1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
1599
1600
1601
1602
1603
1604
1605
1606
1607
1608
1609
1610
1611
1612
1613
1614
1615
1616
1617
1618
1619
1620
1621
1622
1623
1624
1625
1626
1627
1628
1629
1630
1631
1632
1633
1634
1635
1636
1637
1638
1639
1640
1641
1642
1643
1644
1645
1646
1647
1648
1649
1650
1651
1652
1653
1654
1655
1656
1657
1658
1659
1660
1661
1662
1663
1664
1665
1666
1667
1668
1669
1670
1671
1672
1673
1674
1675
1676
1677
1678
1679
1680
1681
1682
1683
1684
1685
1686
1687
1688
1689
1690
1691
1692
1693
1694
1695
1696
1697
1698
1699
1700
1701
1702
1703
1704
1705
1706
1707
1708
1709
1710
1711
1712
1713
1714
1715
1716
1717
1718
1719
1720
1721
1722
1723
1724
1725
1726
1727
1728
1729
1730
1731
1732
1733
1734
1735
1736
1737
1738
1739
1740
1741
1742
1743
1744
1745
1746
1747
1748
1749
1750
1751
1752
1753
1754
1755
1756
1757
1758
1759
1760
1761
1762
1763
|
{-
(c) The University of Glasgow 2006
(c) The GRASP/AQUA Project, Glasgow University, 1992-1998
\section[TcBinds]{TcBinds}
-}
{-# LANGUAGE CPP, RankNTypes, ScopedTypeVariables #-}
{-# LANGUAGE FlexibleContexts #-}
module TcBinds ( tcLocalBinds, tcTopBinds, tcRecSelBinds,
tcValBinds, tcHsBootSigs, tcPolyCheck,
tcVectDecls, addTypecheckedBinds,
chooseInferredQuantifiers,
badBootDeclErr ) where
import {-# SOURCE #-} TcMatches ( tcGRHSsPat, tcMatchesFun )
import {-# SOURCE #-} TcExpr ( tcMonoExpr )
import {-# SOURCE #-} TcPatSyn ( tcInferPatSynDecl, tcCheckPatSynDecl
, tcPatSynBuilderBind )
import DynFlags
import HsSyn
import HscTypes( isHsBootOrSig )
import TcSigs
import TcRnMonad
import TcEnv
import TcUnify
import TcSimplify
import TcEvidence
import TcHsType
import TcPat
import TcMType
import Inst( deeplyInstantiate )
import FamInstEnv( normaliseType )
import FamInst( tcGetFamInstEnvs )
import TyCon
import TcType
import TysPrim
import TysWiredIn( cTupleTyConName )
import Id
import Var
import VarSet
import VarEnv( TidyEnv )
import Module
import Name
import NameSet
import NameEnv
import SrcLoc
import Bag
import ListSetOps
import ErrUtils
import Digraph
import Maybes
import Util
import BasicTypes
import Outputable
import Type(mkStrLitTy, tidyOpenType)
import PrelNames( gHC_PRIM, ipClassName )
import TcValidity (checkValidType)
import UniqFM
import qualified GHC.LanguageExtensions as LangExt
import Control.Monad
#include "HsVersions.h"
{- *********************************************************************
* *
A useful helper function
* *
********************************************************************* -}
addTypecheckedBinds :: TcGblEnv -> [LHsBinds Id] -> TcGblEnv
addTypecheckedBinds tcg_env binds
| isHsBootOrSig (tcg_src tcg_env) = tcg_env
-- Do not add the code for record-selector bindings
-- when compiling hs-boot files
| otherwise = tcg_env { tcg_binds = foldr unionBags
(tcg_binds tcg_env)
binds }
{-
************************************************************************
* *
\subsection{Type-checking bindings}
* *
************************************************************************
@tcBindsAndThen@ typechecks a @HsBinds@. The "and then" part is because
it needs to know something about the {\em usage} of the things bound,
so that it can create specialisations of them. So @tcBindsAndThen@
takes a function which, given an extended environment, E, typechecks
the scope of the bindings returning a typechecked thing and (most
important) an LIE. It is this LIE which is then used as the basis for
specialising the things bound.
@tcBindsAndThen@ also takes a "combiner" which glues together the
bindings and the "thing" to make a new "thing".
The real work is done by @tcBindWithSigsAndThen@.
Recursive and non-recursive binds are handled in essentially the same
way: because of uniques there are no scoping issues left. The only
difference is that non-recursive bindings can bind primitive values.
Even for non-recursive binding groups we add typings for each binder
to the LVE for the following reason. When each individual binding is
checked the type of its LHS is unified with that of its RHS; and
type-checking the LHS of course requires that the binder is in scope.
At the top-level the LIE is sure to contain nothing but constant
dictionaries, which we resolve at the module level.
Note [Polymorphic recursion]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The game plan for polymorphic recursion in the code above is
* Bind any variable for which we have a type signature
to an Id with a polymorphic type. Then when type-checking
the RHSs we'll make a full polymorphic call.
This fine, but if you aren't a bit careful you end up with a horrendous
amount of partial application and (worse) a huge space leak. For example:
f :: Eq a => [a] -> [a]
f xs = ...f...
If we don't take care, after typechecking we get
f = /\a -> \d::Eq a -> let f' = f a d
in
\ys:[a] -> ...f'...
Notice the the stupid construction of (f a d), which is of course
identical to the function we're executing. In this case, the
polymorphic recursion isn't being used (but that's a very common case).
This can lead to a massive space leak, from the following top-level defn
(post-typechecking)
ff :: [Int] -> [Int]
ff = f Int dEqInt
Now (f dEqInt) evaluates to a lambda that has f' as a free variable; but
f' is another thunk which evaluates to the same thing... and you end
up with a chain of identical values all hung onto by the CAF ff.
ff = f Int dEqInt
= let f' = f Int dEqInt in \ys. ...f'...
= let f' = let f' = f Int dEqInt in \ys. ...f'...
in \ys. ...f'...
Etc.
NOTE: a bit of arity anaysis would push the (f a d) inside the (\ys...),
which would make the space leak go away in this case
Solution: when typechecking the RHSs we always have in hand the
*monomorphic* Ids for each binding. So we just need to make sure that
if (Method f a d) shows up in the constraints emerging from (...f...)
we just use the monomorphic Id. We achieve this by adding monomorphic Ids
to the "givens" when simplifying constraints. That's what the "lies_avail"
is doing.
Then we get
f = /\a -> \d::Eq a -> letrec
fm = \ys:[a] -> ...fm...
in
fm
-}
tcTopBinds :: [(RecFlag, LHsBinds Name)] -> [LSig Name] -> TcM (TcGblEnv, TcLclEnv)
-- The TcGblEnv contains the new tcg_binds and tcg_spects
-- The TcLclEnv has an extended type envt for the new bindings
tcTopBinds binds sigs
= do { -- Pattern synonym bindings populate the global environment
(binds', (tcg_env, tcl_env)) <- tcValBinds TopLevel binds sigs $
do { gbl <- getGblEnv
; lcl <- getLclEnv
; return (gbl, lcl) }
; specs <- tcImpPrags sigs -- SPECIALISE prags for imported Ids
; let { tcg_env' = tcg_env { tcg_imp_specs = specs ++ tcg_imp_specs tcg_env }
`addTypecheckedBinds` map snd binds' }
; return (tcg_env', tcl_env) }
-- The top level bindings are flattened into a giant
-- implicitly-mutually-recursive LHsBinds
tcRecSelBinds :: HsValBinds Name -> TcM TcGblEnv
tcRecSelBinds (ValBindsOut binds sigs)
= tcExtendGlobalValEnv [sel_id | L _ (IdSig sel_id) <- sigs] $
do { (rec_sel_binds, tcg_env) <- discardWarnings $
tcValBinds TopLevel binds sigs getGblEnv
; let tcg_env' = tcg_env `addTypecheckedBinds` map snd rec_sel_binds
; return tcg_env' }
tcRecSelBinds (ValBindsIn {}) = panic "tcRecSelBinds"
tcHsBootSigs :: [(RecFlag, LHsBinds Name)] -> [LSig Name] -> TcM [Id]
-- A hs-boot file has only one BindGroup, and it only has type
-- signatures in it. The renamer checked all this
tcHsBootSigs binds sigs
= do { checkTc (null binds) badBootDeclErr
; concat <$> mapM (addLocM tc_boot_sig) (filter isTypeLSig sigs) }
where
tc_boot_sig (TypeSig lnames hs_ty) = mapM f lnames
where
f (L _ name)
= do { sigma_ty <- solveEqualities $
tcHsSigWcType (FunSigCtxt name False) hs_ty
; return (mkVanillaGlobal name sigma_ty) }
-- Notice that we make GlobalIds, not LocalIds
tc_boot_sig s = pprPanic "tcHsBootSigs/tc_boot_sig" (ppr s)
badBootDeclErr :: MsgDoc
badBootDeclErr = text "Illegal declarations in an hs-boot file"
------------------------
tcLocalBinds :: HsLocalBinds Name -> TcM thing
-> TcM (HsLocalBinds TcId, thing)
tcLocalBinds EmptyLocalBinds thing_inside
= do { thing <- thing_inside
; return (EmptyLocalBinds, thing) }
tcLocalBinds (HsValBinds (ValBindsOut binds sigs)) thing_inside
= do { (binds', thing) <- tcValBinds NotTopLevel binds sigs thing_inside
; return (HsValBinds (ValBindsOut binds' sigs), thing) }
tcLocalBinds (HsValBinds (ValBindsIn {})) _ = panic "tcLocalBinds"
tcLocalBinds (HsIPBinds (IPBinds ip_binds _)) thing_inside
= do { ipClass <- tcLookupClass ipClassName
; (given_ips, ip_binds') <-
mapAndUnzipM (wrapLocSndM (tc_ip_bind ipClass)) ip_binds
-- If the binding binds ?x = E, we must now
-- discharge any ?x constraints in expr_lie
-- See Note [Implicit parameter untouchables]
; (ev_binds, result) <- checkConstraints (IPSkol ips)
[] given_ips thing_inside
; return (HsIPBinds (IPBinds ip_binds' ev_binds), result) }
where
ips = [ip | L _ (IPBind (Left (L _ ip)) _) <- ip_binds]
-- I wonder if we should do these one at at time
-- Consider ?x = 4
-- ?y = ?x + 1
tc_ip_bind ipClass (IPBind (Left (L _ ip)) expr)
= do { ty <- newOpenFlexiTyVarTy
; let p = mkStrLitTy $ hsIPNameFS ip
; ip_id <- newDict ipClass [ p, ty ]
; expr' <- tcMonoExpr expr (mkCheckExpType ty)
; let d = toDict ipClass p ty `fmap` expr'
; return (ip_id, (IPBind (Right ip_id) d)) }
tc_ip_bind _ (IPBind (Right {}) _) = panic "tc_ip_bind"
-- Coerces a `t` into a dictionry for `IP "x" t`.
