aboutsummaryrefslogtreecommitdiffstats
path: root/lib/tools/doc/src/xref.xml
blob: 11c6fa56f6044cb3e25d7995bb848c21af35600f (plain) (blame)
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
<?xml version="1.0" encoding="utf-8" ?>
<!DOCTYPE erlref SYSTEM "erlref.dtd">

<erlref>
  <header>
    <copyright>
      <year>2000</year><year>2016</year>
      <holder>Ericsson AB. All Rights Reserved.</holder>
    </copyright>
    <legalnotice>
      Licensed under the Apache License, Version 2.0 (the "License");
      you may not use this file except in compliance with the License.
      You may obtain a copy of the License at
 
          http://www.apache.org/licenses/LICENSE-2.0

      Unless required by applicable law or agreed to in writing, software
      distributed under the License is distributed on an "AS IS" BASIS,
      WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
      See the License for the specific language governing permissions and
      limitations under the License.

    </legalnotice>

    <title>xref</title>
    <prepared>Hans Bolinder</prepared>
    <responsible>nobody</responsible>
    <docno></docno>
    <approved>nobody</approved>
    <checked>no</checked>
    <date>2000-08-15</date>
    <rev>PA1</rev>
    <file>xref.sgml</file>
  </header>
  <module>xref</module>
  <modulesummary>A Cross Reference Tool for analyzing dependencies between functions, modules, applications and releases.</modulesummary>
  <description>
    <p>Xref is a cross reference tool that can be used for finding
      dependencies between functions, modules, applications and
      releases.
      </p>
    <p>Calls between functions are either       <marker id="local_call"></marker>
<em>local calls</em> like <c>f()</c>, or       <marker id="external_call"></marker>
<em>external calls</em> like
      <c>m:f()</c>.       <marker id="module_data"></marker>
<em>Module data</em>,
      which are extracted from BEAM files, include local functions,
      exported functions, local calls and external calls. By default,
      calls to built-in functions (<term id="BIF"></term>) are ignored, but
      if the option <c>builtins</c>, accepted by some of this
      module's functions, is set to <c>true</c>, calls to BIFs
      are included as well. It is the analyzing OTP version that
      decides what functions are BIFs. Functional objects are assumed
      to be called where they are created (and nowhere else).       <marker id="unresolved_call"></marker>
<em>Unresolved calls</em> are calls to
      <c>apply</c> or <c>spawn</c> with variable module, variable
      function, or variable arguments. Examples are <c>M:F(a)</c>,
      <c>apply(M,&nbsp;f,&nbsp;[a])</c>, and
      <c>spawn(m,&nbsp;f(),&nbsp;Args)</c>. Unresolved calls are
      represented by calls where variable modules have been replaced
      with the atom <c>'$M_EXPR'</c>, variable functions have been
      replaced with the atom <c>'$F_EXPR'</c>, and variable number of
      arguments have been replaced with the number <c>-1</c>. The
      above mentioned examples are represented by calls to
      <c>'$M_EXPR':'$F_EXPR'/1</c>, <c>'$M_EXPR':f/1</c>, and
      <c>m:'$F_EXPR'/-1</c>. The unresolved calls are a subset of the
      external calls.
      </p>
    <warning>
      <p>Unresolved calls make module data incomplete, which
        implies that the results of analyses may be invalid.</p>
    </warning>
    <p><em>Applications</em> are collections of modules. The
      modules' BEAM files are located in the <c>ebin</c>
      subdirectory of the application directory. The name of the
      application directory determines the name and version of the
      application.
      <em>Releases</em> are collections of applications
      located in the <c>lib</c> subdirectory of the release directory. 
      There is more to read about applications and releases in the
      Design Principles book.
      </p>
    <p>      <marker id="xref_server"></marker>
<em>Xref servers</em> are identified
      by names, supplied when creating new servers. Each Xref server
      holds a set of releases, a set of applications, and a set of
      modules with module data. Xref servers are independent of each
      other, and all analyses are evaluated in the context of one
      single Xref server (exceptions are the functions <c>m/1</c> and
      <c>d/1</c> which do not use servers at all). The       <marker id="mode"></marker>
<em>mode</em> of an Xref server determines what module
      data are extracted from BEAM files as modules are added to the
      server. Starting with R7, BEAM files compiled with the option
      <c>debug_info</c> contain so called       <marker id="debug_info"></marker>
debug information, which is an abstract
      representation of the code. In <c>functions</c> mode, which is
      the default mode, function calls and line numbers are extracted
      from debug information. In <c>modules</c> mode, debug
      information is ignored if present, but dependencies between
      modules are extracted from other parts of the BEAM files. The
      <c>modules</c> mode is significantly less time and space
      consuming than the <c>functions</c> mode, but the analyses that
      can be done are limited.
      </p>
    <p>An       <marker id="analyzed_module"></marker>
<em>analyzed module</em> is a
      module that has been added to an Xref server together with its
      module data.
      A       <marker id="library_module"></marker>
<em>library module</em> is a
      module located in some directory mentioned in the       <marker id="library_path"></marker>
<em>library path</em>. 
      A library module is said to be used if some of its exported
      functions are used by some analyzed module.
      An       <marker id="unknown_module"></marker>
<em>unknown module</em> is a
      module that is neither an analyzed module nor a library module,
      but whose exported functions are used by some analyzed module. 
      An       <marker id="unknown_function"></marker>
<em>unknown function</em> is a
      used function that is neither local or exported by any 
      analyzed module nor exported by any library module. 
      An       <marker id="undefined_function"></marker>
<em>undefined function</em> is an externally used function that
      is not exported by any analyzed module or library module. With
      this notion, a local function can be an undefined function, namely
      if it is externally used from some module. All unknown functions
      are also undefined functions; there is a <seealso marker="xref_chapter#venn2">figure</seealso> in the
      User's Guide that illustrates this relationship.
      </p>
    <p>Starting with R9C, the module attribute tag <c>deprecated</c>
      can be used to inform Xref about       <marker id="deprecated_function"></marker>
<em>deprecated functions</em> and
      optionally when functions are planned to be removed. A few
      examples show the idea:
      </p>
    <taglist>
      <tag>-deprecated({f,1}).</tag>
      <item>The exported function <c>f/1</c> is deprecated. Nothing is
       said whether <c>f/1</c> will be removed or not.</item>
      <tag>-deprecated({f,'_'}).</tag>
      <item>All exported functions <c>f/0</c>, <c>f/1</c> and so on are
       deprecated.</item>
      <tag>-deprecated(module).</tag>
      <item>All exported functions in the module are deprecated.
       Equivalent to <c>-deprecated({'_','_'}).</c>.</item>
      <tag>-deprecated([{g,1,next_version}]).</tag>
      <item>The function <c>g/1</c> is deprecated and will be
       removed in next version.</item>
      <tag>-deprecated([{g,2,next_major_release}]).</tag>
      <item>The function <c>g/2</c> is deprecated and will be
       removed in next major release.</item>
      <tag>-deprecated([{g,3,eventually}]).</tag>
      <item>The function <c>g/3</c> is deprecated and will
       eventually be removed.</item>
      <tag>-deprecated({'_','_',eventually}).</tag>
      <item>All exported functions in the module are deprecated and
       will eventually be removed.</item>
    </taglist>
    <p>Before any analysis can take place, module data must be <em>set up</em>. For instance, the cross reference and the unknown
      functions are computed when all module data are known. The
      functions that need complete data (<c>analyze</c>, <c>q</c>,
      <c>variables</c>) take care of setting up data automatically.
      Module data need to be set up (again) after calls to any of the
      <c>add</c>, <c>replace</c>, <c>remove</c>,
      <c>set_library_path</c> or <c>update</c> functions.
      </p>
    <p>The result of setting up module data is the       <marker id="call_graph"></marker>
<em>Call Graph</em>. A (directed) graph
      consists of a set of vertices and a set of (directed) edges. The
      edges represent       <marker id="call"></marker>
<em>calls</em> (From,&nbsp;To)
      between functions, modules, applications or releases. From is
      said to call To, and To is said to be used by From. The vertices
      of the Call Graph are the functions of all module data: local
      and exported functions of analyzed modules; used BIFs; used
      exported functions of library modules; and unknown functions.
      The functions <c>module_info/0,1</c> added by the compiler are
      included among the exported functions, but only when called from
      some module. The edges are the function calls of all module
      data. A consequence of the edges being a set is that there is
      only one edge if a function is locally or externally used
      several times on one and the same line of code.
      </p>
    <p>The Call Graph is       <marker id="representation"></marker>
represented by
      Erlang terms (the sets are lists), which is suitable for many
      analyses. But for analyses that look at chains of calls, a list
      representation is much too
      slow. Instead the representation offered by the <c>digraph</c>
      module is used. The translation of the list representation of
      the Call Graph - or a subgraph thereof - to the <c>digraph</c>
      representation does not
      come for free, so the language used for expressing queries to be
      described below has a special operator for this task and a
      possibility to save the <c>digraph</c> representation for
      subsequent analyses.
      </p>
    <p>In addition to the Call Graph there is a graph called the
            <marker id="inter_call_graph"></marker>
<em>Inter Call Graph</em>. This is
      a graph of calls (From,&nbsp;To) such that there is a chain of
      calls from From to To in the Call Graph, and every From and To
      is an exported function or an unused local function.
