ea65a736435ca33d76b4d6f5deb0e0c67d5c4a96
[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 #-}
9
10 module TcHsType (
11 -- Type signatures
12 kcHsSigType, tcClassSigType,
13 tcHsSigType, tcHsSigWcType,
14 tcHsPartialSigType,
15 funsSigCtxt, addSigCtxt, pprSigCtxt,
16
17 tcHsClsInstType,
18 tcHsDeriv, tcHsVectInst,
19 tcHsTypeApp,
20 UserTypeCtxt(..),
21 tcImplicitTKBndrs, tcImplicitTKBndrsType, tcExplicitTKBndrs,
22
23 -- Type checking type and class decls
24 kcLookupTcTyCon, kcTyClTyVars, tcTyClTyVars,
25 tcHsConArgType, tcDataKindSig,
26
27 -- Kind-checking types
28 -- No kind generalisation, no checkValidType
29 tcWildCardBinders,
30 kcHsTyVarBndrs,
31 tcHsLiftedType, tcHsOpenType,
32 tcHsLiftedTypeNC, tcHsOpenTypeNC,
33 tcLHsType, tcCheckLHsType,
34 tcHsContext, tcLHsPredType, tcInferApps, tcInferArgs,
35 solveEqualities, -- useful re-export
36
37 kindGeneralize,
38
39 -- Sort-checking kinds
40 tcLHsKind,
41
42 -- Pattern type signatures
43 tcHsPatSigType, tcPatSig, funAppCtxt
44 ) where
45
46 #include "HsVersions.h"
47
48 import HsSyn
49 import TcRnMonad
50 import TcEvidence
51 import TcEnv
52 import TcMType
53 import TcValidity
54 import TcUnify
55 import TcIface
56 import TcSimplify ( solveEqualities )
57 import TcType
58 import Inst ( tcInstBinders, tcInstBindersX, tcInstBinderX )
59 import Type
60 import Kind
61 import RdrName( lookupLocalRdrOcc )
62 import Var
63 import VarSet
64 import TyCon
65 import ConLike
66 import DataCon
67 import TysPrim ( tYPE )
68 import Class
69 import Name
70 import NameEnv
71 import NameSet
72 import VarEnv
73 import TysWiredIn
74 import BasicTypes
75 import SrcLoc
76 import Constants ( mAX_CTUPLE_SIZE )
77 import ErrUtils( MsgDoc )
78 import Unique
79 import Util
80 import UniqSupply
81 import Outputable
82 import FastString
83 import PrelNames hiding ( wildCardName )
84 import qualified GHC.LanguageExtensions as LangExt
85
86 import Maybes
87 import Data.List ( partition, zipWith4 )
88 import Control.Monad
89
90 {-
91 ----------------------------
92 General notes
93 ----------------------------
94
95 Unlike with expressions, type-checking types both does some checking and
96 desugars at the same time. This is necessary because we often want to perform
97 equality checks on the types right away, and it would be incredibly painful
98 to do this on un-desugared types. Luckily, desugared types are close enough
99 to HsTypes to make the error messages sane.
100
101 During type-checking, we perform as little validity checking as possible.
102 This is because some type-checking is done in a mutually-recursive knot, and
103 if we look too closely at the tycons, we'll loop. This is why we always must
104 use mkNakedTyConApp and mkNakedAppTys, etc., which never look at a tycon.
105 The mkNamed... functions don't uphold Type invariants, but zonkTcTypeToType
106 will repair this for us. Note that zonkTcType *is* safe within a knot, and
107 can be done repeatedly with no ill effect: it just squeezes out metavariables.
108
109 Generally, after type-checking, you will want to do validity checking, say
110 with TcValidity.checkValidType.
111
112 Validity checking
113 ~~~~~~~~~~~~~~~~~
114 Some of the validity check could in principle be done by the kind checker,
115 but not all:
116
117 - During desugaring, we normalise by expanding type synonyms. Only
118 after this step can we check things like type-synonym saturation
119 e.g. type T k = k Int
120 type S a = a
121 Then (T S) is ok, because T is saturated; (T S) expands to (S Int);
122 and then S is saturated. This is a GHC extension.
123
124 - Similarly, also a GHC extension, we look through synonyms before complaining
125 about the form of a class or instance declaration
126
127 - Ambiguity checks involve functional dependencies, and it's easier to wait
128 until knots have been resolved before poking into them
129
130 Also, in a mutually recursive group of types, we can't look at the TyCon until we've
131 finished building the loop. So to keep things simple, we postpone most validity
132 checking until step (3).
133
134 Knot tying
135 ~~~~~~~~~~
136 During step (1) we might fault in a TyCon defined in another module, and it might
137 (via a loop) refer back to a TyCon defined in this module. So when we tie a big
138 knot around type declarations with ARecThing, so that the fault-in code can get
139 the TyCon being defined.
140
141 %************************************************************************
142 %* *
143 Check types AND do validity checking
144 * *
145 ************************************************************************
146 -}
147
148 funsSigCtxt :: [Located Name] -> UserTypeCtxt
149 -- Returns FunSigCtxt, with no redundant-context-reporting,
150 -- form a list of located names
151 funsSigCtxt (L _ name1 : _) = FunSigCtxt name1 False
152 funsSigCtxt [] = panic "funSigCtxt"
153
154 addSigCtxt :: UserTypeCtxt -> LHsType Name -> TcM a -> TcM a
155 addSigCtxt ctxt hs_ty thing_inside
156 = setSrcSpan (getLoc hs_ty) $
157 addErrCtxt (pprSigCtxt ctxt hs_ty) $
158 thing_inside
159
160 pprSigCtxt :: UserTypeCtxt -> LHsType Name -> SDoc
161 -- (pprSigCtxt ctxt <extra> <type>)
162 -- prints In the type signature for 'f':
163 -- f :: <type>
164 -- The <extra> is either empty or "the ambiguity check for"
165 pprSigCtxt ctxt hs_ty
166 | Just n <- isSigMaybe ctxt
167 = hang (text "In the type signature:")
168 2 (pprPrefixOcc n <+> dcolon <+> ppr hs_ty)
169
170 | otherwise
171 = hang (text "In" <+> pprUserTypeCtxt ctxt <> colon)
172 2 (ppr hs_ty)
173
174 tcHsSigWcType :: UserTypeCtxt -> LHsSigWcType Name -> TcM Type
175 -- This one is used when we have a LHsSigWcType, but in
176 -- a place where wildards aren't allowed. The renamer has
177 -- alrady checked this, so we can simply ignore it.
178 tcHsSigWcType ctxt sig_ty = tcHsSigType ctxt (dropWildCards sig_ty)
179
180 kcHsSigType :: [Located Name] -> LHsSigType Name -> TcM ()
181 kcHsSigType names (HsIB { hsib_body = hs_ty
182 , hsib_vars = sig_vars })
183 = addSigCtxt (funsSigCtxt names) hs_ty $
184 discardResult $
185 tcImplicitTKBndrsType sig_vars $
186 tc_lhs_type typeLevelMode hs_ty liftedTypeKind
187
188 tcClassSigType :: [Located Name] -> LHsSigType Name -> TcM Type
189 -- Does not do validity checking; this must be done outside
190 -- the recursive class declaration "knot"
191 tcClassSigType names sig_ty
192 = addSigCtxt (funsSigCtxt names) (hsSigType sig_ty) $
193 do { ty <- tc_hs_sig_type sig_ty liftedTypeKind
194 ; kindGeneralizeType ty }
195
196 tcHsSigType :: UserTypeCtxt -> LHsSigType Name -> TcM Type
197 -- Does validity checking
198 tcHsSigType ctxt sig_ty
199 = addSigCtxt ctxt (hsSigType sig_ty) $
200 do { kind <- case expectedKindInCtxt ctxt of
201 AnythingKind -> newMetaKindVar
202 TheKind k -> return k
203 OpenKind -> do { rr <- newFlexiTyVarTy runtimeRepTy
204 ; return $ tYPE rr }
205 -- The kind is checked by checkValidType, and isn't necessarily
206 -- of kind * in a Template Haskell quote eg [t| Maybe |]
207
208 ; ty <- tc_hs_sig_type sig_ty kind
209
210 -- Generalise here: see Note [Kind generalisation]
211 ; do_kind_gen <- decideKindGeneralisationPlan ty
212 ; ty <- if do_kind_gen
213 then kindGeneralizeType ty
214 else zonkTcType ty
215
216 ; checkValidType ctxt ty
217 ; return ty }
218
219 tc_hs_sig_type :: LHsSigType Name -> Kind -> TcM Type
220 -- Does not do validity checking or zonking
221 tc_hs_sig_type (HsIB { hsib_body = hs_ty
222 , hsib_vars = sig_vars }) kind
223 = do { (tkvs, ty) <- solveEqualities $
224 tcImplicitTKBndrsType sig_vars $
225 tc_lhs_type typeLevelMode hs_ty kind
226 ; return (mkSpecForAllTys tkvs ty) }
227
228 -----------------
229 tcHsDeriv :: LHsSigType Name -> TcM ([TyVar], Class, [Type], Kind)
230 -- Like tcHsSigType, but for the ...deriving( C t1 ty2 ) clause
231 -- Returns the C, [ty1, ty2, and the kind of C's *next* argument
232 -- E.g. class C (a::*) (b::k->k)
233 -- data T a b = ... deriving( C Int )
234 -- returns ([k], C, [k, Int], k->k)
235 -- Also checks that (C ty1 ty2 arg) :: Constraint
236 -- if arg has a suitable kind
237 tcHsDeriv hs_ty
238 = do { arg_kind <- newMetaKindVar
239 -- always safe to kind-generalize, because there
240 -- can be no covars in an outer scope
241 ; ty <- checkNoErrs $
242 -- avoid redundant error report with "illegal deriving", below
243 tc_hs_sig_type hs_ty (mkFunTy arg_kind constraintKind)
244 ; ty <- kindGeneralizeType ty -- also zonks
245 ; arg_kind <- zonkTcType arg_kind
246 ; let (tvs, pred) = splitForAllTys ty
247 ; case getClassPredTys_maybe pred of
248 Just (cls, tys) -> return (tvs, cls, tys, arg_kind)
249 Nothing -> failWithTc (text "Illegal deriving item" <+> quotes (ppr hs_ty)) }
250
251 tcHsClsInstType :: UserTypeCtxt -- InstDeclCtxt or SpecInstCtxt
252 -> LHsSigType Name
253 -> TcM ([TyVar], ThetaType, Class, [Type])
254 -- Like tcHsSigType, but for a class instance declaration
255 tcHsClsInstType user_ctxt hs_inst_ty
256 = setSrcSpan (getLoc (hsSigType hs_inst_ty)) $
257 do { inst_ty <- tc_hs_sig_type hs_inst_ty constraintKind
258 ; inst_ty <- kindGeneralizeType inst_ty
259 ; checkValidInstance user_ctxt hs_inst_ty inst_ty }
260
261 -- Used for 'VECTORISE [SCALAR] instance' declarations
262 tcHsVectInst :: LHsSigType Name -> TcM (Class, [Type])
263 tcHsVectInst ty
264 | Just (L _ cls_name, tys) <- hsTyGetAppHead_maybe (hsSigType ty)
265 -- Ignoring the binders looks pretty dodgy to me
266 = do { (cls, cls_kind) <- tcClass cls_name
267 ; (applied_class, _res_kind)
268 <- tcInferApps typeLevelMode cls_name (mkClassPred cls []) cls_kind tys
269 ; case tcSplitTyConApp_maybe applied_class of
270 Just (_tc, args) -> ASSERT( _tc == classTyCon cls )
271 return (cls, args)
272 _ -> failWithTc (text "Too many arguments passed to" <+> ppr cls_name) }
273 | otherwise
274 = failWithTc $ text "Malformed instance type"
275
276 ----------------------------------------------
277 -- | Type-check a visible type application
278 tcHsTypeApp :: LHsWcType Name -> Kind -> TcM Type
279 tcHsTypeApp wc_ty kind
280 | HsWC { hswc_wcs = sig_wcs, hswc_body = hs_ty } <- wc_ty
281 = do { ty <- solveEqualities $
282 tcWildCardBindersX newWildTyVar sig_wcs $ \ _ ->
283 tcCheckLHsType hs_ty kind
284 ; ty <- zonkTcType ty
285 ; checkValidType TypeAppCtxt ty
286 ; return ty }
287 -- NB: we don't call emitWildcardHoleConstraints here, because
288 -- we want any holes in visible type applications to be used
289 -- without fuss. No errors, warnings, extensions, etc.
