aboutsummaryrefslogtreecommitdiff
path: root/guix/gexp.scm
blob: dd5eb81bd329bfe763dad83e654ba122b1304027 (plain)
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
;;; GNU Guix --- Functional package management for GNU
;;; Copyright © 2014, 2015, 2016, 2017, 2018 Ludovic Courtès <ludo@gnu.org>
;;; Copyright © 2018 Clément Lassieur <clement@lassieur.org>
;;;
;;; This file is part of GNU Guix.
;;;
;;; GNU Guix is free software; you can redistribute it and/or modify it
;;; under the terms of the GNU General Public License as published by
;;; the Free Software Foundation; either version 3 of the License, or (at
;;; your option) any later version.
;;;
;;; GNU Guix is distributed in the hope that it will be useful, but
;;; WITHOUT ANY WARRANTY; without even the implied warranty of
;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
;;; GNU General Public License for more details.
;;;
;;; You should have received a copy of the GNU General Public License
;;; along with GNU Guix.  If not, see <http://www.gnu.org/licenses/>.

(define-module (guix gexp)
  #:use-module (guix store)
  #:use-module (guix monads)
  #:use-module (guix derivations)
  #:use-module (guix grafts)
  #:use-module (guix utils)
  #:use-module (srfi srfi-1)
  #:use-module (srfi srfi-9)
  #:use-module (srfi srfi-9 gnu)
  #:use-module (srfi srfi-26)
  #:use-module (srfi srfi-34)
  #:use-module (srfi srfi-35)
  #:use-module (ice-9 match)
  #:export (gexp
            gexp?
            with-imported-modules

            gexp-input
            gexp-input?

            local-file
            local-file?
            local-file-file
            local-file-absolute-file-name
            local-file-name
            local-file-recursive?

            plain-file
            plain-file?
            plain-file-name
            plain-file-content

            computed-file
            computed-file?
            computed-file-name
            computed-file-gexp
            computed-file-options

            program-file
            program-file?
            program-file-name
            program-file-gexp
            program-file-guile
            program-file-module-path

            scheme-file
            scheme-file?
            scheme-file-name
            scheme-file-gexp

            file-append
            file-append?
            file-append-base
            file-append-suffix

            load-path-expression
            gexp-modules

            gexp->derivation
            gexp->file
            gexp->script
            text-file*
            mixed-text-file
            file-union
            directory-union
            imported-files
            imported-modules
            compiled-modules

            define-gexp-compiler
            gexp-compiler?
            file-like?
            lower-object

            lower-inputs

            &gexp-error
            gexp-error?
            &gexp-input-error
            gexp-input-error?
            gexp-error-invalid-input))

;;; Commentary:
;;;
;;; This module implements "G-expressions", or "gexps".  Gexps are like
;;; S-expressions (sexps), with two differences:
;;;
;;;   1. References (un-quotations) to derivations or packages in a gexp are
;;;      replaced by the corresponding output file name; in addition, the
;;;      'ungexp-native' unquote-like form allows code to explicitly refer to
;;;      the native code of a given package, in case of cross-compilation;
;;;
;;;   2. Gexps embed information about the derivations they refer to.
;;;
;;; Gexps make it easy to write to files Scheme code that refers to store
;;; items, or to write Scheme code to build derivations.
;;;
;;; Code:

;; "G expressions".
(define-record-type <gexp>
  (make-gexp references modules proc)
  gexp?
  (references gexp-references)                    ;list of <gexp-input>
  (modules    gexp-self-modules)                  ;list of module names
  (proc       gexp-proc))                         ;procedure

(define (write-gexp gexp port)
  "Write GEXP on PORT."
  (display "#<gexp " port)

  ;; Try to write the underlying sexp.  Now, this trick doesn't work when
  ;; doing things like (ungexp-splicing (gexp ())) because GEXP's procedure
  ;; tries to use 'append' on that, which fails with wrong-type-arg.
  (false-if-exception
   (write (apply (gexp-proc gexp)
                 (gexp-references gexp))
          port))
  (format port " ~a>"
          (number->string (object-address gexp) 16)))

(set-record-type-printer! <gexp> write-gexp)


;;;
;;; Methods.
;;;

;; Compiler for a type of objects that may be introduced in a gexp.
(define-record-type <gexp-compiler>
  (gexp-compiler type lower expand)
  gexp-compiler?
  (type       gexp-compiler-type)                 ;record type descriptor
  (lower      gexp-compiler-lower)
  (expand     gexp-compiler-expand))              ;#f | DRV -> sexp

(define-condition-type &gexp-error &error
  gexp-error?)

(define-condition-type &gexp-input-error &gexp-error
  gexp-input-error?
  (input gexp-error-invalid-input))


(define %gexp-compilers
  ;; 'eq?' mapping of record type descriptor to <gexp-compiler>.
  (make-hash-table 20))

(define (default-expander thing obj output)
  "This is the default expander for \"things\" that appear in gexps.  It
returns its output file name of OBJ's OUTPUT."
  (match obj
    ((? derivation? drv)
     (derivation->output-path drv output))
    ((? string? file)
     file)))

(define (register-compiler! compiler)
  "Register COMPILER as a gexp compiler."
  (hashq-set! %gexp-compilers
              (gexp-compiler-type compiler) compiler))

(define (lookup-compiler object)
  "Search for a compiler for OBJECT.  Upon success, return the three argument
procedure to lower it; otherwise return #f."
  (and=> (hashq-ref %gexp-compilers (struct-vtable object))
         gexp-compiler-lower))

(define (file-like? object)
  "Return #t if OBJECT leads to a file in the store once unquoted in a
G-expression; otherwise return #f."
  (and (struct? object) (->bool (lookup-compiler object))))

(define (lookup-expander object)
  "Search for an expander for OBJECT.  Upon success, return the three argument
procedure to expand it; otherwise return #f."
  (and=> (hashq-ref %gexp-compilers (struct-vtable object))
         gexp-compiler-expand))

(define* (lower-object obj
                       #:optional (system (%current-system))
                       #:key target)
  "Return as a value in %STORE-MONAD the derivation or store item
corresponding to OBJ for SYSTEM, cross-compiling for TARGET if TARGET is true.
OBJ must be an object that has an associated gexp compiler, such as a
<package>."
  (match (lookup-compiler obj)
    (#f
     (raise (condition (&gexp-input-error (input obj)))))
    (lower
     (lower obj system target))))

(define-syntax define-gexp-compiler
  (syntax-rules (=> compiler expander)
    "Define NAME as a compiler for objects matching PREDICATE encountered in
gexps.

