Remove bad debugging output.
[ghc.git] / compiler / typecheck / TcHsType.hs
1 {-
2 (c) The University of Glasgow 2006
3 (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4
5 \section[TcMonoType]{Typechecking user-specified @MonoTypes@}
6 -}
7
8 {-# LANGUAGE CPP, TupleSections, MultiWayIf, RankNTypes #-}
9 {-# LANGUAGE ScopedTypeVariables #-}
10
11 module TcHsType (
12 -- Type signatures
13 kcHsSigType, tcClassSigType,
14 tcHsSigType, tcHsSigWcType,
15 tcHsPartialSigType,
16 funsSigCtxt, addSigCtxt, pprSigCtxt,
17
18 tcHsClsInstType,
19 tcHsDeriv, tcDerivStrategy,
20 tcHsTypeApp,
21 UserTypeCtxt(..),
22 tcImplicitTKBndrs, tcImplicitQTKBndrs,
23 tcExplicitTKBndrs,
24 kcExplicitTKBndrs, kcImplicitTKBndrs,
25
26 -- Type checking type and class decls
27 kcLookupTcTyCon, kcTyClTyVars, tcTyClTyVars,
28 tcDataKindSig,
29
30 -- tyvars
31 scopeTyVars, scopeTyVars2,
32
33 -- Kind-checking types
34 -- No kind generalisation, no checkValidType
35 kcLHsQTyVars,
36 tcWildCardBinders,
37 tcHsLiftedType, tcHsOpenType,
38 tcHsLiftedTypeNC, tcHsOpenTypeNC,
39 tcLHsType, tcLHsTypeUnsaturated, tcCheckLHsType,
40 tcHsMbContext, tcHsContext, tcLHsPredType, tcInferApps,
41 solveEqualities, -- useful re-export
42
43 typeLevelMode, kindLevelMode,
44
45 kindGeneralize, checkExpectedKindX, instantiateTyUntilN,
46 reportFloatingKvs,
47
48 -- Sort-checking kinds
49 tcLHsKindSig, badKindSig,
50
51 -- Zonking and promoting
52 zonkPromoteType,
53
54 -- Pattern type signatures
55 tcHsPatSigType, tcPatSig, funAppCtxt
56 ) where
57
58 #include "HsVersions.h"
59
60 import GhcPrelude
61
62 import HsSyn
63 import TcRnMonad
64 import TcEvidence
65 import TcEnv
66 import TcMType
67 import TcValidity
68 import TcUnify
69 import TcIface
70 import TcSimplify
71 import TcType
72 import TcHsSyn( zonkSigType )
73 import Inst ( tcInstTyBinders, tcInstTyBinder )
74 import TyCoRep( TyBinder(..) ) -- Used in tcDataKindSig
75 import Type
76 import Coercion
77 import Kind
78 import RdrName( lookupLocalRdrOcc )
79 import Var
80 import VarSet
81 import TyCon
82 import ConLike
83 import DataCon
84 import Class
85 import Name
86 import NameEnv
87 import NameSet
88 import VarEnv
89 import TysWiredIn
90 import BasicTypes
91 import SrcLoc
92 import Constants ( mAX_CTUPLE_SIZE )
93 import ErrUtils( MsgDoc )
94 import Unique
95 import Util
96 import UniqSupply
97 import Outputable
98 import FastString
99 import PrelNames hiding ( wildCardName )
100 import qualified GHC.LanguageExtensions as LangExt
101
102 import Maybes
103 import Data.List ( find, mapAccumR )
104 import Control.Monad
105
106 {-
107 ----------------------------
108 General notes
109 ----------------------------
110
111 Unlike with expressions, type-checking types both does some checking and
112 desugars at the same time. This is necessary because we often want to perform
113 equality checks on the types right away, and it would be incredibly painful
114 to do this on un-desugared types. Luckily, desugared types are close enough
115 to HsTypes to make the error messages sane.
116
117 During type-checking, we perform as little validity checking as possible.
118 This is because some type-checking is done in a mutually-recursive knot, and
119 if we look too closely at the tycons, we'll loop. This is why we always must
120 use mkNakedTyConApp and mkNakedAppTys, etc., which never look at a tycon.
121 The mkNamed... functions don't uphold Type invariants, but zonkTcTypeToType
122 will repair this for us. Note that zonkTcType *is* safe within a knot, and
123 can be done repeatedly with no ill effect: it just squeezes out metavariables.
124
125 Generally, after type-checking, you will want to do validity checking, say
126 with TcValidity.checkValidType.
127
128 Validity checking
129 ~~~~~~~~~~~~~~~~~
130 Some of the validity check could in principle be done by the kind checker,
131 but not all:
132
133 - During desugaring, we normalise by expanding type synonyms. Only
134 after this step can we check things like type-synonym saturation
135 e.g. type T k = k Int
136 type S a = a
137 Then (T S) is ok, because T is saturated; (T S) expands to (S Int);
138 and then S is saturated. This is a GHC extension.
139
140 - Similarly, also a GHC extension, we look through synonyms before complaining
141 about the form of a class or instance declaration
142
143 - Ambiguity checks involve functional dependencies, and it's easier to wait
144 until knots have been resolved before poking into them
145
146 Also, in a mutually recursive group of types, we can't look at the TyCon until we've
147 finished building the loop. So to keep things simple, we postpone most validity
148 checking until step (3).
149
150 Knot tying
151 ~~~~~~~~~~
152 During step (1) we might fault in a TyCon defined in another module, and it might
153 (via a loop) refer back to a TyCon defined in this module. So when we tie a big
154 knot around type declarations with ARecThing, so that the fault-in code can get
155 the TyCon being defined.
156
157 %************************************************************************
158 %* *
159 Check types AND do validity checking
160 * *
161 ************************************************************************
162 -}
163
164 funsSigCtxt :: [Located Name] -> UserTypeCtxt
165 -- Returns FunSigCtxt, with no redundant-context-reporting,
166 -- form a list of located names
167 funsSigCtxt (L _ name1 : _) = FunSigCtxt name1 False
168 funsSigCtxt [] = panic "funSigCtxt"
169
170 addSigCtxt :: UserTypeCtxt -> LHsType GhcRn -> TcM a -> TcM a
171 addSigCtxt ctxt hs_ty thing_inside
172 = setSrcSpan (getLoc hs_ty) $
173 addErrCtxt (pprSigCtxt ctxt hs_ty) $
174 thing_inside
175
176 pprSigCtxt :: UserTypeCtxt -> LHsType GhcRn -> SDoc
177 -- (pprSigCtxt ctxt <extra> <type>)
178 -- prints In the type signature for 'f':
179 -- f :: <type>
180 -- The <extra> is either empty or "the ambiguity check for"
181 pprSigCtxt ctxt hs_ty
182 | Just n <- isSigMaybe ctxt
183 = hang (text "In the type signature:")
184 2 (pprPrefixOcc n <+> dcolon <+> ppr hs_ty)
185
186 | otherwise
187 = hang (text "In" <+> pprUserTypeCtxt ctxt <> colon)
188 2 (ppr hs_ty)
189
190 tcHsSigWcType :: UserTypeCtxt -> LHsSigWcType GhcRn -> TcM Type
191 -- This one is used when we have a LHsSigWcType, but in
192 -- a place where wildards aren't allowed. The renamer has
193 -- already checked this, so we can simply ignore it.
194 tcHsSigWcType ctxt sig_ty = tcHsSigType ctxt (dropWildCards sig_ty)
195
196 kcHsSigType :: SkolemInfo -> [Located Name] -> LHsSigType GhcRn -> TcM ()
197 kcHsSigType skol_info names (HsIB { hsib_body = hs_ty
198 , hsib_ext = HsIBRn { hsib_vars = sig_vars }})
199 = addSigCtxt (funsSigCtxt names) hs_ty $
200 discardResult $
201 tcImplicitTKBndrs skol_info sig_vars $
202 tc_lhs_type typeLevelMode hs_ty liftedTypeKind
203 kcHsSigType _ _ (XHsImplicitBndrs _) = panic "kcHsSigType"
204
205 tcClassSigType :: SkolemInfo -> [Located Name] -> LHsSigType GhcRn -> TcM Type
206 -- Does not do validity checking; this must be done outside
207 -- the recursive class declaration "knot"
208 tcClassSigType skol_info names sig_ty
209 = addSigCtxt (funsSigCtxt names) (hsSigType sig_ty) $
210 tc_hs_sig_type_and_gen skol_info sig_ty liftedTypeKind
211
212 tcHsSigType :: UserTypeCtxt -> LHsSigType GhcRn -> TcM Type
213 -- Does validity checking
214 -- See Note [Recipe for checking a signature]
215 tcHsSigType ctxt sig_ty
216 = addSigCtxt ctxt (hsSigType sig_ty) $
217 do { traceTc "tcHsSigType {" (ppr sig_ty)
218 ; kind <- case expectedKindInCtxt ctxt of
219 AnythingKind -> newMetaKindVar
220 TheKind k -> return k
221 OpenKind -> newOpenTypeKind
222 -- The kind is checked by checkValidType, and isn't necessarily
223 -- of kind * in a Template Haskell quote eg [t| Maybe |]
224
225 -- Generalise here: see Note [Kind generalisation]
226 ; do_kind_gen <- decideKindGeneralisationPlan sig_ty
227 ; ty <- if do_kind_gen
228 then tc_hs_sig_type_and_gen skol_info sig_ty kind
229 else tc_hs_sig_type skol_info sig_ty kind
230
231 ; checkValidType ctxt ty
232 ; traceTc "end tcHsSigType }" (ppr ty)
233 ; return ty }
234 where
235 skol_info = SigTypeSkol ctxt
236
237 tc_hs_sig_type_and_gen :: SkolemInfo -> LHsSigType GhcRn -> Kind -> TcM Type
238 -- Kind-checks/desugars an 'LHsSigType',
239 -- solve equalities,
240 -- and then kind-generalizes.
241 -- This will never emit constraints, as it uses solveEqualities interally.
242 -- No validity checking, but it does zonk en route to generalization
243 tc_hs_sig_type_and_gen skol_info (HsIB { hsib_ext
244 = HsIBRn { hsib_vars = sig_vars }
245 , hsib_body = hs_ty }) kind
246 = do { (tkvs, ty) <- solveEqualities $
247 tcImplicitTKBndrs skol_info sig_vars $
248 tc_lhs_type typeLevelMode hs_ty kind
249 -- NB the call to solveEqualities, which unifies all those
250 -- kind variables floating about, immediately prior to
251 -- kind generalisation
252
253 -- We use the "InKnot" zonker, because this is called
254 -- on class method sigs in the knot
255 ; ty1 <- zonkPromoteTypeInKnot $ mkSpecForAllTys tkvs ty
256 ; kvs <- kindGeneralize ty1
257 ; zonkSigType (mkInvForAllTys kvs ty1) }
258
259 tc_hs_sig_type_and_gen _ (XHsImplicitBndrs _) _ = panic "tc_hs_sig_type_and_gen"
260
261 tc_hs_sig_type :: SkolemInfo -> LHsSigType GhcRn -> Kind -> TcM Type
262 -- Kind-check/desugar a 'LHsSigType', but does not solve
263 -- the equalities that arise from doing so; instead it may
264 -- emit kind-equality constraints into the monad
265 -- Zonking, but no validity checking
266 tc_hs_sig_type skol_info (HsIB { hsib_ext = HsIBRn { hsib_vars = sig_vars }
267 , hsib_body = hs_ty }) kind
268 = do { (tkvs, ty) <- tcImplicitTKBndrs skol_info sig_vars $
269 tc_lhs_type typeLevelMode hs_ty kind
270
271 -- need to promote any remaining metavariables; test case:
272 -- dependent/should_fail/T14066e.
273 ; zonkPromoteType (mkSpecForAllTys tkvs ty) }
274
275 tc_hs_sig_type _ (XHsImplicitBndrs _) _ = panic "tc_hs_sig_type"
276
277 -----------------
278 tcHsDeriv :: LHsSigType GhcRn -> TcM ([TyVar], (Class, [Type], [Kind]))
279 -- Like tcHsSigType, but for the ...deriving( C t1 ty2 ) clause
280 -- Returns the C, [ty1, ty2, and the kinds of C's remaining arguments
281 -- E.g. class C (a::*) (b::k->k)
282 -- data T a b = ... deriving( C Int )
283 -- returns ([k], C, [k, Int], [k->k])
284 tcHsDeriv hs_ty
285 = do { cls_kind <- newMetaKindVar
286 -- always safe to kind-generalize, because there
287 -- can be no covars in an outer scope
288 ; ty <- checkNoErrs $
289 -- avoid redundant error report with "illegal deriving", below
290 tc_hs_sig_type_and_gen (SigTypeSkol DerivClauseCtxt) hs_ty cls_kind
291 ; cls_kind <- zonkTcType cls_kind
292 ; let (tvs, pred) = splitForAllTys ty
293 ; let (args, _) = splitFunTys cls_kind
294 ; case getClassPredTys_maybe pred of
295 Just (cls, tys) -> return (tvs, (cls, tys, args))
296 Nothing -> failWithTc (text "Illegal deriving item" <+> quotes (ppr hs_ty)) }
297
298 -- | Typecheck something within the context of a deriving strategy.
299 -- This is of particular importance when the deriving strategy is @via@.
300 -- For instance:
301 --
302 -- @
303 -- deriving via (S a) instance C (T a)
304 -- @
305 --
306 -- We need to typecheck @S a@, and moreover, we need to extend the tyvar
307 -- environment with @a@ before typechecking @C (T a)@, since @S a@ quantified
308 -- the type variable @a@.
309 tcDerivStrategy
310 :: forall a.
311 UserTypeCtxt
312 -> Maybe (DerivStrategy GhcRn) -- ^ The deriving strategy
313 -> TcM ([TyVar], a) -- ^ The thing to typecheck within the context of the
314 -- deriving strategy, which might quantify some type
315 -- variables of its own.
316 -> TcM (Maybe (DerivStrategy GhcTc), [TyVar], a)
317 -- ^ The typechecked deriving strategy, all quantified tyvars, and
318 -- the payload of the typechecked thing.
319 tcDerivStrategy user_ctxt mds thing_inside
320 = case mds of
321 Nothing -> boring_case Nothing
322 Just ds -> do (ds', tvs, thing) <- tc_deriv_strategy ds
323 pure (Just ds', tvs, thing)
324 where
325 tc_deriv_strategy :: DerivStrategy GhcRn
326 -> TcM (DerivStrategy GhcTc, [TyVar], a)
327 tc_deriv_strategy StockStrategy = boring_case StockStrategy
328 tc_deriv_strategy AnyclassStrategy = boring_case AnyclassStrategy
329 tc_deriv_strategy NewtypeStrategy = boring_case NewtypeStrategy
330 tc_deriv_strategy (ViaStrategy ty) = do
331 cls_kind <- newMetaKindVar
332 ty' <- checkNoErrs $
333 tc_hs_sig_type_and_gen (SigTypeSkol user_ctxt) ty cls_kind
334 let (via_tvs, via_pred) = splitForAllTys ty'
335 tcExtendTyVarEnv via_tvs $ do
336 (thing_tvs, thing) <- thing_inside
337 pure (ViaStrategy via_pred, via_tvs ++ thing_tvs, thing)
338
339 boring_case :: mds -> TcM (mds, [TyVar], a)
340 boring_case mds = do
341 (thing_tvs, thing) <- thing_inside
342 pure (mds, thing_tvs, thing)
343
344 tcHsClsInstType :: UserTypeCtxt -- InstDeclCtxt or SpecInstCtxt
345 -> LHsSigType GhcRn
346 -> TcM ([TyVar], ThetaType, Class, [Type])
347 -- Like tcHsSigType, but for a class instance declaration
348 tcHsClsInstType user_ctxt hs_inst_ty
349 = setSrcSpan (getLoc (hsSigType hs_inst_ty)) $
350 do { inst_ty <- tc_hs_sig_type_and_gen (SigTypeSkol user_ctxt) hs_inst_ty constraintKind
351 ; checkValidInstance user_ctxt hs_inst_ty inst_ty }
352
353 ----------------------------------------------
354 -- | Type-check a visible type application
355 tcHsTypeApp :: LHsWcType GhcRn -> Kind -> TcM Type
356 -- See Note [Recipe for checking a signature] in TcHsType
357 tcHsTypeApp wc_ty kind
358 | HsWC { hswc_ext = sig_wcs, hswc_body = hs_ty } <- wc_ty
359 = do { ty <- solveLocalEqualities $
360 -- We are looking at a user-written type, very like a
361 -- signature so we want to solve its equalities right now
362 tcWildCardBindersX newWildTyVar Nothing sig_wcs $ \ _ ->
363 tcCheckLHsType hs_ty kind
364 ; ty <- zonkPromoteType ty
365 ; checkValidType TypeAppCtxt ty
366 ; return ty }
367 -- NB: we don't call emitWildcardHoleConstraints here, because
368 -- we want any holes in visible type applications to be used
369 -- without fuss. No errors, warnings, extensions, etc.
