More tc-tracing
[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 If tc_ty = tc_hs_type hs_ty exp_kind
544 then
545 typeKind tc_ty = exp_kind
546 without any zonking needed. The reason for this is that in
547 tcInferApps we see (F ty), and we kind-check 'ty' with an
548 expected-kind coming from F. Then, to make the resulting application
549 well kinded --- see Note [Ensure well-kinded types] in TcType --- we
550 need the kind-checked 'ty' to have exactly the kind that F expects,
551 with no funny zonking nonsense in between.
552
553 The tcType invariant also applies to checkExpectedKind: if
554 (tc_ty, _, _) = checkExpectedKind ty act_ki exp_ki
555 then
556 typeKind tc_ty = exp_ki
557 -}
558
559 ------------------------------------------
560 -- | Check and desugar a type, returning the core type and its
561 -- possibly-polymorphic kind. Much like 'tcInferRho' at the expression
562 -- level.
563 tc_infer_lhs_type :: TcTyMode -> LHsType GhcRn -> TcM (TcType, TcKind)
564 tc_infer_lhs_type mode (L span ty)
565 = setSrcSpan span $
566 do { (ty', kind) <- tc_infer_hs_type mode ty
567 ; return (ty', kind) }
568
569 -- | Infer the kind of a type and desugar. This is the "up" type-checker,
570 -- as described in Note [Bidirectional type checking]
571 tc_infer_hs_type :: TcTyMode -> HsType GhcRn -> TcM (TcType, TcKind)
572 tc_infer_hs_type mode (HsParTy _ t) = tc_infer_lhs_type mode t
573 tc_infer_hs_type mode (HsTyVar _ _ (L _ tv)) = tcTyVar mode tv
574
575 tc_infer_hs_type mode (HsAppTy _ ty1 ty2)
576 = do { let (hs_fun_ty, hs_arg_tys) = splitHsAppTys ty1 [ty2]
577 ; (fun_ty, fun_kind) <- tc_infer_lhs_type mode hs_fun_ty
578 -- A worry: what if fun_kind needs zoonking?
579 -- We used to zonk it here, but that got fun_ty and fun_kind
580 -- out of sync (see the precondition to tcTyApps), which caused
581 -- Trac #14873. So I'm now zonking in tcTyVar, and not here.
582 -- Is that enough? Seems so, but I can't see how to be certain.
583 ; tcTyApps mode hs_fun_ty fun_ty fun_kind hs_arg_tys }
584
585 tc_infer_hs_type mode (HsOpTy _ lhs lhs_op@(L _ hs_op) rhs)
586 | not (hs_op `hasKey` funTyConKey)
587 = do { (op, op_kind) <- tcTyVar mode hs_op
588 -- See "A worry" in the HsApp case
589 ; tcTyApps mode (noLoc $ HsTyVar noExt NotPromoted lhs_op) op op_kind
590 [lhs, rhs] }
591
592 tc_infer_hs_type mode (HsKindSig _ ty sig)
593 = do { sig' <- tcLHsKindSig KindSigCtxt sig
594 -- We must typecheck the kind signature, and solve all
595 -- its equalities etc; from this point on we may do
596 -- things like instantiate its foralls, so it needs
597 -- to be fully determined (Trac #14904)
598 ; traceTc "tc_infer_hs_type:sig" (ppr ty $$ ppr sig')
599 ; ty' <- tc_lhs_type mode ty sig'
600 ; return (ty', sig') }
601
602 -- HsSpliced is an annotation produced by 'RnSplice.rnSpliceType' to communicate
603 -- the splice location to the typechecker. Here we skip over it in order to have
604 -- the same kind inferred for a given expression whether it was produced from
605 -- splices or not.
606 --
607 -- See Note [Delaying modFinalizers in untyped splices].
608 tc_infer_hs_type mode (HsSpliceTy _ (HsSpliced _ _ (HsSplicedTy ty)))
609 = tc_infer_hs_type mode ty
610
611 tc_infer_hs_type mode (HsDocTy _ ty _) = tc_infer_lhs_type mode ty
612 tc_infer_hs_type _ (XHsType (NHsCoreTy ty)) = return (ty, typeKind ty)
613 tc_infer_hs_type mode other_ty
614 = do { kv <- newMetaKindVar
615 ; ty' <- tc_hs_type mode other_ty kv
616 ; return (ty', kv) }
617
618 ------------------------------------------
619 tc_lhs_type :: TcTyMode -> LHsType GhcRn -> TcKind -> TcM TcType
620 tc_lhs_type mode (L span ty) exp_kind
621 = setSrcSpan span $
622 tc_hs_type mode ty exp_kind
623
624 ------------------------------------------
625 tc_fun_type :: TcTyMode -> LHsType GhcRn -> LHsType GhcRn -> TcKind
626 -> TcM TcType
627 tc_fun_type mode ty1 ty2 exp_kind = case mode_level mode of
628 TypeLevel ->
629 do { arg_k <- newOpenTypeKind
630 ; res_k <- newOpenTypeKind
631 ; ty1' <- tc_lhs_type mode ty1 arg_k
632 ; ty2' <- tc_lhs_type mode ty2 res_k
633 ; checkExpectedKind (HsFunTy noExt ty1 ty2) (mkFunTy ty1' ty2')
634 liftedTypeKind exp_kind }
635 KindLevel -> -- no representation polymorphism in kinds. yet.
636 do { ty1' <- tc_lhs_type mode ty1 liftedTypeKind
637 ; ty2' <- tc_lhs_type mode ty2 liftedTypeKind
638 ; checkExpectedKind (HsFunTy noExt ty1 ty2) (mkFunTy ty1' ty2')
639 liftedTypeKind exp_kind }
640
641 ------------------------------------------
642 tc_hs_type :: TcTyMode -> HsType GhcRn -> TcKind -> TcM TcType
643 -- See Note [The tcType invariant]
644 -- See Note [Bidirectional type checking]
645
646 tc_hs_type mode (HsParTy _ ty) exp_kind = tc_lhs_type mode ty exp_kind
647 tc_hs_type mode (HsDocTy _ ty _) exp_kind = tc_lhs_type mode ty exp_kind
648 tc_hs_type _ ty@(HsBangTy _ bang _) _
649 -- While top-level bangs at this point are eliminated (eg !(Maybe Int)),
650 -- other kinds of bangs are not (eg ((!Maybe) Int)). These kinds of
651 -- bangs are invalid, so fail. (#7210, #14761)
652 = do { let bangError err = failWith $
653 text "Unexpected" <+> text err <+> text "annotation:" <+> ppr ty $$
654 text err <+> text "annotation cannot appear nested inside a type"
655 ; case bang of
656 HsSrcBang _ SrcUnpack _ -> bangError "UNPACK"
657 HsSrcBang _ SrcNoUnpack _ -> bangError "NOUNPACK"
658 HsSrcBang _ NoSrcUnpack SrcLazy -> bangError "laziness"
659 HsSrcBang _ _ _ -> bangError "strictness" }
660 tc_hs_type _ ty@(HsRecTy {}) _
661 -- Record types (which only show up temporarily in constructor
662 -- signatures) should have been removed by now
663 = failWithTc (text "Record syntax is illegal here:" <+> ppr ty)
664
665 -- HsSpliced is an annotation produced by 'RnSplice.rnSpliceType'.
666 -- Here we get rid of it and add the finalizers to the global environment
667 -- while capturing the local environment.
668 --
669 -- See Note [Delaying modFinalizers in untyped splices].
670 tc_hs_type mode (HsSpliceTy _ (HsSpliced _ mod_finalizers (HsSplicedTy ty)))
671 exp_kind
672 = do addModFinalizersWithLclEnv mod_finalizers
673 tc_hs_type mode ty exp_kind
674
675 -- This should never happen; type splices are expanded by the renamer
676 tc_hs_type _ ty@(HsSpliceTy {}) _exp_kind
677 = failWithTc (text "Unexpected type splice:" <+> ppr ty)
678
679 ---------- Functions and applications
680 tc_hs_type mode (HsFunTy _ ty1 ty2) exp_kind
681 = tc_fun_type mode ty1 ty2 exp_kind
682
683 tc_hs_type mode (HsOpTy _ ty1 (L _ op) ty2) exp_kind
684 | op `hasKey` funTyConKey
685 = tc_fun_type mode ty1 ty2 exp_kind
686
687 --------- Foralls
688 tc_hs_type mode forall@(HsForAllTy { hst_bndrs = hs_tvs, hst_body = ty }) exp_kind
689 = do { (tvs', ty') <- tcExplicitTKBndrs (ForAllSkol (ppr forall)) hs_tvs $
690 tc_lhs_type mode ty exp_kind
691 -- Do not kind-generalise here! See Note [Kind generalisation]
692 -- Why exp_kind? See Note [Body kind of HsForAllTy]
693 ; let bndrs = mkTyVarBinders Specified tvs'
694 ; return (mkForAllTys bndrs ty') }
695
696 tc_hs_type mode (HsQualTy { hst_ctxt = ctxt, hst_body = ty }) exp_kind
697 | null (unLoc ctxt)
698 = tc_lhs_type mode ty exp_kind
699
700 | otherwise
701 = do { ctxt' <- tc_hs_context mode ctxt
702
703 -- See Note [Body kind of a HsQualTy]
704 ; ty' <- if isConstraintKind exp_kind
705 then tc_lhs_type mode ty constraintKind
706 else do { ek <- newOpenTypeKind
707 -- The body kind (result of the function)
708 -- can be * or #, hence newOpenTypeKind
709 ; ty' <- tc_lhs_type mode ty ek
710 ; checkExpectedKind (unLoc ty) ty' liftedTypeKind exp_kind }
711
712 ; return (mkPhiTy ctxt' ty') }
713
714 --------- Lists, arrays, and tuples
715 tc_hs_type mode rn_ty@(HsListTy _ elt_ty) exp_kind
716 = do { tau_ty <- tc_lhs_type mode elt_ty liftedTypeKind
717 ; checkWiredInTyCon listTyCon
718 ; checkExpectedKind rn_ty (mkListTy tau_ty) liftedTypeKind exp_kind }
719
720 -- See Note [Distinguishing tuple kinds] in HsTypes
721 -- See Note [Inferring tuple kinds]
722 tc_hs_type mode rn_ty@(HsTupleTy _ HsBoxedOrConstraintTuple hs_tys) exp_kind
723 -- (NB: not zonking before looking at exp_k, to avoid left-right bias)
724 | Just tup_sort <- tupKindSort_maybe exp_kind
725 = traceTc "tc_hs_type tuple" (ppr hs_tys) >>
726 tc_tuple rn_ty mode tup_sort hs_tys exp_kind
727 | otherwise
728 = do { traceTc "tc_hs_type tuple 2" (ppr hs_tys)
729 ; (tys, kinds) <- mapAndUnzipM (tc_infer_lhs_type mode) hs_tys
730 ; kinds <- mapM zonkTcType kinds
731 -- Infer each arg type separately, because errors can be
732 -- confusing if we give them a shared kind. Eg Trac #7410
733 -- (Either Int, Int), we do not want to get an error saying
734 -- "the second argument of a tuple should have kind *->*"
735
736 ; let (arg_kind, tup_sort)
737 = case [ (k,s) | k <- kinds
738 , Just s <- [tupKindSort_maybe k] ] of
739 ((k,s) : _) -> (k,s)
740 [] -> (liftedTypeKind, BoxedTuple)
741 -- In the [] case, it's not clear what the kind is, so guess *
742
743 ; tys' <- sequence [ setSrcSpan loc $
744 checkExpectedKind hs_ty ty kind arg_kind
745 | ((L loc hs_ty),ty,kind) <- zip3 hs_tys tys kinds ]
746
747 ; finish_tuple rn_ty tup_sort tys' (map (const arg_kind) tys') exp_kind }
748
749
750 tc_hs_type mode rn_ty@(HsTupleTy _ hs_tup_sort tys) exp_kind
751 = tc_tuple rn_ty mode tup_sort tys exp_kind
752 where
753 tup_sort = case hs_tup_sort of -- Fourth case dealt with above
754 HsUnboxedTuple -> UnboxedTuple
755 HsBoxedTuple -> BoxedTuple
756 HsConstraintTuple -> ConstraintTuple
757 _ -> panic "tc_hs_type HsTupleTy"
758
759 tc_hs_type mode rn_ty@(HsSumTy _ hs_tys) exp_kind
760 = do { let arity = length hs_tys
761 ; arg_kinds <- mapM (\_ -> newOpenTypeKind) hs_tys
762 ; tau_tys <- zipWithM (tc_lhs_type mode) hs_tys arg_kinds
763 ; let arg_reps = map getRuntimeRepFromKind arg_kinds
764 arg_tys = arg_reps ++ tau_tys
765 ; checkExpectedKind rn_ty
766 (mkTyConApp (sumTyCon arity) arg_tys)
767 (unboxedSumKind arg_reps)
768 exp_kind
769 }
770
771 --------- Promoted lists and tuples
772 tc_hs_type mode rn_ty@(HsExplicitListTy _ _ tys) exp_kind
773 = do { tks <- mapM (tc_infer_lhs_type mode) tys
774 ; (taus', kind) <- unifyKinds tys tks
775 ; let ty = (foldr (mk_cons kind) (mk_nil kind) taus')
776 ; checkExpectedKind rn_ty ty (mkListTy kind) exp_kind }
777 where
778 mk_cons k a b = mkTyConApp (promoteDataCon consDataCon) [k, a, b]
779 mk_nil k = mkTyConApp (promoteDataCon nilDataCon) [k]
780
781 tc_hs_type mode rn_ty@(HsExplicitTupleTy _ tys) exp_kind
782 -- using newMetaKindVar means that we force instantiations of any polykinded
783 -- types. At first, I just used tc_infer_lhs_type, but that led to #11255.
784 = do { ks <- replicateM arity newMetaKindVar
785 ; taus <- zipWithM (tc_lhs_type mode) tys ks
786 ; let kind_con = tupleTyCon Boxed arity
787 ty_con = promotedTupleDataCon Boxed arity
788 tup_k = mkTyConApp kind_con ks
789 ; checkExpectedKind rn_ty (mkTyConApp ty_con (ks ++ taus)) tup_k exp_kind }
790 where
791 arity = length tys
792
793 --------- Constraint types
794 tc_hs_type mode rn_ty@(HsIParamTy _ (L _ n) ty) exp_kind
795 = do { MASSERT( isTypeLevel (mode_level mode) )
796 ; ty' <- tc_lhs_type mode ty liftedTypeKind
797 ; let n' = mkStrLitTy $ hsIPNameFS n
798 ; ipClass <- tcLookupClass ipClassName
799 ; checkExpectedKind rn_ty (mkClassPred ipClass [n',ty'])
800 constraintKind exp_kind }
801
802 tc_hs_type _ rn_ty@(HsStarTy _ _) exp_kind
803 -- Desugaring 'HsStarTy' to 'Data.Kind.Type' here means that we don't have to
804 -- handle it in 'coreView' and 'tcView'.
