose elements are the
arguments, @var{objects}.
@example
@group
(vector 'foo 23 [bar baz] "rats")
@result{} [foo 23 [bar baz] "rats"]
(vector)
@result{} []
@end group
@end example
@end defun
@defun make-vector length object
This function returns a new vector consisting of @var{length} elements,
each initialized to @var{object}.
@example
@group
(setq sleepy (make-vector 9 'Z))
@result{} [Z Z Z Z Z Z Z Z Z]
@end group
@end example
@end defun
@defun vconcat &rest sequences
@cindex copying vectors
This function returns a new vector containing all the elements of
@var{sequences}. The arguments @var{sequences} may be proper lists,
vectors, strings or bool-vectors. If no @var{sequences} are given,
the empty vector is returned.
The value is either the empty vector, or is a newly constructed
nonempty vector that is not @code{eq} to any existing vector.
@example
@group
(setq a (vconcat '(A B C) '(D E F)))
@result{} [A B C D E F]
(eq a (vconcat a))
@result{} nil
@end group
@group
(vconcat)
@result{} []
(vconcat [A B C] "aa" '(foo (6 7)))
@result{} [A B C 97 97 foo (6 7)]
@end group
@end example
The @code{vconcat} function also allows byte-code function objects as
arguments. This is a special feature to make it easy to access the entire
contents of a byte-code function object. @xref{Byte-Code Objects}.
For other concatenation functions, see @code{mapconcat} in @ref{Mapping
Functions}, @code{concat} in @ref{Creating Strings}, and @code{append}
in @ref{Building Lists}.
@end defun
The @code{append} function also provides a way to convert a vector into a
list with the same elements:
@example
@group
(setq avector [1 two (quote (three)) "four" [five]])
@result{} [1 two '(three) "four" [five]]
(append avector nil)
@result{} (1 two '(three) "four" [five])
@end group
@end example
@node Char-Tables
@section Char-Tables
@cindex char-tables
@cindex extra slots of char-table
A char-table is much like a vector, except that it is indexed by
character codes. Any valid character code, without modifiers, can be
used as an index in a char-table. You can access a char-table's
elements with @code{aref} and @code{aset}, as with any array. In
addition, a char-table can have @dfn{extra slots} to hold additional
data not associated with particular character codes. Like vectors,
char-tables are constants when evaluated, and can hold elements of any
type.
@cindex subtype of char-table
Each char-table has a @dfn{subtype}, a symbol, which serves two
purposes:
@itemize @bullet
@item
The subtype provides an easy way to tell what the char-table is for.
For instance, display tables are char-tables with @code{display-table}
as the subtype, and syntax tables are char-tables with
@code{syntax-table} as the subtype. The subtype can be queried using
the function @code{char-table-subtype}, described below.
@item
The subtype controls the number of @dfn{extra slots} in the
char-table. This number is specified by the subtype's
@code{char-table-extra-slots} symbol property (@pxref{Symbol
Properties}), whose value should be an integer between 0 and 10. If
the subtype has no such symbol property, the char-table has no extra
slots.
@end itemize
@cindex parent of char-table
A char-table can have a @dfn{parent}, which is another char-table. If
it does, then whenever the char-table specifies @code{nil} for a
particular character @var{c}, it inherits the value specified in the
parent. In other words, @code{(aref @var{char-table} @var{c})} returns
the value from the parent of @var{char-table} if @var{char-table} itself
specifies @code{nil}.
@cindex default value of char-table
A char-table can also have a @dfn{default value}. If so, then
@code{(aref @var{char-table} @var{c})} returns the default value
whenever the char-table does not specify any other non-@code{nil} value.
@defun make-char-table subtype &optional init
Return a newly-created char-table, with subtype @var{subtype} (a
symbol). Each element is initialized to @var{init}, which defaults to
@code{nil}. You cannot alter the subtype of a char-table after the
char-table is created.
There is no argument to specify the length of the char-table, because
all char-tables have room for any valid character code as an index.
If @var{subtype} has the @code{char-table-extra-slots} symbol
property, that specifies the number of extra slots in the char-table.
This should be an integer between 0 and 10; otherwise,
@code{make-char-table} raises an error. If @var{subtype} has no
@code{char-table-extra-slots} symbol property (@pxref{Property
Lists}), the char-table has no extra slots.
@end defun
@defun char-table-p object
This function returns @code{t} if @var{object} is a char-table, and
@code{nil} otherwise.
@end defun
@defun char-table-subtype char-table
This function returns the subtype symbol of @var{char-table}.
@end defun
There is no special function to access default values in a char-table.
To do that, use @code{char-table-range} (see below).
@defun char-table-parent char-table
This function returns the parent of @var{char-table}. The parent is
always either @code{nil} or another char-table.
