7fb77e6a39389f50169ef37c2a62494f2c47643b
[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 )
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 )
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 -- This should never happen; type splices are expanded by the renamer
505 tc_hs_type _ ty@(HsSpliceTy {}) _exp_kind
506 = failWithTc (text "Unexpected type splice:" <+> ppr ty)
507
508 ---------- Functions and applications
509 tc_hs_type mode (HsFunTy ty1 ty2) exp_kind
510 = tc_fun_type mode ty1 ty2 exp_kind
511
512 tc_hs_type mode (HsOpTy ty1 (L _ op) ty2) exp_kind
513 | op `hasKey` funTyConKey
514 = tc_fun_type mode ty1 ty2 exp_kind
515
516 --------- Foralls
517 tc_hs_type mode (HsForAllTy { hst_bndrs = hs_tvs, hst_body = ty }) exp_kind
518 = fmap fst $
519 tcExplicitTKBndrs hs_tvs $ \ tvs' ->
520 -- Do not kind-generalise here! See Note [Kind generalisation]
521 -- Why exp_kind? See Note [Body kind of HsForAllTy]
522 do { ty' <- tc_lhs_type mode ty exp_kind
523 ; let bound_vars = allBoundVariables ty'
524 bndrs = mkNamedBinders Specified tvs'
525 ; return (mkForAllTys bndrs ty', bound_vars) }
526
527 tc_hs_type mode (HsQualTy { hst_ctxt = ctxt, hst_body = ty }) exp_kind
528 | null (unLoc ctxt)
529 = tc_lhs_type mode ty exp_kind
530
531 | otherwise
532 = do { ctxt' <- tc_hs_context mode ctxt
533
534 -- See Note [Body kind of a HsQualTy]
535 ; ty' <- if isConstraintKind exp_kind
536 then tc_lhs_type mode ty constraintKind
537 else do { ek <- ekOpen -- The body kind (result of the
538 -- function) can be * or #, hence ekOpen
539 ; ty <- tc_lhs_type mode ty ek
540 ; checkExpectedKind ty liftedTypeKind exp_kind }
541
542 ; return (mkPhiTy ctxt' ty') }
543
544 --------- Lists, arrays, and tuples
545 tc_hs_type mode (HsListTy elt_ty) exp_kind
546 = do { tau_ty <- tc_lhs_type mode elt_ty liftedTypeKind
547 ; checkWiredInTyCon listTyCon
548 ; checkExpectedKind (mkListTy tau_ty) liftedTypeKind exp_kind }
549
550 tc_hs_type mode (HsPArrTy elt_ty) exp_kind
551 = do { MASSERT( isTypeLevel (mode_level mode) )
552 ; tau_ty <- tc_lhs_type mode elt_ty liftedTypeKind
553 ; checkWiredInTyCon parrTyCon
554 ; checkExpectedKind (mkPArrTy tau_ty) liftedTypeKind exp_kind }
555
556 -- See Note [Distinguishing tuple kinds] in HsTypes
557 -- See Note [Inferring tuple kinds]
558 tc_hs_type mode (HsTupleTy HsBoxedOrConstraintTuple hs_tys) exp_kind
559 -- (NB: not zonking before looking at exp_k, to avoid left-right bias)
560 | Just tup_sort <- tupKindSort_maybe exp_kind
561 = traceTc "tc_hs_type tuple" (ppr hs_tys) >>
562 tc_tuple mode tup_sort hs_tys exp_kind
563 | otherwise
564 = do { traceTc "tc_hs_type tuple 2" (ppr hs_tys)
565 ; (tys, kinds) <- mapAndUnzipM (tc_infer_lhs_type mode) hs_tys
566 ; kinds <- mapM zonkTcType kinds
567 -- Infer each arg type separately, because errors can be
568 -- confusing if we give them a shared kind. Eg Trac #7410
569 -- (Either Int, Int), we do not want to get an error saying
570 -- "the second argument of a tuple should have kind *->*"
571
572 ; let (arg_kind, tup_sort)
573 = case [ (k,s) | k <- kinds
574 , Just s <- [tupKindSort_maybe k] ] of
575 ((k,s) : _) -> (k,s)
576 [] -> (liftedTypeKind, BoxedTuple)
577 -- In the [] case, it's not clear what the kind is, so guess *
578
579 ; tys' <- sequence [ setSrcSpan loc $
580 checkExpectedKind ty kind arg_kind
581 | ((L loc _),ty,kind) <- zip3 hs_tys tys kinds ]
582
583 ; finish_tuple tup_sort tys' (map (const arg_kind) tys') exp_kind }
584
585
586 tc_hs_type mode (HsTupleTy hs_tup_sort tys) exp_kind
587 = tc_tuple mode tup_sort tys exp_kind
588 where
589 tup_sort = case hs_tup_sort of -- Fourth case dealt with above
590 HsUnboxedTuple -> UnboxedTuple
591 HsBoxedTuple -> BoxedTuple
592 HsConstraintTuple -> ConstraintTuple
593 _ -> panic "tc_hs_type HsTupleTy"
594
595
596 --------- Promoted lists and tuples
597 tc_hs_type mode (HsExplicitListTy _k tys) exp_kind
598 = do { tks <- mapM (tc_infer_lhs_type mode) tys
599 ; (taus', kind) <- unifyKinds tks
600 ; let ty = (foldr (mk_cons kind) (mk_nil kind) taus')
601 ; checkExpectedKind ty (mkListTy kind) exp_kind }
602 where
603 mk_cons k a b = mkTyConApp (promoteDataCon consDataCon) [k, a, b]
604 mk_nil k = mkTyConApp (promoteDataCon nilDataCon) [k]
605
606 tc_hs_type mode (HsExplicitTupleTy _ tys) exp_kind
607 -- using newMetaKindVar means that we force instantiations of any polykinded
608 -- types. At first, I just used tc_infer_lhs_type, but that led to #11255.
609 = do { ks <- replicateM arity newMetaKindVar
610 ; taus <- zipWithM (tc_lhs_type mode) tys ks
611 ; let kind_con = tupleTyCon Boxed arity
612 ty_con = promotedTupleDataCon Boxed arity
613 tup_k = mkTyConApp kind_con ks
614 ; checkExpectedKind (mkTyConApp ty_con (ks ++ taus)) tup_k exp_kind }
615 where
616 arity = length tys
617
618 --------- Constraint types
619 tc_hs_type mode (HsIParamTy n ty) exp_kind
620 = do { MASSERT( isTypeLevel (mode_level mode) )
621 ; ty' <- tc_lhs_type mode ty liftedTypeKind
622 ; let n' = mkStrLitTy $ hsIPNameFS n
623 ; ipClass <- tcLookupClass ipClassName
624 ; checkExpectedKind (mkClassPred ipClass [n',ty'])
625 constraintKind exp_kind }
626
627 tc_hs_type mode (HsEqTy ty1 ty2) exp_kind
628 = do { (ty1', kind1) <- tc_infer_lhs_type mode ty1
629 ; (ty2', kind2) <- tc_infer_lhs_type mode ty2
630 ; ty2'' <- checkExpectedKind ty2' kind2 kind1
631 ; eq_tc <- tcLookupTyCon eqTyConName
632 ; let ty' = mkNakedTyConApp eq_tc [kind1, ty1', ty2'']
633 ; checkExpectedKind ty' constraintKind exp_kind }
634
635 --------- Literals
636 tc_hs_type _ (HsTyLit (HsNumTy _ n)) exp_kind
637 = do { checkWiredInTyCon typeNatKindCon
638 ; checkExpectedKind (mkNumLitTy n) typeNatKind exp_kind }
639
640 tc_hs_type _ (HsTyLit (HsStrTy _ s)) exp_kind
641 = do { checkWiredInTyCon typeSymbolKindCon
642 ; checkExpectedKind (mkStrLitTy s) typeSymbolKind exp_kind }
643
644 --------- Potentially kind-polymorphic types: call the "up" checker
645 -- See Note [Future-proofing the type checker]
646 tc_hs_type mode ty@(HsTyVar {}) ek = tc_infer_hs_type_ek mode ty ek
647 tc_hs_type mode ty@(HsAppTy {}) ek = tc_infer_hs_type_ek mode ty ek
648 tc_hs_type mode ty@(HsOpTy {}) ek = tc_infer_hs_type_ek mode ty ek
649 tc_hs_type mode ty@(HsKindSig {}) ek = tc_infer_hs_type_ek mode ty ek
650 tc_hs_type mode ty@(HsCoreTy {}) ek = tc_infer_hs_type_ek mode ty ek
651
652 tc_hs_type _ (HsWildCardTy wc) exp_kind
653 = do { wc_tv <- tcWildCardOcc wc exp_kind
654 ; return (mkTyVarTy wc_tv) }
655
656 -- disposed of by renamer
657 tc_hs_type _ ty@(HsAppsTy {}) _
658 = pprPanic "tc_hs_tyep HsAppsTy" (ppr ty)
659
660 tcWildCardOcc :: HsWildCardInfo Name -> Kind -> TcM TcTyVar
661 tcWildCardOcc wc_info exp_kind
662 = do { wc_tv <- tcLookupTyVar (wildCardName wc_info)
663 -- The wildcard's kind should be an un-filled-in meta tyvar
664 ; let Just wc_kind_var = tcGetTyVar_maybe (tyVarKind wc_tv)
665 ; writeMetaTyVar wc_kind_var exp_kind
666 ; return wc_tv }
667
668 ---------------------------
669 -- | Call 'tc_infer_hs_type' and check its result against an expected kind.