290
291 {-
292 ************************************************************************
293 * *
294 The main kind checker: no validity checks here
295 %* *
296 %************************************************************************
297
298 First a couple of simple wrappers for kcHsType
299 -}
300
301 tcHsConArgType :: NewOrData -> LHsType Name -> TcM Type
302 -- Permit a bang, but discard it
303 tcHsConArgType NewType bty = tcHsLiftedType (getBangType bty)
304 -- Newtypes can't have bangs, but we don't check that
305 -- until checkValidDataCon, so do not want to crash here
306
307 tcHsConArgType DataType bty = tcHsOpenType (getBangType bty)
308 -- Can't allow an unlifted type for newtypes, because we're effectively
309 -- going to remove the constructor while coercing it to a lifted type.
310 -- And newtypes can't be bang'd
311
312 ---------------------------
313 tcHsOpenType, tcHsLiftedType,
314 tcHsOpenTypeNC, tcHsLiftedTypeNC :: LHsType Name -> TcM TcType
315 -- Used for type signatures
316 -- Do not do validity checking
317 tcHsOpenType ty = addTypeCtxt ty $ tcHsOpenTypeNC ty
318 tcHsLiftedType ty = addTypeCtxt ty $ tcHsLiftedTypeNC ty
319
320 tcHsOpenTypeNC ty = do { ek <- ekOpen
321 ; tc_lhs_type typeLevelMode ty ek }
322 tcHsLiftedTypeNC ty = tc_lhs_type typeLevelMode ty liftedTypeKind
323
324 -- Like tcHsType, but takes an expected kind
325 tcCheckLHsType :: LHsType Name -> Kind -> TcM Type
326 tcCheckLHsType hs_ty exp_kind
327 = addTypeCtxt hs_ty $
328 tc_lhs_type typeLevelMode hs_ty exp_kind
329
330 tcLHsType :: LHsType Name -> TcM (TcType, TcKind)
331 -- Called from outside: set the context
332 tcLHsType ty = addTypeCtxt ty (tc_infer_lhs_type typeLevelMode ty)
333
334 ---------------------------
335 -- | Should we generalise the kind of this type signature?
336 -- We *should* generalise if the type is mentions no scoped type variables
337 -- or if NoMonoLocalBinds is set. Otherwise, nope.
338 decideKindGeneralisationPlan :: Type -> TcM Bool
339 decideKindGeneralisationPlan ty
340 = do { mono_locals <- xoptM LangExt.MonoLocalBinds
341 ; in_scope <- getInLocalScope
342 ; let fvs = tyCoVarsOfTypeList ty
343 should_gen = not mono_locals || all (not . in_scope . getName) fvs
344 ; traceTc "decideKindGeneralisationPlan"
345 (vcat [ text "type:" <+> ppr ty
346 , text "ftvs:" <+> ppr fvs
347 , text "should gen?" <+> ppr should_gen ])
348 ; return should_gen }
349
350 {-
351 ************************************************************************
352 * *
353 Type-checking modes
354 * *
355 ************************************************************************
356
357 The kind-checker is parameterised by a TcTyMode, which contains some
358 information about where we're checking a type.
359
360 The renamer issues errors about what it can. All errors issued here must
361 concern things that the renamer can't handle.
362
363 -}
364
365 -- | Info about the context in which we're checking a type. Currently,
366 -- differentiates only between types and kinds, but this will likely
367 -- grow, at least to include the distinction between patterns and
368 -- not-patterns.
369 newtype TcTyMode
370 = TcTyMode { mode_level :: TypeOrKind -- True <=> type, False <=> kind
371 }
372
373 typeLevelMode :: TcTyMode
374 typeLevelMode = TcTyMode { mode_level = TypeLevel }
375
376 kindLevelMode :: TcTyMode
377 kindLevelMode = TcTyMode { mode_level = KindLevel }
378
379 -- switch to kind level
380 kindLevel :: TcTyMode -> TcTyMode
381 kindLevel mode = mode { mode_level = KindLevel }
382
383 instance Outputable TcTyMode where
384 ppr = ppr . mode_level
385
386 {-
387 Note [Bidirectional type checking]
388 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
389 In expressions, whenever we see a polymorphic identifier, say `id`, we are
390 free to instantiate it with metavariables, knowing that we can always
391 re-generalize with type-lambdas when necessary. For example:
392
393 rank2 :: (forall a. a -> a) -> ()
394 x = rank2 id
395
396 When checking the body of `x`, we can instantiate `id` with a metavariable.
397 Then, when we're checking the application of `rank2`, we notice that we really
398 need a polymorphic `id`, and then re-generalize over the unconstrained
399 metavariable.
400
401 In types, however, we're not so lucky, because *we cannot re-generalize*!
402 There is no lambda. So, we must be careful only to instantiate at the last
403 possible moment, when we're sure we're never going to want the lost polymorphism
404 again. This is done in calls to tcInstBinders and tcInstBindersX.
405
406 To implement this behavior, we use bidirectional type checking, where we
407 explicitly think about whether we know the kind of the type we're checking
408 or not. Note that there is a difference between not knowing a kind and
409 knowing a metavariable kind: the metavariables are TauTvs, and cannot become
410 forall-quantified kinds. Previously (before dependent types), there were
411 no higher-rank kinds, and so we could instantiate early and be sure that
412 no types would have polymorphic kinds, and so we could always assume that
413 the kind of a type was a fresh metavariable. Not so anymore, thus the
414 need for two algorithms.
415
416 For HsType forms that can never be kind-polymorphic, we implement only the
417 "down" direction, where we safely assume a metavariable kind. For HsType forms
418 that *can* be kind-polymorphic, we implement just the "up" (functions with
419 "infer" in their name) version, as we gain nothing by also implementing the
420 "down" version.
421
422 Note [Future-proofing the type checker]
423 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
424 As discussed in Note [Bidirectional type checking], each HsType form is
425 handled in *either* tc_infer_hs_type *or* tc_hs_type. These functions
426 are mutually recursive, so that either one can work for any type former.
427 But, we want to make sure that our pattern-matches are complete. So,
428 we have a bunch of repetitive code just so that we get warnings if we're
429 missing any patterns.
430 -}
431
432 ------------------------------------------
433 -- | Check and desugar a type, returning the core type and its
434 -- possibly-polymorphic kind. Much like 'tcInferRho' at the expression
435 -- level.
436 tc_infer_lhs_type :: TcTyMode -> LHsType Name -> TcM (TcType, TcKind)
437 tc_infer_lhs_type mode (L span ty)
438 = setSrcSpan span $
439 do { (ty', kind) <- tc_infer_hs_type mode ty
440 ; return (ty', kind) }
441
442 -- | Infer the kind of a type and desugar. This is the "up" type-checker,
443 -- as described in Note [Bidirectional type checking]
444 tc_infer_hs_type :: TcTyMode -> HsType Name -> TcM (TcType, TcKind)
445 tc_infer_hs_type mode (HsTyVar (L _ tv)) = tcTyVar mode tv
446 tc_infer_hs_type mode (HsAppTy ty1 ty2)
447 = do { let (fun_ty, arg_tys) = splitHsAppTys ty1 [ty2]
448 ; (fun_ty', fun_kind) <- tc_infer_lhs_type mode fun_ty
449 ; fun_kind' <- zonkTcType fun_kind
450 ; tcInferApps mode fun_ty fun_ty' fun_kind' arg_tys }
451 tc_infer_hs_type mode (HsParTy t) = tc_infer_lhs_type mode t
452 tc_infer_hs_type mode (HsOpTy lhs (L _ op) rhs)
453 | not (op `hasKey` funTyConKey)
454 = do { (op', op_kind) <- tcTyVar mode op
455 ; op_kind' <- zonkTcType op_kind
456 ; tcInferApps mode op op' op_kind' [lhs, rhs] }
457 tc_infer_hs_type mode (HsKindSig ty sig)
458 = do { sig' <- tc_lhs_kind (kindLevel mode) sig
459 ; ty' <- tc_lhs_type mode ty sig'
460 ; return (ty', sig') }
461 tc_infer_hs_type mode (HsDocTy ty _) = tc_infer_lhs_type mode ty
462 tc_infer_hs_type _ (HsCoreTy ty) = return (ty, typeKind ty)
463 tc_infer_hs_type mode other_ty
464 = do { kv <- newMetaKindVar
465 ; ty' <- tc_hs_type mode other_ty kv
466 ; return (ty', kv) }
467
468 ------------------------------------------
469 tc_lhs_type :: TcTyMode -> LHsType Name -> TcKind -> TcM TcType
470 tc_lhs_type mode (L span ty) exp_kind
471 = setSrcSpan span $
472 do { ty' <- tc_hs_type mode ty exp_kind
473 ; return ty' }
474
475 ------------------------------------------
476 tc_fun_type :: TcTyMode -> LHsType Name -> LHsType Name -> TcKind -> TcM TcType
477 tc_fun_type mode ty1 ty2 exp_kind = case mode_level mode of
478 TypeLevel ->
479 do { arg_rr <- newFlexiTyVarTy runtimeRepTy
480 ; res_rr <- newFlexiTyVarTy runtimeRepTy
481 ; ty1' <- tc_lhs_type mode ty1 (tYPE arg_rr)
482 ; ty2' <- tc_lhs_type mode ty2 (tYPE res_rr)
483 ; checkExpectedKind (mkFunTy ty1' ty2') liftedTypeKind exp_kind }
484 KindLevel -> -- no representation polymorphism in kinds. yet.
485 do { ty1' <- tc_lhs_type mode ty1 liftedTypeKind
486 ; ty2' <- tc_lhs_type mode ty2 liftedTypeKind
487 ; checkExpectedKind (mkFunTy ty1' ty2') liftedTypeKind exp_kind }
488
489 ------------------------------------------
490 -- See also Note [Bidirectional type checking]
491 tc_hs_type :: TcTyMode -> HsType Name -> TcKind -> TcM TcType
492 tc_hs_type mode (HsParTy ty) exp_kind = tc_lhs_type mode ty exp_kind
493 tc_hs_type mode (HsDocTy ty _) exp_kind = tc_lhs_type mode ty exp_kind
494 tc_hs_type _ ty@(HsBangTy {}) _
495 -- While top-level bangs at this point are eliminated (eg !(Maybe Int)),
496 -- other kinds of bangs are not (eg ((!Maybe) Int)). These kinds of
497 -- bangs are invalid, so fail. (#7210)
498 = failWithTc (text "Unexpected strictness annotation:" <+> ppr ty)
499 tc_hs_type _ ty@(HsRecTy _) _
500 -- Record types (which only show up temporarily in constructor
501 -- signatures) should have been removed by now
502 = failWithTc (text "Record syntax is illegal here:" <+> ppr ty)
503
504 -- HsSpliced is an annotation produced by 'RnSplice.rnSpliceType'.
505 -- Here we get rid of it and add the finalizers to the global environment
506 -- while capturing the local environment.
507 --
508 -- See Note [Delaying modFinalizers in untyped splices].
