Re-engineer Given flatten-skolems
[ghc.git] / compiler / typecheck / TcMType.hs
1 {-
2 (c) The University of Glasgow 2006
3 (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4
5
6 Monadic type operations
7
8 This module contains monadic operations over types that contain
9 mutable type variables
10 -}
11
12 {-# LANGUAGE CPP, TupleSections, MultiWayIf #-}
13
14 module TcMType (
15 TcTyVar, TcKind, TcType, TcTauType, TcThetaType, TcTyVarSet,
16
17 --------------------------------
18 -- Creating new mutable type variables
19 newFlexiTyVar,
20 newFlexiTyVarTy, -- Kind -> TcM TcType
21 newFlexiTyVarTys, -- Int -> Kind -> TcM [TcType]
22 newOpenFlexiTyVarTy, newOpenTypeKind,
23 newMetaKindVar, newMetaKindVars, newMetaTyVarTyAtLevel,
24 cloneMetaTyVar,
25 newFmvTyVar, newFskTyVar,
26
27 readMetaTyVar, writeMetaTyVar, writeMetaTyVarRef,
28 newMetaDetails, isFilledMetaTyVar, isUnfilledMetaTyVar,
29
30 --------------------------------
31 -- Expected types
32 ExpType(..), ExpSigmaType, ExpRhoType,
33 mkCheckExpType,
34 newInferExpType, newInferExpTypeInst, newInferExpTypeNoInst,
35 readExpType, readExpType_maybe,
36 expTypeToType, checkingExpType_maybe, checkingExpType,
37 tauifyExpType, inferResultToType,
38
39 --------------------------------
40 -- Creating fresh type variables for pm checking
41 genInstSkolTyVarsX,
42
43 --------------------------------
44 -- Creating new evidence variables
45 newEvVar, newEvVars, newDict,
46 newWanted, newWanteds, cloneWanted, cloneWC,
47 emitWanted, emitWantedEq, emitWantedEvVar, emitWantedEvVars,
48 newTcEvBinds, addTcEvBind,
49
50 newCoercionHole, fillCoercionHole, isFilledCoercionHole,
51 unpackCoercionHole, unpackCoercionHole_maybe,
52 checkCoercionHole,
53
54 --------------------------------
55 -- Instantiation
56 newMetaTyVars, newMetaTyVarX, newMetaTyVarsX,
57 newMetaSigTyVars, newMetaSigTyVarX,
58 newSigTyVar, newWildCardX,
59 tcInstType,
60 tcInstSkolTyVars,tcInstSkolTyVarsX,
61 tcInstSuperSkolTyVarsX,
62 tcSkolDFunType, tcSuperSkolTyVars,
63
64 instSkolTyCoVars, freshenTyVarBndrs, freshenCoVarBndrsX,
65
66 --------------------------------
67 -- Zonking and tidying
68 zonkTidyTcType, zonkTidyOrigin,
69 mkTypeErrorThing, mkTypeErrorThingArgs,
70 tidyEvVar, tidyCt, tidySkolemInfo,
71 skolemiseRuntimeUnk,
72 zonkTcTyVar, zonkTcTyVars, zonkTcTyVarToTyVar,
73 zonkTyCoVarsAndFV, zonkTcTypeAndFV,
74 zonkTyCoVarsAndFVList,
75 zonkTcTypeAndSplitDepVars, zonkTcTypesAndSplitDepVars,
76 zonkQuantifiedTyVar, defaultTyVar,
77 quantifyTyVars,
78 zonkTcTyCoVarBndr, zonkTcTyVarBinder,
79 zonkTcType, zonkTcTypes, zonkCo,
80 zonkTyCoVarKind, zonkTcTypeMapper,
81
82 zonkEvVar, zonkWC, zonkSimples, zonkId, zonkCt, zonkSkolemInfo,
83
84 tcGetGlobalTyCoVars,
85
86 ------------------------------
87 -- Levity polymorphism
88 ensureNotLevPoly, checkForLevPoly, checkForLevPolyX, formatLevPolyErr
89 ) where
90
91 #include "HsVersions.h"
92
93 -- friends:
94 import TyCoRep
95 import TcType
96 import Type
97 import Kind
98 import Coercion
99 import Class
100 import Var
101
102 -- others:
103 import TcRnMonad -- TcType, amongst others
104 import TcEvidence
105 import Id
106 import Name
107 import VarSet
108 import TysWiredIn
109 import TysPrim
110 import VarEnv
111 import NameEnv
112 import PrelNames
113 import Util
114 import Outputable
115 import FastString
116 import SrcLoc
117 import Bag
118 import Pair
119 import UniqSet
120 import qualified GHC.LanguageExtensions as LangExt
121
122 import Control.Monad
123 import Maybes
124 import Data.List ( mapAccumL )
125 import Control.Arrow ( second )
126
127 {-
128 ************************************************************************
129 * *
130 Kind variables
131 * *
132 ************************************************************************
133 -}
134
135 mkKindName :: Unique -> Name
136 mkKindName unique = mkSystemName unique kind_var_occ
137
138 kind_var_occ :: OccName -- Just one for all MetaKindVars
139 -- They may be jiggled by tidying
140 kind_var_occ = mkOccName tvName "k"
141
142 newMetaKindVar :: TcM TcKind
143 newMetaKindVar = do { uniq <- newUnique
144 ; details <- newMetaDetails TauTv
145 ; let kv = mkTcTyVar (mkKindName uniq) liftedTypeKind details
146 ; return (mkTyVarTy kv) }
147
148 newMetaKindVars :: Int -> TcM [TcKind]
149 newMetaKindVars n = mapM (\ _ -> newMetaKindVar) (nOfThem n ())
150
151 {-
152 ************************************************************************
153 * *
154 Evidence variables; range over constraints we can abstract over
155 * *
156 ************************************************************************
157 -}
158
159 newEvVars :: TcThetaType -> TcM [EvVar]
160 newEvVars theta = mapM newEvVar theta
161
162 --------------
163
164 newEvVar :: TcPredType -> TcRnIf gbl lcl EvVar
165 -- Creates new *rigid* variables for predicates
166 newEvVar ty = do { name <- newSysName (predTypeOccName ty)
167 ; return (mkLocalIdOrCoVar name ty) }
168
169 newWanted :: CtOrigin -> Maybe TypeOrKind -> PredType -> TcM CtEvidence
170 -- Deals with both equality and non-equality predicates
171 newWanted orig t_or_k pty
172 = do loc <- getCtLocM orig t_or_k
173 d <- if isEqPred pty then HoleDest <$> newCoercionHole
174 else EvVarDest <$> newEvVar pty
175 return $ CtWanted { ctev_dest = d
176 , ctev_pred = pty
177 , ctev_nosh = WDeriv
178 , ctev_loc = loc }
179
180 newWanteds :: CtOrigin -> ThetaType -> TcM [CtEvidence]
181 newWanteds orig = mapM (newWanted orig Nothing)
182
183 cloneWanted :: Ct -> TcM CtEvidence
184 cloneWanted ct
185 = newWanted (ctEvOrigin ev) Nothing (ctEvPred ev)
186 where
187 ev = ctEvidence ct
188
189 cloneWC :: WantedConstraints -> TcM WantedConstraints
190 cloneWC wc@(WC { wc_simple = simples, wc_impl = implics })
191 = do { simples' <- mapBagM clone_one simples
192 ; implics' <- mapBagM clone_implic implics
193 ; return (wc { wc_simple = simples', wc_impl = implics' }) }
194 where
195 clone_one ct = do { ev <- cloneWanted ct; return (mkNonCanonical ev) }
196
197 clone_implic implic@(Implic { ic_wanted = inner_wanted })
198 = do { inner_wanted' <- cloneWC inner_wanted
199 ; return (implic { ic_wanted = inner_wanted' }) }
200
201 -- | Emits a new Wanted. Deals with both equalities and non-equalities.
202 emitWanted :: CtOrigin -> TcPredType -> TcM EvTerm
203 emitWanted origin pty
204 = do { ev <- newWanted origin Nothing pty
205 ; emitSimple $ mkNonCanonical ev
206 ; return $ ctEvTerm ev }
207
208 -- | Emits a new equality constraint
209 emitWantedEq :: CtOrigin -> TypeOrKind -> Role -> TcType -> TcType -> TcM Coercion
210 emitWantedEq origin t_or_k role ty1 ty2
211 = do { hole <- newCoercionHole
212 ; loc <- getCtLocM origin (Just t_or_k)
213 ; emitSimple $ mkNonCanonical $
214 CtWanted { ctev_pred = pty, ctev_dest = HoleDest hole
215 , ctev_nosh = WDeriv, ctev_loc = loc }
216 ; return (mkHoleCo hole role ty1 ty2) }
217 where
218 pty = mkPrimEqPredRole role ty1 ty2
219
220 -- | Creates a new EvVar and immediately emits it as a Wanted.
221 -- No equality predicates here.
222 emitWantedEvVar :: CtOrigin -> TcPredType -> TcM EvVar
223 emitWantedEvVar origin ty
224 = do { new_cv <- newEvVar ty
225 ; loc <- getCtLocM origin Nothing
226 ; let ctev = CtWanted { ctev_dest = EvVarDest new_cv
227 , ctev_pred = ty
228 , ctev_nosh = WDeriv
229 , ctev_loc = loc }
230 ; emitSimple $ mkNonCanonical ctev
231 ; return new_cv }
232
233 emitWantedEvVars :: CtOrigin -> [TcPredType] -> TcM [EvVar]
234 emitWantedEvVars orig = mapM (emitWantedEvVar orig)
235
236 newDict :: Class -> [TcType] -> TcM DictId
237 newDict cls tys
238 = do { name <- newSysName (mkDictOcc (getOccName cls))
239 ; return (mkLocalId name (mkClassPred cls tys)) }
240
241 predTypeOccName :: PredType -> OccName
242 predTypeOccName ty = case classifyPredType ty of
243 ClassPred cls _ -> mkDictOcc (getOccName cls)
244 EqPred _ _ _ -> mkVarOccFS (fsLit "cobox")
245 IrredPred _ -> mkVarOccFS (fsLit "irred")
246
247 {-
248 ************************************************************************
249 * *
250 Coercion holes
251 * *
252 ************************************************************************
253 -}
254
255 newCoercionHole :: TcM CoercionHole
256 newCoercionHole
257 = do { u <- newUnique
258 ; traceTc "New coercion hole:" (ppr u)
259 ; ref <- newMutVar Nothing
260 ; return $ CoercionHole u ref }
261
262 -- | Put a value in a coercion hole
263 fillCoercionHole :: CoercionHole -> Coercion -> TcM ()
264 fillCoercionHole (CoercionHole u ref) co
265 = do {
266 #if defined(DEBUG)
267 ; cts <- readTcRef ref
268 ; whenIsJust cts $ \old_co ->
269 pprPanic "Filling a filled coercion hole" (ppr u $$ ppr co $$ ppr old_co)
270 #endif
271 ; traceTc "Filling coercion hole" (ppr u <+> text ":=" <+> ppr co)
272 ; writeTcRef ref (Just co) }
273
274 -- | Is a coercion hole filled in?