-- co : t -> IP "x" t
toDict ipClass x ty = HsWrap $ mkWpCastR $
wrapIP $ mkClassPred ipClass [x,ty]
{- Note [Implicit parameter untouchables]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
We add the type variables in the types of the implicit parameters
as untouchables, not so much because we really must not unify them,
but rather because we otherwise end up with constraints like this
Num alpha, Implic { wanted = alpha ~ Int }
The constraint solver solves alpha~Int by unification, but then
doesn't float that solved constraint out (it's not an unsolved
wanted). Result disaster: the (Num alpha) is again solved, this
time by defaulting. No no no.
However [Oct 10] this is all handled automatically by the
untouchable-range idea.
Note [Inlining and hs-boot files]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Consider this example (Trac #10083):
---------- RSR.hs-boot ------------
module RSR where
data RSR
eqRSR :: RSR -> RSR -> Bool
---------- SR.hs ------------
module SR where
import {-# SOURCE #-} RSR
data SR = MkSR RSR
eqSR (MkSR r1) (MkSR r2) = eqRSR r1 r2
---------- RSR.hs ------------
module RSR where
import SR
data RSR = MkRSR SR -- deriving( Eq )
eqRSR (MkRSR s1) (MkRSR s2) = (eqSR s1 s2)
foo x y = not (eqRSR x y)
When compiling RSR we get this code
RSR.eqRSR :: RSR -> RSR -> Bool
RSR.eqRSR = \ (ds1 :: RSR.RSR) (ds2 :: RSR.RSR) ->
case ds1 of _ { RSR.MkRSR s1 ->
case ds2 of _ { RSR.MkRSR s2 ->
SR.eqSR s1 s2 }}
RSR.foo :: RSR -> RSR -> Bool
RSR.foo = \ (x :: RSR) (y :: RSR) -> not (RSR.eqRSR x y)
Now, when optimising foo:
Inline eqRSR (small, non-rec)
Inline eqSR (small, non-rec)
but the result of inlining eqSR from SR is another call to eqRSR, so
everything repeats. Neither eqSR nor eqRSR are (apparently) loop
breakers.
Solution: when compiling RSR, add a NOINLINE pragma to every function
exported by the boot-file for RSR (if it exists).
ALAS: doing so makes the boostrappted GHC itself slower by 8% overall
(on Trac #9872a-d, and T1969. So I un-did this change, and
parked it for now. Sigh.
-}
tcValBinds :: TopLevelFlag
-> [(RecFlag, LHsBinds Name)] -> [LSig Name]
-> TcM thing
-> TcM ([(RecFlag, LHsBinds TcId)], thing)
tcValBinds top_lvl binds sigs thing_inside
= do { let patsyns = getPatSynBinds binds
-- Typecheck the signature
; (poly_ids, sig_fn) <- tcAddPatSynPlaceholders patsyns $
tcTySigs sigs
; _self_boot <- tcSelfBootInfo
; let prag_fn = mkPragEnv sigs (foldr (unionBags . snd) emptyBag binds)
-- ------- See Note [Inlining and hs-boot files] (change parked) --------
-- prag_fn | isTopLevel top_lvl -- See Note [Inlining and hs-boot files]
-- , SelfBoot { sb_ids = boot_id_names } <- self_boot
-- = foldNameSet add_no_inl prag_fn1 boot_id_names
-- | otherwise
-- = prag_fn1
-- add_no_inl boot_id_name prag_fn
-- = extendPragEnv prag_fn (boot_id_name, no_inl_sig boot_id_name)
-- no_inl_sig name = L boot_loc (InlineSig (L boot_loc name) neverInlinePragma)
-- boot_loc = mkGeneralSrcSpan (fsLit "The hs-boot file for this module")
-- Extend the envt right away with all the Ids
-- declared with complete type signatures
-- Do not extend the TcIdBinderStack; instead
-- we extend it on a per-rhs basis in tcExtendForRhs
; tcExtendLetEnvIds top_lvl [(idName id, id) | id <- poly_ids] $ do
{ (binds', (extra_binds', thing)) <- tcBindGroups top_lvl sig_fn prag_fn binds $ do
{ thing <- thing_inside
-- See Note [Pattern synonym builders don't yield dependencies]
; patsyn_builders <- mapM tcPatSynBuilderBind patsyns
; let extra_binds = [ (NonRecursive, builder) | builder <- patsyn_builders ]
; return (extra_binds, thing) }
; return (binds' ++ extra_binds', thing) }}
------------------------
tcBindGroups :: TopLevelFlag -> TcSigFun -> TcPragEnv
-> [(RecFlag, LHsBinds Name)] -> TcM thing
-> TcM ([(RecFlag, LHsBinds TcId)], thing)
-- Typecheck a whole lot of value bindings,
-- one strongly-connected component at a time
-- Here a "strongly connected component" has the strightforward
-- meaning of a group of bindings that mention each other,
-- ignoring type signatures (that part comes later)
tcBindGroups _ _ _ [] thing_inside
= do { thing <- thing_inside
; return ([], thing) }
tcBindGroups top_lvl sig_fn prag_fn (group : groups) thing_inside
= do { -- See Note [Closed binder groups]
closed <- isClosedBndrGroup $ snd group
; (group', (groups', thing))
<- tc_group top_lvl sig_fn prag_fn group closed $
tcBindGroups top_lvl sig_fn prag_fn groups thing_inside
; return (group' ++ groups', thing) }
-- Note [Closed binder groups]
-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~
--
-- A mutually recursive group is "closed" if all of the free variables of
-- the bindings are closed. For example
--
-- > h = \x -> let f = ...g...
-- > g = ....f...x...
-- > in ...
--
-- Here @g@ is not closed because it mentions @x@; and hence neither is @f@
-- closed.
--
-- So we need to compute closed-ness on each strongly connected components,
-- before we sub-divide it based on what type signatures it has.
--
------------------------
tc_group :: forall thing.
TopLevelFlag -> TcSigFun -> TcPragEnv
-> (RecFlag, LHsBinds Name) -> IsGroupClosed -> TcM thing
-> TcM ([(RecFlag, LHsBinds TcId)], thing)
-- Typecheck one strongly-connected component of the original program.
-- We get a list of groups back, because there may
-- be specialisations etc as well
tc_group top_lvl sig_fn prag_fn (NonRecursive, binds) closed thing_inside
-- A single non-recursive binding
-- We want to keep non-recursive things non-recursive
-- so that we desugar unlifted bindings correctly
= do { let bind = case bagToList binds of
[bind] -> bind
[] -> panic "tc_group: empty list of binds"
_ -> panic "tc_group: NonRecursive binds is not a singleton bag"
; (bind', thing) <- tc_single top_lvl sig_fn prag_fn bind closed
thing_inside
; return ( [(NonRecursive, bind')], thing) }
tc_group top_lvl sig_fn prag_fn (Recursive, binds) closed thing_inside
= -- To maximise polymorphism, we do a new
-- strongly-connected-component analysis, this time omitting
-- any references to variables with type signatures.
-- (This used to be optional, but isn't now.)