509 tc_hs_type mode (HsSpliceTy (HsSpliced mod_finalizers (HsSplicedTy ty))
510 _
511 )
512 exp_kind
513 = do addModFinalizersWithLclEnv mod_finalizers
514 tc_hs_type mode ty exp_kind
515
516 -- This should never happen; type splices are expanded by the renamer
517 tc_hs_type _ ty@(HsSpliceTy {}) _exp_kind
518 = failWithTc (text "Unexpected type splice:" <+> ppr ty)
519
520 ---------- Functions and applications
521 tc_hs_type mode (HsFunTy ty1 ty2) exp_kind
522 = tc_fun_type mode ty1 ty2 exp_kind
523
524 tc_hs_type mode (HsOpTy ty1 (L _ op) ty2) exp_kind
525 | op `hasKey` funTyConKey
526 = tc_fun_type mode ty1 ty2 exp_kind
527
528 --------- Foralls
529 tc_hs_type mode (HsForAllTy { hst_bndrs = hs_tvs, hst_body = ty }) exp_kind
530 = fmap fst $
531 tcExplicitTKBndrs hs_tvs $ \ tvs' ->
532 -- Do not kind-generalise here! See Note [Kind generalisation]
533 -- Why exp_kind? See Note [Body kind of HsForAllTy]
534 do { ty' <- tc_lhs_type mode ty exp_kind
535 ; let bound_vars = allBoundVariables ty'
536 bndrs = mkTyVarBinders Specified tvs'
537 ; return (mkForAllTys bndrs ty', bound_vars) }
538
539 tc_hs_type mode (HsQualTy { hst_ctxt = ctxt, hst_body = ty }) exp_kind
540 | null (unLoc ctxt)
541 = tc_lhs_type mode ty exp_kind
542
543 | otherwise
544 = do { ctxt' <- tc_hs_context mode ctxt
545
546 -- See Note [Body kind of a HsQualTy]
547 ; ty' <- if isConstraintKind exp_kind
548 then tc_lhs_type mode ty constraintKind
549 else do { ek <- ekOpen -- The body kind (result of the
550 -- function) can be * or #, hence ekOpen
551 ; ty <- tc_lhs_type mode ty ek
552 ; checkExpectedKind ty liftedTypeKind exp_kind }
553
554 ; return (mkPhiTy ctxt' ty') }
555
556 --------- Lists, arrays, and tuples
557 tc_hs_type mode (HsListTy elt_ty) exp_kind
558 = do { tau_ty <- tc_lhs_type mode elt_ty liftedTypeKind
559 ; checkWiredInTyCon listTyCon
560 ; checkExpectedKind (mkListTy tau_ty) liftedTypeKind exp_kind }
561
562 tc_hs_type mode (HsPArrTy elt_ty) exp_kind
563 = do { MASSERT( isTypeLevel (mode_level mode) )
564 ; tau_ty <- tc_lhs_type mode elt_ty liftedTypeKind
565 ; checkWiredInTyCon parrTyCon
566 ; checkExpectedKind (mkPArrTy tau_ty) liftedTypeKind exp_kind }
567
568 -- See Note [Distinguishing tuple kinds] in HsTypes
569 -- See Note [Inferring tuple kinds]
570 tc_hs_type mode (HsTupleTy HsBoxedOrConstraintTuple hs_tys) exp_kind
571 -- (NB: not zonking before looking at exp_k, to avoid left-right bias)
572 | Just tup_sort <- tupKindSort_maybe exp_kind
573 = traceTc "tc_hs_type tuple" (ppr hs_tys) >>
574 tc_tuple mode tup_sort hs_tys exp_kind
575 | otherwise
576 = do { traceTc "tc_hs_type tuple 2" (ppr hs_tys)
577 ; (tys, kinds) <- mapAndUnzipM (tc_infer_lhs_type mode) hs_tys
578 ; kinds <- mapM zonkTcType kinds
579 -- Infer each arg type separately, because errors can be
580 -- confusing if we give them a shared kind. Eg Trac #7410
581 -- (Either Int, Int), we do not want to get an error saying
582 -- "the second argument of a tuple should have kind *->*"
583
584 ; let (arg_kind, tup_sort)
585 = case [ (k,s) | k <- kinds
586 , Just s <- [tupKindSort_maybe k] ] of
587 ((k,s) : _) -> (k,s)
588 [] -> (liftedTypeKind, BoxedTuple)
589 -- In the [] case, it's not clear what the kind is, so guess *
590
591 ; tys' <- sequence [ setSrcSpan loc $
592 checkExpectedKind ty kind arg_kind
593 | ((L loc _),ty,kind) <- zip3 hs_tys tys kinds ]
594
595 ; finish_tuple tup_sort tys' (map (const arg_kind) tys') exp_kind }
596
597
598 tc_hs_type mode (HsTupleTy hs_tup_sort tys) exp_kind
599 = tc_tuple mode tup_sort tys exp_kind
600 where
601 tup_sort = case hs_tup_sort of -- Fourth case dealt with above
602 HsUnboxedTuple -> UnboxedTuple
603 HsBoxedTuple -> BoxedTuple
604 HsConstraintTuple -> ConstraintTuple
605 _ -> panic "tc_hs_type HsTupleTy"
606
607
608 --------- Promoted lists and tuples
609 tc_hs_type mode (HsExplicitListTy _k tys) exp_kind
610 = do { tks <- mapM (tc_infer_lhs_type mode) tys
611 ; (taus', kind) <- unifyKinds tks
612 ; let ty = (foldr (mk_cons kind) (mk_nil kind) taus')
613 ; checkExpectedKind ty (mkListTy kind) exp_kind }
614 where
615 mk_cons k a b = mkTyConApp (promoteDataCon consDataCon) [k, a, b]
616 mk_nil k = mkTyConApp (promoteDataCon nilDataCon) [k]
617
618 tc_hs_type mode (HsExplicitTupleTy _ tys) exp_kind
619 -- using newMetaKindVar means that we force instantiations of any polykinded
620 -- types. At first, I just used tc_infer_lhs_type, but that led to #11255.
621 = do { ks <- replicateM arity newMetaKindVar
622 ; taus <- zipWithM (tc_lhs_type mode) tys ks
623 ; let kind_con = tupleTyCon Boxed arity
624 ty_con = promotedTupleDataCon Boxed arity
625 tup_k = mkTyConApp kind_con ks
626 ; checkExpectedKind (mkTyConApp ty_con (ks ++ taus)) tup_k exp_kind }
627 where
628 arity = length tys
629
630 --------- Constraint types
631 tc_hs_type mode (HsIParamTy n ty) exp_kind
632 = do { MASSERT( isTypeLevel (mode_level mode) )
633 ; ty' <- tc_lhs_type mode ty liftedTypeKind
634 ; let n' = mkStrLitTy $ hsIPNameFS n
635 ; ipClass <- tcLookupClass ipClassName
636 ; checkExpectedKind (mkClassPred ipClass [n',ty'])
637 constraintKind exp_kind }
638
639 tc_hs_type mode (HsEqTy ty1 ty2) exp_kind
640 = do { (ty1', kind1) <- tc_infer_lhs_type mode ty1
641 ; (ty2', kind2) <- tc_infer_lhs_type mode ty2
642 ; ty2'' <- checkExpectedKind ty2' kind2 kind1
643 ; eq_tc <- tcLookupTyCon eqTyConName
644 ; let ty' = mkNakedTyConApp eq_tc [kind1, ty1', ty2'']
645 ; checkExpectedKind ty' constraintKind exp_kind }
646
647 --------- Literals
648 tc_hs_type _ (HsTyLit (HsNumTy _ n)) exp_kind
649 = do { checkWiredInTyCon typeNatKindCon
650 ; checkExpectedKind (mkNumLitTy n) typeNatKind exp_kind }
651
652 tc_hs_type _ (HsTyLit (HsStrTy _ s)) exp_kind
653 = do { checkWiredInTyCon typeSymbolKindCon
654 ; checkExpectedKind (mkStrLitTy s) typeSymbolKind exp_kind }
655
656 --------- Potentially kind-polymorphic types: call the "up" checker
657 -- See Note [Future-proofing the type checker]
658 tc_hs_type mode ty@(HsTyVar {}) ek = tc_infer_hs_type_ek mode ty ek
659 tc_hs_type mode ty@(HsAppTy {}) ek = tc_infer_hs_type_ek mode ty ek
660 tc_hs_type mode ty@(HsOpTy {}) ek = tc_infer_hs_type_ek mode ty ek
661 tc_hs_type mode ty@(HsKindSig {}) ek = tc_infer_hs_type_ek mode ty ek
662 tc_hs_type mode ty@(HsCoreTy {}) ek = tc_infer_hs_type_ek mode ty ek
663
664 tc_hs_type _ (HsWildCardTy wc) exp_kind
665 = do { wc_tv <- tcWildCardOcc wc exp_kind
666 ; return (mkTyVarTy wc_tv) }
667
668 -- disposed of by renamer
669 tc_hs_type _ ty@(HsAppsTy {}) _
670 = pprPanic "tc_hs_tyep HsAppsTy" (ppr ty)
671
672 tcWildCardOcc :: HsWildCardInfo Name -> Kind -> TcM TcTyVar
673 tcWildCardOcc wc_info exp_kind
674 = do { wc_tv <- tcLookupTyVar (wildCardName wc_info)
675 -- The wildcard's kind should be an un-filled-in meta tyvar
676 ; let Just wc_kind_var = tcGetTyVar_maybe (tyVarKind wc_tv)
677 ; writeMetaTyVar wc_kind_var exp_kind
678 ; return wc_tv }
679
680 ---------------------------
681 -- | Call 'tc_infer_hs_type' and check its result against an expected kind.
682 tc_infer_hs_type_ek :: TcTyMode -> HsType Name -> TcKind -> TcM TcType
683 tc_infer_hs_type_ek mode ty ek
684 = do { (ty', k) <- tc_infer_hs_type mode ty
685 ; checkExpectedKind ty' k ek }
686
687 ---------------------------
688 tupKindSort_maybe :: TcKind -> Maybe TupleSort
689 tupKindSort_maybe k
690 | Just (k', _) <- splitCastTy_maybe k = tupKindSort_maybe k'
691 | Just k' <- coreView k = tupKindSort_maybe k'
692 | isConstraintKind k = Just ConstraintTuple
693 | isLiftedTypeKind k = Just BoxedTuple
694 | otherwise = Nothing
695
696 tc_tuple :: TcTyMode -> TupleSort -> [LHsType Name] -> TcKind -> TcM TcType
697 tc_tuple mode tup_sort tys exp_kind
698 = do { arg_kinds <- case tup_sort of
699 BoxedTuple -> return (nOfThem arity liftedTypeKind)
700 UnboxedTuple -> do { rrs <- newFlexiTyVarTys arity runtimeRepTy
701 ; return $ map tYPE rrs }
702 ConstraintTuple -> return (nOfThem arity constraintKind)
703 ; tau_tys <- zipWithM (tc_lhs_type mode) tys arg_kinds
704 ; finish_tuple tup_sort tau_tys arg_kinds exp_kind }
705 where
706 arity = length tys
707
708 finish_tuple :: TupleSort
709 -> [TcType] -- ^ argument types
710 -> [TcKind] -- ^ of these kinds
711 -> TcKind -- ^ expected kind of the whole tuple
712 -> TcM TcType
713 finish_tuple tup_sort tau_tys tau_kinds exp_kind
714 = do { traceTc "finish_tuple" (ppr res_kind $$ ppr tau_kinds $$ ppr exp_kind)
715 ; let arg_tys = case tup_sort of
716 -- See also Note [Unboxed tuple RuntimeRep vars] in TyCon
717 UnboxedTuple -> map (getRuntimeRepFromKind "finish_tuple") tau_kinds
718 ++ tau_tys
719 BoxedTuple -> tau_tys
720 ConstraintTuple -> tau_tys
721 ; tycon <- case tup_sort of
722 ConstraintTuple
723 | arity > mAX_CTUPLE_SIZE
724 -> failWith (bigConstraintTuple arity)
725 | otherwise -> tcLookupTyCon (cTupleTyConName arity)
726 BoxedTuple -> do { let tc = tupleTyCon Boxed arity
727 ; checkWiredInTyCon tc
728 ; return tc }
729 UnboxedTuple -> return (tupleTyCon Unboxed arity)
730 ; checkExpectedKind (mkTyConApp tycon arg_tys) res_kind exp_kind }
731 where
732 arity = length tau_tys
733 res_kind = case tup_sort of
734 UnboxedTuple -> unboxedTupleKind
735 BoxedTuple -> liftedTypeKind
736 ConstraintTuple -> constraintKind
737
738 bigConstraintTuple :: Arity -> MsgDoc
739 bigConstraintTuple arity
740 = hang (text "Constraint tuple arity too large:" <+> int arity
741 <+> parens (text "max arity =" <+> int mAX_CTUPLE_SIZE))
742 2 (text "Instead, use a nested tuple")
743
744 ---------------------------
745 -- | Apply a type of a given kind to a list of arguments. This instantiates
746 -- invisible parameters as necessary. However, it does *not* necessarily
747 -- apply all the arguments, if the kind runs out of binders.
748 -- Never calls 'matchExpectedFunKind'; when the kind runs out of binders,
749 -- this stops processing.
750 -- This takes an optional @VarEnv Kind@ which maps kind variables to kinds.
751 -- These kinds should be used to instantiate invisible kind variables;
752 -- they come from an enclosing class for an associated type/data family.
753 -- This version will instantiate all invisible arguments left over after
754 -- the visible ones. Used only when typechecking type/data family patterns
755 -- (where we need to instantiate all remaining invisible parameters; for
756 -- example, consider @type family F :: k where F = Int; F = Maybe@. We
757 -- need to instantiate the @k@.)
758 tcInferArgs :: Outputable fun
759 => fun -- ^ the function
760 -> [TyConBinder] -- ^ function kind's binders
761 -> Maybe (VarEnv Kind) -- ^ possibly, kind info (see above)
762 -> [LHsType Name] -- ^ args
763 -> TcM (TCvSubst, [TyBinder], [TcType], [LHsType Name], Int)
764 -- ^ (instantiating subst, un-insted leftover binders,
765 -- typechecked args, untypechecked args, n)
766 tcInferArgs fun tc_binders mb_kind_info args
767 = do { let binders = tyConBindersTyBinders tc_binders -- UGH!
768 ; (subst, leftover_binders, args', leftovers, n)
769 <- tc_infer_args typeLevelMode fun binders mb_kind_info args 1
770 -- now, we need to instantiate any remaining invisible arguments
771 ; let (invis_bndrs, other_binders) = break isVisibleBinder leftover_binders
772 ; (subst', invis_args)
773 <- tcInstBindersX subst mb_kind_info invis_bndrs
774 ; return ( subst'
775 , other_binders
776 , args' `chkAppend` invis_args
777 , leftovers, n ) }
778
779 -- | See comments for 'tcInferArgs'. But this version does not instantiate
780 -- any remaining invisible arguments.