805 = checkExpectedKind rn_ty liftedTypeKind liftedTypeKind exp_kind
806
807 --------- Literals
808 tc_hs_type _ rn_ty@(HsTyLit _ (HsNumTy _ n)) exp_kind
809 = do { checkWiredInTyCon typeNatKindCon
810 ; checkExpectedKind rn_ty (mkNumLitTy n) typeNatKind exp_kind }
811
812 tc_hs_type _ rn_ty@(HsTyLit _ (HsStrTy _ s)) exp_kind
813 = do { checkWiredInTyCon typeSymbolKindCon
814 ; checkExpectedKind rn_ty (mkStrLitTy s) typeSymbolKind exp_kind }
815
816 --------- Potentially kind-polymorphic types: call the "up" checker
817 -- See Note [Future-proofing the type checker]
818 tc_hs_type mode ty@(HsTyVar {}) ek = tc_infer_hs_type_ek mode ty ek
819 tc_hs_type mode ty@(HsAppTy {}) ek = tc_infer_hs_type_ek mode ty ek
820 tc_hs_type mode ty@(HsOpTy {}) ek = tc_infer_hs_type_ek mode ty ek
821 tc_hs_type mode ty@(HsKindSig {}) ek = tc_infer_hs_type_ek mode ty ek
822 tc_hs_type mode ty@(XHsType (NHsCoreTy{})) ek = tc_infer_hs_type_ek mode ty ek
823
824 tc_hs_type _ (HsWildCardTy wc) exp_kind
825 = do { wc_ty <- tcWildCardOcc wc exp_kind
826 ; return (mkNakedCastTy wc_ty (mkTcNomReflCo exp_kind))
827 -- Take care here! Even though the coercion is Refl,
828 -- we still need it to establish Note [The tcType invariant]
829 }
830
831 tcWildCardOcc :: HsWildCardInfo -> Kind -> TcM TcType
832 tcWildCardOcc wc_info exp_kind
833 = do { wc_tv <- tcLookupTyVar (wildCardName wc_info)
834 -- The wildcard's kind should be an un-filled-in meta tyvar
835 ; checkExpectedKind (HsWildCardTy wc_info) (mkTyVarTy wc_tv)
836 (tyVarKind wc_tv) exp_kind }
837
838 ---------------------------
839 -- | Call 'tc_infer_hs_type' and check its result against an expected kind.
840 tc_infer_hs_type_ek :: HasDebugCallStack => TcTyMode -> HsType GhcRn -> TcKind -> TcM TcType
841 tc_infer_hs_type_ek mode hs_ty ek
842 = do { (ty, k) <- tc_infer_hs_type mode hs_ty
843 ; checkExpectedKind hs_ty ty k ek }
844
845 ---------------------------
846 tupKindSort_maybe :: TcKind -> Maybe TupleSort
847 tupKindSort_maybe k
848 | Just (k', _) <- splitCastTy_maybe k = tupKindSort_maybe k'
849 | Just k' <- tcView k = tupKindSort_maybe k'
850 | isConstraintKind k = Just ConstraintTuple
851 | isLiftedTypeKind k = Just BoxedTuple
852 | otherwise = Nothing
853
854 tc_tuple :: HsType GhcRn -> TcTyMode -> TupleSort -> [LHsType GhcRn] -> TcKind -> TcM TcType
855 tc_tuple rn_ty mode tup_sort tys exp_kind
856 = do { arg_kinds <- case tup_sort of
857 BoxedTuple -> return (nOfThem arity liftedTypeKind)
858 UnboxedTuple -> mapM (\_ -> newOpenTypeKind) tys
859 ConstraintTuple -> return (nOfThem arity constraintKind)
860 ; tau_tys <- zipWithM (tc_lhs_type mode) tys arg_kinds
861 ; finish_tuple rn_ty tup_sort tau_tys arg_kinds exp_kind }
862 where
863 arity = length tys
864
865 finish_tuple :: HsType GhcRn
866 -> TupleSort
867 -> [TcType] -- ^ argument types
868 -> [TcKind] -- ^ of these kinds
869 -> TcKind -- ^ expected kind of the whole tuple
870 -> TcM TcType
871 finish_tuple rn_ty tup_sort tau_tys tau_kinds exp_kind
872 = do { traceTc "finish_tuple" (ppr res_kind $$ ppr tau_kinds $$ ppr exp_kind)
873 ; let arg_tys = case tup_sort of
874 -- See also Note [Unboxed tuple RuntimeRep vars] in TyCon
875 UnboxedTuple -> tau_reps ++ tau_tys
876 BoxedTuple -> tau_tys
877 ConstraintTuple -> tau_tys
878 ; tycon <- case tup_sort of
879 ConstraintTuple
880 | arity > mAX_CTUPLE_SIZE
881 -> failWith (bigConstraintTuple arity)
882 | otherwise -> tcLookupTyCon (cTupleTyConName arity)
883 BoxedTuple -> do { let tc = tupleTyCon Boxed arity
884 ; checkWiredInTyCon tc
885 ; return tc }
886 UnboxedTuple -> return (tupleTyCon Unboxed arity)
887 ; checkExpectedKind rn_ty (mkTyConApp tycon arg_tys) res_kind exp_kind }
888 where
889 arity = length tau_tys
890 tau_reps = map getRuntimeRepFromKind tau_kinds
891 res_kind = case tup_sort of
892 UnboxedTuple -> unboxedTupleKind tau_reps
893 BoxedTuple -> liftedTypeKind
894 ConstraintTuple -> constraintKind
895
896 bigConstraintTuple :: Arity -> MsgDoc
897 bigConstraintTuple arity
898 = hang (text "Constraint tuple arity too large:" <+> int arity
899 <+> parens (text "max arity =" <+> int mAX_CTUPLE_SIZE))
900 2 (text "Instead, use a nested tuple")
901
902 ---------------------------
903 -- | Apply a type of a given kind to a list of arguments. This instantiates
904 -- invisible parameters as necessary. Always consumes all the arguments,
905 -- using matchExpectedFunKind as necessary.
906 -- This takes an optional @VarEnv Kind@ which maps kind variables to kinds.
907 -- These kinds should be used to instantiate invisible kind variables;
908 -- they come from an enclosing class for an associated type/data family.
909 tcInferApps :: TcTyMode
910 -> Maybe (VarEnv Kind) -- ^ Possibly, kind info (see above)
911 -> LHsType GhcRn -- ^ Function (for printing only)
912 -> TcType -- ^ Function (could be knot-tied)
913 -> TcKind -- ^ Function kind (zonked)
914 -> [LHsType GhcRn] -- ^ Args
915 -> TcM (TcType, [TcType], TcKind) -- ^ (f args, args, result kind)
916 -- Precondition: typeKind fun_ty = fun_ki
917 -- Reason: we will return a type application like (fun_ty arg1 ... argn),
918 -- and that type must be well-kinded
919 -- See Note [The tcType invariant]
920 tcInferApps mode mb_kind_info orig_hs_ty fun_ty fun_ki orig_hs_args
921 = do { traceTc "tcInferApps {" (ppr orig_hs_ty $$ ppr orig_hs_args $$ ppr fun_ki)
922 ; stuff <- go 1 [] empty_subst fun_ty orig_ki_binders orig_inner_ki orig_hs_args
923 ; traceTc "tcInferApps }" empty
924 ; return stuff }
925 where
926 empty_subst = mkEmptyTCvSubst $ mkInScopeSet $
927 tyCoVarsOfType fun_ki
928 (orig_ki_binders, orig_inner_ki) = tcSplitPiTys fun_ki
929
930 go :: Int -- the # of the next argument
931 -> [TcType] -- already type-checked args, in reverse order
932 -> TCvSubst -- instantiating substitution
933 -> TcType -- function applied to some args, could be knot-tied
934 -> [TyBinder] -- binders in function kind (both vis. and invis.)
935 -> TcKind -- function kind body (not a Pi-type)
936 -> [LHsType GhcRn] -- un-type-checked args
937 -> TcM (TcType, [TcType], TcKind) -- same as overall return type
938
939 -- no user-written args left. We're done!
940 go _ acc_args subst fun ki_binders inner_ki []
941 = return (fun, reverse acc_args, substTy subst $ mkPiTys ki_binders inner_ki)
942
943 -- The function's kind has a binder. Is it visible or invisible?
944 go n acc_args subst fun (ki_binder:ki_binders) inner_ki
945 all_args@(arg:args)
946 | isInvisibleBinder ki_binder
947 -- It's invisible. Instantiate.
948 = do { traceTc "tcInferApps (invis)" (ppr ki_binder $$ ppr subst)
949 ; (subst', arg') <- tcInstTyBinder mb_kind_info subst ki_binder
950 ; go n (arg' : acc_args) subst' (mkNakedAppTy fun arg')
951 ki_binders inner_ki all_args }
952
953 | otherwise
954 -- It's visible. Check the next user-written argument
955 = do { traceTc "tcInferApps (vis)" (vcat [ ppr ki_binder, ppr arg
956 , ppr (tyBinderType ki_binder)
957 , ppr subst ])
958 ; arg' <- addErrCtxt (funAppCtxt orig_hs_ty arg n) $
959 tc_lhs_type mode arg (substTy subst $ tyBinderType ki_binder)
960 ; let subst' = extendTvSubstBinderAndInScope subst ki_binder arg'
961 ; go (n+1) (arg' : acc_args) subst'
962 (mkNakedAppTy fun arg')
963 ki_binders inner_ki args }
964
965 -- We've run out of known binders in the functions's kind.
966 go n acc_args subst fun [] inner_ki all_args
967 | not (null new_ki_binders)
968 -- But, after substituting, we have more binders.
969 = go n acc_args zapped_subst fun new_ki_binders new_inner_ki all_args
970
971 | otherwise
972 -- Even after substituting, still no binders. Use matchExpectedFunKind
973 = do { traceTc "tcInferApps (no binder)" (ppr new_inner_ki $$ ppr zapped_subst)
974 ; (co, arg_k, res_k) <- matchExpectedFunKind hs_ty substed_inner_ki
975 ; let new_in_scope = tyCoVarsOfTypes [arg_k, res_k]
976 subst' = zapped_subst `extendTCvInScopeSet` new_in_scope
977 ; go n acc_args subst'
978 (fun `mkNakedCastTy` co)
979 [mkAnonBinder arg_k]
980 res_k all_args }
981 where
982 substed_inner_ki = substTy subst inner_ki
983 (new_ki_binders, new_inner_ki) = tcSplitPiTys substed_inner_ki
984 zapped_subst = zapTCvSubst subst
985 hs_ty = mkHsAppTys orig_hs_ty (take (n-1) orig_hs_args)
986
987
988 -- | Applies a type to a list of arguments.
989 -- Always consumes all the arguments, using 'matchExpectedFunKind' as
990 -- necessary. If you wish to apply a type to a list of HsTypes, this is
991 -- your function.
992 -- Used for type-checking types only.
993 tcTyApps :: TcTyMode
994 -> LHsType GhcRn -- ^ Function (for printing only)
995 -> TcType -- ^ Function (could be knot-tied)
996 -> TcKind -- ^ Function kind (zonked)
997 -> [LHsType GhcRn] -- ^ Args
998 -> TcM (TcType, TcKind) -- ^ (f args, result kind)
999 -- Precondition: see precondition for tcInferApps
1000 tcTyApps mode orig_hs_ty fun_ty fun_ki args
1001 = do { (ty', _args, ki') <- tcInferApps mode Nothing orig_hs_ty fun_ty fun_ki args
1002 ; return (ty', ki') }
1003
1004 --------------------------
1005 -- Like checkExpectedKindX, but returns only the final type; convenient wrapper
1006 -- Obeys Note [The tcType invariant]
1007 checkExpectedKind :: HasDebugCallStack
1008 => HsType GhcRn -- type we're checking (for printing)
1009 -> TcType -- type we're checking (might be knot-tied)
1010 -> TcKind -- the known kind of that type
1011 -> TcKind -- the expected kind
1012 -> TcM TcType
1013 checkExpectedKind hs_ty ty act exp
1014 = fstOf3 <$> checkExpectedKindX Nothing (ppr hs_ty) ty act exp
1015
1016 checkExpectedKindX :: HasDebugCallStack
1017 => Maybe (VarEnv Kind) -- Possibly, instantiations for kind vars
1018 -> SDoc -- HsType whose kind we're checking
1019 -> TcType -- the type whose kind we're checking
1020 -> TcKind -- the known kind of that type, k
1021 -> TcKind -- the expected kind, exp_kind
1022 -> TcM (TcType, [TcType], TcCoercionN)
1023 -- (the new args, the coercion)
1024 -- Instantiate a kind (if necessary) and then call unifyType
1025 -- (checkExpectedKind ty act_kind exp_kind)
1026 -- checks that the actual kind act_kind is compatible
1027 -- with the expected kind exp_kind
1028 checkExpectedKindX mb_kind_env pp_hs_ty ty act_kind exp_kind
1029 = do { -- We need to make sure that both kinds have the same number of implicit
1030 -- foralls out front. If the actual kind has more, instantiate accordingly.
1031 -- Otherwise, just pass the type & kind through: the errors are caught
1032 -- in unifyType.