670 tc_infer_hs_type_ek :: TcTyMode -> HsType Name -> TcKind -> TcM TcType
671 tc_infer_hs_type_ek mode ty ek
672 = do { (ty', k) <- tc_infer_hs_type mode ty
673 ; checkExpectedKind ty' k ek }
674
675 ---------------------------
676 tupKindSort_maybe :: TcKind -> Maybe TupleSort
677 tupKindSort_maybe k
678 | Just (k', _) <- splitCastTy_maybe k = tupKindSort_maybe k'
679 | Just k' <- coreView k = tupKindSort_maybe k'
680 | isConstraintKind k = Just ConstraintTuple
681 | isLiftedTypeKind k = Just BoxedTuple
682 | otherwise = Nothing
683
684 tc_tuple :: TcTyMode -> TupleSort -> [LHsType Name] -> TcKind -> TcM TcType
685 tc_tuple mode tup_sort tys exp_kind
686 = do { arg_kinds <- case tup_sort of
687 BoxedTuple -> return (nOfThem arity liftedTypeKind)
688 UnboxedTuple -> do { rrs <- newFlexiTyVarTys arity runtimeRepTy
689 ; return $ map tYPE rrs }
690 ConstraintTuple -> return (nOfThem arity constraintKind)
691 ; tau_tys <- zipWithM (tc_lhs_type mode) tys arg_kinds
692 ; finish_tuple tup_sort tau_tys arg_kinds exp_kind }
693 where
694 arity = length tys
695
696 finish_tuple :: TupleSort
697 -> [TcType] -- ^ argument types
698 -> [TcKind] -- ^ of these kinds
699 -> TcKind -- ^ expected kind of the whole tuple
700 -> TcM TcType
701 finish_tuple tup_sort tau_tys tau_kinds exp_kind
702 = do { traceTc "finish_tuple" (ppr res_kind $$ ppr tau_kinds $$ ppr exp_kind)
703 ; let arg_tys = case tup_sort of
704 -- See also Note [Unboxed tuple RuntimeRep vars] in TyCon
705 UnboxedTuple -> map (getRuntimeRepFromKind "finish_tuple") tau_kinds
706 ++ tau_tys
707 BoxedTuple -> tau_tys
708 ConstraintTuple -> tau_tys
709 ; tycon <- case tup_sort of
710 ConstraintTuple
711 | arity > mAX_CTUPLE_SIZE
712 -> failWith (bigConstraintTuple arity)
713 | otherwise -> tcLookupTyCon (cTupleTyConName arity)
714 BoxedTuple -> do { let tc = tupleTyCon Boxed arity
715 ; checkWiredInTyCon tc
716 ; return tc }
717 UnboxedTuple -> return (tupleTyCon Unboxed arity)
718 ; checkExpectedKind (mkTyConApp tycon arg_tys) res_kind exp_kind }
719 where
720 arity = length tau_tys
721 res_kind = case tup_sort of
722 UnboxedTuple -> unboxedTupleKind
723 BoxedTuple -> liftedTypeKind
724 ConstraintTuple -> constraintKind
725
726 bigConstraintTuple :: Arity -> MsgDoc
727 bigConstraintTuple arity
728 = hang (text "Constraint tuple arity too large:" <+> int arity
729 <+> parens (text "max arity =" <+> int mAX_CTUPLE_SIZE))
730 2 (text "Instead, use a nested tuple")
731
732 ---------------------------
733 -- | Apply a type of a given kind to a list of arguments. This instantiates
734 -- invisible parameters as necessary. However, it does *not* necessarily
735 -- apply all the arguments, if the kind runs out of binders.
736 -- This takes an optional @VarEnv Kind@ which maps kind variables to kinds.
737 -- These kinds should be used to instantiate invisible kind variables;
738 -- they come from an enclosing class for an associated type/data family.
739 -- This version will instantiate all invisible arguments left over after
740 -- the visible ones.
741 tcInferArgs :: Outputable fun
742 => fun -- ^ the function
743 -> [TyBinder] -- ^ function kind's binders
744 -> Maybe (VarEnv Kind) -- ^ possibly, kind info (see above)
745 -> [LHsType Name] -- ^ args
746 -> TcM (TCvSubst, [TyBinder], [TcType], [LHsType Name], Int)
747 -- ^ (instantiating subst, un-insted leftover binders,
748 -- typechecked args, untypechecked args, n)
749 tcInferArgs fun binders mb_kind_info args
750 = do { (subst, leftover_binders, args', leftovers, n)
751 <- tc_infer_args typeLevelMode fun binders mb_kind_info args 1
752 -- now, we need to instantiate any remaining invisible arguments
753 ; let (invis_bndrs, other_binders) = span isInvisibleBinder leftover_binders
754 ; (subst', invis_args)
755 <- tcInstBindersX subst mb_kind_info invis_bndrs
756 ; return ( subst'
757 , other_binders
758 , args' `chkAppend` invis_args
759 , leftovers, n ) }
760
761 -- | See comments for 'tcInferArgs'. But this version does not instantiate
762 -- any remaining invisible arguments.
763 tc_infer_args :: Outputable fun
764 => TcTyMode
765 -> fun -- ^ the function
766 -> [TyBinder] -- ^ function kind's binders (zonked)
767 -> Maybe (VarEnv Kind) -- ^ possibly, kind info (see above)
768 -> [LHsType Name] -- ^ args
769 -> Int -- ^ number to start arg counter at
770 -> TcM (TCvSubst, [TyBinder], [TcType], [LHsType Name], Int)
771 tc_infer_args mode orig_ty binders mb_kind_info orig_args n0
772 = go emptyTCvSubst binders orig_args n0 []
773 where
774 go subst binders [] n acc
775 = return ( subst, binders, reverse acc, [], n )
776 -- when we call this when checking type family patterns, we really
777 -- do want to instantiate all invisible arguments. During other
778 -- typechecking, we don't.
779
780 go subst binders all_args n acc
781 | (inv_binders, other_binders) <- span isInvisibleBinder binders
782 , not (null inv_binders)
783 = do { traceTc "tc_infer_args 1" (ppr inv_binders)
784 ; (subst', args') <- tcInstBindersX subst mb_kind_info inv_binders
785 ; go subst' other_binders all_args n (reverse args' ++ acc) }
786
787 go subst (binder:binders) (arg:args) n acc
788 = ASSERT( isVisibleBinder binder )
789 do { traceTc "tc_infer_args 2" (ppr binder $$ ppr arg)
790 ; arg' <- addErrCtxt (funAppCtxt orig_ty arg n) $
791 tc_lhs_type mode arg (substTyUnchecked subst $ binderType binder)
792 ; let subst' = case binderVar_maybe binder of
793 Just tv -> extendTvSubst subst tv arg'
794 Nothing -> subst
795 ; go subst' binders args (n+1) (arg' : acc) }
796
797 go subst [] all_args n acc
798 = return (subst, [], reverse acc, all_args, n)
799
800 -- | Applies a type to a list of arguments.
801 -- Always consumes all the arguments.
802 -- Used for types only
803 tcInferApps :: Outputable fun
804 => TcTyMode
805 -> fun -- ^ Function (for printing only)
806 -> TcType -- ^ Function (could be knot-tied)
807 -> TcKind -- ^ Function kind (zonked)
808 -> [LHsType Name] -- ^ Args
809 -> TcM (TcType, TcKind) -- ^ (f args, result kind)
810 tcInferApps mode orig_ty ty ki args = go ty ki args 1
811 where
812 go fun fun_kind [] _ = return (fun, fun_kind)
813 go fun fun_kind args n
814 | let (binders, res_kind) = splitPiTys fun_kind
815 , not (null binders)
816 = do { (subst, leftover_binders, args', leftover_args, n')
817 <- tc_infer_args mode orig_ty binders Nothing args n
818 ; let fun_kind' = substTyUnchecked subst $
819 mkForAllTys leftover_binders res_kind
820 ; go (mkNakedAppTys fun args') fun_kind' leftover_args n' }
821
822 go fun fun_kind all_args@(arg:args) n
823 = do { (co, arg_k, res_k) <- matchExpectedFunKind (length all_args)
824 fun fun_kind
825 ; arg' <- addErrCtxt (funAppCtxt orig_ty arg n) $
826 tc_lhs_type mode arg arg_k
827 ; go (mkNakedAppTy (fun `mkNakedCastTy` co) arg')
828 res_k args (n+1) }
829
830 --------------------------
831 checkExpectedKind :: TcType -- the type whose kind we're checking
832 -> TcKind -- the known kind of that type, k
833 -> TcKind -- the expected kind, exp_kind
834 -> TcM TcType -- a possibly-inst'ed, casted type :: exp_kind
835 -- Instantiate a kind (if necessary) and then call unifyType
836 -- (checkExpectedKind ty act_kind exp_kind)
837 -- checks that the actual kind act_kind is compatible
838 -- with the expected kind exp_kind
839 checkExpectedKind ty act_kind exp_kind
840 = do { (ty', act_kind') <- instantiate ty act_kind exp_kind
841 ; let origin = TypeEqOrigin { uo_actual = act_kind'
842 , uo_expected = mkCheckExpType exp_kind
843 , uo_thing = Just $ mkTypeErrorThing ty'
844 }
845 ; co_k <- uType origin KindLevel act_kind' exp_kind
846 ; traceTc "checkExpectedKind" (vcat [ ppr act_kind
847 , ppr exp_kind
848 , ppr co_k ])
849 ; let result_ty = ty' `mkNakedCastTy` co_k
850 ; return result_ty }
851 where
852 -- we need to make sure that both kinds have the same number of implicit
853 -- foralls out front. If the actual kind has more, instantiate accordingly.
854 -- Otherwise, just pass the type & kind through -- the errors are caught
855 -- in unifyType.
856 instantiate :: TcType -- the type
857 -> TcKind -- of this kind
858 -> TcKind -- but expected to be of this one
859 -> TcM ( TcType -- the inst'ed type
860 , TcKind ) -- its new kind
861 instantiate ty act_ki exp_ki
862 = let (exp_bndrs, _) = splitPiTysInvisible exp_ki in
863 instantiateTyN (length exp_bndrs) ty act_ki
864
865 -- | Instantiate a type to have at most @n@ invisible arguments.