781 tc_infer_args :: Outputable fun
782 => TcTyMode
783 -> fun -- ^ the function
784 -> [TyBinder] -- ^ function kind's binders (zonked)
785 -> Maybe (VarEnv Kind) -- ^ possibly, kind info (see above)
786 -> [LHsType Name] -- ^ args
787 -> Int -- ^ number to start arg counter at
788 -> TcM (TCvSubst, [TyBinder], [TcType], [LHsType Name], Int)
789 tc_infer_args mode orig_ty binders mb_kind_info orig_args n0
790 = go emptyTCvSubst binders orig_args n0 []
791 where
792 go subst binders [] n acc
793 = return ( subst, binders, reverse acc, [], n )
794 -- when we call this when checking type family patterns, we really
795 -- do want to instantiate all invisible arguments. During other
796 -- typechecking, we don't.
797
798 go subst (binder:binders) all_args@(arg:args) n acc
799 | isInvisibleBinder binder
800 = do { traceTc "tc_infer_args (invis)" (ppr binder)
801 ; (subst', arg') <- tcInstBinderX mb_kind_info subst binder
802 ; go subst' binders all_args n (arg' : acc) }
803
804 | otherwise
805 = do { traceTc "tc_infer_args (vis)" (ppr binder $$ ppr arg)
806 ; arg' <- addErrCtxt (funAppCtxt orig_ty arg n) $
807 tc_lhs_type mode arg (substTyUnchecked subst $
808 tyBinderType binder)
809 ; let subst' = extendTvSubstBinder subst binder arg'
810 ; go subst' binders args (n+1) (arg' : acc) }
811
812 go subst [] all_args n acc
813 = return (subst, [], reverse acc, all_args, n)
814
815 -- | Applies a type to a list of arguments.
816 -- Always consumes all the arguments, using 'matchExpectedFunKind' as
817 -- necessary. If you wish to apply a type to a list of HsTypes, this is
818 -- your function.
819 -- Used for type-checking types only.
820 tcInferApps :: Outputable fun
821 => TcTyMode
822 -> fun -- ^ Function (for printing only)
823 -> TcType -- ^ Function (could be knot-tied)
824 -> TcKind -- ^ Function kind (zonked)
825 -> [LHsType Name] -- ^ Args
826 -> TcM (TcType, TcKind) -- ^ (f args, result kind)
827 tcInferApps mode orig_ty ty ki args = go ty ki args 1
828 where
829 go fun fun_kind [] _ = return (fun, fun_kind)
830 go fun fun_kind args n
831 | let (binders, res_kind) = splitPiTys fun_kind
832 , not (null binders)
833 = do { (subst, leftover_binders, args', leftover_args, n')
834 <- tc_infer_args mode orig_ty binders Nothing args n
835 ; let fun_kind' = substTyUnchecked subst $
836 mkPiTys leftover_binders res_kind
837 ; go (mkNakedAppTys fun args') fun_kind' leftover_args n' }
838
839 go fun fun_kind all_args@(arg:args) n
840 = do { (co, arg_k, res_k) <- matchExpectedFunKind (length all_args)
841 fun fun_kind
842 ; arg' <- addErrCtxt (funAppCtxt orig_ty arg n) $
843 tc_lhs_type mode arg arg_k
844 ; go (mkNakedAppTy (fun `mkNakedCastTy` co) arg')
845 res_k args (n+1) }
846
847 --------------------------
848 checkExpectedKind :: TcType -- the type whose kind we're checking
849 -> TcKind -- the known kind of that type, k
850 -> TcKind -- the expected kind, exp_kind
851 -> TcM TcType -- a possibly-inst'ed, casted type :: exp_kind
852 -- Instantiate a kind (if necessary) and then call unifyType
853 -- (checkExpectedKind ty act_kind exp_kind)
854 -- checks that the actual kind act_kind is compatible
855 -- with the expected kind exp_kind
856 checkExpectedKind ty act_kind exp_kind
857 = do { (ty', act_kind') <- instantiate ty act_kind exp_kind
858 ; let origin = TypeEqOrigin { uo_actual = act_kind'
859 , uo_expected = mkCheckExpType exp_kind
860 , uo_thing = Just $ mkTypeErrorThing ty'
861 }
862 ; co_k <- uType origin KindLevel act_kind' exp_kind
863 ; traceTc "checkExpectedKind" (vcat [ ppr act_kind
864 , ppr exp_kind
865 , ppr co_k ])
866 ; let result_ty = ty' `mkNakedCastTy` co_k
867 ; return result_ty }
868 where
869 -- we need to make sure that both kinds have the same number of implicit
870 -- foralls out front. If the actual kind has more, instantiate accordingly.
871 -- Otherwise, just pass the type & kind through -- the errors are caught
872 -- in unifyType.
873 instantiate :: TcType -- the type
874 -> TcKind -- of this kind
875 -> TcKind -- but expected to be of this one
876 -> TcM ( TcType -- the inst'ed type
877 , TcKind ) -- its new kind
878 instantiate ty act_ki exp_ki
879 = let (exp_bndrs, _) = splitPiTysInvisible exp_ki in
880 instantiateTyN (length exp_bndrs) ty act_ki
881
882 -- | Instantiate a type to have at most @n@ invisible arguments.
883 instantiateTyN :: Int -- ^ @n@
884 -> TcType -- ^ the type
885 -> TcKind -- ^ its kind
886 -> TcM (TcType, TcKind) -- ^ The inst'ed type with kind
887 instantiateTyN n ty ki
888 = let (bndrs, inner_ki) = splitPiTysInvisible ki
889 num_to_inst = length bndrs - n
890 -- NB: splitAt is forgiving with invalid numbers
891 (inst_bndrs, leftover_bndrs) = splitAt num_to_inst bndrs
892 in
893 if num_to_inst <= 0 then return (ty, ki) else
894 do { (subst, inst_args) <- tcInstBinders inst_bndrs
895 ; let rebuilt_ki = mkPiTys leftover_bndrs inner_ki
896 ki' = substTy subst rebuilt_ki
897 ; return (mkNakedAppTys ty inst_args, ki') }
898
899 ---------------------------
900 tcHsContext :: LHsContext Name -> TcM [PredType]
901 tcHsContext = tc_hs_context typeLevelMode
902
903 tcLHsPredType :: LHsType Name -> TcM PredType
904 tcLHsPredType = tc_lhs_pred typeLevelMode
905
906 tc_hs_context :: TcTyMode -> LHsContext Name -> TcM [PredType]
907 tc_hs_context mode ctxt = mapM (tc_lhs_pred mode) (unLoc ctxt)
908
909 tc_lhs_pred :: TcTyMode -> LHsType Name -> TcM PredType
910 tc_lhs_pred mode pred = tc_lhs_type mode pred constraintKind
911
912 ---------------------------
913 tcTyVar :: TcTyMode -> Name -> TcM (TcType, TcKind)
914 -- See Note [Type checking recursive type and class declarations]
915 -- in TcTyClsDecls
916 tcTyVar mode name -- Could be a tyvar, a tycon, or a datacon
917 = do { traceTc "lk1" (ppr name)
918 ; thing <- tcLookup name
919 ; case thing of
920 ATyVar _ tv -> return (mkTyVarTy tv, tyVarKind tv)
921
922 ATcTyCon tc_tc -> do { -- See Note [GADT kind self-reference]
923 unless
924 (isTypeLevel (mode_level mode))
925 (promotionErr name TyConPE)
926 ; check_tc tc_tc
927 ; tc <- get_loopy_tc name tc_tc
928 ; handle_tyfams tc tc_tc }
929 -- mkNakedTyConApp: see Note [Type-checking inside the knot]
930 -- NB: we really should check if we're at the kind level
931 -- and if the tycon is promotable if -XNoTypeInType is set.
932 -- But this is a terribly large amount of work! Not worth it.
933
934 AGlobal (ATyCon tc)
935 -> do { check_tc tc
936 ; handle_tyfams tc tc }
937
938 AGlobal (AConLike (RealDataCon dc))
939 -> do { data_kinds <- xoptM LangExt.DataKinds
940 ; unless (data_kinds || specialPromotedDc dc) $
941 promotionErr name NoDataKindsDC
942 ; type_in_type <- xoptM LangExt.TypeInType
943 ; unless ( type_in_type ||
944 ( isTypeLevel (mode_level mode) &&
945 isLegacyPromotableDataCon dc ) ||
946 ( isKindLevel (mode_level mode) &&
947 specialPromotedDc dc ) ) $
948 promotionErr name NoTypeInTypeDC
949 ; let tc = promoteDataCon dc
950 ; return (mkNakedTyConApp tc [], tyConKind tc) }
951
952 APromotionErr err -> promotionErr name err
953
954 _ -> wrongThingErr "type" thing name }
955 where
956 check_tc :: TyCon -> TcM ()
957 check_tc tc = do { type_in_type <- xoptM LangExt.TypeInType
958 ; data_kinds <- xoptM LangExt.DataKinds
959 ; unless (isTypeLevel (mode_level mode) ||
960 data_kinds ||
961 isKindTyCon tc) $
962 promotionErr name NoDataKindsTC
963 ; unless (isTypeLevel (mode_level mode) ||
964 type_in_type ||
965 isLegacyPromotableTyCon tc) $
966 promotionErr name NoTypeInTypeTC }
967
968 -- if we are type-checking a type family tycon, we must instantiate
969 -- any invisible arguments right away. Otherwise, we get #11246
970 handle_tyfams :: TyCon -- the tycon to instantiate (might be loopy)
971 -> TyCon -- a non-loopy version of the tycon
972 -> TcM (TcType, TcKind)
973 handle_tyfams tc tc_tc
974 | mightBeUnsaturatedTyCon tc_tc
975 = do { traceTc "tcTyVar2a" (ppr tc_tc $$ ppr tc_kind)
976 ; return (ty, tc_kind) }
977
978 | otherwise
979 = do { (tc_ty, kind) <- instantiateTyN 0 ty tc_kind
980 -- tc and tc_ty must not be traced here, because that would
981 -- force the evaluation of a potentially knot-tied variable (tc),
982 -- and the typechecker would hang, as per #11708
983 ; traceTc "tcTyVar2b" (vcat [ ppr tc_tc <+> dcolon <+> ppr tc_kind
984 , ppr kind ])
985 ; return (tc_ty, kind) }
986 where
987 ty = mkNakedTyConApp tc []
988 tc_kind = tyConKind tc_tc
989
990 get_loopy_tc :: Name -> TyCon -> TcM TyCon
991 -- Return the knot-tied global TyCon if there is one
992 -- Otherwise the local TcTyCon; we must be doing kind checking
993 -- but we still want to return a TyCon of some sort to use in
994 -- error messages
995 get_loopy_tc name tc_tc
996 = do { env <- getGblEnv
997 ; case lookupNameEnv (tcg_type_env env) name of
998 Just (ATyCon tc) -> return tc
999 _ -> do { traceTc "lk1 (loopy)" (ppr name)
1000 ; return tc_tc } }
1001
1002 tcClass :: Name -> TcM (Class, TcKind)
1003 tcClass cls -- Must be a class
1004 = do { thing <- tcLookup cls
1005 ; case thing of
1006 ATcTyCon tc -> return (aThingErr "tcClass" cls, tyConKind tc)
1007 AGlobal (ATyCon tc)
1008 | Just cls <- tyConClass_maybe tc
1009 -> return (cls, tyConKind tc)
1010 _ -> wrongThingErr "class" thing cls }
1011
1012
1013 aThingErr :: String -> Name -> b
1014 -- The type checker for types is sometimes called simply to
1015 -- do *kind* checking; and in that case it ignores the type
1016 -- returned. Which is a good thing since it may not be available yet!
1017 aThingErr str x = pprPanic "AThing evaluated unexpectedly" (text str <+> ppr x)
1018
1019 {-
1020 Note [Type-checking inside the knot]
1021 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1022 Suppose we are checking the argument types of a data constructor. We
1023 must zonk the types before making the DataCon, because once built we
1024 can't change it. So we must traverse the type.
1025
1026 BUT the parent TyCon is knot-tied, so we can't look at it yet.
1027
1028 So we must be careful not to use "smart constructors" for types that
1029 look at the TyCon or Class involved.
1030
1031 * Hence the use of mkNakedXXX functions. These do *not* enforce
1032 the invariants (for example that we use (FunTy s t) rather
1033 than (TyConApp (->) [s,t])).
1034
1035 * The zonking functions establish invariants (even zonkTcType, a change from
1036 previous behaviour). So we must never inspect the result of a
1037 zonk that might mention a knot-tied TyCon. This is generally OK
1038 because we zonk *kinds* while kind-checking types. And the TyCons
1039 in kinds shouldn't be knot-tied, because they come from a previous
1040 mutually recursive group.
1041
1042 * TcHsSyn.zonkTcTypeToType also can safely check/establish
1043 invariants.