-- See Note [Polymorphic recursion] in HsBinds.
do { traceTc "tc_group rec" (pprLHsBinds binds)
; when hasPatSyn $ recursivePatSynErr binds
; (binds1, thing) <- go sccs
; return ([(Recursive, binds1)], thing) }
-- Rec them all together
where
hasPatSyn = anyBag (isPatSyn . unLoc) binds
isPatSyn PatSynBind{} = True
isPatSyn _ = False
sccs :: [SCC (LHsBind Name)]
sccs = stronglyConnCompFromEdgedVertices (mkEdges sig_fn binds)
go :: [SCC (LHsBind Name)] -> TcM (LHsBinds TcId, thing)
go (scc:sccs) = do { (binds1, ids1) <- tc_scc scc
; (binds2, thing) <- tcExtendLetEnv top_lvl closed ids1
(go sccs)
; return (binds1 `unionBags` binds2, thing) }
go [] = do { thing <- thing_inside; return (emptyBag, thing) }
tc_scc (AcyclicSCC bind) = tc_sub_group NonRecursive [bind]
tc_scc (CyclicSCC binds) = tc_sub_group Recursive binds
tc_sub_group rec_tc binds =
tcPolyBinds top_lvl sig_fn prag_fn Recursive rec_tc closed binds
recursivePatSynErr :: OutputableBndr name => LHsBinds name -> TcM a
recursivePatSynErr binds
= failWithTc $
hang (text "Recursive pattern synonym definition with following bindings:")
2 (vcat $ map pprLBind . bagToList $ binds)
where
pprLoc loc = parens (text "defined at" <+> ppr loc)
pprLBind (L loc bind) = pprWithCommas ppr (collectHsBindBinders bind) <+>
pprLoc loc
tc_single :: forall thing.
TopLevelFlag -> TcSigFun -> TcPragEnv
-> LHsBind Name -> IsGroupClosed -> TcM thing
-> TcM (LHsBinds TcId, thing)
tc_single _top_lvl sig_fn _prag_fn
(L _ (PatSynBind psb@PSB{ psb_id = L _ name }))
_ thing_inside
= do { (aux_binds, tcg_env) <- tc_pat_syn_decl
; thing <- setGblEnv tcg_env thing_inside
; return (aux_binds, thing)
}
where
tc_pat_syn_decl :: TcM (LHsBinds TcId, TcGblEnv)
tc_pat_syn_decl = case sig_fn name of
Nothing -> tcInferPatSynDecl psb
Just (TcPatSynSig tpsi) -> tcCheckPatSynDecl psb tpsi
Just _ -> panic "tc_single"
tc_single top_lvl sig_fn prag_fn lbind closed thing_inside
= do { (binds1, ids) <- tcPolyBinds top_lvl sig_fn prag_fn
NonRecursive NonRecursive
closed
[lbind]
; thing <- tcExtendLetEnv top_lvl closed ids thing_inside
; return (binds1, thing) }
------------------------
type BKey = Int -- Just number off the bindings
mkEdges :: TcSigFun -> LHsBinds Name -> [Node BKey (LHsBind Name)]
-- See Note [Polymorphic recursion] in HsBinds.
mkEdges sig_fn binds
= [ (bind, key, [key | n <- nonDetEltsUFM (bind_fvs (unLoc bind)),
Just key <- [lookupNameEnv key_map n], no_sig n ])
| (bind, key) <- keyd_binds
]
-- It's OK to use nonDetEltsUFM here as stronglyConnCompFromEdgedVertices
-- is still deterministic even if the edges are in nondeterministic order
-- as explained in Note [Deterministic SCC] in Digraph.
where
no_sig :: Name -> Bool
no_sig n = noCompleteSig (sig_fn n)
keyd_binds = bagToList binds `zip` [0::BKey ..]
key_map :: NameEnv BKey -- Which binding it comes from
key_map = mkNameEnv [(bndr, key) | (L _ bind, key) <- keyd_binds
, bndr <- collectHsBindBinders bind ]
------------------------
tcPolyBinds :: TopLevelFlag -> TcSigFun -> TcPragEnv
-> RecFlag -- Whether the group is really recursive
-> RecFlag -- Whether it's recursive after breaking
-- dependencies based on type signatures
-> IsGroupClosed -- Whether the group is closed
-> [LHsBind Name] -- None are PatSynBind
-> TcM (LHsBinds TcId, [TcId])
-- Typechecks a single bunch of values bindings all together,
-- and generalises them. The bunch may be only part of a recursive
-- group, because we use type signatures to maximise polymorphism
--
-- Returns a list because the input may be a single non-recursive binding,
-- in which case the dependency order of the resulting bindings is
-- important.
--
-- Knows nothing about the scope of the bindings
-- None of the bindings are pattern synonyms
tcPolyBinds top_lvl sig_fn prag_fn rec_group rec_tc closed bind_list
= setSrcSpan loc $
recoverM (recoveryCode binder_names sig_fn) $ do
-- Set up main recover; take advantage of any type sigs
{ traceTc "------------------------------------------------" Outputable.empty
; traceTc "Bindings for {" (ppr binder_names)
; dflags <- getDynFlags
; let plan = decideGeneralisationPlan dflags bind_list closed sig_fn
; traceTc "Generalisation plan" (ppr plan)
; result@(tc_binds, poly_ids) <- case plan of
NoGen -> tcPolyNoGen rec_tc prag_fn sig_fn bind_list
InferGen mn -> tcPolyInfer rec_tc prag_fn sig_fn mn bind_list
CheckGen lbind sig -> tcPolyCheck prag_fn sig lbind
-- Check whether strict bindings are ok
-- These must be non-recursive etc, and are not generalised
-- They desugar to a case expression in the end
; checkStrictBinds top_lvl rec_group bind_list tc_binds poly_ids
; traceTc "} End of bindings for" (vcat [ ppr binder_names, ppr rec_group
, vcat [ppr id <+> ppr (idType id) | id <- poly_ids]
])
; return result }
where
binder_names = collectHsBindListBinders bind_list
loc = foldr1 combineSrcSpans (map getLoc bind_list)
-- The mbinds have been dependency analysed and
-- may no longer be adjacent; so find the narrowest
-- span that includes them all
--------------
-- If typechecking the binds fails, then return with each
-- signature-less binder given type (forall a.a), to minimise
-- subsequent error messages
recoveryCode :: [Name] -> TcSigFun -> TcM (LHsBinds TcId, [Id])
recoveryCode binder_names sig_fn
= do { traceTc "tcBindsWithSigs: error recovery" (ppr binder_names)
; let poly_ids = map mk_dummy binder_names
; return (emptyBag, poly_ids) }
where
mk_dummy name
| Just sig <- sig_fn name
, Just poly_id <- completeSigPolyId_maybe sig
= poly_id
| otherwise
= mkLocalId name forall_a_a
forall_a_a :: TcType
forall_a_a = mkSpecForAllTys [runtimeRep1TyVar, openAlphaTyVar] openAlphaTy
{- *********************************************************************
* *
tcPolyNoGen
* *
********************************************************************* -}
tcPolyNoGen -- No generalisation whatsoever
:: RecFlag -- Whether it's recursive after breaking
-- dependencies based on type signatures
-> TcPragEnv -> TcSigFun
-> [LHsBind Name]
-> TcM (LHsBinds TcId, [TcId])
tcPolyNoGen rec_tc prag_fn tc_sig_fn bind_list
= do { (binds', mono_infos) <- tcMonoBinds rec_tc tc_sig_fn
(LetGblBndr prag_fn)
bind_list
; mono_ids' <- mapM tc_mono_info mono_infos
; return (binds', mono_ids') }
where
tc_mono_info (MBI { mbi_poly_name = name, mbi_mono_id = mono_id })
= do { mono_ty' <- zonkTcType (idType mono_id)
-- Zonk, mainly to expose unboxed types to checkStrictBinds
; let mono_id' = setIdType mono_id mono_ty'
; _specs <- tcSpecPrags mono_id' (lookupPragEnv prag_fn name)
; return mono_id' }
-- NB: tcPrags generates error messages for
-- specialisation pragmas for non-overloaded sigs
-- Indeed that is why we call it here!
-- So we can safely ignore _specs
{- *********************************************************************
* *
tcPolyCheck
* *
********************************************************************* -}
tcPolyCheck :: TcPragEnv
-> TcIdSigInfo -- Must be a complete signature
-> LHsBind Name -- Must be a FunBind
-> TcM (LHsBinds TcId, [TcId])
-- There is just one binding,
-- it is a Funbind
-- it has a complete type signature,
tcPolyCheck prag_fn
(CompleteSig { sig_bndr = poly_id
, sig_ctxt = ctxt
, sig_loc = sig_loc })
(L loc (FunBind { fun_id = L nm_loc name
, fun_matches = matches }))
= setSrcSpan sig_loc $
do { traceTc "tcPolyCheck" (ppr poly_id $$ ppr sig_loc)
; (tv_prs, theta, tau) <- tcInstType (tcInstSigTyVars sig_loc) poly_id
-- See Note [Instantiate sig with fresh variables]
; mono_name <- newNameAt (nameOccName name) nm_loc
; ev_vars <- newEvVars theta
; let mono_id = mkLocalId mono_name tau
skol_info = SigSkol ctxt (mkPhiTy theta tau)
skol_tvs = map snd tv_prs
; (ev_binds, (co_fn, matches'))
<- checkConstraints skol_info skol_tvs ev_vars $
tcExtendIdBndrs [TcIdBndr mono_id NotTopLevel] $
tcExtendTyVarEnv2 tv_prs $
setSrcSpan loc $
tcMatchesFun (L nm_loc mono_name) matches (mkCheckExpType tau)
; let prag_sigs = lookupPragEnv prag_fn name
; spec_prags <- tcSpecPrags poly_id prag_sigs
; poly_id <- addInlinePrags poly_id prag_sigs
; let bind' = FunBind { fun_id = L nm_loc mono_id
, fun_matches = matches'
, fun_co_fn = co_fn
, bind_fvs = placeHolderNamesTc
, fun_tick = [] }
abs_bind = L loc $ AbsBindsSig
{ abs_sig_export = poly_id
, abs_tvs = skol_tvs
, abs_ev_vars = ev_vars
, abs_sig_prags = SpecPrags spec_prags
, abs_sig_ev_bind = ev_binds
, abs_sig_bind = L loc bind' }
; return (unitBag abs_bind, [poly_id]) }
tcPolyCheck _prag_fn sig bind
= pprPanic "tcPolyCheck" (ppr sig $$ ppr bind)
{- Note [Instantiate sig with fresh variables]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
It's vital to instantiate a type signature with fresh variables.