866 instantiateTyN :: Int -- ^ @n@
867 -> TcType -- ^ the type
868 -> TcKind -- ^ its kind
869 -> TcM (TcType, TcKind) -- ^ The inst'ed type with kind
870 instantiateTyN n ty ki
871 = let (bndrs, inner_ki) = splitPiTysInvisible ki
872 num_to_inst = length bndrs - n
873 -- NB: splitAt is forgiving with invalid numbers
874 (inst_bndrs, leftover_bndrs) = splitAt num_to_inst bndrs
875 in
876 if num_to_inst <= 0 then return (ty, ki) else
877 do { (subst, inst_args) <- tcInstBinders inst_bndrs
878 ; let rebuilt_ki = mkForAllTys leftover_bndrs inner_ki
879 ki' = substTy subst rebuilt_ki
880 ; return (mkNakedAppTys ty inst_args, ki') }
881
882 ---------------------------
883 tcHsContext :: LHsContext Name -> TcM [PredType]
884 tcHsContext = tc_hs_context typeLevelMode
885
886 tcLHsPredType :: LHsType Name -> TcM PredType
887 tcLHsPredType = tc_lhs_pred typeLevelMode
888
889 tc_hs_context :: TcTyMode -> LHsContext Name -> TcM [PredType]
890 tc_hs_context mode ctxt = mapM (tc_lhs_pred mode) (unLoc ctxt)
891
892 tc_lhs_pred :: TcTyMode -> LHsType Name -> TcM PredType
893 tc_lhs_pred mode pred = tc_lhs_type mode pred constraintKind
894
895 ---------------------------
896 tcTyVar :: TcTyMode -> Name -> TcM (TcType, TcKind)
897 -- See Note [Type checking recursive type and class declarations]
898 -- in TcTyClsDecls
899 tcTyVar mode name -- Could be a tyvar, a tycon, or a datacon
900 = do { traceTc "lk1" (ppr name)
901 ; thing <- tcLookup name
902 ; case thing of
903 ATyVar _ tv -> return (mkTyVarTy tv, tyVarKind tv)
904
905 ATcTyCon tc_tc -> do { check_tc tc_tc
906 ; tc <- get_loopy_tc name tc_tc
907 ; handle_tyfams tc tc_tc }
908 -- mkNakedTyConApp: see Note [Type-checking inside the knot]
909 -- NB: we really should check if we're at the kind level
910 -- and if the tycon is promotable if -XNoTypeInType is set.
911 -- But this is a terribly large amount of work! Not worth it.
912
913 AGlobal (ATyCon tc)
914 -> do { check_tc tc
915 ; handle_tyfams tc tc }
916
917 AGlobal (AConLike (RealDataCon dc))
918 -> do { data_kinds <- xoptM LangExt.DataKinds
919 ; unless (data_kinds || specialPromotedDc dc) $
920 promotionErr name NoDataKindsDC
921 ; type_in_type <- xoptM LangExt.TypeInType
922 ; unless ( type_in_type ||
923 ( isTypeLevel (mode_level mode) &&
924 isLegacyPromotableDataCon dc ) ||
925 ( isKindLevel (mode_level mode) &&
926 specialPromotedDc dc ) ) $
927 promotionErr name NoTypeInTypeDC
928 ; let tc = promoteDataCon dc
929 ; return (mkNakedTyConApp tc [], tyConKind tc) }
930
931 APromotionErr err -> promotionErr name err
932
933 _ -> wrongThingErr "type" thing name }
934 where
935 check_tc :: TyCon -> TcM ()
936 check_tc tc = do { type_in_type <- xoptM LangExt.TypeInType
937 ; data_kinds <- xoptM LangExt.DataKinds
938 ; unless (isTypeLevel (mode_level mode) ||
939 data_kinds ||
940 isKindTyCon tc) $
941 promotionErr name NoDataKindsTC
942 ; unless (isTypeLevel (mode_level mode) ||
943 type_in_type ||
944 isLegacyPromotableTyCon tc) $
945 promotionErr name NoTypeInTypeTC }
946
947 -- if we are type-checking a type family tycon, we must instantiate
948 -- any invisible arguments right away. Otherwise, we get #11246
949 handle_tyfams :: TyCon -- the tycon to instantiate (might be loopy)
950 -> TyCon -- a non-loopy version of the tycon
951 -> TcM (TcType, TcKind)
952 handle_tyfams tc tc_tc
953 | mightBeUnsaturatedTyCon tc_tc
954 = do { traceTc "tcTyVar2a" (ppr tc_tc $$ ppr tc_kind)
955 ; return (ty, tc_kind) }
956
957 | otherwise
958 = do { (tc_ty, kind) <- instantiateTyN 0 ty tc_kind
959 -- tc and tc_ty must not be traced here, because that would
960 -- force the evaluation of a potentially knot-tied variable (tc),
961 -- and the typechecker would hang, as per #11708
962 ; traceTc "tcTyVar2b" (vcat [ ppr tc_tc <+> dcolon <+> ppr tc_kind
963 , ppr kind ])
964 ; return (tc_ty, kind) }
965 where
966 ty = mkNakedTyConApp tc []
967 tc_kind = tyConKind tc_tc
968
969 get_loopy_tc :: Name -> TyCon -> TcM TyCon
970 -- Return the knot-tied global TyCon if there is one
971 -- Otherwise the local TcTyCon; we must be doing kind checking
972 -- but we still want to return a TyCon of some sort to use in
973 -- error messages
974 get_loopy_tc name tc_tc
975 = do { env <- getGblEnv
976 ; case lookupNameEnv (tcg_type_env env) name of
977 Just (ATyCon tc) -> return tc
978 _ -> do { traceTc "lk1 (loopy)" (ppr name)
979 ; return tc_tc } }
980
981 tcClass :: Name -> TcM (Class, TcKind)
982 tcClass cls -- Must be a class
983 = do { thing <- tcLookup cls
984 ; case thing of
985 ATcTyCon tc -> return (aThingErr "tcClass" cls, tyConKind tc)
986 AGlobal (ATyCon tc)
987 | Just cls <- tyConClass_maybe tc
988 -> return (cls, tyConKind tc)
989 _ -> wrongThingErr "class" thing cls }
990
991
992 aThingErr :: String -> Name -> b
993 -- The type checker for types is sometimes called simply to
994 -- do *kind* checking; and in that case it ignores the type
995 -- returned. Which is a good thing since it may not be available yet!
996 aThingErr str x = pprPanic "AThing evaluated unexpectedly" (text str <+> ppr x)
997
998 {-
999 Note [Type-checking inside the knot]
1000 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1001 Suppose we are checking the argument types of a data constructor. We
1002 must zonk the types before making the DataCon, because once built we
1003 can't change it. So we must traverse the type.
1004
1005 BUT the parent TyCon is knot-tied, so we can't look at it yet.
1006
1007 So we must be careful not to use "smart constructors" for types that
1008 look at the TyCon or Class involved.
1009
1010 * Hence the use of mkNakedXXX functions. These do *not* enforce
1011 the invariants (for example that we use (ForAllTy (Anon s) t) rather
1012 than (TyConApp (->) [s,t])).
1013
1014 * The zonking functions establish invariants (even zonkTcType, a change from
1015 previous behaviour). So we must never inspect the result of a
1016 zonk that might mention a knot-tied TyCon. This is generally OK
1017 because we zonk *kinds* while kind-checking types. And the TyCons
1018 in kinds shouldn't be knot-tied, because they come from a previous
1019 mutually recursive group.
1020
1021 * TcHsSyn.zonkTcTypeToType also can safely check/establish
1022 invariants.
1023
1024 This is horribly delicate. I hate it. A good example of how
1025 delicate it is can be seen in Trac #7903.
1026
1027 Note [Body kind of a HsForAllTy]
1028 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1029 The body of a forall is usually a type, but in principle
1030 there's no reason to prohibit *unlifted* types.
1031 In fact, GHC can itself construct a function with an
1032 unboxed tuple inside a for-all (via CPR analyis; see
1033 typecheck/should_compile/tc170).
1034
1035 Moreover in instance heads we get forall-types with
1036 kind Constraint.
1037
1038 It's tempting to check that the body kind is either * or #. But this is
1039 wrong. For example:
1040
1041 class C a b
1042 newtype N = Mk Foo deriving (C a)
1043
1044 We're doing newtype-deriving for C. But notice how `a` isn't in scope in
1045 the predicate `C a`. So we quantify, yielding `forall a. C a` even though
1046 `C a` has kind `* -> Constraint`. The `forall a. C a` is a bit cheeky, but
1047 convenient. Bottom line: don't check for * or # here.
1048
1049 Note [Body kind of a HsQualTy]
1050 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1051 If ctxt is non-empty, the HsQualTy really is a /function/, so the
1052 kind of the result really is '*', and in that case the kind of the
1053 body-type can be lifted or unlifted.
1054
1055 However, consider
1056 instance Eq a => Eq [a] where ...
1057 or
1058 f :: (Eq a => Eq [a]) => blah
1059 Here both body-kind of the HsQualTy is Constraint rather than *.
1060 Rather crudely we tell the difference by looking at exp_kind. It's
1061 very convenient to typecheck instance types like any other HsSigType.
1062
1063 Admittedly the '(Eq a => Eq [a]) => blah' case is erroneous, but it's
1064 better to reject in checkValidType. If we say that the body kind
1065 should be '*' we risk getting TWO error messages, one saying that Eq
1066 [a] doens't have kind '*', and one saying that we need a Constraint to
1067 the left of the outer (=>).
