Split up RnEnv into 4 modules, RnUnbound, RnUtils and RnFixity
[ghc.git] / compiler / typecheck / TcRnTypes.hs
1 {-
2 (c) The University of Glasgow 2006-2012
3 (c) The GRASP Project, Glasgow University, 1992-2002
4
5
6 Various types used during typechecking, please see TcRnMonad as well for
7 operations on these types. You probably want to import it, instead of this
8 module.
9
10 All the monads exported here are built on top of the same IOEnv monad. The
11 monad functions like a Reader monad in the way it passes the environment
12 around. This is done to allow the environment to be manipulated in a stack
13 like fashion when entering expressions... ect.
14
15 For state that is global and should be returned at the end (e.g not part
16 of the stack mechanism), you should use an TcRef (= IORef) to store them.
17 -}
18
19 {-# LANGUAGE CPP, ExistentialQuantification, GeneralizedNewtypeDeriving,
20 ViewPatterns #-}
21
22 module TcRnTypes(
23 TcRnIf, TcRn, TcM, RnM, IfM, IfL, IfG, -- The monad is opaque outside this module
24 TcRef,
25
26 -- The environment types
27 Env(..),
28 TcGblEnv(..), TcLclEnv(..),
29 IfGblEnv(..), IfLclEnv(..),
30 tcVisibleOrphanMods,
31
32 -- Frontend types (shouldn't really be here)
33 FrontendResult(..),
34
35 -- Renamer types
36 ErrCtxt, RecFieldEnv,
37 ImportAvails(..), emptyImportAvails, plusImportAvails,
38 WhereFrom(..), mkModDeps,
39
40 -- Typechecker types
41 TcTypeEnv, TcIdBinderStack, TcIdBinder(..),
42 TcTyThing(..), PromotionErr(..),
43 IdBindingInfo(..),
44 IsGroupClosed(..),
45 SelfBootInfo(..),
46 pprTcTyThingCategory, pprPECategory, CompleteMatch(..),
47
48 -- Desugaring types
49 DsM, DsLclEnv(..), DsGblEnv(..), PArrBuiltin(..),
50 DsMetaEnv, DsMetaVal(..), CompleteMatchMap,
51 mkCompleteMatchMap, extendCompleteMatchMap,
52
53 -- Template Haskell
54 ThStage(..), SpliceType(..), PendingStuff(..),
55 topStage, topAnnStage, topSpliceStage,
56 ThLevel, impLevel, outerLevel, thLevel,
57 ForeignSrcLang(..),
58
59 -- Arrows
60 ArrowCtxt(..),
61
62 -- TcSigInfo
63 TcSigInfo(..), TcIdSigInfo(..),
64 TcIdSigInst(..), TcPatSynInfo(..),
65 isPartialSig,
66
67 -- Canonical constraints
68 Xi, Ct(..), Cts, emptyCts, andCts, andManyCts, pprCts,
69 singleCt, listToCts, ctsElts, consCts, snocCts, extendCtsList,
70 isEmptyCts, isCTyEqCan, isCFunEqCan,
71 isPendingScDict, superClassesMightHelp,
72 isCDictCan_Maybe, isCFunEqCan_maybe,
73 isCIrredEvCan, isCNonCanonical, isWantedCt, isDerivedCt,
74 isGivenCt, isHoleCt, isOutOfScopeCt, isExprHoleCt, isTypeHoleCt,
75 isUserTypeErrorCt, getUserTypeErrorMsg,
76 ctEvidence, ctLoc, setCtLoc, ctPred, ctFlavour, ctEqRel, ctOrigin,
77 mkTcEqPredLikeEv,
78 mkNonCanonical, mkNonCanonicalCt, mkGivens,
79 ctEvPred, ctEvLoc, ctEvOrigin, ctEvEqRel,
80 ctEvTerm, ctEvCoercion, ctEvId,
81 tyCoVarsOfCt, tyCoVarsOfCts,
82 tyCoVarsOfCtList, tyCoVarsOfCtsList,
83
84 WantedConstraints(..), insolubleWC, emptyWC, isEmptyWC,
85 andWC, unionsWC, mkSimpleWC, mkImplicWC,
86 addInsols, getInsolubles, insolublesOnly, addSimples, addImplics,
87 tyCoVarsOfWC, dropDerivedWC, dropDerivedSimples, dropDerivedInsols,
88 tyCoVarsOfWCList,
89 isDroppableDerivedLoc, insolubleImplic,
90 arisesFromGivens,
91
92 Implication(..), ImplicStatus(..), isInsolubleStatus, isSolvedStatus,
93 SubGoalDepth, initialSubGoalDepth, maxSubGoalDepth,
94 bumpSubGoalDepth, subGoalDepthExceeded,
95 CtLoc(..), ctLocSpan, ctLocEnv, ctLocLevel, ctLocOrigin,
96 ctLocTypeOrKind_maybe,
97 ctLocDepth, bumpCtLocDepth,
98 setCtLocOrigin, setCtLocEnv, setCtLocSpan,
99 CtOrigin(..), exprCtOrigin, lexprCtOrigin, matchesCtOrigin, grhssCtOrigin,
100 ErrorThing(..), mkErrorThing, errorThingNumArgs_maybe,
101 TypeOrKind(..), isTypeLevel, isKindLevel,
102 pprCtOrigin, pprCtLoc,
103 pushErrCtxt, pushErrCtxtSameOrigin,
104
105 SkolemInfo(..), pprSigSkolInfo, pprSkolInfo,
106 termEvidenceAllowed,
107
108 CtEvidence(..), TcEvDest(..),
109 mkGivenLoc, mkKindLoc, toKindLoc,
110 isWanted, isGiven, isDerived, isGivenOrWDeriv,
111 ctEvRole,
112
113 -- Constraint solver plugins
114 TcPlugin(..), TcPluginResult(..), TcPluginSolver,
115 TcPluginM, runTcPluginM, unsafeTcPluginTcM,
116 getEvBindsTcPluginM,
117
118 CtFlavour(..), ShadowInfo(..), ctEvFlavour,
119 CtFlavourRole, ctEvFlavourRole, ctFlavourRole,
120 eqCanRewriteFR, eqMayRewriteFR,
121 eqCanDischarge,
122 funEqCanDischarge, funEqCanDischargeF,
123
124 -- Pretty printing
125 pprEvVarTheta,
126 pprEvVars, pprEvVarWithType,
127
128 -- Misc other types
129 TcId, TcIdSet,
130 Hole(..), holeOcc,
131 NameShape(..),
132
133 -- Role annotations
134 RoleAnnotEnv, emptyRoleAnnotEnv, mkRoleAnnotEnv,
135 lookupRoleAnnot, getRoleAnnots,
136
137 ) where
138
139 #include "HsVersions.h"
140
141 import HsSyn
142 import CoreSyn
143 import HscTypes
144 import TcEvidence
145 import Type
146 import Class ( Class )
147 import TyCon ( TyCon )
148 import Coercion ( Coercion, mkHoleCo )
149 import ConLike ( ConLike(..) )
150 import DataCon ( DataCon, dataConUserType, dataConOrigArgTys )
151 import PatSyn ( PatSyn, pprPatSynType )
152 import Id ( idType, idName )
153 import FieldLabel ( FieldLabel )
154 import TcType
155 import Annotations
156 import InstEnv
157 import FamInstEnv
158 import PmExpr
159 import IOEnv
160 import RdrName
161 import Name
162 import NameEnv
163 import NameSet
164 import Avail
165 import Var
166 import FV
167 import VarEnv
168 import Module
169 import SrcLoc
170 import VarSet
171 import ErrUtils
172 import UniqDFM
173 import UniqSupply
174 import BasicTypes
175 import Bag
176 import DynFlags
177 import Outputable
178 import ListSetOps
179 import FastString
180 import qualified GHC.LanguageExtensions as LangExt
181 import Fingerprint
182 import Util
183 import PrelNames ( isUnboundName )
184
185 import Control.Monad (ap, liftM, msum)
186 #if __GLASGOW_HASKELL__ > 710
187 import qualified Control.Monad.Fail as MonadFail
188 #endif
189 import Data.Set ( Set )
190 import qualified Data.Set as S
191
192 import Data.Map ( Map )
193 import Data.Dynamic ( Dynamic )
194 import Data.Typeable ( TypeRep )
195 import Data.Maybe ( mapMaybe )
196 import GHCi.Message
197 import GHCi.RemoteTypes
198
199 import qualified Language.Haskell.TH as TH
200
201 -- | A 'NameShape' is a substitution on 'Name's that can be used
202 -- to refine the identities of a hole while we are renaming interfaces
203 -- (see 'RnModIface'). Specifically, a 'NameShape' for
204 -- 'ns_module_name' @A@, defines a mapping from @{A.T}@
205 -- (for some 'OccName' @T@) to some arbitrary other 'Name'.
206 --
207 -- The most intruiging thing about a 'NameShape', however, is
208 -- how it's constructed. A 'NameShape' is *implied* by the
209 -- exported 'AvailInfo's of the implementor of an interface:
210 -- if an implementor of signature @<H>@ exports @M.T@, you implicitly
211 -- define a substitution from @{H.T}@ to @M.T@. So a 'NameShape'
212 -- is computed from the list of 'AvailInfo's that are exported
213 -- by the implementation of a module, or successively merged
214 -- together by the export lists of signatures which are joining
215 -- together.
216 --
217 -- It's not the most obvious way to go about doing this, but it
218 -- does seem to work!
219 --
220 -- NB: Can't boot this and put it in NameShape because then we
221 -- start pulling in too many DynFlags things.
222 data NameShape = NameShape {
223 ns_mod_name :: ModuleName,
224 ns_exports :: [AvailInfo],
225 ns_map :: OccEnv Name
226 }
227
228
229 {-
230 ************************************************************************
231 * *
232 Standard monad definition for TcRn
233 All the combinators for the monad can be found in TcRnMonad
234 * *
235 ************************************************************************
236
237 The monad itself has to be defined here, because it is mentioned by ErrCtxt
238 -}
239
240 type TcRnIf a b = IOEnv (Env a b)
241 type TcRn = TcRnIf TcGblEnv TcLclEnv -- Type inference
242 type IfM lcl = TcRnIf IfGblEnv lcl -- Iface stuff
243 type IfG = IfM () -- Top level
244 type IfL = IfM IfLclEnv -- Nested
245 type DsM = TcRnIf DsGblEnv DsLclEnv -- Desugaring
246
247 -- TcRn is the type-checking and renaming monad: the main monad that
248 -- most type-checking takes place in. The global environment is
249 -- 'TcGblEnv', which tracks all of the top-level type-checking
250 -- information we've accumulated while checking a module, while the
251 -- local environment is 'TcLclEnv', which tracks local information as
252 -- we move inside expressions.
253
254 -- | Historical "renaming monad" (now it's just 'TcRn').
255 type RnM = TcRn
256
257 -- | Historical "type-checking monad" (now it's just 'TcRn').
258 type TcM = TcRn
259
260 -- We 'stack' these envs through the Reader like monad infrastructure
261 -- as we move into an expression (although the change is focused in
262 -- the lcl type).
263 data Env gbl lcl
264 = Env {
265 env_top :: HscEnv, -- Top-level stuff that never changes
266 -- Includes all info about imported things
267
268 env_us :: {-# UNPACK #-} !(IORef UniqSupply),
269 -- Unique supply for local variables
270
271 env_gbl :: gbl, -- Info about things defined at the top level
272 -- of the module being compiled
273
274 env_lcl :: lcl -- Nested stuff; changes as we go into
275 }
276
277 instance ContainsDynFlags (Env gbl lcl) where
278 extractDynFlags env = hsc_dflags (env_top env)
279
280 instance ContainsModule gbl => ContainsModule (Env gbl lcl) where
281 extractModule env = extractModule (env_gbl env)
282
283
284 {-
285 ************************************************************************
286 * *
287 The interface environments
288 Used when dealing with IfaceDecls
289 * *
290 ************************************************************************
291 -}
292
293 data IfGblEnv
294 = IfGblEnv {
295 -- Some information about where this environment came from;
296 -- useful for debugging.
297 if_doc :: SDoc,
298 -- The type environment for the module being compiled,
299 -- in case the interface refers back to it via a reference that
300 -- was originally a hi-boot file.
301 -- We need the module name so we can test when it's appropriate
302 -- to look in this env.
303 -- See Note [Tying the knot] in TcIface
304 if_rec_types :: Maybe (Module, IfG TypeEnv)
305 -- Allows a read effect, so it can be in a mutable
306 -- variable; c.f. handling the external package type env
307 -- Nothing => interactive stuff, no loops possible
308 }
309
310 data IfLclEnv
311 = IfLclEnv {
312 -- The module for the current IfaceDecl
313 -- So if we see f = \x -> x
314 -- it means M.f = \x -> x, where M is the if_mod
315 -- NB: This is a semantic module, see
316 -- Note [Identity versus semantic module]
317 if_mod :: Module,
318
319 -- Whether or not the IfaceDecl came from a boot
320 -- file or not; we'll use this to choose between
321 -- NoUnfolding and BootUnfolding
322 if_boot :: Bool,
323
324 -- The field is used only for error reporting
325 -- if (say) there's a Lint error in it
326 if_loc :: SDoc,
327 -- Where the interface came from:
328 -- .hi file, or GHCi state, or ext core
329 -- plus which bit is currently being examined
330
331 if_nsubst :: Maybe NameShape,
332
333 -- This field is used to make sure "implicit" declarations
334 -- (anything that cannot be exported in mi_exports) get
335 -- wired up correctly in typecheckIfacesForMerging. Most
336 -- of the time it's @Nothing@. See Note [Resolving never-exported Names in TcIface]
337 -- in TcIface.
338 if_implicits_env :: Maybe TypeEnv,
339
340 if_tv_env :: FastStringEnv TyVar, -- Nested tyvar bindings
341 if_id_env :: FastStringEnv Id -- Nested id binding
342 }
343
344 {-
345 ************************************************************************
346 * *
347 Desugarer monad
348 * *
349 ************************************************************************
350
351 Now the mondo monad magic (yes, @DsM@ is a silly name)---carry around
352 a @UniqueSupply@ and some annotations, which
353 presumably include source-file location information:
354 -}
355
356 -- If '-XParallelArrays' is given, the desugarer populates this table with the corresponding
357 -- variables found in 'Data.Array.Parallel'.
358 --
359 data PArrBuiltin
360 = PArrBuiltin
361 { lengthPVar :: Var -- ^ lengthP
362 , replicatePVar :: Var -- ^ replicateP
363 , singletonPVar :: Var -- ^ singletonP
364 , mapPVar :: Var -- ^ mapP
365 , filterPVar :: Var -- ^ filterP
366 , zipPVar :: Var -- ^ zipP
367 , crossMapPVar :: Var -- ^ crossMapP
368 , indexPVar :: Var -- ^ (!:)
369 , emptyPVar :: Var -- ^ emptyP
370 , appPVar :: Var -- ^ (+:+)
371 , enumFromToPVar :: Var -- ^ enumFromToP
372 , enumFromThenToPVar :: Var -- ^ enumFromThenToP
373 }
374
375 data DsGblEnv
376 = DsGblEnv
377 { ds_mod :: Module -- For SCC profiling
378 , ds_fam_inst_env :: FamInstEnv -- Like tcg_fam_inst_env
379 , ds_unqual :: PrintUnqualified
380 , ds_msgs :: IORef Messages -- Warning messages
381 , ds_if_env :: (IfGblEnv, IfLclEnv) -- Used for looking up global,
382 -- possibly-imported things
383 , ds_dph_env :: GlobalRdrEnv -- exported entities of 'Data.Array.Parallel.Prim'
384 -- iff '-fvectorise' flag was given as well as
385 -- exported entities of 'Data.Array.Parallel' iff
386 -- '-XParallelArrays' was given; otherwise, empty
387 , ds_parr_bi :: PArrBuiltin -- desugarar names for '-XParallelArrays'
388 , ds_complete_matches :: CompleteMatchMap
389 -- Additional complete pattern matches
390 }
391
392 instance ContainsModule DsGblEnv where
393 extractModule = ds_mod
394
395 data DsLclEnv = DsLclEnv {
396 dsl_meta :: DsMetaEnv, -- Template Haskell bindings
397 dsl_loc :: RealSrcSpan, -- To put in pattern-matching error msgs
398 dsl_dicts :: Bag EvVar, -- Constraints from GADT pattern-matching
399 dsl_tm_cs :: Bag SimpleEq,
400 dsl_pm_iter :: IORef Int -- no iterations for pmcheck
401 }
402
403 -- Inside [| |] brackets, the desugarer looks
404 -- up variables in the DsMetaEnv
405 type DsMetaEnv = NameEnv DsMetaVal
406
407 data DsMetaVal
408 = DsBound Id -- Bound by a pattern inside the [| |].
409 -- Will be dynamically alpha renamed.
410 -- The Id has type THSyntax.Var
411
412 | DsSplice (HsExpr Id) -- These bindings are introduced by
413 -- the PendingSplices on a HsBracketOut
414
415
416 {-
417 ************************************************************************
418 * *
419 Global typechecker environment
420 * *
421 ************************************************************************
422 -}
423
424 -- | 'FrontendResult' describes the result of running the
425 -- frontend of a Haskell module. Usually, you'll get
426 -- a 'FrontendTypecheck', since running the frontend involves
427 -- typechecking a program, but for an hs-boot merge you'll
428 -- just get a ModIface, since no actual typechecking occurred.
429 --
430 -- This data type really should be in HscTypes, but it needs
431 -- to have a TcGblEnv which is only defined here.
432 data FrontendResult
433 = FrontendTypecheck TcGblEnv
434
435 -- Note [Identity versus semantic module]
436 -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
437 -- When typechecking an hsig file, it is convenient to keep track
438 -- of two different "this module" identifiers:
439 --
440 -- - The IDENTITY module is simply thisPackage + the module
441 -- name; i.e. it uniquely *identifies* the interface file
442 -- we're compiling. For example, p[A=<A>]:A is an
443 -- identity module identifying the requirement named A
444 -- from library p.
445 --
446 -- - The SEMANTIC module, which is the actual module that
447 -- this signature is intended to represent (e.g. if
448 -- we have a identity module p[A=base:Data.IORef]:A,
449 -- then the semantic module is base:Data.IORef)
450 --
451 -- Which one should you use?
452 --
453 -- - In the desugarer and later phases of compilation,
454 -- identity and semantic modules coincide, since we never compile
455 -- signatures (we just generate blank object files for
456 -- hsig files.)
457 --
458 -- A corrolary of this is that the following invariant holds at any point
459 -- past desugaring,
460 --
461 -- if I have a Module, this_mod, in hand representing the module
462 -- currently being compiled,
463 -- then moduleUnitId this_mod == thisPackage dflags
464 --
465 -- - For any code involving Names, we want semantic modules.
466 -- See lookupIfaceTop in IfaceEnv, mkIface and addFingerprints
467 -- in MkIface, and tcLookupGlobal in TcEnv
468 --
469 -- - When reading interfaces, we want the identity module to
470 -- identify the specific interface we want (such interfaces
471 -- should never be loaded into the EPS). However, if a
472 -- hole module <A> is requested, we look for A.hi
473 -- in the home library we are compiling. (See LoadIface.)
474 -- Similarly, in RnNames we check for self-imports using
475 -- identity modules, to allow signatures to import their implementor.
476 --
477 -- - For recompilation avoidance, you want the identity module,
478 -- since that will actually say the specific interface you
479 -- want to track (and recompile if it changes)
480
481 -- | 'TcGblEnv' describes the top-level of the module at the
482 -- point at which the typechecker is finished work.
483 -- It is this structure that is handed on to the desugarer
484 -- For state that needs to be updated during the typechecking
485 -- phase and returned at end, use a 'TcRef' (= 'IORef').