In the simplest form of the macro, BODY must return a derivation for PARAM, an
object that matches PREDICATE, for SYSTEM and TARGET (the latter of which is
#f except when cross-compiling.)

The more elaborate form allows you to specify an expander:

  (define-gexp-compiler something something?
    compiler => (lambda (param system target) ...)
    expander => (lambda (param drv output) ...))

The expander specifies how an object is converted to its sexp representation."
    ((_ (name (param record-type) system target) body ...)
     (define-gexp-compiler name record-type
       compiler => (lambda (param system target) body ...)
       expander => default-expander))
    ((_ name record-type
        compiler => compile
        expander => expand)
     (begin
       (define name
         (gexp-compiler record-type compile expand))
       (register-compiler! name)))))

(define-gexp-compiler (derivation-compiler (drv <derivation>) system target)
  ;; Derivations are the lowest-level representation, so this is the identity
  ;; compiler.
  (with-monad %store-monad
    (return drv)))


;;;
;;; File declarations.
;;;

;; A local file name.  FILE is the file name the user entered, which can be a
;; relative file name, and ABSOLUTE is a promise that computes its canonical
;; absolute file name.  We keep it in a promise to compute it lazily and avoid
;; repeated 'stat' calls.
(define-record-type <local-file>
  (%%local-file file absolute name recursive? select?)
  local-file?
  (file       local-file-file)                    ;string
  (absolute   %local-file-absolute-file-name)     ;promise string
  (name       local-file-name)                    ;string
  (recursive? local-file-recursive?)              ;Boolean
  (select?    local-file-select?))                ;string stat -> Boolean

(define (true file stat) #t)

(define* (%local-file file promise #:optional (name (basename file))
                      #:key recursive? (select? true))
  ;; This intermediate procedure is part of our ABI, but the underlying
  ;; %%LOCAL-FILE is not.
  (%%local-file file promise name recursive? select?))

(define (absolute-file-name file directory)
  "Return the canonical absolute file name for FILE, which lives in the
vicinity of DIRECTORY."
  (canonicalize-path
   (cond ((string-prefix? "/" file) file)
         ((not directory) file)
         ((string-prefix? "/" directory)
          (string-append directory "/" file))
         (else file))))

(define-syntax local-file
  (lambda (s)
    "Return an object representing local file FILE to add to the store; this
object can be used in a gexp.  If FILE is a relative file name, it is looked
up relative to the source file where this form appears.  FILE will be added to
the store under NAME--by default the base name of FILE.

When RECURSIVE? is true, the contents of FILE are added recursively; if FILE
designates a flat file and RECURSIVE? is true, its contents are added, and its
permission bits are kept.

When RECURSIVE? is true, call (SELECT?  FILE STAT) for each directory entry,
where FILE is the entry's absolute file name and STAT is the result of
'lstat'; exclude entries for which SELECT? does not return true.

This is the declarative counterpart of the 'interned-file' monadic procedure.
It is implemented as a macro to capture the current source directory where it
appears."
    (syntax-case s ()
      ((_ file rest ...)
       #'(%local-file file
                      (delay (absolute-file-name file (current-source-directory)))
                      rest ...))
      ((_)
       #'(syntax-error "missing file name"))
      (id
       (identifier? #'id)
       ;; XXX: We could return #'(lambda (file . rest) ...).  However,
       ;; (syntax-source #'id) is #f so (current-source-directory) would not
       ;; work.  Thus, simply forbid this form.
       #'(syntax-error
          "'local-file' is a macro and cannot be used like this")))))

(define (local-file-absolute-file-name file)
  "Return the absolute file name for FILE, a <local-file> instance.  A
'system-error' exception is raised if FILE could not be found."
  (force (%local-file-absolute-file-name file)))

(define-gexp-compiler (local-file-compiler (file <local-file>) system target)
  ;; "Compile" FILE by adding it to the store.
  (match file
    (($ <local-file> file (= force absolute) name recursive? select?)
     ;; Canonicalize FILE so that if it's a symlink, it is resolved.  Failing
     ;; to do that, when RECURSIVE? is #t, we could end up creating a dangling
     ;; symlink in the store, and when RECURSIVE? is #f 'add-to-store' would
     ;; just throw an error, both of which are inconvenient.
     (interned-file absolute name
                    #:recursive? recursive? #:select? select?))))

(define-record-type <plain-file>
  (%plain-file name content references)
  plain-file?
  (name        plain-file-name)                   ;string
  (content     plain-file-content)                ;string
  (references  plain-file-references))            ;list (currently unused)

(define (plain-file name content)
  "Return an object representing a text file called NAME with the given
CONTENT (a string) to be added to the store.

This is the declarative counterpart of 'text-file'."
  ;; XXX: For now just ignore 'references' because it's not clear how to use
  ;; them in a declarative context.
  (%plain-file name content '()))

(define-gexp-compiler (plain-file-compiler (file <plain-file>) system target)
  ;; "Compile" FILE by adding it to the store.
  (match file
    (($ <plain-file> name content references)
     (text-file name content references))))

(define-record-type <computed-file>
  (%computed-file name gexp guile options)
  computed-file?
  (name       computed-file-name)                 ;string
  (gexp       computed-file-gexp)                 ;gexp
  (guile      computed-file-guile)                ;<package>
  (options    computed-file-options))             ;list of arguments

(define* (computed-file name gexp
                        #:key guile (options '(#:local-build? #t)))
  "Return an object representing the store item NAME, a file or directory
computed by GEXP.  OPTIONS is a list of additional arguments to pass
to 'gexp->derivation'.