1068
1069 How do we figure out the right body kind? Well, it's a bit of a
1070 kludge: I just look at the expected kind. If it's Constraint, we
1071 must be in this instance situation context. It's a kludge because it
1072 wouldn't work if any unification was involved to compute that result
1073 kind -- but it isn't. (The true way might be to use the 'mode'
1074 parameter, but that seemed like a sledgehammer to crack a nut.)
1075
1076 Note [Inferring tuple kinds]
1077 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1078 Give a tuple type (a,b,c), which the parser labels as HsBoxedOrConstraintTuple,
1079 we try to figure out whether it's a tuple of kind * or Constraint.
1080 Step 1: look at the expected kind
1081 Step 2: infer argument kinds
1082
1083 If after Step 2 it's not clear from the arguments that it's
1084 Constraint, then it must be *. Once having decided that we re-check
1085 the Check the arguments again to give good error messages
1086 in eg. `(Maybe, Maybe)`
1087
1088 Note that we will still fail to infer the correct kind in this case:
1089
1090 type T a = ((a,a), D a)
1091 type family D :: Constraint -> Constraint
1092
1093 While kind checking T, we do not yet know the kind of D, so we will default the
1094 kind of T to * -> *. It works if we annotate `a` with kind `Constraint`.
1095
1096 Note [Desugaring types]
1097 ~~~~~~~~~~~~~~~~~~~~~~~
1098 The type desugarer is phase 2 of dealing with HsTypes. Specifically:
1099
1100 * It transforms from HsType to Type
1101
1102 * It zonks any kinds. The returned type should have no mutable kind
1103 or type variables (hence returning Type not TcType):
1104 - any unconstrained kind variables are defaulted to (Any *) just
1105 as in TcHsSyn.
1106 - there are no mutable type variables because we are
1107 kind-checking a type
1108 Reason: the returned type may be put in a TyCon or DataCon where
1109 it will never subsequently be zonked.
1110
1111 You might worry about nested scopes:
1112 ..a:kappa in scope..
1113 let f :: forall b. T '[a,b] -> Int
1114 In this case, f's type could have a mutable kind variable kappa in it;
1115 and we might then default it to (Any *) when dealing with f's type
1116 signature. But we don't expect this to happen because we can't get a
1117 lexically scoped type variable with a mutable kind variable in it. A
1118 delicate point, this. If it becomes an issue we might need to
1119 distinguish top-level from nested uses.
1120
1121 Moreover
1122 * it cannot fail,
1123 * it does no unifications
1124 * it does no validity checking, except for structural matters, such as
1125 (a) spurious ! annotations.
1126 (b) a class used as a type
1127
1128 Note [Kind of a type splice]
1129 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1130 Consider these terms, each with TH type splice inside:
1131 [| e1 :: Maybe $(..blah..) |]
1132 [| e2 :: $(..blah..) |]
1133 When kind-checking the type signature, we'll kind-check the splice
1134 $(..blah..); we want to give it a kind that can fit in any context,
1135 as if $(..blah..) :: forall k. k.
1136
1137 In the e1 example, the context of the splice fixes kappa to *. But
1138 in the e2 example, we'll desugar the type, zonking the kind unification
1139 variables as we go. When we encounter the unconstrained kappa, we
1140 want to default it to '*', not to (Any *).
1141
1142
1143 Help functions for type applications
1144 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1145 -}
1146
1147 addTypeCtxt :: LHsType Name -> TcM a -> TcM a
1148 -- Wrap a context around only if we want to show that contexts.
1149 -- Omit invisble ones and ones user's won't grok
1150 addTypeCtxt (L _ ty) thing
1151 = addErrCtxt doc thing
1152 where
1153 doc = text "In the type" <+> quotes (ppr ty)
1154
1155 {-
1156 ************************************************************************
1157 * *
1158 Type-variable binders
1159 %* *
1160 %************************************************************************
1161
1162 Note [Scope-check inferred kinds]
1163 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1164 Consider
1165
1166 data SameKind :: k -> k -> *
1167 foo :: forall a (b :: Proxy a) (c :: Proxy d). SameKind b c
1168
1169 d has no binding site. So it gets bound implicitly, at the top. The
1170 problem is that d's kind mentions `a`. So it's all ill-scoped.
1171
1172 The way we check for this is to gather all variables *bound* in a
1173 type variable's scope. The type variable's kind should not mention
1174 any of these variables. That is, d's kind can't mention a, b, or c.
1175 We can't just check to make sure that d's kind is in scope, because
1176 we might be about to kindGeneralize.
1177
1178 A little messy, but it works.
1179
1180 Note [Dependent LHsQTyVars]
1181 ~~~~~~~~~~~~~~~~~~~~~~~~~~~
1182 We track (in the renamer) which explicitly bound variables in a
1183 LHsQTyVars are manifestly dependent; only precisely these variables
1184 may be used within the LHsQTyVars. We must do this so that kcHsTyVarBndrs
1185 can produce the right TcTyBinders, and tell Anon vs. Named. Earlier,
1186 I thought it would work simply to do a free-variable check during
1187 kcHsTyVarBndrs, but this is bogus, because there may be unsolved
1188 equalities about. And we don't want to eagerly solve the equalities,
1189 because we may get further information after kcHsTyVarBndrs is called.
1190 (Recall that kcHsTyVarBndrs is usually called from getInitialKind.
1191 The only other case is in kcConDecl.) This is what implements the rule
1192 that all variables intended to be dependent must be manifestly so.
1193
1194 Sidenote: It's quite possible that later, we'll consider (t -> s)
1195 as a degenerate case of some (pi (x :: t) -> s) and then this will
1196 all get more permissive.
1197
1198 -}
1199
1200 tcWildCardBinders :: [Name]
1201 -> ([(Name, TcTyVar)] -> TcM a)
1202 -> TcM a
1203 tcWildCardBinders = tcWildCardBindersX new_tv
1204 where
1205 new_tv name = do { kind <- newMetaKindVar
1206 ; newSkolemTyVar name kind }
1207
1208 tcWildCardBindersX :: (Name -> TcM TcTyVar)
1209 -> [Name]
1210 -> ([(Name, TcTyVar)] -> TcM a)
1211 -> TcM a
1212 tcWildCardBindersX new_wc wc_names thing_inside
1213 = do { wcs <- mapM new_wc wc_names
1214 ; let wc_prs = wc_names `zip` wcs
1215 ; tcExtendTyVarEnv2 wc_prs $
1216 thing_inside wc_prs }
1217
1218 -- | Kind-check a 'LHsQTyVars'. If the decl under consideration has a complete,
1219 -- user-supplied kind signature (CUSK), generalise the result.
1220 -- Used in 'getInitialKind' (for tycon kinds and other kinds)
1221 -- and in kind-checking (but not for tycon kinds, which are checked with
1222 -- tcTyClDecls). See also Note [Complete user-supplied kind signatures] in
1223 -- HsDecls.
1224 --
1225 -- This function does not do telescope checking.
1226 kcHsTyVarBndrs :: Name -- ^ of the thing being checked
1227 -> Bool -- ^ True <=> the decl being checked has a CUSK
1228 -> Bool -- ^ True <=> the decl is an open type/data family
1229 -> Bool -- ^ True <=> all the hsq_implicit are *kind* vars
1230 -- (will give these kind * if -XNoTypeInType)
1231 -> LHsQTyVars Name
1232 -> TcM (Kind, r) -- ^ the result kind, possibly with other info
1233 -> TcM (Bool -> TcTyCon, r)
1234 -- ^ a way to make a TcTyCon, with the other info.
1235 -- The Bool says whether the tycon can be unsaturated.
1236 kcHsTyVarBndrs name cusk open_fam all_kind_vars
1237 (HsQTvs { hsq_implicit = kv_ns, hsq_explicit = hs_tvs
1238 , hsq_dependent = dep_names }) thing_inside
1239 | cusk
1240 = do { kv_kinds <- mk_kv_kinds
1241 ; let scoped_kvs = zipWith mk_skolem_tv kv_ns kv_kinds
1242 ; tcExtendTyVarEnv2 (kv_ns `zip` scoped_kvs) $
1243 do { (tvs, binders, res_kind, stuff) <- solveEqualities $
1244 bind_telescope hs_tvs thing_inside
1245
1246 -- Now, because we're in a CUSK, quantify over the mentioned
1247 -- kind vars, in dependency order.
1248 ; binders <- mapM zonkTcTyBinder binders
1249 ; res_kind <- zonkTcType res_kind
1250 ; let qkvs = tyCoVarsOfTypeWellScoped (mkForAllTys binders res_kind)
1251 -- the visibility of tvs doesn't matter here; we just
1252 -- want the free variables not to include the tvs
1253
1254 -- if there are any meta-tvs left, the user has lied about having
1255 -- a CUSK. Error.