For example:
type T = forall a. [a] -> [a]
f :: T;
f = g where { g :: T; g = <rhs> }
We must not use the same 'a' from the defn of T at both places!!
(Instantiation is only necessary because of type synonyms. Otherwise,
it's all cool; each signature has distinct type variables from the renamer.)
-}
{- *********************************************************************
* *
tcPolyInfer
* *
********************************************************************* -}
tcPolyInfer
:: RecFlag -- Whether it's recursive after breaking
-- dependencies based on type signatures
-> TcPragEnv -> TcSigFun
-> Bool -- True <=> apply the monomorphism restriction
-> [LHsBind Name]
-> TcM (LHsBinds TcId, [TcId])
tcPolyInfer rec_tc prag_fn tc_sig_fn mono bind_list
= do { (tclvl, wanted, (binds', mono_infos))
<- pushLevelAndCaptureConstraints $
tcMonoBinds rec_tc tc_sig_fn LetLclBndr bind_list
; let name_taus = [ (mbi_poly_name info, idType (mbi_mono_id info))
| info <- mono_infos ]
sigs = [ sig | MBI { mbi_sig = Just sig } <- mono_infos ]
; mapM_ (checkOverloadedSig mono) sigs
; traceTc "simplifyInfer call" (ppr tclvl $$ ppr name_taus $$ ppr wanted)
; (qtvs, givens, ev_binds)
<- simplifyInfer tclvl mono sigs name_taus wanted
; let inferred_theta = map evVarPred givens
; exports <- checkNoErrs $
mapM (mkExport prag_fn qtvs inferred_theta) mono_infos
; loc <- getSrcSpanM
; let poly_ids = map abe_poly exports
abs_bind = L loc $
AbsBinds { abs_tvs = qtvs
, abs_ev_vars = givens, abs_ev_binds = [ev_binds]
, abs_exports = exports, abs_binds = binds' }
; traceTc "Binding:" (ppr (poly_ids `zip` map idType poly_ids))
; return (unitBag abs_bind, poly_ids) }
-- poly_ids are guaranteed zonked by mkExport
--------------
mkExport :: TcPragEnv
-> [TyVar] -> TcThetaType -- Both already zonked
-> MonoBindInfo
-> TcM (ABExport Id)
-- Only called for generalisation plan InferGen, not by CheckGen or NoGen
--
-- mkExport generates exports with
-- zonked type variables,
-- zonked poly_ids
-- The former is just because no further unifications will change
-- the quantified type variables, so we can fix their final form
-- right now.
-- The latter is needed because the poly_ids are used to extend the
-- type environment; see the invariant on TcEnv.tcExtendIdEnv
-- Pre-condition: the qtvs and theta are already zonked
mkExport prag_fn qtvs theta
mono_info@(MBI { mbi_poly_name = poly_name
, mbi_sig = mb_sig
, mbi_mono_id = mono_id })
= do { mono_ty <- zonkTcType (idType mono_id)
; poly_id <- mkInferredPolyId qtvs theta poly_name mb_sig mono_ty
-- NB: poly_id has a zonked type
; poly_id <- addInlinePrags poly_id prag_sigs
; spec_prags <- tcSpecPrags poly_id prag_sigs
-- tcPrags requires a zonked poly_id
-- See Note [Impedence matching]
-- NB: we have already done checkValidType, including an ambiguity check,
-- on the type; either when we checked the sig or in mkInferredPolyId
; let poly_ty = idType poly_id
sel_poly_ty = mkInvSigmaTy qtvs theta mono_ty
-- This type is just going into tcSubType,
-- so Inv vs. Spec doesn't matter
; wrap <- if sel_poly_ty `eqType` poly_ty -- NB: eqType ignores visibility
then return idHsWrapper -- Fast path; also avoids complaint when we infer
-- an ambiguouse type and have AllowAmbiguousType
-- e..g infer x :: forall a. F a -> Int
else addErrCtxtM (mk_impedence_match_msg mono_info sel_poly_ty poly_ty) $
tcSubType_NC sig_ctxt sel_poly_ty (mkCheckExpType poly_ty)
; warn_missing_sigs <- woptM Opt_WarnMissingLocalSignatures
; when warn_missing_sigs $
localSigWarn Opt_WarnMissingLocalSignatures poly_id mb_sig
; return (ABE { abe_wrap = wrap
-- abe_wrap :: idType poly_id ~ (forall qtvs. theta => mono_ty)
, abe_poly = poly_id
, abe_mono = mono_id
, abe_prags = SpecPrags spec_prags}) }
where
prag_sigs = lookupPragEnv prag_fn poly_name
sig_ctxt = InfSigCtxt poly_name
mkInferredPolyId :: [TyVar] -> TcThetaType
-> Name -> Maybe TcIdSigInst -> TcType
-> TcM TcId
mkInferredPolyId qtvs inferred_theta poly_name mb_sig_inst mono_ty
| Just (TISI { sig_inst_sig = sig }) <- mb_sig_inst
, CompleteSig { sig_bndr = poly_id } <- sig
= return poly_id
| otherwise -- Either no type sig or partial type sig
= checkNoErrs $ -- The checkNoErrs ensures that if the type is ambiguous
-- we don't carry on to the impedence matching, and generate
-- a duplicate ambiguity error. There is a similar
-- checkNoErrs for complete type signatures too.
do { fam_envs <- tcGetFamInstEnvs
; let (_co, mono_ty') = normaliseType fam_envs Nominal mono_ty
-- Unification may not have normalised the type,
-- (see Note [Lazy flattening] in TcFlatten) so do it
-- here to make it as uncomplicated as possible.
-- Example: f :: [F Int] -> Bool
-- should be rewritten to f :: [Char] -> Bool, if possible
--
-- We can discard the coercion _co, because we'll reconstruct
-- it in the call to tcSubType below
; (binders, theta') <- chooseInferredQuantifiers inferred_theta
(tyCoVarsOfType mono_ty') qtvs mb_sig_inst
; let inferred_poly_ty = mkForAllTys binders (mkPhiTy theta' mono_ty')
; traceTc "mkInferredPolyId" (vcat [ppr poly_name, ppr qtvs, ppr theta'
, ppr inferred_poly_ty])
; addErrCtxtM (mk_inf_msg poly_name inferred_poly_ty) $
checkValidType (InfSigCtxt poly_name) inferred_poly_ty
-- See Note [Validity of inferred types]
; return (mkLocalIdOrCoVar poly_name inferred_poly_ty) }
chooseInferredQuantifiers :: TcThetaType -- inferred
-> TcTyVarSet -- tvs free in tau type
-> [TcTyVar] -- inferred quantified tvs
-> Maybe TcIdSigInst
-> TcM ([TcTyBinder], TcThetaType)
chooseInferredQuantifiers inferred_theta tau_tvs qtvs Nothing
= -- No type signature (partial or complete) for this binder,
do { let free_tvs = closeOverKinds (growThetaTyVars inferred_theta tau_tvs)
-- Include kind variables! Trac #7916
my_theta = pickCapturedPreds free_tvs inferred_theta
binders = [ mkNamedBinder Invisible tv
| tv <- qtvs
, tv `elemVarSet` free_tvs ]
; return (binders, my_theta) }
chooseInferredQuantifiers inferred_theta tau_tvs qtvs
(Just (TISI { sig_inst_sig = sig -- Always PartialSig
, sig_inst_wcx = wcx
, sig_inst_theta = annotated_theta
, sig_inst_skols = annotated_tvs }))
| Nothing <- wcx
= do { annotated_theta <- zonkTcTypes annotated_theta
; let free_tvs = closeOverKinds (tyCoVarsOfTypes annotated_theta
`unionVarSet` tau_tvs)
; traceTc "ciq" (vcat [ ppr sig, ppr annotated_theta, ppr free_tvs])
; return (mk_binders free_tvs, annotated_theta) }
| Just wc_var <- wcx
= do { annotated_theta <- zonkTcTypes annotated_theta
; let free_tvs = closeOverKinds (tyCoVarsOfTypes annotated_theta
`unionVarSet` tau_tvs)
my_theta = pickCapturedPreds free_tvs inferred_theta
-- Report the inferred constraints for an extra-constraints wildcard/hole as
-- an error message, unless the PartialTypeSignatures flag is enabled. In this
-- case, the extra inferred constraints are accepted without complaining.