370 tcHsTypeApp (XHsWildCardBndrs _) _ = panic "tcHsTypeApp"
371
372 {-
373 ************************************************************************
374 * *
375 The main kind checker: no validity checks here
376 * *
377 ************************************************************************
378
379 First a couple of simple wrappers for kcHsType
380 -}
381
382 ---------------------------
383 tcHsOpenType, tcHsLiftedType,
384 tcHsOpenTypeNC, tcHsLiftedTypeNC :: LHsType GhcRn -> TcM TcType
385 -- Used for type signatures
386 -- Do not do validity checking
387 tcHsOpenType ty = addTypeCtxt ty $ tcHsOpenTypeNC ty
388 tcHsLiftedType ty = addTypeCtxt ty $ tcHsLiftedTypeNC ty
389
390 tcHsOpenTypeNC ty = do { ek <- newOpenTypeKind
391 ; tc_lhs_type typeLevelMode ty ek }
392 tcHsLiftedTypeNC ty = tc_lhs_type typeLevelMode ty liftedTypeKind
393
394 -- Like tcHsType, but takes an expected kind
395 tcCheckLHsType :: LHsType GhcRn -> Kind -> TcM TcType
396 tcCheckLHsType hs_ty exp_kind
397 = addTypeCtxt hs_ty $
398 tc_lhs_type typeLevelMode hs_ty exp_kind
399
400 tcLHsType :: LHsType GhcRn -> TcM (TcType, TcKind)
401 -- Called from outside: set the context
402 tcLHsType ty = addTypeCtxt ty (tc_infer_lhs_type typeLevelMode ty)
403
404 -- Like tcLHsType, but use it in a context where type synonyms and type families
405 -- do not need to be saturated, like in a GHCi :kind call
406 tcLHsTypeUnsaturated :: LHsType GhcRn -> TcM (TcType, TcKind)
407 tcLHsTypeUnsaturated ty = addTypeCtxt ty (tc_infer_lhs_type mode ty)
408 where
409 mode = allowUnsaturated typeLevelMode
410
411 ---------------------------
412 -- | Should we generalise the kind of this type signature?
413 -- We *should* generalise if the type is closed
414 -- or if NoMonoLocalBinds is set. Otherwise, nope.
415 -- See Note [Kind generalisation plan]
416 decideKindGeneralisationPlan :: LHsSigType GhcRn -> TcM Bool
417 decideKindGeneralisationPlan sig_ty@(HsIB { hsib_ext
418 = HsIBRn { hsib_closed = closed } })
419 = do { mono_locals <- xoptM LangExt.MonoLocalBinds
420 ; let should_gen = not mono_locals || closed
421 ; traceTc "decideKindGeneralisationPlan"
422 (ppr sig_ty $$ text "should gen?" <+> ppr should_gen)
423 ; return should_gen }
424 decideKindGeneralisationPlan(XHsImplicitBndrs _)
425 = panic "decideKindGeneralisationPlan"
426
427 {- Note [Kind generalisation plan]
428 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
429 When should we do kind-generalisation for user-written type signature?
430 Answer: we use the same rule as for value bindings:
431
432 * We always kind-generalise if the type signature is closed
433 * Additionally, we attempt to generalise if we have NoMonoLocalBinds
434
435 Trac #13337 shows the problem if we kind-generalise an open type (i.e.
436 one that mentions in-scope type variable
437 foo :: forall k (a :: k) proxy. (Typeable k, Typeable a)
438 => proxy a -> String
439 foo _ = case eqT :: Maybe (k :~: Type) of
440 Nothing -> ...
441 Just Refl -> case eqT :: Maybe (a :~: Int) of ...
442
443 In the expression type sig on the last line, we have (a :: k)
444 but (Int :: Type). Since (:~:) is kind-homogeneous, this requires
445 k ~ *, which is true in the Refl branch of the outer case.
446
447 That equality will be solved if we allow it to float out to the
448 implication constraint for the Refl match, but not not if we aggressively
449 attempt to solve all equalities the moment they occur; that is, when
450 checking (Maybe (a :~: Int)). (NB: solveEqualities fails unless it
451 solves all the kind equalities, which is the right thing at top level.)
452
453 So here the right thing is simply not to do kind generalisation!
454
455 ************************************************************************
456 * *
457 Type-checking modes
458 * *
459 ************************************************************************
460
461 The kind-checker is parameterised by a TcTyMode, which contains some
462 information about where we're checking a type.
463
464 The renamer issues errors about what it can. All errors issued here must
465 concern things that the renamer can't handle.
466
467 -}
468
469 -- | Info about the context in which we're checking a type. Currently,
470 -- differentiates only between types and kinds, but this will likely
471 -- grow, at least to include the distinction between patterns and
472 -- not-patterns.
473 data TcTyMode
474 = TcTyMode { mode_level :: TypeOrKind
475 , mode_unsat :: Bool -- True <=> allow unsaturated type families
476 }
477 -- The mode_unsat field is solely so that type families/synonyms can be unsaturated
478 -- in GHCi :kind calls
479
480 typeLevelMode :: TcTyMode
481 typeLevelMode = TcTyMode { mode_level = TypeLevel, mode_unsat = False }
482
483 kindLevelMode :: TcTyMode
484 kindLevelMode = TcTyMode { mode_level = KindLevel, mode_unsat = False }
485
486 allowUnsaturated :: TcTyMode -> TcTyMode
487 allowUnsaturated mode = mode { mode_unsat = True }
488
489 -- switch to kind level
490 kindLevel :: TcTyMode -> TcTyMode
491 kindLevel mode = mode { mode_level = KindLevel }
492
493 instance Outputable TcTyMode where
494 ppr = ppr . mode_level
495
496 {-
497 Note [Bidirectional type checking]
498 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
499 In expressions, whenever we see a polymorphic identifier, say `id`, we are
500 free to instantiate it with metavariables, knowing that we can always
501 re-generalize with type-lambdas when necessary. For example:
502
503 rank2 :: (forall a. a -> a) -> ()
504 x = rank2 id
505
506 When checking the body of `x`, we can instantiate `id` with a metavariable.
507 Then, when we're checking the application of `rank2`, we notice that we really
508 need a polymorphic `id`, and then re-generalize over the unconstrained
509 metavariable.
510
511 In types, however, we're not so lucky, because *we cannot re-generalize*!
512 There is no lambda. So, we must be careful only to instantiate at the last
513 possible moment, when we're sure we're never going to want the lost polymorphism
514 again. This is done in calls to tcInstTyBinders.
515
516 To implement this behavior, we use bidirectional type checking, where we
517 explicitly think about whether we know the kind of the type we're checking
518 or not. Note that there is a difference between not knowing a kind and
519 knowing a metavariable kind: the metavariables are TauTvs, and cannot become
520 forall-quantified kinds. Previously (before dependent types), there were
521 no higher-rank kinds, and so we could instantiate early and be sure that
522 no types would have polymorphic kinds, and so we could always assume that
523 the kind of a type was a fresh metavariable. Not so anymore, thus the
524 need for two algorithms.
525
526 For HsType forms that can never be kind-polymorphic, we implement only the
527 "down" direction, where we safely assume a metavariable kind. For HsType forms
528 that *can* be kind-polymorphic, we implement just the "up" (functions with
529 "infer" in their name) version, as we gain nothing by also implementing the
530 "down" version.
531
532 Note [Future-proofing the type checker]
533 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
534 As discussed in Note [Bidirectional type checking], each HsType form is
535 handled in *either* tc_infer_hs_type *or* tc_hs_type. These functions
536 are mutually recursive, so that either one can work for any type former.
537 But, we want to make sure that our pattern-matches are complete. So,
538 we have a bunch of repetitive code just so that we get warnings if we're
539 missing any patterns.
540
541 Note [The tcType invariant]
542 ~~~~~~~~~~~~~~~~~~~~~~~~~~~
543 (IT1) If tc_ty = tc_hs_type hs_ty exp_kind
544 then typeKind tc_ty = exp_kind
545 without any zonking needed. The reason for this is that in
546 tcInferApps we see (F ty), and we kind-check 'ty' with an
547 expected-kind coming from F. Then, to make the resulting application
548 well kinded --- see Note [The well-kinded type invariant] in TcType ---
549 we need the kind-checked 'ty' to have exactly the kind that F expects,
550 with no funny zonking nonsense in between.
551
552 The tcType invariant also applies to checkExpectedKind:
553
554 (IT2) if
555 (tc_ty, _, _) = checkExpectedKind ty act_ki exp_ki
556 then
557 typeKind tc_ty = exp_ki
558
559 These other invariants are all necessary, too, as these functions
560 are used within tc_hs_type:
561
562 (IT3) If (ty, ki) <- tc_infer_hs_type ..., then typeKind ty == ki.
563
564 (IT4) If (ty, ki) <- tc_infer_hs_type ..., then zonk ki == ki.
565 (In other words, the result kind of tc_infer_hs_type is zonked.)
566
567 (IT5) If (ty, ki) <- tcTyVar ..., then typeKind ty == ki.
568
569 (IT6) If (ty, ki) <- tcTyVar ..., then zonk ki == ki.
570 (In other words, the result kind of tcTyVar is zonked.)
571
572 -}
573
574 ------------------------------------------
575 -- | Check and desugar a type, returning the core type and its
576 -- possibly-polymorphic kind. Much like 'tcInferRho' at the expression
577 -- level.
578 tc_infer_lhs_type :: TcTyMode -> LHsType GhcRn -> TcM (TcType, TcKind)
579 tc_infer_lhs_type mode (L span ty)
580 = setSrcSpan span $
581 do { (ty', kind) <- tc_infer_hs_type mode ty
582 ; return (ty', kind) }
583
584 -- | Infer the kind of a type and desugar. This is the "up" type-checker,
585 -- as described in Note [Bidirectional type checking]
586 tc_infer_hs_type :: TcTyMode -> HsType GhcRn -> TcM (TcType, TcKind)
587 tc_infer_hs_type mode (HsParTy _ t) = tc_infer_lhs_type mode t
588 tc_infer_hs_type mode (HsTyVar _ _ (L _ tv)) = tcTyVar mode tv
589
590 tc_infer_hs_type mode (HsAppTy _ ty1 ty2)
591 = do { let (hs_fun_ty, hs_arg_tys) = splitHsAppTys ty1 [ty2]
592 ; (fun_ty, fun_kind) <- tc_infer_lhs_type mode hs_fun_ty
593 -- NB: (IT4) of Note [The tcType invariant] ensures that fun_kind is zonked
594 ; tcTyApps mode hs_fun_ty fun_ty fun_kind hs_arg_tys }
595
596 tc_infer_hs_type mode (HsOpTy _ lhs lhs_op@(L _ hs_op) rhs)
597 | not (hs_op `hasKey` funTyConKey)
598 = do { (op, op_kind) <- tcTyVar mode hs_op
599 ; tcTyApps mode (noLoc $ HsTyVar noExt NotPromoted lhs_op) op op_kind
600 [lhs, rhs] }
601
602 tc_infer_hs_type mode (HsKindSig _ ty sig)
603 = do { sig' <- tcLHsKindSig KindSigCtxt sig
604 -- We must typecheck the kind signature, and solve all
605 -- its equalities etc; from this point on we may do
606 -- things like instantiate its foralls, so it needs
607 -- to be fully determined (Trac #14904)
608 ; traceTc "tc_infer_hs_type:sig" (ppr ty $$ ppr sig')
609 ; ty' <- tc_lhs_type mode ty sig'
610 ; return (ty', sig') }
611
612 -- HsSpliced is an annotation produced by 'RnSplice.rnSpliceType' to communicate
613 -- the splice location to the typechecker. Here we skip over it in order to have
614 -- the same kind inferred for a given expression whether it was produced from
615 -- splices or not.
616 --
617 -- See Note [Delaying modFinalizers in untyped splices].
618 tc_infer_hs_type mode (HsSpliceTy _ (HsSpliced _ _ (HsSplicedTy ty)))
619 = tc_infer_hs_type mode ty
620
621 tc_infer_hs_type mode (HsDocTy _ ty _) = tc_infer_lhs_type mode ty
622 tc_infer_hs_type _ (XHsType (NHsCoreTy ty))
623 = do { ty <- zonkTcType ty -- (IT3) and (IT4) of Note [The tcType invariant]
624 ; return (ty, typeKind ty) }
625 tc_infer_hs_type mode other_ty
626 = do { kv <- newMetaKindVar
627 ; ty' <- tc_hs_type mode other_ty kv
628 ; return (ty', kv) }
629
630 ------------------------------------------
631 tc_lhs_type :: TcTyMode -> LHsType GhcRn -> TcKind -> TcM TcType
632 tc_lhs_type mode (L span ty) exp_kind
633 = setSrcSpan span $
634 tc_hs_type mode ty exp_kind
635
636 ------------------------------------------
637 tc_fun_type :: TcTyMode -> LHsType GhcRn -> LHsType GhcRn -> TcKind
638 -> TcM TcType
639 tc_fun_type mode ty1 ty2 exp_kind = case mode_level mode of
640 TypeLevel ->
641 do { arg_k <- newOpenTypeKind
642 ; res_k <- newOpenTypeKind
643 ; ty1' <- tc_lhs_type mode ty1 arg_k
644 ; ty2' <- tc_lhs_type mode ty2 res_k
645 ; checkExpectedKind (HsFunTy noExt ty1 ty2) (mkFunTy ty1' ty2')
646 liftedTypeKind exp_kind }
647 KindLevel -> -- no representation polymorphism in kinds. yet.
648 do { ty1' <- tc_lhs_type mode ty1 liftedTypeKind
649 ; ty2' <- tc_lhs_type mode ty2 liftedTypeKind
650 ; checkExpectedKind (HsFunTy noExt ty1 ty2) (mkFunTy ty1' ty2')
651 liftedTypeKind exp_kind }
652
653 ------------------------------------------
654 tc_hs_type :: TcTyMode -> HsType GhcRn -> TcKind -> TcM TcType
655 -- See Note [The tcType invariant]
656 -- See Note [Bidirectional type checking]
657
658 tc_hs_type mode (HsParTy _ ty) exp_kind = tc_lhs_type mode ty exp_kind
659 tc_hs_type mode (HsDocTy _ ty _) exp_kind = tc_lhs_type mode ty exp_kind
660 tc_hs_type _ ty@(HsBangTy _ bang _) _
661 -- While top-level bangs at this point are eliminated (eg !(Maybe Int)),
662 -- other kinds of bangs are not (eg ((!Maybe) Int)). These kinds of
663 -- bangs are invalid, so fail. (#7210, #14761)
664 = do { let bangError err = failWith $
665 text "Unexpected" <+> text err <+> text "annotation:" <+> ppr ty $$
666 text err <+> text "annotation cannot appear nested inside a type"
667 ; case bang of
668 HsSrcBang _ SrcUnpack _ -> bangError "UNPACK"
669 HsSrcBang _ SrcNoUnpack _ -> bangError "NOUNPACK"
670 HsSrcBang _ NoSrcUnpack SrcLazy -> bangError "laziness"
671 HsSrcBang _ _ _ -> bangError "strictness" }
672 tc_hs_type _ ty@(HsRecTy {}) _
673 -- Record types (which only show up temporarily in constructor
674 -- signatures) should have been removed by now
675 = failWithTc (text "Record syntax is illegal here:" <+> ppr ty)
676
677 -- HsSpliced is an annotation produced by 'RnSplice.rnSpliceType'.
678 -- Here we get rid of it and add the finalizers to the global environment
679 -- while capturing the local environment.
680 --
681 -- See Note [Delaying modFinalizers in untyped splices].