486 data TcGblEnv
487 = TcGblEnv {
488 tcg_mod :: Module, -- ^ Module being compiled
489 tcg_semantic_mod :: Module, -- ^ If a signature, the backing module
490 -- See also Note [Identity versus semantic module]
491 tcg_src :: HscSource,
492 -- ^ What kind of module (regular Haskell, hs-boot, hsig)
493
494 tcg_rdr_env :: GlobalRdrEnv, -- ^ Top level envt; used during renaming
495 tcg_default :: Maybe [Type],
496 -- ^ Types used for defaulting. @Nothing@ => no @default@ decl
497
498 tcg_fix_env :: FixityEnv, -- ^ Just for things in this module
499 tcg_field_env :: RecFieldEnv, -- ^ Just for things in this module
500 -- See Note [The interactive package] in HscTypes
501
502 tcg_type_env :: TypeEnv,
503 -- ^ Global type env for the module we are compiling now. All
504 -- TyCons and Classes (for this module) end up in here right away,
505 -- along with their derived constructors, selectors.
506 --
507 -- (Ids defined in this module start in the local envt, though they
508 -- move to the global envt during zonking)
509 --
510 -- NB: for what "things in this module" means, see
511 -- Note [The interactive package] in HscTypes
512
513 tcg_type_env_var :: TcRef TypeEnv,
514 -- Used only to initialise the interface-file
515 -- typechecker in initIfaceTcRn, so that it can see stuff
516 -- bound in this module when dealing with hi-boot recursions
517 -- Updated at intervals (e.g. after dealing with types and classes)
518
519 tcg_inst_env :: InstEnv,
520 -- ^ Instance envt for all /home-package/ modules;
521 -- Includes the dfuns in tcg_insts
522 tcg_fam_inst_env :: FamInstEnv, -- ^ Ditto for family instances
523 tcg_ann_env :: AnnEnv, -- ^ And for annotations
524
525 -- | Family instances we have to check for consistency.
526 -- Invariant: each FamInst in the list's fi_fam matches the
527 -- key of the entry in the 'NameEnv'. This gets consumed
528 -- by 'checkRecFamInstConsistency'.
529 -- See Note [Don't check hs-boot type family instances too early]
530 tcg_pending_fam_checks :: NameEnv [([FamInst], FamInstEnv)],
531
532 -- Now a bunch of things about this module that are simply
533 -- accumulated, but never consulted until the end.
534 -- Nevertheless, it's convenient to accumulate them along
535 -- with the rest of the info from this module.
536 tcg_exports :: [AvailInfo], -- ^ What is exported
537 tcg_imports :: ImportAvails,
538 -- ^ Information about what was imported from where, including
539 -- things bound in this module. Also store Safe Haskell info
540 -- here about transitive trusted package requirements.
541 --
542 -- There are not many uses of this field, so you can grep for
543 -- all them.
544 --
545 -- The ImportAvails records information about the following
546 -- things:
547 --
548 -- 1. All of the modules you directly imported (tcRnImports)
549 -- 2. The orphans (only!) of all imported modules in a GHCi
550 -- session (runTcInteractive)
551 -- 3. The module that instantiated a signature
552 -- 4. Each of the signatures that merged in
553 --
554 -- It is used in the following ways:
555 -- - imp_orphs is used to determine what orphan modules should be
556 -- visible in the context (tcVisibleOrphanMods)
557 -- - imp_finsts is used to determine what family instances should
558 -- be visible (tcExtendLocalFamInstEnv)
559 -- - To resolve the meaning of the export list of a module
560 -- (tcRnExports)
561 -- - imp_mods is used to compute usage info (mkIfaceTc, deSugar)
562 -- - imp_trust_own_pkg is used for Safe Haskell in interfaces
563 -- (mkIfaceTc, as well as in HscMain)
564 -- - To create the Dependencies field in interface (mkDependencies)
565
566 tcg_dus :: DefUses, -- ^ What is defined in this module and what is used.
567 tcg_used_gres :: TcRef [GlobalRdrElt], -- ^ Records occurrences of imported entities
568 -- See Note [Tracking unused binding and imports]
569
570 tcg_keep :: TcRef NameSet,
571 -- ^ Locally-defined top-level names to keep alive.
572 --
573 -- "Keep alive" means give them an Exported flag, so that the
574 -- simplifier does not discard them as dead code, and so that they
575 -- are exposed in the interface file (but not to export to the
576 -- user).
577 --
578 -- Some things, like dict-fun Ids and default-method Ids are "born"
579 -- with the Exported flag on, for exactly the above reason, but some
580 -- we only discover as we go. Specifically:
581 --
582 -- * The to/from functions for generic data types
583 --
584 -- * Top-level variables appearing free in the RHS of an orphan
585 -- rule
586 --
587 -- * Top-level variables appearing free in a TH bracket
588
589 tcg_th_used :: TcRef Bool,
590 -- ^ @True@ <=> Template Haskell syntax used.
591 --
592 -- We need this so that we can generate a dependency on the
593 -- Template Haskell package, because the desugarer is going
594 -- to emit loads of references to TH symbols. The reference
595 -- is implicit rather than explicit, so we have to zap a
596 -- mutable variable.
597
598 tcg_th_splice_used :: TcRef Bool,
599 -- ^ @True@ <=> A Template Haskell splice was used.
600 --
601 -- Splices disable recompilation avoidance (see #481)
602
603 tcg_th_top_level_locs :: TcRef (Set RealSrcSpan),
604 -- ^ Locations of the top-level splices; used for providing details on
605 -- scope in error messages for out-of-scope variables
606
607 tcg_dfun_n :: TcRef OccSet,
608 -- ^ Allows us to choose unique DFun names.
609
610 tcg_merged :: [(Module, Fingerprint)],
611 -- ^ The requirements we merged with; we always have to recompile
612 -- if any of these changed.
613
614 -- The next fields accumulate the payload of the module
615 -- The binds, rules and foreign-decl fields are collected
616 -- initially in un-zonked form and are finally zonked in tcRnSrcDecls
617
618 tcg_rn_exports :: Maybe [Located (IE Name)],
619 -- Nothing <=> no explicit export list
620 -- Is always Nothing if we don't want to retain renamed
621 -- exports
622
623 tcg_rn_imports :: [LImportDecl Name],
624 -- Keep the renamed imports regardless. They are not
625 -- voluminous and are needed if you want to report unused imports
626
627 tcg_rn_decls :: Maybe (HsGroup Name),
628 -- ^ Renamed decls, maybe. @Nothing@ <=> Don't retain renamed
629 -- decls.
630
631 tcg_dependent_files :: TcRef [FilePath], -- ^ dependencies from addDependentFile
632
633 tcg_th_topdecls :: TcRef [LHsDecl RdrName],
634 -- ^ Top-level declarations from addTopDecls
635
636 tcg_th_foreign_files :: TcRef [(ForeignSrcLang, String)],
637 -- ^ Foreign files emitted from TH.
638
639 tcg_th_topnames :: TcRef NameSet,
640 -- ^ Exact names bound in top-level declarations in tcg_th_topdecls
641
642 tcg_th_modfinalizers :: TcRef [TcM ()],
643 -- ^ Template Haskell module finalizers.
644 --
645 -- They are computations in the @TcM@ monad rather than @Q@ because we
646 -- set them to use particular local environments.
647
648 tcg_th_state :: TcRef (Map TypeRep Dynamic),
649 tcg_th_remote_state :: TcRef (Maybe (ForeignRef (IORef QState))),
650 -- ^ Template Haskell state
651
652 tcg_ev_binds :: Bag EvBind, -- Top-level evidence bindings
653
654 -- Things defined in this module, or (in GHCi)
655 -- in the declarations for a single GHCi command.
656 -- For the latter, see Note [The interactive package] in HscTypes
657 tcg_tr_module :: Maybe Id, -- Id for $trModule :: GHC.Types.Module
658 -- for which every module has a top-level defn
659 -- except in GHCi in which case we have Nothing
660 tcg_binds :: LHsBinds Id, -- Value bindings in this module
661 tcg_sigs :: NameSet, -- ...Top-level names that *lack* a signature
662 tcg_imp_specs :: [LTcSpecPrag], -- ...SPECIALISE prags for imported Ids
663 tcg_warns :: Warnings, -- ...Warnings and deprecations
664 tcg_anns :: [Annotation], -- ...Annotations
665 tcg_tcs :: [TyCon], -- ...TyCons and Classes
666 tcg_insts :: [ClsInst], -- ...Instances
667 tcg_fam_insts :: [FamInst], -- ...Family instances
668 tcg_rules :: [LRuleDecl Id], -- ...Rules
669 tcg_fords :: [LForeignDecl Id], -- ...Foreign import & exports
670 tcg_vects :: [LVectDecl Id], -- ...Vectorisation declarations
671 tcg_patsyns :: [PatSyn], -- ...Pattern synonyms
672
673 tcg_doc_hdr :: Maybe LHsDocString, -- ^ Maybe Haddock header docs
674 tcg_hpc :: AnyHpcUsage, -- ^ @True@ if any part of the
675 -- prog uses hpc instrumentation.
676
677 tcg_self_boot :: SelfBootInfo, -- ^ Whether this module has a
678 -- corresponding hi-boot file
679
680 tcg_main :: Maybe Name, -- ^ The Name of the main
681 -- function, if this module is
682 -- the main module.
683
684 tcg_safeInfer :: TcRef (Bool, WarningMessages),
685 -- ^ Has the typechecker inferred this module as -XSafe (Safe Haskell)
686 -- See Note [Safe Haskell Overlapping Instances Implementation],
687 -- although this is used for more than just that failure case.
688
689 tcg_tc_plugins :: [TcPluginSolver],
690 -- ^ A list of user-defined plugins for the constraint solver.
691
692 tcg_top_loc :: RealSrcSpan,
693 -- ^ The RealSrcSpan this module came from
694
695 tcg_static_wc :: TcRef WantedConstraints,
696 -- ^ Wanted constraints of static forms.
697 -- See Note [Constraints in static forms].
698 tcg_complete_matches :: [CompleteMatch]
699 }
700
701 -- NB: topModIdentity, not topModSemantic!
702 -- Definition sites of orphan identities will be identity modules, not semantic
703 -- modules.
704
705 -- Note [Constraints in static forms]
706 -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
707 --
708 -- When a static form produces constraints like
709 --
710 -- f :: StaticPtr (Bool -> String)
711 -- f = static show
712 --
713 -- we collect them in tcg_static_wc and resolve them at the end
714 -- of type checking. They need to be resolved separately because
715 -- we don't want to resolve them in the context of the enclosing
716 -- expression. Consider
717 --
718 -- g :: Show a => StaticPtr (a -> String)
719 -- g = static show
720 --
721 -- If the @Show a0@ constraint that the body of the static form produces was
722 -- resolved in the context of the enclosing expression, then the body of the
723 -- static form wouldn't be closed because the Show dictionary would come from
724 -- g's context instead of coming from the top level.
725
726 tcVisibleOrphanMods :: TcGblEnv -> ModuleSet
727 tcVisibleOrphanMods tcg_env
728 = mkModuleSet (tcg_mod tcg_env : imp_orphs (tcg_imports tcg_env))
729
730 instance ContainsModule TcGblEnv where
731 extractModule env = tcg_semantic_mod env
732
733 type RecFieldEnv = NameEnv [FieldLabel]
734 -- Maps a constructor name *in this module*
735 -- to the fields for that constructor.
736 -- This is used when dealing with ".." notation in record
737 -- construction and pattern matching.
738 -- The FieldEnv deals *only* with constructors defined in *this*
739 -- module. For imported modules, we get the same info from the
740 -- TypeEnv
741
742 data SelfBootInfo
743 = NoSelfBoot -- No corresponding hi-boot file
744 | SelfBoot
745 { sb_mds :: ModDetails -- There was a hi-boot file,
746 , sb_tcs :: NameSet } -- defining these TyCons,
747 -- What is sb_tcs used for? See Note [Extra dependencies from .hs-boot files]
748 -- in RnSource
749
750
751 {- Note [Tracking unused binding and imports]
752 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
753 We gather two sorts of usage information
754
755 * tcg_dus (defs/uses)
756 Records *defined* Names (local, top-level)
757 and *used* Names (local or imported)
758
759 Used (a) to report "defined but not used"
760 (see RnNames.reportUnusedNames)
761 (b) to generate version-tracking usage info in interface
762 files (see MkIface.mkUsedNames)
763 This usage info is mainly gathered by the renamer's
764 gathering of free-variables
765
766 * tcg_used_gres
767 Used only to report unused import declarations
768
769 Records each *occurrence* an *imported* (not locally-defined) entity.
770 The occurrence is recorded by keeping a GlobalRdrElt for it.
771 These is not the GRE that is in the GlobalRdrEnv; rather it
772 is recorded *after* the filtering done by pickGREs. So it reflect
773 /how that occurrence is in scope/. See Note [GRE filtering] in
774 RdrName.
775
776
777 ************************************************************************
778 * *
779 The local typechecker environment
780 * *
781 ************************************************************************
782
783 Note [The Global-Env/Local-Env story]
784 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
785 During type checking, we keep in the tcg_type_env
786 * All types and classes
787 * All Ids derived from types and classes (constructors, selectors)
788
789 At the end of type checking, we zonk the local bindings,
790 and as we do so we add to the tcg_type_env
791 * Locally defined top-level Ids
792
793 Why? Because they are now Ids not TcIds. This final GlobalEnv is
794 a) fed back (via the knot) to typechecking the
795 unfoldings of interface signatures
796 b) used in the ModDetails of this module
797 -}
798
799 data TcLclEnv -- Changes as we move inside an expression
800 -- Discarded after typecheck/rename; not passed on to desugarer
801 = TcLclEnv {
802 tcl_loc :: RealSrcSpan, -- Source span
803 tcl_ctxt :: [ErrCtxt], -- Error context, innermost on top
804 tcl_tclvl :: TcLevel, -- Birthplace for new unification variables
805
806 tcl_th_ctxt :: ThStage, -- Template Haskell context
807 tcl_th_bndrs :: ThBindEnv, -- Binding level of in-scope Names
808 -- defined in this module (not imported)
809
810 tcl_arrow_ctxt :: ArrowCtxt, -- Arrow-notation context
811
812 tcl_rdr :: LocalRdrEnv, -- Local name envt
813 -- Maintained during renaming, of course, but also during
814 -- type checking, solely so that when renaming a Template-Haskell
815 -- splice we have the right environment for the renamer.
816 --
817 -- Does *not* include global name envt; may shadow it
818 -- Includes both ordinary variables and type variables;
819 -- they are kept distinct because tyvar have a different
820 -- occurrence constructor (Name.TvOcc)
821 -- We still need the unsullied global name env so that
822 -- we can look up record field names
823
824 tcl_env :: TcTypeEnv, -- The local type environment:
825 -- Ids and TyVars defined in this module
826
827 tcl_bndrs :: TcIdBinderStack, -- Used for reporting relevant bindings
828
829 tcl_tidy :: TidyEnv, -- Used for tidying types; contains all
830 -- in-scope type variables (but not term variables)
831
832 tcl_tyvars :: TcRef TcTyVarSet, -- The "global tyvars"
833 -- Namely, the in-scope TyVars bound in tcl_env,
834 -- plus the tyvars mentioned in the types of Ids bound
835 -- in tcl_lenv.
836 -- Why mutable? see notes with tcGetGlobalTyCoVars
837
838 tcl_lie :: TcRef WantedConstraints, -- Place to accumulate type constraints
839 tcl_errs :: TcRef Messages -- Place to accumulate errors
840 }
841
842 type TcTypeEnv = NameEnv TcTyThing
843
844 type ThBindEnv = NameEnv (TopLevelFlag, ThLevel)
845 -- Domain = all Ids bound in this module (ie not imported)
846 -- The TopLevelFlag tells if the binding is syntactically top level.
847 -- We need to know this, because the cross-stage persistence story allows
848 -- cross-stage at arbitrary types if the Id is bound at top level.
849 --
850 -- Nota bene: a ThLevel of 'outerLevel' is *not* the same as being
851 -- bound at top level! See Note [Template Haskell levels] in TcSplice
852
853 {- Note [Given Insts]
854 ~~~~~~~~~~~~~~~~~~
855 Because of GADTs, we have to pass inwards the Insts provided by type signatures
856 and existential contexts. Consider
857 data T a where { T1 :: b -> b -> T [b] }
858 f :: Eq a => T a -> Bool
859 f (T1 x y) = [x]==[y]
860
861 The constructor T1 binds an existential variable 'b', and we need Eq [b].
862 Well, we have it, because Eq a refines to Eq [b], but we can only spot that if we
863 pass it inwards.
864
865 -}
866
867 -- | Type alias for 'IORef'; the convention is we'll use this for mutable
868 -- bits of data in 'TcGblEnv' which are updated during typechecking and
869 -- returned at the end.
870 type TcRef a = IORef a
871 -- ToDo: when should I refer to it as a 'TcId' instead of an 'Id'?
872 type TcId = Id
873 type TcIdSet = IdSet
874
875 ---------------------------
876 -- The TcIdBinderStack
877 ---------------------------
878
879 type TcIdBinderStack = [TcIdBinder]
880 -- This is a stack of locally-bound ids, innermost on top
881 -- Used ony in error reporting (relevantBindings in TcError)
882 -- We can't use the tcl_env type environment, because it doesn't
883 -- keep track of the nesting order
884
885 data TcIdBinder
886 = TcIdBndr
887 TcId
888 TopLevelFlag -- Tells whether the binding is syntactically top-level
889 -- (The monomorphic Ids for a recursive group count
890 -- as not-top-level for this purpose.)
891 | TcIdBndr_ExpType -- Variant that allows the type to be specified as
892 -- an ExpType
893 Name
894 ExpType
895 TopLevelFlag
896
897 instance Outputable TcIdBinder where
898 ppr (TcIdBndr id top_lvl) = ppr id <> brackets (ppr top_lvl)
899 ppr (TcIdBndr_ExpType id _ top_lvl) = ppr id <> brackets (ppr top_lvl)
900
901 instance HasOccName TcIdBinder where
902 occName (TcIdBndr id _) = (occName (idName id))
903 occName (TcIdBndr_ExpType name _ _) = (occName name)
904
905 ---------------------------
906 -- Template Haskell stages and levels
907 ---------------------------
908
909 data SpliceType = Typed | Untyped
910
911 data ThStage -- See Note [Template Haskell state diagram] in TcSplice
912 = Splice SpliceType -- Inside a top-level splice
913 -- This code will be run *at compile time*;
914 -- the result replaces the splice
915 -- Binding level = 0
916
917 | RunSplice (TcRef [ForeignRef (TH.Q ())])
918 -- Set when running a splice, i.e. NOT when renaming or typechecking the
919 -- Haskell code for the splice. See Note [RunSplice ThLevel].
920 --
921 -- Contains a list of mod finalizers collected while executing the splice.
922 --
923 -- 'addModFinalizer' inserts finalizers here, and from here they are taken
924 -- to construct an @HsSpliced@ annotation for untyped splices. See Note
925 -- [Delaying modFinalizers in untyped splices] in "RnSplice".
926 --
927 -- For typed splices, the typechecker takes finalizers from here and
928 -- inserts them in the list of finalizers in the global environment.
929 --
930 -- See Note [Collecting modFinalizers in typed splices] in "TcSplice".
931
932 | Comp -- Ordinary Haskell code
933 -- Binding level = 1
934
935 | Brack -- Inside brackets
936 ThStage -- Enclosing stage
937 PendingStuff
938
939 data PendingStuff
940 = RnPendingUntyped -- Renaming the inside of an *untyped* bracket
941 (TcRef [PendingRnSplice]) -- Pending splices in here
942
943 | RnPendingTyped -- Renaming the inside of a *typed* bracket
944
945 | TcPending -- Typechecking the inside of a typed bracket
946 (TcRef [PendingTcSplice]) -- Accumulate pending splices here
947 (TcRef WantedConstraints) -- and type constraints here
948
949 topStage, topAnnStage, topSpliceStage :: ThStage
950 topStage = Comp
951 topAnnStage = Splice Untyped
952 topSpliceStage = Splice Untyped
953
954 instance Outputable ThStage where
955 ppr (Splice _) = text "Splice"
956 ppr (RunSplice _) = text "RunSplice"
957 ppr Comp = text "Comp"
958 ppr (Brack s _) = text "Brack" <> parens (ppr s)
959
960 type ThLevel = Int
961 -- NB: see Note [Template Haskell levels] in TcSplice
962 -- Incremented when going inside a bracket,
963 -- decremented when going inside a splice
964 -- NB: ThLevel is one greater than the 'n' in Fig 2 of the
965 -- original "Template meta-programming for Haskell" paper
966
967 impLevel, outerLevel :: ThLevel
968 impLevel = 0 -- Imported things; they can be used inside a top level splice
969 outerLevel = 1 -- Things defined outside brackets
970
971 thLevel :: ThStage -> ThLevel
972 thLevel (Splice _) = 0
973 thLevel (RunSplice _) =
974 -- See Note [RunSplice ThLevel].