275 isFilledCoercionHole :: CoercionHole -> TcM Bool
276 isFilledCoercionHole (CoercionHole _ ref) = isJust <$> readTcRef ref
277
278 -- | Retrieve the contents of a coercion hole. Panics if the hole
279 -- is unfilled
280 unpackCoercionHole :: CoercionHole -> TcM Coercion
281 unpackCoercionHole hole
282 = do { contents <- unpackCoercionHole_maybe hole
283 ; case contents of
284 Just co -> return co
285 Nothing -> pprPanic "Unfilled coercion hole" (ppr hole) }
286
287 -- | Retrieve the contents of a coercion hole, if it is filled
288 unpackCoercionHole_maybe :: CoercionHole -> TcM (Maybe Coercion)
289 unpackCoercionHole_maybe (CoercionHole _ ref) = readTcRef ref
290
291 -- | Check that a coercion is appropriate for filling a hole. (The hole
292 -- itself is needed only for printing. NB: This must be /lazy/ in the coercion,
293 -- as it's used in TcHsSyn in the presence of knots.
294 -- Always returns the checked coercion, but this return value is necessary
295 -- so that the input coercion is forced only when the output is forced.
296 checkCoercionHole :: Coercion -> CoercionHole -> Role -> Type -> Type -> TcM Coercion
297 checkCoercionHole co h r t1 t2
298 -- co is already zonked, but t1 and t2 might not be
299 | debugIsOn
300 = do { t1 <- zonkTcType t1
301 ; t2 <- zonkTcType t2
302 ; let (Pair _t1 _t2, _role) = coercionKindRole co
303 ; return $
304 ASSERT2( t1 `eqType` _t1 && t2 `eqType` _t2 && r == _role
305 , (text "Bad coercion hole" <+>
306 ppr h <> colon <+> vcat [ ppr _t1, ppr _t2, ppr _role
307 , ppr co, ppr t1, ppr t2
308 , ppr r ]) )
309 co }
310 | otherwise
311 = return co
312
313 {-
314 ************************************************************************
315 *
316 Expected types
317 *
318 ************************************************************************
319
320 Note [ExpType]
321 ~~~~~~~~~~~~~~
322
323 An ExpType is used as the "expected type" when type-checking an expression.
324 An ExpType can hold a "hole" that can be filled in by the type-checker.
325 This allows us to have one tcExpr that works in both checking mode and
326 synthesis mode (that is, bidirectional type-checking). Previously, this
327 was achieved by using ordinary unification variables, but we don't need
328 or want that generality. (For example, #11397 was caused by doing the
329 wrong thing with unification variables.) Instead, we observe that these
330 holes should
331
332 1. never be nested
333 2. never appear as the type of a variable
334 3. be used linearly (never be duplicated)
335
336 By defining ExpType, separately from Type, we can achieve goals 1 and 2
337 statically.
338
339 See also [wiki:Typechecking]
340
341 Note [TcLevel of ExpType]
342 ~~~~~~~~~~~~~~~~~~~~~~~~~
343 Consider
344
345 data G a where
346 MkG :: G Bool
347
348 foo MkG = True
349
350 This is a classic untouchable-variable / ambiguous GADT return type
351 scenario. But, with ExpTypes, we'll be inferring the type of the RHS.
352 And, because there is only one branch of the case, we won't trigger
353 Note [Case branches must never infer a non-tau type] of TcMatches.
354 We thus must track a TcLevel in an Inferring ExpType. If we try to
355 fill the ExpType and find that the TcLevels don't work out, we
356 fill the ExpType with a tau-tv at the low TcLevel, hopefully to
357 be worked out later by some means. This is triggered in
358 test gadt/gadt-escape1.
359
360 -}
361
362 -- actual data definition is in TcType
363
364 -- | Make an 'ExpType' suitable for inferring a type of kind * or #.
365 newInferExpTypeNoInst :: TcM ExpSigmaType
366 newInferExpTypeNoInst = newInferExpType False
367
368 newInferExpTypeInst :: TcM ExpRhoType
369 newInferExpTypeInst = newInferExpType True
370
371 newInferExpType :: Bool -> TcM ExpType
372 newInferExpType inst
373 = do { u <- newUnique
374 ; tclvl <- getTcLevel
375 ; traceTc "newOpenInferExpType" (ppr u <+> ppr inst <+> ppr tclvl)
376 ; ref <- newMutVar Nothing
377 ; return (Infer (IR { ir_uniq = u, ir_lvl = tclvl
378 , ir_ref = ref, ir_inst = inst })) }
379
380 -- | Extract a type out of an ExpType, if one exists. But one should always
381 -- exist. Unless you're quite sure you know what you're doing.
382 readExpType_maybe :: ExpType -> TcM (Maybe TcType)
383 readExpType_maybe (Check ty) = return (Just ty)
384 readExpType_maybe (Infer (IR { ir_ref = ref})) = readMutVar ref
385
386 -- | Extract a type out of an ExpType. Otherwise, panics.
387 readExpType :: ExpType -> TcM TcType
388 readExpType exp_ty
389 = do { mb_ty <- readExpType_maybe exp_ty
390 ; case mb_ty of
391 Just ty -> return ty
392 Nothing -> pprPanic "Unknown expected type" (ppr exp_ty) }
393
394 -- | Returns the expected type when in checking mode.
395 checkingExpType_maybe :: ExpType -> Maybe TcType
396 checkingExpType_maybe (Check ty) = Just ty
397 checkingExpType_maybe _ = Nothing
398
399 -- | Returns the expected type when in checking mode. Panics if in inference
400 -- mode.
401 checkingExpType :: String -> ExpType -> TcType
402 checkingExpType _ (Check ty) = ty
403 checkingExpType err et = pprPanic "checkingExpType" (text err $$ ppr et)
404
405 tauifyExpType :: ExpType -> TcM ExpType
406 -- ^ Turn a (Infer hole) type into a (Check alpha),
407 -- where alpha is a fresh unification variable
408 tauifyExpType (Check ty) = return (Check ty) -- No-op for (Check ty)
409 tauifyExpType (Infer inf_res) = do { ty <- inferResultToType inf_res
410 ; return (Check ty) }
411
412 -- | Extracts the expected type if there is one, or generates a new
413 -- TauTv if there isn't.
414 expTypeToType :: ExpType -> TcM TcType
415 expTypeToType (Check ty) = return ty
416 expTypeToType (Infer inf_res) = inferResultToType inf_res
417
418 inferResultToType :: InferResult -> TcM Type
419 inferResultToType (IR { ir_uniq = u, ir_lvl = tc_lvl
420 , ir_ref = ref })
421 = do { rr <- newMetaTyVarTyAtLevel tc_lvl runtimeRepTy
422 ; tau <- newMetaTyVarTyAtLevel tc_lvl (tYPE rr)
423 -- See Note [TcLevel of ExpType]
424 ; writeMutVar ref (Just tau)
425 ; traceTc "Forcing ExpType to be monomorphic:"
426 (ppr u <+> text ":=" <+> ppr tau)
427 ; return tau }
428
429
430 {- *********************************************************************
431 * *
432 SkolemTvs (immutable)
433 * *
434 ********************************************************************* -}
435
436 tcInstType :: ([TyVar] -> TcM (TCvSubst, [TcTyVar]))
437 -- ^ How to instantiate the type variables
438 -> Id -- ^ Type to instantiate
439 -> TcM ([(Name, TcTyVar)], TcThetaType, TcType) -- ^ Result
440 -- (type vars, preds (incl equalities), rho)
441 tcInstType inst_tyvars id
442 = case tcSplitForAllTys (idType id) of
443 ([], rho) -> let -- There may be overloading despite no type variables;
444 -- (?x :: Int) => Int -> Int
445 (theta, tau) = tcSplitPhiTy rho
446 in
447 return ([], theta, tau)
448
449 (tyvars, rho) -> do { (subst, tyvars') <- inst_tyvars tyvars
450 ; let (theta, tau) = tcSplitPhiTy (substTyAddInScope subst rho)
451 tv_prs = map tyVarName tyvars `zip` tyvars'
452 ; return (tv_prs, theta, tau) }
453
454 tcSkolDFunType :: DFunId -> TcM ([TcTyVar], TcThetaType, TcType)
455 -- Instantiate a type signature with skolem constants.
456 -- We could give them fresh names, but no need to do so
457 tcSkolDFunType dfun
458 = do { (tv_prs, theta, tau) <- tcInstType tcInstSuperSkolTyVars dfun
459 ; return (map snd tv_prs, theta, tau) }
460
461 tcSuperSkolTyVars :: [TyVar] -> (TCvSubst, [TcTyVar])
462 -- Make skolem constants, but do *not* give them new names, as above
463 -- Moreover, make them "super skolems"; see comments with superSkolemTv
464 -- see Note [Kind substitution when instantiating]
465 -- Precondition: tyvars should be ordered by scoping
466 tcSuperSkolTyVars = mapAccumL tcSuperSkolTyVar emptyTCvSubst
467
468 tcSuperSkolTyVar :: TCvSubst -> TyVar -> (TCvSubst, TcTyVar)
469 tcSuperSkolTyVar subst tv
470 = (extendTvSubstWithClone subst tv new_tv, new_tv)
471 where
472 kind = substTyUnchecked subst (tyVarKind tv)
473 new_tv = mkTcTyVar (tyVarName tv) kind superSkolemTv
474
475 -- | Given a list of @['TyVar']@, skolemize the type variables,
476 -- returning a substitution mapping the original tyvars to the
477 -- skolems, and the list of newly bound skolems. See also
478 -- tcInstSkolTyVars' for a precondition. The resulting
479 -- skolems are non-overlappable; see Note [Overlap and deriving]
480 -- for an example where this matters.