This is the declarative counterpart of 'gexp->derivation'."
  (%computed-file name gexp guile options))

(define-gexp-compiler (computed-file-compiler (file <computed-file>)
                                              system target)
  ;; Compile FILE by returning a derivation whose build expression is its
  ;; gexp.
  (match file
    (($ <computed-file> name gexp guile options)
     (if guile
         (mlet %store-monad ((guile (lower-object guile system
                                                  #:target target)))
           (apply gexp->derivation name gexp #:guile-for-build guile
                  options))
         (apply gexp->derivation name gexp options)))))

(define-record-type <program-file>
  (%program-file name gexp guile path)
  program-file?
  (name       program-file-name)                  ;string
  (gexp       program-file-gexp)                  ;gexp
  (guile      program-file-guile)                 ;package
  (path       program-file-module-path))          ;list of strings

(define* (program-file name gexp #:key (guile #f) (module-path %load-path))
  "Return an object representing the executable store item NAME that runs
GEXP.  GUILE is the Guile package used to execute that script.  Imported
modules of GEXP are looked up in MODULE-PATH.

This is the declarative counterpart of 'gexp->script'."
  (%program-file name gexp guile module-path))

(define-gexp-compiler (program-file-compiler (file <program-file>)
                                             system target)
  ;; Compile FILE by returning a derivation that builds the script.
  (match file
    (($ <program-file> name gexp guile module-path)
     (gexp->script name gexp
                   #:module-path module-path
                   #:guile (or guile (default-guile))))))

(define-record-type <scheme-file>
  (%scheme-file name gexp splice?)
  scheme-file?
  (name       scheme-file-name)                  ;string
  (gexp       scheme-file-gexp)                  ;gexp
  (splice?    scheme-file-splice?))              ;Boolean

(define* (scheme-file name gexp #:key splice?)
  "Return an object representing the Scheme file NAME that contains GEXP.

This is the declarative counterpart of 'gexp->file'."
  (%scheme-file name gexp splice?))

(define-gexp-compiler (scheme-file-compiler (file <scheme-file>)
                                            system target)
  ;; Compile FILE by returning a derivation that builds the file.
  (match file
    (($ <scheme-file> name gexp splice?)
     (gexp->file name gexp #:splice? splice?))))

;; Appending SUFFIX to BASE's output file name.
(define-record-type <file-append>
  (%file-append base suffix)
  file-append?
  (base   file-append-base)                    ;<package> | <derivation> | ...
  (suffix file-append-suffix))                 ;list of strings

(define (file-append base . suffix)
  "Return a <file-append> object that expands to the concatenation of BASE and
SUFFIX."
  (%file-append base suffix))

(define-gexp-compiler file-append-compiler <file-append>
  compiler => (lambda (obj system target)
                (match obj
                  (($ <file-append> base _)
                   (lower-object base system #:target target))))
  expander => (lambda (obj lowered output)
                (match obj
                  (($ <file-append> base suffix)
                   (let* ((expand (lookup-expander base))
                          (base   (expand base lowered output)))
                     (string-append base (string-concatenate suffix)))))))


;;;
;;; Inputs & outputs.
;;;

;; The input of a gexp.
(define-record-type <gexp-input>
  (%gexp-input thing output native?)
  gexp-input?
  (thing     gexp-input-thing)       ;<package> | <origin> | <derivation> | ...
  (output    gexp-input-output)      ;string
  (native?   gexp-input-native?))    ;Boolean

(define (write-gexp-input input port)
  (match input
    (($ <gexp-input> thing output #f)
     (format port "#<gexp-input ~s:~a>" thing output))
    (($ <gexp-input> thing output #t)
     (format port "#<gexp-input native ~s:~a>" thing output))))

(set-record-type-printer! <gexp-input> write-gexp-input)

(define* (gexp-input thing                        ;convenience procedure
                     #:optional (output "out")
                     #:key native?)
  "Return a new <gexp-input> for the OUTPUT of THING; NATIVE? determines
whether this should be considered a \"native\" input or not."
  (%gexp-input thing output native?))

;; Reference to one of the derivation's outputs, for gexps used in
;; derivations.
(define-record-type <gexp-output>
  (gexp-output name)
  gexp-output?
  (name gexp-output-name))

(define (write-gexp-output output port)
  (match output
    (($ <gexp-output> name)
     (format port "#<gexp-output ~a>" name))))

(set-record-type-printer! <gexp-output> write-gexp-output)

(define (gexp-modules gexp)
  "Return the list of Guile module names GEXP relies on.  If (gexp? GEXP) is
false, meaning that GEXP is a plain Scheme object, return the empty list."
  (if (gexp? gexp)
      (delete-duplicates
       (append (gexp-self-modules gexp)
               (append-map (match-lambda
                             (($ <gexp-input> (? gexp? exp))
                              (gexp-modules exp))
                             (($ <gexp-input> (lst ...))
                              (append-map (lambda (item)
                                            (if (gexp? item)
                                                (gexp-modules item)
                                                '()))
                                          lst))
                             (_
                              '()))
                           (gexp-references gexp))))
      '()))                                       ;plain Scheme data type

(define* (lower-inputs inputs
                       #:key system target)
  "Turn any package from INPUTS into a derivation for SYSTEM; return the
corresponding input list as a monadic value.  When TARGET is true, use it as
the cross-compilation target triplet."
  (with-monad %store-monad
    (sequence %store-monad
              (map (match-lambda
                     (((? struct? thing) sub-drv ...)
                      (mlet %store-monad ((drv (lower-object
                                                thing system #:target target)))
                        (return `(,drv ,@sub-drv))))
                     (input
                      (return input)))
                   inputs))))