1044
1045 This is horribly delicate. I hate it. A good example of how
1046 delicate it is can be seen in Trac #7903.
1047
1048 Note [GADT kind self-reference]
1049 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1050
1051 A promoted type cannot be used in the body of that type's declaration.
1052 Trac #11554 shows this example, which made GHC loop:
1053
1054 import Data.Kind
1055 data P (x :: k) = Q
1056 data A :: Type where
1057 B :: forall (a :: A). P a -> A
1058
1059 In order to check the constructor B, we need have the promoted type A, but in
1060 order to get that promoted type, B must first be checked. To prevent looping, a
1061 TyConPE promotion error is given when tcTyVar checks an ATcTyCon in kind mode.
1062 Any ATcTyCon is a TyCon being defined in the current recursive group (see data
1063 type decl for TcTyThing), and all such TyCons are illegal in kinds.
1064
1065 Trac #11962 proposes checking the head of a data declaration separately from
1066 its constructors. This would allow the example above to pass.
1067
1068 Note [Body kind of a HsForAllTy]
1069 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1070 The body of a forall is usually a type, but in principle
1071 there's no reason to prohibit *unlifted* types.
1072 In fact, GHC can itself construct a function with an
1073 unboxed tuple inside a for-all (via CPR analyis; see
1074 typecheck/should_compile/tc170).
1075
1076 Moreover in instance heads we get forall-types with
1077 kind Constraint.
1078
1079 It's tempting to check that the body kind is either * or #. But this is
1080 wrong. For example:
1081
1082 class C a b
1083 newtype N = Mk Foo deriving (C a)
1084
1085 We're doing newtype-deriving for C. But notice how `a` isn't in scope in
1086 the predicate `C a`. So we quantify, yielding `forall a. C a` even though
1087 `C a` has kind `* -> Constraint`. The `forall a. C a` is a bit cheeky, but
1088 convenient. Bottom line: don't check for * or # here.
1089
1090 Note [Body kind of a HsQualTy]
1091 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1092 If ctxt is non-empty, the HsQualTy really is a /function/, so the
1093 kind of the result really is '*', and in that case the kind of the
1094 body-type can be lifted or unlifted.
1095
1096 However, consider
1097 instance Eq a => Eq [a] where ...
1098 or
1099 f :: (Eq a => Eq [a]) => blah
1100 Here both body-kind of the HsQualTy is Constraint rather than *.
1101 Rather crudely we tell the difference by looking at exp_kind. It's
1102 very convenient to typecheck instance types like any other HsSigType.
1103
1104 Admittedly the '(Eq a => Eq [a]) => blah' case is erroneous, but it's
1105 better to reject in checkValidType. If we say that the body kind
1106 should be '*' we risk getting TWO error messages, one saying that Eq
1107 [a] doens't have kind '*', and one saying that we need a Constraint to
1108 the left of the outer (=>).
1109
1110 How do we figure out the right body kind? Well, it's a bit of a
1111 kludge: I just look at the expected kind. If it's Constraint, we
1112 must be in this instance situation context. It's a kludge because it
1113 wouldn't work if any unification was involved to compute that result
1114 kind -- but it isn't. (The true way might be to use the 'mode'
1115 parameter, but that seemed like a sledgehammer to crack a nut.)
1116
1117 Note [Inferring tuple kinds]
1118 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1119 Give a tuple type (a,b,c), which the parser labels as HsBoxedOrConstraintTuple,
1120 we try to figure out whether it's a tuple of kind * or Constraint.
1121 Step 1: look at the expected kind
1122 Step 2: infer argument kinds
1123
1124 If after Step 2 it's not clear from the arguments that it's
1125 Constraint, then it must be *. Once having decided that we re-check
1126 the Check the arguments again to give good error messages
1127 in eg. `(Maybe, Maybe)`
1128
1129 Note that we will still fail to infer the correct kind in this case:
1130
1131 type T a = ((a,a), D a)
1132 type family D :: Constraint -> Constraint
1133
1134 While kind checking T, we do not yet know the kind of D, so we will default the
1135 kind of T to * -> *. It works if we annotate `a` with kind `Constraint`.
1136
1137 Note [Desugaring types]
1138 ~~~~~~~~~~~~~~~~~~~~~~~
1139 The type desugarer is phase 2 of dealing with HsTypes. Specifically:
1140
1141 * It transforms from HsType to Type
1142
1143 * It zonks any kinds. The returned type should have no mutable kind
1144 or type variables (hence returning Type not TcType):
1145 - any unconstrained kind variables are defaulted to (Any *) just
1146 as in TcHsSyn.
1147 - there are no mutable type variables because we are
1148 kind-checking a type
1149 Reason: the returned type may be put in a TyCon or DataCon where
1150 it will never subsequently be zonked.
1151
1152 You might worry about nested scopes:
1153 ..a:kappa in scope..
1154 let f :: forall b. T '[a,b] -> Int
1155 In this case, f's type could have a mutable kind variable kappa in it;
1156 and we might then default it to (Any *) when dealing with f's type
1157 signature. But we don't expect this to happen because we can't get a
1158 lexically scoped type variable with a mutable kind variable in it. A
1159 delicate point, this. If it becomes an issue we might need to
1160 distinguish top-level from nested uses.
1161
1162 Moreover
1163 * it cannot fail,
1164 * it does no unifications
1165 * it does no validity checking, except for structural matters, such as
1166 (a) spurious ! annotations.
1167 (b) a class used as a type
1168
1169 Note [Kind of a type splice]
1170 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1171 Consider these terms, each with TH type splice inside:
1172 [| e1 :: Maybe $(..blah..) |]
1173 [| e2 :: $(..blah..) |]
1174 When kind-checking the type signature, we'll kind-check the splice
1175 $(..blah..); we want to give it a kind that can fit in any context,
1176 as if $(..blah..) :: forall k. k.
1177
1178 In the e1 example, the context of the splice fixes kappa to *. But
1179 in the e2 example, we'll desugar the type, zonking the kind unification
1180 variables as we go. When we encounter the unconstrained kappa, we
1181 want to default it to '*', not to (Any *).
1182
1183
1184 Help functions for type applications
1185 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1186 -}
1187
1188 addTypeCtxt :: LHsType Name -> TcM a -> TcM a
1189 -- Wrap a context around only if we want to show that contexts.
1190 -- Omit invisble ones and ones user's won't grok
1191 addTypeCtxt (L _ ty) thing
1192 = addErrCtxt doc thing
1193 where
1194 doc = text "In the type" <+> quotes (ppr ty)
1195
1196 {-
1197 ************************************************************************
1198 * *
1199 Type-variable binders
1200 %* *
1201 %************************************************************************
1202
1203 Note [Scope-check inferred kinds]
1204 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1205 Consider
1206
1207 data SameKind :: k -> k -> *
1208 foo :: forall a (b :: Proxy a) (c :: Proxy d). SameKind b c
1209
1210 d has no binding site. So it gets bound implicitly, at the top. The
1211 problem is that d's kind mentions `a`. So it's all ill-scoped.
1212
1213 The way we check for this is to gather all variables *bound* in a
1214 type variable's scope. The type variable's kind should not mention
1215 any of these variables. That is, d's kind can't mention a, b, or c.
1216 We can't just check to make sure that d's kind is in scope, because
1217 we might be about to kindGeneralize.
1218
1219 A little messy, but it works.
1220
1221 Note [Dependent LHsQTyVars]
1222 ~~~~~~~~~~~~~~~~~~~~~~~~~~~
1223 We track (in the renamer) which explicitly bound variables in a
1224 LHsQTyVars are manifestly dependent; only precisely these variables
1225 may be used within the LHsQTyVars. We must do this so that kcHsTyVarBndrs
1226 can produce the right TcTyBinders, and tell Anon vs. Named. Earlier,
1227 I thought it would work simply to do a free-variable check during
1228 kcHsTyVarBndrs, but this is bogus, because there may be unsolved
1229 equalities about. And we don't want to eagerly solve the equalities,
1230 because we may get further information after kcHsTyVarBndrs is called.
1231 (Recall that kcHsTyVarBndrs is usually called from getInitialKind.
1232 The only other case is in kcConDecl.) This is what implements the rule
1233 that all variables intended to be dependent must be manifestly so.
1234
1235 Sidenote: It's quite possible that later, we'll consider (t -> s)
1236 as a degenerate case of some (pi (x :: t) -> s) and then this will
1237 all get more permissive.
1238
1239 -}
1240
1241 tcWildCardBinders :: [Name]
1242 -> ([(Name, TcTyVar)] -> TcM a)
1243 -> TcM a
1244 tcWildCardBinders = tcWildCardBindersX new_tv
1245 where
1246 new_tv name = do { kind <- newMetaKindVar
1247 ; newSkolemTyVar name kind }
1248
1249 tcWildCardBindersX :: (Name -> TcM TcTyVar)
1250 -> [Name]
1251 -> ([(Name, TcTyVar)] -> TcM a)
1252 -> TcM a
1253 tcWildCardBindersX new_wc wc_names thing_inside
1254 = do { wcs <- mapM new_wc wc_names
1255 ; let wc_prs = wc_names `zip` wcs
1256 ; tcExtendTyVarEnv2 wc_prs $
1257 thing_inside wc_prs }
1258
1259 -- | Kind-check a 'LHsQTyVars'. If the decl under consideration has a complete,
1260 -- user-supplied kind signature (CUSK), generalise the result.
1261 -- Used in 'getInitialKind' (for tycon kinds and other kinds)
1262 -- and in kind-checking (but not for tycon kinds, which are checked with
1263 -- tcTyClDecls). See also Note [Complete user-supplied kind signatures] in
1264 -- HsDecls.
1265 --
1266 -- This function does not do telescope checking.
1267 kcHsTyVarBndrs :: Name -- ^ of the thing being checked
1268 -> Bool -- ^ True <=> the decl being checked has a CUSK
1269 -> Bool -- ^ True <=> the decl is an open type/data family
1270 -> Bool -- ^ True <=> all the hsq_implicit are *kind* vars
1271 -- (will give these kind * if -XNoTypeInType)
1272 -> LHsQTyVars Name
1273 -> TcM (Kind, r) -- ^ the result kind, possibly with other info
1274 -> TcM (Bool -> TcTyCon, r)
1275 -- ^ a way to make a TcTyCon, with the other info.
1276 -- The Bool says whether the tycon can be unsaturated.
1277 kcHsTyVarBndrs name cusk open_fam all_kind_vars
1278 (HsQTvs { hsq_implicit = kv_ns, hsq_explicit = hs_tvs
1279 , hsq_dependent = dep_names }) thing_inside
1280 | cusk
1281 = do { kv_kinds <- mk_kv_kinds
1282 ; let scoped_kvs = zipWith mk_skolem_tv kv_ns kv_kinds
1283 ; tcExtendTyVarEnv2 (kv_ns `zip` scoped_kvs) $
1284 do { (tc_binders, res_kind, stuff) <- solveEqualities $
1285 bind_telescope hs_tvs thing_inside
1286
1287 -- Now, because we're in a CUSK, quantify over the mentioned
1288 -- kind vars, in dependency order.
1289 ; tc_binders <- mapM zonkTyConBinder tc_binders
1290 ; res_kind <- zonkTcType res_kind
1291 ; let tc_tvs = binderVars tc_binders
1292 qkvs = tyCoVarsOfTypeWellScoped (mkTyConKind tc_binders res_kind)
1293 -- the visibility of tvs doesn't matter here; we just
1294 -- want the free variables not to include the tvs
1295
1296 -- If there are any meta-tvs left, the user has
1297 -- lied about having a CUSK. Error.