481 tcInstSkolTyVars :: [TyVar] -> TcM (TCvSubst, [TcTyVar])
482 tcInstSkolTyVars = tcInstSkolTyVarsX emptyTCvSubst
483
484 tcInstSkolTyVarsX :: TCvSubst -> [TyVar] -> TcM (TCvSubst, [TcTyVar])
485 tcInstSkolTyVarsX = tcInstSkolTyVars' False
486
487 tcInstSuperSkolTyVars :: [TyVar] -> TcM (TCvSubst, [TcTyVar])
488 tcInstSuperSkolTyVars = tcInstSuperSkolTyVarsX emptyTCvSubst
489
490 tcInstSuperSkolTyVarsX :: TCvSubst -> [TyVar] -> TcM (TCvSubst, [TcTyVar])
491 tcInstSuperSkolTyVarsX subst = tcInstSkolTyVars' True subst
492
493 tcInstSkolTyVars' :: Bool -> TCvSubst -> [TyVar] -> TcM (TCvSubst, [TcTyVar])
494 -- Precondition: tyvars should be ordered (kind vars first)
495 -- see Note [Kind substitution when instantiating]
496 -- Get the location from the monad; this is a complete freshening operation
497 tcInstSkolTyVars' overlappable subst tvs
498 = do { loc <- getSrcSpanM
499 ; lvl <- getTcLevel
500 ; instSkolTyCoVarsX (mkTcSkolTyVar lvl loc overlappable) subst tvs }
501
502 mkTcSkolTyVar :: TcLevel -> SrcSpan -> Bool -> TcTyVarMaker
503 mkTcSkolTyVar lvl loc overlappable
504 = \ uniq old_name kind -> mkTcTyVar (mkInternalName uniq (getOccName old_name) loc)
505 kind details
506 where
507 details = SkolemTv (pushTcLevel lvl) overlappable
508 -- NB: skolems bump the level
509
510 ------------------
511 freshenTyVarBndrs :: [TyVar] -> TcRnIf gbl lcl (TCvSubst, [TyVar])
512 -- ^ Give fresh uniques to a bunch of TyVars, but they stay
513 -- as TyVars, rather than becoming TcTyVars
514 -- Used in FamInst.newFamInst, and Inst.newClsInst
515 freshenTyVarBndrs = instSkolTyCoVars mk_tv
516 where
517 mk_tv uniq old_name kind = mkTyVar (setNameUnique old_name uniq) kind
518
519 freshenCoVarBndrsX :: TCvSubst -> [CoVar] -> TcRnIf gbl lcl (TCvSubst, [CoVar])
520 -- ^ Give fresh uniques to a bunch of CoVars
521 -- Used in FamInst.newFamInst
522 freshenCoVarBndrsX subst = instSkolTyCoVarsX mk_cv subst
523 where
524 mk_cv uniq old_name kind = mkCoVar (setNameUnique old_name uniq) kind
525
526 ------------------
527 type TcTyVarMaker = Unique -> Name -> Kind -> TyCoVar
528 instSkolTyCoVars :: TcTyVarMaker -> [TyVar] -> TcRnIf gbl lcl (TCvSubst, [TyCoVar])
529 instSkolTyCoVars mk_tcv = instSkolTyCoVarsX mk_tcv emptyTCvSubst
530
531 instSkolTyCoVarsX :: TcTyVarMaker
532 -> TCvSubst -> [TyCoVar] -> TcRnIf gbl lcl (TCvSubst, [TyCoVar])
533 instSkolTyCoVarsX mk_tcv = mapAccumLM (instSkolTyCoVarX mk_tcv)
534
535 instSkolTyCoVarX :: TcTyVarMaker
536 -> TCvSubst -> TyCoVar -> TcRnIf gbl lcl (TCvSubst, TyCoVar)
537 instSkolTyCoVarX mk_tcv subst tycovar
538 = do { uniq <- newUnique -- using a new unique is critical. See
539 -- Note [Skolems in zonkSyntaxExpr] in TcHsSyn
540 ; let new_tcv = mk_tcv uniq old_name kind
541 subst1 | isTyVar new_tcv
542 = extendTvSubstWithClone subst tycovar new_tcv
543 | otherwise
544 = extendCvSubstWithClone subst tycovar new_tcv
545 ; return (subst1, new_tcv) }
546 where
547 old_name = tyVarName tycovar
548 kind = substTyUnchecked subst (tyVarKind tycovar)
549
550 newFskTyVar :: TcType -> TcM TcTyVar
551 newFskTyVar fam_ty
552 = do { uniq <- newUnique
553 ; ref <- newMutVar Flexi
554 ; let details = MetaTv { mtv_info = FlatSkolTv
555 , mtv_ref = ref
556 , mtv_tclvl = fmvTcLevel }
557 name = mkMetaTyVarName uniq (fsLit "fsk")
558 ; return (mkTcTyVar name (typeKind fam_ty) details) }
559
560 {-
561 Note [Kind substitution when instantiating]
562 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
563 When we instantiate a bunch of kind and type variables, first we
564 expect them to be topologically sorted.
565 Then we have to instantiate the kind variables, build a substitution
566 from old variables to the new variables, then instantiate the type
567 variables substituting the original kind.
568
569 Exemple: If we want to instantiate
570 [(k1 :: *), (k2 :: *), (a :: k1 -> k2), (b :: k1)]
571 we want
572 [(?k1 :: *), (?k2 :: *), (?a :: ?k1 -> ?k2), (?b :: ?k1)]
573 instead of the buggous
574 [(?k1 :: *), (?k2 :: *), (?a :: k1 -> k2), (?b :: k1)]
575
576
577 ************************************************************************
578 * *
579 MetaTvs (meta type variables; mutable)
580 * *
581 ************************************************************************
582 -}
583
584 mkMetaTyVarName :: Unique -> FastString -> Name
585 -- Makes a /System/ Name, which is eagerly eliminated by
586 -- the unifier; see TcUnify.nicer_to_update_tv1, and
587 -- TcCanonical.canEqTyVarTyVar (nicer_to_update_tv2)
588 mkMetaTyVarName uniq str = mkSysTvName uniq str
589
590 newSigTyVar :: Name -> Kind -> TcM TcTyVar
591 newSigTyVar name kind
592 = do { details <- newMetaDetails SigTv
593 ; return (mkTcTyVar name kind details) }
594
595 newFmvTyVar :: TcType -> TcM TcTyVar
596 -- Very like newMetaTyVar, except sets mtv_tclvl to one less
597 -- so that the fmv is untouchable.
598 newFmvTyVar fam_ty
599 = do { uniq <- newUnique
600 ; ref <- newMutVar Flexi
601 ; let details = MetaTv { mtv_info = FlatMetaTv
602 , mtv_ref = ref
603 , mtv_tclvl = fmvTcLevel }
604 name = mkMetaTyVarName uniq (fsLit "s")
605 ; return (mkTcTyVar name (typeKind fam_ty) details) }
606
607 newMetaDetails :: MetaInfo -> TcM TcTyVarDetails
608 newMetaDetails info
609 = do { ref <- newMutVar Flexi
610 ; tclvl <- getTcLevel
611 ; return (MetaTv { mtv_info = info
612 , mtv_ref = ref
613 , mtv_tclvl = tclvl }) }
614
615 cloneMetaTyVar :: TcTyVar -> TcM TcTyVar
616 cloneMetaTyVar tv
617 = ASSERT( isTcTyVar tv )
618 do { uniq <- newUnique
619 ; ref <- newMutVar Flexi
620 ; let name' = setNameUnique (tyVarName tv) uniq
621 details' = case tcTyVarDetails tv of
622 details@(MetaTv {}) -> details { mtv_ref = ref }
623 _ -> pprPanic "cloneMetaTyVar" (ppr tv)
624 ; return (mkTcTyVar name' (tyVarKind tv) details') }
625
626 -- Works for both type and kind variables
627 readMetaTyVar :: TyVar -> TcM MetaDetails
628 readMetaTyVar tyvar = ASSERT2( isMetaTyVar tyvar, ppr tyvar )
629 readMutVar (metaTyVarRef tyvar)
630
631 isFilledMetaTyVar :: TyVar -> TcM Bool
632 -- True of a filled-in (Indirect) meta type variable
633 isFilledMetaTyVar tv
634 | MetaTv { mtv_ref = ref } <- tcTyVarDetails tv
635 = do { details <- readMutVar ref
636 ; return (isIndirect details) }
637 | otherwise = return False
638
639 isUnfilledMetaTyVar :: TyVar -> TcM Bool
640 -- True of a un-filled-in (Flexi) meta type variable
641 isUnfilledMetaTyVar tv
642 | MetaTv { mtv_ref = ref } <- tcTyVarDetails tv
643 = do { details <- readMutVar ref
644 ; return (isFlexi details) }
645 | otherwise = return False
646
647 --------------------
648 -- Works with both type and kind variables
649 writeMetaTyVar :: TcTyVar -> TcType -> TcM ()
650 -- Write into a currently-empty MetaTyVar
651
652 writeMetaTyVar tyvar ty
653 | not debugIsOn
654 = writeMetaTyVarRef tyvar (metaTyVarRef tyvar) ty
655
656 -- Everything from here on only happens if DEBUG is on
657 | not (isTcTyVar tyvar)
658 = WARN( True, text "Writing to non-tc tyvar" <+> ppr tyvar )
659 return ()
660
661 | MetaTv { mtv_ref = ref } <- tcTyVarDetails tyvar
662 = writeMetaTyVarRef tyvar ref ty
663
664 | otherwise
665 = WARN( True, text "Writing to non-meta tyvar" <+> ppr tyvar )
666 return ()
667
668 --------------------
669 writeMetaTyVarRef :: TcTyVar -> TcRef MetaDetails -> TcType -> TcM ()
670 -- Here the tyvar is for error checking only;
671 -- the ref cell must be for the same tyvar
672 writeMetaTyVarRef tyvar ref ty
673 | not debugIsOn
674 = do { traceTc "writeMetaTyVar" (ppr tyvar <+> dcolon <+> ppr (tyVarKind tyvar)
675 <+> text ":=" <+> ppr ty)
676 ; writeTcRef ref (Indirect ty) }
677
678 -- Everything from here on only happens if DEBUG is on
679 | otherwise
680 = do { meta_details <- readMutVar ref;
681 -- Zonk kinds to allow the error check to work
682 ; zonked_tv_kind <- zonkTcType tv_kind
683 ; zonked_ty_kind <- zonkTcType ty_kind
684 ; let kind_check_ok = isPredTy tv_kind -- Don't check kinds for updates
685 -- to coercion variables
686 || tcEqKind zonked_ty_kind zonked_tv_kind
687
688 kind_msg = hang (text "Ill-kinded update to meta tyvar")
689 2 ( ppr tyvar <+> text "::" <+> (ppr tv_kind $$ ppr zonked_tv_kind)
690 <+> text ":="
691 <+> ppr ty <+> text "::" <+> (ppr ty_kind $$ ppr zonked_ty_kind) )
692
693 ; traceTc "writeMetaTyVar" (ppr tyvar <+> text ":=" <+> ppr ty)
694
695 -- Check for double updates
696 ; MASSERT2( isFlexi meta_details, double_upd_msg meta_details )
697
698 -- Check for level OK
699 -- See Note [Level check when unifying]
700 ; MASSERT2( level_check_ok, level_check_msg )
701
702 -- Check Kinds ok
703 ; MASSERT2( kind_check_ok, kind_msg )
704
705 -- Do the write
706 ; writeMutVar ref (Indirect ty) }
707 where
708 tv_kind = tyVarKind tyvar
709 ty_kind = typeKind ty
710
711 tv_lvl = tcTyVarLevel tyvar
712 ty_lvl = tcTypeLevel ty
713
714 level_check_ok = isFlattenTyVar tyvar
715 || not (ty_lvl `strictlyDeeperThan` tv_lvl)
716 level_check_msg = ppr ty_lvl $$ ppr tv_lvl $$ ppr tyvar $$ ppr ty
717
718 double_upd_msg details = hang (text "Double update of meta tyvar")
719 2 (ppr tyvar $$ ppr details)
720
721
722 {- Note [Level check when unifying]
723 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
724 When unifying
725 alpha:lvl := ty
726 we expect that the TcLevel of 'ty' will be <= lvl.