      The vertices are the same as for the Call Graph.
      </p>
    <p>Calls between modules, applications and releases are also
      directed graphs. The       <marker id="type"></marker>
<em>types</em>
      of the vertices and edges of these graphs are (ranging from the
      most special to the most general):
      <c>Fun</c> for functions; <c>Mod</c> for modules;
      <c>App</c> for applications; and <c>Rel</c> for releases.
      The following paragraphs will describe the different constructs
      of the language used for selecting and analyzing parts of the
      graphs, beginning with the       <marker id="constants"></marker>
<em>constants</em>:
      </p>
    <list type="bulleted">
      <item>Expression ::= Constants</item>
      <item>Constants ::= Consts | Consts <c>:</c> Type | RegExpr</item>
      <item>Consts ::= Constant | <c>[</c>Constant<c>,</c>&nbsp;...<c>]</c>
       | <c>{</c>Constant<c>,</c>&nbsp;...<c>}</c></item>
      <item>Constant ::= Call | Const</item>
      <item>Call ::= FunSpec&nbsp;<c>-></c>&nbsp;FunSpec
       | <c>{</c>MFA<c>,</c>&nbsp;MFA<c>}</c>
       | AtomConst&nbsp;<c>-></c>&nbsp;AtomConst 
       | <c>{</c>AtomConst<c>,</c>&nbsp;AtomConst<c>}</c></item>
      <item>Const ::= AtomConst | FunSpec | MFA</item>
      <item>AtomConst ::= Application | Module | Release</item>
      <item>FunSpec ::= Module <c>:</c> Function <c>/</c> Arity</item>
      <item>MFA ::=
      <c>{</c>Module<c>,</c>&nbsp;Function<c>,</c>&nbsp;Arity<c>}</c></item>
      <item>RegExpr ::= RegString <c>:</c> Type 
       | RegFunc 
       | RegFunc <c>:</c> Type</item>
      <item>RegFunc ::= RegModule <c>:</c> RegFunction <c>/</c> RegArity</item>
      <item>RegModule ::= RegAtom</item>
      <item>RegFunction ::= RegAtom</item>
      <item>RegArity ::= RegString | Number | <c>_</c> | <c>-1</c></item>
      <item>RegAtom ::= RegString | Atom | <c>_</c></item>
      <item>RegString ::= - a regular expression, as described in the 
      <c>re</c> module, enclosed in double quotes -</item>
      <item>Type ::= <c>Fun</c> | <c>Mod</c> | <c>App</c> | <c>Rel</c></item>
      <item>Function ::= Atom</item>
      <item>Application ::= Atom</item>
      <item>Module ::= Atom</item>
      <item>Release ::= Atom</item>
      <item>Arity ::= Number | <c>-1</c></item>
      <item>Atom ::= - same as Erlang atoms -</item>
      <item>Number ::= - same as non-negative Erlang integers -</item>
    </list>
    <p>Examples of constants are: <c>kernel</c>, <c>kernel->stdlib</c>,
      <c>[kernel, sasl]</c>, <c>[pg -> mnesia, {tv, mnesia}] : Mod</c>.
      It is an error if an instance of <c>Const</c> does not match any
      vertex of any graph. 
      If there  are more than one vertex matching an untyped instance
      of <c>AtomConst</c>, then the one of the most general type is
      chosen.
      A list of constants is interpreted as a set of constants, all of
      the same type.
      A tuple of constants constitute a chain of calls (which may,
      but does not have to, correspond to an actual chain of calls of
      some graph).
      Assigning a type to a list or tuple of <c>Constant</c> is
      equivalent to assigning the type to each <c>Constant</c>.
      </p>
    <p><marker id="regexp"></marker><em>Regular expressions</em> are used as a
      means to select some of the vertices of a graph.
      A <c>RegExpr</c> consisting of a <c>RegString</c> and a type -
      an example is <c>"xref_.*" : Mod</c> - is interpreted as those
      modules (or applications or releases, depending on the type)
      that match the expression.
      Similarly, a <c>RegFunc</c> is interpreted as those vertices
      of the Call Graph that match the expression. 
      An example is <c>"xref_.*":"add_.*"/"(2|3)"</c>, which matches
      all <c>add</c> functions of arity two or three of any of the
      xref modules.
      Another example, one that matches all functions of arity 10 or
      more: <c>_:_/"[1-9].+"</c>. Here <c>_</c> is an abbreviation for
      <c>".*"</c>, that is, the regular expression that matches
      anything.
      </p>
    <p>The syntax of       <marker id="variable"></marker>
<em>variables</em> is
      simple:
      </p>
    <list type="bulleted">
      <item>Expression ::= Variable</item>
      <item>Variable ::= - same as Erlang variables -</item>
    </list>
    <p>There are two kinds of variables: predefined variables and user 
      variables. 
            <marker id="predefined_variable"></marker>
<em>Predefined variables</em>
      hold set up module data, and cannot be assigned to but only used 
      in queries. 
            <marker id="user_variable"></marker>
<em>User variables</em> on the other 
      hand can be assigned to, and are typically used for
      temporary results while evaluating a query, and for keeping
      results of queries for use in subsequent queries. 
      The predefined variables are (variables marked with (*) are
      available in <c>functions</c> mode only):
      </p>
    <taglist>
      <tag><c>E</c></tag>
      <item>Call Graph Edges (*).</item>
      <tag><c>V</c></tag>
      <item>Call Graph Vertices (*).
      </item>
      <tag><c>M</c></tag>
      <item>Modules. All modules: analyzed modules, used library
       modules, and unknown modules.</item>
      <tag><c>A</c></tag>
      <item>Applications.</item>
      <tag><c>R</c></tag>
      <item>Releases.
      </item>
      <tag><c>ME</c></tag>
      <item>Module Edges. All module calls.</item>
      <tag><c>AE</c></tag>
      <item>Application Edges. All application calls. </item>
      <tag><c>RE</c></tag>
      <item>Release Edges. All release calls.
      </item>
      <tag><c>L</c></tag>
      <item>Local Functions (*). All local functions of analyzed modules.</item>
      <tag><c>X</c></tag>
      <item>Exported Functions. All exported functions of analyzed 
       modules and all used exported functions of library modules.</item>
      <tag><c>F</c></tag>
      <item>Functions (*).</item>
      <tag><c>B</c></tag>
      <item>Used BIFs. <c>B</c> is empty if <c>builtins</c> is 
      <c>false</c> for all analyzed modules.</item>
      <tag><c>U</c></tag>
      <item>Unknown Functions.</item>
      <tag><c>UU</c></tag>
      <item>Unused Functions (*). All local and exported functions of
       analyzed modules that have not been used. </item>
      <tag><c>XU</c></tag>
      <item>Externally Used Functions. Functions of all modules -
       including local functions - that have been used in some
       external call.</item>
      <tag><c>LU</c></tag>
      <item>Locally Used Functions (*). Functions of all modules that have
       been used in some local call.
      </item>
      <tag><c>LC</c></tag>
      <item>Local Calls (*).</item>
      <tag><c>XC</c></tag>
      <item>External Calls (*).
      </item>
      <tag><c>AM</c></tag>
      <item>Analyzed Modules.</item>
      <tag><c>UM</c></tag>
      <item>Unknown Modules.</item>
      <tag><c>LM</c></tag>
      <item>Used Library Modules.
      </item>
      <tag><c>UC</c></tag>
      <item>Unresolved Calls. Empty in <c>modules</c> mode.
      </item>
      <tag><c>EE</c></tag>
      <item>Inter Call Graph Edges (*).