975 panic "thLevel: called when running a splice"
976 thLevel Comp = 1
977 thLevel (Brack s _) = thLevel s + 1
978
979 {- Node [RunSplice ThLevel]
980 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
981 The 'RunSplice' stage is set when executing a splice, and only when running a
982 splice. In particular it is not set when the splice is renamed or typechecked.
983
984 'RunSplice' is needed to provide a reference where 'addModFinalizer' can insert
985 the finalizer (see Note [Delaying modFinalizers in untyped splices]), and
986 'addModFinalizer' runs when doing Q things. Therefore, It doesn't make sense to
987 set 'RunSplice' when renaming or typechecking the splice, where 'Splice', 'Brak'
988 or 'Comp' are used instead.
989
990 -}
991
992 ---------------------------
993 -- Arrow-notation context
994 ---------------------------
995
996 {- Note [Escaping the arrow scope]
997 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
998 In arrow notation, a variable bound by a proc (or enclosed let/kappa)
999 is not in scope to the left of an arrow tail (-<) or the head of (|..|).
1000 For example
1001
1002 proc x -> (e1 -< e2)
1003
1004 Here, x is not in scope in e1, but it is in scope in e2. This can get
1005 a bit complicated:
1006
1007 let x = 3 in
1008 proc y -> (proc z -> e1) -< e2
1009
1010 Here, x and z are in scope in e1, but y is not.
1011
1012 We implement this by
1013 recording the environment when passing a proc (using newArrowScope),
1014 and returning to that (using escapeArrowScope) on the left of -< and the
1015 head of (|..|).
1016
1017 All this can be dealt with by the *renamer*. But the type checker needs
1018 to be involved too. Example (arrowfail001)
1019 class Foo a where foo :: a -> ()
1020 data Bar = forall a. Foo a => Bar a
1021 get :: Bar -> ()
1022 get = proc x -> case x of Bar a -> foo -< a
1023 Here the call of 'foo' gives rise to a (Foo a) constraint that should not
1024 be captured by the pattern match on 'Bar'. Rather it should join the
1025 constraints from further out. So we must capture the constraint bag
1026 from further out in the ArrowCtxt that we push inwards.
1027 -}
1028
1029 data ArrowCtxt -- Note [Escaping the arrow scope]
1030 = NoArrowCtxt
1031 | ArrowCtxt LocalRdrEnv (TcRef WantedConstraints)
1032
1033
1034 ---------------------------
1035 -- TcTyThing
1036 ---------------------------
1037
1038 -- | A typecheckable thing available in a local context. Could be
1039 -- 'AGlobal' 'TyThing', but also lexically scoped variables, etc.
1040 -- See 'TcEnv' for how to retrieve a 'TyThing' given a 'Name'.
1041 data TcTyThing
1042 = AGlobal TyThing -- Used only in the return type of a lookup
1043
1044 | ATcId { -- Ids defined in this module; may not be fully zonked
1045 tct_id :: TcId,
1046 tct_info :: IdBindingInfo } -- See Note [Bindings with closed types]
1047
1048 | ATyVar Name TcTyVar -- The type variable to which the lexically scoped type
1049 -- variable is bound. We only need the Name
1050 -- for error-message purposes; it is the corresponding
1051 -- Name in the domain of the envt
1052
1053 | ATcTyCon TyCon -- Used temporarily, during kind checking, for the
1054 -- tycons and clases in this recursive group
1055 -- The TyCon is always a TcTyCon. Its kind
1056 -- can be a mono-kind or a poly-kind; in TcTyClsDcls see
1057 -- Note [Type checking recursive type and class declarations]
1058
1059 | APromotionErr PromotionErr
1060
1061 data PromotionErr
1062 = TyConPE -- TyCon used in a kind before we are ready
1063 -- data T :: T -> * where ...
1064 | ClassPE -- Ditto Class
1065
1066 | FamDataConPE -- Data constructor for a data family
1067 -- See Note [AFamDataCon: not promoting data family constructors] in TcRnDriver
1068 | PatSynPE -- Pattern synonyms
1069 -- See Note [Don't promote pattern synonyms] in TcEnv
1070
1071 | RecDataConPE -- Data constructor in a recursive loop
1072 -- See Note [ARecDataCon: recusion and promoting data constructors] in TcTyClsDecls
1073 | NoDataKindsTC -- -XDataKinds not enabled (for a tycon)
1074 | NoDataKindsDC -- -XDataKinds not enabled (for a datacon)
1075 | NoTypeInTypeTC -- -XTypeInType not enabled (for a tycon)
1076 | NoTypeInTypeDC -- -XTypeInType not enabled (for a datacon)
1077
1078 instance Outputable TcTyThing where -- Debugging only
1079 ppr (AGlobal g) = ppr g
1080 ppr elt@(ATcId {}) = text "Identifier" <>
1081 brackets (ppr (tct_id elt) <> dcolon
1082 <> ppr (varType (tct_id elt)) <> comma
1083 <+> ppr (tct_info elt))
1084 ppr (ATyVar n tv) = text "Type variable" <+> quotes (ppr n) <+> equals <+> ppr tv
1085 ppr (ATcTyCon tc) = text "ATcTyCon" <+> ppr tc
1086 ppr (APromotionErr err) = text "APromotionErr" <+> ppr err
1087
1088 -- | Describes how an Id is bound.
1089 --
1090 -- It is used for the following purposes:
1091 --
1092 -- a) for static forms in TcExpr.checkClosedInStaticForm and
1093 -- b) to figure out when a nested binding can be generalised (in
1094 -- TcBinds.decideGeneralisationPlan).
1095 --
1096 -- See Note [Meaning of IdBindingInfo].
1097 data IdBindingInfo
1098 = NotLetBound
1099 | ClosedLet
1100 | NonClosedLet NameSet Bool
1101
1102 -- Note [Meaning of IdBindingInfo]
1103 --
1104 -- @NotLetBound@ means that the Id is not let-bound (e.g. it is bound in a
1105 -- lambda-abstraction or in a case pattern).
1106 --
1107 -- @ClosedLet@ means that the Id is let-bound, it is closed and its type is
1108 -- closed as well.
1109 --
1110 -- @NonClosedLet fvs type-closed@ means that the Id is let-bound but it is not
1111 -- closed. The @fvs@ set contains the free variables of the rhs. The type-closed
1112 -- flag indicates if the type of Id is closed.
1113
1114 instance Outputable IdBindingInfo where
1115 ppr NotLetBound = text "NotLetBound"
1116 ppr ClosedLet = text "TopLevelLet"
1117 ppr (NonClosedLet fvs closed_type) =
1118 text "TopLevelLet" <+> ppr fvs <+> ppr closed_type
1119
1120 -- | Tells if a group of binders is closed.
1121 --
1122 -- When it is not closed, it provides a map of binder ids to the free vars
1123 -- in their right-hand sides.
1124 --
1125 data IsGroupClosed = ClosedGroup
1126 | NonClosedGroup (NameEnv NameSet)
1127
1128 instance Outputable PromotionErr where
1129 ppr ClassPE = text "ClassPE"
1130 ppr TyConPE = text "TyConPE"
1131 ppr PatSynPE = text "PatSynPE"
1132 ppr FamDataConPE = text "FamDataConPE"
1133 ppr RecDataConPE = text "RecDataConPE"
1134 ppr NoDataKindsTC = text "NoDataKindsTC"
1135 ppr NoDataKindsDC = text "NoDataKindsDC"
1136 ppr NoTypeInTypeTC = text "NoTypeInTypeTC"
1137 ppr NoTypeInTypeDC = text "NoTypeInTypeDC"
1138
1139 pprTcTyThingCategory :: TcTyThing -> SDoc
1140 pprTcTyThingCategory (AGlobal thing) = pprTyThingCategory thing
1141 pprTcTyThingCategory (ATyVar {}) = text "Type variable"
1142 pprTcTyThingCategory (ATcId {}) = text "Local identifier"
1143 pprTcTyThingCategory (ATcTyCon {}) = text "Local tycon"
1144 pprTcTyThingCategory (APromotionErr pe) = pprPECategory pe
1145
1146 pprPECategory :: PromotionErr -> SDoc
1147 pprPECategory ClassPE = text "Class"
1148 pprPECategory TyConPE = text "Type constructor"
1149 pprPECategory PatSynPE = text "Pattern synonym"
1150 pprPECategory FamDataConPE = text "Data constructor"
1151 pprPECategory RecDataConPE = text "Data constructor"
1152 pprPECategory NoDataKindsTC = text "Type constructor"
1153 pprPECategory NoDataKindsDC = text "Data constructor"
1154 pprPECategory NoTypeInTypeTC = text "Type constructor"
1155 pprPECategory NoTypeInTypeDC = text "Data constructor"
1156
1157 {- Note [Bindings with closed types]
1158 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1159 Consider
1160
1161 f x = let g ys = map not ys
1162 in ...
1163
1164 Can we generalise 'g' under the OutsideIn algorithm? Yes,
1165 because all g's free variables are top-level; that is they themselves
1166 have no free type variables, and it is the type variables in the
1167 environment that makes things tricky for OutsideIn generalisation.
1168
1169 Definition:
1170 A variable is "closed", and has tct_info set to TopLevel,
1171 iff
1172 a) all its free variables are imported, or are let-bound and closed
1173 b) generalisation is not restricted by the monomorphism restriction
1174
1175 Invariant: a closed variable has no free type variables in its type.
1176 Why? Assume (induction hypothesis) that closed variables have closed
1177 types, and that we have a new binding f = e, satisfying (a) and (b).
1178 Then since monomorphism restriction does not apply, and there are no
1179 free type variables, we can fully generalise, so its type will be closed.
1180
1181 Under OutsideIn we are free to generalise a closed let-binding.
1182 This is an extension compared to the JFP paper on OutsideIn, which
1183 used "top-level" as a proxy for "closed". (It's not a good proxy
1184 anyway -- the MR can make a top-level binding with a free type
1185 variable.)
1186
1187 Note that:
1188 * A top-level binding may not be closed, if it suffers from the MR
1189
1190 * A nested binding may be closed (eg 'g' in the example we started with)
1191 Indeed, that's the point; whether a function is defined at top level
1192 or nested is orthogonal to the question of whether or not it is closed
1193
1194 * A binding may be non-closed because it mentions a lexically scoped
1195 *type variable* Eg
1196 f :: forall a. blah
1197 f x = let g y = ...(y::a)...
1198
1199 -}
1200
1201 type ErrCtxt = (Bool, TidyEnv -> TcM (TidyEnv, MsgDoc))
1202 -- Monadic so that we have a chance
1203 -- to deal with bound type variables just before error
1204 -- message construction
1205
1206 -- Bool: True <=> this is a landmark context; do not
1207 -- discard it when trimming for display
1208
1209 {-
1210 ************************************************************************
1211 * *
1212 Operations over ImportAvails
1213 * *
1214 ************************************************************************
1215 -}
1216
1217 -- | 'ImportAvails' summarises what was imported from where, irrespective of
1218 -- whether the imported things are actually used or not. It is used:
1219 --
1220 -- * when processing the export list,
1221 --
1222 -- * when constructing usage info for the interface file,
1223 --
1224 -- * to identify the list of directly imported modules for initialisation
1225 -- purposes and for optimised overlap checking of family instances,
1226 --
1227 -- * when figuring out what things are really unused
1228 --
1229 data ImportAvails
1230 = ImportAvails {
1231 imp_mods :: ImportedMods,
1232 -- = ModuleEnv [ImportedModsVal],
1233 -- ^ Domain is all directly-imported modules
1234 --
1235 -- See the documentation on ImportedModsVal in HscTypes for the
1236 -- meaning of the fields.
1237 --
1238 -- We need a full ModuleEnv rather than a ModuleNameEnv here,
1239 -- because we might be importing modules of the same name from
1240 -- different packages. (currently not the case, but might be in the
1241 -- future).
1242
1243 imp_dep_mods :: DModuleNameEnv (ModuleName, IsBootInterface),
1244 -- ^ Home-package modules needed by the module being compiled
1245 --
1246 -- It doesn't matter whether any of these dependencies
1247 -- are actually /used/ when compiling the module; they
1248 -- are listed if they are below it at all. For
1249 -- example, suppose M imports A which imports X. Then
1250 -- compiling M might not need to consult X.hi, but X
1251 -- is still listed in M's dependencies.
1252
1253 imp_dep_pkgs :: Set InstalledUnitId,
1254 -- ^ Packages needed by the module being compiled, whether directly,
1255 -- or via other modules in this package, or via modules imported
1256 -- from other packages.
1257
1258 imp_trust_pkgs :: Set InstalledUnitId,
1259 -- ^ This is strictly a subset of imp_dep_pkgs and records the
1260 -- packages the current module needs to trust for Safe Haskell
1261 -- compilation to succeed. A package is required to be trusted if
1262 -- we are dependent on a trustworthy module in that package.
1263 -- While perhaps making imp_dep_pkgs a tuple of (UnitId, Bool)
1264 -- where True for the bool indicates the package is required to be
1265 -- trusted is the more logical design, doing so complicates a lot
1266 -- of code not concerned with Safe Haskell.
1267 -- See Note [RnNames . Tracking Trust Transitively]
1268
1269 imp_trust_own_pkg :: Bool,
1270 -- ^ Do we require that our own package is trusted?
1271 -- This is to handle efficiently the case where a Safe module imports
1272 -- a Trustworthy module that resides in the same package as it.
1273 -- See Note [RnNames . Trust Own Package]
1274
1275 imp_orphs :: [Module],
1276 -- ^ Orphan modules below us in the import tree (and maybe including
1277 -- us for imported modules)
1278
1279 imp_finsts :: [Module]
1280 -- ^ Family instance modules below us in the import tree (and maybe
1281 -- including us for imported modules)
1282 }
1283
1284 mkModDeps :: [(ModuleName, IsBootInterface)]
1285 -> DModuleNameEnv (ModuleName, IsBootInterface)
1286 mkModDeps deps = foldl add emptyUDFM deps
1287 where
1288 add env elt@(m,_) = addToUDFM env m elt
1289
1290 emptyImportAvails :: ImportAvails
1291 emptyImportAvails = ImportAvails { imp_mods = emptyModuleEnv,
1292 imp_dep_mods = emptyUDFM,
1293 imp_dep_pkgs = S.empty,
1294 imp_trust_pkgs = S.empty,
1295 imp_trust_own_pkg = False,
1296 imp_orphs = [],
1297 imp_finsts = [] }
1298
1299 -- | Union two ImportAvails
1300 --
1301 -- This function is a key part of Import handling, basically
1302 -- for each import we create a separate ImportAvails structure
1303 -- and then union them all together with this function.
1304 plusImportAvails :: ImportAvails -> ImportAvails -> ImportAvails
1305 plusImportAvails
1306 (ImportAvails { imp_mods = mods1,
1307 imp_dep_mods = dmods1, imp_dep_pkgs = dpkgs1,
1308 imp_trust_pkgs = tpkgs1, imp_trust_own_pkg = tself1,
1309 imp_orphs = orphs1, imp_finsts = finsts1 })
1310 (ImportAvails { imp_mods = mods2,
1311 imp_dep_mods = dmods2, imp_dep_pkgs = dpkgs2,
1312 imp_trust_pkgs = tpkgs2, imp_trust_own_pkg = tself2,
1313 imp_orphs = orphs2, imp_finsts = finsts2 })
1314 = ImportAvails { imp_mods = plusModuleEnv_C (++) mods1 mods2,
1315 imp_dep_mods = plusUDFM_C plus_mod_dep dmods1 dmods2,
1316 imp_dep_pkgs = dpkgs1 `S.union` dpkgs2,
1317 imp_trust_pkgs = tpkgs1 `S.union` tpkgs2,
1318 imp_trust_own_pkg = tself1 || tself2,
1319 imp_orphs = orphs1 `unionLists` orphs2,
1320 imp_finsts = finsts1 `unionLists` finsts2 }
1321 where
1322 plus_mod_dep (m1, boot1) (m2, boot2)
1323 = WARN( not (m1 == m2), (ppr m1 <+> ppr m2) $$ (ppr boot1 <+> ppr boot2) )
1324 -- Check mod-names match
1325 (m1, boot1 && boot2) -- If either side can "see" a non-hi-boot interface, use that
1326
1327 {-
1328 ************************************************************************
1329 * *
1330 \subsection{Where from}
1331 * *
1332 ************************************************************************
1333
1334 The @WhereFrom@ type controls where the renamer looks for an interface file
1335 -}
1336
1337 data WhereFrom
1338 = ImportByUser IsBootInterface -- Ordinary user import (perhaps {-# SOURCE #-})
1339 | ImportBySystem -- Non user import.
1340 | ImportByPlugin -- Importing a plugin;
1341 -- See Note [Care with plugin imports] in LoadIface
1342
1343 instance Outputable WhereFrom where
1344 ppr (ImportByUser is_boot) | is_boot = text "{- SOURCE -}"
1345 | otherwise = empty
1346 ppr ImportBySystem = text "{- SYSTEM -}"
1347 ppr ImportByPlugin = text "{- PLUGIN -}"
1348
1349
1350 {- *********************************************************************
1351 * *
1352 Type signatures
1353 * *
1354 ********************************************************************* -}
1355
1356 -- These data types need to be here only because
1357 -- TcSimplify uses them, and TcSimplify is fairly
1358 -- low down in the module hierarchy
1359
1360 data TcSigInfo = TcIdSig TcIdSigInfo
1361 | TcPatSynSig TcPatSynInfo
1362
1363 data TcIdSigInfo -- See Note [Complete and partial type signatures]
1364 = CompleteSig -- A complete signature with no wildcards,
1365 -- so the complete polymorphic type is known.
1366 { sig_bndr :: TcId -- The polymorphic Id with that type
1367
1368 , sig_ctxt :: UserTypeCtxt -- In the case of type-class default methods,
1369 -- the Name in the FunSigCtxt is not the same
1370 -- as the TcId; the former is 'op', while the
1371 -- latter is '$dmop' or some such
1372
1373 , sig_loc :: SrcSpan -- Location of the type signature
1374 }
1375
1376 | PartialSig -- A partial type signature (i.e. includes one or more
1377 -- wildcards). In this case it doesn't make sense to give
1378 -- the polymorphic Id, because we are going to /infer/ its
1379 -- type, so we can't make the polymorphic Id ab-initio
1380 { psig_name :: Name -- Name of the function; used when report wildcards
1381 , psig_hs_ty :: LHsSigWcType Name -- The original partial signature in HsSyn form
1382 , sig_ctxt :: UserTypeCtxt
1383 , sig_loc :: SrcSpan -- Location of the type signature
1384 }
1385
1386
1387 {- Note [Complete and partial type signatures]
1388 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1389 A type signature is partial when it contains one or more wildcards
1390 (= type holes). The wildcard can either be:
1391 * A (type) wildcard occurring in sig_theta or sig_tau. These are
1392 stored in sig_wcs.
1393 f :: Bool -> _
1394 g :: Eq _a => _a -> _a -> Bool
1395 * Or an extra-constraints wildcard, stored in sig_cts:
1396 h :: (Num a, _) => a -> a
1397
1398 A type signature is a complete type signature when there are no
1399 wildcards in the type signature, i.e. iff sig_wcs is empty and
1400 sig_extra_cts is Nothing.