@end defun
@defun set-char-table-parent char-table new-parent
This function sets the parent of @var{char-table} to @var{new-parent}.
@end defun
@defun char-table-extra-slot char-table n
This function returns the contents of extra slot @var{n} (zero based)
of @var{char-table}. The number of extra slots in a char-table is
determined by its subtype.
@end defun
@defun set-char-table-extra-slot char-table n value
This function stores @var{value} in extra slot @var{n} (zero based) of
@var{char-table}.
@end defun
A char-table can specify an element value for a single character code;
it can also specify a value for an entire character set.
@defun char-table-range char-table range
This returns the value specified in @var{char-table} for a range of
characters @var{range}. Here are the possibilities for @var{range}:
@table @asis
@item @code{nil}
Refers to the default value.
@item @var{char}
Refers to the element for character @var{char}
(supposing @var{char} is a valid character code).
@item @code{(@var{from} . @var{to})}
A cons cell refers to all the characters in the inclusive range
@samp{[@var{from}..@var{to}]}.
@end table
@end defun
@defun set-char-table-range char-table range value
This function sets the value in @var{char-table} for a range of
characters @var{range}. Here are the possibilities for @var{range}:
@table @asis
@item @code{nil}
Refers to the default value.
@item @code{t}
Refers to the whole range of character codes.
@item @var{char}
Refers to the element for character @var{char}
(supposing @var{char} is a valid character code).
@item @code{(@var{from} . @var{to})}
A cons cell refers to all the characters in the inclusive range
@samp{[@var{from}..@var{to}]}.
@end table
@end defun
@defun map-char-table function char-table
This function calls its argument @var{function} for each element of
@var{char-table} that has a non-@code{nil} value. The call to
@var{function} is with two arguments, a key and a value. The key
is a possible @var{range} argument for @code{char-table-range}---either
a valid character or a cons cell @code{(@var{from} . @var{to})},
specifying a range of characters that share the same value. The value is
what @code{(char-table-range @var{char-table} @var{key})} returns.
Overall, the key-value pairs passed to @var{function} describe all the
values stored in @var{char-table}.
The return value is always @code{nil}; to make calls to
@code{map-char-table} useful, @var{function} should have side effects.
For example, here is how to examine the elements of the syntax table:
@example
(let (accumulator)
(map-char-table
(lambda (key value)
(setq accumulator
(cons (list
(if (consp key)
(list (car key) (cdr key))
key)
value)
accumulator)))
(syntax-table))
accumulator)
@result{}
(((2597602 4194303) (2)) ((2597523 2597601) (3))
... (65379 (5 . 65378)) (65378 (4 . 65379)) (65377 (1))
... (12 (0)) (11 (3)) (10 (12)) (9 (0)) ((0 8) (3)))
@end example
@end defun
@node Bool-Vectors
@section Bool-vectors
@cindex Bool-vectors
A bool-vector is much like a vector, except that it stores only the
values @code{t} and @code{nil}. If you try to store any non-@code{nil}
value into an element of the bool-vector, the effect is to store
@code{t} there. As with all arrays, bool-vector indices start from 0,
and the length cannot be changed once the bool-vector is created.
Bool-vectors are constants when evaluated.
Several functions work specifically with bool-vectors; aside
from that, you manipulate them with same functions used for other kinds
of arrays.
@defun make-bool-vector length initial
Return a new bool-vector of @var{length} elements,
each one initialized to @var{initial}.
@end defun
@defun bool-vector &rest objects
This function creates and returns a bool-vector whose elements are the
arguments, @var{objects}.
@end defun
@defun bool-vector-p object
This returns @code{t} if @var{object} is a bool-vector,
and @code{nil} otherwise.
@end defun
There are also some bool-vector set operation functions, described below:
@defun bool-vector-exclusive-or a b &optional c
Return @dfn{bitwise exclusive or} of bool vectors @var{a} and @var{b}.
If optional argument @var{c} is given, the result of this operation is
stored into @var{c}. All arguments should be bool vectors of the same length.
@end defun
@defun bool-vector-union a b &optional c
Return @dfn{bitwise or} of bool vectors @var{a} and @var{b}. If
optional argument @var{c} is given, the result of this operation is
stored into @var{c}. All arguments should be bool vectors of the same length.
@end defun
@defun bool-vector-intersection a b &optional c
Return @dfn{bitwise and} of bool vectors @var{a} and @var{b}. If
optional argument @var{c} is given, the result of this operation is
stored into @var{c}. All arguments should be bool vectors of the same length.
@end defun
@defun bool-vector-set-difference a b &optional c
Return @dfn{set difference} of bool vectors @var{a} and @var{b}. If
optional argument @var{c} is given, the result of this operation is
stored into @var{c}. All arguments should be bool vectors of the same length.