(define* (lower-reference-graphs graphs #:key system target)
  "Given GRAPHS, a list of (FILE-NAME INPUT ...) lists for use as a
#:reference-graphs argument, lower it such that each INPUT is replaced by the
corresponding derivation."
  (match graphs
    (((file-names . inputs) ...)
     (mlet %store-monad ((inputs (lower-inputs inputs
                                               #:system system
                                               #:target target)))
       (return (map cons file-names inputs))))))

(define* (lower-references lst #:key system target)
  "Based on LST, a list of output names and packages, return a list of output
names and file names suitable for the #:allowed-references argument to
'derivation'."
  (with-monad %store-monad
    (define lower
      (match-lambda
       ((? string? output)
        (return output))
       (($ <gexp-input> thing output native?)
        (mlet %store-monad ((drv (lower-object thing system
                                               #:target (if native?
                                                            #f target))))
          (return (derivation->output-path drv output))))
       (thing
        (mlet %store-monad ((drv (lower-object thing system
                                               #:target target)))
          (return (derivation->output-path drv))))))

    (sequence %store-monad (map lower lst))))

(define default-guile-derivation
  ;; Here we break the abstraction by talking to the higher-level layer.
  ;; Thus, do the resolution lazily to hide the circular dependency.
  (let ((proc (delay
                (let ((iface (resolve-interface '(guix packages))))
                  (module-ref iface 'default-guile-derivation)))))
    (lambda (system)
      ((force proc) system))))

(define* (gexp->derivation name exp
                           #:key
                           system (target 'current)
                           hash hash-algo recursive?
                           (env-vars '())
                           (modules '())
                           (module-path %load-path)
                           (guile-for-build (%guile-for-build))
                           (graft? (%graft?))
                           references-graphs
                           allowed-references disallowed-references
                           leaked-env-vars
                           local-build? (substitutable? #t)
                           deprecation-warnings
                           (script-name (string-append name "-builder")))
  "Return a derivation NAME that runs EXP (a gexp) with GUILE-FOR-BUILD (a
derivation) on SYSTEM; EXP is stored in a file called SCRIPT-NAME.  When
TARGET is true, it is used as the cross-compilation target triplet for
packages referred to by EXP.

MODULES is deprecated in favor of 'with-imported-modules'.  Its meaning is to
make MODULES available in the evaluation context of EXP; MODULES is a list of
names of Guile modules searched in MODULE-PATH to be copied in the store,
compiled, and made available in the load path during the execution of
EXP---e.g., '((guix build utils) (guix build gnu-build-system)).

GRAFT? determines whether packages referred to by EXP should be grafted when
applicable.

When REFERENCES-GRAPHS is true, it must be a list of tuples of one of the
following forms:

  (FILE-NAME PACKAGE)
  (FILE-NAME PACKAGE OUTPUT)
  (FILE-NAME DERIVATION)
  (FILE-NAME DERIVATION OUTPUT)
  (FILE-NAME STORE-ITEM)

The right-hand-side of each element of REFERENCES-GRAPHS is automatically made
an input of the build process of EXP.  In the build environment, each
FILE-NAME contains the reference graph of the corresponding item, in a simple
text format.

ALLOWED-REFERENCES must be either #f or a list of output names and packages.
In the latter case, the list denotes store items that the result is allowed to
refer to.  Any reference to another store item will lead to a build error.
Similarly for DISALLOWED-REFERENCES, which can list items that must not be
referenced by the outputs.

DEPRECATION-WARNINGS determines whether to show deprecation warnings while
compiling modules.  It can be #f, #t, or 'detailed.

The other arguments are as for 'derivation'."
  (define %modules
    (delete-duplicates
     (append modules (gexp-modules exp))))
  (define outputs (gexp-outputs exp))

  (define (graphs-file-names graphs)
    ;; Return a list of (FILE-NAME . STORE-PATH) pairs made from GRAPHS.
    (map (match-lambda
          ;; TODO: Remove 'derivation?' special cases.
           ((file-name (? derivation? drv))
            (cons file-name (derivation->output-path drv)))
           ((file-name (? derivation? drv) sub-drv)
            (cons file-name (derivation->output-path drv sub-drv)))
           ((file-name thing)
            (cons file-name thing)))
         graphs))

  (mlet* %store-monad (;; The following binding forces '%current-system' and
                       ;; '%current-target-system' to be looked up at >>=
                       ;; time.
                       (graft?    (set-grafting graft?))

                       (system -> (or system (%current-system)))
                       (target -> (if (eq? target 'current)
                                      (%current-target-system)
                                      target))
                       (normals  (lower-inputs (gexp-inputs exp)
                                               #:system system
                                               #:target target))
                       (natives  (lower-inputs (gexp-native-inputs exp)
                                               #:system system
                                               #:target #f))
                       (inputs -> (append normals natives))
                       (sexp     (gexp->sexp exp
                                             #:system system
                                             #:target target))
                       (builder  (text-file script-name
                                            (object->string sexp)))
                       (modules  (if (pair? %modules)
                                     (imported-modules %modules
                                                       #:system system
                                                       #:module-path module-path
                                                       #:guile guile-for-build
                                                       #:deprecation-warnings
                                                       deprecation-warnings)
                                     (return #f)))
                       (compiled (if (pair? %modules)
                                     (compiled-modules %modules
                                                       #:system system
                                                       #:module-path module-path
                                                       #:guile guile-for-build
                                                       #:deprecation-warnings
                                                       deprecation-warnings)
                                     (return #f)))
                       (graphs   (if references-graphs
                                     (lower-reference-graphs references-graphs
                                                             #:system system
                                                             #:target target)
                                     (return #f)))
                       (allowed  (if allowed-references
                                     (lower-references allowed-references
                                                       #:system system
                                                       #:target target)
                                     (return #f)))
                       (disallowed (if disallowed-references
                                       (lower-references disallowed-references
                                                         #:system system
                                                         #:target target)
                                       (return #f)))
                       (guile    (if guile-for-build
                                     (return guile-for-build)
                                     (default-guile-derivation system))))
    (mbegin %store-monad
      (set-grafting graft?)                       ;restore the initial setting
      (raw-derivation name
                      (string-append (derivation->output-path guile)
                                     "/bin/guile")
                      `("--no-auto-compile"
                        ,@(if (pair? %modules)
                              `("-L" ,(derivation->output-path modules)
                                "-C" ,(derivation->output-path compiled))
                              '())
                        ,builder)
                      #:outputs outputs
                      #:env-vars env-vars
                      #:system system
                      #:inputs `((,guile)
                                 (,builder)
                                 ,@(if modules
                                       `((,modules) (,compiled) ,@inputs)
                                       inputs)
                                 ,@(match graphs
                                     (((_ . inputs) ...) inputs)
                                     (_ '())))
                      #:hash hash #:hash-algo hash-algo #:recursive? recursive?
                      #:references-graphs (and=> graphs graphs-file-names)
                      #:allowed-references allowed
                      #:disallowed-references disallowed
                      #:leaked-env-vars leaked-env-vars
                      #:local-build? local-build?
                      #:substitutable? substitutable?))))