727 However, during unflatting we do
728 fuv:l := ty:(l+1)
729 which is usually wrong; hence the check isFmmvTyVar in level_check_ok.
730 See Note [TcLevel assignment] in TcType.
731 -}
732
733 {-
734 % Generating fresh variables for pattern match check
735 -}
736
737 -- UNINSTANTIATED VERSION OF tcInstSkolTyCoVars
738 genInstSkolTyVarsX :: SrcSpan -> TCvSubst -> [TyVar]
739 -> TcRnIf gbl lcl (TCvSubst, [TcTyVar])
740 -- Precondition: tyvars should be scoping-ordered
741 -- see Note [Kind substitution when instantiating]
742 -- Get the location from the monad; this is a complete freshening operation
743 genInstSkolTyVarsX loc subst tvs
744 = instSkolTyCoVarsX (mkTcSkolTyVar topTcLevel loc False) subst tvs
745
746 {-
747 ************************************************************************
748 * *
749 MetaTvs: TauTvs
750 * *
751 ************************************************************************
752
753 Note [Never need to instantiate coercion variables]
754 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
755 With coercion variables sloshing around in types, it might seem that we
756 sometimes need to instantiate coercion variables. This would be problematic,
757 because coercion variables inhabit unboxed equality (~#), and the constraint
758 solver thinks in terms only of boxed equality (~). The solution is that
759 we never need to instantiate coercion variables in the first place.
760
761 The tyvars that we need to instantiate come from the types of functions,
762 data constructors, and patterns. These will never be quantified over
763 coercion variables, except for the special case of the promoted Eq#. But,
764 that can't ever appear in user code, so we're safe!
765 -}
766
767 newAnonMetaTyVar :: MetaInfo -> Kind -> TcM TcTyVar
768 -- Make a new meta tyvar out of thin air
769 newAnonMetaTyVar meta_info kind
770 = do { uniq <- newUnique
771 ; let name = mkMetaTyVarName uniq s
772 s = case meta_info of
773 TauTv -> fsLit "t"
774 FlatMetaTv -> fsLit "fmv"
775 FlatSkolTv -> fsLit "fsk"
776 SigTv -> fsLit "a"
777 ; details <- newMetaDetails meta_info
778 ; return (mkTcTyVar name kind details) }
779
780 newFlexiTyVar :: Kind -> TcM TcTyVar
781 newFlexiTyVar kind = newAnonMetaTyVar TauTv kind
782
783 newFlexiTyVarTy :: Kind -> TcM TcType
784 newFlexiTyVarTy kind = do
785 tc_tyvar <- newFlexiTyVar kind
786 return (mkTyVarTy tc_tyvar)
787
788 newFlexiTyVarTys :: Int -> Kind -> TcM [TcType]
789 newFlexiTyVarTys n kind = mapM newFlexiTyVarTy (nOfThem n kind)
790
791 newOpenTypeKind :: TcM TcKind
792 newOpenTypeKind
793 = do { rr <- newFlexiTyVarTy runtimeRepTy
794 ; return (tYPE rr) }
795
796 -- | Create a tyvar that can be a lifted or unlifted type.
797 -- Returns alpha :: TYPE kappa, where both alpha and kappa are fresh
798 newOpenFlexiTyVarTy :: TcM TcType
799 newOpenFlexiTyVarTy
800 = do { kind <- newOpenTypeKind
801 ; newFlexiTyVarTy kind }
802
803 newMetaSigTyVars :: [TyVar] -> TcM (TCvSubst, [TcTyVar])
804 newMetaSigTyVars = mapAccumLM newMetaSigTyVarX emptyTCvSubst
805
806 newMetaTyVars :: [TyVar] -> TcM (TCvSubst, [TcTyVar])
807 -- Instantiate with META type variables
808 -- Note that this works for a sequence of kind, type, and coercion variables
809 -- variables. Eg [ (k:*), (a:k->k) ]
810 -- Gives [ (k7:*), (a8:k7->k7) ]
811 newMetaTyVars = mapAccumLM newMetaTyVarX emptyTCvSubst
812 -- emptyTCvSubst has an empty in-scope set, but that's fine here
813 -- Since the tyvars are freshly made, they cannot possibly be
814 -- captured by any existing for-alls.
815
816 newMetaTyVarX :: TCvSubst -> TyVar -> TcM (TCvSubst, TcTyVar)
817 -- Make a new unification variable tyvar whose Name and Kind come from
818 -- an existing TyVar. We substitute kind variables in the kind.
819 newMetaTyVarX subst tyvar = new_meta_tv_x TauTv subst tyvar
820
821 newMetaTyVarsX :: TCvSubst -> [TyVar] -> TcM (TCvSubst, [TcTyVar])
822 -- Just like newMetaTyVars, but start with an existing substitution.
823 newMetaTyVarsX subst = mapAccumLM newMetaTyVarX subst
824
825 newMetaSigTyVarX :: TCvSubst -> TyVar -> TcM (TCvSubst, TcTyVar)
826 -- Just like newMetaTyVarX, but make a SigTv
827 newMetaSigTyVarX subst tyvar = new_meta_tv_x SigTv subst tyvar
828
829 newWildCardX :: TCvSubst -> TyVar -> TcM (TCvSubst, TcTyVar)
830 newWildCardX subst tv
831 = do { new_tv <- newAnonMetaTyVar TauTv (substTy subst (tyVarKind tv))
832 ; return (extendTvSubstWithClone subst tv new_tv, new_tv) }
833
834 new_meta_tv_x :: MetaInfo -> TCvSubst -> TyVar -> TcM (TCvSubst, TcTyVar)
835 new_meta_tv_x info subst tv
836 = do { uniq <- newUnique
837 ; details <- newMetaDetails info
838 ; let name = mkSystemName uniq (getOccName tv)
839 -- See Note [Name of an instantiated type variable]
840 kind = substTyUnchecked subst (tyVarKind tv)
841 -- NOTE: Trac #12549 is fixed so we could use
842 -- substTy here, but the tc_infer_args problem
843 -- is not yet fixed so leaving as unchecked for now.
844 -- OLD NOTE:
845 -- Unchecked because we call newMetaTyVarX from
846 -- tcInstBinderX, which is called from tc_infer_args
847 -- which does not yet take enough trouble to ensure
848 -- the in-scope set is right; e.g. Trac #12785 trips
849 -- if we use substTy here
850 new_tv = mkTcTyVar name kind details
851 subst1 = extendTvSubstWithClone subst tv new_tv
852 ; return (subst1, new_tv) }
853
854 newMetaTyVarTyAtLevel :: TcLevel -> TcKind -> TcM TcType
855 newMetaTyVarTyAtLevel tc_lvl kind
856 = do { uniq <- newUnique
857 ; ref <- newMutVar Flexi
858 ; let name = mkMetaTyVarName uniq (fsLit "p")
859 details = MetaTv { mtv_info = TauTv
860 , mtv_ref = ref
861 , mtv_tclvl = tc_lvl }
862 ; return (mkTyVarTy (mkTcTyVar name kind details)) }
863
864 {- Note [Name of an instantiated type variable]
865 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
866 At the moment we give a unification variable a System Name, which
867 influences the way it is tidied; see TypeRep.tidyTyVarBndr.
868
869 ************************************************************************
870 * *
871 Quantification
872 * *
873 ************************************************************************
874
875 Note [quantifyTyVars]
876 ~~~~~~~~~~~~~~~~~~~~~
877 quantifyTyVars is given the free vars of a type that we
878 are about to wrap in a forall.
879
880 It takes these free type/kind variables (partitioned into dependent and
881 non-dependent variables) and
882 1. Zonks them and remove globals and covars
883 2. Extends kvs1 with free kind vars in the kinds of tvs (removing globals)
884 3. Calls zonkQuantifiedTyVar on each
885
886 Step (2) is often unimportant, because the kind variable is often
887 also free in the type. Eg
888 Typeable k (a::k)
889 has free vars {k,a}. But the type (see Trac #7916)
890 (f::k->*) (a::k)
891 has free vars {f,a}, but we must add 'k' as well! Hence step (3).
