Refactor tcInferArgs and add comments.
[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 -- 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 = mkTyVarBinders 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 -- Never calls 'matchExpectedFunKind'; when the kind runs out of binders,
737 -- this stops processing.
738 -- This takes an optional @VarEnv Kind@ which maps kind variables to kinds.
739 -- These kinds should be used to instantiate invisible kind variables;
740 -- they come from an enclosing class for an associated type/data family.
741 -- This version will instantiate all invisible arguments left over after
742 -- the visible ones. Used only when typechecking type/data family patterns
743 -- (where we need to instantiate all remaining invisible parameters; for
744 -- example, consider @type family F :: k where F = Int; F = Maybe@. We
745 -- need to instantiate the @k@.)
746 tcInferArgs :: Outputable fun
747 => fun -- ^ the function
748 -> [TyConBinder] -- ^ function kind's binders
749 -> Maybe (VarEnv Kind) -- ^ possibly, kind info (see above)
750 -> [LHsType Name] -- ^ args
751 -> TcM (TCvSubst, [TyBinder], [TcType], [LHsType Name], Int)
752 -- ^ (instantiating subst, un-insted leftover binders,
753 -- typechecked args, untypechecked args, n)
754 tcInferArgs fun tc_binders mb_kind_info args
755 = do { let binders = tyConBindersTyBinders tc_binders -- UGH!
756 ; (subst, leftover_binders, args', leftovers, n)
757 <- tc_infer_args typeLevelMode fun binders mb_kind_info args 1
758 -- now, we need to instantiate any remaining invisible arguments
759 ; let (invis_bndrs, other_binders) = break isVisibleBinder leftover_binders
760 ; (subst', invis_args)
761 <- tcInstBindersX subst mb_kind_info invis_bndrs
762 ; return ( subst'
763 , other_binders
764 , args' `chkAppend` invis_args
765 , leftovers, n ) }
766
767 -- | See comments for 'tcInferArgs'. But this version does not instantiate
768 -- any remaining invisible arguments.
769 tc_infer_args :: Outputable fun
770 => TcTyMode
771 -> fun -- ^ the function
772 -> [TyBinder] -- ^ function kind's binders (zonked)
773 -> Maybe (VarEnv Kind) -- ^ possibly, kind info (see above)
774 -> [LHsType Name] -- ^ args
775 -> Int -- ^ number to start arg counter at
776 -> TcM (TCvSubst, [TyBinder], [TcType], [LHsType Name], Int)
777 tc_infer_args mode orig_ty binders mb_kind_info orig_args n0
778 = go emptyTCvSubst binders orig_args n0 []
779 where
780 go subst binders [] n acc
781 = return ( subst, binders, reverse acc, [], n )
782 -- when we call this when checking type family patterns, we really
783 -- do want to instantiate all invisible arguments. During other
784 -- typechecking, we don't.
785
786 go subst (binder:binders) all_args@(arg:args) n acc
787 | isInvisibleBinder binder
788 = do { traceTc "tc_infer_args (invis)" (ppr binder)
789 ; (subst', arg') <- tcInstBinderX mb_kind_info subst binder
790 ; go subst' binders all_args n (arg' : acc) }
791
792 | otherwise
793 = do { traceTc "tc_infer_args (vis)" (ppr binder $$ ppr arg)
794 ; arg' <- addErrCtxt (funAppCtxt orig_ty arg n) $
795 tc_lhs_type mode arg (substTyUnchecked subst $
796 tyBinderType binder)
797 ; let subst' = extendTvSubstBinder subst binder arg'
798 ; go subst' binders args (n+1) (arg' : acc) }
799
800 go subst [] all_args n acc
801 = return (subst, [], reverse acc, all_args, n)
802
803 -- | Applies a type to a list of arguments.
804 -- Always consumes all the arguments, using 'matchExpectedFunKind' as
805 -- necessary. If you wish to apply a type to a list of HsTypes, this is
806 -- your function.
807 -- Used for type-checking types only.