1033 let (exp_bndrs, _) = splitPiTysInvisible exp_kind
1034 n_exp = length exp_bndrs
1035 ; (new_args, act_kind') <- instantiateTyUntilN mb_kind_env n_exp act_kind
1036
1037 ; let origin = TypeEqOrigin { uo_actual = act_kind'
1038 , uo_expected = exp_kind
1039 , uo_thing = Just pp_hs_ty
1040 , uo_visible = True } -- the hs_ty is visible
1041 ty' = mkNakedAppTys ty new_args
1042
1043 ; traceTc "checkExpectedKind" $
1044 vcat [ pp_hs_ty
1045 , text "act_kind:" <+> ppr act_kind
1046 , text "act_kind':" <+> ppr act_kind'
1047 , text "exp_kind:" <+> ppr exp_kind ]
1048
1049 ; if act_kind' `tcEqType` exp_kind
1050 then return (ty', new_args, mkTcNomReflCo exp_kind) -- This is very common
1051 else do { co_k <- uType KindLevel origin act_kind' exp_kind
1052 ; traceTc "checkExpectedKind" (vcat [ ppr act_kind
1053 , ppr exp_kind
1054 , ppr co_k ])
1055 ; let result_ty = ty' `mkNakedCastTy` co_k
1056 -- See Note [The tcType invariant]
1057 ; return (result_ty, new_args, co_k) } }
1058
1059 -- | Instantiate @n@ invisible arguments to a type. If @n <= 0@, no instantiation
1060 -- occurs. If @n@ is too big, then all available invisible arguments are instantiated.
1061 -- (In other words, this function is very forgiving about bad values of @n@.)
1062 instantiateTyN :: Maybe (VarEnv Kind) -- ^ Predetermined instantiations
1063 -- (for assoc. type patterns)
1064 -> Int -- ^ @n@
1065 -> [TyBinder] -> TcKind -- ^ its kind
1066 -> TcM ([TcType], TcKind) -- ^ The inst'ed type, new args, kind
1067 instantiateTyN mb_kind_env n bndrs inner_ki
1068 | n <= 0
1069 = return ([], ki)
1070
1071 | otherwise
1072 = do { (subst, inst_args) <- tcInstTyBinders empty_subst mb_kind_env inst_bndrs
1073 ; let rebuilt_ki = mkPiTys leftover_bndrs inner_ki
1074 ki' = substTy subst rebuilt_ki
1075 ; traceTc "instantiateTyN" (vcat [ ppr ki
1076 , ppr n
1077 , ppr subst
1078 , ppr rebuilt_ki
1079 , ppr ki' ])
1080 ; return (inst_args, ki') }
1081 where
1082 -- NB: splitAt is forgiving with invalid numbers
1083 (inst_bndrs, leftover_bndrs) = splitAt n bndrs
1084 ki = mkPiTys bndrs inner_ki
1085 empty_subst = mkEmptyTCvSubst (mkInScopeSet (tyCoVarsOfType ki))
1086
1087 -- | Instantiate a type to have at most @n@ invisible arguments.
1088 instantiateTyUntilN :: Maybe (VarEnv Kind) -- ^ Possibly, instantiations for vars
1089 -> Int -- ^ @n@
1090 -> TcKind -- ^ its kind
1091 -> TcM ([TcType], TcKind) -- ^ The new args, final kind
1092 instantiateTyUntilN mb_kind_env n ki
1093 = let (bndrs, inner_ki) = splitPiTysInvisible ki
1094 num_to_inst = length bndrs - n
1095 in
1096 instantiateTyN mb_kind_env num_to_inst bndrs inner_ki
1097
1098 ---------------------------
1099 tcHsMbContext :: Maybe (LHsContext GhcRn) -> TcM [PredType]
1100 tcHsMbContext Nothing = return []
1101 tcHsMbContext (Just cxt) = tcHsContext cxt
1102
1103 tcHsContext :: LHsContext GhcRn -> TcM [PredType]
1104 tcHsContext = tc_hs_context typeLevelMode
1105
1106 tcLHsPredType :: LHsType GhcRn -> TcM PredType
1107 tcLHsPredType = tc_lhs_pred typeLevelMode
1108
1109 tc_hs_context :: TcTyMode -> LHsContext GhcRn -> TcM [PredType]
1110 tc_hs_context mode ctxt = mapM (tc_lhs_pred mode) (unLoc ctxt)
1111
1112 tc_lhs_pred :: TcTyMode -> LHsType GhcRn -> TcM PredType
1113 tc_lhs_pred mode pred = tc_lhs_type mode pred constraintKind
1114
1115 ---------------------------
1116 tcTyVar :: TcTyMode -> Name -> TcM (TcType, TcKind)
1117 -- See Note [Type checking recursive type and class declarations]
1118 -- in TcTyClsDecls
1119 tcTyVar mode name -- Could be a tyvar, a tycon, or a datacon
1120 = do { traceTc "lk1" (ppr name)
1121 ; thing <- tcLookup name
1122 ; case thing of
1123 ATyVar _ tv -> -- Important: zonk before returning
1124 -- We may have the application ((a::kappa) b)
1125 -- where kappa is already unified to (k1 -> k2)
1126 -- Then we want to see that arrow. Best done
1127 -- here because we are also maintaining
1128 -- Note [The tcType invariant], so we don't just
1129 -- want to zonk the kind, leaving the TyVar
1130 -- un-zonked (Trac #114873)
1131 do { ty <- zonkTcTyVar tv
1132 ; return (ty, typeKind ty) }
1133
1134 ATcTyCon tc_tc -> do { -- See Note [GADT kind self-reference]
1135 unless
1136 (isTypeLevel (mode_level mode))
1137 (promotionErr name TyConPE)
1138 ; check_tc tc_tc
1139 ; tc <- get_loopy_tc name tc_tc
1140 ; handle_tyfams tc tc_tc }
1141 -- mkNakedTyConApp: see Note [Type-checking inside the knot]
1142
1143 AGlobal (ATyCon tc)
1144 -> do { check_tc tc
1145 ; handle_tyfams tc tc }
1146
1147 AGlobal (AConLike (RealDataCon dc))
1148 -> do { data_kinds <- xoptM LangExt.DataKinds
1149 ; unless (data_kinds || specialPromotedDc dc) $
1150 promotionErr name NoDataKindsDC
1151 ; when (isFamInstTyCon (dataConTyCon dc)) $
1152 -- see Trac #15245
1153 promotionErr name FamDataConPE
1154 ; let (_, _, _, theta, _, _) = dataConFullSig dc
1155 ; case dc_theta_illegal_constraint theta of
1156 Just pred -> promotionErr name $
1157 ConstrainedDataConPE pred
1158 Nothing -> pure ()
1159 ; let tc = promoteDataCon dc
1160 ; return (mkNakedTyConApp tc [], tyConKind tc) }
1161
1162 APromotionErr err -> promotionErr name err
1163
1164 _ -> wrongThingErr "type" thing name }
1165 where
1166 check_tc :: TyCon -> TcM ()
1167 check_tc tc = do { data_kinds <- xoptM LangExt.DataKinds
1168 ; unless (isTypeLevel (mode_level mode) ||
1169 data_kinds ||
1170 isKindTyCon tc) $
1171 promotionErr name NoDataKindsTC }
1172
1173 -- if we are type-checking a type family tycon, we must instantiate
1174 -- any invisible arguments right away. Otherwise, we get #11246
1175 handle_tyfams :: TyCon -- the tycon to instantiate (might be loopy)
1176 -> TcTyCon -- a non-loopy version of the tycon
1177 -> TcM (TcType, TcKind)
1178 handle_tyfams tc tc_tc
1179 | mightBeUnsaturatedTyCon tc_tc || mode_unsat mode
1180 -- This is where mode_unsat is used
1181 = do { traceTc "tcTyVar2a" (ppr tc_tc $$ ppr tc_kind)
1182 ; return (mkNakedTyConApp tc [], tc_kind) }
1183
1184 | otherwise
1185 = do { (tc_args, kind) <- instantiateTyN Nothing (length (tyConBinders tc_tc))
1186 tc_kind_bndrs tc_inner_ki
1187 ; let tc_ty = mkNakedTyConApp tc tc_args
1188 -- tc and tc_ty must not be traced here, because that would
1189 -- force the evaluation of a potentially knot-tied variable (tc),
1190 -- and the typechecker would hang, as per #11708
1191 ; traceTc "tcTyVar2b" (vcat [ ppr tc_tc <+> dcolon <+> ppr tc_kind
1192 , ppr kind ])
1193 ; return (tc_ty, kind) }
1194 where
1195 tc_kind = tyConKind tc_tc
1196 (tc_kind_bndrs, tc_inner_ki) = splitPiTysInvisible tc_kind
1197
1198 get_loopy_tc :: Name -> TyCon -> TcM TyCon
1199 -- Return the knot-tied global TyCon if there is one
1200 -- Otherwise the local TcTyCon; we must be doing kind checking
1201 -- but we still want to return a TyCon of some sort to use in
1202 -- error messages
1203 get_loopy_tc name tc_tc
1204 = do { env <- getGblEnv
1205 ; case lookupNameEnv (tcg_type_env env) name of
1206 Just (ATyCon tc) -> return tc
1207 _ -> do { traceTc "lk1 (loopy)" (ppr name)
1208 ; return tc_tc } }
1209
1210 -- We cannot promote a data constructor with a context that contains
1211 -- constraints other than equalities, so error if we find one.
1212 -- See Note [Constraints handled in types] in Inst.
1213 dc_theta_illegal_constraint :: ThetaType -> Maybe PredType
1214 dc_theta_illegal_constraint = find go
1215 where
1216 go :: PredType -> Bool
1217 go pred | Just tc <- tyConAppTyCon_maybe pred
1218 = not $ tc `hasKey` eqTyConKey
1219 || tc `hasKey` heqTyConKey
1220 | otherwise = True
1221
1222 {-
1223 Note [Type-checking inside the knot]
1224 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1225 Suppose we are checking the argument types of a data constructor. We
1226 must zonk the types before making the DataCon, because once built we
1227 can't change it. So we must traverse the type.
1228
1229 BUT the parent TyCon is knot-tied, so we can't look at it yet.
1230
1231 So we must be careful not to use "smart constructors" for types that
1232 look at the TyCon or Class involved.
1233
1234 * Hence the use of mkNakedXXX functions. These do *not* enforce
1235 the invariants (for example that we use (FunTy s t) rather
1236 than (TyConApp (->) [s,t])).
1237
1238 * The zonking functions establish invariants (even zonkTcType, a change from
1239 previous behaviour). So we must never inspect the result of a
1240 zonk that might mention a knot-tied TyCon. This is generally OK
1241 because we zonk *kinds* while kind-checking types. And the TyCons
1242 in kinds shouldn't be knot-tied, because they come from a previous
1243 mutually recursive group.
1244
1245 * TcHsSyn.zonkTcTypeToType also can safely check/establish
1246 invariants.
1247
1248 This is horribly delicate. I hate it. A good example of how
1249 delicate it is can be seen in Trac #7903.
1250
1251 Note [GADT kind self-reference]
1252 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1253
1254 A promoted type cannot be used in the body of that type's declaration.
1255 Trac #11554 shows this example, which made GHC loop:
1256
1257 import Data.Kind
1258 data P (x :: k) = Q
1259 data A :: Type where
1260 B :: forall (a :: A). P a -> A
1261
1262 In order to check the constructor B, we need to have the promoted type A, but in
1263 order to get that promoted type, B must first be checked. To prevent looping, a
1264 TyConPE promotion error is given when tcTyVar checks an ATcTyCon in kind mode.
1265 Any ATcTyCon is a TyCon being defined in the current recursive group (see data
1266 type decl for TcTyThing), and all such TyCons are illegal in kinds.
1267
1268 Trac #11962 proposes checking the head of a data declaration separately from
1269 its constructors. This would allow the example above to pass.
1270
1271 Note [Body kind of a HsForAllTy]
1272 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1273 The body of a forall is usually a type, but in principle
1274 there's no reason to prohibit *unlifted* types.
1275 In fact, GHC can itself construct a function with an
1276 unboxed tuple inside a for-all (via CPR analysis; see
1277 typecheck/should_compile/tc170).
1278
1279 Moreover in instance heads we get forall-types with
1280 kind Constraint.
1281
1282 It's tempting to check that the body kind is either * or #. But this is
1283 wrong. For example:
1284
1285 class C a b
1286 newtype N = Mk Foo deriving (C a)
1287
1288 We're doing newtype-deriving for C. But notice how `a` isn't in scope in
1289 the predicate `C a`. So we quantify, yielding `forall a. C a` even though
1290 `C a` has kind `* -> Constraint`. The `forall a. C a` is a bit cheeky, but
1291 convenient. Bottom line: don't check for * or # here.
1292
1293 Note [Body kind of a HsQualTy]
1294 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1295 If ctxt is non-empty, the HsQualTy really is a /function/, so the
1296 kind of the result really is '*', and in that case the kind of the
1297 body-type can be lifted or unlifted.
1298
1299 However, consider
1300 instance Eq a => Eq [a] where ...
1301 or
1302 f :: (Eq a => Eq [a]) => blah
1303 Here both body-kind of the HsQualTy is Constraint rather than *.
1304 Rather crudely we tell the difference by looking at exp_kind. It's
1305 very convenient to typecheck instance types like any other HsSigType.
1306
1307 Admittedly the '(Eq a => Eq [a]) => blah' case is erroneous, but it's
1308 better to reject in checkValidType. If we say that the body kind
1309 should be '*' we risk getting TWO error messages, one saying that Eq
1310 [a] doens't have kind '*', and one saying that we need a Constraint to
1311 the left of the outer (=>).
1312
1313 How do we figure out the right body kind? Well, it's a bit of a
1314 kludge: I just look at the expected kind. If it's Constraint, we
1315 must be in this instance situation context. It's a kludge because it
1316 wouldn't work if any unification was involved to compute that result
1317 kind -- but it isn't. (The true way might be to use the 'mode'
1318 parameter, but that seemed like a sledgehammer to crack a nut.)
1319
1320 Note [Inferring tuple kinds]
1321 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1322 Give a tuple type (a,b,c), which the parser labels as HsBoxedOrConstraintTuple,
1323 we try to figure out whether it's a tuple of kind * or Constraint.
1324 Step 1: look at the expected kind
1325 Step 2: infer argument kinds
1326
1327 If after Step 2 it's not clear from the arguments that it's
1328 Constraint, then it must be *. Once having decided that we re-check
1329 the Check the arguments again to give good error messages
1330 in eg. `(Maybe, Maybe)`
1331
1332 Note that we will still fail to infer the correct kind in this case:
1333
1334 type T a = ((a,a), D a)
1335 type family D :: Constraint -> Constraint
1336
1337 While kind checking T, we do not yet know the kind of D, so we will default the
1338 kind of T to * -> *. It works if we annotate `a` with kind `Constraint`.