1401 -}
1402
1403 data TcIdSigInst
1404 = TISI { sig_inst_sig :: TcIdSigInfo
1405
1406 , sig_inst_skols :: [(Name, TcTyVar)]
1407 -- Instantiated type and kind variables SKOLEMS
1408 -- The Name is the Name that the renamer chose;
1409 -- but the TcTyVar may come from instantiating
1410 -- the type and hence have a different unique.
1411 -- No need to keep track of whether they are truly lexically
1412 -- scoped because the renamer has named them uniquely
1413 -- See Note [Binding scoped type variables] in TcSigs
1414
1415 , sig_inst_theta :: TcThetaType
1416 -- Instantiated theta. In the case of a
1417 -- PartialSig, sig_theta does not include
1418 -- the extra-constraints wildcard
1419
1420 , sig_inst_tau :: TcSigmaType -- Instantiated tau
1421 -- See Note [sig_inst_tau may be polymorphic]
1422
1423 -- Relevant for partial signature only
1424 , sig_inst_wcs :: [(Name, TcTyVar)]
1425 -- Like sig_inst_skols, but for wildcards. The named
1426 -- wildcards scope over the binding, and hence their
1427 -- Names may appear in type signatures in the binding
1428
1429 , sig_inst_wcx :: Maybe TcTyVar
1430 -- Extra-constraints wildcard to fill in, if any
1431 }
1432
1433 {- Note [sig_inst_tau may be polymorphic]
1434 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1435 Note that "sig_inst_tau" might actually be a polymorphic type,
1436 if the original function had a signature like
1437 forall a. Eq a => forall b. Ord b => ....
1438 But that's ok: tcMatchesFun (called by tcRhs) can deal with that
1439 It happens, too! See Note [Polymorphic methods] in TcClassDcl.
1440
1441 Note [Wildcards in partial signatures]
1442 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1443 The wildcards in psig_wcs may stand for a type mentioning
1444 the universally-quantified tyvars of psig_ty
1445
1446 E.g. f :: forall a. _ -> a
1447 f x = x
1448 We get sig_inst_skols = [a]
1449 sig_inst_tau = _22 -> a
1450 sig_inst_wcs = [_22]
1451 and _22 in the end is unified with the type 'a'
1452
1453 Moreover the kind of a wildcard in sig_inst_wcs may mention
1454 the universally-quantified tyvars sig_inst_skols
1455 e.g. f :: t a -> t _
1456 Here we get
1457 sig_inst_skole = [k:*, (t::k ->*), (a::k)]
1458 sig_inst_tau = t a -> t _22
1459 sig_inst_wcs = [ _22::k ]
1460 -}
1461
1462 data TcPatSynInfo
1463 = TPSI {
1464 patsig_name :: Name,
1465 patsig_implicit_bndrs :: [TyVarBinder], -- Implicitly-bound kind vars (Inferred) and
1466 -- implicitly-bound type vars (Specified)
1467 -- See Note [The pattern-synonym signature splitting rule] in TcPatSyn
1468 patsig_univ_bndrs :: [TyVar], -- Bound by explicit user forall
1469 patsig_req :: TcThetaType,
1470 patsig_ex_bndrs :: [TyVar], -- Bound by explicit user forall
1471 patsig_prov :: TcThetaType,
1472 patsig_body_ty :: TcSigmaType
1473 }
1474
1475 instance Outputable TcSigInfo where
1476 ppr (TcIdSig idsi) = ppr idsi
1477 ppr (TcPatSynSig tpsi) = text "TcPatSynInfo" <+> ppr tpsi
1478
1479 instance Outputable TcIdSigInfo where
1480 ppr (CompleteSig { sig_bndr = bndr })
1481 = ppr bndr <+> dcolon <+> ppr (idType bndr)
1482 ppr (PartialSig { psig_name = name, psig_hs_ty = hs_ty })
1483 = text "psig" <+> ppr name <+> dcolon <+> ppr hs_ty
1484
1485 instance Outputable TcIdSigInst where
1486 ppr (TISI { sig_inst_sig = sig, sig_inst_skols = skols
1487 , sig_inst_theta = theta, sig_inst_tau = tau })
1488 = hang (ppr sig) 2 (vcat [ ppr skols, ppr theta <+> darrow <+> ppr tau ])
1489
1490 instance Outputable TcPatSynInfo where
1491 ppr (TPSI{ patsig_name = name}) = ppr name
1492
1493 isPartialSig :: TcIdSigInst -> Bool
1494 isPartialSig (TISI { sig_inst_sig = PartialSig {} }) = True
1495 isPartialSig _ = False
1496
1497
1498
1499 {-
1500 ************************************************************************
1501 * *
1502 * Canonical constraints *
1503 * *
1504 * These are the constraints the low-level simplifier works with *
1505 * *
1506 ************************************************************************
1507 -}
1508
1509 -- The syntax of xi (ΞΎ) types:
1510 -- xi ::= a | T xis | xis -> xis | ... | forall a. tau
1511 -- Two important notes:
1512 -- (i) No type families, unless we are under a ForAll
1513 -- (ii) Note that xi types can contain unexpanded type synonyms;
1514 -- however, the (transitive) expansions of those type synonyms
1515 -- will not contain any type functions, unless we are under a ForAll.
1516 -- We enforce the structure of Xi types when we flatten (TcCanonical)
1517
1518 type Xi = Type -- In many comments, "xi" ranges over Xi
1519
1520 type Cts = Bag Ct
1521
1522 data Ct
1523 -- Atomic canonical constraints
1524 = CDictCan { -- e.g. Num xi
1525 cc_ev :: CtEvidence, -- See Note [Ct/evidence invariant]
1526 cc_class :: Class,
1527 cc_tyargs :: [Xi], -- cc_tyargs are function-free, hence Xi
1528 cc_pend_sc :: Bool -- True <=> (a) cc_class has superclasses
1529 -- (b) we have not (yet) added those
1530 -- superclasses as Givens
1531 -- NB: cc_pend_sc is used for G/W/D. For W/D the reason
1532 -- we need superclasses is to expose possible improvement
1533 -- via fundeps
1534 }
1535
1536 | CIrredEvCan { -- These stand for yet-unusable predicates
1537 cc_ev :: CtEvidence -- See Note [Ct/evidence invariant]
1538 -- The ctev_pred of the evidence is
1539 -- of form (tv xi1 xi2 ... xin)
1540 -- or (tv1 ~ ty2) where the CTyEqCan kind invariant fails
1541 -- or (F tys ~ ty) where the CFunEqCan kind invariant fails
1542 -- See Note [CIrredEvCan constraints]
1543 }
1544
1545 | CTyEqCan { -- tv ~ rhs
1546 -- Invariants:
1547 -- * See Note [Applying the inert substitution] in TcFlatten
1548 -- * tv not in tvs(rhs) (occurs check)
1549 -- * If tv is a TauTv, then rhs has no foralls
1550 -- (this avoids substituting a forall for the tyvar in other types)
1551 -- * typeKind ty `tcEqKind` typeKind tv
1552 -- * rhs may have at most one top-level cast
1553 -- * rhs (perhaps under the one cast) is not necessarily function-free,
1554 -- but it has no top-level function.
1555 -- E.g. a ~ [F b] is fine
1556 -- but a ~ F b is not
1557 -- * If the equality is representational, rhs has no top-level newtype
1558 -- See Note [No top-level newtypes on RHS of representational
1559 -- equalities] in TcCanonical
1560 -- * If rhs (perhaps under the cast) is also a tv, then it is oriented
1561 -- to give best chance of
1562 -- unification happening; eg if rhs is touchable then lhs is too
1563 cc_ev :: CtEvidence, -- See Note [Ct/evidence invariant]
1564 cc_tyvar :: TcTyVar,
1565 cc_rhs :: TcType, -- Not necessarily function-free (hence not Xi)
1566 -- See invariants above
1567
1568 cc_eq_rel :: EqRel -- INVARIANT: cc_eq_rel = ctEvEqRel cc_ev
1569 }
1570
1571 | CFunEqCan { -- F xis ~ fsk
1572 -- Invariants:
1573 -- * isTypeFamilyTyCon cc_fun
1574 -- * typeKind (F xis) = tyVarKind fsk
1575 -- * always Nominal role
1576 cc_ev :: CtEvidence, -- See Note [Ct/evidence invariant]
1577 cc_fun :: TyCon, -- A type function
1578
1579 cc_tyargs :: [Xi], -- cc_tyargs are function-free (hence Xi)
1580 -- Either under-saturated or exactly saturated
1581 -- *never* over-saturated (because if so
1582 -- we should have decomposed)
1583
1584 cc_fsk :: TcTyVar -- [Given] always a FlatSkol skolem
1585 -- [Wanted] always a FlatMetaTv unification variable
1586 -- See Note [The flattening story] in TcFlatten
1587 }
1588
1589 | CNonCanonical { -- See Note [NonCanonical Semantics] in TcSMonad
1590 cc_ev :: CtEvidence
1591 }
1592
1593 | CHoleCan { -- See Note [Hole constraints]
1594 -- Treated as an "insoluble" constraint
1595 -- See Note [Insoluble constraints]
1596 cc_ev :: CtEvidence,
1597 cc_hole :: Hole
1598 }
1599
1600 -- | An expression or type hole
1601 data Hole = ExprHole UnboundVar
1602 -- ^ Either an out-of-scope variable or a "true" hole in an
1603 -- expression (TypedHoles)
1604 | TypeHole OccName
1605 -- ^ A hole in a type (PartialTypeSignatures)
1606
1607 holeOcc :: Hole -> OccName
1608 holeOcc (ExprHole uv) = unboundVarOcc uv
1609 holeOcc (TypeHole occ) = occ
1610
1611 {-
1612 Note [Hole constraints]
1613 ~~~~~~~~~~~~~~~~~~~~~~~
1614 CHoleCan constraints are used for two kinds of holes,
1615 distinguished by cc_hole:
1616
1617 * For holes in expressions (including variables not in scope)
1618 e.g. f x = g _ x
1619
1620 * For holes in type signatures
1621 e.g. f :: _ -> _
1622 f x = [x,True]
1623
1624 Note [CIrredEvCan constraints]
1625 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1626 CIrredEvCan constraints are used for constraints that are "stuck"
1627 - we can't solve them (yet)
1628 - we can't use them to solve other constraints
1629 - but they may become soluble if we substitute for some
1630 of the type variables in the constraint
1631
1632 Example 1: (c Int), where c :: * -> Constraint. We can't do anything
1633 with this yet, but if later c := Num, *then* we can solve it
1634
1635 Example 2: a ~ b, where a :: *, b :: k, where k is a kind variable
1636 We don't want to use this to substitute 'b' for 'a', in case
1637 'k' is subequently unifed with (say) *->*, because then
1638 we'd have ill-kinded types floating about. Rather we want
1639 to defer using the equality altogether until 'k' get resolved.
1640
1641 Note [Ct/evidence invariant]
1642 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1643 If ct :: Ct, then extra fields of 'ct' cache precisely the ctev_pred field
1644 of (cc_ev ct), and is fully rewritten wrt the substitution. Eg for CDictCan,
1645 ctev_pred (cc_ev ct) = (cc_class ct) (cc_tyargs ct)
1646 This holds by construction; look at the unique place where CDictCan is
1647 built (in TcCanonical).
1648
1649 In contrast, the type of the evidence *term* (ccev_evtm or ctev_evar/dest) in
1650 the evidence may *not* be fully zonked; we are careful not to look at it
1651 during constraint solving. See Note [Evidence field of CtEvidence]
1652 -}
1653
1654 mkNonCanonical :: CtEvidence -> Ct
1655 mkNonCanonical ev = CNonCanonical { cc_ev = ev }
1656
1657 mkNonCanonicalCt :: Ct -> Ct
1658 mkNonCanonicalCt ct = CNonCanonical { cc_ev = cc_ev ct }
1659
1660 mkGivens :: CtLoc -> [EvId] -> [Ct]
1661 mkGivens loc ev_ids
1662 = map mk ev_ids
1663 where
1664 mk ev_id = mkNonCanonical (CtGiven { ctev_evar = ev_id
1665 , ctev_pred = evVarPred ev_id
1666 , ctev_loc = loc })
1667
1668 ctEvidence :: Ct -> CtEvidence
1669 ctEvidence = cc_ev
1670
1671 ctLoc :: Ct -> CtLoc
1672 ctLoc = ctEvLoc . ctEvidence
1673
1674 setCtLoc :: Ct -> CtLoc -> Ct
1675 setCtLoc ct loc = ct { cc_ev = (cc_ev ct) { ctev_loc = loc } }
1676
1677 ctOrigin :: Ct -> CtOrigin
1678 ctOrigin = ctLocOrigin . ctLoc
1679
1680 ctPred :: Ct -> PredType
1681 -- See Note [Ct/evidence invariant]
1682 ctPred ct = ctEvPred (cc_ev ct)
1683
1684 -- | Makes a new equality predicate with the same role as the given
1685 -- evidence.
1686 mkTcEqPredLikeEv :: CtEvidence -> TcType -> TcType -> TcType
1687 mkTcEqPredLikeEv ev
1688 = case predTypeEqRel pred of
1689 NomEq -> mkPrimEqPred
1690 ReprEq -> mkReprPrimEqPred
1691 where
1692 pred = ctEvPred ev
1693
1694 -- | Get the flavour of the given 'Ct'
1695 ctFlavour :: Ct -> CtFlavour
1696 ctFlavour = ctEvFlavour . ctEvidence
1697
1698 -- | Get the equality relation for the given 'Ct'
1699 ctEqRel :: Ct -> EqRel
1700 ctEqRel = ctEvEqRel . ctEvidence
1701
1702 instance Outputable Ct where
1703 ppr ct = ppr (cc_ev ct) <+> parens pp_sort
1704 where
1705 pp_sort = case ct of
1706 CTyEqCan {} -> text "CTyEqCan"
1707 CFunEqCan {} -> text "CFunEqCan"
1708 CNonCanonical {} -> text "CNonCanonical"
1709 CDictCan { cc_pend_sc = pend_sc }
1710 | pend_sc -> text "CDictCan(psc)"
1711 | otherwise -> text "CDictCan"
1712 CIrredEvCan {} -> text "CIrredEvCan"
1713 CHoleCan { cc_hole = hole } -> text "CHoleCan:" <+> ppr (holeOcc hole)
1714
1715 {-
1716 ************************************************************************
1717 * *
1718 Simple functions over evidence variables
1719 * *
1720 ************************************************************************
1721 -}
1722
1723 ---------------- Getting free tyvars -------------------------
1724
1725 -- | Returns free variables of constraints as a non-deterministic set
1726 tyCoVarsOfCt :: Ct -> TcTyCoVarSet
1727 tyCoVarsOfCt = fvVarSet . tyCoFVsOfCt
1728
1729 -- | Returns free variables of constraints as a deterministically ordered.
1730 -- list. See Note [Deterministic FV] in FV.
1731 tyCoVarsOfCtList :: Ct -> [TcTyCoVar]
1732 tyCoVarsOfCtList = fvVarList . tyCoFVsOfCt
1733
1734 -- | Returns free variables of constraints as a composable FV computation.
1735 -- See Note [Deterministic FV] in FV.
1736 tyCoFVsOfCt :: Ct -> FV
1737 tyCoFVsOfCt (CTyEqCan { cc_tyvar = tv, cc_rhs = xi })
1738 = tyCoFVsOfType xi `unionFV` FV.unitFV tv
1739 `unionFV` tyCoFVsOfType (tyVarKind tv)
1740 tyCoFVsOfCt (CFunEqCan { cc_tyargs = tys, cc_fsk = fsk })
1741 = tyCoFVsOfTypes tys `unionFV` FV.unitFV fsk
1742 `unionFV` tyCoFVsOfType (tyVarKind fsk)
1743 tyCoFVsOfCt (CDictCan { cc_tyargs = tys }) = tyCoFVsOfTypes tys
1744 tyCoFVsOfCt (CIrredEvCan { cc_ev = ev }) = tyCoFVsOfType (ctEvPred ev)
1745 tyCoFVsOfCt (CHoleCan { cc_ev = ev }) = tyCoFVsOfType (ctEvPred ev)
1746 tyCoFVsOfCt (CNonCanonical { cc_ev = ev }) = tyCoFVsOfType (ctEvPred ev)
1747
1748 -- | Returns free variables of a bag of constraints as a non-deterministic
1749 -- set. See Note [Deterministic FV] in FV.
1750 tyCoVarsOfCts :: Cts -> TcTyCoVarSet
1751 tyCoVarsOfCts = fvVarSet . tyCoFVsOfCts
1752
1753 -- | Returns free variables of a bag of constraints as a deterministically
1754 -- odered list. See Note [Deterministic FV] in FV.
1755 tyCoVarsOfCtsList :: Cts -> [TcTyCoVar]
1756 tyCoVarsOfCtsList = fvVarList . tyCoFVsOfCts
1757
1758 -- | Returns free variables of a bag of constraints as a composable FV
1759 -- computation. See Note [Deterministic FV] in FV.
1760 tyCoFVsOfCts :: Cts -> FV
1761 tyCoFVsOfCts = foldrBag (unionFV . tyCoFVsOfCt) emptyFV
1762
1763 -- | Returns free variables of WantedConstraints as a non-deterministic
1764 -- set. See Note [Deterministic FV] in FV.
1765 tyCoVarsOfWC :: WantedConstraints -> TyCoVarSet
1766 -- Only called on *zonked* things, hence no need to worry about flatten-skolems
1767 tyCoVarsOfWC = fvVarSet . tyCoFVsOfWC
1768
1769 -- | Returns free variables of WantedConstraints as a deterministically
1770 -- ordered list. See Note [Deterministic FV] in FV.
1771 tyCoVarsOfWCList :: WantedConstraints -> [TyCoVar]
1772 -- Only called on *zonked* things, hence no need to worry about flatten-skolems
1773 tyCoVarsOfWCList = fvVarList . tyCoFVsOfWC
1774
1775 -- | Returns free variables of WantedConstraints as a composable FV
1776 -- computation. See Note [Deterministic FV] in FV.
1777 tyCoFVsOfWC :: WantedConstraints -> FV
1778 -- Only called on *zonked* things, hence no need to worry about flatten-skolems
1779 tyCoFVsOfWC (WC { wc_simple = simple, wc_impl = implic, wc_insol = insol })
1780 = tyCoFVsOfCts simple `unionFV`
1781 tyCoFVsOfBag tyCoFVsOfImplic implic `unionFV`
1782 tyCoFVsOfCts insol
1783
1784 -- | Returns free variables of Implication as a composable FV computation.
1785 -- See Note [Deterministic FV] in FV.