-- NB: inferred_theta already includes all the annotated constraints
inferred_diff = [ pred
| pred <- my_theta
, all (not . (`eqType` pred)) annotated_theta ]
; ctuple <- mk_ctuple inferred_diff
; writeMetaTyVar wc_var ctuple
; traceTc "completeTheta" $
vcat [ ppr sig
, ppr annotated_theta, ppr inferred_theta
, ppr inferred_diff ]
; return (mk_binders free_tvs, my_theta) }
| otherwise -- A complete type signature is dealt with in mkInferredPolyId
= pprPanic "chooseInferredQuantifiers" (ppr sig)
where
spec_tv_set = mkVarSet $ map snd annotated_tvs
mk_binders free_tvs
= [ mkNamedBinder vis tv
| tv <- qtvs
, tv `elemVarSet` free_tvs
, let vis | tv `elemVarSet` spec_tv_set = Specified
| otherwise = Invisible ]
-- Pulling from qtvs maintains original order
mk_ctuple [pred] = return pred
mk_ctuple preds = do { tc <- tcLookupTyCon (cTupleTyConName (length preds))
; return (mkTyConApp tc preds) }
mk_impedence_match_msg :: MonoBindInfo
-> TcType -> TcType
-> TidyEnv -> TcM (TidyEnv, SDoc)
-- This is a rare but rather awkward error messages
mk_impedence_match_msg (MBI { mbi_poly_name = name, mbi_sig = mb_sig })
inf_ty sig_ty tidy_env
= do { (tidy_env1, inf_ty) <- zonkTidyTcType tidy_env inf_ty
; (tidy_env2, sig_ty) <- zonkTidyTcType tidy_env1 sig_ty
; let msg = vcat [ text "When checking that the inferred type"
, nest 2 $ ppr name <+> dcolon <+> ppr inf_ty
, text "is as general as its" <+> what <+> text "signature"
, nest 2 $ ppr name <+> dcolon <+> ppr sig_ty ]
; return (tidy_env2, msg) }
where
what = case mb_sig of
Nothing -> text "inferred"
Just sig | isPartialSig sig -> text "(partial)"
| otherwise -> empty
mk_inf_msg :: Name -> TcType -> TidyEnv -> TcM (TidyEnv, SDoc)
mk_inf_msg poly_name poly_ty tidy_env
= do { (tidy_env1, poly_ty) <- zonkTidyTcType tidy_env poly_ty
; let msg = vcat [ text "When checking the inferred type"
, nest 2 $ ppr poly_name <+> dcolon <+> ppr poly_ty ]
; return (tidy_env1, msg) }
-- | Warn the user about polymorphic local binders that lack type signatures.
localSigWarn :: WarningFlag -> Id -> Maybe TcIdSigInst -> TcM ()
localSigWarn flag id mb_sig
| Just _ <- mb_sig = return ()
| not (isSigmaTy (idType id)) = return ()
| otherwise = warnMissingSignatures flag msg id
where
msg = text "Polymorphic local binding with no type signature:"
warnMissingSignatures :: WarningFlag -> SDoc -> Id -> TcM ()
warnMissingSignatures flag msg id
= do { env0 <- tcInitTidyEnv
; let (env1, tidy_ty) = tidyOpenType env0 (idType id)
; addWarnTcM (Reason flag) (env1, mk_msg tidy_ty) }
where
mk_msg ty = sep [ msg, nest 2 $ pprPrefixName (idName id) <+> dcolon <+> ppr ty ]
checkOverloadedSig :: Bool -> TcIdSigInst -> TcM ()
-- Example:
-- f :: Eq a => a -> a
-- K f = e
-- The MR applies, but the signature is overloaded, and it's
-- best to complain about this directly
-- c.f Trac #11339
checkOverloadedSig monomorphism_restriction_applies sig
| not (null (sig_inst_theta sig))
, monomorphism_restriction_applies
, let orig_sig = sig_inst_sig sig
= setSrcSpan (sig_loc orig_sig) $
failWith $
hang (text "Illegal overloaded signature conflicts with monomorphism restriction")
2 (ppr orig_sig)
| otherwise
= return ()
{- Note [Partial type signatures and generalisation]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
If /any/ of the signatures in the gropu is a partial type signature
f :: _ -> Int
then we *always* use the InferGen plan, and hence tcPolyInfer.
We do this even for a local binding with -XMonoLocalBinds, when
we normally use NoGen.
Reasons:
* The TcSigInfo for 'f' has a unification variable for the '_',
whose TcLevel is one level deeper than the current level.
(See pushTcLevelM in tcTySig.) But NoGen doesn't increase
the TcLevel like InferGen, so we lose the level invariant.
* The signature might be f :: forall a. _ -> a
so it really is polymorphic. It's not clear what it would
mean to use NoGen on this, and indeed the ASSERT in tcLhs,
in the (Just sig) case, checks that if there is a signature
then we are using LetLclBndr, and hence a nested AbsBinds with
increased TcLevel
It might be possible to fix these difficulties somehow, but there
doesn't seem much point. Indeed, adding a partial type signature is a
way to get per-binding inferred generalisation.
We apply the MR if /all/ of the partial signatures lack a context.
In particular (Trac #11016):
f2 :: (?loc :: Int) => _
f2 = ?loc
It's stupid to apply the MR here. This test includes an extra-constraints
wildcard; that is, we don't apply the MR if you write
f3 :: _ => blah
Note [Validity of inferred types]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
We need to check inferred type for validity, in case it uses language
extensions that are not turned on. The principle is that if the user
simply adds the inferred type to the program source, it'll compile fine.
See #8883.
Examples that might fail:
- the type might be ambiguous
- an inferred theta that requires type equalities e.g. (F a ~ G b)
or multi-parameter type classes
- an inferred type that includes unboxed tuples
Note [Impedence matching]
~~~~~~~~~~~~~~~~~~~~~~~~~
Consider
f 0 x = x
f n x = g [] (not x)
g [] y = f 10 y
g _ y = f 9 y
After typechecking we'll get
f_mono_ty :: a -> Bool -> Bool
g_mono_ty :: [b] -> Bool -> Bool
with constraints
(Eq a, Num a)
Note that f is polymorphic in 'a' and g in 'b'; and these are not linked.
The types we really want for f and g are
f :: forall a. (Eq a, Num a) => a -> Bool -> Bool
g :: forall b. [b] -> Bool -> Bool
We can get these by "impedance matching":
tuple :: forall a b. (Eq a, Num a) => (a -> Bool -> Bool, [b] -> Bool -> Bool)
tuple a b d1 d1 = let ...bind f_mono, g_mono in (f_mono, g_mono)
f a d1 d2 = case tuple a Any d1 d2 of (f, g) -> f
g b = case tuple Integer b dEqInteger dNumInteger of (f,g) -> g
Suppose the shared quantified tyvars are qtvs and constraints theta.
Then we want to check that
forall qtvs. theta => f_mono_ty is more polymorphic than f's polytype
and the proof is the impedance matcher.
Notice that the impedance matcher may do defaulting. See Trac #7173.
It also cleverly does an ambiguity check; for example, rejecting
f :: F a -> F a
where F is a non-injective type function.
-}
{- *********************************************************************
* *
Vectorisation
* *
********************************************************************* -}
tcVectDecls :: [LVectDecl Name] -> TcM ([LVectDecl TcId])
tcVectDecls decls
= do { decls' <- mapM (wrapLocM tcVect) decls
; let ids = [lvectDeclName decl | decl <- decls', not $ lvectInstDecl decl]
dups = findDupsEq (==) ids
; mapM_ reportVectDups dups
; traceTcConstraints "End of tcVectDecls"
; return decls'
}
where
reportVectDups (first:_second:_more)
= addErrAt (getSrcSpan first) $
text "Duplicate vectorisation declarations for" <+> ppr first
reportVectDups _ = return ()
--------------
tcVect :: VectDecl Name -> TcM (VectDecl TcId)
-- FIXME: We can't typecheck the expression of a vectorisation declaration against the vectorised
-- type of the original definition as this requires internals of the vectoriser not available
-- during type checking. Instead, constrain the rhs of a vectorisation declaration to be a single
-- identifier (this is checked in 'rnHsVectDecl'). Fix this by enabling the use of 'vectType'
-- from the vectoriser here.