1339
1340 Note [Desugaring types]
1341 ~~~~~~~~~~~~~~~~~~~~~~~
1342 The type desugarer is phase 2 of dealing with HsTypes. Specifically:
1343
1344 * It transforms from HsType to Type
1345
1346 * It zonks any kinds. The returned type should have no mutable kind
1347 or type variables (hence returning Type not TcType):
1348 - any unconstrained kind variables are defaulted to (Any *) just
1349 as in TcHsSyn.
1350 - there are no mutable type variables because we are
1351 kind-checking a type
1352 Reason: the returned type may be put in a TyCon or DataCon where
1353 it will never subsequently be zonked.
1354
1355 You might worry about nested scopes:
1356 ..a:kappa in scope..
1357 let f :: forall b. T '[a,b] -> Int
1358 In this case, f's type could have a mutable kind variable kappa in it;
1359 and we might then default it to (Any *) when dealing with f's type
1360 signature. But we don't expect this to happen because we can't get a
1361 lexically scoped type variable with a mutable kind variable in it. A
1362 delicate point, this. If it becomes an issue we might need to
1363 distinguish top-level from nested uses.
1364
1365 Moreover
1366 * it cannot fail,
1367 * it does no unifications
1368 * it does no validity checking, except for structural matters, such as
1369 (a) spurious ! annotations.
1370 (b) a class used as a type
1371
1372 Note [Kind of a type splice]
1373 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1374 Consider these terms, each with TH type splice inside:
1375 [| e1 :: Maybe $(..blah..) |]
1376 [| e2 :: $(..blah..) |]
1377 When kind-checking the type signature, we'll kind-check the splice
1378 $(..blah..); we want to give it a kind that can fit in any context,
1379 as if $(..blah..) :: forall k. k.
1380
1381 In the e1 example, the context of the splice fixes kappa to *. But
1382 in the e2 example, we'll desugar the type, zonking the kind unification
1383 variables as we go. When we encounter the unconstrained kappa, we
1384 want to default it to '*', not to (Any *).
1385
1386 Help functions for type applications
1387 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1388 -}
1389
1390 addTypeCtxt :: LHsType GhcRn -> TcM a -> TcM a
1391 -- Wrap a context around only if we want to show that contexts.
1392 -- Omit invisible ones and ones user's won't grok
1393 addTypeCtxt (L _ ty) thing
1394 = addErrCtxt doc thing
1395 where
1396 doc = text "In the type" <+> quotes (ppr ty)
1397
1398 {-
1399 ************************************************************************
1400 * *
1401 Type-variable binders
1402 %* *
1403 %************************************************************************
1404
1405 Note [Dependent LHsQTyVars]
1406 ~~~~~~~~~~~~~~~~~~~~~~~~~~~
1407 We track (in the renamer) which explicitly bound variables in a
1408 LHsQTyVars are manifestly dependent; only precisely these variables
1409 may be used within the LHsQTyVars. We must do this so that kcLHsQTyVars
1410 can produce the right TyConBinders, and tell Anon vs. Required.
1411
1412 Example data T k1 (a:k1) (b:k2) c
1413 = MkT (Proxy a) (Proxy b) (Proxy c)
1414
1415 Here
1416 (a:k1),(b:k2),(c:k3)
1417 are Anon (explicitly specified as a binder, not used
1418 in the kind of any other binder
1419 k1 is Required (explicitly specifed as a binder, but used
1420 in the kind of another binder i.e. dependently)
1421 k2 is Specified (not explicitly bound, but used in the kind
1422 of another binder)
1423 k3 in Inferred (not lexically in scope at all, but inferred
1424 by kind inference)
1425 and
1426 T :: forall {k3} k1. forall k3 -> k1 -> k2 -> k3 -> *
1427
1428 See Note [TyVarBndrs, TyVarBinders, TyConBinders, and visibility]
1429 in TyCoRep.
1430
1431 kcLHsQTyVars uses the hsq_dependent field to decide whether
1432 k1, a, b, c should be Required or Anon.
1433
1434 Earlier, thought it would work simply to do a free-variable check
1435 during kcLHsQTyVars, but this is bogus, because there may be
1436 unsolved equalities about. And we don't want to eagerly solve the
1437 equalities, because we may get further information after
1438 kcLHsQTyVars is called. (Recall that kcLHsQTyVars is called
1439 only from getInitialKind.)
1440 This is what implements the rule that all variables intended to be
1441 dependent must be manifestly so.
1442
1443 Sidenote: It's quite possible that later, we'll consider (t -> s)
1444 as a degenerate case of some (pi (x :: t) -> s) and then this will
1445 all get more permissive.
1446
1447 Note [Kind generalisation and SigTvs]
1448 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1449 Consider
1450 data T (a :: k1) x = MkT (S a ())
1451 data S (b :: k2) y = MkS (T b ())
1452
1453 While we are doing kind inference for the mutually-recursive S,T,
1454 we will end up unifying k1 and k2 together. So they can't be skolems.
1455 We therefore make them SigTvs, which can unify with type variables,
1456 but not with general types. All this is very similar at the level
1457 of terms: see Note [Quantified variables in partial type signatures]
1458 in TcBinds.
1459
1460 There are some wrinkles
1461
1462 * We always want to kind-generalise over SigTvs, and /not/ default
1463 them to Type. Another way to say this is: a SigTV should /never/
1464 stand for a type, even via defaulting. Hence the check in
1465 TcSimplify.defaultTyVarTcS, and TcMType.defaultTyVar. Here's
1466 another example (Trac #14555):
1467 data Exp :: [TYPE rep] -> TYPE rep -> Type where
1468 Lam :: Exp (a:xs) b -> Exp xs (a -> b)
1469 We want to kind-generalise over the 'rep' variable.
1470 Trac #14563 is another example.
1471
1472 * Consider Trac #11203
1473 data SameKind :: k -> k -> *
1474 data Q (a :: k1) (b :: k2) c = MkQ (SameKind a b)
1475 Here we will unify k1 with k2, but this time doing so is an error,
1476 because k1 and k2 are bound in the same delcaration.
1477
1478 We sort this out using findDupSigTvs, in TcTyClTyVars; very much
1479 as we do with partial type signatures in mk_psig_qtvs in
1480 TcBinds.chooseInferredQuantifiers
1481
1482 Note [Keeping scoped variables in order: Explicit]
1483 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1484 When the user writes `forall a b c. blah`, we bring a, b, and c into
1485 scope and then check blah. In the process of checking blah, we might
1486 learn the kinds of a, b, and c, and these kinds might indicate that
1487 b depends on c, and thus that we should reject the user-written type.
1488
1489 One approach to doing this would be to bring each of a, b, and c into
1490 scope, one at a time, creating an implication constraint and
1491 bumping the TcLevel for each one. This would work, because the kind
1492 of, say, b would be untouchable when c is in scope (and the constraint
1493 couldn't float out because c blocks it). However, it leads to terrible
1494 error messages, complaining about skolem escape. While it is indeed
1495 a problem of skolem escape, we can do better.
1496
1497 Instead, our approach is to bring the block of variables into scope
1498 all at once, creating one implication constraint for the lot. The
1499 user-written variables are skolems in the implication constraint. In
1500 TcSimplify.setImplicationStatus, we check to make sure that the ordering
1501 is correct, choosing ImplicationStatus IC_BadTelescope if they aren't.
1502 Then, in TcErrors, we report if there is a bad telescope. This way,
1503 we can report a suggested ordering to the user if there is a problem.
1504
1505 Note [Keeping scoped variables in order: Implicit]
1506 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1507 When the user implicitly quantifies over variables (say, in a type
1508 signature), we need to come up with some ordering on these variables.
1509 This is done by bumping the TcLevel, bringing the tyvars into scope,
1510 and then type-checking the thing_inside. The constraints are all
1511 wrapped in an implication, which is then solved. Finally, we can
1512 zonk all the binders and then order them with toposortTyVars.
1513
1514 It's critical to solve before zonking and ordering in order to uncover
1515 any unifications. You might worry that this eager solving could cause
1516 trouble elsewhere. I don't think it will. Because it will solve only
1517 in an increased TcLevel, it can't unify anything that was mentioned
1518 elsewhere. Additionally, we require that the order of implicitly
1519 quantified variables is manifest by the scope of these variables, so
1520 we're not going to learn more information later that will help order
1521 these variables.
1522
1523 Note [Recipe for checking a signature]
1524 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1525 Checking a user-written signature requires several steps:
1526
1527 1. Generate constraints.
1528 2. Solve constraints.
1529 3. Zonk and promote tyvars.
1530 4. (Optional) Kind-generalize.
1531 5. Check validity.
1532
1533 There may be some surprises in here:
1534
1535 Step 2 is necessary for two reasons: most signatures also bring
1536 implicitly quantified variables into scope, and solving is necessary
1537 to get these in the right order (see Note [Keeping scoped variables in
1538 order: Implicit]). Additionally, solving is necessary in order to
1539 kind-generalize correctly.
1540
1541 Step 3 requires *promoting* type variables. If there are any foralls
1542 in a type, the TcLevel will be bumped within the forall. This might
1543 lead to the generation of matavars with a high level. If we don't promote,
1544 we violate MetaTvInv of Note [TcLevel and untouchable type variables]
1545 in TcType.
1546
1547 -}
1548
1549 tcWildCardBinders :: SkolemInfo
1550 -> [Name]
1551 -> ([(Name, TcTyVar)] -> TcM a)
1552 -> TcM a
1553 tcWildCardBinders info = tcWildCardBindersX new_tv (Just info)
1554 where
1555 new_tv name = do { kind <- newMetaKindVar
1556 ; newSkolemTyVar name kind }
1557
1558 tcWildCardBindersX :: (Name -> TcM TcTyVar)
1559 -> Maybe SkolemInfo -- Just <=> we're bringing fresh vars
1560 -- into scope; use scopeTyVars
1561 -> [Name]
1562 -> ([(Name, TcTyVar)] -> TcM a)
1563 -> TcM a
1564 tcWildCardBindersX new_wc maybe_skol_info wc_names thing_inside
1565 = do { wcs <- mapM new_wc wc_names
1566 ; let wc_prs = wc_names `zip` wcs
1567 ; scope_tvs wc_prs $
1568 thing_inside wc_prs }
1569 where
1570 scope_tvs
1571 | Just info <- maybe_skol_info = scopeTyVars2 info
1572 | otherwise = tcExtendNameTyVarEnv
1573
1574 -- | Kind-check a 'LHsQTyVars'. If the decl under consideration has a complete,
1575 -- user-supplied kind signature (CUSK), generalise the result.
1576 -- Used in 'getInitialKind' (for tycon kinds and other kinds)
1577 -- and in kind-checking (but not for tycon kinds, which are checked with
1578 -- tcTyClDecls). See also Note [Complete user-supplied kind signatures] in
1579 -- HsDecls.
1580 --
1581 -- This function does not do telescope checking.
1582 kcLHsQTyVars :: Name -- ^ of the thing being checked
1583 -> TyConFlavour -- ^ What sort of 'TyCon' is being checked
1584 -> Bool -- ^ True <=> the decl being checked has a CUSK
1585 -> LHsQTyVars GhcRn
1586 -> TcM (Kind, r) -- ^ The result kind, possibly with other info
1587 -> TcM (TcTyCon, r) -- ^ A suitably-kinded TcTyCon
1588 kcLHsQTyVars name flav cusk
1589 user_tyvars@(HsQTvs { hsq_ext = HsQTvsRn { hsq_implicit = kv_ns
1590 , hsq_dependent = dep_names }
1591 , hsq_explicit = hs_tvs }) thing_inside
1592 | cusk
1593 = do { (scoped_kvs, (tc_tvs, (res_kind, stuff)))
1594 <- solveEqualities $
1595 tcImplicitQTKBndrs skol_info kv_ns $
1596 kcLHsQTyVarBndrs cusk open_fam skol_info hs_tvs thing_inside
1597
1598 -- Now, because we're in a CUSK, quantify over the mentioned
1599 -- kind vars, in dependency order.
1600 ; let tc_binders_unzonked = zipWith mk_tc_binder hs_tvs tc_tvs
1601 ; dvs <- zonkTcTypeAndSplitDepVars (mkSpecForAllTys scoped_kvs $
1602 mkTyConKind tc_binders_unzonked res_kind)
1603 ; qkvs <- quantifyTyVars emptyVarSet dvs
1604 -- don't call tcGetGlobalTyCoVars. For associated types, it gets the
1605 -- tyvars from the enclosing class -- but that's wrong. We *do* want
1606 -- to quantify over those tyvars.
1607
1608 ; scoped_kvs <- mapM zonkTcTyVarToTyVar scoped_kvs
1609 ; tc_tvs <- mapM zonkTcTyVarToTyVar tc_tvs
1610 ; res_kind <- zonkTcType res_kind
1611 ; let tc_binders = zipWith mk_tc_binder hs_tvs tc_tvs
1612
1613 -- If any of the scoped_kvs aren't actually mentioned in a binder's
1614 -- kind (or the return kind), then we're in the CUSK case from
1615 -- Note [Free-floating kind vars]
1616 ; let all_tc_tvs = scoped_kvs ++ tc_tvs
1617 all_mentioned_tvs = mapUnionVarSet (tyCoVarsOfType . tyVarKind)
1618 all_tc_tvs
1619 `unionVarSet` tyCoVarsOfType res_kind
1620 unmentioned_kvs = filterOut (`elemVarSet` all_mentioned_tvs)
1621 scoped_kvs
1622 ; reportFloatingKvs name flav all_tc_tvs unmentioned_kvs
1623
1624 ; let final_binders = map (mkNamedTyConBinder Inferred) qkvs
1625 ++ map (mkNamedTyConBinder Specified) scoped_kvs
1626 ++ tc_binders
1627 tycon = mkTcTyCon name (ppr user_tyvars) final_binders res_kind
1628 (mkTyVarNamePairs (scoped_kvs ++ tc_tvs))
1629 flav
1630 -- the tvs contain the binders already
1631 -- in scope from an enclosing class, but
1632 -- re-adding tvs to the env't doesn't cause
1633 -- harm
1634
1635 ; traceTc "kcLHsQTyVars: cusk" $
1636 vcat [ ppr name, ppr kv_ns, ppr hs_tvs, ppr dep_names
1637 , ppr tc_tvs, ppr (mkTyConKind final_binders res_kind)
1638 , ppr qkvs, ppr final_binders ]
1639
1640 ; return (tycon, stuff) }
1641
1642 | otherwise
1643 = do { (scoped_kvs, (tc_tvs, (res_kind, stuff)))
1644 -- Why kcImplicitTKBndrs which uses newSigTyVar?