808 tcInferApps :: Outputable fun
809 => TcTyMode
810 -> fun -- ^ Function (for printing only)
811 -> TcType -- ^ Function (could be knot-tied)
812 -> TcKind -- ^ Function kind (zonked)
813 -> [LHsType Name] -- ^ Args
814 -> TcM (TcType, TcKind) -- ^ (f args, result kind)
815 tcInferApps mode orig_ty ty ki args = go ty ki args 1
816 where
817 go fun fun_kind [] _ = return (fun, fun_kind)
818 go fun fun_kind args n
819 | let (binders, res_kind) = splitPiTys fun_kind
820 , not (null binders)
821 = do { (subst, leftover_binders, args', leftover_args, n')
822 <- tc_infer_args mode orig_ty binders Nothing args n
823 ; let fun_kind' = substTyUnchecked subst $
824 mkPiTys leftover_binders res_kind
825 ; go (mkNakedAppTys fun args') fun_kind' leftover_args n' }
826
827 go fun fun_kind all_args@(arg:args) n
828 = do { (co, arg_k, res_k) <- matchExpectedFunKind (length all_args)
829 fun fun_kind
830 ; arg' <- addErrCtxt (funAppCtxt orig_ty arg n) $
831 tc_lhs_type mode arg arg_k
832 ; go (mkNakedAppTy (fun `mkNakedCastTy` co) arg')
833 res_k args (n+1) }
834
835 --------------------------
836 checkExpectedKind :: TcType -- the type whose kind we're checking
837 -> TcKind -- the known kind of that type, k
838 -> TcKind -- the expected kind, exp_kind
839 -> TcM TcType -- a possibly-inst'ed, casted type :: exp_kind
840 -- Instantiate a kind (if necessary) and then call unifyType
841 -- (checkExpectedKind ty act_kind exp_kind)
842 -- checks that the actual kind act_kind is compatible
843 -- with the expected kind exp_kind
844 checkExpectedKind ty act_kind exp_kind
845 = do { (ty', act_kind') <- instantiate ty act_kind exp_kind
846 ; let origin = TypeEqOrigin { uo_actual = act_kind'
847 , uo_expected = mkCheckExpType exp_kind
848 , uo_thing = Just $ mkTypeErrorThing ty'
849 }
850 ; co_k <- uType origin KindLevel act_kind' exp_kind
851 ; traceTc "checkExpectedKind" (vcat [ ppr act_kind
852 , ppr exp_kind
853 , ppr co_k ])
854 ; let result_ty = ty' `mkNakedCastTy` co_k
855 ; return result_ty }
856 where
857 -- we need to make sure that both kinds have the same number of implicit
858 -- foralls out front. If the actual kind has more, instantiate accordingly.
859 -- Otherwise, just pass the type & kind through -- the errors are caught
860 -- in unifyType.
861 instantiate :: TcType -- the type
862 -> TcKind -- of this kind
863 -> TcKind -- but expected to be of this one
864 -> TcM ( TcType -- the inst'ed type
865 , TcKind ) -- its new kind
866 instantiate ty act_ki exp_ki
867 = let (exp_bndrs, _) = splitPiTysInvisible exp_ki in
868 instantiateTyN (length exp_bndrs) ty act_ki
869
870 -- | Instantiate a type to have at most @n@ invisible arguments.
871 instantiateTyN :: Int -- ^ @n@
872 -> TcType -- ^ the type
873 -> TcKind -- ^ its kind
874 -> TcM (TcType, TcKind) -- ^ The inst'ed type with kind
875 instantiateTyN n ty ki
876 = let (bndrs, inner_ki) = splitPiTysInvisible ki
877 num_to_inst = length bndrs - n
878 -- NB: splitAt is forgiving with invalid numbers
879 (inst_bndrs, leftover_bndrs) = splitAt num_to_inst bndrs
880 in
881 if num_to_inst <= 0 then return (ty, ki) else
882 do { (subst, inst_args) <- tcInstBinders inst_bndrs
883 ; let rebuilt_ki = mkPiTys leftover_bndrs inner_ki
884 ki' = substTy subst rebuilt_ki
885 ; return (mkNakedAppTys ty inst_args, ki') }
886
887 ---------------------------
888 tcHsContext :: LHsContext Name -> TcM [PredType]
889 tcHsContext = tc_hs_context typeLevelMode
890
891 tcLHsPredType :: LHsType Name -> TcM PredType
892 tcLHsPredType = tc_lhs_pred typeLevelMode
893
894 tc_hs_context :: TcTyMode -> LHsContext Name -> TcM [PredType]
895 tc_hs_context mode ctxt = mapM (tc_lhs_pred mode) (unLoc ctxt)
896
897 tc_lhs_pred :: TcTyMode -> LHsType Name -> TcM PredType
898 tc_lhs_pred mode pred = tc_lhs_type mode pred constraintKind
899
900 ---------------------------
901 tcTyVar :: TcTyMode -> Name -> TcM (TcType, TcKind)
902 -- See Note [Type checking recursive type and class declarations]
903 -- in TcTyClsDecls
904 tcTyVar mode name -- Could be a tyvar, a tycon, or a datacon
905 = do { traceTc "lk1" (ppr name)
906 ; thing <- tcLookup name
907 ; case thing of
908 ATyVar _ tv -> return (mkTyVarTy tv, tyVarKind tv)
909
910 ATcTyCon tc_tc -> do { check_tc tc_tc
911 ; tc <- get_loopy_tc name tc_tc
912 ; handle_tyfams tc tc_tc }
913 -- mkNakedTyConApp: see Note [Type-checking inside the knot]
914 -- NB: we really should check if we're at the kind level
915 -- and if the tycon is promotable if -XNoTypeInType is set.