892
893 * This function distinguishes between dependent and non-dependent
894 variables only to keep correct defaulting behavior with -XNoPolyKinds.
895 With -XPolyKinds, it treats both classes of variables identically.
896
897 * quantifyTyVars never quantifies over
898 - a coercion variable
899 - a runtime-rep variable
900
901 Note [quantifyTyVars determinism]
902 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
903 The results of quantifyTyVars are wrapped in a forall and can end up in the
904 interface file. One such example is inferred type signatures. They also affect
905 the results of optimizations, for example worker-wrapper. This means that to
906 get deterministic builds quantifyTyVars needs to be deterministic.
907
908 To achieve this CandidatesQTvs is backed by deterministic sets which allows them
909 to be later converted to a list in a deterministic order.
910
911 For more information about deterministic sets see
912 Note [Deterministic UniqFM] in UniqDFM.
913 -}
914
915 quantifyTyVars
916 :: TcTyCoVarSet -- Global tvs; already zonked
917 -> CandidatesQTvs -- See Note [Dependent type variables] in TcType
918 -- Already zonked
919 -> TcM [TcTyVar]
920 -- See Note [quantifyTyVars]
921 -- Can be given a mixture of TcTyVars and TyVars, in the case of
922 -- associated type declarations. Also accepts covars, but *never* returns any.
923
924 quantifyTyVars gbl_tvs dvs@(DV{ dv_kvs = dep_tkvs, dv_tvs = nondep_tkvs })
925 = do { traceTc "quantifyTyVars" (vcat [ppr dvs, ppr gbl_tvs])
926 ; let all_cvs = filterVarSet isCoVar $ dVarSetToVarSet dep_tkvs
927 dep_kvs = dVarSetElemsWellScoped $
928 dep_tkvs `dVarSetMinusVarSet` gbl_tvs
929 `dVarSetMinusVarSet` closeOverKinds all_cvs
930 -- dVarSetElemsWellScoped: put the kind variables into
931 -- well-scoped order.
932 -- E.g. [k, (a::k)] not the other way roud
933 -- closeOverKinds all_cvs: do not quantify over coercion
934 -- variables, or any any tvs that a covar depends on
935
936 nondep_tvs = dVarSetElems $
937 (nondep_tkvs `minusDVarSet` dep_tkvs)
938 `dVarSetMinusVarSet` gbl_tvs
939 -- See Note [Dependent type variables] in TcType
940 -- The `minus` dep_tkvs removes any kind-level vars
941 -- e.g. T k (a::k) Since k appear in a kind it'll
942 -- be in dv_kvs, and is dependent. So remove it from
943 -- dv_tvs which will also contain k
944 -- No worry about dependent covars here;
945 -- they are all in dep_tkvs
946 -- No worry about scoping, because these are all
947 -- type variables
948 -- NB kinds of tvs are zonked by zonkTyCoVarsAndFV
949
950 -- In the non-PolyKinds case, default the kind variables
951 -- to *, and zonk the tyvars as usual. Notice that this
952 -- may make quantifyTyVars return a shorter list
953 -- than it was passed, but that's ok
954 ; poly_kinds <- xoptM LangExt.PolyKinds
955 ; dep_kvs' <- mapMaybeM (zonk_quant (not poly_kinds)) dep_kvs
956 ; nondep_tvs' <- mapMaybeM (zonk_quant False) nondep_tvs
957 -- Because of the order, any kind variables
958 -- mentioned in the kinds of the nondep_tvs'
959 -- now refer to the dep_kvs'
960
961 ; traceTc "quantifyTyVars"
962 (vcat [ text "globals:" <+> ppr gbl_tvs
963 , text "nondep:" <+> pprTyVars nondep_tvs
964 , text "dep:" <+> pprTyVars dep_kvs
965 , text "dep_kvs'" <+> pprTyVars dep_kvs'
966 , text "nondep_tvs'" <+> pprTyVars nondep_tvs' ])
967
968 ; return (dep_kvs' ++ nondep_tvs') }
969 where
970 -- zonk_quant returns a tyvar if it should be quantified over;
971 -- otherwise, it returns Nothing. The latter case happens for
972 -- * Kind variables, with -XNoPolyKinds: don't quantify over these
973 -- * RuntimeRep variables: we never quantify over these
974 zonk_quant default_kind tkv
975 | not (isTcTyVar tkv)
976 = return (Just tkv) -- For associated types, we have the class variables
977 -- in scope, and they are TyVars not TcTyVars
978 | otherwise
979 = do { deflt_done <- defaultTyVar default_kind tkv
980 ; case deflt_done of
981 True -> return Nothing
982 False -> do { tv <- zonkQuantifiedTyVar tkv
983 ; return (Just tv) } }
984
985 zonkQuantifiedTyVar :: TcTyVar -> TcM TcTyVar
986 -- The quantified type variables often include meta type variables
987 -- we want to freeze them into ordinary type variables
988 -- The meta tyvar is updated to point to the new skolem TyVar. Now any
989 -- bound occurrences of the original type variable will get zonked to
990 -- the immutable version.
991 --
992 -- We leave skolem TyVars alone; they are immutable.
993 --
994 -- This function is called on both kind and type variables,
995 -- but kind variables *only* if PolyKinds is on.
996
997 zonkQuantifiedTyVar tv
998 = case tcTyVarDetails tv of
999 SkolemTv {} -> do { kind <- zonkTcType (tyVarKind tv)
1000 ; return (setTyVarKind tv kind) }
1001 -- It might be a skolem type variable,
1002 -- for example from a user type signature
1003
1004 MetaTv {} -> skolemiseUnboundMetaTyVar tv
1005
1006 _other -> pprPanic "zonkQuantifiedTyVar" (ppr tv) -- RuntimeUnk
1007
1008 defaultTyVar :: Bool -- True <=> please default this kind variable to *
1009 -> TcTyVar -- If it's a MetaTyVar then it is unbound
1010 -> TcM Bool -- True <=> defaulted away altogether
1011
1012 defaultTyVar default_kind tv
1013 | not (isMetaTyVar tv)
1014 = return False
1015
1016 | isRuntimeRepVar tv && not_sig_tv -- We never quantify over a RuntimeRep var
1017 = do { traceTc "Defaulting a RuntimeRep var to LiftedRep" (ppr tv)
1018 ; writeMetaTyVar tv liftedRepTy
1019 ; return True }
1020
1021 | default_kind && not_sig_tv -- -XNoPolyKinds and this is a kind var
1022 = do { default_kind_var tv -- so default it to * if possible
1023 ; return True }
1024
1025 | otherwise
1026 = return False
1027
1028 where
1029 -- Do not default SigTvs. Doing so would violate the invariants
1030 -- on SigTvs; see Note [Signature skolems] in TcType.
1031 -- Trac #13343 is an example
1032 not_sig_tv = not (isSigTyVar tv)
1033
1034 default_kind_var :: TyVar -> TcM ()
1035 -- defaultKindVar is used exclusively with -XNoPolyKinds
1036 -- See Note [Defaulting with -XNoPolyKinds]
1037 -- It takes an (unconstrained) meta tyvar and defaults it.
1038 -- Works only on vars of type *; for other kinds, it issues an error.
1039 default_kind_var kv
1040 | isStarKind (tyVarKind kv)
1041 = do { traceTc "Defaulting a kind var to *" (ppr kv)
1042 ; writeMetaTyVar kv liftedTypeKind }
1043 | otherwise
1044 = addErr (vcat [ text "Cannot default kind variable" <+> quotes (ppr kv')
1045 , text "of kind:" <+> ppr (tyVarKind kv')
1046 , text "Perhaps enable PolyKinds or add a kind signature" ])
1047 where
1048 (_, kv') = tidyOpenTyCoVar emptyTidyEnv kv
1049
1050 skolemiseRuntimeUnk :: TcTyVar -> TcM TyVar
1051 skolemiseRuntimeUnk tv
1052 = skolemise_tv tv RuntimeUnk
1053
1054 skolemiseUnboundMetaTyVar :: TcTyVar -> TcM TyVar
1055 skolemiseUnboundMetaTyVar tv
1056 = skolemise_tv tv (SkolemTv (metaTyVarTcLevel tv) False)
1057
1058 skolemise_tv :: TcTyVar -> TcTyVarDetails -> TcM TyVar
1059 -- We have a Meta tyvar with a ref-cell inside it
1060 -- Skolemise it, so that
1061 -- we are totally out of Meta-tyvar-land
1062 -- We create a skolem TyVar, not a regular TyVar
1063 -- See Note [Zonking to Skolem]
1064 skolemise_tv tv details
1065 = ASSERT2( isMetaTyVar tv, ppr tv )
1066 do { when debugIsOn (check_empty tv)
1067 ; span <- getSrcSpanM -- Get the location from "here"
1068 -- ie where we are generalising
1069 ; kind <- zonkTcType (tyVarKind tv)
1070 ; let uniq = getUnique tv
1071 -- NB: Use same Unique as original tyvar. This is
1072 -- important for TcHsType.splitTelescopeTvs to work properly
1073
1074 tv_name = getOccName tv
1075 final_name = mkInternalName uniq tv_name span
1076 final_tv = mkTcTyVar final_name kind details
1077
1078 ; traceTc "Skolemising" (ppr tv <+> text ":=" <+> ppr final_tv)
1079 ; writeMetaTyVar tv (mkTyVarTy final_tv)
1080 ; return final_tv }
1081
1082 where
1083 check_empty tv -- [Sept 04] Check for non-empty.