1786 tyCoFVsOfImplic :: Implication -> FV
1787 -- Only called on *zonked* things, hence no need to worry about flatten-skolems
1788 tyCoFVsOfImplic (Implic { ic_skols = skols
1789 , ic_given = givens
1790 , ic_wanted = wanted })
1791 = FV.delFVs (mkVarSet skols `unionVarSet` mkVarSet givens)
1792 (tyCoFVsOfWC wanted `unionFV` tyCoFVsOfTypes (map evVarPred givens))
1793
1794 tyCoFVsOfBag :: (a -> FV) -> Bag a -> FV
1795 tyCoFVsOfBag tvs_of = foldrBag (unionFV . tvs_of) emptyFV
1796
1797 --------------------------
1798 dropDerivedSimples :: Cts -> Cts
1799 -- Drop all Derived constraints, but make [W] back into [WD],
1800 -- so that if we re-simplify these constraints we will get all
1801 -- the right derived constraints re-generated. Forgetting this
1802 -- step led to #12936
1803 dropDerivedSimples simples = mapMaybeBag dropDerivedCt simples
1804
1805 dropDerivedCt :: Ct -> Maybe Ct
1806 dropDerivedCt ct
1807 = case ctEvFlavour ev of
1808 Wanted WOnly -> Just (ct { cc_ev = ev_wd })
1809 Wanted _ -> Just ct
1810 _ -> ASSERT( isDerivedCt ct ) Nothing
1811 -- simples are all Wanted or Derived
1812 where
1813 ev = ctEvidence ct
1814 ev_wd = ev { ctev_nosh = WDeriv }
1815
1816 dropDerivedInsols :: Cts -> Cts
1817 -- See Note [Dropping derived constraints]
1818 dropDerivedInsols insols = filterBag keep insols
1819 where -- insols can include Given
1820 keep ct
1821 | isDerivedCt ct = not (isDroppableDerivedLoc (ctLoc ct))
1822 | otherwise = True
1823
1824 isDroppableDerivedLoc :: CtLoc -> Bool
1825 -- See Note [Dropping derived constraints]
1826 isDroppableDerivedLoc loc
1827 = case ctLocOrigin loc of
1828 HoleOrigin {} -> False
1829 KindEqOrigin {} -> False
1830 GivenOrigin {} -> False
1831
1832 -- See Note [Dropping derived constraints]
1833 -- For fundeps, drop wanted/wanted interactions
1834 FunDepOrigin2 {} -> False
1835 FunDepOrigin1 _ loc1 _ loc2
1836 | isGivenLoc loc1 || isGivenLoc loc2 -> False
1837 | otherwise -> True
1838 _ -> True
1839
1840 arisesFromGivens :: Ct -> Bool
1841 arisesFromGivens ct
1842 = case ctEvidence ct of
1843 CtGiven {} -> True
1844 CtWanted {} -> False
1845 CtDerived { ctev_loc = loc } -> isGivenLoc loc
1846
1847 isGivenLoc :: CtLoc -> Bool
1848 isGivenLoc loc = isGivenOrigin (ctLocOrigin loc)
1849
1850 isGivenOrigin :: CtOrigin -> Bool
1851 isGivenOrigin (GivenOrigin {}) = True
1852 isGivenOrigin (FunDepOrigin1 _ l1 _ l2) = isGivenLoc l1 && isGivenLoc l2
1853 isGivenOrigin (FunDepOrigin2 _ o1 _ _) = isGivenOrigin o1
1854 isGivenOrigin _ = False
1855
1856 {- Note [Dropping derived constraints]
1857 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1858 In general we discard derived constraints at the end of constraint solving;
1859 see dropDerivedWC. For example
1860
1861 * If we have an unsolved [W] (Ord a), we don't want to complain about
1862 an unsolved [D] (Eq a) as well.
1863
1864 * If we have [W] a ~ Int, [W] a ~ Bool, improvement will generate
1865 [D] Int ~ Bool, and we don't want to report that because it's incomprehensible.
1866 That is why we don't rewrite wanteds with wanteds!
1867
1868 But (tiresomely) we do keep *some* Derived insolubles:
1869
1870 * Type holes are derived constraints, because they have no evidence
1871 and we want to keep them, so we get the error report
1872
1873 * Insoluble derived equalities (e.g. [D] Int ~ Bool) may arise from
1874 functional dependency interactions:
1875 - Given or Wanted interacting with an instance declaration (FunDepOrigin2)
1876 - Given/Given interactions (FunDepOrigin1); this reflects unreachable code
1877 - Given/Wanted interactions (FunDepOrigin1); see Trac #9612
1878
1879 But for Wanted/Wanted interactions we do /not/ want to report an
1880 error (Trac #13506). Consider [W] C Int Int, [W] C Int Bool, with
1881 a fundep on class C. We don't want to report an insoluble Int~Bool;
1882 c.f. "wanteds do not rewrite wanteds".
1883
1884 Moreover, we keep *all* derived insolubles under some circumstances:
1885
1886 * They are looked at by simplifyInfer, to decide whether to
1887 generalise. Example: [W] a ~ Int, [W] a ~ Bool
1888 We get [D] Int ~ Bool, and indeed the constraints are insoluble,
1889 and we want simplifyInfer to see that, even though we don't
1890 ultimately want to generate an (inexplicable) error message from it
1891
1892 To distinguish these cases we use the CtOrigin.
1893
1894
1895 ************************************************************************
1896 * *
1897 CtEvidence
1898 The "flavor" of a canonical constraint
1899 * *
1900 ************************************************************************
1901 -}
1902
1903 isWantedCt :: Ct -> Bool
1904 isWantedCt = isWanted . cc_ev
1905
1906 isGivenCt :: Ct -> Bool
1907 isGivenCt = isGiven . cc_ev
1908
1909 isDerivedCt :: Ct -> Bool
1910 isDerivedCt = isDerived . cc_ev
1911
1912 isCTyEqCan :: Ct -> Bool
1913 isCTyEqCan (CTyEqCan {}) = True
1914 isCTyEqCan (CFunEqCan {}) = False
1915 isCTyEqCan _ = False
1916
1917 isCDictCan_Maybe :: Ct -> Maybe Class
1918 isCDictCan_Maybe (CDictCan {cc_class = cls }) = Just cls
1919 isCDictCan_Maybe _ = Nothing
1920
1921 isCIrredEvCan :: Ct -> Bool
1922 isCIrredEvCan (CIrredEvCan {}) = True
1923 isCIrredEvCan _ = False
1924
1925 isCFunEqCan_maybe :: Ct -> Maybe (TyCon, [Type])
1926 isCFunEqCan_maybe (CFunEqCan { cc_fun = tc, cc_tyargs = xis }) = Just (tc, xis)
1927 isCFunEqCan_maybe _ = Nothing
1928
1929 isCFunEqCan :: Ct -> Bool
1930 isCFunEqCan (CFunEqCan {}) = True
1931 isCFunEqCan _ = False
1932
1933 isCNonCanonical :: Ct -> Bool
1934 isCNonCanonical (CNonCanonical {}) = True
1935 isCNonCanonical _ = False
1936
1937 isHoleCt:: Ct -> Bool
1938 isHoleCt (CHoleCan {}) = True
1939 isHoleCt _ = False
1940
1941 isOutOfScopeCt :: Ct -> Bool
1942 -- We treat expression holes representing out-of-scope variables a bit
1943 -- differently when it comes to error reporting
1944 isOutOfScopeCt (CHoleCan { cc_hole = ExprHole (OutOfScope {}) }) = True
1945 isOutOfScopeCt _ = False
1946
1947 isExprHoleCt :: Ct -> Bool
1948 isExprHoleCt (CHoleCan { cc_hole = ExprHole {} }) = True
1949 isExprHoleCt _ = False
1950
1951 isTypeHoleCt :: Ct -> Bool
1952 isTypeHoleCt (CHoleCan { cc_hole = TypeHole {} }) = True
1953 isTypeHoleCt _ = False
1954
1955
1956 {- Note [Custom type errors in constraints]
1957 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1958
1959 When GHC reports a type-error about an unsolved-constraint, we check
1960 to see if the constraint contains any custom-type errors, and if so
1961 we report them. Here are some examples of constraints containing type
1962 errors:
1963
1964 TypeError msg -- The actual constraint is a type error
1965
1966 TypError msg ~ Int -- Some type was supposed to be Int, but ended up
1967 -- being a type error instead
1968
1969 Eq (TypeError msg) -- A class constraint is stuck due to a type error
1970
1971 F (TypeError msg) ~ a -- A type function failed to evaluate due to a type err
1972
1973 It is also possible to have constraints where the type error is nested deeper,
1974 for example see #11990, and also:
1975
1976 Eq (F (TypeError msg)) -- Here the type error is nested under a type-function
1977 -- call, which failed to evaluate because of it,
1978 -- and so the `Eq` constraint was unsolved.
1979 -- This may happen when one function calls another
1980 -- and the called function produced a custom type error.
1981 -}
1982
1983 -- | A constraint is considered to be a custom type error, if it contains
1984 -- custom type errors anywhere in it.
1985 -- See Note [Custom type errors in constraints]
1986 getUserTypeErrorMsg :: Ct -> Maybe Type
1987 getUserTypeErrorMsg ct = findUserTypeError (ctPred ct)
1988 where
1989 findUserTypeError t = msum ( userTypeError_maybe t
1990 : map findUserTypeError (subTys t)
1991 )
1992
1993 subTys t = case splitAppTys t of
1994 (t,[]) ->
1995 case splitTyConApp_maybe t of
1996 Nothing -> []
1997 Just (_,ts) -> ts
1998 (t,ts) -> t : ts
1999
2000
2001
2002
2003 isUserTypeErrorCt :: Ct -> Bool
2004 isUserTypeErrorCt ct = case getUserTypeErrorMsg ct of
2005 Just _ -> True
2006 _ -> False
2007
2008 isPendingScDict :: Ct -> Maybe Ct
2009 -- Says whether cc_pend_sc is True, AND if so flips the flag
2010 isPendingScDict ct@(CDictCan { cc_pend_sc = True })
2011 = Just (ct { cc_pend_sc = False })
2012 isPendingScDict _ = Nothing
2013
2014 superClassesMightHelp :: Ct -> Bool
2015 -- ^ True if taking superclasses of givens, or of wanteds (to perhaps
2016 -- expose more equalities or functional dependencies) might help to
2017 -- solve this constraint. See Note [When superclasses help]
2018 superClassesMightHelp ct
2019 = isWantedCt ct && not (is_ip ct)
2020 where
2021 is_ip (CDictCan { cc_class = cls }) = isIPClass cls
2022 is_ip _ = False
2023
2024 {- Note [When superclasses help]
2025 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2026 First read Note [The superclass story] in TcCanonical.
2027
2028 We expand superclasses and iterate only if there is at unsolved wanted
2029 for which expansion of superclasses (e.g. from given constraints)
2030 might actually help. The function superClassesMightHelp tells if
2031 doing this superclass expansion might help solve this constraint.
2032 Note that
2033
2034 * Superclasses help only for Wanted constraints. Derived constraints
2035 are not really "unsolved" and we certainly don't want them to
2036 trigger superclass expansion. This was a good part of the loop
2037 in Trac #11523
2038
2039 * Even for Wanted constraints, we say "no" for implicit parameters.
2040 we have [W] ?x::ty, expanding superclasses won't help:
2041 - Superclasses can't be implicit parameters
2042 - If we have a [G] ?x:ty2, then we'll have another unsolved
2043 [D] ty ~ ty2 (from the functional dependency)
2044 which will trigger superclass expansion.
2045
2046 It's a bit of a special case, but it's easy to do. The runtime cost
2047 is low because the unsolved set is usually empty anyway (errors
2048 aside), and the first non-imlicit-parameter will terminate the search.
2049
2050 The special case is worth it (Trac #11480, comment:2) because it
2051 applies to CallStack constraints, which aren't type errors. If we have
2052 f :: (C a) => blah
2053 f x = ...undefined...
2054 we'll get a CallStack constraint. If that's the only unsolved
2055 constraint it'll eventually be solved by defaulting. So we don't
2056 want to emit warnings about hitting the simplifier's iteration
2057 limit. A CallStack constraint really isn't an unsolved
2058 constraint; it can always be solved by defaulting.
2059 -}
2060
2061 singleCt :: Ct -> Cts
2062 singleCt = unitBag
2063
2064 andCts :: Cts -> Cts -> Cts
2065 andCts = unionBags
2066
2067 listToCts :: [Ct] -> Cts
2068 listToCts = listToBag
2069
2070 ctsElts :: Cts -> [Ct]
2071 ctsElts = bagToList
2072
2073 consCts :: Ct -> Cts -> Cts
2074 consCts = consBag
2075
2076 snocCts :: Cts -> Ct -> Cts
2077 snocCts = snocBag
2078
2079 extendCtsList :: Cts -> [Ct] -> Cts
2080 extendCtsList cts xs | null xs = cts
2081 | otherwise = cts `unionBags` listToBag xs
2082
2083 andManyCts :: [Cts] -> Cts
2084 andManyCts = unionManyBags
2085
2086 emptyCts :: Cts
2087 emptyCts = emptyBag
2088
2089 isEmptyCts :: Cts -> Bool
2090 isEmptyCts = isEmptyBag
2091
2092 pprCts :: Cts -> SDoc
2093 pprCts cts = vcat (map ppr (bagToList cts))
2094
2095 {-
2096 ************************************************************************
2097 * *
2098 Wanted constraints
2099 These are forced to be in TcRnTypes because
2100 TcLclEnv mentions WantedConstraints
2101 WantedConstraint mentions CtLoc
2102 CtLoc mentions ErrCtxt
2103 ErrCtxt mentions TcM
2104 * *
2105 v%************************************************************************
2106 -}
2107
2108 data WantedConstraints
2109 = WC { wc_simple :: Cts -- Unsolved constraints, all wanted
2110 , wc_impl :: Bag Implication
2111 , wc_insol :: Cts -- Insoluble constraints, can be
2112 -- wanted, given, or derived
2113 -- See Note [Insoluble constraints]
2114 }
2115
2116 emptyWC :: WantedConstraints
2117 emptyWC = WC { wc_simple = emptyBag, wc_impl = emptyBag, wc_insol = emptyBag }
2118
2119 mkSimpleWC :: [CtEvidence] -> WantedConstraints
2120 mkSimpleWC cts
2121 = WC { wc_simple = listToBag (map mkNonCanonical cts)
2122 , wc_impl = emptyBag
2123 , wc_insol = emptyBag }
2124
2125 mkImplicWC :: Bag Implication -> WantedConstraints
2126 mkImplicWC implic
2127 = WC { wc_simple = emptyBag, wc_impl = implic, wc_insol = emptyBag }
2128
2129 isEmptyWC :: WantedConstraints -> Bool
2130 isEmptyWC (WC { wc_simple = f, wc_impl = i, wc_insol = n })
2131 = isEmptyBag f && isEmptyBag i && isEmptyBag n
2132
2133 andWC :: WantedConstraints -> WantedConstraints -> WantedConstraints
2134 andWC (WC { wc_simple = f1, wc_impl = i1, wc_insol = n1 })
2135 (WC { wc_simple = f2, wc_impl = i2, wc_insol = n2 })
2136 = WC { wc_simple = f1 `unionBags` f2
2137 , wc_impl = i1 `unionBags` i2
2138 , wc_insol = n1 `unionBags` n2 }
2139
2140 unionsWC :: [WantedConstraints] -> WantedConstraints
2141 unionsWC = foldr andWC emptyWC
2142
2143 addSimples :: WantedConstraints -> Bag Ct -> WantedConstraints
2144 addSimples wc cts
2145 = wc { wc_simple = wc_simple wc `unionBags` cts }
2146 -- Consider: Put the new constraints at the front, so they get solved first
2147
2148 addImplics :: WantedConstraints -> Bag Implication -> WantedConstraints
2149 addImplics wc implic = wc { wc_impl = wc_impl wc `unionBags` implic }
2150
2151 addInsols :: WantedConstraints -> Bag Ct -> WantedConstraints
2152 addInsols wc cts
2153 = wc { wc_insol = wc_insol wc `unionBags` cts }
2154
2155 getInsolubles :: WantedConstraints -> Cts
2156 getInsolubles = wc_insol
2157
2158 insolublesOnly :: WantedConstraints -> WantedConstraints
2159 -- Keep only the insolubles
2160 insolublesOnly wc = wc { wc_simple = emptyBag, wc_impl = emptyBag }
2161
2162 dropDerivedWC :: WantedConstraints -> WantedConstraints
2163 -- See Note [Dropping derived constraints]
2164 dropDerivedWC wc@(WC { wc_simple = simples, wc_insol = insols })
2165 = wc { wc_simple = dropDerivedSimples simples
2166 , wc_insol = dropDerivedInsols insols }
2167 -- The wc_impl implications are already (recursively) filtered
2168
2169 isSolvedStatus :: ImplicStatus -> Bool
2170 isSolvedStatus (IC_Solved {}) = True
2171 isSolvedStatus _ = False
2172
2173 isInsolubleStatus :: ImplicStatus -> Bool
2174 isInsolubleStatus IC_Insoluble = True
2175 isInsolubleStatus _ = False
2176
2177 insolubleImplic :: Implication -> Bool
2178 insolubleImplic ic = isInsolubleStatus (ic_status ic)
2179
2180 insolubleWC :: WantedConstraints -> Bool
2181 insolubleWC (WC { wc_impl = implics, wc_insol = insols })
2182 = anyBag trulyInsoluble insols
2183 || anyBag insolubleImplic implics
2184
2185 trulyInsoluble :: Ct -> Bool
2186 -- Constraints in the wc_insol set which ARE NOT
2187 -- treated as truly insoluble:
2188 -- a) type holes, arising from PartialTypeSignatures,
2189 -- b) "true" expression holes arising from TypedHoles
2190 --
2191 -- An "expression hole" or "type hole" constraint isn't really an error
2192 -- at all; it's a report saying "_ :: Int" here. But an out-of-scope
2193 -- variable masquerading as expression holes IS treated as truly
2194 -- insoluble, so that it trumps other errors during error reporting.
2195 -- Yuk!
2196 trulyInsoluble insol
2197 | isHoleCt insol = isOutOfScopeCt insol
2198 | otherwise = True
2199
2200 instance Outputable WantedConstraints where
2201 ppr (WC {wc_simple = s, wc_impl = i, wc_insol = n})
2202 = text "WC" <+> braces (vcat
2203 [ ppr_bag (text "wc_simple") s
2204 , ppr_bag (text "wc_insol") n
2205 , ppr_bag (text "wc_impl") i ])
2206
2207 ppr_bag :: Outputable a => SDoc -> Bag a -> SDoc
2208 ppr_bag doc bag
2209 | isEmptyBag bag = empty
2210 | otherwise = hang (doc <+> equals)
2211 2 (foldrBag (($$) . ppr) empty bag)
2212
2213 {-
2214 ************************************************************************
2215 * *
2216 Implication constraints
2217 * *
2218 ************************************************************************
2219 -}
2220
2221 data Implication
2222 = Implic {
2223 ic_tclvl :: TcLevel, -- TcLevel of unification variables
2224 -- allocated /inside/ this implication
2225
2226 ic_skols :: [TcTyVar], -- Introduced skolems
2227 ic_info :: SkolemInfo, -- See Note [Skolems in an implication]
2228 -- See Note [Shadowing in a constraint]
2229
2230 ic_given :: [EvVar], -- Given evidence variables
2231 -- (order does not matter)
2232 -- See Invariant (GivenInv) in TcType
2233
2234 ic_no_eqs :: Bool, -- True <=> ic_givens have no equalities, for sure
2235 -- False <=> ic_givens might have equalities
2236
2237 ic_env :: TcLclEnv, -- Gives the source location and error context
2238 -- for the implication, and hence for all the
2239 -- given evidence variables
2240
2241 ic_wanted :: WantedConstraints, -- The wanted
2242
2243 ic_binds :: EvBindsVar, -- Points to the place to fill in the
2244 -- abstraction and bindings.
2245
2246 ic_needed :: VarSet, -- Union of the ics_need fields of any /discarded/
2247 -- solved implications in ic_wanted
2248
2249 ic_status :: ImplicStatus
2250 }
2251
2252 data ImplicStatus
2253 = IC_Solved -- All wanteds in the tree are solved, all the way down
2254 { ics_need :: VarSet -- Evidence variables bound further out,
2255 -- but needed by this solved implication
2256 , ics_dead :: [EvVar] } -- Subset of ic_given that are not needed
2257 -- See Note [Tracking redundant constraints] in TcSimplify
2258
2259 | IC_Insoluble -- At least one insoluble constraint in the tree
2260
2261 | IC_Unsolved -- Neither of the above; might go either way
2262
2263 instance Outputable Implication where
2264 ppr (Implic { ic_tclvl = tclvl, ic_skols = skols
2265 , ic_given = given, ic_no_eqs = no_eqs
2266 , ic_wanted = wanted, ic_status = status
2267 , ic_binds = binds, ic_needed = needed , ic_info = info })
2268 = hang (text "Implic" <+> lbrace)
2269 2 (sep [ text "TcLevel =" <+> ppr tclvl
2270 , text "Skolems =" <+> pprTyVars skols
2271 , text "No-eqs =" <+> ppr no_eqs
2272 , text "Status =" <+> ppr status
2273 , hang (text "Given =") 2 (pprEvVars given)
2274 , hang (text "Wanted =") 2 (ppr wanted)
2275 , text "Binds =" <+> ppr binds
2276 , text "Needed =" <+> ppr needed
2277 , pprSkolInfo info ] <+> rbrace)
2278
2279 instance Outputable ImplicStatus where
2280 ppr IC_Insoluble = text "Insoluble"
2281 ppr IC_Unsolved = text "Unsolved"
2282 ppr (IC_Solved { ics_need = vs, ics_dead = dead })
2283 = text "Solved"
2284 <+> (braces $ vcat [ text "Dead givens =" <+> ppr dead
2285 , text "Needed =" <+> ppr vs ])
2286
2287 {-
2288 Note [Needed evidence variables]
2289 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2290 Th ic_need_evs field holds the free vars of ic_binds, and all the
2291 ic_binds in nested implications.