      </item>
      <tag><c>DF</c></tag>
      <item>Deprecated Functions. All deprecated exported 
       functions and all used deprecated BIFs.</item>
      <tag><c>DF_1</c></tag>
      <item>Deprecated Functions. All deprecated functions 
       to be removed in next version.</item>
      <tag><c>DF_2</c></tag>
      <item>Deprecated Functions. All deprecated functions 
       to be removed in next version or next major release.</item>
      <tag><c>DF_3</c></tag>
      <item>Deprecated Functions. All deprecated functions to be
       removed in next version, next major release, or later.</item>
    </taglist>
    <p>These are a few       <marker id="simple_facts"></marker>
facts about the
      predefined variables (the set operators <c>+</c> (union) and
      <c>-</c> (difference) as well as the cast operator
      <c>(</c>Type<c>)</c> are described below):
      </p>
    <list type="bulleted">
      <item><c>F</c> is equal to  <c>L + X</c>.</item>
      <item><c>V</c> is equal to <c>X + L + B + U</c>, where <c>X</c>,
      <c>L</c>, <c>B</c> and <c>U</c> are pairwise disjoint (that
       is, have no elements in common).</item>
      <item><c>UU</c> is equal to <c>V - (XU + LU)</c>, where
      <c>LU</c> and <c>XU</c> may have elements in common. Put in
       another way:</item>
      <item><c>V</c> is equal to <c>UU + XU + LU</c>.</item>
      <item><c>E</c> is equal to <c>LC + XC</c>. Note that <c>LC</c>
       and <c>XC</c> may have elements in common, namely if some
       function is locally and externally used from one and the same
       function.</item>
      <item><c>U</c> is a subset of <c>XU</c>.</item>
      <item><c>B</c> is a subset of <c>XU</c>.</item>
      <item><c>LU</c> is equal to <c>range LC</c>.</item>
      <item><c>XU</c> is equal to <c>range XC</c>.</item>
      <item><c>LU</c> is a subset of <c>F</c>.</item>
      <item><c>UU</c> is a subset of <c>F</c>. </item>
      <item><c>range UC</c> is a subset of <c>U</c>.</item>
      <item><c>M</c> is equal to <c>AM + LM + UM</c>, where <c>AM</c>,
      <c>LM</c> and <c>UM</c> are pairwise disjoint. </item>
      <item><c>ME</c> is equal to <c>(Mod) E</c>.</item>
      <item><c>AE</c> is equal to <c>(App) E</c>.</item>
      <item><c>RE</c> is equal to <c>(Rel) E</c>.</item>
      <item><c>(Mod) V</c> is a subset of <c>M</c>. Equality holds
       if all analyzed modules have some local, exported, or unknown 
       function.</item>
      <item><c>(App) M</c> is a subset of <c>A</c>. Equality holds
       if all applications have some module.</item>
      <item><c>(Rel) A</c> is a subset of <c>R</c>. Equality holds
       if all releases have some application.</item>
      <item><c>DF_1</c> is a subset of <c>DF_2</c>.</item>
      <item><c>DF_2</c> is a subset of <c>DF_3</c>.</item>
      <item><c>DF_3</c> is a subset of <c>DF</c>.</item>
      <item><c>DF</c> is a subset of <c>X + B</c>.</item>
    </list>
    <p>An important notion is that of       <marker id="conversion"></marker>
<em>conversion</em> of expressions. The syntax of
      a cast expression is:
      </p>
    <list type="bulleted">
      <item>Expression ::= <c>(</c> Type <c>)</c> Expression</item>
    </list>
    <p>The interpretation of the cast operator depends on the named
      type <c>Type</c>, the type of <c>Expression</c>, and the
      structure of the elements of the interpretation of <c>Expression</c>. 
      If the named type is equal to the
      expression type, no conversion is done. Otherwise, the
      conversion is done one step at a time;
      <c>(Fun)&nbsp;(App)&nbsp;RE</c>, for instance, is equivalent to
      <c>(Fun)&nbsp;(Mod)&nbsp;(App)&nbsp;RE</c>. Now assume that the
      interpretation of <c>Expression</c> is a set of constants
      (functions, modules, applications or releases). If the named
      type is more general than the expression type, say <c>Mod</c>
      and <c>Fun</c> respectively, then the interpretation of the cast
      expression is the set of modules that have at least one
      of their functions mentioned in the interpretation of the
      expression. If the named
      type is more special than the expression type, say <c>Fun</c>
      and <c>Mod</c>, then the interpretation is the set of all the
      functions of the modules (in <c>modules</c> mode, the conversion
      is partial since the local functions are not known).
      The conversions to and from applications and releases
      work analogously. For instance, <c>(App) "xref_.*" : Mod</c>
      returns all applications containing at least one module
      such that <c>xref_</c> is a prefix of the module name.
      </p>
    <p>Now assume that the interpretation of <c>Expression</c> is a
      set of calls. If the named type is more general than the
      expression type, say <c>Mod</c> and <c>Fun</c> respectively,
      then the interpretation of the cast expression is the set of
      calls (M1,&nbsp;M2) such that the interpretation of the 
      expression contains a call from some function
      of M1 to some function of M2. If the named type is more special
      than the expression type, say <c>Fun</c> and <c>Mod</c>, then
      the interpretation is the set of all function calls
      (F1,&nbsp;F2) such that the interpretation of the expression
      contains a call (M1,&nbsp;M2) and F1 is
      a function of M1 and F2 is a function of M2 (in <c>modules</c>
      mode, there are no functions calls, so a cast to <c>Fun</c>
      always yields an empty set). Again, the conversions to and from
      applications and releases work analogously.
      </p>
    <p>The interpretation of constants and variables are sets, and
      those sets can be used as the basis for forming new sets by the
      application of       <marker id="set_operator"></marker>
<em>set operators</em>.
      The syntax:
      </p>
    <list type="bulleted">
      <item>Expression ::= Expression BinarySetOp Expression</item>
      <item>BinarySetOp ::= <c>+</c> | <c>*</c> | <c>-</c></item>
    </list>
    <p><c>+</c>, <c>*</c> and <c>-</c> are interpreted as union,
      intersection and difference respectively: the union of two sets
      contains the elements of both sets; the intersection of two sets
      contains the elements common to both sets; and the difference of
      two sets contains the elements of the first set that are not
      members of the second set. The elements of the two sets must be
      of the same structure; for instance, a function call cannot be
      combined with a function. But if a cast operator can make the
      elements compatible, then the more general elements are
      converted to the less general element type. For instance,
      <c>M&nbsp;+&nbsp;F</c> is equivalent to
      <c>(Fun)&nbsp;M&nbsp;+&nbsp;F</c>, and <c>E&nbsp;-&nbsp;AE</c>
      is equivalent to <c>E&nbsp;-&nbsp;(Fun)&nbsp;AE</c>. One more
      example: <c>X * xref : Mod</c> is interpreted as the set of
      functions exported by the module <c>xref</c>; <c>xref : Mod</c>
      is converted to the more special type of <c>X</c> (<c>Fun</c>,
      that is) yielding all functions of <c>xref</c>, and the
      intersection with <c>X</c> (all functions exported by analyzed 
      modules and library modules) is interpreted as those functions
      that are exported by some module <em>and</em> functions of 
      <c>xref</c>. 
      </p>
    <p>There are also unary set operators:
      </p>
    <list type="bulleted">
      <item>Expression ::= UnarySetOp Expression</item>
      <item>UnarySetOp ::= <c>domain</c> | <c>range</c> | <c>strict</c></item>
    </list>
    <p>Recall that a call is a pair (From,&nbsp;To). <c>domain</c>
      applied to a set of calls is interpreted as the set of all
      vertices From, and <c>range</c> as the set of all vertices To.
      The interpretation of the <c>strict</c> operator is the operand
      with all calls on the form (A,&nbsp;A) removed. 
      </p>
    <p>The interpretation of the       <marker id="restriction"></marker>
<em>restriction operators</em> is a 
      subset of the first operand, a set of calls. The second operand,
      a set of vertices, is converted to the type of the first operand.
      The syntax of the restriction operators:
      </p>
    <list type="bulleted">
      <item>Expression ::= Expression RestrOp Expression</item>
      <item>RestrOp ::= <c>|</c></item>
      <item>RestrOp ::= <c>||</c></item>
      <item>RestrOp ::= <c>|||</c></item>
    </list>
    <p>The interpretation in some detail for the three operators:
      </p>
    <taglist>
      <tag><c>|</c></tag>
      <item>The subset of calls from any of the vertices.</item>
      <tag><c>||</c></tag>
      <item>The subset of calls to any of the vertices.</item>
      <tag><c>|||</c></tag>
      <item>The subset of calls to and from any of the vertices.
       For all sets of calls <c>CS</c> and all sets of vertices
      <c>VS</c>, <c>CS&nbsp;|||&nbsp;VS&nbsp;</c> is equivalent to
      <c>CS&nbsp;|&nbsp;VS&nbsp;*&nbsp;CS&nbsp;||&nbsp;VS</c>.</item>
    </taglist>
    <p>      <marker id="graph_analyses"></marker>
Two functions (modules,
      applications, releases) belong to the same strongly connected
      component if they call each other (in)directly. The
      interpretation of the <c>components</c> operator is the set of
      strongly connected components of a set of calls. The
      <c>condensation</c> of a set of calls is a new set of calls
      between the strongly connected components such that there is an
      edge between two components if there is some constant of the first
      component that calls some constant of the second component.
      </p>
    <p>The interpretation of the <c>of</c> operator is a chain of
      calls of the second operand (a set of calls) that passes throw
      all of the vertices of the first operand (a tuple of
      constants), in the given order. The second operand
      is converted to the type of the first operand.
      For instance, the <c>of</c> operator can be used for finding out
      whether a function calls another function indirectly, and the
      chain of calls demonstrates how. The syntax of the graph
      analyzing operators:
      </p>
    <list type="bulleted">
      <item>Expression ::= Expression BinaryGraphOp Expression</item>
      <item>Expression ::= UnaryGraphOp Expression</item>
      <item>UnaryGraphOp ::= <c>components</c> | <c>condensation</c></item>
      <item>BinaryGraphOp ::= <c>of</c></item>
    </list>
    <p>As was mentioned before, the graph analyses operate on
      the <c>digraph</c> representation of graphs.
      By default, the <c>digraph</c> representation is created when
      needed (and deleted when no longer used), but it can also be
      created explicitly by use of the <c>closure</c> operator:
      </p>
    <list type="bulleted">
      <item>Expression ::= ClosureOp Expression</item>
      <item>ClosureOp ::= <c>closure</c></item>
    </list>
    <p>The interpretation of the <c>closure</c> operator is the
      transitive closure of the operand. 