1645 -- See Note [Kind generalisation and sigTvs]
1646 <- kcImplicitTKBndrs kv_ns $
1647 kcLHsQTyVarBndrs cusk open_fam skol_info hs_tvs thing_inside
1648
1649 ; let -- NB: Don't add scoped_kvs to tyConTyVars, because they
1650 -- must remain lined up with the binders
1651 tc_binders = zipWith mk_tc_binder hs_tvs tc_tvs
1652 tycon = mkTcTyCon name (ppr user_tyvars) tc_binders res_kind
1653 (mkTyVarNamePairs (scoped_kvs ++ tc_tvs))
1654 flav
1655
1656 ; traceTc "kcLHsQTyVars: not-cusk" $
1657 vcat [ ppr name, ppr kv_ns, ppr hs_tvs, ppr dep_names
1658 , ppr tc_tvs, ppr (mkTyConKind tc_binders res_kind) ]
1659 ; return (tycon, stuff) }
1660 where
1661 open_fam = tcFlavourIsOpen flav
1662 skol_info = TyConSkol flav name
1663
1664 mk_tc_binder :: LHsTyVarBndr GhcRn -> TyVar -> TyConBinder
1665 -- See Note [Dependent LHsQTyVars]
1666 mk_tc_binder hs_tv tv
1667 | hsLTyVarName hs_tv `elemNameSet` dep_names
1668 = mkNamedTyConBinder Required tv
1669 | otherwise
1670 = mkAnonTyConBinder tv
1671
1672 kcLHsQTyVars _ _ _ (XLHsQTyVars _) _ = panic "kcLHsQTyVars"
1673
1674 kcLHsQTyVarBndrs :: Bool -- True <=> bump the TcLevel when bringing vars into scope
1675 -> Bool -- True <=> Default un-annotated tyvar
1676 -- binders to kind *
1677 -> SkolemInfo
1678 -> [LHsTyVarBndr GhcRn]
1679 -> TcM r
1680 -> TcM ([TyVar], r)
1681 -- There may be dependency between the explicit "ty" vars.
1682 -- So, we have to handle them one at a time.
1683 kcLHsQTyVarBndrs _ _ _ [] thing
1684 = do { stuff <- thing; return ([], stuff) }
1685
1686 kcLHsQTyVarBndrs cusk open_fam skol_info (L _ hs_tv : hs_tvs) thing
1687 = do { tv_pair@(tv, _) <- kc_hs_tv hs_tv
1688 -- NB: Bring all tvs into scope, even non-dependent ones,
1689 -- as they're needed in type synonyms, data constructors, etc.
1690
1691 ; (tvs, stuff) <- bind_unless_scoped tv_pair $
1692 kcLHsQTyVarBndrs cusk open_fam skol_info hs_tvs $
1693 thing
1694
1695 ; return ( tv : tvs, stuff ) }
1696 where
1697 -- | Bind the tyvar in the env't unless the bool is True
1698 bind_unless_scoped :: (TcTyVar, Bool) -> TcM a -> TcM a
1699 bind_unless_scoped (_, True) thing_inside = thing_inside
1700 bind_unless_scoped (tv, False) thing_inside
1701 | cusk = scopeTyVars skol_info [tv] thing_inside
1702 | otherwise = tcExtendTyVarEnv [tv] thing_inside
1703 -- These variables haven't settled down yet, so we don't want to bump
1704 -- the TcLevel. If we do, then we'll have metavars of too high a level
1705 -- floating about. Changing this causes many, many failures in the
1706 -- `dependent` testsuite directory.
1707
1708 kc_hs_tv :: HsTyVarBndr GhcRn -> TcM (TcTyVar, Bool)
1709 -- Special handling for the case where the binder is already in scope
1710 -- See Note [Associated type tyvar names] in Class and
1711 -- Note [TyVar binders for associated decls] in HsDecls
1712 kc_hs_tv (UserTyVar _ (L _ name))
1713 = do { mb_tv <- tcLookupLcl_maybe name
1714 ; case mb_tv of -- See Note [TyVar binders for associated decls]
1715 Just (ATyVar _ tv) -> return (tv, True)
1716 _ -> do { kind <- if open_fam
1717 then return liftedTypeKind
1718 else newMetaKindVar
1719 -- Open type/data families default their variables
1720 -- variables to kind *. But don't default in-scope
1721 -- class tyvars, of course
1722 ; tv <- newSkolemTyVar name kind
1723 ; return (tv, False) } }
1724
1725 kc_hs_tv (KindedTyVar _ lname@(L _ name) lhs_kind)
1726 = do { kind <- tcLHsKindSig (TyVarBndrKindCtxt name) lhs_kind
1727 ; mb_tv <- tcLookupLcl_maybe name
1728 ; case mb_tv of
1729 Just (ATyVar _ tv)
1730 -> do { discardResult $
1731 unifyKind (Just (HsTyVar noExt NotPromoted lname))
1732 kind (tyVarKind tv)
1733 ; return (tv, True) }
1734 _ -> do { tv <- newSkolemTyVar name kind
1735 ; return (tv, False) } }
1736
1737 kc_hs_tv (XTyVarBndr{}) = panic "kc_hs_tv"
1738
1739 {- Note [Kind-checking tyvar binders for associated types]
1740 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1741 When kind-checking the type-variable binders for associated
1742 data/newtype decls
1743 family decls
1744 we behave specially for type variables that are already in scope;
1745 that is, bound by the enclosing class decl. This is done in
1746 kcLHsQTyVarBndrs:
1747 * The use of tcImplicitQTKBndrs
1748 * The tcLookupLocal_maybe code in kc_hs_tv
1749
1750 See Note [Associated type tyvar names] in Class and
1751 Note [TyVar binders for associated decls] in HsDecls
1752
1753 We must do the same for family instance decls, where the in-scope
1754 variables may be bound by the enclosing class instance decl.
1755 Hence the use of tcImplicitQTKBndrs in tcFamTyPats.
1756 -}
1757
1758
1759 --------------------------------------
1760 -- Implicit binders
1761 --------------------------------------
1762
1763 -- | Bring implicitly quantified type/kind variables into scope during
1764 -- kind checking. Uses SigTvs, as per Note [Use SigTvs in kind-checking pass]
1765 -- in TcTyClsDecls.
1766 kcImplicitTKBndrs :: [Name] -- of the vars
1767 -> TcM a
1768 -> TcM ([TcTyVar], a) -- returns the tyvars created
1769 -- these are *not* dependency ordered
1770 kcImplicitTKBndrs var_ns thing_inside
1771 = do { tkvs <- mapM newFlexiKindedSigTyVar var_ns
1772 ; result <- tcExtendTyVarEnv tkvs thing_inside
1773 ; return (tkvs, result) }
1774
1775
1776 tcImplicitTKBndrs, tcImplicitTKBndrsSig, tcImplicitQTKBndrs
1777 :: SkolemInfo
1778 -> [Name]
1779 -> TcM a
1780 -> TcM ([TcTyVar], a)
1781 tcImplicitTKBndrs = tcImplicitTKBndrsX newFlexiKindedSkolemTyVar
1782 tcImplicitTKBndrsSig = tcImplicitTKBndrsX newFlexiKindedSigTyVar
1783 tcImplicitQTKBndrs = tcImplicitTKBndrsX newFlexiKindedQTyVar
1784
1785 tcImplicitTKBndrsX :: (Name -> TcM TcTyVar) -- new_tv function
1786 -> SkolemInfo
1787 -> [Name]
1788 -> TcM a
1789 -> TcM ([TcTyVar], a) -- these tyvars are dependency-ordered
1790 -- * Guarantees to call solveLocalEqualities to unify
1791 -- all constraints from thing_inside.
1792 --
1793 -- * Returned TcTyVars have the supplied HsTyVarBndrs,
1794 -- but may be in different order to the original [Name]
1795 -- (because of sorting to respect dependency)
1796 --
1797 -- * Returned TcTyVars have zonked kinds
1798 -- See Note [Keeping scoped variables in order: Implicit]
1799 tcImplicitTKBndrsX new_tv skol_info tv_names thing_inside
1800 | null tv_names -- Short cut for the common case where there
1801 -- are no implicit type variables to bind
1802 = do { result <- solveLocalEqualities thing_inside
1803 ; return ([], result) }
1804
1805 | otherwise
1806 = do { (skol_tvs, result)
1807 <- solveLocalEqualities $
1808 checkTvConstraints skol_info Nothing $
1809 do { tkvs <- mapM new_tv tv_names
1810 ; result <- tcExtendTyVarEnv tkvs thing_inside
1811 ; return (tkvs, result) }
1812
1813 ; skol_tvs <- mapM zonkTcTyCoVarBndr skol_tvs
1814 -- use zonkTcTyCoVarBndr because a skol_tv might be a SigTv
1815
1816 ; let final_tvs = toposortTyVars skol_tvs
1817 ; traceTc "tcImplicitTKBndrs" (ppr tv_names $$ ppr final_tvs)
1818 ; return (final_tvs, result) }
1819
1820 newFlexiKindedQTyVar :: Name -> TcM TcTyVar
1821 -- Make a new skolem for an implicit binder in a type/class/type
1822 -- instance declaration, with a flexi-kind
1823 -- But check for in-scope-ness, and if so return that instead
1824 newFlexiKindedQTyVar name
1825 = do { mb_tv <- tcLookupLcl_maybe name
1826 ; case mb_tv of
1827 Just (ATyVar _ tv) -> return tv
1828 _ -> newFlexiKindedSkolemTyVar name }
1829
1830 newFlexiKindedTyVar :: (Name -> Kind -> TcM TyVar) -> Name -> TcM TyVar
1831 newFlexiKindedTyVar new_tv name
1832 = do { kind <- newMetaKindVar
1833 ; new_tv name kind }
1834
1835 newFlexiKindedSkolemTyVar :: Name -> TcM TyVar
1836 newFlexiKindedSkolemTyVar = newFlexiKindedTyVar newSkolemTyVar
1837
1838 newFlexiKindedSigTyVar :: Name -> TcM TyVar
1839 newFlexiKindedSigTyVar = newFlexiKindedTyVar newSigTyVar
1840
1841 --------------------------------------
1842 -- Explicit binders
1843 --------------------------------------
1844
1845 -- | Used during the "kind-checking" pass in TcTyClsDecls only,
1846 -- and even then only for data-con declarations.
1847 -- See Note [Use SigTvs in kind-checking pass] in TcTyClsDecls
1848 kcExplicitTKBndrs :: [LHsTyVarBndr GhcRn]
1849 -> TcM a
1850 -> TcM a
1851 kcExplicitTKBndrs [] thing_inside = thing_inside
1852 kcExplicitTKBndrs (L _ hs_tv : hs_tvs) thing_inside
1853 = do { tv <- tcHsTyVarBndr newSigTyVar hs_tv
1854 ; tcExtendTyVarEnv [tv] $
1855 kcExplicitTKBndrs hs_tvs thing_inside }
1856
1857 tcExplicitTKBndrs :: SkolemInfo
1858 -> [LHsTyVarBndr GhcRn]
1859 -> TcM a
1860 -> TcM ([TcTyVar], a)
1861 tcExplicitTKBndrs skol_info hs_tvs thing_inside
1862 -- Used for the forall'd binders in type signatures of various kinds:
1863 -- - function signatures
1864 -- - data con signatures in GADT-style decls
1865 -- - pattern synonym signatures
1866 -- - expression type signatures
1867 --
1868 -- Specifically NOT used for the binders of a data type
1869 -- or type family decl. So the forall'd variables always /shadow/
1870 -- anything already in scope, and the complications of
1871 -- tcHsQTyVarName to not apply.
1872 --
1873 -- This function brings into scope a telescope of binders as written by
1874 -- the user. At first blush, it would then seem that we should bring
1875 -- them into scope one at a time, bumping the TcLevel each time.
1876 -- (Recall that we bump the level to prevent skolem escape from happening.)
1877 -- However, this leads to terrible error messages, because we end up
1878 -- failing to unify with some `k0`. Better would be to allow type inference
1879 -- to work, potentially creating a skolem-escape problem, and then to
1880 -- notice that the telescope is out of order. That's what we do here,
1881 -- following the logic of tcImplicitTKBndrsX.
1882 -- See also Note [Keeping scoped variables in order: Explicit]
1883 --
1884 -- No cloning: returned TyVars have the same Name as the incoming LHsTyVarBndrs
1885 | null hs_tvs -- Short cut that avoids creating an implication
1886 -- constraint in the common case where none is needed
1887 = do { result <- thing_inside
1888 ; return ([], result) }
1889
1890 | otherwise
1891 = do { (skol_tvs, result) <- checkTvConstraints skol_info (Just doc) $
1892 bind_tvbs hs_tvs
1893
1894 ; traceTc "tcExplicitTKBndrs" $
1895 vcat [ text "Hs vars:" <+> ppr hs_tvs
1896 , text "tvs:" <+> pprTyVars skol_tvs ]
1897
1898 ; return (skol_tvs, result) }
1899
1900 where
1901 bind_tvbs [] = do { result <- thing_inside
1902 ; return ([], result) }
1903 bind_tvbs (L _ tvb : tvbs)
1904 = do { tv <- tcHsTyVarBndr newSkolemTyVar tvb
1905 ; tcExtendTyVarEnv [tv] $
1906 do { (tvs, result) <- bind_tvbs tvbs
1907 ; return (tv : tvs, result) }}
1908
1909 doc = sep (map ppr hs_tvs)
1910
1911 -----------------
1912 tcHsTyVarBndr :: (Name -> Kind -> TcM TyVar)
1913 -> HsTyVarBndr GhcRn -> TcM TcTyVar
1914 -- Return a TcTyVar, built using the provided function
1915 -- Typically the Kind inside the HsTyVarBndr will be a tyvar
1916 -- with a mutable kind in it.