(define* (gexp-inputs exp #:key native?)
  "Return the input list for EXP.  When NATIVE? is true, return only native
references; otherwise, return only non-native references."
  (define (add-reference-inputs ref result)
    (match ref
      (($ <gexp-input> (? gexp? exp) _ #t)
       (if native?
           (append (gexp-inputs exp)
                   (gexp-inputs exp #:native? #t)
                   result)
           result))
      (($ <gexp-input> (? gexp? exp) _ #f)
       (append (gexp-inputs exp #:native? native?)
               result))
      (($ <gexp-input> (? string? str))
       (if (direct-store-path? str)
           (cons `(,str) result)
           result))
      (($ <gexp-input> (? struct? thing) output n?)
       (if (and (eqv? n? native?) (lookup-compiler thing))
           ;; THING is a derivation, or a package, or an origin, etc.
           (cons `(,thing ,output) result)
           result))
      (($ <gexp-input> (lst ...) output n?)
       (fold-right add-reference-inputs result
                   ;; XXX: For now, automatically convert LST to a list of
                   ;; gexp-inputs.  Inherit N?.
                   (map (match-lambda
                          ((? gexp-input? x)
                           (%gexp-input (gexp-input-thing x)
                                        (gexp-input-output x)
                                        n?))
                          (x
                           (%gexp-input x "out" n?)))
                        lst)))
      (_
       ;; Ignore references to other kinds of objects.
       result)))

  (fold-right add-reference-inputs
              '()
              (gexp-references exp)))

(define gexp-native-inputs
  (cut gexp-inputs <> #:native? #t))

(define (gexp-outputs exp)
  "Return the outputs referred to by EXP as a list of strings."
  (define (add-reference-output ref result)
    (match ref
      (($ <gexp-output> name)
       (cons name result))
      (($ <gexp-input> (? gexp? exp))
       (append (gexp-outputs exp) result))
      (($ <gexp-input> (lst ...) output native?)
       ;; XXX: Automatically convert LST.
       (add-reference-output (map (match-lambda
                                   ((? gexp-input? x) x)
                                   (x (%gexp-input x "out" native?)))
                                  lst)
                             result))
      ((lst ...)
       (fold-right add-reference-output result lst))
      (_
       result)))

  (delete-duplicates
   (add-reference-output (gexp-references exp) '())))

(define* (gexp->sexp exp #:key
                     (system (%current-system))
                     (target (%current-target-system)))
  "Return (monadically) the sexp corresponding to EXP for the given OUTPUT,
and in the current monad setting (system type, etc.)"
  (define* (reference->sexp ref #:optional native?)
    (with-monad %store-monad
      (match ref
        (($ <gexp-output> output)
         ;; Output file names are not known in advance but the daemon defines
         ;; an environment variable for each of them at build time, so use
         ;; that trick.
         (return `((@ (guile) getenv) ,output)))
        (($ <gexp-input> (? gexp? exp) output n?)
         (gexp->sexp exp
                     #:system system
                     #:target (if (or n? native?) #f target)))
        (($ <gexp-input> (refs ...) output n?)
         (sequence %store-monad
                   (map (lambda (ref)
                          ;; XXX: Automatically convert REF to an gexp-input.
                          (reference->sexp
                           (if (gexp-input? ref)
                               ref
                               (%gexp-input ref "out" n?))
                           (or n? native?)))
                        refs)))
        (($ <gexp-input> (? struct? thing) output n?)
         (let ((target (if (or n? native?) #f target))
               (expand (lookup-expander thing)))
           (mlet %store-monad ((obj (lower-object thing system
                                                  #:target target)))
             ;; OBJ must be either a derivation or a store file name.
             (return (expand thing obj output)))))
        (($ <gexp-input> x)
         (return x))
        (x
         (return x)))))

  (mlet %store-monad
      ((args (sequence %store-monad
                       (map reference->sexp (gexp-references exp)))))
    (return (apply (gexp-proc exp) args))))

(define (syntax-location-string s)
  "Return a string representing the source code location of S."
  (let ((props (syntax-source s)))
    (if props
        (let ((file   (assoc-ref props 'filename))
              (line   (and=> (assoc-ref props 'line) 1+))
              (column (assoc-ref props 'column)))
          (if file
              (simple-format #f "~a:~a:~a"
                             file line column)
              (simple-format #f "~a:~a" line column)))
        "<unknown location>")))

(define-syntax-parameter current-imported-modules
  ;; Current list of imported modules.
  (identifier-syntax '()))

(define-syntax-rule (with-imported-modules modules body ...)
  "Mark the gexps defined in BODY... as requiring MODULES in their execution
environment."
  (syntax-parameterize ((current-imported-modules
                         (identifier-syntax modules)))
    body ...))