1256 ; let (meta_tvs, good_tvs) = partition isMetaTyVar qkvs
1257 ; when (not (null meta_tvs)) $
1258 report_non_cusk_tvs (qkvs ++ tvs)
1259
1260 -- if any of the scoped_kvs aren't actually mentioned in a binder's
1261 -- kind (or the return kind), then we're in the CUSK case from
1262 -- Note [Free-floating kind vars]
1263 ; let tycon_tyvars = good_tvs ++ tvs
1264 all_mentioned_tvs = mapUnionVarSet (tyCoVarsOfType . tyVarKind)
1265 tycon_tyvars
1266 `unionVarSet` tyCoVarsOfType res_kind
1267 unmentioned_kvs = filterOut (`elemVarSet` all_mentioned_tvs)
1268 scoped_kvs
1269 ; reportFloatingKvs name tycon_tyvars unmentioned_kvs
1270
1271 ; let final_binders = mkNamedBinders Specified good_tvs ++ binders
1272 mk_tctc unsat = mkTcTyCon name tycon_tyvars
1273 final_binders res_kind
1274 unsat (scoped_kvs ++ tvs)
1275 -- the tvs contain the binders already
1276 -- in scope from an enclosing class, but
1277 -- re-adding tvs to the env't doesn't cause
1278 -- harm
1279 ; return ( mk_tctc, stuff ) }}
1280
1281 | otherwise
1282 = do { kv_kinds <- mk_kv_kinds
1283 ; scoped_kvs <- zipWithM newSigTyVar kv_ns kv_kinds
1284 -- the names must line up in splitTelescopeTvs
1285 ; (tvs, binders, res_kind, stuff)
1286 <- tcExtendTyVarEnv2 (kv_ns `zip` scoped_kvs) $
1287 bind_telescope hs_tvs thing_inside
1288 ; let -- NB: Don't add scoped_kvs to tyConTyVars, because they
1289 -- must remain lined up with the binders
1290 mk_tctc unsat = mkTcTyCon name tvs
1291 binders res_kind unsat
1292 (scoped_kvs ++ tvs)
1293 ; return (mk_tctc, stuff) }
1294 where
1295 -- if -XNoTypeInType and we know all the implicits are kind vars,
1296 -- just give the kind *. This prevents test
1297 -- dependent/should_fail/KindLevelsB from compiling, as it should
1298 mk_kv_kinds :: TcM [Kind]
1299 mk_kv_kinds = do { typeintype <- xoptM LangExt.TypeInType
1300 ; if not typeintype && all_kind_vars
1301 then return (map (const liftedTypeKind) kv_ns)
1302 else mapM (const newMetaKindVar) kv_ns }
1303
1304 -- there may be dependency between the explicit "ty" vars. So, we have
1305 -- to handle them one at a time.
1306 bind_telescope :: [LHsTyVarBndr Name]
1307 -> TcM (Kind, r)
1308 -> TcM ([TcTyVar], [TyBinder], TcKind, r)
1309 bind_telescope [] thing
1310 = do { (res_kind, stuff) <- thing
1311 ; return ([], [], res_kind, stuff) }
1312 bind_telescope (L _ hs_tv : hs_tvs) thing
1313 = do { tv_pair@(tv, _) <- kc_hs_tv hs_tv
1314 -- NB: Bring all tvs into scope, even non-dependent ones,
1315 -- as they're needed in type synonyms, data constructors, etc.
1316 ; (tvs, binders, res_kind, stuff) <- bind_unless_scoped tv_pair $
1317 bind_telescope hs_tvs $
1318 thing
1319 -- See Note [Dependent LHsQTyVars]
1320 ; let new_binder | hsTyVarName hs_tv `elemNameSet` dep_names
1321 = mkNamedBinder Visible tv
1322 | otherwise
1323 = mkAnonBinder (tyVarKind tv)
1324 ; return ( tv : tvs
1325 , new_binder : binders
1326 , res_kind, stuff ) }
1327
1328 -- | Bind the tyvar in the env't unless the bool is True
1329 bind_unless_scoped :: (TcTyVar, Bool) -> TcM a -> TcM a
1330 bind_unless_scoped (_, True) thing_inside = thing_inside
1331 bind_unless_scoped (tv, False) thing_inside
1332 = tcExtendTyVarEnv [tv] thing_inside
1333
1334 kc_hs_tv :: HsTyVarBndr Name -> TcM (TcTyVar, Bool)
1335 kc_hs_tv (UserTyVar (L _ name))
1336 = do { tv_pair@(tv, scoped) <- tcHsTyVarName Nothing name
1337
1338 -- Open type/data families default their variables to kind *.
1339 ; when (open_fam && not scoped) $ -- (don't default class tyvars)
1340 discardResult $ unifyKind (Just (mkTyVarTy tv)) liftedTypeKind
1341 (tyVarKind tv)
1342
1343 ; return tv_pair }
1344
1345 kc_hs_tv (KindedTyVar (L _ name) lhs_kind)
1346 = do { kind <- tcLHsKind lhs_kind
1347 ; tcHsTyVarName (Just kind) name }
1348
1349 report_non_cusk_tvs all_tvs
1350 = do { all_tvs <- mapM zonkTyCoVarKind all_tvs
1351 ; let (_, tidy_tvs) = tidyOpenTyCoVars emptyTidyEnv all_tvs
1352 (meta_tvs, other_tvs) = partition isMetaTyVar tidy_tvs
1353
1354 ; addErr $
1355 vcat [ text "You have written a *complete user-suppled kind signature*,"
1356 , hang (text "but the following variable" <> plural meta_tvs <+>
1357 isOrAre meta_tvs <+> text "undetermined:")
1358 2 (vcat (map pp_tv meta_tvs))
1359 , text "Perhaps add a kind signature."
1360 , hang (text "Inferred kinds of user-written variables:")
1361 2 (vcat (map pp_tv other_tvs)) ] }
1362 where
1363 pp_tv tv = ppr tv <+> dcolon <+> ppr (tyVarKind tv)
1364
1365
1366 tcImplicitTKBndrs :: [Name]
1367 -> TcM (a, TyVarSet) -- vars are bound somewhere in the scope
1368 -- see Note [Scope-check inferred kinds]
1369 -> TcM ([TcTyVar], a)
1370 tcImplicitTKBndrs = tcImplicitTKBndrsX (tcHsTyVarName Nothing)
1371
1372 -- | Convenient specialization
1373 tcImplicitTKBndrsType :: [Name]
1374 -> TcM Type
1375 -> TcM ([TcTyVar], Type)
1376 tcImplicitTKBndrsType var_ns thing_inside
1377 = tcImplicitTKBndrs var_ns $
1378 do { res_ty <- thing_inside
1379 ; return (res_ty, allBoundVariables res_ty) }
1380
1381 -- this more general variant is needed in tcHsPatSigType.
1382 -- See Note [Pattern signature binders]
1383 tcImplicitTKBndrsX :: (Name -> TcM (TcTyVar, Bool)) -- new_tv function
1384 -> [Name]
1385 -> TcM (a, TyVarSet)
1386 -> TcM ([TcTyVar], a)
1387 -- Returned TcTyVars have the supplied Names
1388 -- i.e. no cloning of fresh names
1389 tcImplicitTKBndrsX new_tv var_ns thing_inside
1390 = do { tkvs_pairs <- mapM new_tv var_ns
1391 ; let must_scope_tkvs = [ tkv | (tkv, False) <- tkvs_pairs ]
1392 tkvs = map fst tkvs_pairs
1393 ; (result, bound_tvs) <- tcExtendTyVarEnv must_scope_tkvs $
1394 thing_inside
1395
1396 -- it's possible that we guessed the ordering of variables
1397 -- wrongly. Adjust.
1398 ; tkvs <- mapM zonkTyCoVarKind tkvs
1399 ; let extra = text "NB: Implicitly-bound variables always come" <+>
1400 text "before other ones."
1401 ; checkValidInferredKinds tkvs bound_tvs extra
1402
1403 ; let final_tvs = toposortTyVars tkvs
1404 ; traceTc "tcImplicitTKBndrs" (ppr var_ns $$ ppr final_tvs)
1405
1406 ; return (final_tvs, result) }
1407
1408 tcExplicitTKBndrs :: [LHsTyVarBndr Name]
1409 -> ([TyVar] -> TcM (a, TyVarSet))
1410 -- ^ Thing inside returns the set of variables bound
1411 -- in the scope. See Note [Scope-check inferred kinds]
1412 -> TcM (a, TyVarSet) -- ^ returns augmented bound vars
1413 -- No cloning: returned TyVars have the same Name as the incoming LHsTyVarBndrs
1414 tcExplicitTKBndrs orig_hs_tvs thing_inside
1415 = tcExplicitTKBndrsX newSkolemTyVar orig_hs_tvs thing_inside
1416
1417 tcExplicitTKBndrsX :: (Name -> Kind -> TcM TyVar)
1418 -> [LHsTyVarBndr Name]
1419 -> ([TyVar] -> TcM (a, TyVarSet))
1420 -- ^ Thing inside returns the set of variables bound
1421 -- in the scope. See Note [Scope-check inferred kinds]
1422 -> TcM (a, TyVarSet) -- ^ returns augmented bound vars
1423 tcExplicitTKBndrsX new_tv orig_hs_tvs thing_inside
1424 = go orig_hs_tvs $ \ tvs ->
1425 do { (result, bound_tvs) <- thing_inside tvs
1426
1427 -- Issue an error if the ordering is bogus.
1428 -- See Note [Bad telescopes] in TcValidity.
1429 ; tvs <- checkZonkValidTelescope (interppSP orig_hs_tvs) tvs empty
1430 ; checkValidInferredKinds tvs bound_tvs empty
1431
1432 ; traceTc "tcExplicitTKBndrs" $
1433 vcat [ text "Hs vars:" <+> ppr orig_hs_tvs
1434 , text "tvs:" <+> sep (map pprTvBndr tvs) ]
1435
1436 ; return (result, bound_tvs `unionVarSet` mkVarSet tvs)
1437 }
1438 where
1439 go [] thing = thing []
1440 go (L _ hs_tv : hs_tvs) thing
1441 = do { tv <- tcHsTyVarBndr new_tv hs_tv
1442 ; tcExtendTyVarEnv [tv] $
1443 go hs_tvs $ \ tvs ->
1444 thing (tv : tvs) }
1445
1446 tcHsTyVarBndr :: (Name -> Kind -> TcM TyVar)
1447 -> HsTyVarBndr Name -> TcM TcTyVar
1448 -- Return a SkolemTv TcTyVar, initialised with a kind variable.
1449 -- Typically the Kind inside the HsTyVarBndr will be a tyvar
1450 -- with a mutable kind in it.
1451 -- NB: These variables must not be in scope. This function
1452 -- is not appropriate for use with associated types, for example.