@end defun
@defun bool-vector-not a &optional b
Return @dfn{set complement} of bool vector @var{a}. If optional
argument @var{b} is given, the result of this operation is stored into
@var{b}. All arguments should be bool vectors of the same length.
@end defun
@defun bool-vector-subsetp a b
Return @code{t} if every @code{t} value in @var{a} is also @code{t} in
@var{b}, @code{nil} otherwise. All arguments should be bool vectors of the
same length.
@end defun
@defun bool-vector-count-consecutive a b i
Return the number of consecutive elements in @var{a} equal @var{b}
starting at @var{i}. @code{a} is a bool vector, @var{b} is @code{t}
or @code{nil}, and @var{i} is an index into @code{a}.
@end defun
@defun bool-vector-count-population a
Return the number of elements that are @code{t} in bool vector @var{a}.
@end defun
The printed form represents up to 8 boolean values as a single
character:
@example
@group
(bool-vector t nil t nil)
@result{} #&4"^E"
(bool-vector)
@result{} #&0""
@end group
@end example
You can use @code{vconcat} to print a bool-vector like other vectors:
@example
@group
(vconcat (bool-vector nil t nil t))
@result{} [nil t nil t]
@end group
@end example
Here is another example of creating, examining, and updating a
bool-vector:
@example
(setq bv (make-bool-vector 5 t))
@result{} #&5"^_"
(aref bv 1)
@result{} t
(aset bv 3 nil)
@result{} nil
bv
@result{} #&5"^W"
@end example
@noindent
These results make sense because the binary codes for control-_ and
control-W are 11111 and 10111, respectively.
@node Rings
@section Managing a Fixed-Size Ring of Objects
@cindex ring data structure
A @dfn{ring} is a fixed-size data structure that supports insertion,
deletion, rotation, and modulo-indexed reference and traversal. An
efficient ring data structure is implemented by the @code{ring}
package. It provides the functions listed in this section.
Note that several rings in Emacs, like the kill ring and the
mark ring, are actually implemented as simple lists, @emph{not} using
the @code{ring} package; thus the following functions won't work on
them.
@defun make-ring size
This returns a new ring capable of holding @var{size} objects.
@var{size} should be an integer.
@end defun
@defun ring-p object
This returns @code{t} if @var{object} is a ring, @code{nil} otherwise.
@end defun
@defun ring-size ring
This returns the maximum capacity of the @var{ring}.
@end defun
@defun ring-length ring
This returns the number of objects that @var{ring} currently contains.
The value will never exceed that returned by @code{ring-size}.
@end defun
@defun ring-elements ring
This returns a list of the objects in @var{ring}, in order, newest first.
@end defun
@defun ring-copy ring
This returns a new ring which is a copy of @var{ring}.
The new ring contains the same (@code{eq}) objects as @var{ring}.
@end defun
@defun ring-empty-p ring
This returns @code{t} if @var{ring} is empty, @code{nil} otherwise.
@end defun
The newest element in the ring always has index 0. Higher indices
correspond to older elements. Indices are computed modulo the ring
length. Index @minus{}1 corresponds to the oldest element, @minus{}2
to the next-oldest, and so forth.
@defun ring-ref ring index
This returns the object in @var{ring} found at index @var{index}.
@var{index} may be negative or greater than the ring length. If
@var{ring} is empty, @code{ring-ref} signals an error.
@end defun
@defun ring-insert ring object
This inserts @var{object} into @var{ring}, making it the newest
element, and returns @var{object}.
If the ring is full, insertion removes the oldest element to
make room for the new element.
@end defun
@defun ring-remove ring &optional index
Remove an object from @var{ring}, and return that object. The
argument @var{index} specifies which item to remove; if it is
@code{nil}, that means to remove the oldest item. If @var{ring} is
empty, @code{ring-remove} signals an error.
@end defun
@defun ring-insert-at-beginning ring object
This inserts @var{object} into @var{ring}, treating it as the oldest
element. The return value is not significant.
If the ring is full, this function removes the newest element to make
room for the inserted element.
@end defun
@defun ring-resize ring size
Set the size of @var{ring} to @var{size}. If the new size is smaller,
then the oldest items in the ring are discarded.
@end defun
@cindex fifo data structure
If you are careful not to exceed the ring size, you can
use the ring as a first-in-first-out queue. For example:
@lisp
(let ((fifo (make-ring 5)))
(mapc (lambda (obj) (ring-insert fifo obj))
'(0 one "two"))
(list (ring-remove fifo) t
(ring-remove fifo) t
(ring-remove fifo)))
@result{} (0 t one t "two")
@end lisp
|