(define-syntax gexp
  (lambda (s)
    (define (collect-escapes exp)
      ;; Return all the 'ungexp' present in EXP.
      (let loop ((exp    exp)
                 (result '()))
        (syntax-case exp (ungexp
                          ungexp-splicing
                          ungexp-native
                          ungexp-native-splicing)
          ((ungexp _)
           (cons exp result))
          ((ungexp _ _)
           (cons exp result))
          ((ungexp-splicing _ ...)
           (cons exp result))
          ((ungexp-native _ ...)
           (cons exp result))
          ((ungexp-native-splicing _ ...)
           (cons exp result))
          ((exp0 . exp)
           (let ((result (loop #'exp0 result)))
             (loop  #'exp result)))
          (_
           result))))

    (define (escape->ref exp)
      ;; Turn 'ungexp' form EXP into a "reference".
      (syntax-case exp (ungexp ungexp-splicing
                        ungexp-native ungexp-native-splicing
                        output)
        ((ungexp output)
         #'(gexp-output "out"))
        ((ungexp output name)
         #'(gexp-output name))
        ((ungexp thing)
         #'(%gexp-input thing "out" #f))
        ((ungexp drv-or-pkg out)
         #'(%gexp-input drv-or-pkg out #f))
        ((ungexp-splicing lst)
         #'(%gexp-input lst "out" #f))
        ((ungexp-native thing)
         #'(%gexp-input thing "out" #t))
        ((ungexp-native drv-or-pkg out)
         #'(%gexp-input drv-or-pkg out #t))
        ((ungexp-native-splicing lst)
         #'(%gexp-input lst "out" #t))))

    (define (substitute-ungexp exp substs)
      ;; Given EXP, an 'ungexp' or 'ungexp-native' form, substitute it with
      ;; the corresponding form in SUBSTS.
      (match (assoc exp substs)
        ((_ id)
         id)
        (_                                        ;internal error
         (with-syntax ((exp exp))
           #'(syntax-error "error: no 'ungexp' substitution" exp)))))

    (define (substitute-ungexp-splicing exp substs)
      (syntax-case exp ()
        ((exp rest ...)
         (match (assoc #'exp substs)
           ((_ id)
            (with-syntax ((id id))
              #`(append id
                        #,(substitute-references #'(rest ...) substs))))
           (_
            #'(syntax-error "error: no 'ungexp-splicing' substitution"
                            exp))))))

    (define (substitute-references exp substs)
      ;; Return a variant of EXP where all the cars of SUBSTS have been
      ;; replaced by the corresponding cdr.
      (syntax-case exp (ungexp ungexp-native
                        ungexp-splicing ungexp-native-splicing)
        ((ungexp _ ...)
         (substitute-ungexp exp substs))
        ((ungexp-native _ ...)
         (substitute-ungexp exp substs))
        (((ungexp-splicing _ ...) rest ...)
         (substitute-ungexp-splicing exp substs))
        (((ungexp-native-splicing _ ...) rest ...)
         (substitute-ungexp-splicing exp substs))
        ((exp0 . exp)
         #`(cons #,(substitute-references #'exp0 substs)
                 #,(substitute-references #'exp substs)))
        (x #''x)))

    (syntax-case s (ungexp output)
      ((_ exp)
       (let* ((escapes (delete-duplicates (collect-escapes #'exp)))
              (formals (generate-temporaries escapes))
              (sexp    (substitute-references #'exp (zip escapes formals)))
              (refs    (map escape->ref escapes)))
         #`(make-gexp (list #,@refs)
                      current-imported-modules
                      (lambda #,formals
                        #,sexp)))))))


;;;
;;; Module handling.
;;;

(define %utils-module
  ;; This file provides 'mkdir-p', needed to implement 'imported-files' and
  ;; other primitives below.  Note: We give the file name relative to this
  ;; file you are currently reading; 'search-path' could return a file name
  ;; relative to the current working directory.
  (local-file "build/utils.scm"
              "build-utils.scm"))

(define* (imported-files files
                         #:key (name "file-import")
                         (system (%current-system))
                         (guile (%guile-for-build))

                         ;; XXX: The only reason we have
                         ;; #:deprecation-warnings is because (guix build
                         ;; utils), which we use here, relies on _IO*, which
                         ;; is deprecated in 2.2.  On the next full-rebuild
                         ;; cycle, we should disable such warnings
                         ;; unconditionally.
                         (deprecation-warnings #f))
  "Return a derivation that imports FILES into STORE.  FILES must be a list
of (FINAL-PATH . FILE) pairs.  Each FILE is mapped to FINAL-PATH in the
resulting store path.  FILE can be either a file name, or a file-like object,
as returned by 'local-file' for example."
  (define file-pair
    (match-lambda
     ((final-path . (? string? file-name))
      (mlet %store-monad ((file (interned-file file-name
                                               (basename final-path))))
        (return (list final-path file))))
     ((final-path . file-like)
      (mlet %store-monad ((file (lower-object file-like system)))
        (return (list final-path file))))))

  (mlet %store-monad ((files (sequence %store-monad
                                       (map file-pair files))))
    (define build
      (gexp
       (begin
         (primitive-load (ungexp %utils-module))  ;for 'mkdir-p'
         (use-modules (ice-9 match))

         (mkdir (ungexp output)) (chdir (ungexp output))
         (for-each (match-lambda
                    ((final-path store-path)
                     (mkdir-p (dirname final-path))
                     (symlink store-path final-path)))
                   '(ungexp files)))))

    ;; TODO: Pass FILES as an environment variable so that BUILD remains
    ;; exactly the same regardless of FILES: less disk space, and fewer
    ;; 'add-to-store' RPCs.
    (gexp->derivation name build
                      #:system system
                      #:guile-for-build guile
                      #:local-build? #t