      </p>
    <p>The restriction operators are defined for closures as well;
      <c>closure&nbsp;E&nbsp;|&nbsp;xref&nbsp;:&nbsp;Mod</c> is
      interpreted as the direct or indirect function calls from the
      <c>xref</c> module, while the interpretation of
      <c>E&nbsp;|&nbsp;xref&nbsp;:&nbsp;Mod</c> is the set of direct
      calls from <c>xref</c>. 
      If some graph is to be used in several graph analyses, it saves
      time to assign the <c>digraph</c> representation of the graph
      to a user variable, 
      and then make sure that every graph analysis operates on that
      variable instead of the list representation of the graph.
      </p>
    <p>The lines where functions are defined (more precisely: where
      the first clause begins) and the lines where functions are used
      are available in <c>functions</c> mode. The line numbers refer
      to the files where the functions are defined. This holds also for
      files included with the <c>-include</c> and <c>-include_lib</c>
      directives, which may result in functions defined apparently in
      the same line. The <em>line operators</em> are used for assigning
      line numbers to functions and for assigning sets of line numbers
      to function calls. 
      The syntax is similar to the one of the cast operator:
      </p>
    <list type="bulleted">
      <item>Expression ::= <c>(</c> LineOp<c>)</c> Expression</item>
      <item>Expression ::= <c>(</c> XLineOp<c>)</c> Expression</item>
      <item>LineOp ::= <c>Lin</c> | <c>ELin</c> | <c>LLin</c> | <c>XLin</c></item>
      <item>XLineOp ::= <c>XXL</c></item>
    </list>
    <p>The interpretation of the <c>Lin</c> operator applied to a set
      of functions assigns to each function the line number where the
      function is defined. Unknown functions and functions of library
      modules are assigned the number 0.
      </p>
    <p>The interpretation of some LineOp operator applied to a
      set of function calls assigns to each call the set of line
      numbers where the first function calls the second function. Not
      all calls are assigned line numbers by all operators:
      </p>
    <list type="bulleted">
      <item>the <c>Lin</c> operator is defined for Call Graph Edges;</item>
      <item>the <c>LLin</c> operator is defined for Local Calls.</item>
      <item>the <c>XLin</c> operator is defined for External Calls.</item>
      <item>the <c>ELin</c> operator is defined for Inter Call Graph Edges.</item>
    </list>
    <p>The <c>Lin</c> (<c>LLin</c>, <c>XLin</c>) operator assigns
      the lines where calls (local calls, external calls) are made.
      The <c>ELin</c> operator assigns to each call (From,&nbsp;To),
      for which it is defined, every line L such that there is
      a chain of calls from From to To beginning with a call on line
      L.
      </p>
    <p>The <c>XXL</c> operator is defined for the interpretation of
      any of the LineOp operators applied to a set of function
      calls. The result is that of replacing the function call with
      a line numbered function call, that is, each of the two
      functions of the call is replaced by a pair of the function and
      the line where the function is defined. The effect of the
      <c>XXL</c> operator can be undone by the LineOp operators. For
      instance, <c>(Lin)&nbsp;(XXL)&nbsp;(Lin)&nbsp;E</c> is
      equivalent to <c>(Lin)&nbsp;E</c>.
      </p>
    <p>The <c>+</c>, <c>-</c>, <c>*</c> and <c>#</c> operators are
      defined for line number expressions, provided the operands are
      compatible. The LineOp operators are also defined for
      modules, applications, and releases; the operand is implicitly
      converted to functions. Similarly, the cast operator is defined
      for the interpretation of the LineOp operators.
      </p>
    <p>The interpretation of the       <marker id="count"></marker>
<em>counting operator</em> is the number of elements of a set. The operator
      is undefined for closures. The <c>+</c>, <c>-</c> and <c>*</c>
      operators are interpreted as the obvious arithmetical operators
      when applied to numbers. The syntax of the counting operator:
      </p>
    <list type="bulleted">
      <item>Expression ::= CountOp Expression</item>
      <item>CountOp ::= <c>#</c></item>
    </list>
    <p>All binary operators are left associative; for instance,
      <c>A&nbsp;|&nbsp;B &nbsp;||&nbsp;C</c> is equivalent to
      <c>(A&nbsp;|&nbsp;B)&nbsp;||&nbsp;C</c>. The following is a list
      of all operators, in increasing order of       <marker id="precedence"></marker>
<em>precedence</em>:
      </p>
    <list type="bulleted">
      <item><c>+</c>, <c>-</c></item>
      <item><c>*</c></item>
      <item><c>#</c></item>
      <item><c>|</c>, <c>||</c>, <c>|||</c></item>
      <item><c>of</c></item>
      <item><c>(</c>Type<c>)</c></item>
      <item><c>closure</c>, <c>components</c>, <c>condensation</c>,
      <c>domain</c>, <c>range</c>, <c>strict</c></item>
    </list>
    <p>Parentheses are used for grouping, either to make an expression
      more readable or to override the default precedence of operators:
      </p>
    <list type="bulleted">
      <item>Expression ::= <c>(</c> Expression <c>)</c></item>
    </list>
    <p>A       <marker id="query"></marker>
<em>query</em> is a non-empty sequence of
      statements. A statement is either an assignment of a user
      variable or an expression. The value of an assignment is the
      value of the right hand side expression. It makes no sense to
      put a plain expression anywhere else but last in queries. The
      syntax of queries is summarized by these productions:
      </p>
    <list type="bulleted">
      <item>Query ::= Statement<c>,</c>&nbsp;...</item>
      <item>Statement ::= Assignment | Expression</item>
      <item>Assignment ::= Variable <c>:=</c> Expression 
       | Variable <c>=</c> Expression</item>
    </list>
    <p>A variable cannot be assigned a new value unless first removed.
      Variables assigned to by the <c>=</c> operator are removed at
      the end of the query, while variables assigned to by the
      <c>:=</c> operator can only be removed by calls to
      <c>forget</c>. There are no user variables when module data
      need to be set up again; if any of the functions that make it
      necessary to set up module data again is called, all user
      variables are forgotten.
      </p>
    <p><em>Types</em></p>
    <pre>
application() = atom()
arity() = int() | -1
bool() = true | false
call() = {atom(), atom()} | funcall()
constant() = mfa() | module() | application() | release()
directory() = string()
file() = string()
funcall() = {mfa(), mfa()}
function() = atom()
int() = integer() >= 0
library() = atom()
library_path() = path() | code_path
mfa() = {module(), function(), arity()}
mode() = functions | modules
module() = atom()
release() = atom()
string_position() = int() | at_end
variable() = atom()
xref() = atom() | pid()  </pre>
  </description>
  <funcs>
    <func>
      <name>add_application(Xref, Directory [, Options]) ->  {ok, application()} | Error</name>
      <fsummary>Add the modules of an application.</fsummary>
      <type>
        <v>Directory = directory()</v>
        <v>Error = {error, module(), Reason}</v>
        <v>Options = [Option] | Option</v>
        <v>Option = {builtins, bool()} | {name, application()}  | {verbose, bool()} | {warnings, bool()}</v>
        <v>Reason =  {application_clash, {application(), directory(), directory()}} | {file_error, file(), error()} | {invalid_filename, term()} | {invalid_options, term()} | -&nbsp;see&nbsp;also&nbsp;add_directory&nbsp;-</v>
        <v>Xref = xref()</v>
      </type>
      <desc>
        <p>Adds an application, the modules of the application and <seealso marker="#module_data">module data</seealso> of the
          modules to an <seealso marker="#xref_server">Xref server</seealso>.
          The modules will be members of the application.
          The default is to use the base name of the
          directory with the version removed as application name, but
          this can be overridden by the <c>name</c> option. Returns the
          name of the application.
          </p>
        <p>If the given directory has a subdirectory named
          <c>ebin</c>, modules (BEAM files) are searched for in that
          directory, otherwise modules are searched for in the given
          directory.
          </p>
        <p>If the <seealso marker="#mode">mode</seealso> of the Xref
          server is <c>functions</c>, BEAM files that contain no
          <seealso marker="#debug_info">debug information</seealso> are
          ignored.
          </p>
      </desc>
    </func>
    <func>
      <name>add_directory(Xref, Directory [, Options]) ->  {ok, Modules} | Error</name>
      <fsummary>Add the modules in a directory.</fsummary>
      <type>
        <v>Directory = directory()</v>
        <v>Error = {error, module(), Reason}</v>
        <v>Modules = [module()]</v>
        <v>Options = [Option] | Option</v>
        <v>Option = {builtins, bool()} | {recurse, bool()}  | {verbose, bool()} | {warnings, bool()}</v>
        <v>Reason = {file_error, file(), error()} | {invalid_filename, term()} | {invalid_options, term()} | {unrecognized_file, file()} | -&nbsp;error from beam_lib:chunks/2&nbsp;-</v>
        <v>Xref = xref()</v>
      </type>
      <desc>
        <p>Adds the modules found in the given directory and the <seealso marker="#module_data">modules' data</seealso>
          to an <seealso marker="#xref_server">Xref server</seealso>. 
          The default is not to examine subdirectories, but if the option
          <c>recurse</c> has the value <c>true</c>, modules are searched
          for in subdirectories on all levels as well as in the given 
          directory.