682 tc_hs_type mode (HsSpliceTy _ (HsSpliced _ mod_finalizers (HsSplicedTy ty)))
683 exp_kind
684 = do addModFinalizersWithLclEnv mod_finalizers
685 tc_hs_type mode ty exp_kind
686
687 -- This should never happen; type splices are expanded by the renamer
688 tc_hs_type _ ty@(HsSpliceTy {}) _exp_kind
689 = failWithTc (text "Unexpected type splice:" <+> ppr ty)
690
691 ---------- Functions and applications
692 tc_hs_type mode (HsFunTy _ ty1 ty2) exp_kind
693 = tc_fun_type mode ty1 ty2 exp_kind
694
695 tc_hs_type mode (HsOpTy _ ty1 (L _ op) ty2) exp_kind
696 | op `hasKey` funTyConKey
697 = tc_fun_type mode ty1 ty2 exp_kind
698
699 --------- Foralls
700 tc_hs_type mode forall@(HsForAllTy { hst_bndrs = hs_tvs, hst_body = ty }) exp_kind
701 = do { (tvs', ty') <- tcExplicitTKBndrs (ForAllSkol (ppr forall)) hs_tvs $
702 tc_lhs_type mode ty exp_kind
703 -- Do not kind-generalise here! See Note [Kind generalisation]
704 -- Why exp_kind? See Note [Body kind of HsForAllTy]
705 ; let bndrs = mkTyVarBinders Specified tvs'
706 ; return (mkForAllTys bndrs ty') }
707
708 tc_hs_type mode (HsQualTy { hst_ctxt = ctxt, hst_body = ty }) exp_kind
709 | null (unLoc ctxt)
710 = tc_lhs_type mode ty exp_kind
711
712 | otherwise
713 = do { ctxt' <- tc_hs_context mode ctxt
714
715 -- See Note [Body kind of a HsQualTy]
716 ; ty' <- if isConstraintKind exp_kind
717 then tc_lhs_type mode ty constraintKind
718 else do { ek <- newOpenTypeKind
719 -- The body kind (result of the function)
720 -- can be TYPE r, for any r, hence newOpenTypeKind
721 ; ty' <- tc_lhs_type mode ty ek
722 ; checkExpectedKind (unLoc ty) ty' liftedTypeKind exp_kind }
723
724 ; return (mkPhiTy ctxt' ty') }
725
726 --------- Lists, arrays, and tuples
727 tc_hs_type mode rn_ty@(HsListTy _ elt_ty) exp_kind
728 = do { tau_ty <- tc_lhs_type mode elt_ty liftedTypeKind
729 ; checkWiredInTyCon listTyCon
730 ; checkExpectedKind rn_ty (mkListTy tau_ty) liftedTypeKind exp_kind }
731
732 -- See Note [Distinguishing tuple kinds] in HsTypes
733 -- See Note [Inferring tuple kinds]
734 tc_hs_type mode rn_ty@(HsTupleTy _ HsBoxedOrConstraintTuple hs_tys) exp_kind
735 -- (NB: not zonking before looking at exp_k, to avoid left-right bias)
736 | Just tup_sort <- tupKindSort_maybe exp_kind
737 = traceTc "tc_hs_type tuple" (ppr hs_tys) >>
738 tc_tuple rn_ty mode tup_sort hs_tys exp_kind
739 | otherwise
740 = do { traceTc "tc_hs_type tuple 2" (ppr hs_tys)
741 ; (tys, kinds) <- mapAndUnzipM (tc_infer_lhs_type mode) hs_tys
742 ; kinds <- mapM zonkTcType kinds
743 -- Infer each arg type separately, because errors can be
744 -- confusing if we give them a shared kind. Eg Trac #7410
745 -- (Either Int, Int), we do not want to get an error saying
746 -- "the second argument of a tuple should have kind *->*"
747
748 ; let (arg_kind, tup_sort)
749 = case [ (k,s) | k <- kinds
750 , Just s <- [tupKindSort_maybe k] ] of
751 ((k,s) : _) -> (k,s)
752 [] -> (liftedTypeKind, BoxedTuple)
753 -- In the [] case, it's not clear what the kind is, so guess *
754
755 ; tys' <- sequence [ setSrcSpan loc $
756 checkExpectedKind hs_ty ty kind arg_kind
757 | ((L loc hs_ty),ty,kind) <- zip3 hs_tys tys kinds ]
758
759 ; finish_tuple rn_ty tup_sort tys' (map (const arg_kind) tys') exp_kind }
760
761
762 tc_hs_type mode rn_ty@(HsTupleTy _ hs_tup_sort tys) exp_kind
763 = tc_tuple rn_ty mode tup_sort tys exp_kind
764 where
765 tup_sort = case hs_tup_sort of -- Fourth case dealt with above
766 HsUnboxedTuple -> UnboxedTuple
767 HsBoxedTuple -> BoxedTuple
768 HsConstraintTuple -> ConstraintTuple
769 _ -> panic "tc_hs_type HsTupleTy"
770
771 tc_hs_type mode rn_ty@(HsSumTy _ hs_tys) exp_kind
772 = do { let arity = length hs_tys
773 ; arg_kinds <- mapM (\_ -> newOpenTypeKind) hs_tys
774 ; tau_tys <- zipWithM (tc_lhs_type mode) hs_tys arg_kinds
775 ; let arg_reps = map getRuntimeRepFromKind arg_kinds
776 arg_tys = arg_reps ++ tau_tys
777 ; checkExpectedKind rn_ty
778 (mkTyConApp (sumTyCon arity) arg_tys)
779 (unboxedSumKind arg_reps)
780 exp_kind
781 }
782
783 --------- Promoted lists and tuples
784 tc_hs_type mode rn_ty@(HsExplicitListTy _ _ tys) exp_kind
785 = do { tks <- mapM (tc_infer_lhs_type mode) tys
786 ; (taus', kind) <- unifyKinds tys tks
787 ; let ty = (foldr (mk_cons kind) (mk_nil kind) taus')
788 ; checkExpectedKind rn_ty ty (mkListTy kind) exp_kind }
789 where
790 mk_cons k a b = mkTyConApp (promoteDataCon consDataCon) [k, a, b]
791 mk_nil k = mkTyConApp (promoteDataCon nilDataCon) [k]
792
793 tc_hs_type mode rn_ty@(HsExplicitTupleTy _ tys) exp_kind
794 -- using newMetaKindVar means that we force instantiations of any polykinded
795 -- types. At first, I just used tc_infer_lhs_type, but that led to #11255.
796 = do { ks <- replicateM arity newMetaKindVar
797 ; taus <- zipWithM (tc_lhs_type mode) tys ks
798 ; let kind_con = tupleTyCon Boxed arity
799 ty_con = promotedTupleDataCon Boxed arity
800 tup_k = mkTyConApp kind_con ks
801 ; checkExpectedKind rn_ty (mkTyConApp ty_con (ks ++ taus)) tup_k exp_kind }
802 where
803 arity = length tys
804
805 --------- Constraint types
806 tc_hs_type mode rn_ty@(HsIParamTy _ (L _ n) ty) exp_kind
807 = do { MASSERT( isTypeLevel (mode_level mode) )
808 ; ty' <- tc_lhs_type mode ty liftedTypeKind
809 ; let n' = mkStrLitTy $ hsIPNameFS n
810 ; ipClass <- tcLookupClass ipClassName
811 ; checkExpectedKind rn_ty (mkClassPred ipClass [n',ty'])
812 constraintKind exp_kind }
813
814 tc_hs_type _ rn_ty@(HsStarTy _ _) exp_kind
815 -- Desugaring 'HsStarTy' to 'Data.Kind.Type' here means that we don't have to
816 -- handle it in 'coreView' and 'tcView'.
817 = checkExpectedKind rn_ty liftedTypeKind liftedTypeKind exp_kind
818
819 --------- Literals
820 tc_hs_type _ rn_ty@(HsTyLit _ (HsNumTy _ n)) exp_kind
821 = do { checkWiredInTyCon typeNatKindCon
822 ; checkExpectedKind rn_ty (mkNumLitTy n) typeNatKind exp_kind }
823
824 tc_hs_type _ rn_ty@(HsTyLit _ (HsStrTy _ s)) exp_kind
825 = do { checkWiredInTyCon typeSymbolKindCon
826 ; checkExpectedKind rn_ty (mkStrLitTy s) typeSymbolKind exp_kind }
827
828 --------- Potentially kind-polymorphic types: call the "up" checker
829 -- See Note [Future-proofing the type checker]
830 tc_hs_type mode ty@(HsTyVar {}) ek = tc_infer_hs_type_ek mode ty ek
831 tc_hs_type mode ty@(HsAppTy {}) ek = tc_infer_hs_type_ek mode ty ek
832 tc_hs_type mode ty@(HsOpTy {}) ek = tc_infer_hs_type_ek mode ty ek
833 tc_hs_type mode ty@(HsKindSig {}) ek = tc_infer_hs_type_ek mode ty ek
834 tc_hs_type mode ty@(XHsType (NHsCoreTy{})) ek = tc_infer_hs_type_ek mode ty ek
835
836 tc_hs_type _ (HsWildCardTy wc) exp_kind
837 = do { wc_ty <- tcWildCardOcc wc exp_kind
838 ; return (mkNakedCastTy wc_ty (mkTcNomReflCo exp_kind))
839 -- Take care here! Even though the coercion is Refl,
840 -- we still need it to establish Note [The tcType invariant]
841 }
842
843 tcWildCardOcc :: HsWildCardInfo -> Kind -> TcM TcType
844 tcWildCardOcc wc_info exp_kind
845 = do { wc_tv <- tcLookupTyVar (wildCardName wc_info)
846 -- The wildcard's kind should be an un-filled-in meta tyvar
847 ; checkExpectedKind (HsWildCardTy wc_info) (mkTyVarTy wc_tv)
848 (tyVarKind wc_tv) exp_kind }
849
850 ---------------------------
851 -- | Call 'tc_infer_hs_type' and check its result against an expected kind.
852 tc_infer_hs_type_ek :: HasDebugCallStack => TcTyMode -> HsType GhcRn -> TcKind -> TcM TcType
853 tc_infer_hs_type_ek mode hs_ty ek
854 = do { (ty, k) <- tc_infer_hs_type mode hs_ty
855 ; checkExpectedKind hs_ty ty k ek }
856
857 ---------------------------
858 tupKindSort_maybe :: TcKind -> Maybe TupleSort
859 tupKindSort_maybe k
860 | Just (k', _) <- splitCastTy_maybe k = tupKindSort_maybe k'
861 | Just k' <- tcView k = tupKindSort_maybe k'
862 | isConstraintKind k = Just ConstraintTuple
863 | isLiftedTypeKind k = Just BoxedTuple
864 | otherwise = Nothing
865
866 tc_tuple :: HsType GhcRn -> TcTyMode -> TupleSort -> [LHsType GhcRn] -> TcKind -> TcM TcType
867 tc_tuple rn_ty mode tup_sort tys exp_kind
868 = do { arg_kinds <- case tup_sort of
869 BoxedTuple -> return (nOfThem arity liftedTypeKind)
870 UnboxedTuple -> mapM (\_ -> newOpenTypeKind) tys
871 ConstraintTuple -> return (nOfThem arity constraintKind)
872 ; tau_tys <- zipWithM (tc_lhs_type mode) tys arg_kinds
873 ; finish_tuple rn_ty tup_sort tau_tys arg_kinds exp_kind }
874 where
875 arity = length tys
876
877 finish_tuple :: HsType GhcRn
878 -> TupleSort
879 -> [TcType] -- ^ argument types
880 -> [TcKind] -- ^ of these kinds
881 -> TcKind -- ^ expected kind of the whole tuple
882 -> TcM TcType
883 finish_tuple rn_ty tup_sort tau_tys tau_kinds exp_kind
884 = do { traceTc "finish_tuple" (ppr res_kind $$ ppr tau_kinds $$ ppr exp_kind)
885 ; let arg_tys = case tup_sort of
886 -- See also Note [Unboxed tuple RuntimeRep vars] in TyCon
887 UnboxedTuple -> tau_reps ++ tau_tys
888 BoxedTuple -> tau_tys
889 ConstraintTuple -> tau_tys
890 ; tycon <- case tup_sort of
891 ConstraintTuple
892 | arity > mAX_CTUPLE_SIZE
893 -> failWith (bigConstraintTuple arity)
894 | otherwise -> tcLookupTyCon (cTupleTyConName arity)
895 BoxedTuple -> do { let tc = tupleTyCon Boxed arity
896 ; checkWiredInTyCon tc
897 ; return tc }
898 UnboxedTuple -> return (tupleTyCon Unboxed arity)
899 ; checkExpectedKind rn_ty (mkTyConApp tycon arg_tys) res_kind exp_kind }
900 where
901 arity = length tau_tys
902 tau_reps = map getRuntimeRepFromKind tau_kinds
903 res_kind = case tup_sort of
904 UnboxedTuple -> unboxedTupleKind tau_reps
905 BoxedTuple -> liftedTypeKind
906 ConstraintTuple -> constraintKind
907
908 bigConstraintTuple :: Arity -> MsgDoc
909 bigConstraintTuple arity
910 = hang (text "Constraint tuple arity too large:" <+> int arity
911 <+> parens (text "max arity =" <+> int mAX_CTUPLE_SIZE))
912 2 (text "Instead, use a nested tuple")
913
914 ---------------------------
915 -- | Apply a type of a given kind to a list of arguments. This instantiates
916 -- invisible parameters as necessary. Always consumes all the arguments,
917 -- using matchExpectedFunKind as necessary.
918 -- This takes an optional @VarEnv Kind@ which maps kind variables to kinds.
919 -- These kinds should be used to instantiate invisible kind variables;
920 -- they come from an enclosing class for an associated type/data family.
921 tcInferApps :: TcTyMode
922 -> Maybe (VarEnv Kind) -- ^ Possibly, kind info (see above)
923 -> LHsType GhcRn -- ^ Function (for printing only)
924 -> TcType -- ^ Function (could be knot-tied)
925 -> TcKind -- ^ Function kind (zonked)
926 -> [LHsType GhcRn] -- ^ Args
927 -> TcM (TcType, [TcType], TcKind) -- ^ (f args, args, result kind)
928 -- Precondition: typeKind fun_ty = fun_ki
929 -- Reason: we will return a type application like (fun_ty arg1 ... argn),
930 -- and that type must be well-kinded
931 -- See Note [The tcType invariant]
932 -- Postcondition: Result kind is zonked.
933 tcInferApps mode mb_kind_info orig_hs_ty fun_ty fun_ki orig_hs_args
934 = do { traceTc "tcInferApps {" (ppr orig_hs_ty $$ ppr orig_hs_args $$ ppr fun_ki)
935 ; (f_args, args, res_k) <- go 1 [] empty_subst fun_ty orig_ki_binders orig_inner_ki orig_hs_args
936 ; traceTc "tcInferApps }" empty
937 ; res_k <- zonkTcType res_k -- nec'y to uphold (IT4) of Note [The tcType invariant]
938 ; return (f_args, args, res_k) }
939 where
940 empty_subst = mkEmptyTCvSubst $ mkInScopeSet $
941 tyCoVarsOfType fun_ki
942 (orig_ki_binders, orig_inner_ki) = tcSplitPiTys fun_ki
943
944 go :: Int -- the # of the next argument
945 -> [TcType] -- already type-checked args, in reverse order
946 -> TCvSubst -- instantiating substitution
947 -> TcType -- function applied to some args, could be knot-tied
948 -> [TyBinder] -- binders in function kind (both vis. and invis.)
949 -> TcKind -- function kind body (not a Pi-type)
950 -> [LHsType GhcRn] -- un-type-checked args
951 -> TcM (TcType, [TcType], TcKind) -- same as overall return type
952
953 -- no user-written args left. We're done!
954 go _ acc_args subst fun ki_binders inner_ki []
955 = return ( fun
956 , reverse acc_args
957 , nakedSubstTy subst $ mkPiTys ki_binders inner_ki)
958 -- nakedSubstTy: see Note [The well-kinded type invariant]
959
960 -- The function's kind has a binder. Is it visible or invisible?
961 go n acc_args subst fun (ki_binder:ki_binders) inner_ki
962 all_args@(arg:args)
963 | isInvisibleBinder ki_binder
964 -- It's invisible. Instantiate.
965 = do { traceTc "tcInferApps (invis)" (ppr ki_binder $$ ppr subst)
966 ; (subst', arg') <- tcInstTyBinder mb_kind_info subst ki_binder
967 ; go n (arg' : acc_args) subst' (mkNakedAppTy fun arg')
968 ki_binders inner_ki all_args }
969
970 | otherwise
971 -- It's visible. Check the next user-written argument
972 = do { traceTc "tcInferApps (vis)" (vcat [ ppr ki_binder, ppr arg
973 , ppr (tyBinderType ki_binder)
974 , ppr subst ])
975 ; let exp_kind = nakedSubstTy subst $ tyBinderType ki_binder
976 -- nakedSubstTy: see Note [The well-kinded type invariant]
977 ; arg' <- addErrCtxt (funAppCtxt orig_hs_ty arg n) $
978 tc_lhs_type mode arg exp_kind
979 ; traceTc "tcInferApps (vis 1)" (vcat [ ppr exp_kind
980 , ppr (typeKind arg') ])
981 ; let subst' = extendTvSubstBinderAndInScope subst ki_binder arg'
982 ; go (n+1) (arg' : acc_args) subst'
983 (mkNakedAppTy fun arg') -- See Note [The well-kinded type invariant]
984 ki_binders inner_ki args }
985
986 -- We've run out of known binders in the functions's kind.
987 go n acc_args subst fun [] inner_ki all_args
988 | not (null new_ki_binders)
989 -- But, after substituting, we have more binders.
990 = go n acc_args zapped_subst fun new_ki_binders new_inner_ki all_args
991
992 | otherwise
993 -- Even after substituting, still no binders. Use matchExpectedFunKind
994 = do { traceTc "tcInferApps (no binder)" (ppr new_inner_ki $$ ppr zapped_subst)
995 ; (co, arg_k, res_k) <- matchExpectedFunKind hs_ty substed_inner_ki
996 ; let new_in_scope = tyCoVarsOfTypes [arg_k, res_k]
997 subst' = zapped_subst `extendTCvInScopeSet` new_in_scope
998 ; go n acc_args subst'
999 (fun `mkNakedCastTy` co) -- See Note [The well-kinded type invariant]
1000 [mkAnonBinder arg_k]
1001 res_k all_args }
1002 where
1003 substed_inner_ki = substTy subst inner_ki
1004 (new_ki_binders, new_inner_ki) = tcSplitPiTys substed_inner_ki
1005 zapped_subst = zapTCvSubst subst
1006 hs_ty = mkHsAppTys orig_hs_ty (take (n-1) orig_hs_args)
1007
1008
1009 -- | Applies a type to a list of arguments.
1010 -- Always consumes all the arguments, using 'matchExpectedFunKind' as
1011 -- necessary. If you wish to apply a type to a list of HsTypes, this is
1012 -- your function.
1013 -- Used for type-checking types only.
1014 tcTyApps :: TcTyMode
1015 -> LHsType GhcRn -- ^ Function (for printing only)
1016 -> TcType -- ^ Function (could be knot-tied)
1017 -> TcKind -- ^ Function kind (zonked)
1018 -> [LHsType GhcRn] -- ^ Args
1019 -> TcM (TcType, TcKind) -- ^ (f args, result kind) result kind is zonked
1020 -- Precondition: see precondition for tcInferApps
1021 tcTyApps mode orig_hs_ty fun_ty fun_ki args
1022 = do { (ty', _args, ki') <- tcInferApps mode Nothing orig_hs_ty fun_ty fun_ki args
1023 ; return (ty' `mkNakedCastTy` mkRepReflCo ki', ki') }
1024 -- The mkNakedCastTy is for (IT3) of Note [The tcType invariant]
1025
1026 --------------------------
1027 -- Like checkExpectedKindX, but returns only the final type; convenient wrapper
1028 -- Obeys Note [The tcType invariant]
1029 checkExpectedKind :: HasDebugCallStack
1030 => HsType GhcRn -- type we're checking (for printing)
1031 -> TcType -- type we're checking (might be knot-tied)
1032 -> TcKind -- the known kind of that type
1033 -> TcKind -- the expected kind
1034 -> TcM TcType
1035 checkExpectedKind hs_ty ty act exp
1036 = fstOf3 <$> checkExpectedKindX Nothing (ppr hs_ty) ty act exp
1037
1038 checkExpectedKindX :: HasDebugCallStack
1039 => Maybe (VarEnv Kind) -- Possibly, instantiations for kind vars
1040 -> SDoc -- HsType whose kind we're checking
1041 -> TcType -- the type whose kind we're checking
1042 -> TcKind -- the known kind of that type, k
1043 -> TcKind -- the expected kind, exp_kind
1044 -> TcM (TcType, [TcType], TcCoercionN)
1045 -- (the new args, the coercion)
1046 -- Instantiate a kind (if necessary) and then call unifyType
1047 -- (checkExpectedKind ty act_kind exp_kind)
1048 -- checks that the actual kind act_kind is compatible
1049 -- with the expected kind exp_kind
1050 checkExpectedKindX mb_kind_env pp_hs_ty ty act_kind exp_kind
1051 = do { -- We need to make sure that both kinds have the same number of implicit
1052 -- foralls out front. If the actual kind has more, instantiate accordingly.