1917 --
1918 -- Returned TcTyVar has the same name; no cloning
1919 tcHsTyVarBndr new_tv (UserTyVar _ (L _ tv_nm))
1920 = newFlexiKindedTyVar new_tv tv_nm
1921 tcHsTyVarBndr new_tv (KindedTyVar _ (L _ tv_nm) lhs_kind)
1922 = do { kind <- tcLHsKindSig (TyVarBndrKindCtxt tv_nm) lhs_kind
1923 ; new_tv tv_nm kind }
1924 tcHsTyVarBndr _ (XTyVarBndr _) = panic "tcHsTyVarBndr"
1925
1926 -----------------
1927 newWildTyVar :: Name -> TcM TcTyVar
1928 -- ^ New unification variable for a wildcard
1929 newWildTyVar _name
1930 = do { kind <- newMetaKindVar
1931 ; uniq <- newUnique
1932 ; details <- newMetaDetails TauTv
1933 ; let name = mkSysTvName uniq (fsLit "w")
1934 tyvar = (mkTcTyVar name kind details)
1935 ; traceTc "newWildTyVar" (ppr tyvar)
1936 ; return tyvar }
1937
1938 --------------------------
1939 -- Bringing tyvars into scope
1940 --------------------------
1941
1942 -- | Bring tyvars into scope, wrapping the thing_inside in an implication
1943 -- constraint. The implication constraint is necessary to provide SkolemInfo
1944 -- for the tyvars and to ensure that no unification variables made outside
1945 -- the scope of these tyvars (i.e. lower TcLevel) unify with the locally-scoped
1946 -- tyvars (i.e. higher TcLevel).
1947 --
1948 -- INVARIANT: The thing_inside must check only types, never terms.
1949 --
1950 -- Use this (not tcExtendTyVarEnv) wherever you expect a Λ or ∀ in Core.
1951 -- Use tcExtendTyVarEnv otherwise.
1952 scopeTyVars :: SkolemInfo -> [TcTyVar] -> TcM a -> TcM a
1953 scopeTyVars skol_info tvs = scopeTyVars2 skol_info [(tyVarName tv, tv) | tv <- tvs]
1954
1955 -- | Like 'scopeTyVars', but allows you to specify different scoped names
1956 -- than the Names stored within the tyvars.
1957 scopeTyVars2 :: SkolemInfo -> [(Name, TcTyVar)] -> TcM a -> TcM a
1958 scopeTyVars2 skol_info prs thing_inside
1959 = fmap snd $ -- discard the TcEvBinds, which will always be empty
1960 checkConstraints skol_info (map snd prs) [{- no EvVars -}] $
1961 tcExtendNameTyVarEnv prs $
1962 thing_inside
1963
1964 ------------------
1965 kindGeneralize :: TcType -> TcM [KindVar]
1966 -- Quantify the free kind variables of a kind or type
1967 -- In the latter case the type is closed, so it has no free
1968 -- type variables. So in both cases, all the free vars are kind vars
1969 -- Input must be zonked.
1970 -- NB: You must call solveEqualities or solveLocalEqualities before
1971 -- kind generalization
1972 kindGeneralize kind_or_type
1973 = do { let kvs = tyCoVarsOfTypeDSet kind_or_type
1974 dvs = DV { dv_kvs = kvs, dv_tvs = emptyDVarSet }
1975 ; gbl_tvs <- tcGetGlobalTyCoVars -- Already zonked
1976 ; quantifyTyVars gbl_tvs dvs }
1977
1978 {-
1979 Note [Kind generalisation]
1980 ~~~~~~~~~~~~~~~~~~~~~~~~~~
1981 We do kind generalisation only at the outer level of a type signature.
1982 For example, consider
1983 T :: forall k. k -> *
1984 f :: (forall a. T a -> Int) -> Int
1985 When kind-checking f's type signature we generalise the kind at
1986 the outermost level, thus:
1987 f1 :: forall k. (forall (a:k). T k a -> Int) -> Int -- YES!
1988 and *not* at the inner forall:
1989 f2 :: (forall k. forall (a:k). T k a -> Int) -> Int -- NO!
1990 Reason: same as for HM inference on value level declarations,
1991 we want to infer the most general type. The f2 type signature
1992 would be *less applicable* than f1, because it requires a more
1993 polymorphic argument.
1994
1995 NB: There are no explicit kind variables written in f's signature.
1996 When there are, the renamer adds these kind variables to the list of
1997 variables bound by the forall, so you can indeed have a type that's
1998 higher-rank in its kind. But only by explicit request.
1999
2000 Note [Kinds of quantified type variables]
2001 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2002 tcTyVarBndrsGen quantifies over a specified list of type variables,
2003 *and* over the kind variables mentioned in the kinds of those tyvars.
2004
2005 Note that we must zonk those kinds (obviously) but less obviously, we
2006 must return type variables whose kinds are zonked too. Example
2007 (a :: k7) where k7 := k9 -> k9
2008 We must return
2009 [k9, a:k9->k9]
2010 and NOT
2011 [k9, a:k7]
2012 Reason: we're going to turn this into a for-all type,
2013 forall k9. forall (a:k7). blah
2014 which the type checker will then instantiate, and instantiate does not
2015 look through unification variables!
2016
2017 Hence using zonked_kinds when forming tvs'.
2018
2019 Note [Free-floating kind vars]
2020 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2021 Consider
2022
2023 data T = MkT (forall (a :: k). Proxy a)
2024 -- from test ghci/scripts/T7873
2025
2026 This is not an existential datatype, but a higher-rank one (the forall
2027 to the right of MkT). Also consider
2028
2029 data S a = MkS (Proxy (a :: k))
2030
2031 According to the rules around implicitly-bound kind variables, in both
2032 cases those k's scope over the whole declaration. The renamer grabs
2033 it and adds it to the hsq_implicits field of the HsQTyVars of the
2034 tycon. So it must be in scope during type-checking, but we want to
2035 reject T while accepting S.
2036
2037 Why reject T? Because the kind variable isn't fixed by anything. For
2038 a variable like k to be implicit, it needs to be mentioned in the kind
2039 of a tycon tyvar. But it isn't.
2040
2041 Why accept S? Because kind inference tells us that a has kind k, so it's
2042 all OK.
2043
2044 Our approach depends on whether or not the datatype has a CUSK.
2045
2046 Non-CUSK: In the first pass (kcTyClTyVars) we just bring
2047 k into scope. In the second pass (tcTyClTyVars),
2048 we check to make sure that k has been unified with some other variable
2049 (or generalized over, making k into a skolem). If it hasn't been, then
2050 it must be a free-floating kind var. Error.
2051
2052 CUSK: When we determine the tycon's final, never-to-be-changed kind
2053 in kcLHsQTyVars, we check to make sure all implicitly-bound kind
2054 vars are indeed mentioned in a kind somewhere. If not, error.
2055
2056 We also perform free-floating kind var analysis for type family instances
2057 (see #13985). Here is an interesting example:
2058
2059 type family T :: k
2060 type instance T = (Nothing :: Maybe a)
2061
2062 Upon a cursory glance, it may appear that the kind variable `a` is
2063 free-floating above, since there are no (visible) LHS patterns in `T`. However,
2064 there is an *invisible* pattern due to the return kind, so inside of GHC, the
2065 instance looks closer to this:
2066
2067 type family T @k :: k
2068 type instance T @(Maybe a) = (Nothing :: Maybe a)
2069
2070 Here, we can see that `a` really is bound by a LHS type pattern, so `a` is in
2071 fact not free-floating. Contrast that with this example:
2072
2073 type instance T = Proxy (Nothing :: Maybe a)
2074
2075 This would looks like this inside of GHC:
2076
2077 type instance T @(*) = Proxy (Nothing :: Maybe a)
2078
2079 So this time, `a` is neither bound by a visible nor invisible type pattern on
2080 the LHS, so it would be reported as free-floating.
2081
2082 Finally, here's one more brain-teaser (from #9574). In the example below:
2083
2084 class Funct f where
2085 type Codomain f :: *
2086 instance Funct ('KProxy :: KProxy o) where
2087 type Codomain 'KProxy = NatTr (Proxy :: o -> *)
2088
2089 As it turns out, `o` is not free-floating in this example. That is because `o`
2090 bound by the kind signature of the LHS type pattern 'KProxy. To make this more
2091 obvious, one can also write the instance like so:
2092
2093 instance Funct ('KProxy :: KProxy o) where
2094 type Codomain ('KProxy :: KProxy o) = NatTr (Proxy :: o -> *)
2095
2096 -}
2097
2098 --------------------
2099 -- getInitialKind has made a suitably-shaped kind for the type or class
2100 -- Look it up in the local environment. This is used only for tycons
2101 -- that we're currently type-checking, so we're sure to find a TcTyCon.
2102 kcLookupTcTyCon :: Name -> TcM TcTyCon
2103 kcLookupTcTyCon nm
2104 = do { tc_ty_thing <- tcLookup nm
2105 ; return $ case tc_ty_thing of
2106 ATcTyCon tc -> tc
2107 _ -> pprPanic "kcLookupTcTyCon" (ppr tc_ty_thing) }
2108
2109 -----------------------
2110 -- | Bring tycon tyvars into scope. This is used during the "kind-checking"
2111 -- pass in TcTyClsDecls. (Never in getInitialKind, never in the
2112 -- "type-checking"/desugaring pass.)
2113 -- Never emits constraints, though the thing_inside might.
2114 kcTyClTyVars :: Name -> TcM a -> TcM a
2115 kcTyClTyVars tycon_name thing_inside
2116 -- See Note [Use SigTvs in kind-checking pass] in TcTyClsDecls
2117 = do { tycon <- kcLookupTcTyCon tycon_name
2118 ; tcExtendNameTyVarEnv (tcTyConScopedTyVars tycon) $ thing_inside }
2119
2120 tcTyClTyVars :: Name
2121 -> ([TyConBinder] -> Kind -> TcM a) -> TcM a
2122 -- ^ Used for the type variables of a type or class decl
2123 -- on the second full pass (type-checking/desugaring) in TcTyClDecls.
2124 -- This is *not* used in the initial-kind run, nor in the "kind-checking" pass.
2125 -- Accordingly, everything passed to the continuation is fully zonked.
2126 --
2127 -- (tcTyClTyVars T [a,b] thing_inside)
2128 -- where T : forall k1 k2 (a:k1 -> *) (b:k1). k2 -> *
2129 -- calls thing_inside with arguments
2130 -- [k1,k2,a,b] [k1:*, k2:*, Anon (k1 -> *), Anon k1] (k2 -> *)
2131 -- having also extended the type environment with bindings
2132 -- for k1,k2,a,b
2133 --
2134 -- Never emits constraints.
2135 --
2136 -- The LHsTyVarBndrs is always user-written, and the full, generalised
2137 -- kind of the tycon is available in the local env.
2138 tcTyClTyVars tycon_name thing_inside
2139 = do { tycon <- kcLookupTcTyCon tycon_name
2140
2141 -- Do checks on scoped tyvars
2142 -- See Note [Free-floating kind vars]
2143 ; let flav = tyConFlavour tycon
2144 scoped_prs = tcTyConScopedTyVars tycon
2145 scoped_tvs = map snd scoped_prs
2146 still_sig_tvs = filter isSigTyVar scoped_tvs
2147
2148 ; mapM_ report_sig_tv_err (findDupSigTvs scoped_prs)
2149
2150 ; checkNoErrs $ reportFloatingKvs tycon_name flav
2151 scoped_tvs still_sig_tvs
2152
2153 ; let res_kind = tyConResKind tycon
2154 binders = correct_binders (tyConBinders tycon) res_kind
2155 ; traceTc "tcTyClTyVars" (ppr tycon_name <+> ppr binders)
2156 ; scopeTyVars2 (TyConSkol flav tycon_name) scoped_prs $
2157 thing_inside binders res_kind }
2158 where
2159 report_sig_tv_err (n1, n2)
2160 = setSrcSpan (getSrcSpan n2) $
2161 addErrTc (text "Couldn't match" <+> quotes (ppr n1)
2162 <+> text "with" <+> quotes (ppr n2))
2163
2164 -- Given some TyConBinders and a TyCon's result kind, make sure that the
2165 -- correct any wrong Named/Anon choices. For example, consider
2166 -- type Syn k = forall (a :: k). Proxy a
2167 -- At first, it looks like k should be named -- after all, it appears on the RHS.
2168 -- However, the correct kind for Syn is (* -> *).
2169 -- (Why? Because k is the kind of a type, so k's kind is *. And the RHS also has
2170 -- kind *.) See also #13963.
2171 correct_binders :: [TyConBinder] -> Kind -> [TyConBinder]
2172 correct_binders binders kind
2173 = binders'
2174 where
2175 (_, binders') = mapAccumR go (tyCoVarsOfType kind) binders
2176
2177 go :: TyCoVarSet -> TyConBinder -> (TyCoVarSet, TyConBinder)
2178 go fvs binder
2179 | isNamedTyConBinder binder
2180 , not (tv `elemVarSet` fvs)
2181 = (new_fvs, mkAnonTyConBinder tv)
2182
2183 | not (isNamedTyConBinder binder)
2184 , tv `elemVarSet` fvs
2185 = (new_fvs, mkNamedTyConBinder Required tv)
2186 -- always Required, because it was anonymous (i.e. visible) previously
2187
2188 | otherwise
2189 = (new_fvs, binder)
2190
2191 where
2192 tv = binderVar binder
2193 new_fvs = fvs `delVarSet` tv `unionVarSet` tyCoVarsOfType (tyVarKind tv)
2194
2195 -----------------------------------
2196 tcDataKindSig :: [TyConBinder]
2197 -> Kind
2198 -> TcM ([TyConBinder], Kind)
2199 -- GADT decls can have a (perhaps partial) kind signature
2200 -- e.g. data T a :: * -> * -> * where ...
2201 -- This function makes up suitable (kinded) TyConBinders for the
2202 -- argument kinds. E.g. in this case it might return
2203 -- ([b::*, c::*], *)
2204 -- Never emits constraints.