tcVect (HsVect s name rhs)
= addErrCtxt (vectCtxt name) $
do { var <- wrapLocM tcLookupId name
; let L rhs_loc (HsVar (L lv rhs_var_name)) = rhs
; rhs_id <- tcLookupId rhs_var_name
; return $ HsVect s var (L rhs_loc (HsVar (L lv rhs_id)))
}
tcVect (HsNoVect s name)
= addErrCtxt (vectCtxt name) $
do { var <- wrapLocM tcLookupId name
; return $ HsNoVect s var
}
tcVect (HsVectTypeIn _ isScalar lname rhs_name)
= addErrCtxt (vectCtxt lname) $
do { tycon <- tcLookupLocatedTyCon lname
; checkTc ( not isScalar -- either we have a non-SCALAR declaration
|| isJust rhs_name -- or we explicitly provide a vectorised type
|| tyConArity tycon == 0 -- otherwise the type constructor must be nullary
)
scalarTyConMustBeNullary
; rhs_tycon <- fmapMaybeM (tcLookupTyCon . unLoc) rhs_name
; return $ HsVectTypeOut isScalar tycon rhs_tycon
}
tcVect (HsVectTypeOut _ _ _)
= panic "TcBinds.tcVect: Unexpected 'HsVectTypeOut'"
tcVect (HsVectClassIn _ lname)
= addErrCtxt (vectCtxt lname) $
do { cls <- tcLookupLocatedClass lname
; return $ HsVectClassOut cls
}
tcVect (HsVectClassOut _)
= panic "TcBinds.tcVect: Unexpected 'HsVectClassOut'"
tcVect (HsVectInstIn linstTy)
= addErrCtxt (vectCtxt linstTy) $
do { (cls, tys) <- tcHsVectInst linstTy
; inst <- tcLookupInstance cls tys
; return $ HsVectInstOut inst
}
tcVect (HsVectInstOut _)
= panic "TcBinds.tcVect: Unexpected 'HsVectInstOut'"
vectCtxt :: Outputable thing => thing -> SDoc
vectCtxt thing = text "When checking the vectorisation declaration for" <+> ppr thing
scalarTyConMustBeNullary :: MsgDoc
scalarTyConMustBeNullary = text "VECTORISE SCALAR type constructor must be nullary"
{-
Note [SPECIALISE pragmas]
~~~~~~~~~~~~~~~~~~~~~~~~~
There is no point in a SPECIALISE pragma for a non-overloaded function:
reverse :: [a] -> [a]
{-# SPECIALISE reverse :: [Int] -> [Int] #-}
But SPECIALISE INLINE *can* make sense for GADTS:
data Arr e where
ArrInt :: !Int -> ByteArray# -> Arr Int
ArrPair :: !Int -> Arr e1 -> Arr e2 -> Arr (e1, e2)
(!:) :: Arr e -> Int -> e
{-# SPECIALISE INLINE (!:) :: Arr Int -> Int -> Int #-}
{-# SPECIALISE INLINE (!:) :: Arr (a, b) -> Int -> (a, b) #-}
(ArrInt _ ba) !: (I# i) = I# (indexIntArray# ba i)
(ArrPair _ a1 a2) !: i = (a1 !: i, a2 !: i)
When (!:) is specialised it becomes non-recursive, and can usefully
be inlined. Scary! So we only warn for SPECIALISE *without* INLINE
for a non-overloaded function.
************************************************************************
* *
tcMonoBinds
* *
************************************************************************
@tcMonoBinds@ deals with a perhaps-recursive group of HsBinds.
The signatures have been dealt with already.
Note [Pattern bindings]
~~~~~~~~~~~~~~~~~~~~~~~
The rule for typing pattern bindings is this:
..sigs..
p = e
where 'p' binds v1..vn, and 'e' may mention v1..vn,
typechecks exactly like
..sigs..
x = e -- Inferred type
v1 = case x of p -> v1
..
vn = case x of p -> vn
Note that
(f :: forall a. a -> a) = id
should not typecheck because
case id of { (f :: forall a. a->a) -> f }
will not typecheck.
Note [Instantiate when inferring a type]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Consider
f = (*)
As there is no incentive to instantiate the RHS, tcMonoBinds will
produce a type of forall a. Num a => a -> a -> a for `f`. This will then go
through simplifyInfer and such, remaining unchanged.
There are two problems with this:
1) If the definition were `g _ = (*)`, we get a very unusual type of
`forall {a}. a -> forall b. Num b => b -> b -> b` for `g`. This is
surely confusing for users.
2) The monomorphism restriction can't work. The MR is dealt with in
simplifyInfer, and simplifyInfer has no way of instantiating. This
could perhaps be worked around, but it may be hard to know even
when instantiation should happen.
There is an easy solution to both problems: instantiate (deeply) when
inferring a type. So that's what we do. Note that this decision is
user-facing.
We do this deep instantiation in tcMonoBinds, in the FunBind case
only, and only when we do not have a type signature. Conveniently,
the fun_co_fn field of FunBind gives a place to record the coercion.
We do not need to do this
* for PatBinds, because we don't have a function type
* for FunBinds where we have a signature, bucause we aren't doing inference
-}
data MonoBindInfo = MBI { mbi_poly_name :: Name
, mbi_sig :: Maybe TcIdSigInst
, mbi_mono_id :: TcId }
tcMonoBinds :: RecFlag -- Whether the binding is recursive for typechecking purposes
-- i.e. the binders are mentioned in their RHSs, and
-- we are not rescued by a type signature
-> TcSigFun -> LetBndrSpec
-> [LHsBind Name]
-> TcM (LHsBinds TcId, [MonoBindInfo])
tcMonoBinds is_rec sig_fn no_gen
[ L b_loc (FunBind { fun_id = L nm_loc name,
fun_matches = matches, bind_fvs = fvs })]
-- Single function binding,
| NonRecursive <- is_rec -- ...binder isn't mentioned in RHS
, Nothing <- sig_fn name -- ...with no type signature
= -- In this very special case we infer the type of the
-- right hand side first (it may have a higher-rank type)
-- and *then* make the monomorphic Id for the LHS
-- e.g. f = \(x::forall a. a->a) -> <body>
-- We want to infer a higher-rank type for f
setSrcSpan b_loc $
do { rhs_ty <- newOpenInferExpType
; (co_fn, matches')
<- tcExtendIdBndrs [TcIdBndr_ExpType name rhs_ty NotTopLevel] $
-- We extend the error context even for a non-recursive
-- function so that in type error messages we show the
-- type of the thing whose rhs we are type checking
tcMatchesFun (L nm_loc name) matches rhs_ty
; rhs_ty <- readExpType rhs_ty
-- Deeply instantiate the inferred type
-- See Note [Instantiate when inferring a type]
; let orig = matchesCtOrigin matches
; rhs_ty <- zonkTcType rhs_ty -- NB: zonk to uncover any foralls
; (inst_wrap, rhs_ty) <- addErrCtxtM (instErrCtxt name rhs_ty) $
deeplyInstantiate orig rhs_ty
; mono_id <- newLetBndr no_gen name rhs_ty
; return (unitBag $ L b_loc $
FunBind { fun_id = L nm_loc mono_id,
fun_matches = matches', bind_fvs = fvs,
fun_co_fn = inst_wrap <.> co_fn, fun_tick = [] },
[MBI { mbi_poly_name = name
, mbi_sig = Nothing
, mbi_mono_id = mono_id }]) }
tcMonoBinds _ sig_fn no_gen binds
= do { tc_binds <- mapM (wrapLocM (tcLhs sig_fn no_gen)) binds
-- Bring the monomorphic Ids, into scope for the RHSs
; let mono_infos = getMonoBindInfo tc_binds
rhs_id_env = [ (name, mono_id)
| MBI { mbi_poly_name = name
, mbi_sig = mb_sig
, mbi_mono_id = mono_id } <- mono_infos
, case mb_sig of
Just sig -> isPartialSig sig
Nothing -> True ]
-- A monomorphic binding for each term variable that lacks
-- a complete type sig. (Ones with a sig are already in scope.)
; traceTc "tcMonoBinds" $ vcat [ ppr n <+> ppr id <+> ppr (idType id)
| (n,id) <- rhs_id_env]
; binds' <- tcExtendLetEnvIds NotTopLevel rhs_id_env $
mapM (wrapLocM tcRhs) tc_binds
; return (listToBag binds', mono_infos) }
------------------------
-- tcLhs typechecks the LHS of the bindings, to construct the environment in which
-- we typecheck the RHSs. Basically what we are doing is this: for each binder:
-- if there's a signature for it, use the instantiated signature type
-- otherwise invent a type variable
-- You see that quite directly in the FunBind case.
--
-- But there's a complication for pattern bindings:
-- data T = MkT (forall a. a->a)
-- MkT f = e
-- Here we can guess a type variable for the entire LHS (which will be refined to T)
-- but we want to get (f::forall a. a->a) as the RHS environment.
-- The simplest way to do this is to typecheck the pattern, and then look up the
-- bound mono-ids. Then we want to retain the typechecked pattern to avoid re-doing
-- it; hence the TcMonoBind data type in which the LHS is done but the RHS isn't
data TcMonoBind -- Half completed; LHS done, RHS not done
= TcFunBind MonoBindInfo SrcSpan (MatchGroup Name (LHsExpr Name))
| TcPatBind [MonoBindInfo] (LPat TcId) (GRHSs Name (LHsExpr Name)) TcSigmaType
tcLhs :: TcSigFun -> LetBndrSpec -> HsBind Name -> TcM TcMonoBind
tcLhs sig_fn no_gen (FunBind { fun_id = L nm_loc name, fun_matches = matches })
= do { mono_info <- tcLhsId sig_fn no_gen name
; return (TcFunBind mono_info nm_loc matches) }
tcLhs sig_fn no_gen (PatBind { pat_lhs = pat, pat_rhs = grhss })
= do { let bndr_names = collectPatBinders pat
; mbis <- mapM (tcLhsId sig_fn no_gen) bndr_names
-- See Note [Existentials in pattern bindings]
; let inst_sig_fun = lookupNameEnv $ mkNameEnv $
bndr_names `zip` map mbi_mono_id mbis
; traceTc "tcLhs" (vcat [ ppr id <+> dcolon <+> ppr (idType id)
| mbi <- mbis, let id = mbi_mono_id mbi ]
$$ ppr no_gen)
; ((pat', _), pat_ty) <- addErrCtxt (patMonoBindsCtxt pat grhss) $
tcInfer $ \ exp_ty ->
tcLetPat inst_sig_fun pat exp_ty $
return () -- mapM (lookup_info inst_sig_fun) bndr_names
; return (TcPatBind mbis pat' grhss pat_ty) }
tcLhs _ _ other_bind = pprPanic "tcLhs" (ppr other_bind)
-- AbsBind, VarBind impossible
-------------------
data LetBndrSpec
= LetLclBndr -- We are going to generalise, and wrap in an AbsBinds
-- so clone a fresh binder for the local monomorphic Id
| LetGblBndr TcPragEnv -- Generalisation plan is NoGen, so there isn't going
-- to be an AbsBinds; So we must bind the global version
-- of the binder right away.