1053 -- Otherwise, just pass the type & kind through: the errors are caught
1054 -- in unifyType.
1055 let (exp_bndrs, _) = splitPiTysInvisible exp_kind
1056 n_exp = length exp_bndrs
1057 ; (new_args, act_kind') <- instantiateTyUntilN mb_kind_env n_exp act_kind
1058
1059 ; let origin = TypeEqOrigin { uo_actual = act_kind'
1060 , uo_expected = exp_kind
1061 , uo_thing = Just pp_hs_ty
1062 , uo_visible = True } -- the hs_ty is visible
1063 ty' = mkNakedAppTys ty new_args
1064
1065 ; traceTc "checkExpectedKind" $
1066 vcat [ pp_hs_ty
1067 , text "act_kind:" <+> ppr act_kind
1068 , text "act_kind':" <+> ppr act_kind'
1069 , text "exp_kind:" <+> ppr exp_kind ]
1070
1071 ; if act_kind' `tcEqType` exp_kind
1072 then return (ty', new_args, mkTcNomReflCo exp_kind) -- This is very common
1073 else do { co_k <- uType KindLevel origin act_kind' exp_kind
1074 ; traceTc "checkExpectedKind" (vcat [ ppr act_kind
1075 , ppr exp_kind
1076 , ppr co_k ])
1077 ; let result_ty = ty' `mkNakedCastTy` co_k
1078 -- See Note [The tcType invariant]
1079 ; return (result_ty, new_args, co_k) } }
1080
1081 -- | Instantiate @n@ invisible arguments to a type. If @n <= 0@, no instantiation
1082 -- occurs. If @n@ is too big, then all available invisible arguments are instantiated.
1083 -- (In other words, this function is very forgiving about bad values of @n@.)
1084 -- Why zonk the result? So that tcTyVar can obey (IT6) of Note [The tcType invariant]
1085 instantiateTyN :: Maybe (VarEnv Kind) -- ^ Predetermined instantiations
1086 -- (for assoc. type patterns)
1087 -> Int -- ^ @n@
1088 -> [TyBinder] -> TcKind -- ^ its kind (zonked)
1089 -> TcM ([TcType], TcKind) -- ^ The inst'ed type, new args, kind (zonked)
1090 instantiateTyN mb_kind_env n bndrs inner_ki
1091 | n <= 0
1092 = return ([], ki)
1093
1094 | otherwise
1095 = do { (subst, inst_args) <- tcInstTyBinders empty_subst mb_kind_env inst_bndrs
1096 ; let rebuilt_ki = mkPiTys leftover_bndrs inner_ki
1097 ; ki' <- zonkTcType (substTy subst rebuilt_ki)
1098 ; traceTc "instantiateTyN" (vcat [ ppr ki
1099 , ppr n
1100 , ppr subst
1101 , ppr rebuilt_ki
1102 , ppr ki' ])
1103 ; return (inst_args, ki') }
1104 where
1105 -- NB: splitAt is forgiving with invalid numbers
1106 (inst_bndrs, leftover_bndrs) = splitAt n bndrs
1107 ki = mkPiTys bndrs inner_ki
1108 empty_subst = mkEmptyTCvSubst (mkInScopeSet (tyCoVarsOfType ki))
1109
1110 -- | Instantiate a type to have at most @n@ invisible arguments.
1111 instantiateTyUntilN :: Maybe (VarEnv Kind) -- ^ Possibly, instantiations for vars
1112 -> Int -- ^ @n@
1113 -> TcKind -- ^ its kind
1114 -> TcM ([TcType], TcKind) -- ^ The new args, final kind
1115 instantiateTyUntilN mb_kind_env n ki
1116 = let (bndrs, inner_ki) = splitPiTysInvisible ki
1117 num_to_inst = length bndrs - n
1118 in
1119 instantiateTyN mb_kind_env num_to_inst bndrs inner_ki
1120
1121 ---------------------------
1122 tcHsMbContext :: Maybe (LHsContext GhcRn) -> TcM [PredType]
1123 tcHsMbContext Nothing = return []
1124 tcHsMbContext (Just cxt) = tcHsContext cxt
1125
1126 tcHsContext :: LHsContext GhcRn -> TcM [PredType]
1127 tcHsContext = tc_hs_context typeLevelMode
1128
1129 tcLHsPredType :: LHsType GhcRn -> TcM PredType
1130 tcLHsPredType = tc_lhs_pred typeLevelMode
1131
1132 tc_hs_context :: TcTyMode -> LHsContext GhcRn -> TcM [PredType]
1133 tc_hs_context mode ctxt = mapM (tc_lhs_pred mode) (unLoc ctxt)
1134
1135 tc_lhs_pred :: TcTyMode -> LHsType GhcRn -> TcM PredType
1136 tc_lhs_pred mode pred = tc_lhs_type mode pred constraintKind
1137
1138 ---------------------------
1139 tcTyVar :: TcTyMode -> Name -> TcM (TcType, TcKind)
1140 -- See Note [Type checking recursive type and class declarations]
1141 -- in TcTyClsDecls
1142 tcTyVar mode name -- Could be a tyvar, a tycon, or a datacon
1143 = do { traceTc "lk1" (ppr name)
1144 ; thing <- tcLookup name
1145 ; case thing of
1146 ATyVar _ tv -> -- Important: zonk before returning
1147 -- We may have the application ((a::kappa) b)
1148 -- where kappa is already unified to (k1 -> k2)
1149 -- Then we want to see that arrow. Best done
1150 -- here because we are also maintaining
1151 -- Note [The tcType invariant], so we don't just
1152 -- want to zonk the kind, leaving the TyVar
1153 -- un-zonked (Trac #114873)
1154 do { ty <- zonkTcTyVar tv
1155 ; return (ty, typeKind ty) }
1156
1157 ATcTyCon tc_tc -> do { -- See Note [GADT kind self-reference]
1158 unless
1159 (isTypeLevel (mode_level mode))
1160 (promotionErr name TyConPE)
1161 ; check_tc tc_tc
1162 ; tc <- get_loopy_tc name tc_tc
1163 ; handle_tyfams tc tc_tc }
1164 -- mkNakedTyConApp: see Note [Type-checking inside the knot]
1165
1166 AGlobal (ATyCon tc)
1167 -> do { check_tc tc
1168 ; handle_tyfams tc tc }
1169
1170 AGlobal (AConLike (RealDataCon dc))
1171 -> do { data_kinds <- xoptM LangExt.DataKinds
1172 ; unless (data_kinds || specialPromotedDc dc) $
1173 promotionErr name NoDataKindsDC
1174 ; when (isFamInstTyCon (dataConTyCon dc)) $
1175 -- see Trac #15245
1176 promotionErr name FamDataConPE
1177 ; let (_, _, _, theta, _, _) = dataConFullSig dc
1178 ; case dc_theta_illegal_constraint theta of
1179 Just pred -> promotionErr name $
1180 ConstrainedDataConPE pred
1181 Nothing -> pure ()
1182 ; let tc = promoteDataCon dc
1183 ; return (mkNakedTyConApp tc [], tyConKind tc) }
1184
1185 APromotionErr err -> promotionErr name err
1186
1187 _ -> wrongThingErr "type" thing name }
1188 where
1189 check_tc :: TyCon -> TcM ()
1190 check_tc tc = do { data_kinds <- xoptM LangExt.DataKinds
1191 ; unless (isTypeLevel (mode_level mode) ||
1192 data_kinds ||
1193 isKindTyCon tc) $
1194 promotionErr name NoDataKindsTC }
1195
1196 -- if we are type-checking a type family tycon, we must instantiate
1197 -- any invisible arguments right away. Otherwise, we get #11246
1198 handle_tyfams :: TyCon -- the tycon to instantiate (might be loopy)
1199 -> TcTyCon -- a non-loopy version of the tycon
1200 -> TcM (TcType, TcKind)
1201 handle_tyfams tc tc_tc
1202 | mightBeUnsaturatedTyCon tc_tc || mode_unsat mode
1203 -- This is where mode_unsat is used
1204 = do { tc_kind <- zonkTcType (tyConKind tc_tc) -- (IT6) of Note [The tcType invariant]
1205 ; traceTc "tcTyVar2a" (ppr tc_tc $$ ppr tc_kind)
1206 ; return (mkNakedTyConApp tc [] `mkNakedCastTy` mkRepReflCo tc_kind, tc_kind) }
1207 -- the mkNakedCastTy ensures (IT5) of Note [The tcType invariant]
1208
1209 | otherwise
1210 = do { tc_kind <- zonkTcType (tyConKind tc_tc)
1211 ; let (tc_kind_bndrs, tc_inner_ki) = splitPiTysInvisible tc_kind
1212 ; (tc_args, kind) <- instantiateTyN Nothing (length (tyConBinders tc_tc))
1213 tc_kind_bndrs tc_inner_ki
1214 ; let tc_ty = mkNakedTyConApp tc tc_args `mkNakedCastTy` mkRepReflCo kind
1215 -- mkNakedCastTy is for (IT5) of Note [The tcType invariant]
1216 -- tc and tc_ty must not be traced here, because that would
1217 -- force the evaluation of a potentially knot-tied variable (tc),
1218 -- and the typechecker would hang, as per #11708
1219 ; traceTc "tcTyVar2b" (vcat [ ppr tc_tc <+> dcolon <+> ppr tc_kind
1220 , ppr kind ])
1221 ; return (tc_ty, kind) }
1222
1223 get_loopy_tc :: Name -> TyCon -> TcM TyCon
1224 -- Return the knot-tied global TyCon if there is one
1225 -- Otherwise the local TcTyCon; we must be doing kind checking
1226 -- but we still want to return a TyCon of some sort to use in
1227 -- error messages
1228 get_loopy_tc name tc_tc
1229 = do { env <- getGblEnv
1230 ; case lookupNameEnv (tcg_type_env env) name of
1231 Just (ATyCon tc) -> return tc
1232 _ -> do { traceTc "lk1 (loopy)" (ppr name)
1233 ; return tc_tc } }
1234
1235 -- We cannot promote a data constructor with a context that contains
1236 -- constraints other than equalities, so error if we find one.
1237 -- See Note [Constraints handled in types] in Inst.
1238 dc_theta_illegal_constraint :: ThetaType -> Maybe PredType
1239 dc_theta_illegal_constraint = find go
1240 where
1241 go :: PredType -> Bool
1242 go pred | Just tc <- tyConAppTyCon_maybe pred
1243 = not $ tc `hasKey` eqTyConKey
1244 || tc `hasKey` heqTyConKey
1245 | otherwise = True
1246
1247 {-
1248 Note [Type-checking inside the knot]
1249 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1250 Suppose we are checking the argument types of a data constructor. We
1251 must zonk the types before making the DataCon, because once built we
1252 can't change it. So we must traverse the type.
1253
1254 BUT the parent TyCon is knot-tied, so we can't look at it yet.
1255
1256 So we must be careful not to use "smart constructors" for types that
1257 look at the TyCon or Class involved.
1258
1259 * Hence the use of mkNakedXXX functions. These do *not* enforce
1260 the invariants (for example that we use (FunTy s t) rather
1261 than (TyConApp (->) [s,t])).
1262
1263 * The zonking functions establish invariants (even zonkTcType, a change from
1264 previous behaviour). So we must never inspect the result of a
1265 zonk that might mention a knot-tied TyCon. This is generally OK
1266 because we zonk *kinds* while kind-checking types. And the TyCons
1267 in kinds shouldn't be knot-tied, because they come from a previous
1268 mutually recursive group.
1269
1270 * TcHsSyn.zonkTcTypeToType also can safely check/establish
1271 invariants.
1272
1273 This is horribly delicate. I hate it. A good example of how
1274 delicate it is can be seen in Trac #7903.
1275
1276 Note [GADT kind self-reference]
1277 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1278
1279 A promoted type cannot be used in the body of that type's declaration.
1280 Trac #11554 shows this example, which made GHC loop:
1281
1282 import Data.Kind
1283 data P (x :: k) = Q
1284 data A :: Type where
1285 B :: forall (a :: A). P a -> A
1286
1287 In order to check the constructor B, we need to have the promoted type A, but in
1288 order to get that promoted type, B must first be checked. To prevent looping, a
1289 TyConPE promotion error is given when tcTyVar checks an ATcTyCon in kind mode.
1290 Any ATcTyCon is a TyCon being defined in the current recursive group (see data
1291 type decl for TcTyThing), and all such TyCons are illegal in kinds.
1292
1293 Trac #11962 proposes checking the head of a data declaration separately from
1294 its constructors. This would allow the example above to pass.
1295
1296 Note [Body kind of a HsForAllTy]
1297 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1298 The body of a forall is usually a type, but in principle
1299 there's no reason to prohibit *unlifted* types.
1300 In fact, GHC can itself construct a function with an
1301 unboxed tuple inside a for-all (via CPR analysis; see
1302 typecheck/should_compile/tc170).
1303
1304 Moreover in instance heads we get forall-types with
1305 kind Constraint.
1306
1307 It's tempting to check that the body kind is either * or #. But this is
1308 wrong. For example:
1309
1310 class C a b
1311 newtype N = Mk Foo deriving (C a)
1312
1313 We're doing newtype-deriving for C. But notice how `a` isn't in scope in
1314 the predicate `C a`. So we quantify, yielding `forall a. C a` even though
1315 `C a` has kind `* -> Constraint`. The `forall a. C a` is a bit cheeky, but
1316 convenient. Bottom line: don't check for * or # here.
1317
1318 Note [Body kind of a HsQualTy]
1319 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1320 If ctxt is non-empty, the HsQualTy really is a /function/, so the
1321 kind of the result really is '*', and in that case the kind of the
1322 body-type can be lifted or unlifted.
1323
1324 However, consider
1325 instance Eq a => Eq [a] where ...
1326 or
1327 f :: (Eq a => Eq [a]) => blah
1328 Here both body-kind of the HsQualTy is Constraint rather than *.
1329 Rather crudely we tell the difference by looking at exp_kind. It's
1330 very convenient to typecheck instance types like any other HsSigType.
1331
1332 Admittedly the '(Eq a => Eq [a]) => blah' case is erroneous, but it's
1333 better to reject in checkValidType. If we say that the body kind
1334 should be '*' we risk getting TWO error messages, one saying that Eq
1335 [a] doens't have kind '*', and one saying that we need a Constraint to
1336 the left of the outer (=>).
1337
1338 How do we figure out the right body kind? Well, it's a bit of a
1339 kludge: I just look at the expected kind. If it's Constraint, we
1340 must be in this instance situation context. It's a kludge because it
1341 wouldn't work if any unification was involved to compute that result
1342 kind -- but it isn't. (The true way might be to use the 'mode'
1343 parameter, but that seemed like a sledgehammer to crack a nut.)
1344
1345 Note [Inferring tuple kinds]
1346 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1347 Give a tuple type (a,b,c), which the parser labels as HsBoxedOrConstraintTuple,
1348 we try to figure out whether it's a tuple of kind * or Constraint.
1349 Step 1: look at the expected kind
1350 Step 2: infer argument kinds
1351
1352 If after Step 2 it's not clear from the arguments that it's
1353 Constraint, then it must be *. Once having decided that we re-check
1354 the Check the arguments again to give good error messages
1355 in eg. `(Maybe, Maybe)`
1356
1357 Note that we will still fail to infer the correct kind in this case:
1358
1359 type T a = ((a,a), D a)
1360 type family D :: Constraint -> Constraint
1361
1362 While kind checking T, we do not yet know the kind of D, so we will default the
1363 kind of T to * -> *. It works if we annotate `a` with kind `Constraint`.
1364
1365 Note [Desugaring types]
1366 ~~~~~~~~~~~~~~~~~~~~~~~
1367 The type desugarer is phase 2 of dealing with HsTypes. Specifically:
1368
1369 * It transforms from HsType to Type
1370
1371 * It zonks any kinds. The returned type should have no mutable kind
1372 or type variables (hence returning Type not TcType):
1373 - any unconstrained kind variables are defaulted to (Any *) just
1374 as in TcHsSyn.
1375 - there are no mutable type variables because we are
1376 kind-checking a type
1377 Reason: the returned type may be put in a TyCon or DataCon where
1378 it will never subsequently be zonked.
1379
1380 You might worry about nested scopes:
1381 ..a:kappa in scope..
1382 let f :: forall b. T '[a,b] -> Int
1383 In this case, f's type could have a mutable kind variable kappa in it;
1384 and we might then default it to (Any *) when dealing with f's type
1385 signature. But we don't expect this to happen because we can't get a
1386 lexically scoped type variable with a mutable kind variable in it. A
1387 delicate point, this. If it becomes an issue we might need to
1388 distinguish top-level from nested uses.
1389
1390 Moreover
1391 * it cannot fail,
1392 * it does no unifications
1393 * it does no validity checking, except for structural matters, such as
1394 (a) spurious ! annotations.