1084 = when debugIsOn $ -- See note [Silly Type Synonym]
1085 do { cts <- readMetaTyVar tv
1086 ; case cts of
1087 Flexi -> return ()
1088 Indirect ty -> WARN( True, ppr tv $$ ppr ty )
1089 return () }
1090
1091 {- Note [Defaulting with -XNoPolyKinds]
1092 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1093 Consider
1094
1095 data Compose f g a = Mk (f (g a))
1096
1097 We infer
1098
1099 Compose :: forall k1 k2. (k2 -> *) -> (k1 -> k2) -> k1 -> *
1100 Mk :: forall k1 k2 (f :: k2 -> *) (g :: k1 -> k2) (a :: k1).
1101 f (g a) -> Compose k1 k2 f g a
1102
1103 Now, in another module, we have -XNoPolyKinds -XDataKinds in effect.
1104 What does 'Mk mean? Pre GHC-8.0 with -XNoPolyKinds,
1105 we just defaulted all kind variables to *. But that's no good here,
1106 because the kind variables in 'Mk aren't of kind *, so defaulting to *
1107 is ill-kinded.
1108
1109 After some debate on #11334, we decided to issue an error in this case.
1110 The code is in defaultKindVar.
1111
1112 Note [What is a meta variable?]
1113 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1114 A "meta type-variable", also know as a "unification variable" is a placeholder
1115 introduced by the typechecker for an as-yet-unknown monotype.
1116
1117 For example, when we see a call `reverse (f xs)`, we know that we calling
1118 reverse :: forall a. [a] -> [a]
1119 So we know that the argument `f xs` must be a "list of something". But what is
1120 the "something"? We don't know until we explore the `f xs` a bit more. So we set
1121 out what we do know at the call of `reverse` by instantiate its type with a fresh
1122 meta tyvar, `alpha` say. So now the type of the argument `f xs`, and of the
1123 result, is `[alpha]`. The unification variable `alpha` stands for the
1124 as-yet-unknown type of the elements of the list.
1125
1126 As type inference progresses we may learn more about `alpha`. For example, suppose
1127 `f` has the type
1128 f :: forall b. b -> [Maybe b]
1129 Then we instantiate `f`'s type with another fresh unification variable, say
1130 `beta`; and equate `f`'s result type with reverse's argument type, thus
1131 `[alpha] ~ [Maybe beta]`.
1132
1133 Now we can solve this equality to learn that `alpha ~ Maybe beta`, so we've
1134 refined our knowledge about `alpha`. And so on.
1135
1136 If you found this Note useful, you may also want to have a look at
1137 Section 5 of "Practical type inference for higher rank types" (Peyton Jones,
1138 Vytiniotis, Weirich and Shields. J. Functional Programming. 2011).
1139
1140 Note [What is zonking?]
1141 ~~~~~~~~~~~~~~~~~~~~~~~
1142 GHC relies heavily on mutability in the typechecker for efficient operation.
1143 For this reason, throughout much of the type checking process meta type
1144 variables (the MetaTv constructor of TcTyVarDetails) are represented by mutable
1145 variables (known as TcRefs).
1146
1147 Zonking is the process of ripping out these mutable variables and replacing them
1148 with a real Type. This involves traversing the entire type expression, but the
1149 interesting part of replacing the mutable variables occurs in zonkTyVarOcc.
1150
1151 There are two ways to zonk a Type:
1152
1153 * zonkTcTypeToType, which is intended to be used at the end of type-checking
1154 for the final zonk. It has to deal with unfilled metavars, either by filling
1155 it with a value like Any or failing (determined by the UnboundTyVarZonker
1156 used).
1157
1158 * zonkTcType, which will happily ignore unfilled metavars. This is the
1159 appropriate function to use while in the middle of type-checking.
1160
1161 Note [Zonking to Skolem]
1162 ~~~~~~~~~~~~~~~~~~~~~~~~
1163 We used to zonk quantified type variables to regular TyVars. However, this
1164 leads to problems. Consider this program from the regression test suite:
1165
1166 eval :: Int -> String -> String -> String
1167 eval 0 root actual = evalRHS 0 root actual
1168
1169 evalRHS :: Int -> a
1170 evalRHS 0 root actual = eval 0 root actual
1171
1172 It leads to the deferral of an equality (wrapped in an implication constraint)
1173
1174 forall a. () => ((String -> String -> String) ~ a)
1175
1176 which is propagated up to the toplevel (see TcSimplify.tcSimplifyInferCheck).
1177 In the meantime `a' is zonked and quantified to form `evalRHS's signature.
1178 This has the *side effect* of also zonking the `a' in the deferred equality
1179 (which at this point is being handed around wrapped in an implication
1180 constraint).
1181
1182 Finally, the equality (with the zonked `a') will be handed back to the
1183 simplifier by TcRnDriver.tcRnSrcDecls calling TcSimplify.tcSimplifyTop.
1184 If we zonk `a' with a regular type variable, we will have this regular type
1185 variable now floating around in the simplifier, which in many places assumes to
1186 only see proper TcTyVars.
1187
1188 We can avoid this problem by zonking with a skolem. The skolem is rigid
1189 (which we require for a quantified variable), but is still a TcTyVar that the
1190 simplifier knows how to deal with.
1191
1192 Note [Silly Type Synonyms]
1193 ~~~~~~~~~~~~~~~~~~~~~~~~~~
1194 Consider this:
1195 type C u a = u -- Note 'a' unused
1196
1197 foo :: (forall a. C u a -> C u a) -> u
1198 foo x = ...
1199
1200 bar :: Num u => u
1201 bar = foo (\t -> t + t)
1202
1203 * From the (\t -> t+t) we get type {Num d} => d -> d
1204 where d is fresh.
1205
1206 * Now unify with type of foo's arg, and we get:
1207 {Num (C d a)} => C d a -> C d a
1208 where a is fresh.
1209
1210 * Now abstract over the 'a', but float out the Num (C d a) constraint
1211 because it does not 'really' mention a. (see exactTyVarsOfType)
1212 The arg to foo becomes
1213 \/\a -> \t -> t+t
1214
1215 * So we get a dict binding for Num (C d a), which is zonked to give
1216 a = ()
1217 [Note Sept 04: now that we are zonking quantified type variables
1218 on construction, the 'a' will be frozen as a regular tyvar on
1219 quantification, so the floated dict will still have type (C d a).
1220 Which renders this whole note moot; happily!]
1221
1222 * Then the \/\a abstraction has a zonked 'a' in it.
1223
1224 All very silly. I think its harmless to ignore the problem. We'll end up with
1225 a \/\a in the final result but all the occurrences of a will be zonked to ()
1226
1227 ************************************************************************
1228 * *
1229 Zonking types
1230 * *
1231 ************************************************************************
1232
1233 -}
1234
1235 -- | @tcGetGlobalTyCoVars@ returns a fully-zonked set of *scoped* tyvars free in
1236 -- the environment. To improve subsequent calls to the same function it writes
1237 -- the zonked set back into the environment. Note that this returns all
1238 -- variables free in anything (term-level or type-level) in scope. We thus
1239 -- don't have to worry about clashes with things that are not in scope, because
1240 -- if they are reachable, then they'll be returned here.
1241 tcGetGlobalTyCoVars :: TcM TcTyVarSet
1242 tcGetGlobalTyCoVars
1243 = do { (TcLclEnv {tcl_tyvars = gtv_var}) <- getLclEnv
1244 ; gbl_tvs <- readMutVar gtv_var
1245 ; gbl_tvs' <- zonkTyCoVarsAndFV gbl_tvs
1246 ; writeMutVar gtv_var gbl_tvs'
1247 ; return gbl_tvs' }
1248
1249 -- | Zonk a type without using the smart constructors; the result type
1250 -- is available for inspection within the type-checking knot.
1251 zonkTcTypeInKnot :: TcType -> TcM TcType
1252 zonkTcTypeInKnot = mapType (zonkTcTypeMapper { tcm_smart = False }) ()
1253
1254 zonkTcTypeAndFV :: TcType -> TcM DTyCoVarSet
1255 -- Zonk a type and take its free variables
1256 -- With kind polymorphism it can be essential to zonk *first*
1257 -- so that we find the right set of free variables. Eg
1258 -- forall k1. forall (a:k2). a
1259 -- where k2:=k1 is in the substitution. We don't want
1260 -- k2 to look free in this type!
1261 -- NB: This might be called from within the knot, so don't use
1262 -- smart constructors. See Note [Zonking within the knot] in TcHsType
1263 zonkTcTypeAndFV ty
1264 = tyCoVarsOfTypeDSet <$> zonkTcTypeInKnot ty
1265
1266 -- | Zonk a type and call 'candidateQTyVarsOfType' on it.
1267 -- Works within the knot.
1268 zonkTcTypeAndSplitDepVars :: TcType -> TcM CandidatesQTvs
1269 zonkTcTypeAndSplitDepVars ty
1270 = candidateQTyVarsOfType <$> zonkTcTypeInKnot ty
1271
1272 zonkTcTypesAndSplitDepVars :: [TcType] -> TcM CandidatesQTvs
1273 zonkTcTypesAndSplitDepVars tys
1274 = candidateQTyVarsOfTypes <$> mapM zonkTcTypeInKnot tys
1275
1276 zonkTyCoVar :: TyCoVar -> TcM TcType
1277 -- Works on TyVars and TcTyVars
1278 zonkTyCoVar tv | isTcTyVar tv = zonkTcTyVar tv
1279 | isTyVar tv = mkTyVarTy <$> zonkTyCoVarKind tv
1280 | otherwise = ASSERT2( isCoVar tv, ppr tv )
1281 mkCoercionTy . mkCoVarCo <$> zonkTyCoVarKind tv
1282 -- Hackily, when typechecking type and class decls
1283 -- we have TyVars in scopeadded (only) in
1284 -- TcHsType.tcTyClTyVars, but it seems
1285 -- painful to make them into TcTyVars there
1286
1287 zonkTyCoVarsAndFV :: TyCoVarSet -> TcM TyCoVarSet
1288 zonkTyCoVarsAndFV tycovars =
1289 tyCoVarsOfTypes <$> mapM zonkTyCoVar (nonDetEltsUniqSet tycovars)
1290 -- It's OK to use nonDetEltsUniqSet here because we immediately forget about
1291 -- the ordering by turning it into a nondeterministic set and the order
1292 -- of zonking doesn't matter for determinism.
1293
1294 -- Takes a list of TyCoVars, zonks them and returns a
1295 -- deterministically ordered list of their free variables.