916 -- But this is a terribly large amount of work! Not worth it.
917
918 AGlobal (ATyCon tc)
919 -> do { check_tc tc
920 ; handle_tyfams tc tc }
921
922 AGlobal (AConLike (RealDataCon dc))
923 -> do { data_kinds <- xoptM LangExt.DataKinds
924 ; unless (data_kinds || specialPromotedDc dc) $
925 promotionErr name NoDataKindsDC
926 ; type_in_type <- xoptM LangExt.TypeInType
927 ; unless ( type_in_type ||
928 ( isTypeLevel (mode_level mode) &&
929 isLegacyPromotableDataCon dc ) ||
930 ( isKindLevel (mode_level mode) &&
931 specialPromotedDc dc ) ) $
932 promotionErr name NoTypeInTypeDC
933 ; let tc = promoteDataCon dc
934 ; return (mkNakedTyConApp tc [], tyConKind tc) }
935
936 APromotionErr err -> promotionErr name err
937
938 _ -> wrongThingErr "type" thing name }
939 where
940 check_tc :: TyCon -> TcM ()
941 check_tc tc = do { type_in_type <- xoptM LangExt.TypeInType
942 ; data_kinds <- xoptM LangExt.DataKinds
943 ; unless (isTypeLevel (mode_level mode) ||
944 data_kinds ||
945 isKindTyCon tc) $
946 promotionErr name NoDataKindsTC
947 ; unless (isTypeLevel (mode_level mode) ||
948 type_in_type ||
949 isLegacyPromotableTyCon tc) $
950 promotionErr name NoTypeInTypeTC }
951
952 -- if we are type-checking a type family tycon, we must instantiate
953 -- any invisible arguments right away. Otherwise, we get #11246
954 handle_tyfams :: TyCon -- the tycon to instantiate (might be loopy)
955 -> TyCon -- a non-loopy version of the tycon
956 -> TcM (TcType, TcKind)
957 handle_tyfams tc tc_tc
958 | mightBeUnsaturatedTyCon tc_tc
959 = do { traceTc "tcTyVar2a" (ppr tc_tc $$ ppr tc_kind)
960 ; return (ty, tc_kind) }
961
962 | otherwise
963 = do { (tc_ty, kind) <- instantiateTyN 0 ty tc_kind
964 -- tc and tc_ty must not be traced here, because that would
965 -- force the evaluation of a potentially knot-tied variable (tc),
966 -- and the typechecker would hang, as per #11708
967 ; traceTc "tcTyVar2b" (vcat [ ppr tc_tc <+> dcolon <+> ppr tc_kind
968 , ppr kind ])
969 ; return (tc_ty, kind) }
970 where
971 ty = mkNakedTyConApp tc []
972 tc_kind = tyConKind tc_tc
973
974 get_loopy_tc :: Name -> TyCon -> TcM TyCon
975 -- Return the knot-tied global TyCon if there is one
976 -- Otherwise the local TcTyCon; we must be doing kind checking
977 -- but we still want to return a TyCon of some sort to use in
978 -- error messages
979 get_loopy_tc name tc_tc
980 = do { env <- getGblEnv
981 ; case lookupNameEnv (tcg_type_env env) name of
982 Just (ATyCon tc) -> return tc
983 _ -> do { traceTc "lk1 (loopy)" (ppr name)
984 ; return tc_tc } }
985
986 tcClass :: Name -> TcM (Class, TcKind)
987 tcClass cls -- Must be a class
988 = do { thing <- tcLookup cls
989 ; case thing of
990 ATcTyCon tc -> return (aThingErr "tcClass" cls, tyConKind tc)
991 AGlobal (ATyCon tc)
992 | Just cls <- tyConClass_maybe tc
993 -> return (cls, tyConKind tc)
994 _ -> wrongThingErr "class" thing cls }
995
996
997 aThingErr :: String -> Name -> b
998 -- The type checker for types is sometimes called simply to
999 -- do *kind* checking; and in that case it ignores the type
1000 -- returned. Which is a good thing since it may not be available yet!