1395 (b) a class used as a type
1396
1397 Note [Kind of a type splice]
1398 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1399 Consider these terms, each with TH type splice inside:
1400 [| e1 :: Maybe $(..blah..) |]
1401 [| e2 :: $(..blah..) |]
1402 When kind-checking the type signature, we'll kind-check the splice
1403 $(..blah..); we want to give it a kind that can fit in any context,
1404 as if $(..blah..) :: forall k. k.
1405
1406 In the e1 example, the context of the splice fixes kappa to *. But
1407 in the e2 example, we'll desugar the type, zonking the kind unification
1408 variables as we go. When we encounter the unconstrained kappa, we
1409 want to default it to '*', not to (Any *).
1410
1411 Help functions for type applications
1412 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1413 -}
1414
1415 addTypeCtxt :: LHsType GhcRn -> TcM a -> TcM a
1416 -- Wrap a context around only if we want to show that contexts.
1417 -- Omit invisible ones and ones user's won't grok
1418 addTypeCtxt (L _ ty) thing
1419 = addErrCtxt doc thing
1420 where
1421 doc = text "In the type" <+> quotes (ppr ty)
1422
1423 {-
1424 ************************************************************************
1425 * *
1426 Type-variable binders
1427 %* *
1428 %************************************************************************
1429
1430 Note [Dependent LHsQTyVars]
1431 ~~~~~~~~~~~~~~~~~~~~~~~~~~~
1432 We track (in the renamer) which explicitly bound variables in a
1433 LHsQTyVars are manifestly dependent; only precisely these variables
1434 may be used within the LHsQTyVars. We must do this so that kcLHsQTyVars
1435 can produce the right TyConBinders, and tell Anon vs. Required.
1436
1437 Example data T k1 (a:k1) (b:k2) c
1438 = MkT (Proxy a) (Proxy b) (Proxy c)
1439
1440 Here
1441 (a:k1),(b:k2),(c:k3)
1442 are Anon (explicitly specified as a binder, not used
1443 in the kind of any other binder
1444 k1 is Required (explicitly specifed as a binder, but used
1445 in the kind of another binder i.e. dependently)
1446 k2 is Specified (not explicitly bound, but used in the kind
1447 of another binder)
1448 k3 in Inferred (not lexically in scope at all, but inferred
1449 by kind inference)
1450 and
1451 T :: forall {k3} k1. forall k3 -> k1 -> k2 -> k3 -> *
1452
1453 See Note [TyVarBndrs, TyVarBinders, TyConBinders, and visibility]
1454 in TyCoRep.
1455
1456 kcLHsQTyVars uses the hsq_dependent field to decide whether
1457 k1, a, b, c should be Required or Anon.
1458
1459 Earlier, thought it would work simply to do a free-variable check
1460 during kcLHsQTyVars, but this is bogus, because there may be
1461 unsolved equalities about. And we don't want to eagerly solve the
1462 equalities, because we may get further information after
1463 kcLHsQTyVars is called. (Recall that kcLHsQTyVars is called
1464 only from getInitialKind.)
1465 This is what implements the rule that all variables intended to be
1466 dependent must be manifestly so.
1467
1468 Sidenote: It's quite possible that later, we'll consider (t -> s)
1469 as a degenerate case of some (pi (x :: t) -> s) and then this will
1470 all get more permissive.
1471
1472 Note [Kind generalisation and SigTvs]
1473 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1474 Consider
1475 data T (a :: k1) x = MkT (S a ())
1476 data S (b :: k2) y = MkS (T b ())
1477
1478 While we are doing kind inference for the mutually-recursive S,T,
1479 we will end up unifying k1 and k2 together. So they can't be skolems.
1480 We therefore make them SigTvs, which can unify with type variables,
1481 but not with general types. All this is very similar at the level
1482 of terms: see Note [Quantified variables in partial type signatures]
1483 in TcBinds.
1484
1485 There are some wrinkles
1486
1487 * We always want to kind-generalise over SigTvs, and /not/ default
1488 them to Type. Another way to say this is: a SigTV should /never/
1489 stand for a type, even via defaulting. Hence the check in
1490 TcSimplify.defaultTyVarTcS, and TcMType.defaultTyVar. Here's
1491 another example (Trac #14555):
1492 data Exp :: [TYPE rep] -> TYPE rep -> Type where
1493 Lam :: Exp (a:xs) b -> Exp xs (a -> b)
1494 We want to kind-generalise over the 'rep' variable.
1495 Trac #14563 is another example.
1496
1497 * Consider Trac #11203
1498 data SameKind :: k -> k -> *
1499 data Q (a :: k1) (b :: k2) c = MkQ (SameKind a b)
1500 Here we will unify k1 with k2, but this time doing so is an error,
1501 because k1 and k2 are bound in the same delcaration.
1502
1503 We sort this out using findDupSigTvs, in TcTyClTyVars; very much
1504 as we do with partial type signatures in mk_psig_qtvs in
1505 TcBinds.chooseInferredQuantifiers
1506
1507 Note [Keeping scoped variables in order: Explicit]
1508 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1509 When the user writes `forall a b c. blah`, we bring a, b, and c into
1510 scope and then check blah. In the process of checking blah, we might
1511 learn the kinds of a, b, and c, and these kinds might indicate that
1512 b depends on c, and thus that we should reject the user-written type.
1513
1514 One approach to doing this would be to bring each of a, b, and c into
1515 scope, one at a time, creating an implication constraint and
1516 bumping the TcLevel for each one. This would work, because the kind
1517 of, say, b would be untouchable when c is in scope (and the constraint
1518 couldn't float out because c blocks it). However, it leads to terrible
1519 error messages, complaining about skolem escape. While it is indeed
1520 a problem of skolem escape, we can do better.
1521
1522 Instead, our approach is to bring the block of variables into scope
1523 all at once, creating one implication constraint for the lot. The
1524 user-written variables are skolems in the implication constraint. In
1525 TcSimplify.setImplicationStatus, we check to make sure that the ordering
1526 is correct, choosing ImplicationStatus IC_BadTelescope if they aren't.
1527 Then, in TcErrors, we report if there is a bad telescope. This way,
1528 we can report a suggested ordering to the user if there is a problem.
1529
1530 Note [Keeping scoped variables in order: Implicit]
1531 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1532 When the user implicitly quantifies over variables (say, in a type
1533 signature), we need to come up with some ordering on these variables.
1534 This is done by bumping the TcLevel, bringing the tyvars into scope,
1535 and then type-checking the thing_inside. The constraints are all
1536 wrapped in an implication, which is then solved. Finally, we can
1537 zonk all the binders and then order them with toposortTyVars.
1538
1539 It's critical to solve before zonking and ordering in order to uncover
1540 any unifications. You might worry that this eager solving could cause
1541 trouble elsewhere. I don't think it will. Because it will solve only
1542 in an increased TcLevel, it can't unify anything that was mentioned
1543 elsewhere. Additionally, we require that the order of implicitly
1544 quantified variables is manifest by the scope of these variables, so
1545 we're not going to learn more information later that will help order
1546 these variables.
1547
1548 Note [Recipe for checking a signature]
1549 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1550 Checking a user-written signature requires several steps:
1551
1552 1. Generate constraints.
1553 2. Solve constraints.
1554 3. Zonk and promote tyvars.
1555 4. (Optional) Kind-generalize.
1556 5. Check validity.
1557
1558 There may be some surprises in here:
1559
1560 Step 2 is necessary for two reasons: most signatures also bring
1561 implicitly quantified variables into scope, and solving is necessary
1562 to get these in the right order (see Note [Keeping scoped variables in
1563 order: Implicit]). Additionally, solving is necessary in order to
1564 kind-generalize correctly.
1565
1566 Step 3 requires *promoting* type variables. If there are any foralls
1567 in a type, the TcLevel will be bumped within the forall. This might
1568 lead to the generation of matavars with a high level. If we don't promote,
1569 we violate MetaTvInv of Note [TcLevel and untouchable type variables]
1570 in TcType.
1571
1572 -}
1573
1574 tcWildCardBinders :: SkolemInfo
1575 -> [Name]
1576 -> ([(Name, TcTyVar)] -> TcM a)
1577 -> TcM a
1578 tcWildCardBinders info = tcWildCardBindersX new_tv (Just info)
1579 where
1580 new_tv name = do { kind <- newMetaKindVar
1581 ; newSkolemTyVar name kind }
1582
1583 tcWildCardBindersX :: (Name -> TcM TcTyVar)
1584 -> Maybe SkolemInfo -- Just <=> we're bringing fresh vars
1585 -- into scope; use scopeTyVars
1586 -> [Name]
1587 -> ([(Name, TcTyVar)] -> TcM a)
1588 -> TcM a
1589 tcWildCardBindersX new_wc maybe_skol_info wc_names thing_inside
1590 = do { wcs <- mapM new_wc wc_names
1591 ; let wc_prs = wc_names `zip` wcs
1592 ; scope_tvs wc_prs $
1593 thing_inside wc_prs }
1594 where
1595 scope_tvs
1596 | Just info <- maybe_skol_info = scopeTyVars2 info
1597 | otherwise = tcExtendNameTyVarEnv
1598
1599 -- | Kind-check a 'LHsQTyVars'. If the decl under consideration has a complete,
1600 -- user-supplied kind signature (CUSK), generalise the result.
1601 -- Used in 'getInitialKind' (for tycon kinds and other kinds)
1602 -- and in kind-checking (but not for tycon kinds, which are checked with
1603 -- tcTyClDecls). See also Note [Complete user-supplied kind signatures] in
1604 -- HsDecls.
1605 --
1606 -- This function does not do telescope checking.
1607 kcLHsQTyVars :: Name -- ^ of the thing being checked
1608 -> TyConFlavour -- ^ What sort of 'TyCon' is being checked
1609 -> Bool -- ^ True <=> the decl being checked has a CUSK
1610 -> LHsQTyVars GhcRn
1611 -> TcM Kind -- ^ The result kind
1612 -> TcM TcTyCon -- ^ A suitably-kinded TcTyCon
1613 kcLHsQTyVars name flav cusk
1614 user_tyvars@(HsQTvs { hsq_ext = HsQTvsRn { hsq_implicit = kv_ns
1615 , hsq_dependent = dep_names }
1616 , hsq_explicit = hs_tvs }) thing_inside
1617 | cusk
1618 = do { (scoped_kvs, (tc_tvs, res_kind))
1619 <- solveEqualities $
1620 tcImplicitQTKBndrs skol_info kv_ns $
1621 kcLHsQTyVarBndrs cusk open_fam skol_info hs_tvs thing_inside
1622
1623 -- Now, because we're in a CUSK, quantify over the mentioned
1624 -- kind vars, in dependency order.
1625 ; let tc_binders_unzonked = zipWith mk_tc_binder hs_tvs tc_tvs
1626 ; dvs <- zonkTcTypeAndSplitDepVars (mkSpecForAllTys scoped_kvs $
1627 mkTyConKind tc_binders_unzonked res_kind)
1628 ; qkvs <- quantifyTyVars emptyVarSet dvs
1629 -- don't call tcGetGlobalTyCoVars. For associated types, it gets the
1630 -- tyvars from the enclosing class -- but that's wrong. We *do* want
1631 -- to quantify over those tyvars.
1632
1633 ; scoped_kvs <- mapM zonkTcTyVarToTyVar scoped_kvs
1634 ; tc_tvs <- mapM zonkTcTyVarToTyVar tc_tvs
1635 ; res_kind <- zonkTcType res_kind
1636 ; let tc_binders = zipWith mk_tc_binder hs_tvs tc_tvs
1637
1638 -- If any of the scoped_kvs aren't actually mentioned in a binder's
1639 -- kind (or the return kind), then we're in the CUSK case from
1640 -- Note [Free-floating kind vars]
1641 ; let all_tc_tvs = scoped_kvs ++ tc_tvs
1642 all_mentioned_tvs = mapUnionVarSet (tyCoVarsOfType . tyVarKind)
1643 all_tc_tvs
1644 `unionVarSet` tyCoVarsOfType res_kind
1645 unmentioned_kvs = filterOut (`elemVarSet` all_mentioned_tvs)
1646 scoped_kvs
1647 ; reportFloatingKvs name flav all_tc_tvs unmentioned_kvs
1648
1649 ; let final_binders = map (mkNamedTyConBinder Inferred) qkvs
1650 ++ map (mkNamedTyConBinder Specified) scoped_kvs
1651 ++ tc_binders
1652 tycon = mkTcTyCon name (ppr user_tyvars) final_binders res_kind
1653 (mkTyVarNamePairs (scoped_kvs ++ tc_tvs))
1654 flav
1655 -- the tvs contain the binders already
1656 -- in scope from an enclosing class, but
1657 -- re-adding tvs to the env't doesn't cause
1658 -- harm
1659
1660 ; traceTc "kcLHsQTyVars: cusk" $
1661 vcat [ ppr name, ppr kv_ns, ppr hs_tvs, ppr dep_names
1662 , ppr tc_tvs, ppr (mkTyConKind final_binders res_kind)
1663 , ppr qkvs, ppr final_binders ]
1664
1665 ; return tycon }
1666
1667 | otherwise
1668 = do { (scoped_kvs, (tc_tvs, res_kind))
1669 -- Why kcImplicitTKBndrs which uses newSigTyVar?
1670 -- See Note [Kind generalisation and sigTvs]
1671 <- kcImplicitTKBndrs kv_ns $
1672 kcLHsQTyVarBndrs cusk open_fam skol_info hs_tvs thing_inside
1673
1674 ; let -- NB: Don't add scoped_kvs to tyConTyVars, because they
1675 -- must remain lined up with the binders
1676 tc_binders = zipWith mk_tc_binder hs_tvs tc_tvs
1677 tycon = mkTcTyCon name (ppr user_tyvars) tc_binders res_kind
1678 (mkTyVarNamePairs (scoped_kvs ++ tc_tvs))
1679 flav
1680
1681 ; traceTc "kcLHsQTyVars: not-cusk" $
1682 vcat [ ppr name, ppr kv_ns, ppr hs_tvs, ppr dep_names
1683 , ppr tc_tvs, ppr (mkTyConKind tc_binders res_kind) ]
1684 ; return tycon }
1685 where
1686 open_fam = tcFlavourIsOpen flav
1687 skol_info = TyConSkol flav name
1688
1689 mk_tc_binder :: LHsTyVarBndr GhcRn -> TyVar -> TyConBinder
1690 -- See Note [Dependent LHsQTyVars]
1691 mk_tc_binder hs_tv tv
1692 | hsLTyVarName hs_tv `elemNameSet` dep_names
1693 = mkNamedTyConBinder Required tv
1694 | otherwise
1695 = mkAnonTyConBinder tv
1696
1697 kcLHsQTyVars _ _ _ (XLHsQTyVars _) _ = panic "kcLHsQTyVars"
1698
1699 kcLHsQTyVarBndrs :: Bool -- True <=> bump the TcLevel when bringing vars into scope
1700 -> Bool -- True <=> Default un-annotated tyvar
1701 -- binders to kind *
1702 -> SkolemInfo
1703 -> [LHsTyVarBndr GhcRn]
1704 -> TcM r
1705 -> TcM ([TyVar], r)
1706 -- There may be dependency between the explicit "ty" vars.
1707 -- So, we have to handle them one at a time.
1708 kcLHsQTyVarBndrs _ _ _ [] thing
1709 = do { stuff <- thing; return ([], stuff) }
1710
1711 kcLHsQTyVarBndrs cusk open_fam skol_info (L _ hs_tv : hs_tvs) thing
1712 = do { tv_pair@(tv, _) <- kc_hs_tv hs_tv
1713 -- NB: Bring all tvs into scope, even non-dependent ones,
1714 -- as they're needed in type synonyms, data constructors, etc.
1715
1716 ; (tvs, stuff) <- bind_unless_scoped tv_pair $
1717 kcLHsQTyVarBndrs cusk open_fam skol_info hs_tvs $
1718 thing
1719
1720 ; return ( tv : tvs, stuff ) }
1721 where
1722 -- | Bind the tyvar in the env't unless the bool is True
1723 bind_unless_scoped :: (TcTyVar, Bool) -> TcM a -> TcM a
1724 bind_unless_scoped (_, True) thing_inside = thing_inside
1725 bind_unless_scoped (tv, False) thing_inside
1726 | cusk = scopeTyVars skol_info [tv] thing_inside
1727 | otherwise = tcExtendTyVarEnv [tv] thing_inside
1728 -- These variables haven't settled down yet, so we don't want to bump
1729 -- the TcLevel. If we do, then we'll have metavars of too high a level
1730 -- floating about. Changing this causes many, many failures in the
1731 -- `dependent` testsuite directory.