2205 -- It's a little trickier than you might think: see
2206 -- Note [TyConBinders for the result kind signature of a data type]
2207 tcDataKindSig tc_bndrs kind
2208 = do { loc <- getSrcSpanM
2209 ; uniqs <- newUniqueSupply
2210 ; rdr_env <- getLocalRdrEnv
2211 ; let new_occs = [ occ
2212 | str <- allNameStrings
2213 , let occ = mkOccName tvName str
2214 , isNothing (lookupLocalRdrOcc rdr_env occ)
2215 -- Note [Avoid name clashes for associated data types]
2216 , not (occ `elem` lhs_occs) ]
2217 new_uniqs = uniqsFromSupply uniqs
2218 subst = mkEmptyTCvSubst (mkInScopeSet (mkVarSet lhs_tvs))
2219 ; return (go loc new_occs new_uniqs subst [] kind) }
2220 where
2221 lhs_tvs = map binderVar tc_bndrs
2222 lhs_occs = map getOccName lhs_tvs
2223
2224 go loc occs uniqs subst acc kind
2225 = case splitPiTy_maybe kind of
2226 Nothing -> (reverse acc, substTy subst kind)
2227
2228 Just (Anon arg, kind')
2229 -> go loc occs' uniqs' subst' (tcb : acc) kind'
2230 where
2231 arg' = substTy subst arg
2232 tv = mkTyVar (mkInternalName uniq occ loc) arg'
2233 subst' = extendTCvInScope subst tv
2234 tcb = TvBndr tv AnonTCB
2235 (uniq:uniqs') = uniqs
2236 (occ:occs') = occs
2237
2238 Just (Named (TvBndr tv vis), kind')
2239 -> go loc occs uniqs subst' (tcb : acc) kind'
2240 where
2241 (subst', tv') = substTyVarBndr subst tv
2242 tcb = TvBndr tv' (NamedTCB vis)
2243
2244 badKindSig :: Bool -> Kind -> SDoc
2245 badKindSig check_for_type kind
2246 = hang (sep [ text "Kind signature on data type declaration has non-*"
2247 , (if check_for_type then empty else text "and non-variable") <+>
2248 text "return kind" ])
2249 2 (ppr kind)
2250
2251 {- Note [TyConBinders for the result kind signature of a data type]
2252 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2253 Given
2254 data T (a::*) :: * -> forall k. k -> *
2255 we want to generate the extra TyConBinders for T, so we finally get
2256 (a::*) (b::*) (k::*) (c::k)
2257 The function tcDataKindSig generates these extra TyConBinders from
2258 the result kind signature.
2259
2260 We need to take care to give the TyConBinders
2261 (a) OccNames that are fresh (because the TyConBinders of a TyCon
2262 must have distinct OccNames
2263
2264 (b) Uniques that are fresh (obviously)
2265
2266 For (a) we need to avoid clashes with the tyvars declared by
2267 the user before the "::"; in the above example that is 'a'.
2268 And also see Note [Avoid name clashes for associated data types].
2269
2270 For (b) suppose we have
2271 data T :: forall k. k -> forall k. k -> *
2272 where the two k's are identical even up to their uniques. Surprisingly,
2273 this can happen: see Trac #14515.
2274
2275 It's reasonably easy to solve all this; just run down the list with a
2276 substitution; hence the recursive 'go' function. But it has to be
2277 done.
2278
2279 Note [Avoid name clashes for associated data types]
2280 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2281 Consider class C a b where
2282 data D b :: * -> *
2283 When typechecking the decl for D, we'll invent an extra type variable
2284 for D, to fill out its kind. Ideally we don't want this type variable
2285 to be 'a', because when pretty printing we'll get
2286 class C a b where
2287 data D b a0
2288 (NB: the tidying happens in the conversion to IfaceSyn, which happens
2289 as part of pretty-printing a TyThing.)
2290
2291 That's why we look in the LocalRdrEnv to see what's in scope. This is
2292 important only to get nice-looking output when doing ":info C" in GHCi.
2293 It isn't essential for correctness.
2294
2295
2296 ************************************************************************
2297 * *
2298 Partial signatures
2299 * *
2300 ************************************************************************
2301
2302 -}
2303
2304 tcHsPartialSigType
2305 :: UserTypeCtxt
2306 -> LHsSigWcType GhcRn -- The type signature
2307 -> TcM ( [(Name, TcTyVar)] -- Wildcards
2308 , Maybe TcType -- Extra-constraints wildcard
2309 , [Name] -- Original tyvar names, in correspondence with ...
2310 , [TcTyVar] -- ... Implicitly and explicitly bound type variables
2311 , TcThetaType -- Theta part
2312 , TcType ) -- Tau part
2313 -- See Note [Recipe for checking a signature]
2314 tcHsPartialSigType ctxt sig_ty
2315 | HsWC { hswc_ext = sig_wcs, hswc_body = ib_ty } <- sig_ty
2316 , HsIB { hsib_ext = HsIBRn { hsib_vars = implicit_hs_tvs }
2317 , hsib_body = hs_ty } <- ib_ty
2318 , (explicit_hs_tvs, L _ hs_ctxt, hs_tau) <- splitLHsSigmaTy hs_ty
2319 = addSigCtxt ctxt hs_ty $
2320 do { (implicit_tvs, (explicit_tvs, (wcs, wcx, theta, tau)))
2321 <- tcWildCardBindersX newWildTyVar Nothing sig_wcs $ \ wcs ->
2322 tcImplicitTKBndrsSig skol_info implicit_hs_tvs $
2323 tcExplicitTKBndrs skol_info explicit_hs_tvs $
2324 do { -- Instantiate the type-class context; but if there
2325 -- is an extra-constraints wildcard, just discard it here
2326 (theta, wcx) <- tcPartialContext hs_ctxt
2327
2328 ; tau <- tcHsOpenType hs_tau
2329
2330 ; return (wcs, wcx, theta, tau) }
2331
2332 -- We must return these separately, because all the zonking below
2333 -- might change the name of a SigTv. This, in turn, causes trouble
2334 -- in partial type signatures that bind scoped type variables, as
2335 -- we bring the wrong name into scope in the function body.
2336 -- Test case: partial-sigs/should_compile/LocalDefinitionBug
2337 ; let tv_names = map tyVarName (implicit_tvs ++ explicit_tvs)
2338
2339 -- Spit out the wildcards (including the extra-constraints one)
2340 -- as "hole" constraints, so that they'll be reported if necessary
2341 -- See Note [Extra-constraint holes in partial type signatures]
2342 ; emitWildCardHoleConstraints wcs
2343
2344 -- The SigTvs created above will sometimes have too high a TcLevel
2345 -- (note that they are generated *after* bumping the level in
2346 -- the tc{Im,Ex}plicitTKBndrsSig functions. Bumping the level
2347 -- is still important here, because the kinds of these variables
2348 -- do indeed need to have the higher level, so they can unify
2349 -- with other local type variables. But, now that we've type-checked
2350 -- everything (and solved equalities in the tcImplicit call)
2351 -- we need to promote the SigTvs so we don't violate the TcLevel
2352 -- invariant
2353 ; all_tvs <- mapM zonkPromoteTyCoVarBndr (implicit_tvs ++ explicit_tvs)
2354 -- zonkPromoteTyCoVarBndr deals well with SigTvs
2355
2356 ; theta <- mapM zonkPromoteType theta
2357 ; tau <- zonkPromoteType tau
2358
2359 ; checkValidType ctxt (mkSpecForAllTys all_tvs $ mkPhiTy theta tau)
2360
2361 ; traceTc "tcHsPartialSigType" (ppr all_tvs)
2362 ; return (wcs, wcx, tv_names, all_tvs, theta, tau) }
2363 where
2364 skol_info = SigTypeSkol ctxt
2365 tcHsPartialSigType _ (HsWC _ (XHsImplicitBndrs _)) = panic "tcHsPartialSigType"
2366 tcHsPartialSigType _ (XHsWildCardBndrs _) = panic "tcHsPartialSigType"
2367
2368 tcPartialContext :: HsContext GhcRn -> TcM (TcThetaType, Maybe TcType)
2369 tcPartialContext hs_theta
2370 | Just (hs_theta1, hs_ctxt_last) <- snocView hs_theta
2371 , L _ (HsWildCardTy wc) <- ignoreParens hs_ctxt_last
2372 = do { wc_tv_ty <- tcWildCardOcc wc constraintKind
2373 ; theta <- mapM tcLHsPredType hs_theta1
2374 ; return (theta, Just wc_tv_ty) }
2375 | otherwise
2376 = do { theta <- mapM tcLHsPredType hs_theta
2377 ; return (theta, Nothing) }
2378
2379 {- Note [Extra-constraint holes in partial type signatures]
2380 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2381 Consider
2382 f :: (_) => a -> a
2383 f x = ...
2384
2385 * The renamer makes a wildcard name for the "_", and puts it in
2386 the hswc_wcs field.
2387
2388 * Then, in tcHsPartialSigType, we make a new hole TcTyVar, in
2389 tcWildCardBindersX.
2390
2391 * TcBinds.chooseInferredQuantifiers fills in that hole TcTyVar
2392 with the inferred constraints, e.g. (Eq a, Show a)
2393
2394 * TcErrors.mkHoleError finally reports the error.
2395
2396 An annoying difficulty happens if there are more than 62 inferred
2397 constraints. Then we need to fill in the TcTyVar with (say) a 70-tuple.
2398 Where do we find the TyCon? For good reasons we only have constraint
2399 tuples up to 62 (see Note [How tuples work] in TysWiredIn). So how
2400 can we make a 70-tuple? This was the root cause of Trac #14217.
2401
2402 It's incredibly tiresome, because we only need this type to fill
2403 in the hole, to communicate to the error reporting machinery. Nothing
2404 more. So I use a HACK:
2405
2406 * I make an /ordinary/ tuple of the constraints, in
2407 TcBinds.chooseInferredQuantifiers. This is ill-kinded because
2408 ordinary tuples can't contain constraints, but it works fine. And for
2409 ordinary tuples we don't have the same limit as for constraint
2410 tuples (which need selectors and an assocated class).
2411
2412 * Because it is ill-kinded, it trips an assert in writeMetaTyVar,
2413 so now I disable the assertion if we are writing a type of
2414 kind Constraint. (That seldom/never normally happens so we aren't
2415 losing much.)
2416
2417 Result works fine, but it may eventually bite us.
2418
2419
2420 ************************************************************************
2421 * *
2422 Pattern signatures (i.e signatures that occur in patterns)
2423 * *
2424 ********************************************************************* -}
2425
2426 tcHsPatSigType :: UserTypeCtxt
2427 -> LHsSigWcType GhcRn -- The type signature
2428 -> TcM ( [(Name, TcTyVar)] -- Wildcards
2429 , [(Name, TcTyVar)] -- The new bit of type environment, binding
2430 -- the scoped type variables
2431 , TcType) -- The type
2432 -- Used for type-checking type signatures in
2433 -- (a) patterns e.g f (x::Int) = e
2434 -- (b) RULE forall bndrs e.g. forall (x::Int). f x = x
2435 --
2436 -- This may emit constraints
2437 -- See Note [Recipe for checking a signature]
2438 tcHsPatSigType ctxt sig_ty
2439 | HsWC { hswc_ext = sig_wcs, hswc_body = ib_ty } <- sig_ty
2440 , HsIB { hsib_ext = HsIBRn { hsib_vars = sig_vars}
2441 , hsib_body = hs_ty } <- ib_ty
2442 = addSigCtxt ctxt hs_ty $
2443 do { sig_tkvs <- mapM new_implicit_tv sig_vars
2444 ; (wcs, sig_ty)
2445 <- tcWildCardBindersX newWildTyVar Nothing sig_wcs $ \ wcs ->
2446 tcExtendTyVarEnv sig_tkvs $
2447 do { sig_ty <- tcHsOpenType hs_ty
2448 ; return (wcs, sig_ty) }
2449
2450 ; emitWildCardHoleConstraints wcs
2451
2452 -- sig_ty might have tyvars that are at a higher TcLevel (if hs_ty
2453 -- contains a forall). Promote these.
2454 ; sig_ty <- zonkPromoteType sig_ty
2455 ; checkValidType ctxt sig_ty
2456
2457 ; tv_pairs <- mapM mk_tv_pair sig_tkvs
2458
2459 ; traceTc "tcHsPatSigType" (ppr sig_vars)
2460 ; return (wcs, tv_pairs, sig_ty) }
2461 where
2462 new_implicit_tv name = do { kind <- newMetaKindVar
2463 ; new_tv name kind }
2464
2465 new_tv = case ctxt of
2466 RuleSigCtxt {} -> newSkolemTyVar
2467 _ -> newSigTyVar
2468 -- See Note [Pattern signature binders]
2469 -- See Note [Unifying SigTvs]
2470
2471 mk_tv_pair tv = do { tv' <- zonkTcTyVarToTyVar tv
2472 ; return (tyVarName tv, tv') }
2473 -- The Name is one of sig_vars, the lexically scoped name
2474 -- But if it's a SigTyVar, it might have been unified
2475 -- with an existing in-scope skolem, so we must zonk
2476 -- here. See Note [Pattern signature binders]
2477 tcHsPatSigType _ (HsWC _ (XHsImplicitBndrs _)) = panic "tcHsPatSigType"
2478 tcHsPatSigType _ (XHsWildCardBndrs _) = panic "tcHsPatSigType"
2479
2480 tcPatSig :: Bool -- True <=> pattern binding
2481 -> LHsSigWcType GhcRn
2482 -> ExpSigmaType
2483 -> TcM (TcType, -- The type to use for "inside" the signature
2484 [(Name,TcTyVar)], -- The new bit of type environment, binding
2485 -- the scoped type variables
2486 [(Name,TcTyVar)], -- The wildcards
2487 HsWrapper) -- Coercion due to unification with actual ty
2488 -- Of shape: res_ty ~ sig_ty
2489 tcPatSig in_pat_bind sig res_ty
2490 = do { (sig_wcs, sig_tvs, sig_ty) <- tcHsPatSigType PatSigCtxt sig
2491 -- sig_tvs are the type variables free in 'sig',
2492 -- and not already in scope. These are the ones
2493 -- that should be brought into scope
2494
2495 ; if null sig_tvs then do {
2496 -- Just do the subsumption check and return
2497 wrap <- addErrCtxtM (mk_msg sig_ty) $
2498 tcSubTypeET PatSigOrigin PatSigCtxt res_ty sig_ty
2499 ; return (sig_ty, [], sig_wcs, wrap)
2500 } else do
2501 -- Type signature binds at least one scoped type variable
2502
2503 -- A pattern binding cannot bind scoped type variables
2504 -- It is more convenient to make the test here
2505 -- than in the renamer
2506 { when in_pat_bind (addErr (patBindSigErr sig_tvs))
2507
2508 -- Check that all newly-in-scope tyvars are in fact
2509 -- constrained by the pattern. This catches tiresome
2510 -- cases like
2511 -- type T a = Int
2512 -- f :: Int -> Int
2513 -- f (x :: T a) = ...