          Returns a sorted list of the names of the added modules.
          </p>
        <p>The modules added will not be members of any applications. 
          </p>
        <p>If the <seealso marker="#mode">mode</seealso> of the Xref
          server is <c>functions</c>, BEAM files that contain no
          <seealso marker="#debug_info">debug information</seealso> are
          ignored.
          </p>
      </desc>
    </func>
    <func>
      <name>add_module(Xref, File [, Options]) -> {ok, module()} | Error</name>
      <fsummary>Add a module.</fsummary>
      <type>
        <v>Error = {error, module(), Reason}</v>
        <v>File = file()</v>
        <v>Options = [Option] | Option</v>
        <v>Option = {builtins, bool()} | {verbose, bool()}  | {warnings, bool()}</v>
        <v>Reason = {file_error, file(), error()} | {invalid_filename, term()} | {invalid_options, term()} | {module_clash, {module(), file(), file()}} | {no_debug_info, file()} | -&nbsp;error from beam_lib:chunks/2&nbsp;-</v>
        <v>Xref = xref()</v>
      </type>
      <desc>
        <p>Adds a module and its <seealso marker="#module_data">module data</seealso> to an <seealso marker="#xref_server">Xref server</seealso>.
          The module will not be member of any application.
          Returns the name of the module.
          </p>
        <p>If the <seealso marker="#mode">mode</seealso> of the Xref
          server is <c>functions</c>, and the BEAM file contains no
          <seealso marker="#debug_info">debug information</seealso>,
          the error message <c>no_debug_info</c> is returned.
          </p>
      </desc>
    </func>
    <func>
      <name>add_release(Xref, Directory [, Options]) ->  {ok, release()} | Error</name>
      <fsummary>Add the modules of a release.</fsummary>
      <type>
        <v>Directory = directory()</v>
        <v>Error = {error, module(), Reason}</v>
        <v>Options = [Option] | Option</v>
        <v>Option = {builtins, bool()} | {name, release()}  | {verbose, bool()} | {warnings, bool()}</v>
        <v>Reason =  {application_clash, {application(), directory(), directory()}} | {file_error, file(), error()} | {invalid_filename, term()} | {invalid_options, term()} | {release_clash, {release(), directory(), directory()}} | -&nbsp;see&nbsp;also&nbsp;add_directory&nbsp;-</v>
        <v>Xref = xref()</v>
      </type>
      <desc>
        <p>Adds a release, the applications of the release, the
          modules of the applications, and <seealso marker="#module_data">module data</seealso> of the
          modules to an <seealso marker="#xref_server">Xref server</seealso>.
          The applications will be members of the release, 
          and the modules will be members of the applications.
          The default is to use the base name of the
          directory as release name, but this can be overridden by the
          <c>name</c> option. Returns the name of the release.
          </p>
        <p>If the given directory has a subdirectory named <c>lib</c>,
          the directories in that directory are assumed to be
          application directories, otherwise all subdirectories of the
          given directory are assumed to be application directories.
          If there are several versions of some application, the one
          with the highest version is chosen.
          </p>
        <p>If the <seealso marker="#mode">mode</seealso> of the Xref
          server is <c>functions</c>, BEAM files that contain no
          <seealso marker="#debug_info">debug information</seealso> are
          ignored.
          </p>
      </desc>
    </func>
    <func>
      <name>analyze(Xref, Analysis [, Options]) ->  {ok, Answer} | Error</name>
      <fsummary>Evaluate a predefined analysis.</fsummary>
      <type>
        <v>Analysis = undefined_function_calls  | undefined_functions | locals_not_used | exports_not_used | deprecated_function_calls | {deprecated_function_calls, DeprFlag} | deprecated_functions | {deprecated_functions, DeprFlag} | {call, FuncSpec} | {use, FuncSpec} | {module_call, ModSpec} | {module_use, ModSpec} | {application_call, AppSpec} | {application_use, AppSpec} | {release_call, RelSpec} | {release_use, RelSpec}</v>
        <v>Answer = [term()]</v>
        <v>AppSpec = application() | [application()]</v>
        <v>DeprFlag = next_version | next_major_release | eventually</v>
        <v>Error = {error, module(), Reason}</v>
        <v>FuncSpec = mfa() | [mfa()]</v>
        <v>ModSpec = module() | [module()]</v>
        <v>Options = [Option] | Option</v>
        <v>Option = {verbose, bool()}</v>
        <v>RelSpec = release() | [release()]</v>
        <v>Reason = {invalid_options, term()} | {parse_error, string_position(), term()} | {unavailable_analysis, term()} | {unknown_analysis, term()} | {unknown_constant, string()} | {unknown_variable, variable()}</v>
        <v>Xref = xref()</v>
      </type>
      <desc>
        <p>          <marker id="analyze"></marker>
Evaluates a predefined analysis.
          Returns a sorted list without duplicates of <c>call()</c> or
          <c>constant()</c>, depending on the chosen analysis. The
          predefined analyses, which operate on all <seealso marker="#analyzed_module">analyzed modules</seealso>, are
          (analyses marked with (*) are available in <c>functions</c><seealso marker="#mode">mode</seealso> only):</p>
        <taglist>
          <tag><c>undefined_function_calls</c>(*)</tag>
          <item>Returns a list of calls to <seealso marker="#undefined_function">undefined functions</seealso>.</item>
          <tag><c>undefined_functions</c></tag>
          <item>Returns a list of <seealso marker="#undefined_function">undefined functions</seealso>. </item>
          <tag><c>locals_not_used</c>(*)</tag>
          <item>Returns a list of local functions that have not been
           locally used.</item>
          <tag><c>exports_not_used</c></tag>
          <item>Returns a list of exported functions that have not been
           externally used.</item>
          <tag><c>deprecated_function_calls</c>(*)</tag>
          <item>Returns a list of external calls to <seealso marker="#deprecated_function">deprecated functions</seealso>.</item>
          <tag><c>{deprecated_function_calls, DeprFlag}</c>(*)</tag>
          <item>Returns a list of external calls to deprecated
           functions. If <c>DeprFlag</c> is equal to
          <c>next_version</c>, calls to functions to be removed in
           next version are returned. If <c>DeprFlag</c> is equal to
          <c>next_major_release</c>, calls to functions to be
           removed in next major release are returned as well as
           calls to functions to be removed in next version. Finally,
           if <c>DeprFlag</c> is equal to <c>eventually</c>, all
           calls to functions to be removed are returned, including
           calls to functions to be removed in next version or next
           major release.</item>
          <tag><c>deprecated_functions</c></tag>
          <item>Returns a list of externally used deprecated
           functions.</item>
          <tag><c>{deprecated_functions, DeprFlag}</c></tag>
          <item>Returns a list of externally used deprecated
           functions. If <c>DeprFlag</c> is equal to
          <c>next_version</c>, functions to be removed in next
           version are returned. If <c>DeprFlag</c> is equal to
          <c>next_major_release</c>, functions to be removed in next
           major release are returned as well as functions to be
           removed in next version. Finally, if <c>DeprFlag</c> is
           equal to <c>eventually</c>, all functions to be removed
           are returned, including functions to be removed in next
           version or next major release.</item>
          <tag><c>{call, FuncSpec}</c>(*)</tag>
          <item>Returns a list of functions called by some of the given 
           functions.</item>
          <tag><c>{use, FuncSpec}</c>(*)</tag>
          <item>Returns a list of functions that use some of the given 
           functions.</item>
          <tag><c>{module_call, ModSpec}</c></tag>
          <item>Returns a list of modules called by some of the given 
           modules.</item>
          <tag><c>{module_use, ModSpec}</c></tag>
          <item>Returns a list of modules that use some of the given 
           modules.</item>
          <tag><c>{application_call, AppSpec}</c></tag>
          <item>Returns a list of applications called by some of the given 
           applications.</item>
          <tag><c>{application_use, AppSpec}</c></tag>
          <item>Returns a list of applications that use some of the given 
           applications.</item>
          <tag><c>{release_call, RelSpec}</c></tag>
          <item>Returns a list of releases called by some of the given 
           releases.</item>
          <tag><c>{release_use, RelSpec}</c></tag>
          <item>Returns a list of releases that use some of the given 
           releases.</item>
        </taglist>
      </desc>
    </func>
    <func>
      <name>d(Directory) -> [DebugInfoResult] | [NoDebugInfoResult] | Error</name>
      <fsummary>Check the modules in a directory using the code path.</fsummary>
      <type>
        <v>Directory = directory()</v>
        <v>DebugInfoResult = {deprecated, [funcall()]} | {undefined, [funcall()]} | {unused, [mfa()]}</v>
        <v>Error = {error, module(), Reason}</v>
        <v>NoDebugInfoResult = {deprecated, [mfa()]} | {undefined, [mfa()]}</v>
        <v>Reason = {file_error, file(), error()} | {invalid_filename, term()} | {unrecognized_file, file()} | -&nbsp;error from beam_lib:chunks/2&nbsp;-</v>
      </type>
      <desc>
        <p>The modules found in the given directory are checked for
          calls to <seealso marker="#deprecated_function">deprecated functions</seealso>, calls to <seealso marker="#undefined_function">undefined functions</seealso>,
          and for unused local functions. The code path is used as
          <seealso marker="#library_path">library path</seealso>.