-- And here is the inline-pragma information
instance Outputable LetBndrSpec where
ppr LetLclBndr = text "LetLclBndr"
ppr (LetGblBndr {}) = text "LetGblBndr"
tcLhsId :: TcSigFun -> LetBndrSpec -> Name -> TcM MonoBindInfo
tcLhsId sig_fn no_gen name
| Just (TcIdSig sig) <- sig_fn name
= -- A partial type signature on a FunBind, in a mixed group
-- e.g. f :: _ -> _
-- f x = ...g...
-- Just g = ...f...
-- Hence always typechecked with InferGen; hence LetLclBndr
--
-- A compelete type sig on a FunBind is checked with CheckGen
-- and does not go via tcLhsId
do { inst_sig <- tcInstSig sig
; the_id <- newSigLetBndr no_gen name inst_sig
; return (MBI { mbi_poly_name = name
, mbi_sig = Just inst_sig
, mbi_mono_id = the_id }) }
| otherwise
= -- No type signature, plan InferGen (LetLclBndr) or NoGen (LetGblBndr)
do { mono_ty <- newOpenFlexiTyVarTy
; mono_id <- newLetBndr no_gen name mono_ty
; return (MBI { mbi_poly_name = name
, mbi_sig = Nothing
, mbi_mono_id = mono_id }) }
------------
newSigLetBndr :: LetBndrSpec -> Name -> TcIdSigInst -> TcM TcId
newSigLetBndr (LetGblBndr prags) name (TISI { sig_inst_sig = id_sig })
| CompleteSig { sig_bndr = poly_id } <- id_sig
= addInlinePrags poly_id (lookupPragEnv prags name)
newSigLetBndr no_gen name (TISI { sig_inst_tau = tau })
= newLetBndr no_gen name tau
newLetBndr :: LetBndrSpec -> Name -> TcType -> TcM TcId
-- In the polymorphic case when we are going to generalise
-- (plan InferGen, no_gen = LetLclBndr), generate a "monomorphic version"
-- of the Id; the original name will be bound to the polymorphic version
-- by the AbsBinds
-- In the monomorphic case when we are not going to generalise
-- (plan NoGen, no_gen = LetGblBndr) there is no AbsBinds,
-- and we use the original name directly
newLetBndr LetLclBndr name ty
= do { mono_name <- cloneLocalName name
; return (mkLocalId mono_name ty) }
newLetBndr (LetGblBndr prags) name ty
= addInlinePrags (mkLocalId name ty) (lookupPragEnv prags name)
-------------------
tcRhs :: TcMonoBind -> TcM (HsBind TcId)
tcRhs (TcFunBind info@(MBI { mbi_sig = mb_sig, mbi_mono_id = mono_id })
loc matches)
= tcExtendIdBinderStackForRhs [info] $
tcExtendTyVarEnvForRhs mb_sig $
do { traceTc "tcRhs: fun bind" (ppr mono_id $$ ppr (idType mono_id))
; (co_fn, matches') <- tcMatchesFun (L loc (idName mono_id))
matches (mkCheckExpType $ idType mono_id)
; return ( FunBind { fun_id = L loc mono_id
, fun_matches = matches'
, fun_co_fn = co_fn
, bind_fvs = placeHolderNamesTc
, fun_tick = [] } ) }
tcRhs (TcPatBind infos pat' grhss pat_ty)
= -- When we are doing pattern bindings we *don't* bring any scoped
-- type variables into scope unlike function bindings
-- Wny not? They are not completely rigid.
-- That's why we have the special case for a single FunBind in tcMonoBinds
tcExtendIdBinderStackForRhs infos $
do { traceTc "tcRhs: pat bind" (ppr pat' $$ ppr pat_ty)
; grhss' <- addErrCtxt (patMonoBindsCtxt pat' grhss) $
tcGRHSsPat grhss pat_ty
; return ( PatBind { pat_lhs = pat', pat_rhs = grhss'
, pat_rhs_ty = pat_ty
, bind_fvs = placeHolderNamesTc
, pat_ticks = ([],[]) } )}
tcExtendTyVarEnvForRhs :: Maybe TcIdSigInst -> TcM a -> TcM a
tcExtendTyVarEnvForRhs Nothing thing_inside
= thing_inside
tcExtendTyVarEnvForRhs (Just sig) thing_inside
= tcExtendTyVarEnvFromSig sig thing_inside
tcExtendTyVarEnvFromSig :: TcIdSigInst -> TcM a -> TcM a
tcExtendTyVarEnvFromSig sig_inst thing_inside
| TISI { sig_inst_skols = skol_prs, sig_inst_wcs = wcs } <- sig_inst
= tcExtendTyVarEnv2 wcs $
tcExtendTyVarEnv2 skol_prs $
thing_inside
tcExtendIdBinderStackForRhs :: [MonoBindInfo] -> TcM a -> TcM a
-- Extend the TcIdBinderStack for the RHS of the binding, with
-- the monomorphic Id. That way, if we have, say
-- f = \x -> blah
-- and something goes wrong in 'blah', we get a "relevant binding"
-- looking like f :: alpha -> beta
-- This applies if 'f' has a type signature too:
-- f :: forall a. [a] -> [a]
-- f x = True
-- We can't unify True with [a], and a relevant binding is f :: [a] -> [a]
-- If we had the *polymorphic* version of f in the TcIdBinderStack, it
-- would not be reported as relevant, because its type is closed
tcExtendIdBinderStackForRhs infos thing_inside
= tcExtendIdBndrs [ TcIdBndr mono_id NotTopLevel
| MBI { mbi_mono_id = mono_id } <- infos ]
thing_inside
-- NotTopLevel: it's a monomorphic binding
---------------------
getMonoBindInfo :: [Located TcMonoBind] -> [MonoBindInfo]
getMonoBindInfo tc_binds
= foldr (get_info . unLoc) [] tc_binds
where
get_info (TcFunBind info _ _) rest = info : rest
get_info (TcPatBind infos _ _ _) rest = infos ++ rest
{- Note [Existentials in pattern bindings]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Consider (typecheck/should_compile/ExPat):
data T where
MkT :: Integral a => a -> Int -> T
and suppose t :: T. Which of these pattern bindings are ok?
E1. let { MkT p _ = t } in <body>
E2. let { MkT _ q = t } in <body>
E3. let { MkT (toInteger -> r) _ = t } in <body>
Well (E1) is clearly wrong becuase the existential 'a' escapes.
What type could 'p' possibly have?
But (E2) is fine, despite the existential pattern, because
q::Int, and nothing escapes.
Even (E3) is fine. The existential pattern binds a dictionary
for (Integral a) which the view pattern can use to convert the
a-valued field to an Integer, so r :: Integer.
An easy way to see all three is to imagine the desugaring.
For (2) it would look like
let q = case t of MkT _ q' -> q'
in <body>
We typecheck pattern bindings as follows:
1. In tcLhs we bind q'::alpha, for each varibable q bound by the
pattern, where q' is a fresh name, and alpha is a fresh
unification variable; it will be the monomorphic verion of q that
we later generalise
It's very important that these fresh unification variables
alpha are born here, not deep under implications as would happen
if we allocated them when we encountered q during tcPat.
2. Still in tcLhs, we build a little environment mappting "q" ->
q':alpha, and pass that to tcLetPet.
3. Then tcLhs invokes tcLetPat to typecheck the patter as usual:
- When tcLetPat finds an existential constructor, it binds fresh
type variables and dictionaries as usual, and emits an
implication constraint.
- When tcLetPat finds a variable (TcPat.tcPatBndr) it looks it up
in the little environment, which should always succeed. And
uses tcSubTypeET to connect the type of that variable with the
expected type of the pattern.
And that's it! The implication constraints check for the skolem
escape. It's quite simple and neat, and more exressive than before
e.g. GHC 8.0 rejects (E2) and (E3).