1001 aThingErr str x = pprPanic "AThing evaluated unexpectedly" (text str <+> ppr x)
1002
1003 {-
1004 Note [Type-checking inside the knot]
1005 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1006 Suppose we are checking the argument types of a data constructor. We
1007 must zonk the types before making the DataCon, because once built we
1008 can't change it. So we must traverse the type.
1009
1010 BUT the parent TyCon is knot-tied, so we can't look at it yet.
1011
1012 So we must be careful not to use "smart constructors" for types that
1013 look at the TyCon or Class involved.
1014
1015 * Hence the use of mkNakedXXX functions. These do *not* enforce
1016 the invariants (for example that we use (FunTy s t) rather
1017 than (TyConApp (->) [s,t])).
1018
1019 * The zonking functions establish invariants (even zonkTcType, a change from
1020 previous behaviour). So we must never inspect the result of a
1021 zonk that might mention a knot-tied TyCon. This is generally OK
1022 because we zonk *kinds* while kind-checking types. And the TyCons
1023 in kinds shouldn't be knot-tied, because they come from a previous
1024 mutually recursive group.
1025
1026 * TcHsSyn.zonkTcTypeToType also can safely check/establish
1027 invariants.
1028
1029 This is horribly delicate. I hate it. A good example of how
1030 delicate it is can be seen in Trac #7903.
1031
1032 Note [Body kind of a HsForAllTy]
1033 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1034 The body of a forall is usually a type, but in principle
1035 there's no reason to prohibit *unlifted* types.
1036 In fact, GHC can itself construct a function with an
1037 unboxed tuple inside a for-all (via CPR analyis; see
1038 typecheck/should_compile/tc170).
1039
1040 Moreover in instance heads we get forall-types with
1041 kind Constraint.
1042
1043 It's tempting to check that the body kind is either * or #. But this is
1044 wrong. For example:
1045
1046 class C a b
1047 newtype N = Mk Foo deriving (C a)
1048
1049 We're doing newtype-deriving for C. But notice how `a` isn't in scope in
1050 the predicate `C a`. So we quantify, yielding `forall a. C a` even though
1051 `C a` has kind `* -> Constraint`. The `forall a. C a` is a bit cheeky, but
1052 convenient. Bottom line: don't check for * or # here.
1053
1054 Note [Body kind of a HsQualTy]
1055 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1056 If ctxt is non-empty, the HsQualTy really is a /function/, so the
1057 kind of the result really is '*', and in that case the kind of the
1058 body-type can be lifted or unlifted.
1059
1060 However, consider
1061 instance Eq a => Eq [a] where ...
1062 or
1063 f :: (Eq a => Eq [a]) => blah
1064 Here both body-kind of the HsQualTy is Constraint rather than *.
1065 Rather crudely we tell the difference by looking at exp_kind. It's
1066 very convenient to typecheck instance types like any other HsSigType.
1067
1068 Admittedly the '(Eq a => Eq [a]) => blah' case is erroneous, but it's
1069 better to reject in checkValidType. If we say that the body kind
1070 should be '*' we risk getting TWO error messages, one saying that Eq
1071 [a] doens't have kind '*', and one saying that we need a Constraint to
1072 the left of the outer (=>).
1073
1074 How do we figure out the right body kind? Well, it's a bit of a
1075 kludge: I just look at the expected kind. If it's Constraint, we
1076 must be in this instance situation context. It's a kludge because it
1077 wouldn't work if any unification was involved to compute that result
1078 kind -- but it isn't. (The true way might be to use the 'mode'
1079 parameter, but that seemed like a sledgehammer to crack a nut.)
1080
1081 Note [Inferring tuple kinds]
1082 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1083 Give a tuple type (a,b,c), which the parser labels as HsBoxedOrConstraintTuple,
1084 we try to figure out whether it's a tuple of kind * or Constraint.