          </p>
        <p>If some of the found BEAM files contain <seealso marker="#debug_info">debug information</seealso>, then those
          modules are checked and a list of tuples is returned. The
          first element of each tuple is one of:
          </p>
        <list type="bulleted">
          <item><c>deprecated</c>, the second element is a sorted list
           of calls to deprecated functions;</item>
          <item><c>undefined</c>, the second element is a sorted list
           of calls to undefined functions;</item>
          <item><c>unused</c>, the second element is a sorted list of
           unused local functions.</item>
        </list>
        <p>If no BEAM file contains debug information, then a list of
          tuples is returned. The first element of each tuple is one
          of:
          </p>
        <list type="bulleted">
          <item><c>deprecated</c>, the second element is a sorted list
           of externally used deprecated functions;</item>
          <item><c>undefined</c>, the second element is a sorted list
           of undefined functions.</item>
        </list>
      </desc>
    </func>
    <func>
      <name>forget(Xref) -> ok</name>
      <name>forget(Xref, Variables) -> ok | Error</name>
      <fsummary>Remove user variables and their values.</fsummary>
      <type>
        <v>Error = {error, module(), Reason}</v>
        <v>Reason = {not_user_variable, term()}</v>
        <v>Variables = [variable()] | variable()</v>
        <v>Xref = xref()</v>
      </type>
      <desc>
        <p><c>forget/1</c> and <c>forget/2</c> remove all or some of
          the <seealso marker="#user_variable">user variables</seealso> of an <seealso marker="#xref_server">xref server</seealso>.</p>
      </desc>
    </func>
    <func>
      <name>format_error(Error) -> Chars</name>
      <fsummary>Return an English description of an Xref error reply.</fsummary>
      <type>
        <v>Error = {error, module(), term()}</v>
        <v>Chars = [char() | Chars]</v>
      </type>
      <desc>
        <p>Given the error returned by any function of this module, 
          the function <c>format_error</c> returns a descriptive string
          of the error in English. For file errors, the function 
          <c>format_error/1</c> in the <c>file</c> module is called.</p>
      </desc>
    </func>
    <func>
      <name>get_default(Xref) -> [{Option, Value}]</name>
      <name>get_default(Xref, Option) -> {ok, Value} | Error</name>
      <fsummary>Return the default values of options.</fsummary>
      <type>
        <v>Error = {error, module(), Reason}</v>
        <v>Option = builtins | recurse | verbose | warnings</v>
        <v>Reason = {invalid_options, term()}</v>
        <v>Value = bool()</v>
        <v>Xref = xref()</v>
      </type>
      <desc>
        <p>Returns the default values of one or more options.</p>
      </desc>
    </func>
    <func>
      <name>get_library_path(Xref) -> {ok, LibraryPath}</name>
      <fsummary>Return the library path.</fsummary>
      <type>
        <v>LibraryPath = library_path()</v>
        <v>Xref = xref()</v>
      </type>
      <desc>
        <p>Returns the <seealso marker="#library_path">library path</seealso>.</p>
      </desc>
    </func>
    <func>
      <name>info(Xref) -> [Info]</name>
      <name>info(Xref, Category) -> [{Item, [Info]}]</name>
      <name>info(Xref, Category, Items) ->  [{Item, [Info]}]</name>
      <fsummary>Return information about an Xref server.</fsummary>
      <type>
        <v>Application = [] | [application()]</v>
        <v>Category = modules | applications | releases | libraries</v>
        <v>Info = {application, Application} | {builtins, bool()} | {directory, directory()} | {library_path, library_path()} | {mode, mode()} | {no_analyzed_modules, int()} | {no_applications, int()} | {no_calls, {NoResolved, NoUnresolved}} | {no_function_calls, {NoLocal, NoResolvedExternal, NoUnresolved}} | {no_functions, {NoLocal, NoExternal}} | {no_inter_function_calls, int()} | {no_releases, int()} | {release, Release} | {version, Version}</v>
        <v>Item = module() | application() | release() | library()</v>
        <v>Items = Item | [Item]</v>
        <v>NoLocal = NoExternal = NoResolvedExternal, NoResolved = NoUnresolved = int()</v>
        <v>Release = [] | [release()]</v>
        <v>Version = [int()]</v>
        <v>Xref = xref()</v>
      </type>
      <desc>
        <p>The <c>info</c> functions return information as a list of
          pairs {Tag,&nbsp;term()} in some order about the state and the 
          <seealso marker="#module_data">module data</seealso> of an <seealso marker="#xref_server">Xref server</seealso>.
          </p>
        <p><c>info/1</c> returns information with the following tags
          (tags  marked with (*) are available in <c>functions</c>
          mode only):</p>
        <list type="bulleted">
          <item><c>library_path</c>, the <seealso marker="#library_path">library path</seealso>;</item>
          <item><c>mode</c>, the <seealso marker="#mode">mode</seealso>;</item>
          <item><c>no_releases</c>, number of releases;</item>
          <item><c>no_applications</c>, total number of applications
           (of all releases);</item>
          <item><c>no_analyzed_modules</c>, total number of <seealso marker="#analyzed_module">analyzed modules</seealso>;</item>
          <item><c>no_calls</c> (*), total number of calls (in all
           modules), regarding instances of one function call in 
           different lines as separate calls;</item>
          <item><c>no_function_calls</c> (*), total number of <seealso marker="#local_call">local calls</seealso>, resolved <seealso marker="#external_call">external calls</seealso> and 
          <seealso marker="#unresolved_call">unresolved calls</seealso>;</item>
          <item><c>no_functions</c> (*), total number of local and exported
           functions;</item>
          <item><c>no_inter_function_calls</c> (*), total number of
           calls of the <seealso marker="#inter_call_graph">Inter Call Graph</seealso>.</item>
        </list>
        <p><c>info/2</c> and <c>info/3</c> return information about
          all or some of the analyzed modules, applications, releases
          or library modules of an Xref server. 
          The following information is returned for every analyzed module:</p>
        <list type="bulleted">
          <item><c>application</c>, an empty list if the module does 
           not belong to any application, otherwise a list of 
           the application name;</item>
          <item><c>builtins</c>, whether calls to BIFs are included
           in the module's data;</item>
          <item><c>directory</c>, the directory where the
           module's BEAM file is located;</item>
          <item><c>no_calls</c> (*), number of calls, regarding
           instances of one function call in different lines as
           separate calls;</item>
          <item><c>no_function_calls</c> (*), number of local
           calls, resolved external calls and unresolved calls;</item>
          <item><c>no_functions</c> (*), number of local and exported
           functions;</item>
          <item><c>no_inter_function_calls</c> (*), number of calls
           of the Inter Call Graph;</item>
        </list>
        <p>The following information is returned for every application:</p>
        <list type="bulleted">
          <item><c>directory</c>, the directory where the
           modules' BEAM files are located;</item>
          <item><c>no_analyzed_modules</c>, number of analyzed
           modules;</item>
          <item><c>no_calls</c> (*), number of calls of the
           application's modules, regarding instances of
           one function call in different lines as separate calls;</item>
          <item><c>no_function_calls</c> (*), number of local
           calls, resolved external calls and unresolved calls of the
           application's modules;</item>
          <item><c>no_functions</c> (*), number of local and exported
           functions of the application's modules;</item>
          <item><c>no_inter_function_calls</c> (*), number of calls
           of the Inter Call Graph of the
           application's modules;</item>
          <item><c>release</c>, an empty list if the application does not
           belong to any release, otherwise a list of the release name;</item>
          <item><c>version</c>, the application's version as
           a list of numbers. For instance, the directory "kernel-2.6"
           results in the application name <c>kernel</c> and the
           application version [2,6]; "kernel" yields the name
          <c>kernel</c> and the version [].</item>
        </list>
        <p>The following information is returned for every release:</p>
        <list type="bulleted">
          <item><c>directory</c>, the release directory;</item>
          <item><c>no_analyzed_modules</c>, number of analyzed
           modules;</item>
          <item><c>no_applications</c>, number of applications;</item>
          <item><c>no_calls</c> (*), number of calls of the
           release's modules, regarding
           instances of one function call in different lines as
           separate calls;</item>
          <item><c>no_function_calls</c> (*), number of local
           calls, resolved external calls and unresolved
           calls of the release's modules;</item>
          <item><c>no_functions</c> (*), number of local and exported
           functions of the release's modules;</item>
          <item><c>no_inter_function_calls</c> (*), number of calls
           of the Inter Call Graph of the release's modules.</item>
        </list>
        <p>The following information is returned for every library module:</p>
        <list type="bulleted">
          <item><c>directory</c>, the directory where the <seealso marker="#library_module">library module's</seealso> BEAM file is located.</item>
        </list>
        <p>For every number of calls, functions etc. returned by the
          <c>no_</c> tags, there is a query returning the same number.
          Listed below are examples of such queries. Some of the
          queries return the sum of a two or more of the <c>no_</c>
          tags numbers. <c>mod</c> (<c>app</c>, <c>rel</c>) refers to
          any module (application, release).