2292
2293 * Main purpose: if one of the ic_givens is not mentioned in here, it
2294 is redundant.
2295
2296 * solveImplication may drop an implication altogether if it has no
2297 remaining 'wanteds'. But we still track the free vars of its
2298 evidence binds, even though it has now disappeared.
2299
2300 Note [Shadowing in a constraint]
2301 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2302 We assume NO SHADOWING in a constraint. Specifically
2303 * The unification variables are all implicitly quantified at top
2304 level, and are all unique
2305 * The skolem variables bound in ic_skols are all freah when the
2306 implication is created.
2307 So we can safely substitute. For example, if we have
2308 forall a. a~Int => ...(forall b. ...a...)...
2309 we can push the (a~Int) constraint inwards in the "givens" without
2310 worrying that 'b' might clash.
2311
2312 Note [Skolems in an implication]
2313 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2314 The skolems in an implication are not there to perform a skolem escape
2315 check. That happens because all the environment variables are in the
2316 untouchables, and therefore cannot be unified with anything at all,
2317 let alone the skolems.
2318
2319 Instead, ic_skols is used only when considering floating a constraint
2320 outside the implication in TcSimplify.floatEqualities or
2321 TcSimplify.approximateImplications
2322
2323 Note [Insoluble constraints]
2324 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2325 Some of the errors that we get during canonicalization are best
2326 reported when all constraints have been simplified as much as
2327 possible. For instance, assume that during simplification the
2328 following constraints arise:
2329
2330 [Wanted] F alpha ~ uf1
2331 [Wanted] beta ~ uf1 beta
2332
2333 When canonicalizing the wanted (beta ~ uf1 beta), if we eagerly fail
2334 we will simply see a message:
2335 'Can't construct the infinite type beta ~ uf1 beta'
2336 and the user has no idea what the uf1 variable is.
2337
2338 Instead our plan is that we will NOT fail immediately, but:
2339 (1) Record the "frozen" error in the ic_insols field
2340 (2) Isolate the offending constraint from the rest of the inerts
2341 (3) Keep on simplifying/canonicalizing
2342
2343 At the end, we will hopefully have substituted uf1 := F alpha, and we
2344 will be able to report a more informative error:
2345 'Can't construct the infinite type beta ~ F alpha beta'
2346
2347 Insoluble constraints *do* include Derived constraints. For example,
2348 a functional dependency might give rise to [D] Int ~ Bool, and we must
2349 report that. If insolubles did not contain Deriveds, reportErrors would
2350 never see it.
2351
2352
2353 ************************************************************************
2354 * *
2355 Pretty printing
2356 * *
2357 ************************************************************************
2358 -}
2359
2360 pprEvVars :: [EvVar] -> SDoc -- Print with their types
2361 pprEvVars ev_vars = vcat (map pprEvVarWithType ev_vars)
2362
2363 pprEvVarTheta :: [EvVar] -> SDoc
2364 pprEvVarTheta ev_vars = pprTheta (map evVarPred ev_vars)
2365
2366 pprEvVarWithType :: EvVar -> SDoc
2367 pprEvVarWithType v = ppr v <+> dcolon <+> pprType (evVarPred v)
2368
2369 {-
2370 ************************************************************************
2371 * *
2372 CtEvidence
2373 * *
2374 ************************************************************************
2375
2376 Note [Evidence field of CtEvidence]
2377 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2378 During constraint solving we never look at the type of ctev_evar/ctev_dest;
2379 instead we look at the ctev_pred field. The evtm/evar field
2380 may be un-zonked.
2381
2382 Note [Bind new Givens immediately]
2383 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2384 For Givens we make new EvVars and bind them immediately. Two main reasons:
2385 * Gain sharing. E.g. suppose we start with g :: C a b, where
2386 class D a => C a b
2387 class (E a, F a) => D a
2388 If we generate all g's superclasses as separate EvTerms we might
2389 get selD1 (selC1 g) :: E a
2390 selD2 (selC1 g) :: F a
2391 selC1 g :: D a
2392 which we could do more economically as:
2393 g1 :: D a = selC1 g
2394 g2 :: E a = selD1 g1
2395 g3 :: F a = selD2 g1
2396
2397 * For *coercion* evidence we *must* bind each given:
2398 class (a~b) => C a b where ....
2399 f :: C a b => ....
2400 Then in f's Givens we have g:(C a b) and the superclass sc(g,0):a~b.
2401 But that superclass selector can't (yet) appear in a coercion
2402 (see evTermCoercion), so the easy thing is to bind it to an Id.
2403
2404 So a Given has EvVar inside it rather than (as previously) an EvTerm.
2405 -}
2406
2407 -- | A place for type-checking evidence to go after it is generated.
2408 -- Wanted equalities are always HoleDest; other wanteds are always
2409 -- EvVarDest.
2410 data TcEvDest
2411 = EvVarDest EvVar -- ^ bind this var to the evidence
2412 | HoleDest CoercionHole -- ^ fill in this hole with the evidence
2413 -- See Note [Coercion holes] in TyCoRep
2414
2415 data CtEvidence
2416 = CtGiven -- Truly given, not depending on subgoals
2417 -- NB: Spontaneous unifications belong here
2418 { ctev_pred :: TcPredType -- See Note [Ct/evidence invariant]
2419 , ctev_evar :: EvVar -- See Note [Evidence field of CtEvidence]
2420 , ctev_loc :: CtLoc }
2421
2422
2423 | CtWanted -- Wanted goal
2424 { ctev_pred :: TcPredType -- See Note [Ct/evidence invariant]
2425 , ctev_dest :: TcEvDest
2426 , ctev_nosh :: ShadowInfo -- See Note [Constraint flavours]
2427 , ctev_loc :: CtLoc }
2428
2429 | CtDerived -- A goal that we don't really have to solve and can't
2430 -- immediately rewrite anything other than a derived
2431 -- (there's no evidence!) but if we do manage to solve
2432 -- it may help in solving other goals.
2433 { ctev_pred :: TcPredType
2434 , ctev_loc :: CtLoc }
2435
2436 ctEvPred :: CtEvidence -> TcPredType
2437 -- The predicate of a flavor
2438 ctEvPred = ctev_pred
2439
2440 ctEvLoc :: CtEvidence -> CtLoc
2441 ctEvLoc = ctev_loc
2442
2443 ctEvOrigin :: CtEvidence -> CtOrigin
2444 ctEvOrigin = ctLocOrigin . ctEvLoc
2445
2446 -- | Get the equality relation relevant for a 'CtEvidence'
2447 ctEvEqRel :: CtEvidence -> EqRel
2448 ctEvEqRel = predTypeEqRel . ctEvPred
2449
2450 -- | Get the role relevant for a 'CtEvidence'
2451 ctEvRole :: CtEvidence -> Role
2452 ctEvRole = eqRelRole . ctEvEqRel
2453
2454 ctEvTerm :: CtEvidence -> EvTerm
2455 ctEvTerm ev@(CtWanted { ctev_dest = HoleDest _ }) = EvCoercion $ ctEvCoercion ev
2456 ctEvTerm ev = EvId (ctEvId ev)
2457
2458 ctEvCoercion :: CtEvidence -> Coercion
2459 ctEvCoercion ev@(CtWanted { ctev_dest = HoleDest hole, ctev_pred = pred })
2460 = case getEqPredTys_maybe pred of
2461 Just (role, ty1, ty2) -> mkHoleCo hole role ty1 ty2
2462 _ -> pprPanic "ctEvTerm" (ppr ev)
2463 ctEvCoercion (CtGiven { ctev_evar = ev_id }) = mkTcCoVarCo ev_id
2464 ctEvCoercion ev = pprPanic "ctEvCoercion" (ppr ev)
2465
2466 ctEvId :: CtEvidence -> TcId
2467 ctEvId (CtWanted { ctev_dest = EvVarDest ev }) = ev
2468 ctEvId (CtGiven { ctev_evar = ev }) = ev
2469 ctEvId ctev = pprPanic "ctEvId:" (ppr ctev)
2470
2471 instance Outputable TcEvDest where
2472 ppr (HoleDest h) = text "hole" <> ppr h
2473 ppr (EvVarDest ev) = ppr ev
2474
2475 instance Outputable CtEvidence where
2476 ppr ev = ppr (ctEvFlavour ev)
2477 <+> pp_ev
2478 <+> braces (ppr (ctl_depth (ctEvLoc ev))) <> dcolon
2479 -- Show the sub-goal depth too
2480 <+> ppr (ctEvPred ev)
2481 where
2482 pp_ev = case ev of
2483 CtGiven { ctev_evar = v } -> ppr v
2484 CtWanted {ctev_dest = d } -> ppr d
2485 CtDerived {} -> text "_"
2486
2487 isWanted :: CtEvidence -> Bool
2488 isWanted (CtWanted {}) = True
2489 isWanted _ = False
2490
2491 isGiven :: CtEvidence -> Bool
2492 isGiven (CtGiven {}) = True
2493 isGiven _ = False
2494
2495 isDerived :: CtEvidence -> Bool
2496 isDerived (CtDerived {}) = True
2497 isDerived _ = False
2498
2499 {-
2500 %************************************************************************
2501 %* *
2502 CtFlavour
2503 %* *
2504 %************************************************************************
2505
2506 Note [Constraint flavours]
2507 ~~~~~~~~~~~~~~~~~~~~~~~~~~
2508 Constraints come in four flavours:
2509
2510 * [G] Given: we have evidence
2511
2512 * [W] Wanted WOnly: we want evidence
2513
2514 * [D] Derived: any solution must satisfy this constraint, but
2515 we don't need evidence for it. Examples include:
2516 - superclasses of [W] class constraints
2517 - equalities arising from functional dependencies
2518 or injectivity
2519
2520 * [WD] Wanted WDeriv: a single constraint that represents
2521 both [W] and [D]
2522 We keep them paired as one both for efficiency, and because
2523 when we have a finite map F tys -> CFunEqCan, it's inconvenient
2524 to have two CFunEqCans in the range
2525
2526 The ctev_nosh field of a Wanted distinguishes between [W] and [WD]
2527
2528 Wanted constraints are born as [WD], but are split into [W] and its
2529 "shadow" [D] in TcSMonad.maybeEmitShadow.
2530
2531 See Note [The improvement story and derived shadows] in TcSMonad
2532 -}
2533
2534 data CtFlavour -- See Note [Constraint flavours]
2535 = Given
2536 | Wanted ShadowInfo
2537 | Derived
2538 deriving Eq
2539
2540 data ShadowInfo
2541 = WDeriv -- [WD] This Wanted constraint has no Derived shadow,
2542 -- so it behaves like a pair of a Wanted and a Derived
2543 | WOnly -- [W] It has a separate derived shadow
2544 -- See Note [Derived shadows]
2545 deriving( Eq )
2546
2547 isGivenOrWDeriv :: CtFlavour -> Bool
2548 isGivenOrWDeriv Given = True
2549 isGivenOrWDeriv (Wanted WDeriv) = True
2550 isGivenOrWDeriv _ = False
2551
2552 instance Outputable CtFlavour where
2553 ppr Given = text "[G]"
2554 ppr (Wanted WDeriv) = text "[WD]"
2555 ppr (Wanted WOnly) = text "[W]"
2556 ppr Derived = text "[D]"
2557
2558 ctEvFlavour :: CtEvidence -> CtFlavour
2559 ctEvFlavour (CtWanted { ctev_nosh = nosh }) = Wanted nosh
2560 ctEvFlavour (CtGiven {}) = Given
2561 ctEvFlavour (CtDerived {}) = Derived
2562
2563 -- | Whether or not one 'Ct' can rewrite another is determined by its
2564 -- flavour and its equality relation. See also
2565 -- Note [Flavours with roles] in TcSMonad
2566 type CtFlavourRole = (CtFlavour, EqRel)
2567
2568 -- | Extract the flavour, role, and boxity from a 'CtEvidence'
2569 ctEvFlavourRole :: CtEvidence -> CtFlavourRole
2570 ctEvFlavourRole ev = (ctEvFlavour ev, ctEvEqRel ev)
2571
2572 -- | Extract the flavour, role, and boxity from a 'Ct'
2573 ctFlavourRole :: Ct -> CtFlavourRole
2574 ctFlavourRole = ctEvFlavourRole . cc_ev
2575
2576 {- Note [eqCanRewrite]
2577 ~~~~~~~~~~~~~~~~~~~~~~
2578 (eqCanRewrite ct1 ct2) holds if the constraint ct1 (a CTyEqCan of form
2579 tv ~ ty) can be used to rewrite ct2. It must satisfy the properties of
2580 a can-rewrite relation, see Definition [Can-rewrite relation] in
2581 TcSMonad.
2582
2583 With the solver handling Coercible constraints like equality constraints,
2584 the rewrite conditions must take role into account, never allowing
2585 a representational equality to rewrite a nominal one.
2586
2587 Note [Wanteds do not rewrite Wanteds]
2588 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2589 We don't allow Wanteds to rewrite Wanteds, because that can give rise
2590 to very confusing type error messages. A good example is Trac #8450.
2591 Here's another
2592 f :: a -> Bool
2593 f x = ( [x,'c'], [x,True] ) `seq` True
2594 Here we get
2595 [W] a ~ Char
2596 [W] a ~ Bool
2597 but we do not want to complain about Bool ~ Char!
2598
2599 Note [Deriveds do rewrite Deriveds]
2600 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2601 However we DO allow Deriveds to rewrite Deriveds, because that's how
2602 improvement works; see Note [The improvement story] in TcInteract.
2603
2604 However, for now at least I'm only letting (Derived,NomEq) rewrite
2605 (Derived,NomEq) and not doing anything for ReprEq. If we have
2606 eqCanRewriteFR (Derived, NomEq) (Derived, _) = True
2607 then we lose property R2 of Definition [Can-rewrite relation]
2608 in TcSMonad
2609 R2. If f1 >= f, and f2 >= f,
2610 then either f1 >= f2 or f2 >= f1
2611 Consider f1 = (Given, ReprEq)
2612 f2 = (Derived, NomEq)
2613 f = (Derived, ReprEq)
2614
2615 I thought maybe we could never get Derived ReprEq constraints, but
2616 we can; straight from the Wanteds during improvement. And from a Derived
2617 ReprEq we could conceivably get a Derived NomEq improvement (by decomposing
2618 a type constructor with Nomninal role), and hence unify.
2619 -}
2620
2621 eqCanRewriteFR :: CtFlavourRole -> CtFlavourRole -> Bool
2622 -- Can fr1 actually rewrite fr2?
2623 -- Very important function!
2624 -- See Note [eqCanRewrite]
2625 -- See Note [Wanteds do not rewrite Wanteds]
2626 -- See Note [Deriveds do rewrite Deriveds]
2627 eqCanRewriteFR (Given, NomEq) (_, _) = True
2628 eqCanRewriteFR (Given, ReprEq) (_, ReprEq) = True
2629 eqCanRewriteFR (Wanted WDeriv, NomEq) (Derived, NomEq) = True
2630 eqCanRewriteFR (Derived, NomEq) (Derived, NomEq) = True
2631 eqCanRewriteFR _ _ = False
2632
2633 eqMayRewriteFR :: CtFlavourRole -> CtFlavourRole -> Bool
2634 -- Is it /possible/ that fr1 can rewrite fr2?
2635 -- This is used when deciding which inerts to kick out,
2636 -- at which time a [WD] inert may be split into [W] and [D]
2637 eqMayRewriteFR (Wanted WDeriv, NomEq) (Wanted WDeriv, NomEq) = True
2638 eqMayRewriteFR (Derived, NomEq) (Wanted WDeriv, NomEq) = True
2639 eqMayRewriteFR fr1 fr2 = eqCanRewriteFR fr1 fr2
2640
2641 -----------------
2642 {- Note [funEqCanDischarge]
2643 ~~~~~~~~~~~~~~~~~~~~~~~~~~~
2644 Suppose we have two CFunEqCans with the same LHS:
2645 (x1:F ts ~ f1) `funEqCanDischarge` (x2:F ts ~ f2)
2646 Can we drop x2 in favour of x1, either unifying
2647 f2 (if it's a flatten meta-var) or adding a new Given
2648 (f1 ~ f2), if x2 is a Given?
2649
2650 Answer: yes if funEqCanDischarge is true.
2651 -}
2652
2653 funEqCanDischarge
2654 :: CtEvidence -> CtEvidence
2655 -> ( SwapFlag -- NotSwapped => lhs can discharge rhs
2656 -- Swapped => rhs can discharge lhs
2657 , Bool) -- True <=> upgrade non-discharded one
2658 -- from [W] to [WD]
2659 -- See Note [funEqCanDischarge]
2660 funEqCanDischarge ev1 ev2
2661 = ASSERT2( ctEvEqRel ev1 == NomEq, ppr ev1 )
2662 ASSERT2( ctEvEqRel ev2 == NomEq, ppr ev2 )
2663 -- CFunEqCans are all Nominal, hence asserts
2664 funEqCanDischargeF (ctEvFlavour ev1) (ctEvFlavour ev2)
2665
2666 funEqCanDischargeF :: CtFlavour -> CtFlavour -> (SwapFlag, Bool)
2667 funEqCanDischargeF Given _ = (NotSwapped, False)
2668 funEqCanDischargeF _ Given = (IsSwapped, False)
2669 funEqCanDischargeF (Wanted WDeriv) _ = (NotSwapped, False)
2670 funEqCanDischargeF _ (Wanted WDeriv) = (IsSwapped, True)
2671 funEqCanDischargeF (Wanted WOnly) (Wanted WOnly) = (NotSwapped, False)
2672 funEqCanDischargeF (Wanted WOnly) Derived = (NotSwapped, True)
2673 funEqCanDischargeF Derived (Wanted WOnly) = (IsSwapped, True)
2674 funEqCanDischargeF Derived Derived = (NotSwapped, False)
2675
2676
2677 {- Note [eqCanDischarge]
2678 ~~~~~~~~~~~~~~~~~~~~~~~~
2679 Suppose we have two identical CTyEqCan equality constraints
2680 (i.e. both LHS and RHS are the same)
2681 (x1:a~t) `eqCanDischarge` (xs:a~t)
2682 Can we just drop x2 in favour of x1?
2683
2684 Answer: yes if eqCanDischarge is true.
2685
2686 Note that we do /not/ allow Wanted to discharge Derived.
2687 We must keep both. Why? Because the Derived may rewrite
2688 other Deriveds in the model whereas the Wanted cannot.
2689
2690 However a Wanted can certainly discharge an identical Wanted. So
2691 eqCanDischarge does /not/ define a can-rewrite relation in the
2692 sense of Definition [Can-rewrite relation] in TcSMonad.