1085 Step 1: look at the expected kind
1086 Step 2: infer argument kinds
1087
1088 If after Step 2 it's not clear from the arguments that it's
1089 Constraint, then it must be *. Once having decided that we re-check
1090 the Check the arguments again to give good error messages
1091 in eg. `(Maybe, Maybe)`
1092
1093 Note that we will still fail to infer the correct kind in this case:
1094
1095 type T a = ((a,a), D a)
1096 type family D :: Constraint -> Constraint
1097
1098 While kind checking T, we do not yet know the kind of D, so we will default the
1099 kind of T to * -> *. It works if we annotate `a` with kind `Constraint`.
1100
1101 Note [Desugaring types]
1102 ~~~~~~~~~~~~~~~~~~~~~~~
1103 The type desugarer is phase 2 of dealing with HsTypes. Specifically:
1104
1105 * It transforms from HsType to Type
1106
1107 * It zonks any kinds. The returned type should have no mutable kind
1108 or type variables (hence returning Type not TcType):
1109 - any unconstrained kind variables are defaulted to (Any *) just
1110 as in TcHsSyn.
1111 - there are no mutable type variables because we are
1112 kind-checking a type
1113 Reason: the returned type may be put in a TyCon or DataCon where
1114 it will never subsequently be zonked.
1115
1116 You might worry about nested scopes:
1117 ..a:kappa in scope..
1118 let f :: forall b. T '[a,b] -> Int
1119 In this case, f's type could have a mutable kind variable kappa in it;
1120 and we might then default it to (Any *) when dealing with f's type
1121 signature. But we don't expect this to happen because we can't get a
1122 lexically scoped type variable with a mutable kind variable in it. A
1123 delicate point, this. If it becomes an issue we might need to
1124 distinguish top-level from nested uses.
1125
1126 Moreover
1127 * it cannot fail,
1128 * it does no unifications
1129 * it does no validity checking, except for structural matters, such as
1130 (a) spurious ! annotations.
1131 (b) a class used as a type
1132
1133 Note [Kind of a type splice]
1134 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1135 Consider these terms, each with TH type splice inside:
1136 [| e1 :: Maybe $(..blah..) |]
1137 [| e2 :: $(..blah..) |]
1138 When kind-checking the type signature, we'll kind-check the splice
1139 $(..blah..); we want to give it a kind that can fit in any context,
1140 as if $(..blah..) :: forall k. k.
1141
1142 In the e1 example, the context of the splice fixes kappa to *. But
1143 in the e2 example, we'll desugar the type, zonking the kind unification
1144 variables as we go. When we encounter the unconstrained kappa, we
1145 want to default it to '*', not to (Any *).
1146
1147
1148 Help functions for type applications
1149 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1150 -}
1151
1152 addTypeCtxt :: LHsType Name -> TcM a -> TcM a
1153 -- Wrap a context around only if we want to show that contexts.
1154 -- Omit invisble ones and ones user's won't grok
1155 addTypeCtxt (L _ ty) thing
1156 = addErrCtxt doc thing
1157 where
1158 doc = text "In the type" <+> quotes (ppr ty)
1159
1160 {-
1161 ************************************************************************
1162 * *
1163 Type-variable binders
1164 %* *
1165 %************************************************************************
1166
1167 Note [Scope-check inferred kinds]
1168 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1169 Consider
1170
1171 data SameKind :: k -> k -> *
1172 foo :: forall a (b :: Proxy a) (c :: Proxy d). SameKind b c
1173
1174 d has no binding site. So it gets bound implicitly, at the top. The
1175 problem is that d's kind mentions `a`. So it's all ill-scoped.
1176
1177 The way we check for this is to gather all variables *bound* in a
1178 type variable's scope. The type variable's kind should not mention
1179 any of these variables. That is, d's kind can't mention a, b, or c.
1180 We can't just check to make sure that d's kind is in scope, because
1181 we might be about to kindGeneralize.
1182
1183 A little messy, but it works.
1184
1185 Note [Dependent LHsQTyVars]
1186 ~~~~~~~~~~~~~~~~~~~~~~~~~~~
1187 We track (in the renamer) which explicitly bound variables in a
1188 LHsQTyVars are manifestly dependent; only precisely these variables
1189 may be used within the LHsQTyVars. We must do this so that kcHsTyVarBndrs
1190 can produce the right TcTyBinders, and tell Anon vs. Named. Earlier,
1191 I thought it would work simply to do a free-variable check during
1192 kcHsTyVarBndrs, but this is bogus, because there may be unsolved
1193 equalities about. And we don't want to eagerly solve the equalities,
1194 because we may get further information after kcHsTyVarBndrs is called.