1296 zonkTyCoVarsAndFVList :: [TyCoVar] -> TcM [TyCoVar]
1297 zonkTyCoVarsAndFVList tycovars =
1298 tyCoVarsOfTypesList <$> mapM zonkTyCoVar tycovars
1299
1300 zonkTcTyVars :: [TcTyVar] -> TcM [TcType]
1301 zonkTcTyVars tyvars = mapM zonkTcTyVar tyvars
1302
1303 ----------------- Types
1304 zonkTyCoVarKind :: TyCoVar -> TcM TyCoVar
1305 zonkTyCoVarKind tv = do { kind' <- zonkTcType (tyVarKind tv)
1306 ; return (setTyVarKind tv kind') }
1307
1308 zonkTcTypes :: [TcType] -> TcM [TcType]
1309 zonkTcTypes tys = mapM zonkTcType tys
1310
1311 {-
1312 ************************************************************************
1313 * *
1314 Zonking constraints
1315 * *
1316 ************************************************************************
1317 -}
1318
1319 zonkImplication :: Implication -> TcM Implication
1320 zonkImplication implic@(Implic { ic_skols = skols
1321 , ic_given = given
1322 , ic_wanted = wanted
1323 , ic_info = info })
1324 = do { skols' <- mapM zonkTcTyCoVarBndr skols -- Need to zonk their kinds!
1325 -- as Trac #7230 showed
1326 ; given' <- mapM zonkEvVar given
1327 ; info' <- zonkSkolemInfo info
1328 ; wanted' <- zonkWCRec wanted
1329 ; return (implic { ic_skols = skols'
1330 , ic_given = given'
1331 , ic_wanted = wanted'
1332 , ic_info = info' }) }
1333
1334 zonkEvVar :: EvVar -> TcM EvVar
1335 zonkEvVar var = do { ty' <- zonkTcType (varType var)
1336 ; return (setVarType var ty') }
1337
1338
1339 zonkWC :: WantedConstraints -> TcM WantedConstraints
1340 zonkWC wc = zonkWCRec wc
1341
1342 zonkWCRec :: WantedConstraints -> TcM WantedConstraints
1343 zonkWCRec (WC { wc_simple = simple, wc_impl = implic, wc_insol = insol })
1344 = do { simple' <- zonkSimples simple
1345 ; implic' <- mapBagM zonkImplication implic
1346 ; insol' <- zonkSimples insol
1347 ; return (WC { wc_simple = simple', wc_impl = implic', wc_insol = insol' }) }
1348
1349 zonkSimples :: Cts -> TcM Cts
1350 zonkSimples cts = do { cts' <- mapBagM zonkCt' cts
1351 ; traceTc "zonkSimples done:" (ppr cts')
1352 ; return cts' }
1353
1354 zonkCt' :: Ct -> TcM Ct
1355 zonkCt' ct = zonkCt ct
1356
1357 {- Note [zonkCt behaviour]
1358 zonkCt tries to maintain the canonical form of a Ct. For example,
1359 - a CDictCan should stay a CDictCan;
1360 - a CTyEqCan should stay a CTyEqCan (if the LHS stays as a variable.).
1361 - a CHoleCan should stay a CHoleCan
1362
1363 Why?, for example:
1364 - For CDictCan, the @TcSimplify.expandSuperClasses@ step, which runs after the
1365 simple wanted and plugin loop, looks for @CDictCan@s. If a plugin is in use,
1366 constraints are zonked before being passed to the plugin. This means if we
1367 don't preserve a canonical form, @expandSuperClasses@ fails to expand
1368 superclasses. This is what happened in Trac #11525.
1369
1370 - For CHoleCan, once we forget that it's a hole, we can never recover that info.
1371
1372 NB: we do not expect to see any CFunEqCans, because zonkCt is only
1373 called on unflattened constraints.
1374 NB: Constraints are always re-flattened etc by the canonicaliser in
1375 @TcCanonical@ even if they come in as CDictCan. Only canonical constraints that
1376 are actually in the inert set carry all the guarantees. So it is okay if zonkCt
1377 creates e.g. a CDictCan where the cc_tyars are /not/ function free.
1378 -}
1379 zonkCt :: Ct -> TcM Ct
1380 zonkCt ct@(CHoleCan { cc_ev = ev })
1381 = do { ev' <- zonkCtEvidence ev
1382 ; return $ ct { cc_ev = ev' } }
1383 zonkCt ct@(CDictCan { cc_ev = ev, cc_tyargs = args })
1384 = do { ev' <- zonkCtEvidence ev
1385 ; args' <- mapM zonkTcType args
1386 ; return $ ct { cc_ev = ev', cc_tyargs = args' } }
1387 zonkCt ct@(CTyEqCan { cc_ev = ev, cc_tyvar = tv, cc_rhs = rhs })
1388 = do { ev' <- zonkCtEvidence ev
1389 ; tv_ty' <- zonkTcTyVar tv
1390 ; case getTyVar_maybe tv_ty' of
1391 Just tv' -> do { rhs' <- zonkTcType rhs
1392 ; return ct { cc_ev = ev'
1393 , cc_tyvar = tv'
1394 , cc_rhs = rhs' } }
1395 Nothing -> return (mkNonCanonical ev') }
1396 zonkCt ct
1397 = ASSERT( not (isCFunEqCan ct) )
1398 -- We do not expect to see any CFunEqCans, because zonkCt is only called on
1399 -- unflattened constraints.
1400 do { fl' <- zonkCtEvidence (cc_ev ct)
1401 ; return (mkNonCanonical fl') }
1402
1403 zonkCtEvidence :: CtEvidence -> TcM CtEvidence
1404 zonkCtEvidence ctev@(CtGiven { ctev_pred = pred })
1405 = do { pred' <- zonkTcType pred
1406 ; return (ctev { ctev_pred = pred'}) }
1407 zonkCtEvidence ctev@(CtWanted { ctev_pred = pred, ctev_dest = dest })
1408 = do { pred' <- zonkTcType pred
1409 ; let dest' = case dest of
1410 EvVarDest ev -> EvVarDest $ setVarType ev pred'
1411 -- necessary in simplifyInfer
1412 HoleDest h -> HoleDest h
1413 ; return (ctev { ctev_pred = pred', ctev_dest = dest' }) }
1414 zonkCtEvidence ctev@(CtDerived { ctev_pred = pred })
1415 = do { pred' <- zonkTcType pred
1416 ; return (ctev { ctev_pred = pred' }) }
1417
1418 zonkSkolemInfo :: SkolemInfo -> TcM SkolemInfo
1419 zonkSkolemInfo (SigSkol cx ty tv_prs) = do { ty' <- zonkTcType ty
1420 ; return (SigSkol cx ty' tv_prs) }
1421 zonkSkolemInfo (InferSkol ntys) = do { ntys' <- mapM do_one ntys
1422 ; return (InferSkol ntys') }
1423 where
1424 do_one (n, ty) = do { ty' <- zonkTcType ty; return (n, ty') }
1425 zonkSkolemInfo skol_info = return skol_info
1426
1427 {-
1428 %************************************************************************
1429 %* *
1430 \subsection{Zonking -- the main work-horses: zonkTcType, zonkTcTyVar}
1431 * *
1432 * For internal use only! *
1433 * *
1434 ************************************************************************
1435
1436 -}
1437
1438 -- zonkId is used *during* typechecking just to zonk the Id's type
1439 zonkId :: TcId -> TcM TcId
1440 zonkId id
1441 = do { ty' <- zonkTcType (idType id)
1442 ; return (Id.setIdType id ty') }
1443
1444 -- | A suitable TyCoMapper for zonking a type inside the knot, and
1445 -- before all metavars are filled in.
1446 zonkTcTypeMapper :: TyCoMapper () TcM
1447 zonkTcTypeMapper = TyCoMapper
1448 { tcm_smart = True
1449 , tcm_tyvar = const zonkTcTyVar
1450 , tcm_covar = const (\cv -> mkCoVarCo <$> zonkTyCoVarKind cv)
1451 , tcm_hole = hole
1452 , tcm_tybinder = \_env tv _vis -> ((), ) <$> zonkTcTyCoVarBndr tv }
1453 where
1454 hole :: () -> CoercionHole -> Role -> Type -> Type
1455 -> TcM Coercion
1456 hole _ h r t1 t2
1457 = do { contents <- unpackCoercionHole_maybe h
1458 ; case contents of
1459 Just co -> do { co <- zonkCo co
1460 ; checkCoercionHole co h r t1 t2 }
1461 Nothing -> do { t1 <- zonkTcType t1
1462 ; t2 <- zonkTcType t2
1463 ; return $ mkHoleCo h r t1 t2 } }
1464
1465
1466 -- For unbound, mutable tyvars, zonkType uses the function given to it
1467 -- For tyvars bound at a for-all, zonkType zonks them to an immutable
1468 -- type variable and zonks the kind too
1469 zonkTcType :: TcType -> TcM TcType
1470 zonkTcType = mapType zonkTcTypeMapper ()
1471
1472 -- | "Zonk" a coercion -- really, just zonk any types in the coercion
1473 zonkCo :: Coercion -> TcM Coercion
1474 zonkCo = mapCoercion zonkTcTypeMapper ()
1475
1476 zonkTcTyCoVarBndr :: TcTyCoVar -> TcM TcTyCoVar
1477 -- A tyvar binder is never a unification variable (MetaTv),
1478 -- rather it is always a skolems. BUT it may have a kind
1479 -- that has not yet been zonked, and may include kind
1480 -- unification variables.
1481 zonkTcTyCoVarBndr tyvar
1482 -- can't use isCoVar, because it looks at a TyCon. Argh.
1483 = ASSERT2( isImmutableTyVar tyvar || (not $ isTyVar tyvar), pprTyVar tyvar )
1484 updateTyVarKindM zonkTcType tyvar
1485
1486 zonkTcTyVarBinder :: TyVarBndr TcTyVar vis -> TcM (TyVarBndr TcTyVar vis)
1487 zonkTcTyVarBinder (TvBndr tv vis)
1488 = do { tv' <- zonkTcTyCoVarBndr tv
1489 ; return (TvBndr tv' vis) }
1490
1491 zonkTcTyVar :: TcTyVar -> TcM TcType
1492 -- Simply look through all Flexis
1493 zonkTcTyVar tv
1494 | isTcTyVar tv
1495 = case tcTyVarDetails tv of
1496 SkolemTv {} -> zonk_kind_and_return
1497 RuntimeUnk {} -> zonk_kind_and_return
1498 MetaTv { mtv_ref = ref }
1499 -> do { cts <- readMutVar ref
1500 ; case cts of
1501 Flexi -> zonk_kind_and_return
1502 Indirect ty -> zonkTcType ty }
1503
1504 | otherwise -- coercion variable
1505 = zonk_kind_and_return
1506 where
1507 zonk_kind_and_return = do { z_tv <- zonkTyCoVarKind tv
1508 ; return (mkTyVarTy z_tv) }
1509
1510 -- Variant that assumes that any result of zonking is still a TyVar.