************************************************************************
* *
Generalisation
* *
********************************************************************* -}
data GeneralisationPlan
= NoGen -- No generalisation, no AbsBinds
| InferGen -- Implicit generalisation; there is an AbsBinds
Bool -- True <=> apply the MR; generalise only unconstrained type vars
| CheckGen (LHsBind Name) TcIdSigInfo
-- One FunBind with a signature
-- Explicit generalisation; there is an AbsBindsSig
-- A consequence of the no-AbsBinds choice (NoGen) is that there is
-- no "polymorphic Id" and "monmomorphic Id"; there is just the one
instance Outputable GeneralisationPlan where
ppr NoGen = text "NoGen"
ppr (InferGen b) = text "InferGen" <+> ppr b
ppr (CheckGen _ s) = text "CheckGen" <+> ppr s
decideGeneralisationPlan
:: DynFlags -> [LHsBind Name] -> IsGroupClosed -> TcSigFun
-> GeneralisationPlan
decideGeneralisationPlan dflags lbinds closed sig_fn
| unlifted_pat_binds = NoGen
| has_partial_sigs = InferGen (and partial_sig_mrs)
| Just (bind, sig) <- one_funbind_with_sig = CheckGen bind sig
| mono_local_binds closed = NoGen
| otherwise = InferGen mono_restriction
where
binds = map unLoc lbinds
partial_sig_mrs :: [Bool]
-- One for each parital signature (so empty => no partial sigs)
-- The Bool is True if the signature has no constraint context
-- so we should apply the MR
-- See Note [Partial type signatures and generalisation]
partial_sig_mrs
= [ null theta
| TcIdSig (PartialSig { psig_hs_ty = hs_ty })
<- mapMaybe sig_fn (collectHsBindListBinders lbinds)
, let (_, L _ theta, _) = splitLHsSigmaTy (hsSigWcType hs_ty) ]
has_partial_sigs = not (null partial_sig_mrs)
unlifted_pat_binds = any isUnliftedHsBind binds
-- Unlifted patterns (unboxed tuple) must not
-- be polymorphic, because we are going to force them
-- See Trac #4498, #8762
mono_restriction = xopt LangExt.MonomorphismRestriction dflags
&& any restricted binds
mono_local_binds ClosedGroup = False
mono_local_binds _ = xopt LangExt.MonoLocalBinds dflags
-- With OutsideIn, all nested bindings are monomorphic
-- except a single function binding with a signature
one_funbind_with_sig
| [lbind@(L _ (FunBind { fun_id = v }))] <- lbinds
, Just (TcIdSig sig) <- sig_fn (unLoc v)
= Just (lbind, sig)
| otherwise
= Nothing
-- The Haskell 98 monomorphism restriction
restricted (PatBind {}) = True
restricted (VarBind { var_id = v }) = no_sig v
restricted (FunBind { fun_id = v, fun_matches = m }) = restricted_match m
&& no_sig (unLoc v)
restricted (PatSynBind {}) = panic "isRestrictedGroup/unrestricted PatSynBind"
restricted (AbsBinds {}) = panic "isRestrictedGroup/unrestricted AbsBinds"
restricted (AbsBindsSig {}) = panic "isRestrictedGroup/unrestricted AbsBindsSig"
restricted_match (MG { mg_alts = L _ (L _ (Match _ [] _ _) : _ )}) = True
restricted_match _ = False
-- No args => like a pattern binding
-- Some args => a function binding
no_sig n = noCompleteSig (sig_fn n)
isClosedBndrGroup :: Bag (LHsBind Name) -> TcM IsGroupClosed
isClosedBndrGroup binds = do
type_env <- getLclTypeEnv
if foldUFM (is_closed_ns type_env) True fv_env
then return ClosedGroup
else return $ NonClosedGroup fv_env
where
fv_env :: NameEnv NameSet
fv_env = mkNameEnv $ concatMap (bindFvs . unLoc) binds
bindFvs :: HsBindLR Name idR -> [(Name, NameSet)]
bindFvs (FunBind { fun_id = f, bind_fvs = fvs })
= [(unLoc f, fvs)]
bindFvs (PatBind { pat_lhs = pat, bind_fvs = fvs })
= [(b, fvs) | b <- collectPatBinders pat]
bindFvs _
= []
is_closed_ns :: TcTypeEnv -> NameSet -> Bool -> Bool
is_closed_ns type_env ns b = b && nameSetAll (is_closed_id type_env) ns
-- ns are the Names referred to from the RHS of this bind
is_closed_id :: TcTypeEnv -> Name -> Bool
-- See Note [Bindings with closed types] in TcRnTypes
is_closed_id type_env name
| Just thing <- lookupNameEnv type_env name
= case thing of
ATcId { tct_info = ClosedLet } -> True -- This is the key line
ATcId {} -> False
ATyVar {} -> False -- In-scope type variables
AGlobal {} -> True -- are not closed!
_ -> pprPanic "is_closed_id" (ppr name)
| otherwise
= True
-- The free-var set for a top level binding mentions
-- imported things too, so that we can report unused imports
-- These won't be in the local type env.
-- Ditto class method etc from the current module
-------------------
checkStrictBinds :: TopLevelFlag -> RecFlag
-> [LHsBind Name]
-> LHsBinds TcId -> [Id]
-> TcM ()
-- Check that non-overloaded unlifted bindings are
-- a) non-recursive,
-- b) not top level,
-- c) not a multiple-binding group (more or less implied by (a))
checkStrictBinds top_lvl rec_group orig_binds tc_binds poly_ids
| any_unlifted_bndr || any_strict_pat -- This binding group must be matched strictly
= do { check (isNotTopLevel top_lvl)
(strictBindErr "Top-level" any_unlifted_bndr orig_binds)
; check (isNonRec rec_group)
(strictBindErr "Recursive" any_unlifted_bndr orig_binds)
; check (all is_monomorphic (bagToList tc_binds))
(polyBindErr orig_binds)
-- data Ptr a = Ptr Addr#
-- f x = let p@(Ptr y) = ... in ...
-- Here the binding for 'p' is polymorphic, but does
-- not mix with an unlifted binding for 'y'. You should
-- use a bang pattern. Trac #6078.
; check (isSingleton orig_binds)
(strictBindErr "Multiple" any_unlifted_bndr orig_binds)
-- Complain about a binding that looks lazy
-- e.g. let I# y = x in ...
-- Remember, in checkStrictBinds we are going to do strict
-- matching, so (for software engineering reasons) we insist
-- that the strictness is manifest on each binding
-- However, lone (unboxed) variables are ok
; check (not any_pat_looks_lazy)
(unliftedMustBeBang orig_binds) }
| otherwise
= traceTc "csb2" (ppr [(id, idType id) | id <- poly_ids]) >>
return ()
where
any_unlifted_bndr = any is_unlifted poly_ids
any_strict_pat = any (isUnliftedHsBind . unLoc) orig_binds
any_pat_looks_lazy = any (looksLazyPatBind . unLoc) orig_binds
is_unlifted id = case tcSplitSigmaTy (idType id) of
(_, _, rho) -> isUnliftedType rho
-- For the is_unlifted check, we need to look inside polymorphism
-- and overloading. E.g. x = (# 1, True #)
-- would get type forall a. Num a => (# a, Bool #)
-- and we want to reject that. See Trac #9140
is_monomorphic (L _ (AbsBinds { abs_tvs = tvs, abs_ev_vars = evs }))
= null tvs && null evs
is_monomorphic (L _ (AbsBindsSig { abs_tvs = tvs, abs_ev_vars = evs }))
= null tvs && null evs
is_monomorphic _ = True
check :: Bool -> MsgDoc -> TcM ()
-- Just like checkTc, but with a special case for module GHC.Prim:
-- see Note [Compiling GHC.Prim]
check True _ = return ()
check False err = do { mod <- getModule
; checkTc (mod == gHC_PRIM) err }
unliftedMustBeBang :: [LHsBind Name] -> SDoc
unliftedMustBeBang binds
= hang (text "Pattern bindings containing unlifted types should use an outermost bang pattern:")
2 (vcat (map ppr binds))
polyBindErr :: [LHsBind Name] -> SDoc
polyBindErr binds
= hang (text "You can't mix polymorphic and unlifted bindings")
2 (vcat [vcat (map ppr binds),
text "Probable fix: add a type signature"])
strictBindErr :: String -> Bool -> [LHsBind Name] -> SDoc
strictBindErr flavour any_unlifted_bndr binds
= hang (text flavour <+> msg <+> text "aren't allowed:")
2 (vcat (map ppr binds))
where
msg | any_unlifted_bndr = text "bindings for unlifted types"
| otherwise = text "bang-pattern or unboxed-tuple bindings"
{- Note [Compiling GHC.Prim]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Module GHC.Prim has no source code: it is the host module for
primitive, built-in functions and types. However, for Haddock-ing
purposes we generate (via utils/genprimopcode) a fake source file
GHC/Prim.hs, and give it to Haddock, so that it can generate
documentation. It contains definitions like
nullAddr# :: NullAddr#
which would normally be rejected as a top-level unlifted binding. But
we don't want to complain, because we are only "compiling" this fake
mdule for documentation purposes. Hence this hacky test for gHC_PRIM
in checkStrictBinds.
(We only make the test if things look wrong, so there is no cost in
the common case.) -}
{- *********************************************************************
* *
Error contexts and messages
* *
********************************************************************* -}
-- This one is called on LHS, when pat and grhss are both Name
-- and on RHS, when pat is TcId and grhss is still Name
patMonoBindsCtxt :: (OutputableBndrId id, Outputable body)
=> LPat id -> GRHSs Name body -> SDoc
patMonoBindsCtxt pat grhss
= hang (text "In a pattern binding:") 2 (pprPatBind pat grhss)
instErrCtxt :: Name -> TcType -> TidyEnv -> TcM (TidyEnv, SDoc)
instErrCtxt name ty env
= do { let (env', ty') = tidyOpenType env ty
; return (env', hang (text "When instantiating" <+> quotes (ppr name) <>
text ", initially inferred to have" $$
text "this overly-general type:")
2 (ppr ty') $$
extra) }
where
extra = sdocWithDynFlags $ \dflags ->
ppWhen (xopt LangExt.MonomorphismRestriction dflags) $
text "NB: This instantiation can be caused by the" <+>
text "monomorphism restriction."
|