                      ;; TODO: On the next rebuild cycle, set to "no"
                      ;; unconditionally.
                      #:env-vars
                      (case deprecation-warnings
                        ((#f)
                         '(("GUILE_WARN_DEPRECATED" . "no")))
                        ((detailed)
                         '(("GUILE_WARN_DEPRECATED" . "detailed")))
                        (else
                         '())))))

(define* (imported-modules modules
                           #:key (name "module-import")
                           (system (%current-system))
                           (guile (%guile-for-build))
                           (module-path %load-path)
                           (deprecation-warnings #f))
  "Return a derivation that contains the source files of MODULES, a list of
module names such as `(ice-9 q)'.  All of MODULES must be either names of
modules to be found in the MODULE-PATH search path, or a module name followed
by an arrow followed by a file-like object.  For example:

  (imported-modules `((guix build utils)
                      (guix gcrypt)
                      ((guix config) => ,(scheme-file …))))

In this example, the first two modules are taken from MODULE-PATH, and the
last one is created from the given <scheme-file> object."
  (mlet %store-monad ((files
                       (mapm %store-monad
                             (match-lambda
                               (((module ...) '=> file)
                                (return
                                 (cons (module->source-file-name module)
                                       file)))
                               ((module ...)
                                (let ((f (module->source-file-name module)))
                                  (return
                                   (cons f (search-path* module-path f))))))
                             modules)))
    (imported-files files #:name name #:system system
                    #:guile guile
                    #:deprecation-warnings deprecation-warnings)))

(define* (compiled-modules modules
                           #:key (name "module-import-compiled")
                           (system (%current-system))
                           (guile (%guile-for-build))
                           (module-path %load-path)
                           (deprecation-warnings #f))
  "Return a derivation that builds a tree containing the `.go' files
corresponding to MODULES.  All the MODULES are built in a context where
they can refer to each other."
  (mlet %store-monad ((modules (imported-modules modules
                                                 #:system system
                                                 #:guile guile
                                                 #:module-path
                                                 module-path
                                                 #:deprecation-warnings
                                                 deprecation-warnings)))
    (define build
      (gexp
       (begin
         (primitive-load (ungexp %utils-module))  ;for 'mkdir-p'

         (use-modules (ice-9 ftw)
                      (srfi srfi-26)
                      (system base compile))

         (define (regular? file)
           (not (member file '("." ".."))))

         (define (process-directory directory output)
           (let ((entries (map (cut string-append directory "/" <>)
                               (scandir directory regular?))))
             (for-each (lambda (entry)
                         (if (file-is-directory? entry)
                             (let ((output (string-append output "/"
                                                          (basename entry))))
                               (mkdir-p output)
                               (process-directory entry output))
                             (let* ((base   (string-drop-right
                                             (basename entry)
                                             4)) ;.scm
                                    (output (string-append output "/" base
                                                           ".go")))
                               (compile-file entry
                                             #:output-file output
                                             #:opts
                                             %auto-compilation-options))))
                       entries)))

         (set! %load-path (cons (ungexp modules) %load-path))
         (mkdir (ungexp output))
         (chdir (ungexp modules))
         (process-directory "." (ungexp output)))))

    ;; TODO: Pass MODULES as an environment variable.
    (gexp->derivation name build
                      #:system system
                      #:guile-for-build guile
                      #:local-build? #t
                      #:env-vars
                      (case deprecation-warnings
                        ((#f)
                         '(("GUILE_WARN_DEPRECATED" . "no")))
                        ((detailed)
                         '(("GUILE_WARN_DEPRECATED" . "detailed")))
                        (else
                         '())))))


;;;
;;; Convenience procedures.
;;;

(define (default-guile)
  ;; Lazily resolve 'guile-2.2' (not 'guile-final' because this is for
  ;; programs returned by 'program-file' and we don't want to keep references
  ;; to several Guile packages).  This module must not refer to (gnu …)
  ;; modules directly, to avoid circular dependencies, hence this hack.
  (module-ref (resolve-interface '(gnu packages guile))
              'guile-2.2))

(define* (load-path-expression modules #:optional (path %load-path))
  "Return as a monadic value a gexp that sets '%load-path' and
'%load-compiled-path' to point to MODULES, a list of module names.  MODULES
are searched for in PATH."
  (mlet %store-monad ((modules  (imported-modules modules
                                                  #:module-path path))
                      (compiled (compiled-modules modules
                                                  #:module-path path)))
    (return (gexp (eval-when (expand load eval)
                    (set! %load-path
                      (cons (ungexp modules) %load-path))
                    (set! %load-compiled-path
                      (cons (ungexp compiled)
                            %load-compiled-path)))))))

(define* (gexp->script name exp
                       #:key (guile (default-guile))
                       (module-path %load-path))
  "Return an executable script NAME that runs EXP using GUILE, with EXP's
imported modules in its search path.  Look up EXP's modules in MODULE-PATH."
  (mlet %store-monad ((set-load-path
                       (load-path-expression (gexp-modules exp)
                                             module-path)))
    (gexp->derivation name
                      (gexp
                       (call-with-output-file (ungexp output)
                         (lambda (port)
                           ;; Note: that makes a long shebang.  When the store
                           ;; is /gnu/store, that fits within the 128-byte
                           ;; limit imposed by Linux, but that may go beyond
                           ;; when running tests.
                           (format port
                                   "#!~a/bin/guile --no-auto-compile~%!#~%"
                                   (ungexp guile))

                           (write '(ungexp set-load-path) port)
                           (write '(ungexp exp) port)
                           (chmod port #o555))))
                      #:module-path module-path)))

(define* (gexp->file name exp #:key
                     (set-load-path? #t)
                     (module-path %load-path)
                     (splice? #f))
  "Return a derivation that builds a file NAME containing EXP.  When SPLICE?
is true, EXP is considered to be a list of expressions that will be spliced in
the resulting file.