1453 --
1454 -- Returned TcTyVar has the same name; no cloning
1455 --
1456 -- See also Note [Associated type tyvar names] in Class
1457 --
1458 tcHsTyVarBndr new_tv (UserTyVar (L _ name))
1459 = do { kind <- newMetaKindVar
1460 ; new_tv name kind }
1461
1462 tcHsTyVarBndr new_tv (KindedTyVar (L _ name) kind)
1463 = do { kind <- tcLHsKind kind
1464 ; new_tv name kind }
1465
1466 newWildTyVar :: Name -> TcM TcTyVar
1467 -- ^ New unification variable for a wildcard
1468 newWildTyVar _name
1469 = do { kind <- newMetaKindVar
1470 ; uniq <- newUnique
1471 ; details <- newMetaDetails TauTv
1472 ; let name = mkSysTvName uniq (fsLit "w")
1473 ; return (mkTcTyVar name kind details) }
1474
1475 -- | Produce a tyvar of the given name (with the kind provided, or
1476 -- otherwise a meta-var kind). If
1477 -- the name is already in scope, return the scoped variable, checking
1478 -- to make sure the known kind matches any kind provided. The
1479 -- second return value says whether the variable is in scope (True)
1480 -- or not (False). (Use this for associated types, for example.)
1481 tcHsTyVarName :: Maybe Kind -> Name -> TcM (TcTyVar, Bool)
1482 tcHsTyVarName m_kind name
1483 = do { mb_tv <- tcLookupLcl_maybe name
1484 ; case mb_tv of
1485 Just (ATyVar _ tv)
1486 -> do { whenIsJust m_kind $ \ kind ->
1487 discardResult $
1488 unifyKind (Just (mkTyVarTy tv)) kind (tyVarKind tv)
1489 ; return (tv, True) }
1490 _ -> do { kind <- case m_kind of
1491 Just kind -> return kind
1492 Nothing -> newMetaKindVar
1493 ; return (mk_skolem_tv name kind, False) }}
1494
1495 -- makes a new skolem tv
1496 newSkolemTyVar :: Name -> Kind -> TcM TcTyVar
1497 newSkolemTyVar name kind = return (mk_skolem_tv name kind)
1498
1499 mk_skolem_tv :: Name -> Kind -> TcTyVar
1500 mk_skolem_tv n k = mkTcTyVar n k vanillaSkolemTv
1501
1502 ------------------
1503 kindGeneralizeType :: Type -> TcM Type
1504 -- Result is zonked
1505 kindGeneralizeType ty
1506 = do { kvs <- kindGeneralize ty
1507 ; zonkTcType (mkInvForAllTys kvs ty) }
1508
1509 kindGeneralize :: TcType -> TcM [KindVar]
1510 -- Quantify the free kind variables of a kind or type
1511 -- In the latter case the type is closed, so it has no free
1512 -- type variables. So in both cases, all the free vars are kind vars
1513 kindGeneralize kind_or_type
1514 = do { kvs <- zonkTcTypeAndFV kind_or_type
1515 ; let dvs = DV { dv_kvs = kvs, dv_tvs = emptyDVarSet }
1516 ; gbl_tvs <- tcGetGlobalTyCoVars -- Already zonked
1517 ; quantifyZonkedTyVars gbl_tvs dvs }
1518
1519 {-
1520 Note [Kind generalisation]
1521 ~~~~~~~~~~~~~~~~~~~~~~~~~~
1522 We do kind generalisation only at the outer level of a type signature.
1523 For example, consider
1524 T :: forall k. k -> *
1525 f :: (forall a. T a -> Int) -> Int
1526 When kind-checking f's type signature we generalise the kind at
1527 the outermost level, thus:
1528 f1 :: forall k. (forall (a:k). T k a -> Int) -> Int -- YES!
1529 and *not* at the inner forall:
1530 f2 :: (forall k. forall (a:k). T k a -> Int) -> Int -- NO!
1531 Reason: same as for HM inference on value level declarations,
1532 we want to infer the most general type. The f2 type signature
1533 would be *less applicable* than f1, because it requires a more
1534 polymorphic argument.
1535
1536 NB: There are no explicit kind variables written in f's signature.
1537 When there are, the renamer adds these kind variables to the list of
1538 variables bound by the forall, so you can indeed have a type that's
1539 higher-rank in its kind. But only by explicit request.
1540
1541 Note [Kinds of quantified type variables]
1542 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1543 tcTyVarBndrsGen quantifies over a specified list of type variables,
1544 *and* over the kind variables mentioned in the kinds of those tyvars.
1545
1546 Note that we must zonk those kinds (obviously) but less obviously, we
1547 must return type variables whose kinds are zonked too. Example
1548 (a :: k7) where k7 := k9 -> k9
1549 We must return
1550 [k9, a:k9->k9]
1551 and NOT
1552 [k9, a:k7]
1553 Reason: we're going to turn this into a for-all type,
1554 forall k9. forall (a:k7). blah
1555 which the type checker will then instantiate, and instantiate does not
1556 look through unification variables!
1557
1558 Hence using zonked_kinds when forming tvs'.
1559
1560 Note [Free-floating kind vars]
1561 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1562 Consider
1563
1564 data T = MkT (forall (a :: k). Proxy a)
1565 -- from test ghci/scripts/T7873
1566
1567 This is not an existential datatype, but a higher-rank one. Note that
1568 the forall to the right of MkT. Also consider
1569
1570 data S a = MkS (Proxy (a :: k))
1571
1572 According to the rules around implicitly-bound kind variables, those
1573 k's scope over the whole declarations. The renamer grabs it and adds it
1574 to the hsq_implicits field of the HsQTyVars of the tycon. So it must
1575 be in scope during type-checking, but we want to reject T while accepting
1576 S.
1577
1578 Why reject T? Because the kind variable isn't fixed by anything. For
1579 a variable like k to be implicit, it needs to be mentioned in the kind
1580 of a tycon tyvar. But it isn't.
1581
1582 Why accept S? Because kind inference tells us that a has kind k, so it's
1583 all OK.
1584
1585 Our approach depends on whether or not the datatype has a CUSK.
1586
1587 Non-CUSK: In the first pass (kcTyClTyVars) we just bring
1588 k into scope. In the second pass (tcTyClTyVars),
1589 we check to make sure that k has been unified with some other variable
1590 (or generalized over, making k into a skolem). If it hasn't been, then
1591 it must be a free-floating kind var. Error.
1592
1593 CUSK: When we determine the tycon's final, never-to-be-changed kind
1594 in kcHsTyVarBndrs, we check to make sure all implicitly-bound kind
1595 vars are indeed mentioned in a kind somewhere. If not, error.
1596
1597 -}
1598
1599 --------------------
1600 -- getInitialKind has made a suitably-shaped kind for the type or class
1601 -- Look it up in the local environment. This is used only for tycons
1602 -- that we're currently type-checking, so we're sure to find a TcTyCon.
1603 kcLookupTcTyCon :: Name -> TcM TcTyCon
1604 kcLookupTcTyCon nm
1605 = do { tc_ty_thing <- tcLookup nm
1606 ; return $ case tc_ty_thing of
1607 ATcTyCon tc -> tc
1608 _ -> pprPanic "kcLookupTcTyCon" (ppr tc_ty_thing) }
1609
1610 -----------------------
1611 -- | Bring tycon tyvars into scope. This is used during the "kind-checking"
1612 -- pass in TcTyClsDecls. (Never in getInitialKind, never in the
1613 -- "type-checking"/desugaring pass.)
1614 -- Never emits constraints, though the thing_inside might.
1615 kcTyClTyVars :: Name -> TcM a -> TcM a
1616 kcTyClTyVars tycon_name thing_inside
1617 = do { tycon <- kcLookupTcTyCon tycon_name
1618 ; tcExtendTyVarEnv (tcTyConScopedTyVars tycon) $ thing_inside }
1619
1620 tcTyClTyVars :: Name
1621 -> ([TyVar] -> [TyBinder] -> Kind -> TcM a) -> TcM a
1622 -- ^ Used for the type variables of a type or class decl
1623 -- on the second full pass (type-checking/desugaring) in TcTyClDecls.
1624 -- This is *not* used in the initial-kind run, nor in the "kind-checking" pass.
1625 -- Accordingly, everything passed to the continuation is fully zonked.
1626 --
1627 -- (tcTyClTyVars T [a,b] thing_inside)
1628 -- where T : forall k1 k2 (a:k1 -> *) (b:k1). k2 -> *
1629 -- calls thing_inside with arguments
1630 -- [k1,k2,a,b] [k1:*, k2:*, Anon (k1 -> *), Anon k1] (k2 -> *)
1631 -- having also extended the type environment with bindings
1632 -- for k1,k2,a,b
1633 --
1634 -- Never emits constraints.
1635 --
1636 -- The LHsTyVarBndrs is always user-written, and the full, generalised
1637 -- kind of the tycon is available in the local env.
1638 tcTyClTyVars tycon_name thing_inside
1639 = do { tycon <- kcLookupTcTyCon tycon_name
1640
1641 ; let scoped_tvs = tcTyConScopedTyVars tycon
1642
1643 -- these are all zonked:
1644 tkvs = tyConTyVars tycon
1645 binders = tyConBinders tycon
1646 res_kind = tyConResKind tycon
1647
1648 -- See Note [Free-floating kind vars]
1649 ; zonked_scoped_tvs <- mapM zonkTcTyVarToTyVar scoped_tvs
1650 ; let still_sig_tvs = filter isSigTyVar zonked_scoped_tvs
1651 ; checkNoErrs $ reportFloatingKvs tycon_name
1652 zonked_scoped_tvs still_sig_tvs
1653
1654 -- Add the *unzonked* tyvars to the env't, because those
1655 -- are the ones mentioned in the source.
1656 ; tcExtendTyVarEnv scoped_tvs $
1657 thing_inside tkvs binders res_kind }
1658 where
1659
1660 -----------------------------------
1661 tcDataKindSig :: Kind -> TcM ([TyVar], [TyBinder], Kind)
1662 -- GADT decls can have a (perhaps partial) kind signature
1663 -- e.g. data T :: * -> * -> * where ...