1511 -- Should be used only on skolems and SigTvs
1512 zonkTcTyVarToTyVar :: TcTyVar -> TcM TcTyVar
1513 zonkTcTyVarToTyVar tv
1514 = do { ty <- zonkTcTyVar tv
1515 ; return (tcGetTyVar "zonkTcTyVarToVar" ty) }
1516
1517 {-
1518 %************************************************************************
1519 %* *
1520 Tidying
1521 * *
1522 ************************************************************************
1523 -}
1524
1525 zonkTidyTcType :: TidyEnv -> TcType -> TcM (TidyEnv, TcType)
1526 zonkTidyTcType env ty = do { ty' <- zonkTcType ty
1527 ; return (tidyOpenType env ty') }
1528
1529 -- | Make an 'ErrorThing' storing a type.
1530 mkTypeErrorThing :: TcType -> ErrorThing
1531 mkTypeErrorThing ty = ErrorThing ty (Just $ length $ snd $ repSplitAppTys ty)
1532 zonkTidyTcType
1533 -- NB: Use *rep*splitAppTys, else we get #11313
1534
1535 -- | Make an 'ErrorThing' storing a type, with some extra args known about
1536 mkTypeErrorThingArgs :: TcType -> Int -> ErrorThing
1537 mkTypeErrorThingArgs ty num_args
1538 = ErrorThing ty (Just $ (length $ snd $ repSplitAppTys ty) + num_args)
1539 zonkTidyTcType
1540
1541 zonkTidyOrigin :: TidyEnv -> CtOrigin -> TcM (TidyEnv, CtOrigin)
1542 zonkTidyOrigin env (GivenOrigin skol_info)
1543 = do { skol_info1 <- zonkSkolemInfo skol_info
1544 ; let skol_info2 = tidySkolemInfo env skol_info1
1545 ; return (env, GivenOrigin skol_info2) }
1546 zonkTidyOrigin env orig@(TypeEqOrigin { uo_actual = act
1547 , uo_expected = exp
1548 , uo_thing = m_thing })
1549 = do { (env1, act') <- zonkTidyTcType env act
1550 ; (env2, exp') <- zonkTidyTcType env1 exp
1551 ; (env3, m_thing') <- zonkTidyErrorThing env2 m_thing
1552 ; return ( env3, orig { uo_actual = act'
1553 , uo_expected = exp'
1554 , uo_thing = m_thing' }) }
1555 zonkTidyOrigin env (KindEqOrigin ty1 m_ty2 orig t_or_k)
1556 = do { (env1, ty1') <- zonkTidyTcType env ty1
1557 ; (env2, m_ty2') <- case m_ty2 of
1558 Just ty2 -> second Just <$> zonkTidyTcType env1 ty2
1559 Nothing -> return (env1, Nothing)
1560 ; (env3, orig') <- zonkTidyOrigin env2 orig
1561 ; return (env3, KindEqOrigin ty1' m_ty2' orig' t_or_k) }
1562 zonkTidyOrigin env (FunDepOrigin1 p1 l1 p2 l2)
1563 = do { (env1, p1') <- zonkTidyTcType env p1
1564 ; (env2, p2') <- zonkTidyTcType env1 p2
1565 ; return (env2, FunDepOrigin1 p1' l1 p2' l2) }
1566 zonkTidyOrigin env (FunDepOrigin2 p1 o1 p2 l2)
1567 = do { (env1, p1') <- zonkTidyTcType env p1
1568 ; (env2, p2') <- zonkTidyTcType env1 p2
1569 ; (env3, o1') <- zonkTidyOrigin env2 o1
1570 ; return (env3, FunDepOrigin2 p1' o1' p2' l2) }
1571 zonkTidyOrigin env orig = return (env, orig)
1572
1573 zonkTidyErrorThing :: TidyEnv -> Maybe ErrorThing
1574 -> TcM (TidyEnv, Maybe ErrorThing)
1575 zonkTidyErrorThing env (Just (ErrorThing thing n_args zonker))
1576 = do { (env', thing') <- zonker env thing
1577 ; return (env', Just $ ErrorThing thing' n_args zonker) }
1578 zonkTidyErrorThing env Nothing
1579 = return (env, Nothing)
1580
1581 ----------------
1582 tidyCt :: TidyEnv -> Ct -> Ct
1583 -- Used only in error reporting
1584 -- Also converts it to non-canonical
1585 tidyCt env ct
1586 = case ct of
1587 CHoleCan { cc_ev = ev }
1588 -> ct { cc_ev = tidy_ev env ev }
1589 _ -> mkNonCanonical (tidy_ev env (ctEvidence ct))
1590 where
1591 tidy_ev :: TidyEnv -> CtEvidence -> CtEvidence
1592 -- NB: we do not tidy the ctev_evar field because we don't
1593 -- show it in error messages
1594 tidy_ev env ctev@(CtGiven { ctev_pred = pred })
1595 = ctev { ctev_pred = tidyType env pred }
1596 tidy_ev env ctev@(CtWanted { ctev_pred = pred })
1597 = ctev { ctev_pred = tidyType env pred }
1598 tidy_ev env ctev@(CtDerived { ctev_pred = pred })
1599 = ctev { ctev_pred = tidyType env pred }
1600
1601 ----------------
1602 tidyEvVar :: TidyEnv -> EvVar -> EvVar
1603 tidyEvVar env var = setVarType var (tidyType env (varType var))
1604
1605 ----------------
1606 tidySkolemInfo :: TidyEnv -> SkolemInfo -> SkolemInfo
1607 tidySkolemInfo env (DerivSkol ty) = DerivSkol (tidyType env ty)
1608 tidySkolemInfo env (SigSkol cx ty tv_prs) = tidySigSkol env cx ty tv_prs
1609 tidySkolemInfo env (InferSkol ids) = InferSkol (mapSnd (tidyType env) ids)
1610 tidySkolemInfo env (UnifyForAllSkol ty) = UnifyForAllSkol (tidyType env ty)
1611 tidySkolemInfo _ info = info
1612
1613 tidySigSkol :: TidyEnv -> UserTypeCtxt
1614 -> TcType -> [(Name,TcTyVar)] -> SkolemInfo
1615 -- We need to take special care when tidying SigSkol
1616 -- See Note [SigSkol SkolemInfo] in TcRnTypes
1617 tidySigSkol env cx ty tv_prs
1618 = SigSkol cx (tidy_ty env ty) tv_prs'
1619 where
1620 tv_prs' = mapSnd (tidyTyVarOcc env) tv_prs
1621 inst_env = mkNameEnv tv_prs'
1622
1623 tidy_ty env (ForAllTy (TvBndr tv vis) ty)
1624 = ForAllTy (TvBndr tv' vis) (tidy_ty env' ty)
1625 where
1626 (env', tv') = tidy_tv_bndr env tv
1627
1628 tidy_ty env (FunTy arg res)
1629 = FunTy (tidyType env arg) (tidy_ty env res)
1630
1631 tidy_ty env ty = tidyType env ty
1632
1633 tidy_tv_bndr :: TidyEnv -> TyVar -> (TidyEnv, TyVar)
1634 tidy_tv_bndr env@(occ_env, subst) tv
1635 | Just tv' <- lookupNameEnv inst_env (tyVarName tv)
1636 = ((occ_env, extendVarEnv subst tv tv'), tv')
1637
1638 | otherwise
1639 = tidyTyCoVarBndr env tv
1640
1641 -------------------------------------------------------------------------
1642 {-
1643 %************************************************************************
1644 %* *
1645 Levity polymorphism checks
1646 * *
1647 ************************************************************************
1648
1649 See Note [Levity polymorphism checking] in DsMonad
1650
1651 -}
1652
1653 -- | According to the rules around representation polymorphism
1654 -- (see https://ghc.haskell.org/trac/ghc/wiki/NoSubKinds), no binder
1655 -- can have a representation-polymorphic type. This check ensures
1656 -- that we respect this rule. It is a bit regrettable that this error
1657 -- occurs in zonking, after which we should have reported all errors.
1658 -- But it's hard to see where else to do it, because this can be discovered
1659 -- only after all solving is done. And, perhaps most importantly, this
1660 -- isn't really a compositional property of a type system, so it's
1661 -- not a terrible surprise that the check has to go in an awkward spot.
1662 ensureNotLevPoly :: Type -- its zonked type
1663 -> SDoc -- where this happened
1664 -> TcM ()
1665 ensureNotLevPoly ty doc
1666 = whenNoErrs $ -- sometimes we end up zonking bogus definitions of type
1667 -- forall a. a. See, for example, test ghci/scripts/T9140
1668 checkForLevPoly doc ty
1669
1670 -- See Note [Levity polymorphism checking] in DsMonad
1671 checkForLevPoly :: SDoc -> Type -> TcM ()
1672 checkForLevPoly = checkForLevPolyX addErr
1673
1674 checkForLevPolyX :: Monad m
1675 => (SDoc -> m ()) -- how to report an error
1676 -> SDoc -> Type -> m ()
1677 checkForLevPolyX add_err extra ty
1678 | isTypeLevPoly ty
1679 = add_err (formatLevPolyErr ty $$ extra)
1680 | otherwise
1681 = return ()
1682
1683 formatLevPolyErr :: Type -- levity-polymorphic type
1684 -> SDoc
1685 formatLevPolyErr ty
1686 = hang (text "A levity-polymorphic type is not allowed here:")
1687 2 (vcat [ text "Type:" <+> ppr tidy_ty
1688 , text "Kind:" <+> ppr tidy_ki ])
1689 where
1690 (tidy_env, tidy_ty) = tidyOpenType emptyTidyEnv ty
1691 tidy_ki = tidyType tidy_env (typeKind ty)