When SET-LOAD-PATH? is true, emit code in the resulting file to set
'%load-path' and '%load-compiled-path' to honor EXP's imported modules.
Lookup EXP's modules in MODULE-PATH."
  (match (if set-load-path? (gexp-modules exp) '())
    (()                                           ;zero modules
     (gexp->derivation name
                       (gexp
                        (call-with-output-file (ungexp output)
                          (lambda (port)
                            (for-each (lambda (exp)
                                        (write exp port))
                                      '(ungexp (if splice?
                                                   exp
                                                   (gexp ((ungexp exp)))))))))
                       #:local-build? #t
                       #:substitutable? #f))
    ((modules ...)
     (mlet %store-monad ((set-load-path (load-path-expression modules
                                                              module-path)))
       (gexp->derivation name
                         (gexp
                          (call-with-output-file (ungexp output)
                            (lambda (port)
                              (write '(ungexp set-load-path) port)
                              (for-each (lambda (exp)
                                          (write exp port))
                                        '(ungexp (if splice?
                                                     exp
                                                     (gexp ((ungexp exp)))))))))
                         #:module-path module-path
                         #:local-build? #t
                         #:substitutable? #f)))))

(define* (text-file* name #:rest text)
  "Return as a monadic value a derivation that builds a text file containing
all of TEXT.  TEXT may list, in addition to strings, objects of any type that
can be used in a gexp: packages, derivations, local file objects, etc.  The
resulting store file holds references to all these."
  (define builder
    (gexp (call-with-output-file (ungexp output "out")
            (lambda (port)
              (display (string-append (ungexp-splicing text)) port)))))

  (gexp->derivation name builder
                    #:local-build? #t
                    #:substitutable? #f))

(define* (mixed-text-file name #:rest text)
  "Return an object representing store file NAME containing TEXT.  TEXT is a
sequence of strings and file-like objects, as in:

  (mixed-text-file \"profile\"
                   \"export PATH=\" coreutils \"/bin:\" grep \"/bin\")

This is the declarative counterpart of 'text-file*'."
  (define build
    (gexp (call-with-output-file (ungexp output "out")
            (lambda (port)
              (display (string-append (ungexp-splicing text)) port)))))

  (computed-file name build))

(define (file-union name files)
  "Return a <computed-file> that builds a directory containing all of FILES.
Each item in FILES must be a two-element list where the first element is the
file name to use in the new directory, and the second element is a gexp
denoting the target file.  Here's an example:

  (file-union \"etc\"
              `((\"hosts\" ,(plain-file \"hosts\"
                                        \"127.0.0.1 localhost\"))
                (\"bashrc\" ,(plain-file \"bashrc\"
                                         \"alias ls='ls --color'\"))))

This yields an 'etc' directory containing these two files."
  (computed-file name
                 (gexp
                  (begin
                    (mkdir (ungexp output))
                    (chdir (ungexp output))
                    (ungexp-splicing
                     (map (match-lambda
                            ((target source)
                             (gexp
                              (begin
                                ;; Stat the source to abort early if it does
                                ;; not exist.
                                (stat (ungexp source))

                                (symlink (ungexp source)
                                         (ungexp target))))))
                          files))))))

(define* (directory-union name things
                          #:key (copy? #f) (quiet? #f)
                          (resolve-collision 'warn-about-collision))
  "Return a directory that is the union of THINGS, where THINGS is a list of
file-like objects denoting directories.  For example:

  (directory-union \"guile+emacs\" (list guile emacs))

yields a directory that is the union of the 'guile' and 'emacs' packages.

Call RESOLVE-COLLISION when several files collide, passing it the list of
colliding files.  RESOLVE-COLLISION must return the chosen file or #f, in
which case the colliding entry is skipped altogether.

When HARD-LINKS? is true, create hard links instead of symlinks.  When QUIET?
is true, the derivation will not print anything."
  (define symlink
    (if copy?
        (gexp (lambda (old new)
                (if (file-is-directory? old)
                    (symlink old new)
                    (copy-file old new))))
        (gexp symlink)))

  (define log-port
    (if quiet?
        (gexp (%make-void-port "w"))
        (gexp (current-error-port))))

  (match things
    ((one)
     ;; Only one thing; return it.
     one)
    (_
     (computed-file name
                    (with-imported-modules '((guix build union))
                      (gexp (begin
                              (use-modules (guix build union)
                                           (srfi srfi-1)) ;for 'first' and 'last'

                              (union-build (ungexp output)
                                           '(ungexp things)

                                           #:log-port (ungexp log-port)
                                           #:symlink (ungexp symlink)
                                           #:resolve-collision
                                           (ungexp resolve-collision)))))))))


;;;
;;; Syntactic sugar.
;;;

(eval-when (expand load eval)
  (define* (read-ungexp chr port #:optional native?)
    "Read an 'ungexp' or 'ungexp-splicing' form from PORT.  When NATIVE? is
true, use 'ungexp-native' and 'ungexp-native-splicing' instead."
    (define unquote-symbol
      (match (peek-char port)
        (#\@
         (read-char port)
         (if native?
             'ungexp-native-splicing
             'ungexp-splicing))
        (_
         (if native?
             'ungexp-native
             'ungexp))))

    (match (read port)
      ((? symbol? symbol)
       (let ((str (symbol->string symbol)))
         (match (string-index-right str #\:)
           (#f
            `(,unquote-symbol ,symbol))
           (colon
            (let ((name   (string->symbol (substring str 0 colon)))
                  (output (substring str (+ colon 1))))
              `(,unquote-symbol ,name ,output))))))
      (x
       `(,unquote-symbol ,x))))

  (define (read-gexp chr port)
    "Read a 'gexp' form from PORT."
    `(gexp ,(read port)))

  ;; Extend the reader
  (read-hash-extend #\~ read-gexp)
  (read-hash-extend #\$ read-ungexp)
  (read-hash-extend #\+ (cut read-ungexp <> <> #t)))

;;; gexp.scm ends here