2693
2694 We /do/ say that a [W] can discharge a [WD]. In evidence terms it
2695 certainly can, and the /caller/ arranges that the otherwise-lost [D]
2696 is spat out as a new Derived. -}
2697
2698 eqCanDischarge :: CtEvidence -> CtEvidence -> Bool
2699 -- See Note [eqCanDischarge]
2700 eqCanDischarge ev1 ev2 = eqCanDischargeFR (ctEvFlavourRole ev1)
2701 (ctEvFlavourRole ev2)
2702
2703 eqCanDischargeFR :: CtFlavourRole -> CtFlavourRole -> Bool
2704 eqCanDischargeFR (_, ReprEq) (_, NomEq) = False
2705 eqCanDischargeFR (f1,_) (f2, _) = eqCanDischargeF f1 f2
2706
2707 eqCanDischargeF :: CtFlavour -> CtFlavour -> Bool
2708 eqCanDischargeF Given _ = True
2709 eqCanDischargeF (Wanted _) (Wanted _) = True
2710 eqCanDischargeF (Wanted WDeriv) Derived = True
2711 eqCanDischargeF Derived Derived = True
2712 eqCanDischargeF _ _ = False
2713
2714
2715 {-
2716 ************************************************************************
2717 * *
2718 SubGoalDepth
2719 * *
2720 ************************************************************************
2721
2722 Note [SubGoalDepth]
2723 ~~~~~~~~~~~~~~~~~~~
2724 The 'SubGoalDepth' takes care of stopping the constraint solver from looping.
2725
2726 The counter starts at zero and increases. It includes dictionary constraints,
2727 equality simplification, and type family reduction. (Why combine these? Because
2728 it's actually quite easy to mistake one for another, in sufficiently involved
2729 scenarios, like ConstraintKinds.)
2730
2731 The flag -fcontext-stack=n (not very well named!) fixes the maximium
2732 level.
2733
2734 * The counter includes the depth of type class instance declarations. Example:
2735 [W] d{7} : Eq [Int]
2736 That is d's dictionary-constraint depth is 7. If we use the instance
2737 $dfEqList :: Eq a => Eq [a]
2738 to simplify it, we get
2739 d{7} = $dfEqList d'{8}
2740 where d'{8} : Eq Int, and d' has depth 8.
2741
2742 For civilised (decidable) instance declarations, each increase of
2743 depth removes a type constructor from the type, so the depth never
2744 gets big; i.e. is bounded by the structural depth of the type.
2745
2746 * The counter also increments when resolving
2747 equalities involving type functions. Example:
2748 Assume we have a wanted at depth 7:
2749 [W] d{7} : F () ~ a
2750 If there is an type function equation "F () = Int", this would be rewritten to
2751 [W] d{8} : Int ~ a
2752 and remembered as having depth 8.
2753
2754 Again, without UndecidableInstances, this counter is bounded, but without it
2755 can resolve things ad infinitum. Hence there is a maximum level.
2756
2757 * Lastly, every time an equality is rewritten, the counter increases. Again,
2758 rewriting an equality constraint normally makes progress, but it's possible
2759 the "progress" is just the reduction of an infinitely-reducing type family.
2760 Hence we need to track the rewrites.
2761
2762 When compiling a program requires a greater depth, then GHC recommends turning
2763 off this check entirely by setting -freduction-depth=0. This is because the
2764 exact number that works is highly variable, and is likely to change even between
2765 minor releases. Because this check is solely to prevent infinite compilation
2766 times, it seems safe to disable it when a user has ascertained that their program
2767 doesn't loop at the type level.
2768
2769 -}
2770
2771 -- | See Note [SubGoalDepth]
2772 newtype SubGoalDepth = SubGoalDepth Int
2773 deriving (Eq, Ord, Outputable)
2774
2775 initialSubGoalDepth :: SubGoalDepth
2776 initialSubGoalDepth = SubGoalDepth 0
2777
2778 bumpSubGoalDepth :: SubGoalDepth -> SubGoalDepth
2779 bumpSubGoalDepth (SubGoalDepth n) = SubGoalDepth (n + 1)
2780
2781 maxSubGoalDepth :: SubGoalDepth -> SubGoalDepth -> SubGoalDepth
2782 maxSubGoalDepth (SubGoalDepth n) (SubGoalDepth m) = SubGoalDepth (n `max` m)
2783
2784 subGoalDepthExceeded :: DynFlags -> SubGoalDepth -> Bool
2785 subGoalDepthExceeded dflags (SubGoalDepth d)
2786 = mkIntWithInf d > reductionDepth dflags
2787
2788 {-
2789 ************************************************************************
2790 * *
2791 CtLoc
2792 * *
2793 ************************************************************************
2794
2795 The 'CtLoc' gives information about where a constraint came from.
2796 This is important for decent error message reporting because
2797 dictionaries don't appear in the original source code.
2798 type will evolve...
2799 -}
2800
2801 data CtLoc = CtLoc { ctl_origin :: CtOrigin
2802 , ctl_env :: TcLclEnv
2803 , ctl_t_or_k :: Maybe TypeOrKind -- OK if we're not sure
2804 , ctl_depth :: !SubGoalDepth }
2805 -- The TcLclEnv includes particularly
2806 -- source location: tcl_loc :: RealSrcSpan
2807 -- context: tcl_ctxt :: [ErrCtxt]
2808 -- binder stack: tcl_bndrs :: TcIdBinderStack
2809 -- level: tcl_tclvl :: TcLevel
2810
2811 mkGivenLoc :: TcLevel -> SkolemInfo -> TcLclEnv -> CtLoc
2812 mkGivenLoc tclvl skol_info env
2813 = CtLoc { ctl_origin = GivenOrigin skol_info
2814 , ctl_env = env { tcl_tclvl = tclvl }
2815 , ctl_t_or_k = Nothing -- this only matters for error msgs
2816 , ctl_depth = initialSubGoalDepth }
2817
2818 mkKindLoc :: TcType -> TcType -- original *types* being compared
2819 -> CtLoc -> CtLoc
2820 mkKindLoc s1 s2 loc = setCtLocOrigin (toKindLoc loc)
2821 (KindEqOrigin s1 (Just s2) (ctLocOrigin loc)
2822 (ctLocTypeOrKind_maybe loc))
2823
2824 -- | Take a CtLoc and moves it to the kind level
2825 toKindLoc :: CtLoc -> CtLoc
2826 toKindLoc loc = loc { ctl_t_or_k = Just KindLevel }
2827
2828 ctLocEnv :: CtLoc -> TcLclEnv
2829 ctLocEnv = ctl_env
2830
2831 ctLocLevel :: CtLoc -> TcLevel
2832 ctLocLevel loc = tcl_tclvl (ctLocEnv loc)
2833
2834 ctLocDepth :: CtLoc -> SubGoalDepth
2835 ctLocDepth = ctl_depth
2836
2837 ctLocOrigin :: CtLoc -> CtOrigin
2838 ctLocOrigin = ctl_origin
2839
2840 ctLocSpan :: CtLoc -> RealSrcSpan
2841 ctLocSpan (CtLoc { ctl_env = lcl}) = tcl_loc lcl
2842
2843 ctLocTypeOrKind_maybe :: CtLoc -> Maybe TypeOrKind
2844 ctLocTypeOrKind_maybe = ctl_t_or_k
2845
2846 setCtLocSpan :: CtLoc -> RealSrcSpan -> CtLoc
2847 setCtLocSpan ctl@(CtLoc { ctl_env = lcl }) loc = setCtLocEnv ctl (lcl { tcl_loc = loc })
2848
2849 bumpCtLocDepth :: CtLoc -> CtLoc
2850 bumpCtLocDepth loc@(CtLoc { ctl_depth = d }) = loc { ctl_depth = bumpSubGoalDepth d }
2851
2852 setCtLocOrigin :: CtLoc -> CtOrigin -> CtLoc
2853 setCtLocOrigin ctl orig = ctl { ctl_origin = orig }
2854
2855 setCtLocEnv :: CtLoc -> TcLclEnv -> CtLoc
2856 setCtLocEnv ctl env = ctl { ctl_env = env }
2857
2858 pushErrCtxt :: CtOrigin -> ErrCtxt -> CtLoc -> CtLoc
2859 pushErrCtxt o err loc@(CtLoc { ctl_env = lcl })
2860 = loc { ctl_origin = o, ctl_env = lcl { tcl_ctxt = err : tcl_ctxt lcl } }
2861
2862 pushErrCtxtSameOrigin :: ErrCtxt -> CtLoc -> CtLoc
2863 -- Just add information w/o updating the origin!
2864 pushErrCtxtSameOrigin err loc@(CtLoc { ctl_env = lcl })
2865 = loc { ctl_env = lcl { tcl_ctxt = err : tcl_ctxt lcl } }
2866
2867 {-
2868 ************************************************************************
2869 * *
2870 SkolemInfo
2871 * *
2872 ************************************************************************
2873 -}
2874
2875 -- SkolemInfo gives the origin of *given* constraints
2876 -- a) type variables are skolemised
2877 -- b) an implication constraint is generated
2878 data SkolemInfo
2879 = SigSkol -- A skolem that is created by instantiating
2880 -- a programmer-supplied type signature
2881 -- Location of the binding site is on the TyVar
2882 -- See Note [SigSkol SkolemInfo]
2883 UserTypeCtxt -- What sort of signature
2884 TcType -- Original type signature (before skolemisation)
2885 [(Name,TcTyVar)] -- Maps the original name of the skolemised tyvar
2886 -- to its instantiated version
2887
2888 | ClsSkol Class -- Bound at a class decl
2889
2890 | DerivSkol Type -- Bound by a 'deriving' clause;
2891 -- the type is the instance we are trying to derive
2892
2893 | InstSkol -- Bound at an instance decl
2894 | InstSC TypeSize -- A "given" constraint obtained by superclass selection.
2895 -- If (C ty1 .. tyn) is the largest class from
2896 -- which we made a superclass selection in the chain,
2897 -- then TypeSize = sizeTypes [ty1, .., tyn]
2898 -- See Note [Solving superclass constraints] in TcInstDcls
2899
2900 | DataSkol -- Bound at a data type declaration
2901 | FamInstSkol -- Bound at a family instance decl
2902 | PatSkol -- An existential type variable bound by a pattern for
2903 ConLike -- a data constructor with an existential type.
2904 (HsMatchContext Name)
2905 -- e.g. data T = forall a. Eq a => MkT a
2906 -- f (MkT x) = ...
2907 -- The pattern MkT x will allocate an existential type
2908 -- variable for 'a'.
2909
2910 | ArrowSkol -- An arrow form (see TcArrows)
2911
2912 | IPSkol [HsIPName] -- Binding site of an implicit parameter
2913
2914 | RuleSkol RuleName -- The LHS of a RULE
2915
2916 | InferSkol [(Name,TcType)]
2917 -- We have inferred a type for these (mutually-recursivive)
2918 -- polymorphic Ids, and are now checking that their RHS
2919 -- constraints are satisfied.
2920
2921 | BracketSkol -- Template Haskell bracket
2922
2923 | UnifyForAllSkol -- We are unifying two for-all types
2924 TcType -- The instantiated type *inside* the forall
2925
2926 | UnkSkol -- Unhelpful info (until I improve it)
2927
2928 instance Outputable SkolemInfo where
2929 ppr = pprSkolInfo
2930
2931 termEvidenceAllowed :: SkolemInfo -> Bool
2932 -- Whether an implication constraint with this SkolemInfo
2933 -- is permitted to have term-level evidence. There is
2934 -- only one that is not, associated with unifiying
2935 -- forall-types
2936 termEvidenceAllowed (UnifyForAllSkol {}) = False
2937 termEvidenceAllowed _ = True
2938
2939 pprSkolInfo :: SkolemInfo -> SDoc
2940 -- Complete the sentence "is a rigid type variable bound by..."
2941 pprSkolInfo (SigSkol cx ty _) = pprSigSkolInfo cx ty
2942 pprSkolInfo (IPSkol ips) = text "the implicit-parameter binding" <> plural ips <+> text "for"
2943 <+> pprWithCommas ppr ips
2944 pprSkolInfo (ClsSkol cls) = text "the class declaration for" <+> quotes (ppr cls)
2945 pprSkolInfo (DerivSkol pred) = text "the deriving clause for" <+> quotes (ppr pred)
2946 pprSkolInfo InstSkol = text "the instance declaration"
2947 pprSkolInfo (InstSC n) = text "the instance declaration" <> ifPprDebug (parens (ppr n))
2948 pprSkolInfo DataSkol = text "a data type declaration"
2949 pprSkolInfo FamInstSkol = text "a family instance declaration"
2950 pprSkolInfo BracketSkol = text "a Template Haskell bracket"
2951 pprSkolInfo (RuleSkol name) = text "the RULE" <+> pprRuleName name
2952 pprSkolInfo ArrowSkol = text "an arrow form"
2953 pprSkolInfo (PatSkol cl mc) = sep [ pprPatSkolInfo cl
2954 , text "in" <+> pprMatchContext mc ]
2955 pprSkolInfo (InferSkol ids) = sep [ text "the inferred type of"
2956 , vcat [ ppr name <+> dcolon <+> ppr ty
2957 | (name,ty) <- ids ]]
2958 pprSkolInfo (UnifyForAllSkol ty) = text "the type" <+> ppr ty
2959
2960 -- UnkSkol
2961 -- For type variables the others are dealt with by pprSkolTvBinding.
2962 -- For Insts, these cases should not happen
2963 pprSkolInfo UnkSkol = WARN( True, text "pprSkolInfo: UnkSkol" ) text "UnkSkol"
2964
2965 pprSigSkolInfo :: UserTypeCtxt -> TcType -> SDoc
2966 -- The type is already tidied
2967 pprSigSkolInfo ctxt ty
2968 = case ctxt of
2969 FunSigCtxt f _ -> vcat [ text "the type signature for:"
2970 , nest 2 (pprPrefixOcc f <+> dcolon <+> ppr ty) ]
2971 PatSynCtxt {} -> pprUserTypeCtxt ctxt -- See Note [Skolem info for pattern synonyms]
2972 _ -> vcat [ pprUserTypeCtxt ctxt <> colon
2973 , nest 2 (ppr ty) ]
2974
2975 pprPatSkolInfo :: ConLike -> SDoc
2976 pprPatSkolInfo (RealDataCon dc)
2977 = sep [ text "a pattern with constructor:"
2978 , nest 2 $ ppr dc <+> dcolon
2979 <+> pprType (dataConUserType dc) <> comma ]
2980 -- pprType prints forall's regardless of -fprint-explicit-foralls
2981 -- which is what we want here, since we might be saying
2982 -- type variable 't' is bound by ...
2983
2984 pprPatSkolInfo (PatSynCon ps)
2985 = sep [ text "a pattern with pattern synonym:"
2986 , nest 2 $ ppr ps <+> dcolon
2987 <+> pprPatSynType ps <> comma ]
2988
2989 {- Note [Skolem info for pattern synonyms]
2990 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2991 For pattern synonym SkolemInfo we have
2992 SigSkol (PatSynCtxt p) ty _
2993 but the type 'ty' is not very helpful. The full pattern-synonym type
2994 has the provided and required pieces, which it is inconvenient to
2995 record and display here. So we simply don't display the type at all,
2996 contenting outselves with just the name of the pattern synonym, which
2997 is fine. We could do more, but it doesn't seem worth it.
2998
2999 Note [SigSkol SkolemInfo]
3000 ~~~~~~~~~~~~~~~~~~~~~~~~~
3001 Suppose we (deeply) skolemise a type
3002 f :: forall a. a -> forall b. b -> a
3003 Then we'll instantiate [a :-> a', b :-> b'], and with the instantiated
3004 a' -> b' -> a.
3005 But when, in an error message, we report that "b is a rigid type
3006 variable bound by the type signature for f", we want to show the foralls
3007 in the right place. So we proceed as follows:
3008
3009 * In SigSkol we record
3010 - the original signature forall a. a -> forall b. b -> a
3011 - the instantiation mapping [a :-> a', b :-> b']
3012
3013 * Then when tidying in TcMType.tidySkolemInfo, we first tidy a' to
3014 whatever it tidies to, say a''; and then we walk over the type
3015 replacing the binder a by the tidied version a'', to give
3016 forall a''. a'' -> forall b''. b'' -> a''
3017 We need to do this under function arrows, to match what deeplySkolemise
3018 does.
3019
3020 * Typically a'' will have a nice pretty name like "a", but the point is
3021 that the foral-bound variables of the signature we report line up with
3022 the instantiated skolems lying around in other types.
3023
3024
3025 ************************************************************************
3026 * *
3027 CtOrigin
3028 * *
3029 ************************************************************************
3030 -}
3031
3032 data CtOrigin
3033 = GivenOrigin SkolemInfo
3034
3035 -- All the others are for *wanted* constraints
3036 | OccurrenceOf Name -- Occurrence of an overloaded identifier
3037 | OccurrenceOfRecSel RdrName -- Occurrence of a record selector
3038 | AppOrigin -- An application of some kind
3039
3040 | SpecPragOrigin UserTypeCtxt -- Specialisation pragma for
3041 -- function or instance
3042
3043 | TypeEqOrigin { uo_actual :: TcType
3044 , uo_expected :: TcType
3045 , uo_thing :: Maybe ErrorThing
3046 -- ^ The thing that has type "actual"
3047 }
3048
3049 | KindEqOrigin
3050 TcType (Maybe TcType) -- A kind equality arising from unifying these two types
3051 CtOrigin -- originally arising from this
3052 (Maybe TypeOrKind) -- the level of the eq this arises from
3053
3054 | IPOccOrigin HsIPName -- Occurrence of an implicit parameter
3055 | OverLabelOrigin FastString -- Occurrence of an overloaded label
3056
3057 | LiteralOrigin (HsOverLit Name) -- Occurrence of a literal
3058 | NegateOrigin -- Occurrence of syntactic negation
3059
3060 | ArithSeqOrigin (ArithSeqInfo Name) -- [x..], [x..y] etc
3061 | PArrSeqOrigin (ArithSeqInfo Name) -- [:x..y:] and [:x,y..z:]
3062 | SectionOrigin
3063 | TupleOrigin -- (..,..)
3064 | ExprSigOrigin -- e :: ty
3065 | PatSigOrigin -- p :: ty
3066 | PatOrigin -- Instantiating a polytyped pattern at a constructor
3067 | ProvCtxtOrigin -- The "provided" context of a pattern synonym signature
3068 (PatSynBind Name Name) -- Information about the pattern synonym, in particular
3069 -- the name and the right-hand side
3070 | RecordUpdOrigin
3071 | ViewPatOrigin
3072
3073 | ScOrigin TypeSize -- Typechecking superclasses of an instance declaration
3074 -- If the instance head is C ty1 .. tyn
3075 -- then TypeSize = sizeTypes [ty1, .., tyn]
3076 -- See Note [Solving superclass constraints] in TcInstDcls
3077
3078 | DerivOrigin -- Typechecking deriving
3079 | DerivOriginDC DataCon Int
3080 -- Checking constraints arising from this data con and field index
3081 | DerivOriginCoerce Id Type Type
3082 -- DerivOriginCoerce id ty1 ty2: Trying to coerce class method `id` from
3083 -- `ty1` to `ty2`.
3084 | StandAloneDerivOrigin -- Typechecking stand-alone deriving
3085 | DefaultOrigin -- Typechecking a default decl
3086 | DoOrigin -- Arising from a do expression
3087 | DoPatOrigin (LPat Name) -- Arising from a failable pattern in
3088 -- a do expression
3089 | MCompOrigin -- Arising from a monad comprehension
3090 | MCompPatOrigin (LPat Name) -- Arising from a failable pattern in a
3091 -- monad comprehension
3092 | IfOrigin -- Arising from an if statement
3093 | ProcOrigin -- Arising from a proc expression
3094 | AnnOrigin -- An annotation
3095
3096 | FunDepOrigin1 -- A functional dependency from combining
3097 PredType CtLoc -- This constraint arising from ...
3098 PredType CtLoc -- and this constraint arising from ...
3099
3100 | FunDepOrigin2 -- A functional dependency from combining
3101 PredType CtOrigin -- This constraint arising from ...
3102 PredType SrcSpan -- and this top-level instance
3103 -- We only need a CtOrigin on the first, because the location
3104 -- is pinned on the entire error message
3105
3106 | HoleOrigin
3107 | UnboundOccurrenceOf OccName
3108 | ListOrigin -- An overloaded list
3109 | StaticOrigin -- A static form
3110 | FailablePattern (LPat TcId) -- A failable pattern in do-notation for the
3111 -- MonadFail Proposal (MFP). Obsolete when
3112 -- actual desugaring to MonadFail.fail is live.