1298 ; let (meta_tvs, good_tvs) = partition isMetaTyVar qkvs
1299 ; when (not (null meta_tvs)) $
1300 report_non_cusk_tvs (qkvs ++ tc_tvs)
1301
1302 -- If any of the scoped_kvs aren't actually mentioned in a binder's
1303 -- kind (or the return kind), then we're in the CUSK case from
1304 -- Note [Free-floating kind vars]
1305 ; let all_tc_tvs = good_tvs ++ tc_tvs
1306 all_mentioned_tvs = mapUnionVarSet (tyCoVarsOfType . tyVarKind)
1307 all_tc_tvs
1308 `unionVarSet` tyCoVarsOfType res_kind
1309 unmentioned_kvs = filterOut (`elemVarSet` all_mentioned_tvs)
1310 scoped_kvs
1311 ; reportFloatingKvs name all_tc_tvs unmentioned_kvs
1312
1313 ; let final_binders = map (mkNamedTyConBinder Specified) good_tvs
1314 ++ tc_binders
1315 mk_tctc unsat = mkTcTyCon name final_binders res_kind
1316 unsat (scoped_kvs ++ tc_tvs)
1317 -- the tvs contain the binders already
1318 -- in scope from an enclosing class, but
1319 -- re-adding tvs to the env't doesn't cause
1320 -- harm
1321 ; return ( mk_tctc, stuff ) }}
1322
1323 | otherwise
1324 = do { kv_kinds <- mk_kv_kinds
1325 ; scoped_kvs <- zipWithM newSigTyVar kv_ns kv_kinds
1326 -- the names must line up in splitTelescopeTvs
1327 ; (binders, res_kind, stuff)
1328 <- tcExtendTyVarEnv2 (kv_ns `zip` scoped_kvs) $
1329 bind_telescope hs_tvs thing_inside
1330 ; let -- NB: Don't add scoped_kvs to tyConTyVars, because they
1331 -- must remain lined up with the binders
1332 mk_tctc unsat = mkTcTyCon name binders res_kind unsat
1333 (scoped_kvs ++ binderVars binders)
1334 ; return (mk_tctc, stuff) }
1335 where
1336 -- if -XNoTypeInType and we know all the implicits are kind vars,
1337 -- just give the kind *. This prevents test
1338 -- dependent/should_fail/KindLevelsB from compiling, as it should
1339 mk_kv_kinds :: TcM [Kind]
1340 mk_kv_kinds = do { typeintype <- xoptM LangExt.TypeInType
1341 ; if not typeintype && all_kind_vars
1342 then return (map (const liftedTypeKind) kv_ns)
1343 else mapM (const newMetaKindVar) kv_ns }
1344
1345 -- there may be dependency between the explicit "ty" vars. So, we have
1346 -- to handle them one at a time.
1347 bind_telescope :: [LHsTyVarBndr Name]
1348 -> TcM (Kind, r)
1349 -> TcM ([TyConBinder], TcKind, r)
1350 bind_telescope [] thing
1351 = do { (res_kind, stuff) <- thing
1352 ; return ([], res_kind, stuff) }
1353 bind_telescope (L _ hs_tv : hs_tvs) thing
1354 = do { tv_pair@(tv, _) <- kc_hs_tv hs_tv
1355 -- NB: Bring all tvs into scope, even non-dependent ones,
1356 -- as they're needed in type synonyms, data constructors, etc.
1357 ; (binders, res_kind, stuff) <- bind_unless_scoped tv_pair $
1358 bind_telescope hs_tvs $
1359 thing
1360 -- See Note [Dependent LHsQTyVars]
1361 ; let new_binder | hsTyVarName hs_tv `elemNameSet` dep_names
1362 = mkNamedTyConBinder Required tv
1363 | otherwise
1364 = mkAnonTyConBinder tv
1365 ; return ( new_binder : binders
1366 , res_kind, stuff ) }
1367
1368 -- | Bind the tyvar in the env't unless the bool is True
1369 bind_unless_scoped :: (TcTyVar, Bool) -> TcM a -> TcM a
1370 bind_unless_scoped (_, True) thing_inside = thing_inside
1371 bind_unless_scoped (tv, False) thing_inside
1372 = tcExtendTyVarEnv [tv] thing_inside
1373
1374 kc_hs_tv :: HsTyVarBndr Name -> TcM (TcTyVar, Bool)
1375 kc_hs_tv (UserTyVar (L _ name))
1376 = do { tv_pair@(tv, scoped) <- tcHsTyVarName Nothing name
1377
1378 -- Open type/data families default their variables to kind *.
1379 ; when (open_fam && not scoped) $ -- (don't default class tyvars)
1380 discardResult $ unifyKind (Just (mkTyVarTy tv)) liftedTypeKind
1381 (tyVarKind tv)
1382
1383 ; return tv_pair }
1384
1385 kc_hs_tv (KindedTyVar (L _ name) lhs_kind)
1386 = do { kind <- tcLHsKind lhs_kind
1387 ; tcHsTyVarName (Just kind) name }
1388
1389 report_non_cusk_tvs all_tvs
1390 = do { all_tvs <- mapM zonkTyCoVarKind all_tvs
1391 ; let (_, tidy_tvs) = tidyOpenTyCoVars emptyTidyEnv all_tvs
1392 (meta_tvs, other_tvs) = partition isMetaTyVar tidy_tvs
1393
1394 ; addErr $
1395 vcat [ text "You have written a *complete user-suppled kind signature*,"
1396 , hang (text "but the following variable" <> plural meta_tvs <+>
1397 isOrAre meta_tvs <+> text "undetermined:")
1398 2 (vcat (map pp_tv meta_tvs))
1399 , text "Perhaps add a kind signature."
1400 , hang (text "Inferred kinds of user-written variables:")
1401 2 (vcat (map pp_tv other_tvs)) ] }
1402 where
1403 pp_tv tv = ppr tv <+> dcolon <+> ppr (tyVarKind tv)
1404
1405
1406 tcImplicitTKBndrs :: [Name]
1407 -> TcM (a, TyVarSet) -- vars are bound somewhere in the scope
1408 -- see Note [Scope-check inferred kinds]
1409 -> TcM ([TcTyVar], a)
1410 tcImplicitTKBndrs = tcImplicitTKBndrsX (tcHsTyVarName Nothing)
1411
1412 -- | Convenient specialization
1413 tcImplicitTKBndrsType :: [Name]
1414 -> TcM Type
1415 -> TcM ([TcTyVar], Type)
1416 tcImplicitTKBndrsType var_ns thing_inside
1417 = tcImplicitTKBndrs var_ns $
1418 do { res_ty <- thing_inside
1419 ; return (res_ty, allBoundVariables res_ty) }
1420
1421 -- this more general variant is needed in tcHsPatSigType.
1422 -- See Note [Pattern signature binders]
1423 tcImplicitTKBndrsX :: (Name -> TcM (TcTyVar, Bool)) -- new_tv function
1424 -> [Name]
1425 -> TcM (a, TyVarSet)
1426 -> TcM ([TcTyVar], a)
1427 -- Returned TcTyVars have the supplied Names
1428 -- i.e. no cloning of fresh names
1429 tcImplicitTKBndrsX new_tv var_ns thing_inside
1430 = do { tkvs_pairs <- mapM new_tv var_ns
1431 ; let must_scope_tkvs = [ tkv | (tkv, False) <- tkvs_pairs ]
1432 tkvs = map fst tkvs_pairs
1433 ; (result, bound_tvs) <- tcExtendTyVarEnv must_scope_tkvs $
1434 thing_inside
1435
1436 -- it's possible that we guessed the ordering of variables
1437 -- wrongly. Adjust.
1438 ; tkvs <- mapM zonkTyCoVarKind tkvs
1439 ; let extra = text "NB: Implicitly-bound variables always come" <+>
1440 text "before other ones."
1441 ; checkValidInferredKinds tkvs bound_tvs extra
1442
1443 ; let final_tvs = toposortTyVars tkvs
1444 ; traceTc "tcImplicitTKBndrs" (ppr var_ns $$ ppr final_tvs)
1445
1446 ; return (final_tvs, result) }
1447
1448 tcExplicitTKBndrs :: [LHsTyVarBndr Name]
1449 -> ([TyVar] -> TcM (a, TyVarSet))
1450 -- ^ Thing inside returns the set of variables bound
1451 -- in the scope. See Note [Scope-check inferred kinds]
1452 -> TcM (a, TyVarSet) -- ^ returns augmented bound vars
1453 -- No cloning: returned TyVars have the same Name as the incoming LHsTyVarBndrs
1454 tcExplicitTKBndrs orig_hs_tvs thing_inside
1455 = tcExplicitTKBndrsX newSkolemTyVar orig_hs_tvs thing_inside
1456
1457 tcExplicitTKBndrsX :: (Name -> Kind -> TcM TyVar)
1458 -> [LHsTyVarBndr Name]
1459 -> ([TyVar] -> TcM (a, TyVarSet))
1460 -- ^ Thing inside returns the set of variables bound
1461 -- in the scope. See Note [Scope-check inferred kinds]
1462 -> TcM (a, TyVarSet) -- ^ returns augmented bound vars
1463 tcExplicitTKBndrsX new_tv orig_hs_tvs thing_inside
1464 = go orig_hs_tvs $ \ tvs ->
1465 do { (result, bound_tvs) <- thing_inside tvs
1466
1467 -- Issue an error if the ordering is bogus.
1468 -- See Note [Bad telescopes] in TcValidity.
1469 ; tvs <- checkZonkValidTelescope (interppSP orig_hs_tvs) tvs empty
1470 ; checkValidInferredKinds tvs bound_tvs empty
1471
1472 ; traceTc "tcExplicitTKBndrs" $
1473 vcat [ text "Hs vars:" <+> ppr orig_hs_tvs
1474 , text "tvs:" <+> sep (map pprTvBndr tvs) ]
1475
1476 ; return (result, bound_tvs `unionVarSet` mkVarSet tvs)
1477 }
1478 where
1479 go [] thing = thing []
1480 go (L _ hs_tv : hs_tvs) thing
1481 = do { tv <- tcHsTyVarBndr new_tv hs_tv
1482 ; tcExtendTyVarEnv [tv] $
1483 go hs_tvs $ \ tvs ->
1484 thing (tv : tvs) }
1485
1486 tcHsTyVarBndr :: (Name -> Kind -> TcM TyVar)
1487 -> HsTyVarBndr Name -> TcM TcTyVar
1488 -- Return a SkolemTv TcTyVar, initialised with a kind variable.
1489 -- Typically the Kind inside the HsTyVarBndr will be a tyvar
1490 -- with a mutable kind in it.
1491 -- NB: These variables must not be in scope. This function
1492 -- is not appropriate for use with associated types, for example.
1493 --
1494 -- Returned TcTyVar has the same name; no cloning
1495 --
1496 -- See also Note [Associated type tyvar names] in Class
1497 --
1498 tcHsTyVarBndr new_tv (UserTyVar (L _ name))
1499 = do { kind <- newMetaKindVar
1500 ; new_tv name kind }
1501
1502 tcHsTyVarBndr new_tv (KindedTyVar (L _ name) kind)
1503 = do { kind <- tcLHsKind kind
1504 ; new_tv name kind }
1505
1506 newWildTyVar :: Name -> TcM TcTyVar
1507 -- ^ New unification variable for a wildcard
1508 newWildTyVar _name
1509 = do { kind <- newMetaKindVar
1510 ; uniq <- newUnique
1511 ; details <- newMetaDetails TauTv
1512 ; let name = mkSysTvName uniq (fsLit "w")
1513 ; return (mkTcTyVar name kind details) }
1514
1515 -- | Produce a tyvar of the given name (with the kind provided, or
1516 -- otherwise a meta-var kind). If
1517 -- the name is already in scope, return the scoped variable, checking
1518 -- to make sure the known kind matches any kind provided. The
1519 -- second return value says whether the variable is in scope (True)
1520 -- or not (False). (Use this for associated types, for example.)
1521 tcHsTyVarName :: Maybe Kind -> Name -> TcM (TcTyVar, Bool)
1522 tcHsTyVarName m_kind name
1523 = do { mb_tv <- tcLookupLcl_maybe name
1524 ; case mb_tv of
1525 Just (ATyVar _ tv)
1526 -> do { whenIsJust m_kind $ \ kind ->
1527 discardResult $
1528 unifyKind (Just (mkTyVarTy tv)) kind (tyVarKind tv)
1529 ; return (tv, True) }
1530 _ -> do { kind <- case m_kind of
1531 Just kind -> return kind
1532 Nothing -> newMetaKindVar
1533 ; return (mk_skolem_tv name kind, False) }}
1534
1535 -- makes a new skolem tv
1536 newSkolemTyVar :: Name -> Kind -> TcM TcTyVar
1537 newSkolemTyVar name kind = return (mk_skolem_tv name kind)
1538
1539 mk_skolem_tv :: Name -> Kind -> TcTyVar
1540 mk_skolem_tv n k = mkTcTyVar n k vanillaSkolemTv
1541
1542 ------------------
1543 kindGeneralizeType :: Type -> TcM Type
1544 -- Result is zonked
1545 kindGeneralizeType ty
1546 = do { kvs <- kindGeneralize ty
1547 ; zonkTcType (mkInvForAllTys kvs ty) }
1548
1549 kindGeneralize :: TcType -> TcM [KindVar]
1550 -- Quantify the free kind variables of a kind or type
1551 -- In the latter case the type is closed, so it has no free
1552 -- type variables. So in both cases, all the free vars are kind vars
1553 kindGeneralize kind_or_type
1554 = do { kvs <- zonkTcTypeAndFV kind_or_type
1555 ; let dvs = DV { dv_kvs = kvs, dv_tvs = emptyDVarSet }
1556 ; gbl_tvs <- tcGetGlobalTyCoVars -- Already zonked
1557 ; quantifyZonkedTyVars gbl_tvs dvs }
1558
1559 {-
1560 Note [Kind generalisation]
1561 ~~~~~~~~~~~~~~~~~~~~~~~~~~
1562 We do kind generalisation only at the outer level of a type signature.
1563 For example, consider
1564 T :: forall k. k -> *
1565 f :: (forall a. T a -> Int) -> Int
1566 When kind-checking f's type signature we generalise the kind at
1567 the outermost level, thus:
1568 f1 :: forall k. (forall (a:k). T k a -> Int) -> Int -- YES!