          </p>
        <list type="bulleted">
          <item>
            <p><c>no_analyzed_modules</c></p>
            <list type="bulleted">
              <item><c>"# AM"</c> (info/1)</item>
              <item><c>"# (Mod) app:App"</c> 
               (application)</item>
              <item><c>"# (Mod) rel:Rel"</c> (release)</item>
            </list>
          </item>
          <item>
            <p><c>no_applications</c></p>
            <list type="bulleted">
              <item><c>"# A"</c> (info/1)</item>
            </list>
          </item>
          <item>
            <p><c>no_calls</c>. The sum of the number of resolved and
              unresolved calls:</p>
            <list type="bulleted">
              <item><c>"# (XLin) E + # (LLin) E"</c> (info/1)</item>
              <item><c>"T = E | mod:Mod, # (LLin) T + # (XLin) T"</c> 
               (module)</item>
              <item><c>"T = E | app:App, # (LLin) T + # (XLin) T"</c> 
               (application)</item>
              <item><c>"T = E | rel:Rel, # (LLin) T + # (XLin) T"</c> 
               (release)</item>
            </list>
          </item>
          <item>
            <p><c>no_functions</c>. Functions in library modules and
              the functions <c>module_info/0,1</c> are not counted by
              <c>info</c>. Assuming that <c>"Extra := _:module_info/\"(0|1)\" + LM"</c> has been evaluated, the
              sum of the number of local and exported functions are:</p>
            <list type="bulleted">
              <item><c>"# (F - Extra)"</c> (info/1)</item>
              <item><c>"# (F * mod:Mod - Extra)"</c> (module)</item>
              <item><c>"# (F * app:App - Extra)"</c> (application)</item>
              <item><c>"# (F * rel:Rel - Extra)"</c> (release)</item>
            </list>
          </item>
          <item>
            <p><c>no_function_calls</c>. The sum of the number of
              local calls, resolved external calls and unresolved calls:</p>
            <list type="bulleted">
              <item><c>"# LC + # XC"</c> (info/1)</item>
              <item><c>"# LC | mod:Mod + # XC | mod:Mod"</c> (module)</item>
              <item><c>"# LC | app:App + # XC | app:App"</c> (application)</item>
              <item><c>"# LC | rel:Rel + # XC | mod:Rel"</c> (release)</item>
            </list>
          </item>
          <item>
            <p><c>no_inter_function_calls</c></p>
            <list type="bulleted">
              <item><c>"# EE"</c> (info/1)</item>
              <item><c>"# EE | mod:Mod"</c> (module)</item>
              <item><c>"# EE | app:App"</c> (application)</item>
              <item><c>"# EE | rel:Rel"</c> (release)</item>
            </list>
          </item>
          <item>
            <p><c>no_releases</c></p>
            <list type="bulleted">
              <item><c>"# R"</c> (info/1)</item>
            </list>
          </item>
        </list>
      </desc>
    </func>
    <func>
      <name>m(Module) -> [DebugInfoResult] | [NoDebugInfoResult] | Error</name>
      <name>m(File) -> [DebugInfoResult] | [NoDebugInfoResult] | Error</name>
      <fsummary>Check a module using the code path.</fsummary>
      <type>
        <v>DebugInfoResult = {deprecated, [funcall()]} | {undefined, [funcall()]} | {unused, [mfa()]}</v>
        <v>Error = {error, module(), Reason}</v>
        <v>File = file()</v>
        <v>Module = module()</v>
        <v>NoDebugInfoResult = {deprecated, [mfa()]} | {undefined, [mfa()]}</v>
        <v>Reason = {file_error, file(), error()} | {interpreted, module()} | {invalid_filename, term()} | {cover_compiled, module()} | {no_such_module, module()}  | -&nbsp;error from beam_lib:chunks/2&nbsp;-</v>
      </type>
      <desc>
        <p>The given BEAM file (with or without the <c>.beam</c>
          extension) or the file found by calling
          <c>code:which(Module)</c> is checked for calls to <seealso marker="#deprecated_function">deprecated functions</seealso>, calls to <seealso marker="#undefined_function">undefined functions</seealso>,
          and for unused local functions. The code path is used as
          <seealso marker="#library_path">library path</seealso>.
          </p>
        <p>If the BEAM file contains <seealso marker="#debug_info">debug information</seealso>, then a
          list of tuples is returned. The first element of each tuple
          is one of:
          </p>
        <list type="bulleted">
          <item><c>deprecated</c>, the second element is a sorted list
           of calls to deprecated functions;</item>
          <item><c>undefined</c>, the second element is a sorted list
           of calls to undefined functions;</item>
          <item><c>unused</c>, the second element is a sorted list of
           unused local functions.</item>
        </list>
        <p>If the BEAM file does not contain debug information, then a
          list of tuples is returned. The first element of each tuple
          is one of:
          </p>
        <list type="bulleted">
          <item><c>deprecated</c>, the second element is a sorted list
           of externally used deprecated functions;</item>
          <item><c>undefined</c>, the second element is a sorted list
           of undefined functions.</item>
        </list>
      </desc>
    </func>
    <func>
      <name>q(Xref, Query [, Options]) -> {ok, Answer} | Error</name>
      <fsummary>Evaluate a query.</fsummary>
      <type>
        <v>Answer = false | [constant()] | [Call] | [Component] | int() | [DefineAt] | [CallAt] | [AllLines]</v>
        <v>Call = call() | ComponentCall</v>
        <v>ComponentCall = {Component, Component}</v>
        <v>Component = [constant()]</v>
        <v>DefineAt = {mfa(), LineNumber}</v>
        <v>CallAt = {funcall(), LineNumbers}</v>
        <v>AllLines = {{DefineAt, DefineAt}, LineNumbers}</v>
        <v>Error = {error, module(), Reason}</v>
        <v>LineNumbers = [LineNumber]</v>
        <v>LineNumber = int()</v>
        <v>Options = [Option] | Option</v>
        <v>Option = {verbose, bool()}</v>
        <v>Query = string() | atom()</v>
        <v>Reason = {invalid_options, term()} | {parse_error, string_position(), term()} | {type_error, string()} | {type_mismatch, string(), string()} | {unknown_analysis, term()} | {unknown_constant, string()} | {unknown_variable, variable()} | {variable_reassigned, string()}</v>
        <v>Xref = xref()</v>
      </type>
      <desc>
        <p>Evaluates a <seealso marker="#query">query</seealso> in the
          context of an <seealso marker="#xref_server">Xref server</seealso>, and returns the value of the last
          statement. The syntax of the value depends on the
          expression:
          </p>
        <list type="bulleted">
          <item>A set of calls is represented by a sorted list without
           duplicates of <c>call()</c>.</item>
          <item>A set of constants is represented by a sorted list
           without duplicates of <c>constant()</c>.</item>
          <item>A set of strongly connected components is a sorted list
           without duplicates of <c>Component</c>.</item>
          <item>A set of calls between strongly connected components is
           a sorted list without duplicates of <c>ComponentCall</c>.</item>
          <item>A chain of calls is represented by a list of
          <c>constant()</c>. The list contains the From vertex of every
           call and the To vertex of the last call.</item>
          <item>The <c>of</c> operator returns <c>false</c> if no chain
           of calls between the given constants can be found.</item>
          <item>The value of the <c>closure</c> operator (the
          <c>digraph</c> representation) is represented by the atom
          <c>'closure()'</c>.</item>
          <item>A set of line numbered functions is represented by a sorted
           list without duplicates of <c>DefineAt</c>.</item>
          <item>A set of line numbered function calls is represented by
           a sorted list without duplicates of <c>CallAt</c>.</item>
          <item>A set of line numbered functions and function calls is
           represented by a sorted list without duplicates of
          <c>AllLines</c>.</item>
        </list>
        <p>For both <c>CallAt</c> and <c>AllLines</c> it holds that for
          no list element is <c>LineNumbers</c> an empty list; such
          elements have been removed. The constants of <c>component</c>
          and the integers of <c>LineNumbers</c> are sorted and without
          duplicates.