3113 | Shouldn'tHappenOrigin String
3114 -- the user should never see this one,
3115 -- unless ImpredicativeTypes is on, where all
3116 -- bets are off
3117 | InstProvidedOrigin Module ClsInst
3118 -- Skolem variable arose when we were testing if an instance
3119 -- is solvable or not.
3120
3121 -- | A thing that can be stored for error message generation only.
3122 -- It is stored with a function to zonk and tidy the thing.
3123 data ErrorThing
3124 = forall a. Outputable a => ErrorThing a
3125 (Maybe Arity) -- # of args, if known
3126 (TidyEnv -> a -> TcM (TidyEnv, a))
3127
3128 -- | Flag to see whether we're type-checking terms or kind-checking types
3129 data TypeOrKind = TypeLevel | KindLevel
3130 deriving Eq
3131
3132 instance Outputable TypeOrKind where
3133 ppr TypeLevel = text "TypeLevel"
3134 ppr KindLevel = text "KindLevel"
3135
3136 isTypeLevel :: TypeOrKind -> Bool
3137 isTypeLevel TypeLevel = True
3138 isTypeLevel KindLevel = False
3139
3140 isKindLevel :: TypeOrKind -> Bool
3141 isKindLevel TypeLevel = False
3142 isKindLevel KindLevel = True
3143
3144 -- | Make an 'ErrorThing' that doesn't need tidying or zonking
3145 mkErrorThing :: Outputable a => a -> ErrorThing
3146 mkErrorThing thing = ErrorThing thing Nothing (\env x -> return (env, x))
3147
3148 -- | Retrieve the # of arguments in the error thing, if known
3149 errorThingNumArgs_maybe :: ErrorThing -> Maybe Arity
3150 errorThingNumArgs_maybe (ErrorThing _ args _) = args
3151
3152 instance Outputable CtOrigin where
3153 ppr = pprCtOrigin
3154
3155 instance Outputable ErrorThing where
3156 ppr (ErrorThing thing _ _) = ppr thing
3157
3158 ctoHerald :: SDoc
3159 ctoHerald = text "arising from"
3160
3161 -- | Extract a suitable CtOrigin from a HsExpr
3162 lexprCtOrigin :: LHsExpr Name -> CtOrigin
3163 lexprCtOrigin (L _ e) = exprCtOrigin e
3164
3165 exprCtOrigin :: HsExpr Name -> CtOrigin
3166 exprCtOrigin (HsVar (L _ name)) = OccurrenceOf name
3167 exprCtOrigin (HsUnboundVar uv) = UnboundOccurrenceOf (unboundVarOcc uv)
3168 exprCtOrigin (HsConLikeOut {}) = panic "exprCtOrigin HsConLikeOut"
3169 exprCtOrigin (HsRecFld f) = OccurrenceOfRecSel (rdrNameAmbiguousFieldOcc f)
3170 exprCtOrigin (HsOverLabel _ l) = OverLabelOrigin l
3171 exprCtOrigin (HsIPVar ip) = IPOccOrigin ip
3172 exprCtOrigin (HsOverLit lit) = LiteralOrigin lit
3173 exprCtOrigin (HsLit {}) = Shouldn'tHappenOrigin "concrete literal"
3174 exprCtOrigin (HsLam matches) = matchesCtOrigin matches
3175 exprCtOrigin (HsLamCase ms) = matchesCtOrigin ms
3176 exprCtOrigin (HsApp e1 _) = lexprCtOrigin e1
3177 exprCtOrigin (HsAppType e1 _) = lexprCtOrigin e1
3178 exprCtOrigin (HsAppTypeOut {}) = panic "exprCtOrigin HsAppTypeOut"
3179 exprCtOrigin (OpApp _ op _ _) = lexprCtOrigin op
3180 exprCtOrigin (NegApp e _) = lexprCtOrigin e
3181 exprCtOrigin (HsPar e) = lexprCtOrigin e
3182 exprCtOrigin (SectionL _ _) = SectionOrigin
3183 exprCtOrigin (SectionR _ _) = SectionOrigin
3184 exprCtOrigin (ExplicitTuple {}) = Shouldn'tHappenOrigin "explicit tuple"
3185 exprCtOrigin ExplicitSum{} = Shouldn'tHappenOrigin "explicit sum"
3186 exprCtOrigin (HsCase _ matches) = matchesCtOrigin matches
3187 exprCtOrigin (HsIf (Just syn) _ _ _) = exprCtOrigin (syn_expr syn)
3188 exprCtOrigin (HsIf {}) = Shouldn'tHappenOrigin "if expression"
3189 exprCtOrigin (HsMultiIf _ rhs) = lGRHSCtOrigin rhs
3190 exprCtOrigin (HsLet _ e) = lexprCtOrigin e
3191 exprCtOrigin (HsDo _ _ _) = DoOrigin
3192 exprCtOrigin (ExplicitList {}) = Shouldn'tHappenOrigin "list"
3193 exprCtOrigin (ExplicitPArr {}) = Shouldn'tHappenOrigin "parallel array"
3194 exprCtOrigin (RecordCon {}) = Shouldn'tHappenOrigin "record construction"
3195 exprCtOrigin (RecordUpd {}) = Shouldn'tHappenOrigin "record update"
3196 exprCtOrigin (ExprWithTySig {}) = ExprSigOrigin
3197 exprCtOrigin (ExprWithTySigOut {}) = panic "exprCtOrigin ExprWithTySigOut"
3198 exprCtOrigin (ArithSeq {}) = Shouldn'tHappenOrigin "arithmetic sequence"
3199 exprCtOrigin (PArrSeq {}) = Shouldn'tHappenOrigin "parallel array sequence"
3200 exprCtOrigin (HsSCC _ _ e) = lexprCtOrigin e
3201 exprCtOrigin (HsCoreAnn _ _ e) = lexprCtOrigin e
3202 exprCtOrigin (HsBracket {}) = Shouldn'tHappenOrigin "TH bracket"
3203 exprCtOrigin (HsRnBracketOut {})= Shouldn'tHappenOrigin "HsRnBracketOut"
3204 exprCtOrigin (HsTcBracketOut {})= panic "exprCtOrigin HsTcBracketOut"
3205 exprCtOrigin (HsSpliceE {}) = Shouldn'tHappenOrigin "TH splice"
3206 exprCtOrigin (HsProc {}) = Shouldn'tHappenOrigin "proc"
3207 exprCtOrigin (HsStatic {}) = Shouldn'tHappenOrigin "static expression"
3208 exprCtOrigin (HsArrApp {}) = panic "exprCtOrigin HsArrApp"
3209 exprCtOrigin (HsArrForm {}) = panic "exprCtOrigin HsArrForm"
3210 exprCtOrigin (HsTick _ e) = lexprCtOrigin e
3211 exprCtOrigin (HsBinTick _ _ e) = lexprCtOrigin e
3212 exprCtOrigin (HsTickPragma _ _ _ e) = lexprCtOrigin e
3213 exprCtOrigin EWildPat = panic "exprCtOrigin EWildPat"
3214 exprCtOrigin (EAsPat {}) = panic "exprCtOrigin EAsPat"
3215 exprCtOrigin (EViewPat {}) = panic "exprCtOrigin EViewPat"
3216 exprCtOrigin (ELazyPat {}) = panic "exprCtOrigin ELazyPat"
3217 exprCtOrigin (HsWrap {}) = panic "exprCtOrigin HsWrap"
3218
3219 -- | Extract a suitable CtOrigin from a MatchGroup
3220 matchesCtOrigin :: MatchGroup Name (LHsExpr Name) -> CtOrigin
3221 matchesCtOrigin (MG { mg_alts = alts })
3222 | L _ [L _ match] <- alts
3223 , Match { m_grhss = grhss } <- match
3224 = grhssCtOrigin grhss
3225
3226 | otherwise
3227 = Shouldn'tHappenOrigin "multi-way match"
3228
3229 -- | Extract a suitable CtOrigin from guarded RHSs
3230 grhssCtOrigin :: GRHSs Name (LHsExpr Name) -> CtOrigin
3231 grhssCtOrigin (GRHSs { grhssGRHSs = lgrhss }) = lGRHSCtOrigin lgrhss
3232
3233 -- | Extract a suitable CtOrigin from a list of guarded RHSs
3234 lGRHSCtOrigin :: [LGRHS Name (LHsExpr Name)] -> CtOrigin
3235 lGRHSCtOrigin [L _ (GRHS _ (L _ e))] = exprCtOrigin e
3236 lGRHSCtOrigin _ = Shouldn'tHappenOrigin "multi-way GRHS"
3237
3238 pprCtLoc :: CtLoc -> SDoc
3239 -- "arising from ... at ..."
3240 -- Not an instance of Outputable because of the "arising from" prefix
3241 pprCtLoc (CtLoc { ctl_origin = o, ctl_env = lcl})
3242 = sep [ pprCtOrigin o
3243 , text "at" <+> ppr (tcl_loc lcl)]
3244
3245 pprCtOrigin :: CtOrigin -> SDoc
3246 -- "arising from ..."
3247 -- Not an instance of Outputable because of the "arising from" prefix
3248 pprCtOrigin (GivenOrigin sk) = ctoHerald <+> ppr sk
3249
3250 pprCtOrigin (SpecPragOrigin ctxt)
3251 = case ctxt of
3252 FunSigCtxt n _ -> text "a SPECIALISE pragma for" <+> quotes (ppr n)
3253 SpecInstCtxt -> text "a SPECIALISE INSTANCE pragma"
3254 _ -> text "a SPECIALISE pragma" -- Never happens I think
3255
3256 pprCtOrigin (FunDepOrigin1 pred1 loc1 pred2 loc2)
3257 = hang (ctoHerald <+> text "a functional dependency between constraints:")
3258 2 (vcat [ hang (quotes (ppr pred1)) 2 (pprCtLoc loc1)
3259 , hang (quotes (ppr pred2)) 2 (pprCtLoc loc2) ])
3260
3261 pprCtOrigin (FunDepOrigin2 pred1 orig1 pred2 loc2)
3262 = hang (ctoHerald <+> text "a functional dependency between:")
3263 2 (vcat [ hang (text "constraint" <+> quotes (ppr pred1))
3264 2 (pprCtOrigin orig1 )
3265 , hang (text "instance" <+> quotes (ppr pred2))
3266 2 (text "at" <+> ppr loc2) ])
3267
3268 pprCtOrigin (KindEqOrigin t1 (Just t2) _ _)
3269 = hang (ctoHerald <+> text "a kind equality arising from")
3270 2 (sep [ppr t1, char '~', ppr t2])
3271
3272 pprCtOrigin (KindEqOrigin t1 Nothing _ _)
3273 = hang (ctoHerald <+> text "a kind equality when matching")
3274 2 (ppr t1)
3275
3276 pprCtOrigin (UnboundOccurrenceOf name)
3277 = ctoHerald <+> text "an undeclared identifier" <+> quotes (ppr name)
3278
3279 pprCtOrigin (DerivOriginDC dc n)
3280 = hang (ctoHerald <+> text "the" <+> speakNth n
3281 <+> text "field of" <+> quotes (ppr dc))
3282 2 (parens (text "type" <+> quotes (ppr ty)))
3283 where
3284 ty = dataConOrigArgTys dc !! (n-1)
3285
3286 pprCtOrigin (DerivOriginCoerce meth ty1 ty2)
3287 = hang (ctoHerald <+> text "the coercion of the method" <+> quotes (ppr meth))
3288 2 (sep [ text "from type" <+> quotes (ppr ty1)
3289 , nest 2 $ text "to type" <+> quotes (ppr ty2) ])
3290
3291 pprCtOrigin (DoPatOrigin pat)
3292 = ctoHerald <+> text "a do statement"
3293 $$
3294 text "with the failable pattern" <+> quotes (ppr pat)
3295
3296 pprCtOrigin (MCompPatOrigin pat)
3297 = ctoHerald <+> hsep [ text "the failable pattern"
3298 , quotes (ppr pat)
3299 , text "in a statement in a monad comprehension" ]
3300 pprCtOrigin (FailablePattern pat)
3301 = ctoHerald <+> text "the failable pattern" <+> quotes (ppr pat)
3302 $$
3303 text "(this will become an error in a future GHC release)"
3304
3305 pprCtOrigin (Shouldn'tHappenOrigin note)
3306 = sdocWithDynFlags $ \dflags ->
3307 if xopt LangExt.ImpredicativeTypes dflags
3308 then text "a situation created by impredicative types"
3309 else
3310 vcat [ text "<< This should not appear in error messages. If you see this"
3311 , text "in an error message, please report a bug mentioning" <+> quotes (text note) <+> text "at"
3312 , text "https://ghc.haskell.org/trac/ghc/wiki/ReportABug >>" ]
3313
3314 pprCtOrigin (ProvCtxtOrigin PSB{ psb_id = (L _ name) })
3315 = hang (ctoHerald <+> text "the \"provided\" constraints claimed by")
3316 2 (text "the signature of" <+> quotes (ppr name))
3317
3318 pprCtOrigin (InstProvidedOrigin mod cls_inst)
3319 = vcat [ text "arising when attempting to show that"
3320 , ppr cls_inst
3321 , text "is provided by" <+> quotes (ppr mod)]
3322
3323 pprCtOrigin simple_origin
3324 = ctoHerald <+> pprCtO simple_origin
3325
3326 -- | Short one-liners
3327 pprCtO :: CtOrigin -> SDoc
3328 pprCtO (OccurrenceOf name) = hsep [text "a use of", quotes (ppr name)]
3329 pprCtO (OccurrenceOfRecSel name) = hsep [text "a use of", quotes (ppr name)]
3330 pprCtO AppOrigin = text "an application"
3331 pprCtO (IPOccOrigin name) = hsep [text "a use of implicit parameter", quotes (ppr name)]
3332 pprCtO (OverLabelOrigin l) = hsep [text "the overloaded label"
3333 ,quotes (char '#' <> ppr l)]
3334 pprCtO RecordUpdOrigin = text "a record update"
3335 pprCtO ExprSigOrigin = text "an expression type signature"
3336 pprCtO PatSigOrigin = text "a pattern type signature"
3337 pprCtO PatOrigin = text "a pattern"
3338 pprCtO ViewPatOrigin = text "a view pattern"
3339 pprCtO IfOrigin = text "an if expression"
3340 pprCtO (LiteralOrigin lit) = hsep [text "the literal", quotes (ppr lit)]
3341 pprCtO (ArithSeqOrigin seq) = hsep [text "the arithmetic sequence", quotes (ppr seq)]
3342 pprCtO (PArrSeqOrigin seq) = hsep [text "the parallel array sequence", quotes (ppr seq)]
3343 pprCtO SectionOrigin = text "an operator section"
3344 pprCtO TupleOrigin = text "a tuple"
3345 pprCtO NegateOrigin = text "a use of syntactic negation"
3346 pprCtO (ScOrigin n) = text "the superclasses of an instance declaration"
3347 <> ifPprDebug (parens (ppr n))
3348 pprCtO DerivOrigin = text "the 'deriving' clause of a data type declaration"
3349 pprCtO StandAloneDerivOrigin = text "a 'deriving' declaration"
3350 pprCtO DefaultOrigin = text "a 'default' declaration"
3351 pprCtO DoOrigin = text "a do statement"
3352 pprCtO MCompOrigin = text "a statement in a monad comprehension"
3353 pprCtO ProcOrigin = text "a proc expression"
3354 pprCtO (TypeEqOrigin t1 t2 _)= text "a type equality" <+> sep [ppr t1, char '~', ppr t2]
3355 pprCtO AnnOrigin = text "an annotation"
3356 pprCtO HoleOrigin = text "a use of" <+> quotes (text "_")
3357 pprCtO ListOrigin = text "an overloaded list"
3358 pprCtO StaticOrigin = text "a static form"
3359 pprCtO _ = panic "pprCtOrigin"
3360
3361 {-
3362 Constraint Solver Plugins
3363 -------------------------
3364 -}
3365
3366 type TcPluginSolver = [Ct] -- given
3367 -> [Ct] -- derived
3368 -> [Ct] -- wanted
3369 -> TcPluginM TcPluginResult
3370
3371 newtype TcPluginM a = TcPluginM (EvBindsVar -> TcM a)
3372
3373 instance Functor TcPluginM where
3374 fmap = liftM
3375
3376 instance Applicative TcPluginM where
3377 pure x = TcPluginM (const $ pure x)
3378 (<*>) = ap
3379
3380 instance Monad TcPluginM where
3381 fail x = TcPluginM (const $ fail x)
3382 TcPluginM m >>= k =
3383 TcPluginM (\ ev -> do a <- m ev
3384 runTcPluginM (k a) ev)
3385
3386 #if __GLASGOW_HASKELL__ > 710
3387 instance MonadFail.MonadFail TcPluginM where
3388 fail x = TcPluginM (const $ fail x)
3389 #endif
3390
3391 runTcPluginM :: TcPluginM a -> EvBindsVar -> TcM a
3392 runTcPluginM (TcPluginM m) = m
3393
3394 -- | This function provides an escape for direct access to
3395 -- the 'TcM` monad. It should not be used lightly, and
3396 -- the provided 'TcPluginM' API should be favoured instead.
3397 unsafeTcPluginTcM :: TcM a -> TcPluginM a
3398 unsafeTcPluginTcM = TcPluginM . const
3399
3400 -- | Access the 'EvBindsVar' carried by the 'TcPluginM' during
3401 -- constraint solving. Returns 'Nothing' if invoked during
3402 -- 'tcPluginInit' or 'tcPluginStop'.
3403 getEvBindsTcPluginM :: TcPluginM EvBindsVar
3404 getEvBindsTcPluginM = TcPluginM return
3405
3406
3407 data TcPlugin = forall s. TcPlugin
3408 { tcPluginInit :: TcPluginM s
3409 -- ^ Initialize plugin, when entering type-checker.
3410
3411 , tcPluginSolve :: s -> TcPluginSolver
3412 -- ^ Solve some constraints.
3413 -- TODO: WRITE MORE DETAILS ON HOW THIS WORKS.
3414
3415 , tcPluginStop :: s -> TcPluginM ()
3416 -- ^ Clean up after the plugin, when exiting the type-checker.
3417 }
3418
3419 data TcPluginResult
3420 = TcPluginContradiction [Ct]
3421 -- ^ The plugin found a contradiction.
3422 -- The returned constraints are removed from the inert set,
3423 -- and recorded as insoluble.
3424
3425 | TcPluginOk [(EvTerm,Ct)] [Ct]
3426 -- ^ The first field is for constraints that were solved.
3427 -- These are removed from the inert set,
3428 -- and the evidence for them is recorded.
3429 -- The second field contains new work, that should be processed by
3430 -- the constraint solver.
3431
3432 {- *********************************************************************
3433 * *
3434 Role annotations
3435 * *
3436 ********************************************************************* -}
3437
3438 type RoleAnnotEnv = NameEnv (LRoleAnnotDecl Name)
3439
3440 mkRoleAnnotEnv :: [LRoleAnnotDecl Name] -> RoleAnnotEnv
3441 mkRoleAnnotEnv role_annot_decls
3442 = mkNameEnv [ (name, ra_decl)
3443 | ra_decl <- role_annot_decls
3444 , let name = roleAnnotDeclName (unLoc ra_decl)
3445 , not (isUnboundName name) ]
3446 -- Some of the role annots will be unbound;
3447 -- we don't wish to include these
3448
3449 emptyRoleAnnotEnv :: RoleAnnotEnv
3450 emptyRoleAnnotEnv = emptyNameEnv
3451
3452 lookupRoleAnnot :: RoleAnnotEnv -> Name -> Maybe (LRoleAnnotDecl Name)
3453 lookupRoleAnnot = lookupNameEnv
3454
3455 getRoleAnnots :: [Name] -> RoleAnnotEnv -> ([LRoleAnnotDecl Name], RoleAnnotEnv)
3456 getRoleAnnots bndrs role_env
3457 = ( mapMaybe (lookupRoleAnnot role_env) bndrs
3458 , delListFromNameEnv role_env bndrs )