1732
1733 kc_hs_tv :: HsTyVarBndr GhcRn -> TcM (TcTyVar, Bool)
1734 -- Special handling for the case where the binder is already in scope
1735 -- See Note [Associated type tyvar names] in Class and
1736 -- Note [TyVar binders for associated decls] in HsDecls
1737 kc_hs_tv (UserTyVar _ (L _ name))
1738 = do { mb_tv <- tcLookupLcl_maybe name
1739 ; case mb_tv of -- See Note [TyVar binders for associated decls]
1740 Just (ATyVar _ tv) -> return (tv, True)
1741 _ -> do { kind <- if open_fam
1742 then return liftedTypeKind
1743 else newMetaKindVar
1744 -- Open type/data families default their variables
1745 -- variables to kind *. But don't default in-scope
1746 -- class tyvars, of course
1747 ; tv <- newSkolemTyVar name kind
1748 ; return (tv, False) } }
1749
1750 kc_hs_tv (KindedTyVar _ lname@(L _ name) lhs_kind)
1751 = do { kind <- tcLHsKindSig (TyVarBndrKindCtxt name) lhs_kind
1752 ; mb_tv <- tcLookupLcl_maybe name
1753 ; case mb_tv of
1754 Just (ATyVar _ tv)
1755 -> do { discardResult $
1756 unifyKind (Just (HsTyVar noExt NotPromoted lname))
1757 kind (tyVarKind tv)
1758 ; return (tv, True) }
1759 _ -> do { tv <- newSkolemTyVar name kind
1760 ; return (tv, False) } }
1761
1762 kc_hs_tv (XTyVarBndr{}) = panic "kc_hs_tv"
1763
1764 {- Note [Kind-checking tyvar binders for associated types]
1765 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1766 When kind-checking the type-variable binders for associated
1767 data/newtype decls
1768 family decls
1769 we behave specially for type variables that are already in scope;
1770 that is, bound by the enclosing class decl. This is done in
1771 kcLHsQTyVarBndrs:
1772 * The use of tcImplicitQTKBndrs
1773 * The tcLookupLocal_maybe code in kc_hs_tv
1774
1775 See Note [Associated type tyvar names] in Class and
1776 Note [TyVar binders for associated decls] in HsDecls
1777
1778 We must do the same for family instance decls, where the in-scope
1779 variables may be bound by the enclosing class instance decl.
1780 Hence the use of tcImplicitQTKBndrs in tcFamTyPats.
1781 -}
1782
1783
1784 --------------------------------------
1785 -- Implicit binders
1786 --------------------------------------
1787
1788 -- | Bring implicitly quantified type/kind variables into scope during
1789 -- kind checking. Uses SigTvs, as per Note [Use SigTvs in kind-checking pass]
1790 -- in TcTyClsDecls.
1791 kcImplicitTKBndrs :: [Name] -- of the vars
1792 -> TcM a
1793 -> TcM ([TcTyVar], a) -- returns the tyvars created
1794 -- these are *not* dependency ordered
1795 kcImplicitTKBndrs var_ns thing_inside
1796 = do { tkvs <- mapM newFlexiKindedSigTyVar var_ns
1797 ; result <- tcExtendTyVarEnv tkvs thing_inside
1798 ; return (tkvs, result) }
1799
1800
1801 tcImplicitTKBndrs, tcImplicitTKBndrsSig, tcImplicitQTKBndrs
1802 :: SkolemInfo
1803 -> [Name]
1804 -> TcM a
1805 -> TcM ([TcTyVar], a)
1806 tcImplicitTKBndrs = tcImplicitTKBndrsX newFlexiKindedSkolemTyVar
1807 tcImplicitTKBndrsSig = tcImplicitTKBndrsX newFlexiKindedSigTyVar
1808 tcImplicitQTKBndrs = tcImplicitTKBndrsX newFlexiKindedQTyVar
1809
1810 tcImplicitTKBndrsX :: (Name -> TcM TcTyVar) -- new_tv function
1811 -> SkolemInfo
1812 -> [Name]
1813 -> TcM a
1814 -> TcM ([TcTyVar], a) -- these tyvars are dependency-ordered
1815 -- * Guarantees to call solveLocalEqualities to unify
1816 -- all constraints from thing_inside.
1817 --
1818 -- * Returned TcTyVars have the supplied HsTyVarBndrs,
1819 -- but may be in different order to the original [Name]
1820 -- (because of sorting to respect dependency)
1821 --
1822 -- * Returned TcTyVars have zonked kinds
1823 -- See Note [Keeping scoped variables in order: Implicit]
1824 tcImplicitTKBndrsX new_tv skol_info tv_names thing_inside
1825 | null tv_names -- Short cut for the common case where there
1826 -- are no implicit type variables to bind
1827 = do { result <- solveLocalEqualities thing_inside
1828 ; return ([], result) }
1829
1830 | otherwise
1831 = do { (skol_tvs, result)
1832 <- solveLocalEqualities $
1833 checkTvConstraints skol_info Nothing $
1834 do { tkvs <- mapM new_tv tv_names
1835 ; result <- tcExtendTyVarEnv tkvs thing_inside
1836 ; return (tkvs, result) }
1837
1838 ; skol_tvs <- mapM zonkTcTyCoVarBndr skol_tvs
1839 -- use zonkTcTyCoVarBndr because a skol_tv might be a SigTv
1840
1841 -- do a stable topological sort, following
1842 -- Note [Ordering of implicit variables] in HsTypes
1843 ; let final_tvs = toposortTyVars skol_tvs
1844 ; traceTc "tcImplicitTKBndrs" (ppr tv_names $$ ppr final_tvs)
1845 ; return (final_tvs, result) }
1846
1847 newFlexiKindedQTyVar :: Name -> TcM TcTyVar
1848 -- Make a new skolem for an implicit binder in a type/class/type
1849 -- instance declaration, with a flexi-kind
1850 -- But check for in-scope-ness, and if so return that instead
1851 newFlexiKindedQTyVar name
1852 = do { mb_tv <- tcLookupLcl_maybe name
1853 ; case mb_tv of
1854 Just (ATyVar _ tv) -> return tv
1855 _ -> newFlexiKindedSkolemTyVar name }
1856
1857 newFlexiKindedTyVar :: (Name -> Kind -> TcM TyVar) -> Name -> TcM TyVar
1858 newFlexiKindedTyVar new_tv name
1859 = do { kind <- newMetaKindVar
1860 ; new_tv name kind }
1861
1862 newFlexiKindedSkolemTyVar :: Name -> TcM TyVar
1863 newFlexiKindedSkolemTyVar = newFlexiKindedTyVar newSkolemTyVar
1864
1865 newFlexiKindedSigTyVar :: Name -> TcM TyVar
1866 newFlexiKindedSigTyVar = newFlexiKindedTyVar newSigTyVar
1867
1868 --------------------------------------
1869 -- Explicit binders
1870 --------------------------------------
1871
1872 -- | Used during the "kind-checking" pass in TcTyClsDecls only,
1873 -- and even then only for data-con declarations.
1874 -- See Note [Use SigTvs in kind-checking pass] in TcTyClsDecls
1875 kcExplicitTKBndrs :: [LHsTyVarBndr GhcRn]
1876 -> TcM a
1877 -> TcM a
1878 kcExplicitTKBndrs [] thing_inside = thing_inside
1879 kcExplicitTKBndrs (L _ hs_tv : hs_tvs) thing_inside
1880 = do { tv <- tcHsTyVarBndr newSigTyVar hs_tv
1881 ; tcExtendTyVarEnv [tv] $
1882 kcExplicitTKBndrs hs_tvs thing_inside }
1883
1884 tcExplicitTKBndrs :: SkolemInfo
1885 -> [LHsTyVarBndr GhcRn]
1886 -> TcM a
1887 -> TcM ([TcTyVar], a)
1888 tcExplicitTKBndrs skol_info hs_tvs thing_inside
1889 -- Used for the forall'd binders in type signatures of various kinds:
1890 -- - function signatures
1891 -- - data con signatures in GADT-style decls
1892 -- - pattern synonym signatures
1893 -- - expression type signatures
1894 --
1895 -- Specifically NOT used for the binders of a data type
1896 -- or type family decl. So the forall'd variables always /shadow/
1897 -- anything already in scope, and the complications of
1898 -- tcHsQTyVarName to not apply.
1899 --
1900 -- This function brings into scope a telescope of binders as written by
1901 -- the user. At first blush, it would then seem that we should bring
1902 -- them into scope one at a time, bumping the TcLevel each time.
1903 -- (Recall that we bump the level to prevent skolem escape from happening.)
1904 -- However, this leads to terrible error messages, because we end up
1905 -- failing to unify with some `k0`. Better would be to allow type inference
1906 -- to work, potentially creating a skolem-escape problem, and then to
1907 -- notice that the telescope is out of order. That's what we do here,
1908 -- following the logic of tcImplicitTKBndrsX.
1909 -- See also Note [Keeping scoped variables in order: Explicit]
1910 --
1911 -- No cloning: returned TyVars have the same Name as the incoming LHsTyVarBndrs
1912 | null hs_tvs -- Short cut that avoids creating an implication
1913 -- constraint in the common case where none is needed
1914 = do { result <- thing_inside
1915 ; return ([], result) }
1916
1917 | otherwise
1918 = do { (skol_tvs, result) <- checkTvConstraints skol_info (Just doc) $
1919 bind_tvbs hs_tvs
1920
1921 ; traceTc "tcExplicitTKBndrs" $
1922 vcat [ text "Hs vars:" <+> ppr hs_tvs
1923 , text "tvs:" <+> pprTyVars skol_tvs ]
1924
1925 ; return (skol_tvs, result) }
1926
1927 where
1928 bind_tvbs [] = do { result <- thing_inside
1929 ; return ([], result) }
1930 bind_tvbs (L _ tvb : tvbs)
1931 = do { tv <- tcHsTyVarBndr newSkolemTyVar tvb
1932 ; tcExtendTyVarEnv [tv] $
1933 do { (tvs, result) <- bind_tvbs tvbs
1934 ; return (tv : tvs, result) }}
1935
1936 doc = sep (map ppr hs_tvs)
1937
1938 -----------------
1939 tcHsTyVarBndr :: (Name -> Kind -> TcM TyVar)
1940 -> HsTyVarBndr GhcRn -> TcM TcTyVar
1941 -- Return a TcTyVar, built using the provided function
1942 -- Typically the Kind inside the HsTyVarBndr will be a tyvar
1943 -- with a mutable kind in it.
1944 --
1945 -- Returned TcTyVar has the same name; no cloning
1946 tcHsTyVarBndr new_tv (UserTyVar _ (L _ tv_nm))
1947 = newFlexiKindedTyVar new_tv tv_nm
1948 tcHsTyVarBndr new_tv (KindedTyVar _ (L _ tv_nm) lhs_kind)
1949 = do { kind <- tcLHsKindSig (TyVarBndrKindCtxt tv_nm) lhs_kind
1950 ; new_tv tv_nm kind }
1951 tcHsTyVarBndr _ (XTyVarBndr _) = panic "tcHsTyVarBndr"
1952
1953 -----------------
1954 newWildTyVar :: Name -> TcM TcTyVar
1955 -- ^ New unification variable for a wildcard
1956 newWildTyVar _name
1957 = do { kind <- newMetaKindVar
1958 ; uniq <- newUnique
1959 ; details <- newMetaDetails TauTv
1960 ; let name = mkSysTvName uniq (fsLit "w")
1961 tyvar = (mkTcTyVar name kind details)
1962 ; traceTc "newWildTyVar" (ppr tyvar)
1963 ; return tyvar }
1964
1965 --------------------------
1966 -- Bringing tyvars into scope
1967 --------------------------
1968
1969 -- | Bring tyvars into scope, wrapping the thing_inside in an implication
1970 -- constraint. The implication constraint is necessary to provide SkolemInfo
1971 -- for the tyvars and to ensure that no unification variables made outside
1972 -- the scope of these tyvars (i.e. lower TcLevel) unify with the locally-scoped
1973 -- tyvars (i.e. higher TcLevel).
1974 --
1975 -- INVARIANT: The thing_inside must check only types, never terms.
1976 --
1977 -- Use this (not tcExtendTyVarEnv) wherever you expect a Λ or ∀ in Core.
1978 -- Use tcExtendTyVarEnv otherwise.
1979 scopeTyVars :: SkolemInfo -> [TcTyVar] -> TcM a -> TcM a
1980 scopeTyVars skol_info tvs = scopeTyVars2 skol_info [(tyVarName tv, tv) | tv <- tvs]
1981
1982 -- | Like 'scopeTyVars', but allows you to specify different scoped names
1983 -- than the Names stored within the tyvars.
1984 scopeTyVars2 :: SkolemInfo -> [(Name, TcTyVar)] -> TcM a -> TcM a
1985 scopeTyVars2 skol_info prs thing_inside
1986 = fmap snd $ -- discard the TcEvBinds, which will always be empty
1987 checkConstraints skol_info (map snd prs) [{- no EvVars -}] $
1988 tcExtendNameTyVarEnv prs $
1989 thing_inside
1990
1991 ------------------
1992 kindGeneralize :: TcType -> TcM [KindVar]
1993 -- Quantify the free kind variables of a kind or type
1994 -- In the latter case the type is closed, so it has no free
1995 -- type variables. So in both cases, all the free vars are kind vars
1996 -- Input must be zonked.
1997 -- NB: You must call solveEqualities or solveLocalEqualities before
1998 -- kind generalization
1999 kindGeneralize kind_or_type
2000 = do { let kvs = tyCoVarsOfTypeDSet kind_or_type
2001 dvs = DV { dv_kvs = kvs, dv_tvs = emptyDVarSet }
2002 ; gbl_tvs <- tcGetGlobalTyCoVars -- Already zonked
2003 ; quantifyTyVars gbl_tvs dvs }
2004
2005 {-
2006 Note [Kind generalisation]
2007 ~~~~~~~~~~~~~~~~~~~~~~~~~~
2008 We do kind generalisation only at the outer level of a type signature.
2009 For example, consider
2010 T :: forall k. k -> *
2011 f :: (forall a. T a -> Int) -> Int
2012 When kind-checking f's type signature we generalise the kind at
2013 the outermost level, thus:
2014 f1 :: forall k. (forall (a:k). T k a -> Int) -> Int -- YES!
2015 and *not* at the inner forall:
2016 f2 :: (forall k. forall (a:k). T k a -> Int) -> Int -- NO!
2017 Reason: same as for HM inference on value level declarations,
2018 we want to infer the most general type. The f2 type signature
2019 would be *less applicable* than f1, because it requires a more
2020 polymorphic argument.
2021
2022 NB: There are no explicit kind variables written in f's signature.
2023 When there are, the renamer adds these kind variables to the list of
2024 variables bound by the forall, so you can indeed have a type that's
2025 higher-rank in its kind. But only by explicit request.
2026
2027 Note [Kinds of quantified type variables]
2028 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2029 tcTyVarBndrsGen quantifies over a specified list of type variables,
2030 *and* over the kind variables mentioned in the kinds of those tyvars.
2031
2032 Note that we must zonk those kinds (obviously) but less obviously, we
2033 must return type variables whose kinds are zonked too. Example
2034 (a :: k7) where k7 := k9 -> k9
2035 We must return
2036 [k9, a:k9->k9]
2037 and NOT
2038 [k9, a:k7]
2039 Reason: we're going to turn this into a for-all type,
2040 forall k9. forall (a:k7). blah
2041 which the type checker will then instantiate, and instantiate does not
2042 look through unification variables!
2043
2044 Hence using zonked_kinds when forming tvs'.
2045
2046 Note [Free-floating kind vars]
2047 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2048 Consider
2049
2050 data T = MkT (forall (a :: k). Proxy a)
2051 -- from test ghci/scripts/T7873
2052
2053 This is not an existential datatype, but a higher-rank one (the forall
2054 to the right of MkT). Also consider
2055
2056 data S a = MkS (Proxy (a :: k))
2057
2058 According to the rules around implicitly-bound kind variables, in both
2059 cases those k's scope over the whole declaration. The renamer grabs
2060 it and adds it to the hsq_implicits field of the HsQTyVars of the
2061 tycon. So it must be in scope during type-checking, but we want to
2062 reject T while accepting S.
2063
2064 Why reject T? Because the kind variable isn't fixed by anything. For
2065 a variable like k to be implicit, it needs to be mentioned in the kind
2066 of a tycon tyvar. But it isn't.
2067
2068 Why accept S? Because kind inference tells us that a has kind k, so it's
2069 all OK.
2070
2071 Our approach depends on whether or not the datatype has a CUSK.
2072
2073 Non-CUSK: In the first pass (kcTyClTyVars) we just bring
2074 k into scope. In the second pass (tcTyClTyVars),
2075 we check to make sure that k has been unified with some other variable
2076 (or generalized over, making k into a skolem). If it hasn't been, then
2077 it must be a free-floating kind var. Error.
2078
2079 CUSK: When we determine the tycon's final, never-to-be-changed kind
2080 in kcLHsQTyVars, we check to make sure all implicitly-bound kind
2081 vars are indeed mentioned in a kind somewhere. If not, error.
2082
2083 We also perform free-floating kind var analysis for type family instances
2084 (see #13985). Here is an interesting example:
2085
2086 type family T :: k
2087 type instance T = (Nothing :: Maybe a)
2088
2089 Upon a cursory glance, it may appear that the kind variable `a` is
2090 free-floating above, since there are no (visible) LHS patterns in `T`. However,
2091 there is an *invisible* pattern due to the return kind, so inside of GHC, the
2092 instance looks closer to this:
2093
2094 type family T @k :: k
2095 type instance T @(Maybe a) = (Nothing :: Maybe a)
2096
2097 Here, we can see that `a` really is bound by a LHS type pattern, so `a` is in
2098 fact not free-floating. Contrast that with this example:
2099
2100 type instance T = Proxy (Nothing :: Maybe a)
2101
2102 This would looks like this inside of GHC:
2103
2104 type instance T @(*) = Proxy (Nothing :: Maybe a)
2105
2106 So this time, `a` is neither bound by a visible nor invisible type pattern on
2107 the LHS, so it would be reported as free-floating.
2108
2109 Finally, here's one more brain-teaser (from #9574). In the example below:
2110
2111 class Funct f where
2112 type Codomain f :: *
2113 instance Funct ('KProxy :: KProxy o) where
2114 type Codomain 'KProxy = NatTr (Proxy :: o -> *)
2115
2116 As it turns out, `o` is not free-floating in this example. That is because `o`
2117 bound by the kind signature of the LHS type pattern 'KProxy. To make this more
2118 obvious, one can also write the instance like so:
2119
2120 instance Funct ('KProxy :: KProxy o) where
2121 type Codomain ('KProxy :: KProxy o) = NatTr (Proxy :: o -> *)
2122
2123 -}
2124
2125 --------------------
2126 -- getInitialKind has made a suitably-shaped kind for the type or class
2127 -- Look it up in the local environment. This is used only for tycons
2128 -- that we're currently type-checking, so we're sure to find a TcTyCon.