1569 and *not* at the inner forall:
1570 f2 :: (forall k. forall (a:k). T k a -> Int) -> Int -- NO!
1571 Reason: same as for HM inference on value level declarations,
1572 we want to infer the most general type. The f2 type signature
1573 would be *less applicable* than f1, because it requires a more
1574 polymorphic argument.
1575
1576 NB: There are no explicit kind variables written in f's signature.
1577 When there are, the renamer adds these kind variables to the list of
1578 variables bound by the forall, so you can indeed have a type that's
1579 higher-rank in its kind. But only by explicit request.
1580
1581 Note [Kinds of quantified type variables]
1582 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1583 tcTyVarBndrsGen quantifies over a specified list of type variables,
1584 *and* over the kind variables mentioned in the kinds of those tyvars.
1585
1586 Note that we must zonk those kinds (obviously) but less obviously, we
1587 must return type variables whose kinds are zonked too. Example
1588 (a :: k7) where k7 := k9 -> k9
1589 We must return
1590 [k9, a:k9->k9]
1591 and NOT
1592 [k9, a:k7]
1593 Reason: we're going to turn this into a for-all type,
1594 forall k9. forall (a:k7). blah
1595 which the type checker will then instantiate, and instantiate does not
1596 look through unification variables!
1597
1598 Hence using zonked_kinds when forming tvs'.
1599
1600 Note [Free-floating kind vars]
1601 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1602 Consider
1603
1604 data T = MkT (forall (a :: k). Proxy a)
1605 -- from test ghci/scripts/T7873
1606
1607 This is not an existential datatype, but a higher-rank one. Note that
1608 the forall to the right of MkT. Also consider
1609
1610 data S a = MkS (Proxy (a :: k))
1611
1612 According to the rules around implicitly-bound kind variables, those
1613 k's scope over the whole declarations. The renamer grabs it and adds it
1614 to the hsq_implicits field of the HsQTyVars of the tycon. So it must
1615 be in scope during type-checking, but we want to reject T while accepting
1616 S.
1617
1618 Why reject T? Because the kind variable isn't fixed by anything. For
1619 a variable like k to be implicit, it needs to be mentioned in the kind
1620 of a tycon tyvar. But it isn't.
1621
1622 Why accept S? Because kind inference tells us that a has kind k, so it's
1623 all OK.
1624
1625 Our approach depends on whether or not the datatype has a CUSK.
1626
1627 Non-CUSK: In the first pass (kcTyClTyVars) we just bring
1628 k into scope. In the second pass (tcTyClTyVars),
1629 we check to make sure that k has been unified with some other variable
1630 (or generalized over, making k into a skolem). If it hasn't been, then
1631 it must be a free-floating kind var. Error.
1632
1633 CUSK: When we determine the tycon's final, never-to-be-changed kind
1634 in kcHsTyVarBndrs, we check to make sure all implicitly-bound kind
1635 vars are indeed mentioned in a kind somewhere. If not, error.
1636
1637 -}
1638
1639 --------------------
1640 -- getInitialKind has made a suitably-shaped kind for the type or class
1641 -- Look it up in the local environment. This is used only for tycons
1642 -- that we're currently type-checking, so we're sure to find a TcTyCon.
1643 kcLookupTcTyCon :: Name -> TcM TcTyCon
1644 kcLookupTcTyCon nm
1645 = do { tc_ty_thing <- tcLookup nm
1646 ; return $ case tc_ty_thing of
1647 ATcTyCon tc -> tc
1648 _ -> pprPanic "kcLookupTcTyCon" (ppr tc_ty_thing) }
1649
1650 -----------------------
1651 -- | Bring tycon tyvars into scope. This is used during the "kind-checking"
1652 -- pass in TcTyClsDecls. (Never in getInitialKind, never in the
1653 -- "type-checking"/desugaring pass.)
1654 -- Never emits constraints, though the thing_inside might.
1655 kcTyClTyVars :: Name -> TcM a -> TcM a
1656 kcTyClTyVars tycon_name thing_inside
1657 = do { tycon <- kcLookupTcTyCon tycon_name
1658 ; tcExtendTyVarEnv (tcTyConScopedTyVars tycon) $ thing_inside }
1659
1660 tcTyClTyVars :: Name
1661 -> ([TyConBinder] -> Kind -> TcM a) -> TcM a
1662 -- ^ Used for the type variables of a type or class decl
1663 -- on the second full pass (type-checking/desugaring) in TcTyClDecls.
1664 -- This is *not* used in the initial-kind run, nor in the "kind-checking" pass.
1665 -- Accordingly, everything passed to the continuation is fully zonked.
1666 --
1667 -- (tcTyClTyVars T [a,b] thing_inside)
1668 -- where T : forall k1 k2 (a:k1 -> *) (b:k1). k2 -> *
1669 -- calls thing_inside with arguments
1670 -- [k1,k2,a,b] [k1:*, k2:*, Anon (k1 -> *), Anon k1] (k2 -> *)
1671 -- having also extended the type environment with bindings
1672 -- for k1,k2,a,b
1673 --
1674 -- Never emits constraints.
1675 --
1676 -- The LHsTyVarBndrs is always user-written, and the full, generalised
1677 -- kind of the tycon is available in the local env.
1678 tcTyClTyVars tycon_name thing_inside
1679 = do { tycon <- kcLookupTcTyCon tycon_name
1680
1681 ; let scoped_tvs = tcTyConScopedTyVars tycon
1682 -- these are all zonked:
1683 binders = tyConBinders tycon
1684 res_kind = tyConResKind tycon
1685
1686 -- See Note [Free-floating kind vars]
1687 ; zonked_scoped_tvs <- mapM zonkTcTyVarToTyVar scoped_tvs
1688 ; let still_sig_tvs = filter isSigTyVar zonked_scoped_tvs
1689 ; checkNoErrs $ reportFloatingKvs tycon_name
1690 zonked_scoped_tvs still_sig_tvs
1691
1692 -- Add the *unzonked* tyvars to the env't, because those
1693 -- are the ones mentioned in the source.
1694 ; tcExtendTyVarEnv scoped_tvs $
1695 thing_inside binders res_kind }
1696 where
1697
1698 -----------------------------------
1699 tcDataKindSig :: Kind -> TcM ([TyConBinder], Kind)
1700 -- GADT decls can have a (perhaps partial) kind signature
1701 -- e.g. data T :: * -> * -> * where ...
1702 -- This function makes up suitable (kinded) type variables for
1703 -- the argument kinds, and checks that the result kind is indeed *.
1704 -- We use it also to make up argument type variables for for data instances.
1705 -- Never emits constraints.
1706 -- Returns the new TyVars, the extracted TyBinders, and the new, reduced
1707 -- result kind (which should always be Type or a synonym thereof)
1708 tcDataKindSig kind
1709 = do { checkTc (isLiftedTypeKind res_kind) (badKindSig kind)
1710 ; span <- getSrcSpanM
1711 ; us <- newUniqueSupply
1712 ; rdr_env <- getLocalRdrEnv
1713 ; let uniqs = uniqsFromSupply us
1714 occs = [ occ | str <- allNameStrings
1715 , let occ = mkOccName tvName str
1716 , isNothing (lookupLocalRdrOcc rdr_env occ) ]
1717 -- Note [Avoid name clashes for associated data types]
1718
1719 -- NB: Use the tv from a binder if there is one. Otherwise,
1720 -- we end up inventing a new Unique for it, and any other tv
1721 -- that mentions the first ends up with the wrong kind.
1722 extra_bndrs = zipWith4 mkTyBinderTyConBinder
1723 tv_bndrs (repeat span) uniqs occs
1724
1725 ; return (extra_bndrs, res_kind) }
1726 where
1727 (tv_bndrs, res_kind) = splitPiTys kind
1728
1729 badKindSig :: Kind -> SDoc
1730 badKindSig kind
1731 = hang (text "Kind signature on data type declaration has non-* return kind")
1732 2 (ppr kind)
1733
1734 {-
1735 Note [Avoid name clashes for associated data types]
1736 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1737 Consider class C a b where
1738 data D b :: * -> *
1739 When typechecking the decl for D, we'll invent an extra type variable
1740 for D, to fill out its kind. Ideally we don't want this type variable
1741 to be 'a', because when pretty printing we'll get
1742 class C a b where
1743 data D b a0
1744 (NB: the tidying happens in the conversion to IfaceSyn, which happens
1745 as part of pretty-printing a TyThing.)
1746
1747 That's why we look in the LocalRdrEnv to see what's in scope. This is
1748 important only to get nice-looking output when doing ":info C" in GHCi.
1749 It isn't essential for correctness.
1750
1751
1752 ************************************************************************
1753 * *
1754 Partial signatures and pattern signatures
1755 * *
1756 ************************************************************************
1757
1758
1759 Note [Solving equalities in partial type signatures]
1760 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1761 We treat a partial type signature as a "shape constraint" to impose on
1762 the term:
1763 * We make no attempt to kind-generalise it
1764 * We instantiate the explicit and implicit foralls with SigTvs
1765 * We instantiate the wildcards with meta tyvars
1766
1767 We /do/ call solveEqualities, and then zonk to propage the result of
1768 solveEqualities, mainly so that functions like matchExpectedFunTys will
1769 be able to decompose the type, and hence higher-rank signatures will
1770 work. Ugh! For example
1771 f :: (forall a. a->a) -> _
1772 f x = (x True, x 'c')
1773
1774 -}
1775
1776 tcHsPartialSigType
1777 :: UserTypeCtxt
1778 -> LHsSigWcType Name -- The type signature
1779 -> TcM ( [(Name, TcTyVar)] -- Wildcards
1780 , Maybe TcTyVar -- Extra-constraints wildcard
1781 , [TcTyVar] -- Implicitly and explicitly bound type varialbes
1782 , TcThetaType -- Theta part
1783 , TcType ) -- Tau part
1784 tcHsPartialSigType ctxt sig_ty
1785 | HsWC { hswc_wcs = sig_wcs, hswc_body = ib_ty } <- sig_ty
1786 , HsIB { hsib_vars = implicit_hs_tvs, hsib_body = hs_ty } <- ib_ty
1787 , (explicit_hs_tvs, L _ hs_ctxt, hs_tau) <- splitLHsSigmaTy hs_ty
1788 = addSigCtxt ctxt hs_ty $
1789 do { (implicit_tvs, (wcs, wcx, explicit_tvs, theta, tau))
1790 <- -- See Note [Solving equalities in partial type signatures]
1791 solveEqualities $
1792 tcWildCardBindersX newWildTyVar sig_wcs $ \ wcs ->
1793 tcImplicitTKBndrsX new_implicit_tv implicit_hs_tvs $
1794 tcExplicitTKBndrsX newSigTyVar explicit_hs_tvs $ \ explicit_tvs ->
1795 do { -- Instantiate the type-class context; but if there
1796 -- is an extra-constraints wildcard, just discard it here
1797 (theta, wcx) <- tcPartialContext hs_ctxt
1798
1799 ; tau <- tcHsOpenType hs_tau
1800
1801 ; let bound_tvs = unionVarSets [ allBoundVariables tau
1802 , mkVarSet explicit_tvs
1803 , mkVarSet (map snd wcs) ]
1804
1805 ; return ( (wcs, wcx, explicit_tvs, theta, tau)
1806 , bound_tvs) }
1807
1808 ; emitWildCardHoleConstraints wcs
1809
1810 -- See Note [Solving equalities in partial type signatures]
1811 ; all_tvs <- mapM (updateTyVarKindM zonkTcType)
1812 (implicit_tvs ++ explicit_tvs)
1813 ; theta <- mapM zonkTcType theta
1814 ; tau <- zonkTcType tau
1815 ; checkValidType ctxt (mkSpecForAllTys all_tvs $ mkPhiTy theta tau)
1816
1817 ; traceTc "tcHsPatSigType" (ppr all_tvs)
1818 ; return (wcs, wcx, all_tvs, theta, tau) }
1819 where
1820 new_implicit_tv name = do { kind <- newMetaKindVar
1821 ; tv <- newSigTyVar name kind
1822 ; return (tv, False) }
1823
1824 tcPartialContext :: HsContext Name -> TcM (TcThetaType, Maybe TcTyVar)
1825 tcPartialContext hs_theta
1826 | Just (hs_theta1, hs_ctxt_last) <- snocView hs_theta
1827 , L _ (HsWildCardTy wc) <- ignoreParens hs_ctxt_last
1828 = do { wc_tv <- tcWildCardOcc wc constraintKind
1829 ; theta <- mapM tcLHsPredType hs_theta1
1830 ; return (theta, Just wc_tv) }
1831 | otherwise
1832 = do { theta <- mapM tcLHsPredType hs_theta
1833 ; return (theta, Nothing) }
1834
1835 tcHsPatSigType :: UserTypeCtxt
1836 -> LHsSigWcType Name -- The type signature
1837 -> TcM ( [(Name, TcTyVar)] -- Wildcards
1838 , [TcTyVar] -- The new bit of type environment, binding
1839 -- the scoped type variables
1840 , TcType) -- The type
1841 -- Used for type-checking type signatures in
1842 -- (a) patterns e.g f (x::Int) = e
1843 -- (b) RULE forall bndrs e.g. forall (x::Int). f x = x
1844 --
1845 -- This may emit constraints
1846
1847 tcHsPatSigType ctxt sig_ty
1848 | HsWC { hswc_wcs = sig_wcs, hswc_body = ib_ty } <- sig_ty
1849 , HsIB { hsib_vars = sig_vars, hsib_body = hs_ty } <- ib_ty
1850 = addSigCtxt ctxt hs_ty $
1851 do { (implicit_tvs, (wcs, sig_ty))
1852 <- -- See Note [Solving equalities in partial type signatures]
1853 solveEqualities $
1854 tcWildCardBindersX newWildTyVar sig_wcs $ \ wcs ->
1855 tcImplicitTKBndrsX new_implicit_tv sig_vars $
1856 do { sig_ty <- tcHsOpenType hs_ty
1857 ; return ((wcs, sig_ty), allBoundVariables sig_ty) }
1858
1859 ; emitWildCardHoleConstraints wcs
1860
1861 ; sig_ty <- zonkTcType sig_ty
1862 ; checkValidType ctxt sig_ty
1863
1864 ; traceTc "tcHsPatSigType" (ppr sig_vars)
1865 ; return (wcs, implicit_tvs, sig_ty) }
1866 where
1867 new_implicit_tv name = do { kind <- newMetaKindVar
1868 ; tv <- new_tv name kind
1869 ; return (tv, False) }
1870 -- "False" means that these tyvars aren't yet in scope
1871 new_tv = case ctxt of
1872 RuleSigCtxt {} -> newSkolemTyVar
1873 _ -> newSigTyVar
1874 -- See Note [Pattern signature binders]
1875 -- See Note [Unifying SigTvs]
1876
1877
1878 tcPatSig :: Bool -- True <=> pattern binding
1879 -> LHsSigWcType Name
1880 -> ExpSigmaType
1881 -> TcM (TcType, -- The type to use for "inside" the signature
1882 [TcTyVar], -- The new bit of type environment, binding
1883 -- the scoped type variables
1884 [(Name,TcTyVar)], -- The wildcards
1885 HsWrapper) -- Coercion due to unification with actual ty
1886 -- Of shape: res_ty ~ sig_ty
1887 tcPatSig in_pat_bind sig res_ty
1888 = do { (sig_wcs, sig_tvs, sig_ty) <- tcHsPatSigType PatSigCtxt sig
1889 -- sig_tvs are the type variables free in 'sig',
1890 -- and not already in scope. These are the ones
1891 -- that should be brought into scope
1892
1893 ; if null sig_tvs then do {
1894 -- Just do the subsumption check and return
1895 wrap <- addErrCtxtM (mk_msg sig_ty) $
1896 tcSubTypeET_NC PatSigCtxt res_ty sig_ty
1897 ; return (sig_ty, [], sig_wcs, wrap)
1898 } else do
1899 -- Type signature binds at least one scoped type variable
1900
1901 -- A pattern binding cannot bind scoped type variables
1902 -- It is more convenient to make the test here
1903 -- than in the renamer
1904 { when in_pat_bind (addErr (patBindSigErr sig_tvs))
1905
1906 -- Check that all newly-in-scope tyvars are in fact
1907 -- constrained by the pattern. This catches tiresome
1908 -- cases like
1909 -- type T a = Int
1910 -- f :: Int -> Int
1911 -- f (x :: T a) = ...