2514 -- Here 'a' doesn't get a binding. Sigh
2515 ; let bad_tvs = [ tv | (_,tv) <- sig_tvs
2516 , not (tv `elemVarSet` exactTyCoVarsOfType sig_ty) ]
2517 ; checkTc (null bad_tvs) (badPatSigTvs sig_ty bad_tvs)
2518
2519 -- Now do a subsumption check of the pattern signature against res_ty
2520 ; wrap <- addErrCtxtM (mk_msg sig_ty) $
2521 tcSubTypeET PatSigOrigin PatSigCtxt res_ty sig_ty
2522
2523 -- Phew!
2524 ; return (sig_ty, sig_tvs, sig_wcs, wrap)
2525 } }
2526 where
2527 mk_msg sig_ty tidy_env
2528 = do { (tidy_env, sig_ty) <- zonkTidyTcType tidy_env sig_ty
2529 ; res_ty <- readExpType res_ty -- should be filled in by now
2530 ; (tidy_env, res_ty) <- zonkTidyTcType tidy_env res_ty
2531 ; let msg = vcat [ hang (text "When checking that the pattern signature:")
2532 4 (ppr sig_ty)
2533 , nest 2 (hang (text "fits the type of its context:")
2534 2 (ppr res_ty)) ]
2535 ; return (tidy_env, msg) }
2536
2537 patBindSigErr :: [(Name,TcTyVar)] -> SDoc
2538 patBindSigErr sig_tvs
2539 = hang (text "You cannot bind scoped type variable" <> plural sig_tvs
2540 <+> pprQuotedList (map fst sig_tvs))
2541 2 (text "in a pattern binding signature")
2542
2543 {- Note [Pattern signature binders]
2544 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2545 Consider
2546 data T = forall a. T a (a->Int)
2547 f (T x (f :: b->Int)) = blah
2548
2549 Here
2550 * The pattern (T p1 p2) creates a *skolem* type variable 'a_sk',
2551 It must be a skolem so that that it retains its identity, and
2552 TcErrors.getSkolemInfo can thereby find the binding site for the skolem.
2553
2554 * The type signature pattern (f :: b->Int) makes a fresh meta-tyvar b_sig
2555 (a SigTv), and binds "b" :-> b_sig in the envt
2556
2557 * Then unification makes b_sig := a_sk
2558 That's why we must make b_sig a MetaTv (albeit a SigTv),
2559 not a SkolemTv, so that it can unify to a_sk.
2560
2561 * Finally, in 'blah' we must have the envt "b" :-> a_sk. The pair
2562 ("b" :-> a_sk) is returned by tcHsPatSigType, constructed by
2563 mk_tv_pair in that function.
2564
2565 Another example (Trac #13881):
2566 fl :: forall (l :: [a]). Sing l -> Sing l
2567 fl (SNil :: Sing (l :: [y])) = SNil
2568 When we reach the pattern signature, 'l' is in scope from the
2569 outer 'forall':
2570 "a" :-> a_sk :: *
2571 "l" :-> l_sk :: [a_sk]
2572 We make up a fresh meta-SigTv, y_sig, for 'y', and kind-check
2573 the pattern signature
2574 Sing (l :: [y])
2575 That unifies y_sig := a_sk. We return from tcHsPatSigType with
2576 the pair ("y" :-> a_sk).
2577
2578 For RULE binders, though, things are a bit different (yuk).
2579 RULE "foo" forall (x::a) (y::[a]). f x y = ...
2580 Here this really is the binding site of the type variable so we'd like
2581 to use a skolem, so that we get a complaint if we unify two of them
2582 together.
2583
2584 Note [Unifying SigTvs]
2585 ~~~~~~~~~~~~~~~~~~~~~~
2586 ALAS we have no decent way of avoiding two SigTvs getting unified.
2587 Consider
2588 f (x::(a,b)) (y::c)) = [fst x, y]
2589 Here we'd really like to complain that 'a' and 'c' are unified. But
2590 for the reasons above we can't make a,b,c into skolems, so they
2591 are just SigTvs that can unify. And indeed, this would be ok,
2592 f x (y::c) = case x of
2593 (x1 :: a1, True) -> [x,y]
2594 (x1 :: a2, False) -> [x,y,y]
2595 Here the type of x's first component is called 'a1' in one branch and
2596 'a2' in the other. We could try insisting on the same OccName, but
2597 they definitely won't have the sane lexical Name.
2598
2599 I think we could solve this by recording in a SigTv a list of all the
2600 in-scope variables that it should not unify with, but it's fiddly.
2601
2602
2603 ************************************************************************
2604 * *
2605 Checking kinds
2606 * *
2607 ************************************************************************
2608
2609 -}
2610
2611 unifyKinds :: [LHsType GhcRn] -> [(TcType, TcKind)] -> TcM ([TcType], TcKind)
2612 unifyKinds rn_tys act_kinds
2613 = do { kind <- newMetaKindVar
2614 ; let check rn_ty (ty, act_kind) = checkExpectedKind (unLoc rn_ty) ty act_kind kind
2615 ; tys' <- zipWithM check rn_tys act_kinds
2616 ; return (tys', kind) }
2617
2618 {-
2619 ************************************************************************
2620 * *
2621 Promotion
2622 * *
2623 ************************************************************************
2624 -}
2625
2626 -- | Whenever a type is about to be added to the environment, it's necessary
2627 -- to make sure that any free meta-tyvars in the type are promoted to the
2628 -- current TcLevel. (They might be at a higher level due to the level-bumping
2629 -- in tcExplicitTKBndrs, for example.) This function both zonks *and*
2630 -- promotes.
2631 zonkPromoteType :: TcType -> TcM TcType
2632 zonkPromoteType = mapType zonkPromoteMapper ()
2633
2634 -- cf. TcMType.zonkTcTypeMapper
2635 zonkPromoteMapper :: TyCoMapper () TcM
2636 zonkPromoteMapper = TyCoMapper { tcm_smart = True
2637 , tcm_tyvar = const zonkPromoteTcTyVar
2638 , tcm_covar = const covar
2639 , tcm_hole = const hole
2640 , tcm_tybinder = const tybinder }
2641 where
2642 covar cv
2643 = mkCoVarCo <$> zonkPromoteTyCoVarKind cv
2644
2645 hole :: CoercionHole -> TcM Coercion
2646 hole h
2647 = do { contents <- unpackCoercionHole_maybe h
2648 ; case contents of
2649 Just co -> do { co <- zonkPromoteCoercion co
2650 ; checkCoercionHole cv co }
2651 Nothing -> do { cv' <- zonkPromoteTyCoVarKind cv
2652 ; return $ mkHoleCo (setCoHoleCoVar h cv') } }
2653 where
2654 cv = coHoleCoVar h
2655
2656 tybinder :: TyVar -> ArgFlag -> TcM ((), TyVar)
2657 tybinder tv _flag = ((), ) <$> zonkPromoteTyCoVarKind tv
2658
2659 zonkPromoteTcTyVar :: TyCoVar -> TcM TcType
2660 zonkPromoteTcTyVar tv
2661 | isMetaTyVar tv
2662 = do { let ref = metaTyVarRef tv
2663 ; contents <- readTcRef ref
2664 ; case contents of
2665 Flexi -> do { promoted <- promoteTyVar tv
2666 ; if promoted
2667 then zonkPromoteTcTyVar tv -- read it again
2668 else mkTyVarTy <$> zonkPromoteTyCoVarKind tv }
2669 Indirect ty -> zonkPromoteType ty }
2670
2671 | isTcTyVar tv && isSkolemTyVar tv -- NB: isSkolemTyVar says "True" to pure TyVars
2672 = do { tc_lvl <- getTcLevel
2673 ; mkTyVarTy <$> zonkPromoteTyCoVarKind (promoteSkolem tc_lvl tv) }
2674
2675 | otherwise
2676 = mkTyVarTy <$> zonkPromoteTyCoVarKind tv
2677
2678 zonkPromoteTyCoVarKind :: TyCoVar -> TcM TyCoVar
2679 zonkPromoteTyCoVarKind = updateTyVarKindM zonkPromoteType
2680
2681 zonkPromoteTyCoVarBndr :: TyCoVar -> TcM TyCoVar
2682 zonkPromoteTyCoVarBndr tv
2683 | isSigTyVar tv
2684 = tcGetTyVar "zonkPromoteTyCoVarBndr SigTv" <$> zonkPromoteTcTyVar tv
2685
2686 | isTcTyVar tv && isSkolemTyVar tv
2687 = do { tc_lvl <- getTcLevel
2688 ; zonkPromoteTyCoVarKind (promoteSkolem tc_lvl tv) }
2689
2690 | otherwise
2691 = zonkPromoteTyCoVarKind tv
2692
2693 zonkPromoteCoercion :: Coercion -> TcM Coercion
2694 zonkPromoteCoercion = mapCoercion zonkPromoteMapper ()
2695
2696 zonkPromoteTypeInKnot :: TcType -> TcM TcType
2697 zonkPromoteTypeInKnot = mapType (zonkPromoteMapper { tcm_smart = False }) ()
2698 -- NB: Just changing smart to False will still use the smart zonker (not suitable
2699 -- for in-the-knot) for kinds. But that's OK, because kinds aren't knot-tied.
2700
2701 {-
2702 ************************************************************************
2703 * *
2704 Sort checking kinds
2705 * *
2706 ************************************************************************
2707
2708 tcLHsKindSig converts a user-written kind to an internal, sort-checked kind.
2709 It does sort checking and desugaring at the same time, in one single pass.
2710 -}
2711
2712 tcLHsKindSig :: UserTypeCtxt -> LHsKind GhcRn -> TcM Kind
2713 tcLHsKindSig ctxt hs_kind
2714 -- See Note [Recipe for checking a signature] in TcHsType
2715 = do { kind <- solveLocalEqualities $
2716 tc_lhs_kind kindLevelMode hs_kind
2717 ; traceTc "tcLHsKindSig" (ppr kind)
2718 ; kind <- zonkPromoteType kind
2719 -- This zonk is very important in the case of higher rank kinds
2720 -- E.g. Trac #13879 f :: forall (p :: forall z (y::z). <blah>).
2721 -- <more blah>
2722 -- When instantiating p's kind at occurrences of p in <more blah>
2723 -- it's crucial that the kind we instantiate is fully zonked,
2724 -- else we may fail to substitute properly
2725
2726 ; checkValidType ctxt kind
2727 ; traceTc "tcLHsKindSig2" (ppr kind)
2728 ; return kind }
2729
2730 tc_lhs_kind :: TcTyMode -> LHsKind GhcRn -> TcM Kind
2731 tc_lhs_kind mode k
2732 = addErrCtxt (text "In the kind" <+> quotes (ppr k)) $
2733 tc_lhs_type (kindLevel mode) k liftedTypeKind
2734
2735 promotionErr :: Name -> PromotionErr -> TcM a
2736 promotionErr name err
2737 = failWithTc (hang (pprPECategory err <+> quotes (ppr name) <+> text "cannot be used here")
2738 2 (parens reason))
2739 where
2740 reason = case err of
2741 ConstrainedDataConPE pred
2742 -> text "it has an unpromotable context"
2743 <+> quotes (ppr pred)
2744 FamDataConPE -> text "it comes from a data family instance"
2745 NoDataKindsTC -> text "perhaps you intended to use DataKinds"
2746 NoDataKindsDC -> text "perhaps you intended to use DataKinds"
2747 PatSynPE -> text "pattern synonyms cannot be promoted"
2748 PatSynExPE -> sep [ text "the existential variables of a pattern synonym"
2749 , text "signature do not scope over the pattern" ]
2750 _ -> text "it is defined and used in the same recursive group"
2751
2752 {-
2753 ************************************************************************
2754 * *
2755 Scoped type variables
2756 * *
2757 ************************************************************************
2758 -}
2759
2760 badPatSigTvs :: TcType -> [TyVar] -> SDoc
2761 badPatSigTvs sig_ty bad_tvs
2762 = vcat [ fsep [text "The type variable" <> plural bad_tvs,
2763 quotes (pprWithCommas ppr bad_tvs),
2764 text "should be bound by the pattern signature" <+> quotes (ppr sig_ty),
2765 text "but are actually discarded by a type synonym" ]
2766 , text "To fix this, expand the type synonym"
2767 , text "[Note: I hope to lift this restriction in due course]" ]
2768
2769 {-
2770 ************************************************************************
2771 * *
2772 Error messages and such
2773 * *
2774 ************************************************************************
2775 -}
2776
2777 -- | Make an appropriate message for an error in a function argument.
2778 -- Used for both expressions and types.
2779 funAppCtxt :: (Outputable fun, Outputable arg) => fun -> arg -> Int -> SDoc
2780 funAppCtxt fun arg arg_no
2781 = hang (hsep [ text "In the", speakNth arg_no, ptext (sLit "argument of"),
2782 quotes (ppr fun) <> text ", namely"])
2783 2 (quotes (ppr arg))
2784
2785 -- See Note [Free-floating kind vars]
2786 reportFloatingKvs :: Name -- of the tycon
2787 -> TyConFlavour -- What sort of TyCon it is
2788 -> [TcTyVar] -- all tyvars, not necessarily zonked
2789 -> [TcTyVar] -- floating tyvars
2790 -> TcM ()
2791 reportFloatingKvs tycon_name flav all_tvs bad_tvs
2792 = unless (null bad_tvs) $ -- don't bother zonking if there's no error
2793 do { all_tvs <- mapM zonkTcTyVarToTyVar all_tvs
2794 ; bad_tvs <- mapM zonkTcTyVarToTyVar bad_tvs
2795 ; let (tidy_env, tidy_all_tvs) = tidyOpenTyCoVars emptyTidyEnv all_tvs
2796 tidy_bad_tvs = map (tidyTyVarOcc tidy_env) bad_tvs
2797 ; mapM_ (report tidy_all_tvs) tidy_bad_tvs }
2798 where
2799 report tidy_all_tvs tidy_bad_tv
2800 = addErr $
2801 vcat [ text "Kind variable" <+> quotes (ppr tidy_bad_tv) <+>
2802 text "is implicitly bound in" <+> ppr flav
2803 , quotes (ppr tycon_name) <> comma <+>
2804 text "but does not appear as the kind of any"
2805 , text "of its type variables. Perhaps you meant"
2806 , text "to bind it explicitly somewhere?"
2807 , ppWhen (not (null tidy_all_tvs)) $
2808 hang (text "Type variables with inferred kinds:")
2809 2 (ppr_tv_bndrs tidy_all_tvs) ]
2810
2811 ppr_tv_bndrs tvs = sep (map pp_tv tvs)
2812 pp_tv tv = parens (ppr tv <+> dcolon <+> ppr (tyVarKind tv))