2129 kcLookupTcTyCon :: Name -> TcM TcTyCon
2130 kcLookupTcTyCon nm
2131 = do { tc_ty_thing <- tcLookup nm
2132 ; return $ case tc_ty_thing of
2133 ATcTyCon tc -> tc
2134 _ -> pprPanic "kcLookupTcTyCon" (ppr tc_ty_thing) }
2135
2136 -----------------------
2137 -- | Bring tycon tyvars into scope. This is used during the "kind-checking"
2138 -- pass in TcTyClsDecls. (Never in getInitialKind, never in the
2139 -- "type-checking"/desugaring pass.)
2140 -- Never emits constraints, though the thing_inside might.
2141 kcTyClTyVars :: Name -> TcM a -> TcM a
2142 kcTyClTyVars tycon_name thing_inside
2143 -- See Note [Use SigTvs in kind-checking pass] in TcTyClsDecls
2144 = do { tycon <- kcLookupTcTyCon tycon_name
2145 ; tcExtendNameTyVarEnv (tcTyConScopedTyVars tycon) $ thing_inside }
2146
2147 tcTyClTyVars :: Name
2148 -> ([TyConBinder] -> Kind -> TcM a) -> TcM a
2149 -- ^ Used for the type variables of a type or class decl
2150 -- on the second full pass (type-checking/desugaring) in TcTyClDecls.
2151 -- This is *not* used in the initial-kind run, nor in the "kind-checking" pass.
2152 -- Accordingly, everything passed to the continuation is fully zonked.
2153 --
2154 -- (tcTyClTyVars T [a,b] thing_inside)
2155 -- where T : forall k1 k2 (a:k1 -> *) (b:k1). k2 -> *
2156 -- calls thing_inside with arguments
2157 -- [k1,k2,a,b] [k1:*, k2:*, Anon (k1 -> *), Anon k1] (k2 -> *)
2158 -- having also extended the type environment with bindings
2159 -- for k1,k2,a,b
2160 --
2161 -- Never emits constraints.
2162 --
2163 -- The LHsTyVarBndrs is always user-written, and the full, generalised
2164 -- kind of the tycon is available in the local env.
2165 tcTyClTyVars tycon_name thing_inside
2166 = do { tycon <- kcLookupTcTyCon tycon_name
2167
2168 -- Do checks on scoped tyvars
2169 -- See Note [Free-floating kind vars]
2170 ; let flav = tyConFlavour tycon
2171 scoped_prs = tcTyConScopedTyVars tycon
2172 scoped_tvs = map snd scoped_prs
2173 still_sig_tvs = filter isSigTyVar scoped_tvs
2174
2175 ; mapM_ report_sig_tv_err (findDupSigTvs scoped_prs)
2176
2177 ; checkNoErrs $ reportFloatingKvs tycon_name flav
2178 scoped_tvs still_sig_tvs
2179
2180 ; let res_kind = tyConResKind tycon
2181 binders = correct_binders (tyConBinders tycon) res_kind
2182 ; traceTc "tcTyClTyVars" (ppr tycon_name <+> ppr binders)
2183 ; scopeTyVars2 (TyConSkol flav tycon_name) scoped_prs $
2184 thing_inside binders res_kind }
2185 where
2186 report_sig_tv_err (n1, n2)
2187 = setSrcSpan (getSrcSpan n2) $
2188 addErrTc (text "Couldn't match" <+> quotes (ppr n1)
2189 <+> text "with" <+> quotes (ppr n2))
2190
2191 -- Given some TyConBinders and a TyCon's result kind, make sure that the
2192 -- correct any wrong Named/Anon choices. For example, consider
2193 -- type Syn k = forall (a :: k). Proxy a
2194 -- At first, it looks like k should be named -- after all, it appears on the RHS.
2195 -- However, the correct kind for Syn is (* -> *).
2196 -- (Why? Because k is the kind of a type, so k's kind is *. And the RHS also has
2197 -- kind *.) See also #13963.
2198 correct_binders :: [TyConBinder] -> Kind -> [TyConBinder]
2199 correct_binders binders kind
2200 = binders'
2201 where
2202 (_, binders') = mapAccumR go (tyCoVarsOfType kind) binders
2203
2204 go :: TyCoVarSet -> TyConBinder -> (TyCoVarSet, TyConBinder)
2205 go fvs binder
2206 | isNamedTyConBinder binder
2207 , not (tv `elemVarSet` fvs)
2208 = (new_fvs, mkAnonTyConBinder tv)
2209
2210 | not (isNamedTyConBinder binder)
2211 , tv `elemVarSet` fvs
2212 = (new_fvs, mkNamedTyConBinder Required tv)
2213 -- always Required, because it was anonymous (i.e. visible) previously
2214
2215 | otherwise
2216 = (new_fvs, binder)
2217
2218 where
2219 tv = binderVar binder
2220 new_fvs = fvs `delVarSet` tv `unionVarSet` tyCoVarsOfType (tyVarKind tv)
2221
2222 -----------------------------------
2223 tcDataKindSig :: [TyConBinder]
2224 -> Kind
2225 -> TcM ([TyConBinder], Kind)
2226 -- GADT decls can have a (perhaps partial) kind signature
2227 -- e.g. data T a :: * -> * -> * where ...
2228 -- This function makes up suitable (kinded) TyConBinders for the
2229 -- argument kinds. E.g. in this case it might return
2230 -- ([b::*, c::*], *)
2231 -- Never emits constraints.
2232 -- It's a little trickier than you might think: see
2233 -- Note [TyConBinders for the result kind signature of a data type]
2234 tcDataKindSig tc_bndrs kind
2235 = do { loc <- getSrcSpanM
2236 ; uniqs <- newUniqueSupply
2237 ; rdr_env <- getLocalRdrEnv
2238 ; let new_occs = [ occ
2239 | str <- allNameStrings
2240 , let occ = mkOccName tvName str
2241 , isNothing (lookupLocalRdrOcc rdr_env occ)
2242 -- Note [Avoid name clashes for associated data types]
2243 , not (occ `elem` lhs_occs) ]
2244 new_uniqs = uniqsFromSupply uniqs
2245 subst = mkEmptyTCvSubst (mkInScopeSet (mkVarSet lhs_tvs))
2246 ; return (go loc new_occs new_uniqs subst [] kind) }
2247 where
2248 lhs_tvs = map binderVar tc_bndrs
2249 lhs_occs = map getOccName lhs_tvs
2250
2251 go loc occs uniqs subst acc kind
2252 = case splitPiTy_maybe kind of
2253 Nothing -> (reverse acc, substTy subst kind)
2254
2255 Just (Anon arg, kind')
2256 -> go loc occs' uniqs' subst' (tcb : acc) kind'
2257 where
2258 arg' = substTy subst arg
2259 tv = mkTyVar (mkInternalName uniq occ loc) arg'
2260 subst' = extendTCvInScope subst tv
2261 tcb = TvBndr tv AnonTCB
2262 (uniq:uniqs') = uniqs
2263 (occ:occs') = occs
2264
2265 Just (Named (TvBndr tv vis), kind')
2266 -> go loc occs uniqs subst' (tcb : acc) kind'
2267 where
2268 (subst', tv') = substTyVarBndr subst tv
2269 tcb = TvBndr tv' (NamedTCB vis)
2270
2271 badKindSig :: Bool -> Kind -> SDoc
2272 badKindSig check_for_type kind
2273 = hang (sep [ text "Kind signature on data type declaration has non-*"
2274 , (if check_for_type then empty else text "and non-variable") <+>
2275 text "return kind" ])
2276 2 (ppr kind)
2277
2278 {- Note [TyConBinders for the result kind signature of a data type]
2279 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2280 Given
2281 data T (a::*) :: * -> forall k. k -> *
2282 we want to generate the extra TyConBinders for T, so we finally get
2283 (a::*) (b::*) (k::*) (c::k)
2284 The function tcDataKindSig generates these extra TyConBinders from
2285 the result kind signature.
2286
2287 We need to take care to give the TyConBinders
2288 (a) OccNames that are fresh (because the TyConBinders of a TyCon
2289 must have distinct OccNames
2290
2291 (b) Uniques that are fresh (obviously)
2292
2293 For (a) we need to avoid clashes with the tyvars declared by
2294 the user before the "::"; in the above example that is 'a'.
2295 And also see Note [Avoid name clashes for associated data types].
2296
2297 For (b) suppose we have
2298 data T :: forall k. k -> forall k. k -> *
2299 where the two k's are identical even up to their uniques. Surprisingly,
2300 this can happen: see Trac #14515.
2301
2302 It's reasonably easy to solve all this; just run down the list with a
2303 substitution; hence the recursive 'go' function. But it has to be
2304 done.
2305
2306 Note [Avoid name clashes for associated data types]
2307 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2308 Consider class C a b where
2309 data D b :: * -> *
2310 When typechecking the decl for D, we'll invent an extra type variable
2311 for D, to fill out its kind. Ideally we don't want this type variable
2312 to be 'a', because when pretty printing we'll get
2313 class C a b where
2314 data D b a0
2315 (NB: the tidying happens in the conversion to IfaceSyn, which happens
2316 as part of pretty-printing a TyThing.)
2317
2318 That's why we look in the LocalRdrEnv to see what's in scope. This is
2319 important only to get nice-looking output when doing ":info C" in GHCi.
2320 It isn't essential for correctness.
2321
2322
2323 ************************************************************************
2324 * *
2325 Partial signatures
2326 * *
2327 ************************************************************************
2328
2329 -}
2330
2331 tcHsPartialSigType
2332 :: UserTypeCtxt
2333 -> LHsSigWcType GhcRn -- The type signature
2334 -> TcM ( [(Name, TcTyVar)] -- Wildcards
2335 , Maybe TcType -- Extra-constraints wildcard
2336 , [Name] -- Original tyvar names, in correspondence with ...
2337 , [TcTyVar] -- ... Implicitly and explicitly bound type variables
2338 , TcThetaType -- Theta part
2339 , TcType ) -- Tau part
2340 -- See Note [Recipe for checking a signature]
2341 tcHsPartialSigType ctxt sig_ty
2342 | HsWC { hswc_ext = sig_wcs, hswc_body = ib_ty } <- sig_ty
2343 , HsIB { hsib_ext = HsIBRn { hsib_vars = implicit_hs_tvs }
2344 , hsib_body = hs_ty } <- ib_ty
2345 , (explicit_hs_tvs, L _ hs_ctxt, hs_tau) <- splitLHsSigmaTy hs_ty
2346 = addSigCtxt ctxt hs_ty $
2347 do { (implicit_tvs, (explicit_tvs, (wcs, wcx, theta, tau)))
2348 <- tcWildCardBindersX newWildTyVar Nothing sig_wcs $ \ wcs ->
2349 tcImplicitTKBndrsSig skol_info implicit_hs_tvs $
2350 tcExplicitTKBndrs skol_info explicit_hs_tvs $
2351 do { -- Instantiate the type-class context; but if there
2352 -- is an extra-constraints wildcard, just discard it here
2353 (theta, wcx) <- tcPartialContext hs_ctxt
2354
2355 ; tau <- tcHsOpenType hs_tau
2356
2357 ; return (wcs, wcx, theta, tau) }
2358
2359 -- We must return these separately, because all the zonking below
2360 -- might change the name of a SigTv. This, in turn, causes trouble
2361 -- in partial type signatures that bind scoped type variables, as
2362 -- we bring the wrong name into scope in the function body.
2363 -- Test case: partial-sigs/should_compile/LocalDefinitionBug
2364 ; let tv_names = map tyVarName (implicit_tvs ++ explicit_tvs)
2365
2366 -- Spit out the wildcards (including the extra-constraints one)
2367 -- as "hole" constraints, so that they'll be reported if necessary
2368 -- See Note [Extra-constraint holes in partial type signatures]
2369 ; emitWildCardHoleConstraints wcs
2370
2371 -- The SigTvs created above will sometimes have too high a TcLevel
2372 -- (note that they are generated *after* bumping the level in
2373 -- the tc{Im,Ex}plicitTKBndrsSig functions. Bumping the level
2374 -- is still important here, because the kinds of these variables
2375 -- do indeed need to have the higher level, so they can unify
2376 -- with other local type variables. But, now that we've type-checked
2377 -- everything (and solved equalities in the tcImplicit call)
2378 -- we need to promote the SigTvs so we don't violate the TcLevel
2379 -- invariant
2380 ; all_tvs <- mapM zonkPromoteTyCoVarBndr (implicit_tvs ++ explicit_tvs)
2381 -- zonkPromoteTyCoVarBndr deals well with SigTvs
2382
2383 ; theta <- mapM zonkPromoteType theta
2384 ; tau <- zonkPromoteType tau
2385
2386 ; checkValidType ctxt (mkSpecForAllTys all_tvs $ mkPhiTy theta tau)
2387
2388 ; traceTc "tcHsPartialSigType" (ppr all_tvs)
2389 ; return (wcs, wcx, tv_names, all_tvs, theta, tau) }
2390 where
2391 skol_info = SigTypeSkol ctxt
2392 tcHsPartialSigType _ (HsWC _ (XHsImplicitBndrs _)) = panic "tcHsPartialSigType"
2393 tcHsPartialSigType _ (XHsWildCardBndrs _) = panic "tcHsPartialSigType"
2394
2395 tcPartialContext :: HsContext GhcRn -> TcM (TcThetaType, Maybe TcType)
2396 tcPartialContext hs_theta
2397 | Just (hs_theta1, hs_ctxt_last) <- snocView hs_theta
2398 , L _ (HsWildCardTy wc) <- ignoreParens hs_ctxt_last
2399 = do { wc_tv_ty <- tcWildCardOcc wc constraintKind
2400 ; theta <- mapM tcLHsPredType hs_theta1
2401 ; return (theta, Just wc_tv_ty) }
2402 | otherwise
2403 = do { theta <- mapM tcLHsPredType hs_theta
2404 ; return (theta, Nothing) }
2405
2406 {- Note [Extra-constraint holes in partial type signatures]
2407 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2408 Consider
2409 f :: (_) => a -> a
2410 f x = ...
2411
2412 * The renamer makes a wildcard name for the "_", and puts it in
2413 the hswc_wcs field.
2414
2415 * Then, in tcHsPartialSigType, we make a new hole TcTyVar, in
2416 tcWildCardBindersX.
2417
2418 * TcBinds.chooseInferredQuantifiers fills in that hole TcTyVar
2419 with the inferred constraints, e.g. (Eq a, Show a)
2420
2421 * TcErrors.mkHoleError finally reports the error.
2422
2423 An annoying difficulty happens if there are more than 62 inferred
2424 constraints. Then we need to fill in the TcTyVar with (say) a 70-tuple.
2425 Where do we find the TyCon? For good reasons we only have constraint
2426 tuples up to 62 (see Note [How tuples work] in TysWiredIn). So how
2427 can we make a 70-tuple? This was the root cause of Trac #14217.
2428
2429 It's incredibly tiresome, because we only need this type to fill
2430 in the hole, to communicate to the error reporting machinery. Nothing
2431 more. So I use a HACK:
2432
2433 * I make an /ordinary/ tuple of the constraints, in
2434 TcBinds.chooseInferredQuantifiers. This is ill-kinded because
2435 ordinary tuples can't contain constraints, but it works fine. And for
2436 ordinary tuples we don't have the same limit as for constraint
2437 tuples (which need selectors and an assocated class).
2438
2439 * Because it is ill-kinded, it trips an assert in writeMetaTyVar,
2440 so now I disable the assertion if we are writing a type of
2441 kind Constraint. (That seldom/never normally happens so we aren't
2442 losing much.)
2443
2444 Result works fine, but it may eventually bite us.
2445
2446
2447 ************************************************************************
2448 * *
2449 Pattern signatures (i.e signatures that occur in patterns)
2450 * *
2451 ********************************************************************* -}
2452
2453 tcHsPatSigType :: UserTypeCtxt
2454 -> LHsSigWcType GhcRn -- The type signature
2455 -> TcM ( [(Name, TcTyVar)] -- Wildcards
2456 , [(Name, TcTyVar)] -- The new bit of type environment, binding
2457 -- the scoped type variables
2458 , TcType) -- The type
2459 -- Used for type-checking type signatures in
2460 -- (a) patterns e.g f (x::Int) = e
2461 -- (b) RULE forall bndrs e.g. forall (x::Int). f x = x
2462 --
2463 -- This may emit constraints
2464 -- See Note [Recipe for checking a signature]
2465 tcHsPatSigType ctxt sig_ty
2466 | HsWC { hswc_ext = sig_wcs, hswc_body = ib_ty } <- sig_ty
2467 , HsIB { hsib_ext = HsIBRn { hsib_vars = sig_vars}
2468 , hsib_body = hs_ty } <- ib_ty
2469 = addSigCtxt ctxt hs_ty $
2470 do { sig_tkvs <- mapM new_implicit_tv sig_vars
2471 ; (wcs, sig_ty)
2472 <- tcWildCardBindersX newWildTyVar Nothing sig_wcs $ \ wcs ->
2473 tcExtendTyVarEnv sig_tkvs $
2474 do { sig_ty <- tcHsOpenType hs_ty
2475 ; return (wcs, sig_ty) }
2476
2477 ; emitWildCardHoleConstraints wcs
2478
2479 -- sig_ty might have tyvars that are at a higher TcLevel (if hs_ty
2480 -- contains a forall). Promote these.