1912 -- Here 'a' doesn't get a binding. Sigh
1913 ; let bad_tvs = [ tv | tv <- sig_tvs
1914 , not (tv `elemVarSet` exactTyCoVarsOfType sig_ty) ]
1915 ; checkTc (null bad_tvs) (badPatSigTvs sig_ty bad_tvs)
1916
1917 -- Now do a subsumption check of the pattern signature against res_ty
1918 ; wrap <- addErrCtxtM (mk_msg sig_ty) $
1919 tcSubTypeET_NC PatSigCtxt res_ty sig_ty
1920
1921 -- Phew!
1922 ; return (sig_ty, sig_tvs, sig_wcs, wrap)
1923 } }
1924 where
1925 mk_msg sig_ty tidy_env
1926 = do { (tidy_env, sig_ty) <- zonkTidyTcType tidy_env sig_ty
1927 ; res_ty <- readExpType res_ty -- should be filled in by now
1928 ; (tidy_env, res_ty) <- zonkTidyTcType tidy_env res_ty
1929 ; let msg = vcat [ hang (text "When checking that the pattern signature:")
1930 4 (ppr sig_ty)
1931 , nest 2 (hang (text "fits the type of its context:")
1932 2 (ppr res_ty)) ]
1933 ; return (tidy_env, msg) }
1934
1935 patBindSigErr :: [TcTyVar] -> SDoc
1936 patBindSigErr sig_tvs
1937 = hang (text "You cannot bind scoped type variable" <> plural sig_tvs
1938 <+> pprQuotedList sig_tvs)
1939 2 (text "in a pattern binding signature")
1940
1941 {-
1942 Note [Pattern signature binders]
1943 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1944 Consider
1945 data T = forall a. T a (a->Int)
1946 f (T x (f :: a->Int) = blah)
1947
1948 Here
1949 * The pattern (T p1 p2) creates a *skolem* type variable 'a_sk',
1950 It must be a skolem so that that it retains its identity, and
1951 TcErrors.getSkolemInfo can thereby find the binding site for the skolem.
1952
1953 * The type signature pattern (f :: a->Int) binds "a" -> a_sig in the envt
1954
1955 * Then unification makes a_sig := a_sk
1956
1957 That's why we must make a_sig a MetaTv (albeit a SigTv),
1958 not a SkolemTv, so that it can unify to a_sk.
1959
1960 For RULE binders, though, things are a bit different (yuk).
1961 RULE "foo" forall (x::a) (y::[a]). f x y = ...
1962 Here this really is the binding site of the type variable so we'd like
1963 to use a skolem, so that we get a complaint if we unify two of them
1964 together.
1965
1966 Note [Unifying SigTvs]
1967 ~~~~~~~~~~~~~~~~~~~~~~
1968 ALAS we have no decent way of avoiding two SigTvs getting unified.
1969 Consider
1970 f (x::(a,b)) (y::c)) = [fst x, y]
1971 Here we'd really like to complain that 'a' and 'c' are unified. But
1972 for the reasons above we can't make a,b,c into skolems, so they
1973 are just SigTvs that can unify. And indeed, this would be ok,
1974 f x (y::c) = case x of
1975 (x1 :: a1, True) -> [x,y]
1976 (x1 :: a2, False) -> [x,y,y]
1977 Here the type of x's first component is called 'a1' in one branch and
1978 'a2' in the other. We could try insisting on the same OccName, but
1979 they definitely won't have the sane lexical Name.
1980
1981 I think we could solve this by recording in a SigTv a list of all the
1982 in-scope variables that it should not unify with, but it's fiddly.
1983
1984
1985 ************************************************************************
1986 * *
1987 Checking kinds
1988 * *
1989 ************************************************************************
1990
1991 -}
1992
1993 -- | Produce an 'TcKind' suitable for a checking a type that can be * or #.
1994 ekOpen :: TcM TcKind
1995 ekOpen = do { rr <- newFlexiTyVarTy runtimeRepTy
1996 ; return (tYPE rr) }
1997
1998 unifyKinds :: [(TcType, TcKind)] -> TcM ([TcType], TcKind)
1999 unifyKinds act_kinds
2000 = do { kind <- newMetaKindVar
2001 ; let check (ty, act_kind) = checkExpectedKind ty act_kind kind
2002 ; tys' <- mapM check act_kinds
2003 ; return (tys', kind) }
2004
2005 {-
2006 ************************************************************************
2007 * *
2008 Sort checking kinds
2009 * *
2010 ************************************************************************
2011
2012 tcLHsKind converts a user-written kind to an internal, sort-checked kind.
2013 It does sort checking and desugaring at the same time, in one single pass.
2014 -}
2015
2016 tcLHsKind :: LHsKind Name -> TcM Kind
2017 tcLHsKind = tc_lhs_kind kindLevelMode
2018
2019 tc_lhs_kind :: TcTyMode -> LHsKind Name -> TcM Kind
2020 tc_lhs_kind mode k
2021 = addErrCtxt (text "In the kind" <+> quotes (ppr k)) $
2022 tc_lhs_type (kindLevel mode) k liftedTypeKind
2023
2024 promotionErr :: Name -> PromotionErr -> TcM a
2025 promotionErr name err
2026 = failWithTc (hang (pprPECategory err <+> quotes (ppr name) <+> text "cannot be used here")
2027 2 (parens reason))
2028 where
2029 reason = case err of
2030 FamDataConPE -> text "it comes from a data family instance"
2031 NoDataKindsTC -> text "Perhaps you intended to use DataKinds"
2032 NoDataKindsDC -> text "Perhaps you intended to use DataKinds"
2033 NoTypeInTypeTC -> text "Perhaps you intended to use TypeInType"
2034 NoTypeInTypeDC -> text "Perhaps you intended to use TypeInType"
2035 PatSynPE -> text "Pattern synonyms cannot be promoted"
2036 _ -> text "it is defined and used in the same recursive group"
2037
2038 {-
2039 ************************************************************************
2040 * *
2041 Scoped type variables
2042 * *
2043 ************************************************************************
2044 -}
2045
2046 badPatSigTvs :: TcType -> [TyVar] -> SDoc
2047 badPatSigTvs sig_ty bad_tvs
2048 = vcat [ fsep [text "The type variable" <> plural bad_tvs,
2049 quotes (pprWithCommas ppr bad_tvs),
2050 text "should be bound by the pattern signature" <+> quotes (ppr sig_ty),
2051 text "but are actually discarded by a type synonym" ]
2052 , text "To fix this, expand the type synonym"
2053 , text "[Note: I hope to lift this restriction in due course]" ]
2054
2055 {-
2056 ************************************************************************
2057 * *
2058 Error messages and such
2059 * *
2060 ************************************************************************
2061 -}
2062
2063 -- | Make an appropriate message for an error in a function argument.
2064 -- Used for both expressions and types.
2065 funAppCtxt :: (Outputable fun, Outputable arg) => fun -> arg -> Int -> SDoc
2066 funAppCtxt fun arg arg_no
2067 = hang (hsep [ text "In the", speakNth arg_no, ptext (sLit "argument of"),
2068 quotes (ppr fun) <> text ", namely"])
2069 2 (quotes (ppr arg))
2070
2071 -- See Note [Free-floating kind vars]
2072 reportFloatingKvs :: Name -- of the tycon
2073 -> [TcTyVar] -- all tyvars, not necessarily zonked
2074 -> [TcTyVar] -- floating tyvars
2075 -> TcM ()
2076 reportFloatingKvs tycon_name all_tvs bad_tvs
2077 = unless (null bad_tvs) $ -- don't bother zonking if there's no error
2078 do { all_tvs <- mapM zonkTcTyVarToTyVar all_tvs
2079 ; bad_tvs <- mapM zonkTcTyVarToTyVar bad_tvs
2080 ; let (tidy_env, tidy_all_tvs) = tidyOpenTyCoVars emptyTidyEnv all_tvs
2081 tidy_bad_tvs = map (tidyTyVarOcc tidy_env) bad_tvs
2082 ; typeintype <- xoptM LangExt.TypeInType
2083 ; mapM_ (report typeintype tidy_all_tvs) tidy_bad_tvs }
2084 where
2085 report typeintype tidy_all_tvs tidy_bad_tv
2086 = addErr $
2087 vcat [ text "Kind variable" <+> quotes (ppr tidy_bad_tv) <+>
2088 text "is implicitly bound in datatype"
2089 , quotes (ppr tycon_name) <> comma <+>
2090 text "but does not appear as the kind of any"
2091 , text "of its type variables. Perhaps you meant"
2092 , text "to bind it" <+> ppWhen (not typeintype)
2093 (text "(with TypeInType)") <+>
2094 text "explicitly somewhere?"
2095 , ppWhen (not (null tidy_all_tvs)) $
2096 hang (text "Type variables with inferred kinds:")
2097 2 (ppr_tv_bndrs tidy_all_tvs) ]
2098
2099 ppr_tv_bndrs tvs = sep (map pp_tv tvs)
2100 pp_tv tv = parens (ppr tv <+> dcolon <+> ppr (tyVarKind tv))