          </p>
      </desc>
    </func>
    <func>
      <name>remove_application(Xref, Applications) -> ok | Error</name>
      <fsummary>Remove applications and their modules.</fsummary>
      <type>
        <v>Applications = application() | [application()]</v>
        <v>Error = {error, module(), Reason}</v>
        <v>Reason = {no_such_application, application()}</v>
        <v>Xref = xref()</v>
      </type>
      <desc>
        <p>Removes applications and their modules and <seealso marker="#module_data">module data</seealso> from an <seealso marker="#xref_server">Xref server</seealso>.</p>
      </desc>
    </func>
    <func>
      <name>remove_module(Xref, Modules) -> ok | Error</name>
      <fsummary>Remove analyzed modules.</fsummary>
      <type>
        <v>Error = {error, module(), Reason}</v>
        <v>Modules = module() | [module()]</v>
        <v>Reason = {no_such_module, module()}</v>
        <v>Xref = xref()</v>
      </type>
      <desc>
        <p>Removes <seealso marker="#analyzed_module">analyzed modules</seealso> and <seealso marker="#module_data">module data</seealso> from an <seealso marker="#xref_server">Xref server</seealso>.</p>
      </desc>
    </func>
    <func>
      <name>remove_release(Xref, Releases) -> ok | Error</name>
      <fsummary>Remove releases and their applications and modules.</fsummary>
      <type>
        <v>Error = {error, module(), Reason}</v>
        <v>Reason = {no_such_release, release()}</v>
        <v>Releases = release() | [release()]</v>
        <v>Xref = xref()</v>
      </type>
      <desc>
        <p>Removes releases and their applications, modules and
          <seealso marker="#module_data">module data</seealso> from an
          <seealso marker="#xref_server">Xref server</seealso>.</p>
      </desc>
    </func>
    <func>
      <name>replace_application(Xref, Application,  Directory [, Options]) -> {ok, application()} | Error</name>
      <fsummary>Replace an application's modules.</fsummary>
      <type>
        <v>Application = application()</v>
        <v>Directory = directory()</v>
        <v>Error = {error, module(), Reason}</v>
        <v>Options = [Option] | Option</v>
        <v>Option = {builtins, bool()} | {verbose, bool()}  | {warnings, bool()}</v>
        <v>Reason = {no_such_application, application()} | -&nbsp;see&nbsp;also&nbsp;add_application&nbsp;-</v>
        <v>Xref = xref()</v>
      </type>
      <desc>
        <p>Replaces the modules of an application with other modules
          read from an application directory. Release membership of the
          application is retained. Note that the name of the
          application is kept; the name of the given directory is not
          used.
          </p>
      </desc>
    </func>
    <func>
      <name>replace_module(Xref, Module, File [, Options]) ->  {ok, module()} | Error</name>
      <fsummary>Replace an analyzed module.</fsummary>
      <type>
        <v>Error = {error, module(), Reason}</v>
        <v>File = file()</v>
        <v>Module = module()</v>
        <v>Options = [Option] | Option</v>
        <v>Option = {verbose, bool()} | {warnings, bool()}</v>
        <v>ReadModule = module()</v>
        <v>Reason = {module_mismatch, module(), ReadModule} | {no_such_module, module()}  | -&nbsp;see&nbsp;also&nbsp;add_module&nbsp;-</v>
        <v>Xref = xref()</v>
      </type>
      <desc>
        <p>Replaces <seealso marker="#module_data">module data</seealso> of an <seealso marker="#analyzed_module">analyzed module</seealso> with
          data read from a BEAM file. Application membership of the
          module is retained, and so is the value of the
          <c>builtins</c> option of the module. An error is returned
          if the name of the read module differs from the given
          module.
          </p>
        <p>The <c>update</c> function is an alternative for updating
          module data of recompiled modules.</p>
      </desc>
    </func>
    <func>
      <name>set_default(Xref, Option, Value) -> {ok, OldValue} | Error</name>
      <name>set_default(Xref, OptionValues) -> ok | Error</name>
      <fsummary>Set the default values of options.</fsummary>
      <type>
        <v>Error = {error, module(), Reason}</v>
        <v>OptionValues = [OptionValue] | OptionValue</v>
        <v>OptionValue = {Option, Value}</v>
        <v>Option = builtins | recurse | verbose | warnings</v>
        <v>Reason = {invalid_options, term()}</v>
        <v>Value = bool()</v>
        <v>Xref = xref()</v>
      </type>
      <desc>
        <p>Sets the default value of one or more options. 
          The options that can be set this way are:</p>
        <list type="bulleted">
          <item><c>builtins</c>, with initial default value <c>false</c>;</item>
          <item><c>recurse</c>, with initial default value <c>false</c>;</item>
          <item><c>verbose</c>, with initial default value <c>false</c>;</item>
          <item><c>warnings</c>, with initial default value <c>true</c>.</item>
        </list>
        <p>The initial default values are set when creating an <seealso marker="#xref_server">Xref server</seealso>. 
          </p>
      </desc>
    </func>
    <func>
      <name>set_library_path(Xref, LibraryPath [, Options]) ->  ok | Error</name>
      <fsummary>Set the library path and finds the library modules.</fsummary>
      <type>
        <v>Error = {error, module(), Reason}</v>
        <v>LibraryPath = library_path()</v>
        <v>Options = [Option] | Option</v>
        <v>Option = {verbose, bool()}</v>
        <v>Reason = {invalid_options, term()} | {invalid_path, term()}</v>
        <v>Xref = xref()</v>
      </type>
      <desc>
        <p>Sets the <seealso marker="#library_path">library path</seealso>. If the given path is a list of
          directories, the set of <seealso marker="#library_module">library modules</seealso> is
          determined by choosing the first module
          encountered while traversing the directories in
          the given order, for those modules that occur in more than
          one directory. By default, the library path is an empty list.
          </p>
        <p>The library path           <marker id="code_path"></marker>
<c>code_path</c> is
          used by the functions
          <c>m/1</c> and <c>d/1</c>, but can also be set explicitly.
          Note however that the code path will be traversed once for
          each used <seealso marker="#library_module">library module</seealso> while setting up module data.
          On the other hand, if there are only a few modules that are
          used but not analyzed, using <c>code_path</c> may be faster
          than setting the library path to <c>code:get_path()</c>.
          </p>
        <p>If the library path is set to <c>code_path</c>, the set of
          library modules is not determined, and the <c>info</c>
          functions will return empty lists of library modules.</p>
      </desc>
    </func>
    <func>
      <name>start(NameOrOptions) -> Return</name>
      <fsummary>Create an Xref server.</fsummary>
      <type>
        <v>NameOrOptions = Name | Options</v>
        <v>Name = atom()</v>
        <v>Options = [Option] | Option</v>
        <v>Option = {xref_mode, mode()} | term()</v>
        <v>Return = {ok, pid()}  | {error, {already_started, pid()}}</v>
      </type>
      <desc>
        <p>Creates an <seealso marker="#xref_server">Xref server</seealso>.
          The process may optionally be given a name.
          The default <seealso marker="#mode">mode</seealso> is <c>functions</c>.
          Options that are not recognized by Xref
          are passed on to <c>gen_server:start/4</c>.</p>
      </desc>
    </func>
    <func>
      <name>start(Name, Options) -> Return</name>
      <fsummary>Create an Xref server.</fsummary>
      <type>
        <v>Name = atom()</v>
        <v>Options = [Option] | Option</v>
        <v>Option = {xref_mode, mode()} | term()</v>
        <v>Return = {ok, pid()}  | {error, {already_started, pid()}}</v>
      </type>
      <desc>
        <p>Creates an <seealso marker="#xref_server">Xref server</seealso>
          with a given name. 
          The default <seealso marker="#mode">mode</seealso> is <c>functions</c>.
          Options that are not recognized by Xref
          are passed on to <c>gen_server:start/4</c>.</p>
      </desc>
    </func>
    <func>
      <name>stop(Xref)</name>
      <fsummary>Delete an Xref server.</fsummary>
      <type>
        <v>Xref = xref()</v>
      </type>
      <desc>
        <p>Stops an <seealso marker="#xref_server">Xref server</seealso>.</p>
      </desc>
    </func>
    <func>
      <name>update(Xref [, Options]) -> {ok, Modules} | Error</name>
      <fsummary>Replace newly compiled analyzed modules.</fsummary>
      <type>
        <v>Error = {error, module(), Reason}</v>
        <v>Modules = [module()]</v>
        <v>Options = [Option] | Option</v>
        <v>Option = {verbose, bool()} | {warnings, bool()}</v>
        <v>Reason = {invalid_options, term()} | {module_mismatch, module(), ReadModule} | -&nbsp;see&nbsp;also&nbsp;add_module&nbsp;-</v>
        <v>Xref = xref()</v>
      </type>
      <desc>
        <p>Replaces the <seealso marker="#module_data">module data</seealso> of all <seealso marker="#analyzed_module">analyzed modules</seealso> the BEAM
          files of which have been modified since last read by an
          <c>add</c> function or <c>update</c>. Application membership
          of the modules is retained, and so is the value of the
          <c>builtins</c> option. Returns a sorted list
          of the names of the replaced modules.</p>
      </desc>
    </func>
    <func>
      <name>variables(Xref [, Options]) -> {ok, [VariableInfo]}</name>
      <fsummary>Return the names of variables.</fsummary>
      <type>
        <v>Options = [Option] | Option</v>
        <v>Option = predefined | user | {verbose, bool()}</v>
        <v>Reason = {invalid_options, term()}</v>
        <v>VariableInfo = {predefined, [variable()]} | {user, [variable()]}</v>
        <v>Xref = xref()</v>
      </type>
      <desc>
        <p>Returns a sorted lists of the names of the variables of an
          <seealso marker="#xref_server">Xref server</seealso>. 
          The default is to return the <seealso marker="#user_variable">user variables</seealso> only.</p>
      </desc>
    </func>
  </funcs>

  <section>
    <title>See Also</title><p>
      <seealso marker="stdlib:beam_lib">beam_lib(3)</seealso>,
      <seealso marker="stdlib:digraph">digraph(3)</seealso>,
      <seealso marker="stdlib:digraph_utils">digraph_utils(3)</seealso>,
      <seealso marker="stdlib:re">re(3)</seealso>,
      <seealso marker="xref_chapter">TOOLS User's Guide</seealso></p>
  </section>
</erlref>