2481 ; sig_ty <- zonkPromoteType sig_ty
2482 ; checkValidType ctxt sig_ty
2483
2484 ; tv_pairs <- mapM mk_tv_pair sig_tkvs
2485
2486 ; traceTc "tcHsPatSigType" (ppr sig_vars)
2487 ; return (wcs, tv_pairs, sig_ty) }
2488 where
2489 new_implicit_tv name = do { kind <- newMetaKindVar
2490 ; new_tv name kind }
2491
2492 new_tv = case ctxt of
2493 RuleSigCtxt {} -> newSkolemTyVar
2494 _ -> newSigTyVar
2495 -- See Note [Pattern signature binders]
2496 -- See Note [Unifying SigTvs]
2497
2498 mk_tv_pair tv = do { tv' <- zonkTcTyVarToTyVar tv
2499 ; return (tyVarName tv, tv') }
2500 -- The Name is one of sig_vars, the lexically scoped name
2501 -- But if it's a SigTyVar, it might have been unified
2502 -- with an existing in-scope skolem, so we must zonk
2503 -- here. See Note [Pattern signature binders]
2504 tcHsPatSigType _ (HsWC _ (XHsImplicitBndrs _)) = panic "tcHsPatSigType"
2505 tcHsPatSigType _ (XHsWildCardBndrs _) = panic "tcHsPatSigType"
2506
2507 tcPatSig :: Bool -- True <=> pattern binding
2508 -> LHsSigWcType GhcRn
2509 -> ExpSigmaType
2510 -> TcM (TcType, -- The type to use for "inside" the signature
2511 [(Name,TcTyVar)], -- The new bit of type environment, binding
2512 -- the scoped type variables
2513 [(Name,TcTyVar)], -- The wildcards
2514 HsWrapper) -- Coercion due to unification with actual ty
2515 -- Of shape: res_ty ~ sig_ty
2516 tcPatSig in_pat_bind sig res_ty
2517 = do { (sig_wcs, sig_tvs, sig_ty) <- tcHsPatSigType PatSigCtxt sig
2518 -- sig_tvs are the type variables free in 'sig',
2519 -- and not already in scope. These are the ones
2520 -- that should be brought into scope
2521
2522 ; if null sig_tvs then do {
2523 -- Just do the subsumption check and return
2524 wrap <- addErrCtxtM (mk_msg sig_ty) $
2525 tcSubTypeET PatSigOrigin PatSigCtxt res_ty sig_ty
2526 ; return (sig_ty, [], sig_wcs, wrap)
2527 } else do
2528 -- Type signature binds at least one scoped type variable
2529
2530 -- A pattern binding cannot bind scoped type variables
2531 -- It is more convenient to make the test here
2532 -- than in the renamer
2533 { when in_pat_bind (addErr (patBindSigErr sig_tvs))
2534
2535 -- Check that all newly-in-scope tyvars are in fact
2536 -- constrained by the pattern. This catches tiresome
2537 -- cases like
2538 -- type T a = Int
2539 -- f :: Int -> Int
2540 -- f (x :: T a) = ...
2541 -- Here 'a' doesn't get a binding. Sigh
2542 ; let bad_tvs = [ tv | (_,tv) <- sig_tvs
2543 , not (tv `elemVarSet` exactTyCoVarsOfType sig_ty) ]
2544 ; checkTc (null bad_tvs) (badPatSigTvs sig_ty bad_tvs)
2545
2546 -- Now do a subsumption check of the pattern signature against res_ty
2547 ; wrap <- addErrCtxtM (mk_msg sig_ty) $
2548 tcSubTypeET PatSigOrigin PatSigCtxt res_ty sig_ty
2549
2550 -- Phew!
2551 ; return (sig_ty, sig_tvs, sig_wcs, wrap)
2552 } }
2553 where
2554 mk_msg sig_ty tidy_env
2555 = do { (tidy_env, sig_ty) <- zonkTidyTcType tidy_env sig_ty
2556 ; res_ty <- readExpType res_ty -- should be filled in by now
2557 ; (tidy_env, res_ty) <- zonkTidyTcType tidy_env res_ty
2558 ; let msg = vcat [ hang (text "When checking that the pattern signature:")
2559 4 (ppr sig_ty)
2560 , nest 2 (hang (text "fits the type of its context:")
2561 2 (ppr res_ty)) ]
2562 ; return (tidy_env, msg) }
2563
2564 patBindSigErr :: [(Name,TcTyVar)] -> SDoc
2565 patBindSigErr sig_tvs
2566 = hang (text "You cannot bind scoped type variable" <> plural sig_tvs
2567 <+> pprQuotedList (map fst sig_tvs))
2568 2 (text "in a pattern binding signature")
2569
2570 {- Note [Pattern signature binders]
2571 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2572 Consider
2573 data T = forall a. T a (a->Int)
2574 f (T x (f :: b->Int)) = blah
2575
2576 Here
2577 * The pattern (T p1 p2) creates a *skolem* type variable 'a_sk',
2578 It must be a skolem so that that it retains its identity, and
2579 TcErrors.getSkolemInfo can thereby find the binding site for the skolem.
2580
2581 * The type signature pattern (f :: b->Int) makes a fresh meta-tyvar b_sig
2582 (a SigTv), and binds "b" :-> b_sig in the envt
2583
2584 * Then unification makes b_sig := a_sk
2585 That's why we must make b_sig a MetaTv (albeit a SigTv),
2586 not a SkolemTv, so that it can unify to a_sk.
2587
2588 * Finally, in 'blah' we must have the envt "b" :-> a_sk. The pair
2589 ("b" :-> a_sk) is returned by tcHsPatSigType, constructed by
2590 mk_tv_pair in that function.
2591
2592 Another example (Trac #13881):
2593 fl :: forall (l :: [a]). Sing l -> Sing l
2594 fl (SNil :: Sing (l :: [y])) = SNil
2595 When we reach the pattern signature, 'l' is in scope from the
2596 outer 'forall':
2597 "a" :-> a_sk :: *
2598 "l" :-> l_sk :: [a_sk]
2599 We make up a fresh meta-SigTv, y_sig, for 'y', and kind-check
2600 the pattern signature
2601 Sing (l :: [y])
2602 That unifies y_sig := a_sk. We return from tcHsPatSigType with
2603 the pair ("y" :-> a_sk).
2604
2605 For RULE binders, though, things are a bit different (yuk).
2606 RULE "foo" forall (x::a) (y::[a]). f x y = ...
2607 Here this really is the binding site of the type variable so we'd like
2608 to use a skolem, so that we get a complaint if we unify two of them
2609 together.
2610
2611 Note [Unifying SigTvs]
2612 ~~~~~~~~~~~~~~~~~~~~~~
2613 ALAS we have no decent way of avoiding two SigTvs getting unified.
2614 Consider
2615 f (x::(a,b)) (y::c)) = [fst x, y]
2616 Here we'd really like to complain that 'a' and 'c' are unified. But
2617 for the reasons above we can't make a,b,c into skolems, so they
2618 are just SigTvs that can unify. And indeed, this would be ok,
2619 f x (y::c) = case x of
2620 (x1 :: a1, True) -> [x,y]
2621 (x1 :: a2, False) -> [x,y,y]
2622 Here the type of x's first component is called 'a1' in one branch and
2623 'a2' in the other. We could try insisting on the same OccName, but
2624 they definitely won't have the sane lexical Name.
2625
2626 I think we could solve this by recording in a SigTv a list of all the
2627 in-scope variables that it should not unify with, but it's fiddly.
2628
2629
2630 ************************************************************************
2631 * *
2632 Checking kinds
2633 * *
2634 ************************************************************************
2635
2636 -}
2637
2638 unifyKinds :: [LHsType GhcRn] -> [(TcType, TcKind)] -> TcM ([TcType], TcKind)
2639 unifyKinds rn_tys act_kinds
2640 = do { kind <- newMetaKindVar
2641 ; let check rn_ty (ty, act_kind) = checkExpectedKind (unLoc rn_ty) ty act_kind kind
2642 ; tys' <- zipWithM check rn_tys act_kinds
2643 ; return (tys', kind) }
2644
2645 {-
2646 ************************************************************************
2647 * *
2648 Promotion
2649 * *
2650 ************************************************************************
2651 -}
2652
2653 -- | Whenever a type is about to be added to the environment, it's necessary
2654 -- to make sure that any free meta-tyvars in the type are promoted to the
2655 -- current TcLevel. (They might be at a higher level due to the level-bumping
2656 -- in tcExplicitTKBndrs, for example.) This function both zonks *and*
2657 -- promotes.
2658 zonkPromoteType :: TcType -> TcM TcType
2659 zonkPromoteType = mapType zonkPromoteMapper ()
2660
2661 -- cf. TcMType.zonkTcTypeMapper
2662 zonkPromoteMapper :: TyCoMapper () TcM
2663 zonkPromoteMapper = TyCoMapper { tcm_smart = True
2664 , tcm_tyvar = const zonkPromoteTcTyVar
2665 , tcm_covar = const covar
2666 , tcm_hole = const hole
2667 , tcm_tybinder = const tybinder }
2668 where
2669 covar cv
2670 = mkCoVarCo <$> zonkPromoteTyCoVarKind cv
2671
2672 hole :: CoercionHole -> TcM Coercion
2673 hole h
2674 = do { contents <- unpackCoercionHole_maybe h
2675 ; case contents of
2676 Just co -> do { co <- zonkPromoteCoercion co
2677 ; checkCoercionHole cv co }
2678 Nothing -> do { cv' <- zonkPromoteTyCoVarKind cv
2679 ; return $ mkHoleCo (setCoHoleCoVar h cv') } }
2680 where
2681 cv = coHoleCoVar h
2682
2683 tybinder :: TyVar -> ArgFlag -> TcM ((), TyVar)
2684 tybinder tv _flag = ((), ) <$> zonkPromoteTyCoVarKind tv
2685
2686 zonkPromoteTcTyVar :: TyCoVar -> TcM TcType
2687 zonkPromoteTcTyVar tv
2688 | isMetaTyVar tv
2689 = do { let ref = metaTyVarRef tv
2690 ; contents <- readTcRef ref
2691 ; case contents of
2692 Flexi -> do { promoted <- promoteTyVar tv
2693 ; if promoted
2694 then zonkPromoteTcTyVar tv -- read it again
2695 else mkTyVarTy <$> zonkPromoteTyCoVarKind tv }
2696 Indirect ty -> zonkPromoteType ty }
2697
2698 | isTcTyVar tv && isSkolemTyVar tv -- NB: isSkolemTyVar says "True" to pure TyVars
2699 = do { tc_lvl <- getTcLevel
2700 ; mkTyVarTy <$> zonkPromoteTyCoVarKind (promoteSkolem tc_lvl tv) }
2701
2702 | otherwise
2703 = mkTyVarTy <$> zonkPromoteTyCoVarKind tv
2704
2705 zonkPromoteTyCoVarKind :: TyCoVar -> TcM TyCoVar
2706 zonkPromoteTyCoVarKind = updateTyVarKindM zonkPromoteType
2707
2708 zonkPromoteTyCoVarBndr :: TyCoVar -> TcM TyCoVar
2709 zonkPromoteTyCoVarBndr tv
2710 | isSigTyVar tv
2711 = tcGetTyVar "zonkPromoteTyCoVarBndr SigTv" <$> zonkPromoteTcTyVar tv
2712
2713 | isTcTyVar tv && isSkolemTyVar tv
2714 = do { tc_lvl <- getTcLevel
2715 ; zonkPromoteTyCoVarKind (promoteSkolem tc_lvl tv) }
2716
2717 | otherwise
2718 = zonkPromoteTyCoVarKind tv
2719
2720 zonkPromoteCoercion :: Coercion -> TcM Coercion
2721 zonkPromoteCoercion = mapCoercion zonkPromoteMapper ()
2722
2723 zonkPromoteTypeInKnot :: TcType -> TcM TcType
2724 zonkPromoteTypeInKnot = mapType (zonkPromoteMapper { tcm_smart = False }) ()
2725 -- NB: Just changing smart to False will still use the smart zonker (not suitable
2726 -- for in-the-knot) for kinds. But that's OK, because kinds aren't knot-tied.
2727
2728 {-
2729 ************************************************************************
2730 * *
2731 Sort checking kinds
2732 * *
2733 ************************************************************************
2734
2735 tcLHsKindSig converts a user-written kind to an internal, sort-checked kind.
2736 It does sort checking and desugaring at the same time, in one single pass.
2737 -}
2738
2739 tcLHsKindSig :: UserTypeCtxt -> LHsKind GhcRn -> TcM Kind
2740 tcLHsKindSig ctxt hs_kind
2741 -- See Note [Recipe for checking a signature] in TcHsType
2742 -- Result is zonked
2743 = do { kind <- solveLocalEqualities $
2744 tc_lhs_kind kindLevelMode hs_kind
2745 ; traceTc "tcLHsKindSig" (ppr kind)
2746 ; kind <- zonkPromoteType kind
2747 -- This zonk is very important in the case of higher rank kinds
2748 -- E.g. Trac #13879 f :: forall (p :: forall z (y::z). <blah>).
2749 -- <more blah>
2750 -- When instantiating p's kind at occurrences of p in <more blah>
2751 -- it's crucial that the kind we instantiate is fully zonked,
2752 -- else we may fail to substitute properly
2753
2754 ; checkValidType ctxt kind
2755 ; traceTc "tcLHsKindSig2" (ppr kind)
2756 ; return kind }
2757
2758 tc_lhs_kind :: TcTyMode -> LHsKind GhcRn -> TcM Kind
2759 tc_lhs_kind mode k
2760 = addErrCtxt (text "In the kind" <+> quotes (ppr k)) $
2761 tc_lhs_type (kindLevel mode) k liftedTypeKind
2762
2763 promotionErr :: Name -> PromotionErr -> TcM a
2764 promotionErr name err
2765 = failWithTc (hang (pprPECategory err <+> quotes (ppr name) <+> text "cannot be used here")
2766 2 (parens reason))
2767 where
2768 reason = case err of
2769 ConstrainedDataConPE pred
2770 -> text "it has an unpromotable context"
2771 <+> quotes (ppr pred)
2772 FamDataConPE -> text "it comes from a data family instance"
2773 NoDataKindsTC -> text "perhaps you intended to use DataKinds"
2774 NoDataKindsDC -> text "perhaps you intended to use DataKinds"
2775 PatSynPE -> text "pattern synonyms cannot be promoted"
2776 PatSynExPE -> sep [ text "the existential variables of a pattern synonym"
2777 , text "signature do not scope over the pattern" ]
2778 _ -> text "it is defined and used in the same recursive group"
2779
2780 {-
2781 ************************************************************************
2782 * *
2783 Scoped type variables
2784 * *
2785 ************************************************************************
2786 -}
2787
2788 badPatSigTvs :: TcType -> [TyVar] -> SDoc
2789 badPatSigTvs sig_ty bad_tvs
2790 = vcat [ fsep [text "The type variable" <> plural bad_tvs,
2791 quotes (pprWithCommas ppr bad_tvs),
2792 text "should be bound by the pattern signature" <+> quotes (ppr sig_ty),
2793 text "but are actually discarded by a type synonym" ]
2794 , text "To fix this, expand the type synonym"
2795 , text "[Note: I hope to lift this restriction in due course]" ]
2796
2797 {-
2798 ************************************************************************
2799 * *
2800 Error messages and such
2801 * *
2802 ************************************************************************
2803 -}
2804
2805 -- | Make an appropriate message for an error in a function argument.
2806 -- Used for both expressions and types.
2807 funAppCtxt :: (Outputable fun, Outputable arg) => fun -> arg -> Int -> SDoc
2808 funAppCtxt fun arg arg_no
2809 = hang (hsep [ text "In the", speakNth arg_no, ptext (sLit "argument of"),
2810 quotes (ppr fun) <> text ", namely"])
2811 2 (quotes (ppr arg))
2812
2813 -- See Note [Free-floating kind vars]
2814 reportFloatingKvs :: Name -- of the tycon
2815 -> TyConFlavour -- What sort of TyCon it is
2816 -> [TcTyVar] -- all tyvars, not necessarily zonked
2817 -> [TcTyVar] -- floating tyvars
2818 -> TcM ()
2819 reportFloatingKvs tycon_name flav all_tvs bad_tvs
2820 = unless (null bad_tvs) $ -- don't bother zonking if there's no error
2821 do { all_tvs <- mapM zonkTcTyVarToTyVar all_tvs
2822 ; bad_tvs <- mapM zonkTcTyVarToTyVar bad_tvs
2823 ; let (tidy_env, tidy_all_tvs) = tidyOpenTyCoVars emptyTidyEnv all_tvs
2824 tidy_bad_tvs = map (tidyTyVarOcc tidy_env) bad_tvs
2825 ; mapM_ (report tidy_all_tvs) tidy_bad_tvs }
2826 where
2827 report tidy_all_tvs tidy_bad_tv
2828 = addErr $
2829 vcat [ text "Kind variable" <+> quotes (ppr tidy_bad_tv) <+>
2830 text "is implicitly bound in" <+> ppr flav
2831 , quotes (ppr tycon_name) <> comma <+>
2832 text "but does not appear as the kind of any"
2833 , text "of its type variables. Perhaps you meant"
2834 , text "to bind it explicitly somewhere?"
2835 , ppWhen (not (null tidy_all_tvs)) $
2836 hang (text "Type variables with inferred kinds:")
2837 2 (ppr_tv_bndrs tidy_all_tvs) ]
2838
2839 ppr_tv_bndrs tvs = sep (map pp_tv tvs)
2840 pp_tv tv = parens (ppr tv <+> dcolon <+> ppr (tyVarKind tv))