1664 -- This function makes up suitable (kinded) type variables for
1665 -- the argument kinds, and checks that the result kind is indeed *.
1666 -- We use it also to make up argument type variables for for data instances.
1667 -- Never emits constraints.
1668 -- Returns the new TyVars, the extracted TyBinders, and the new, reduced
1669 -- result kind (which should always be Type or a synonym thereof)
1670 tcDataKindSig kind
1671 = do { checkTc (isLiftedTypeKind res_kind) (badKindSig kind)
1672 ; span <- getSrcSpanM
1673 ; us <- newUniqueSupply
1674 ; rdr_env <- getLocalRdrEnv
1675 ; let uniqs = uniqsFromSupply us
1676 occs = [ occ | str <- allNameStrings
1677 , let occ = mkOccName tvName str
1678 , isNothing (lookupLocalRdrOcc rdr_env occ) ]
1679 -- Note [Avoid name clashes for associated data types]
1680
1681 -- NB: Use the tv from a binder if there is one. Otherwise,
1682 -- we end up inventing a new Unique for it, and any other tv
1683 -- that mentions the first ends up with the wrong kind.
1684 ; return ( [ tv
1685 | ((bndr, occ), uniq) <- bndrs `zip` occs `zip` uniqs
1686 , let tv | Just bndr_tv <- binderVar_maybe bndr
1687 = bndr_tv
1688 | otherwise
1689 = mk_tv span uniq occ (binderType bndr) ]
1690 , bndrs, res_kind ) }
1691 where
1692 (bndrs, res_kind) = splitPiTys kind
1693 mk_tv loc uniq occ kind
1694 = mkTyVar (mkInternalName uniq occ loc) kind
1695
1696 badKindSig :: Kind -> SDoc
1697 badKindSig kind
1698 = hang (text "Kind signature on data type declaration has non-* return kind")
1699 2 (ppr kind)
1700
1701 {-
1702 Note [Avoid name clashes for associated data types]
1703 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1704 Consider class C a b where
1705 data D b :: * -> *
1706 When typechecking the decl for D, we'll invent an extra type variable
1707 for D, to fill out its kind. Ideally we don't want this type variable
1708 to be 'a', because when pretty printing we'll get
1709 class C a b where
1710 data D b a0
1711 (NB: the tidying happens in the conversion to IfaceSyn, which happens
1712 as part of pretty-printing a TyThing.)
1713
1714 That's why we look in the LocalRdrEnv to see what's in scope. This is
1715 important only to get nice-looking output when doing ":info C" in GHCi.
1716 It isn't essential for correctness.
1717
1718
1719 ************************************************************************
1720 * *
1721 Partial signatures and pattern signatures
1722 * *
1723 ************************************************************************
1724
1725
1726 Note [Solving equalities in partial type signatures]
1727 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1728 We treat a partial type signature as a "shape constraint" to impose on
1729 the term:
1730 * We make no attempt to kind-generalise it
1731 * We instantiate the explicit and implicit foralls with SigTvs
1732 * We instantiate the wildcards with meta tyvars
1733
1734 We /do/ call solveEqualities, and then zonk to propage the result of
1735 solveEqualities, mainly so that functions like matchExpectedFunTys will
1736 be able to decompose the type, and hence higher-rank signatures will
1737 work. Ugh! For example
1738 f :: (forall a. a->a) -> _
1739 f x = (x True, x 'c')
1740
1741 -}
1742
1743 tcHsPartialSigType
1744 :: UserTypeCtxt
1745 -> LHsSigWcType Name -- The type signature
1746 -> TcM ( [(Name, TcTyVar)] -- Wildcards
1747 , Maybe TcTyVar -- Extra-constraints wildcard
1748 , [TcTyVar] -- Implicitly and explicitly bound type varialbes
1749 , TcThetaType -- Theta part
1750 , TcType ) -- Tau part
1751 tcHsPartialSigType ctxt sig_ty
1752 | HsWC { hswc_wcs = sig_wcs, hswc_body = ib_ty } <- sig_ty
1753 , HsIB { hsib_vars = implicit_hs_tvs, hsib_body = hs_ty } <- ib_ty
1754 , (explicit_hs_tvs, L _ hs_ctxt, hs_tau) <- splitLHsSigmaTy hs_ty
1755 = addSigCtxt ctxt hs_ty $
1756 do { (implicit_tvs, (wcs, wcx, explicit_tvs, theta, tau))
1757 <- -- See Note [Solving equalities in partial type signatures]
1758 solveEqualities $
1759 tcWildCardBindersX newWildTyVar sig_wcs $ \ wcs ->
1760 tcImplicitTKBndrsX new_implicit_tv implicit_hs_tvs $
1761 tcExplicitTKBndrsX newSigTyVar explicit_hs_tvs $ \ explicit_tvs ->
1762 do { -- Instantiate the type-class context; but if there
1763 -- is an extra-constraints wildcard, just discard it here
1764 (theta, wcx) <- tcPartialContext hs_ctxt
1765
1766 ; tau <- tcHsOpenType hs_tau
1767
1768 ; let bound_tvs = unionVarSets [ allBoundVariables tau
1769 , mkVarSet explicit_tvs
1770 , mkVarSet (map snd wcs) ]
1771
1772 ; return ( (wcs, wcx, explicit_tvs, theta, tau)
1773 , bound_tvs) }
1774
1775 ; emitWildCardHoleConstraints wcs
1776
1777 -- See Note [Solving equalities in partial type signatures]
1778 ; all_tvs <- mapM (updateTyVarKindM zonkTcType)
1779 (implicit_tvs ++ explicit_tvs)
1780 ; theta <- mapM zonkTcType theta
1781 ; tau <- zonkTcType tau
1782 ; checkValidType ctxt (mkSpecForAllTys all_tvs $ mkPhiTy theta tau)
1783
1784 ; traceTc "tcHsPatSigType" (ppr all_tvs)
1785 ; return (wcs, wcx, all_tvs, theta, tau) }
1786 where
1787 new_implicit_tv name = do { kind <- newMetaKindVar
1788 ; tv <- newSigTyVar name kind
1789 ; return (tv, False) }
1790
1791 tcPartialContext :: HsContext Name -> TcM (TcThetaType, Maybe TcTyVar)
1792 tcPartialContext hs_theta
1793 | Just (hs_theta1, hs_ctxt_last) <- snocView hs_theta
1794 , L _ (HsWildCardTy wc) <- ignoreParens hs_ctxt_last
1795 = do { wc_tv <- tcWildCardOcc wc constraintKind
1796 ; theta <- mapM tcLHsPredType hs_theta1
1797 ; return (theta, Just wc_tv) }
1798 | otherwise
1799 = do { theta <- mapM tcLHsPredType hs_theta
1800 ; return (theta, Nothing) }
1801
1802 tcHsPatSigType :: UserTypeCtxt
1803 -> LHsSigWcType Name -- The type signature
1804 -> TcM ( [(Name, TcTyVar)] -- Wildcards
1805 , [TcTyVar] -- The new bit of type environment, binding
1806 -- the scoped type variables
1807 , TcType) -- The type
1808 -- Used for type-checking type signatures in
1809 -- (a) patterns e.g f (x::Int) = e
1810 -- (b) RULE forall bndrs e.g. forall (x::Int). f x = x
1811 --
1812 -- This may emit constraints
1813
1814 tcHsPatSigType ctxt sig_ty
1815 | HsWC { hswc_wcs = sig_wcs, hswc_body = ib_ty } <- sig_ty
1816 , HsIB { hsib_vars = sig_vars, hsib_body = hs_ty } <- ib_ty
1817 = addSigCtxt ctxt hs_ty $
1818 do { (implicit_tvs, (wcs, sig_ty))
1819 <- -- See Note [Solving equalities in partial type signatures]
1820 solveEqualities $
1821 tcWildCardBindersX newWildTyVar sig_wcs $ \ wcs ->
1822 tcImplicitTKBndrsX new_implicit_tv sig_vars $
1823 do { sig_ty <- tcHsOpenType hs_ty
1824 ; return ((wcs, sig_ty), allBoundVariables sig_ty) }
1825
1826 ; emitWildCardHoleConstraints wcs
1827
1828 ; sig_ty <- zonkTcType sig_ty
1829 ; checkValidType ctxt sig_ty
1830
1831 ; traceTc "tcHsPatSigType" (ppr sig_vars)
1832 ; return (wcs, implicit_tvs, sig_ty) }
1833 where
1834 new_implicit_tv name = do { kind <- newMetaKindVar
1835 ; tv <- new_tv name kind
1836 ; return (tv, False) }
1837 -- "False" means that these tyvars aren't yet in scope
1838 new_tv = case ctxt of
1839 RuleSigCtxt {} -> newSkolemTyVar
1840 _ -> newSigTyVar
1841 -- See Note [Pattern signature binders]
1842 -- See Note [Unifying SigTvs]
1843
1844
1845 tcPatSig :: Bool -- True <=> pattern binding
1846 -> LHsSigWcType Name
1847 -> ExpSigmaType
1848 -> TcM (TcType, -- The type to use for "inside" the signature
1849 [TcTyVar], -- The new bit of type environment, binding
1850 -- the scoped type variables
1851 [(Name,TcTyVar)], -- The wildcards
1852 HsWrapper) -- Coercion due to unification with actual ty
1853 -- Of shape: res_ty ~ sig_ty
1854 tcPatSig in_pat_bind sig res_ty
1855 = do { (sig_wcs, sig_tvs, sig_ty) <- tcHsPatSigType PatSigCtxt sig
1856 -- sig_tvs are the type variables free in 'sig',
1857 -- and not already in scope. These are the ones
1858 -- that should be brought into scope
1859
1860 ; if null sig_tvs then do {
1861 -- Just do the subsumption check and return
1862 wrap <- addErrCtxtM (mk_msg sig_ty) $
1863 tcSubTypeET_NC PatSigCtxt res_ty sig_ty
1864 ; return (sig_ty, [], sig_wcs, wrap)
1865 } else do
1866 -- Type signature binds at least one scoped type variable
1867
1868 -- A pattern binding cannot bind scoped type variables
1869 -- It is more convenient to make the test here
1870 -- than in the renamer
1871 { when in_pat_bind (addErr (patBindSigErr sig_tvs))
1872
1873 -- Check that all newly-in-scope tyvars are in fact
1874 -- constrained by the pattern. This catches tiresome
1875 -- cases like
1876 -- type T a = Int
1877 -- f :: Int -> Int
1878 -- f (x :: T a) = ...
1879 -- Here 'a' doesn't get a binding. Sigh
1880 ; let bad_tvs = [ tv | tv <- sig_tvs
1881 , not (tv `elemVarSet` exactTyCoVarsOfType sig_ty) ]
1882 ; checkTc (null bad_tvs) (badPatSigTvs sig_ty bad_tvs)
1883
1884 -- Now do a subsumption check of the pattern signature against res_ty
1885 ; wrap <- addErrCtxtM (mk_msg sig_ty) $
1886 tcSubTypeET_NC PatSigCtxt res_ty sig_ty
1887
1888 -- Phew!
1889 ; return (sig_ty, sig_tvs, sig_wcs, wrap)
1890 } }
1891 where
1892 mk_msg sig_ty tidy_env
1893 = do { (tidy_env, sig_ty) <- zonkTidyTcType tidy_env sig_ty
1894 ; res_ty <- readExpType res_ty -- should be filled in by now
1895 ; (tidy_env, res_ty) <- zonkTidyTcType tidy_env res_ty
1896 ; let msg = vcat [ hang (text "When checking that the pattern signature:")
1897 4 (ppr sig_ty)
1898 , nest 2 (hang (text "fits the type of its context:")
1899 2 (ppr res_ty)) ]
1900 ; return (tidy_env, msg) }
1901
1902 patBindSigErr :: [TcTyVar] -> SDoc
1903 patBindSigErr sig_tvs
1904 = hang (text "You cannot bind scoped type variable" <> plural sig_tvs
1905 <+> pprQuotedList sig_tvs)
1906 2 (text "in a pattern binding signature")
1907
1908 {-
1909 Note [Pattern signature binders]
1910 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1911 Consider
1912 data T = forall a. T a (a->Int)
1913 f (T x (f :: a->Int) = blah)
1914
1915 Here
1916 * The pattern (T p1 p2) creates a *skolem* type variable 'a_sk',
1917 It must be a skolem so that that it retains its identity, and
1918 TcErrors.getSkolemInfo can thereby find the binding site for the skolem.
1919
1920 * The type signature pattern (f :: a->Int) binds "a" -> a_sig in the envt
1921
1922 * Then unification makes a_sig := a_sk
1923
1924 That's why we must make a_sig a MetaTv (albeit a SigTv),
1925 not a SkolemTv, so that it can unify to a_sk.
1926
1927 For RULE binders, though, things are a bit different (yuk).
1928 RULE "foo" forall (x::a) (y::[a]). f x y = ...
1929 Here this really is the binding site of the type variable so we'd like
1930 to use a skolem, so that we get a complaint if we unify two of them
1931 together.
1932
1933 Note [Unifying SigTvs]
1934 ~~~~~~~~~~~~~~~~~~~~~~
1935 ALAS we have no decent way of avoiding two SigTvs getting unified.
1936 Consider
1937 f (x::(a,b)) (y::c)) = [fst x, y]
1938 Here we'd really like to complain that 'a' and 'c' are unified. But
1939 for the reasons above we can't make a,b,c into skolems, so they
1940 are just SigTvs that can unify. And indeed, this would be ok,
1941 f x (y::c) = case x of
1942 (x1 :: a1, True) -> [x,y]
1943 (x1 :: a2, False) -> [x,y,y]
1944 Here the type of x's first component is called 'a1' in one branch and
1945 'a2' in the other. We could try insisting on the same OccName, but
1946 they definitely won't have the sane lexical Name.
1947
1948 I think we could solve this by recording in a SigTv a list of all the
1949 in-scope variables that it should not unify with, but it's fiddly.
1950
1951
1952 ************************************************************************
1953 * *
1954 Checking kinds
1955 * *
1956 ************************************************************************
1957
1958 -}
1959
1960 -- | Produce an 'TcKind' suitable for a checking a type that can be * or #.
1961 ekOpen :: TcM TcKind
1962 ekOpen = do { rr <- newFlexiTyVarTy runtimeRepTy
1963 ; return (tYPE rr) }
1964
1965 unifyKinds :: [(TcType, TcKind)] -> TcM ([TcType], TcKind)
1966 unifyKinds act_kinds
1967 = do { kind <- newMetaKindVar
1968 ; let check (ty, act_kind) = checkExpectedKind ty act_kind kind
1969 ; tys' <- mapM check act_kinds
1970 ; return (tys', kind) }
1971
1972 {-
1973 ************************************************************************
1974 * *
1975 Sort checking kinds
1976 * *
1977 ************************************************************************
1978
1979 tcLHsKind converts a user-written kind to an internal, sort-checked kind.
1980 It does sort checking and desugaring at the same time, in one single pass.
1981 -}
1982
1983 tcLHsKind :: LHsKind Name -> TcM Kind
1984 tcLHsKind = tc_lhs_kind kindLevelMode
1985
1986 tc_lhs_kind :: TcTyMode -> LHsKind Name -> TcM Kind
1987 tc_lhs_kind mode k
1988 = addErrCtxt (text "In the kind" <+> quotes (ppr k)) $
1989 tc_lhs_type (kindLevel mode) k liftedTypeKind
1990
1991 promotionErr :: Name -> PromotionErr -> TcM a
1992 promotionErr name err
1993 = failWithTc (hang (pprPECategory err <+> quotes (ppr name) <+> text "cannot be used here")
1994 2 (parens reason))
1995 where
1996 reason = case err of
1997 FamDataConPE -> text "it comes from a data family instance"
1998 NoDataKindsTC -> text "Perhaps you intended to use DataKinds"
1999 NoDataKindsDC -> text "Perhaps you intended to use DataKinds"
2000 NoTypeInTypeTC -> text "Perhaps you intended to use TypeInType"
2001 NoTypeInTypeDC -> text "Perhaps you intended to use TypeInType"
2002 PatSynPE -> text "Pattern synonyms cannot be promoted"
2003 _ -> text "it is defined and used in the same recursive group"
2004
2005 {-
2006 ************************************************************************
2007 * *
2008 Scoped type variables
2009 * *
2010 ************************************************************************
2011 -}
2012
2013 badPatSigTvs :: TcType -> [TyVar] -> SDoc
2014 badPatSigTvs sig_ty bad_tvs
2015 = vcat [ fsep [text "The type variable" <> plural bad_tvs,
2016 quotes (pprWithCommas ppr bad_tvs),
2017 text "should be bound by the pattern signature" <+> quotes (ppr sig_ty),
2018 text "but are actually discarded by a type synonym" ]
2019 , text "To fix this, expand the type synonym"
2020 , text "[Note: I hope to lift this restriction in due course]" ]
2021
2022 {-
2023 ************************************************************************
2024 * *
2025 Error messages and such
2026 * *
2027 ************************************************************************
2028 -}
2029
2030 -- | Make an appropriate message for an error in a function argument.
2031 -- Used for both expressions and types.
2032 funAppCtxt :: (Outputable fun, Outputable arg) => fun -> arg -> Int -> SDoc
2033 funAppCtxt fun arg arg_no
2034 = hang (hsep [ text "In the", speakNth arg_no, ptext (sLit "argument of"),
2035 quotes (ppr fun) <> text ", namely"])
2036 2 (quotes (ppr arg))
2037
2038 -- See Note [Free-floating kind vars]
2039 reportFloatingKvs :: Name -- of the tycon
2040 -> [TcTyVar] -- all tyvars, not necessarily zonked
2041 -> [TcTyVar] -- floating tyvars
2042 -> TcM ()
2043 reportFloatingKvs tycon_name all_tvs bad_tvs
2044 = unless (null bad_tvs) $ -- don't bother zonking if there's no error
2045 do { all_tvs <- mapM zonkTcTyVarToTyVar all_tvs
2046 ; bad_tvs <- mapM zonkTcTyVarToTyVar bad_tvs
2047 ; let (tidy_env, tidy_all_tvs) = tidyOpenTyCoVars emptyTidyEnv all_tvs
2048 tidy_bad_tvs = map (tidyTyVarOcc tidy_env) bad_tvs
2049 ; typeintype <- xoptM LangExt.TypeInType
2050 ; mapM_ (report typeintype tidy_all_tvs) tidy_bad_tvs }
2051 where
2052 report typeintype tidy_all_tvs tidy_bad_tv
2053 = addErr $
2054 vcat [ text "Kind variable" <+> quotes (ppr tidy_bad_tv) <+>
2055 text "is implicitly bound in datatype"
2056 , quotes (ppr tycon_name) <> comma <+>
2057 text "but does not appear as the kind of any"
2058 , text "of its type variables. Perhaps you meant"
2059 , text "to bind it" <+> ppWhen (not typeintype)
2060 (text "(with TypeInType)") <+>
2061 text "explicitly somewhere?"
2062 , ppWhen (not (null tidy_all_tvs)) $
2063 hang (text "Type variables with inferred kinds:")
2064 2 (ppr_tv_bndrs tidy_all_tvs) ]
2065
2066 ppr_tv_bndrs tvs = sep (map pp_tv tvs)
2067 pp_tv tv = parens (ppr tv <+> dcolon <+> ppr (tyVarKind tv))