1195 (Recall that kcHsTyVarBndrs is usually called from getInitialKind.
1196 The only other case is in kcConDecl.) This is what implements the rule
1197 that all variables intended to be dependent must be manifestly so.
1198
1199 Sidenote: It's quite possible that later, we'll consider (t -> s)
1200 as a degenerate case of some (pi (x :: t) -> s) and then this will
1201 all get more permissive.
1202
1203 -}
1204
1205 tcWildCardBinders :: [Name]
1206 -> ([(Name, TcTyVar)] -> TcM a)
1207 -> TcM a
1208 tcWildCardBinders = tcWildCardBindersX new_tv
1209 where
1210 new_tv name = do { kind <- newMetaKindVar
1211 ; newSkolemTyVar name kind }
1212
1213 tcWildCardBindersX :: (Name -> TcM TcTyVar)
1214 -> [Name]
1215 -> ([(Name, TcTyVar)] -> TcM a)
1216 -> TcM a
1217 tcWildCardBindersX new_wc wc_names thing_inside
1218 = do { wcs <- mapM new_wc wc_names
1219 ; let wc_prs = wc_names `zip` wcs
1220 ; tcExtendTyVarEnv2 wc_prs $
1221 thing_inside wc_prs }
1222
1223 -- | Kind-check a 'LHsQTyVars'. If the decl under consideration has a complete,
1224 -- user-supplied kind signature (CUSK), generalise the result.
1225 -- Used in 'getInitialKind' (for tycon kinds and other kinds)
1226 -- and in kind-checking (but not for tycon kinds, which are checked with
1227 -- tcTyClDecls). See also Note [Complete user-supplied kind signatures] in
1228 -- HsDecls.
1229 --
1230 -- This function does not do telescope checking.
1231 kcHsTyVarBndrs :: Name -- ^ of the thing being checked
1232 -> Bool -- ^ True <=> the decl being checked has a CUSK
1233 -> Bool -- ^ True <=> the decl is an open type/data family
1234 -> Bool -- ^ True <=> all the hsq_implicit are *kind* vars
1235 -- (will give these kind * if -XNoTypeInType)
1236 -> LHsQTyVars Name
1237 -> TcM (Kind, r) -- ^ the result kind, possibly with other info
1238 -> TcM (Bool -> TcTyCon, r)
1239 -- ^ a way to make a TcTyCon, with the other info.
1240 -- The Bool says whether the tycon can be unsaturated.
1241 kcHsTyVarBndrs name cusk open_fam all_kind_vars
1242 (HsQTvs { hsq_implicit = kv_ns, hsq_explicit = hs_tvs
1243 , hsq_dependent = dep_names }) thing_inside
1244 | cusk
1245 = do { kv_kinds <- mk_kv_kinds
1246 ; let scoped_kvs = zipWith mk_skolem_tv kv_ns kv_kinds
1247 ; tcExtendTyVarEnv2 (kv_ns `zip` scoped_kvs) $
1248 do { (tc_binders, res_kind, stuff) <- solveEqualities $
1249 bind_telescope hs_tvs thing_inside
1250
1251 -- Now, because we're in a CUSK, quantify over the mentioned
1252 -- kind vars, in dependency order.
1253 ; tc_binders <- mapM zonkTyConBinder tc_binders
1254 ; res_kind <- zonkTcType res_kind
1255 ; let tc_tvs = binderVars tc_binders
1256 qkvs = tyCoVarsOfTypeWellScoped (mkTyConKind tc_binders res_kind)
1257 -- the visibility of tvs doesn't matter here; we just
1258 -- want the free variables not to include the tvs
1259
1260 -- If there are any meta-tvs left, the user has
1261 -- lied about having a CUSK. Error.
1262 ; let (meta_tvs, good_tvs) = partition isMetaTyVar qkvs
1263 ; when (not (null meta_tvs)) $
1264 report_non_cusk_tvs (qkvs ++ tc_tvs)
1265
1266 -- If any of the scoped_kvs aren't actually mentioned in a binder's
1267 -- kind (or the return kind), then we're in the CUSK case from
1268 -- Note [Free-floating kind vars]
1269 ; let all_tc_tvs = good_tvs ++ tc_tvs
1270 all_mentioned_tvs = mapUnionVarSet (tyCoVarsOfType . tyVarKind)
1271 all_tc_tvs
1272 `unionVarSet` tyCoVarsOfType res_kind
1273 unmentioned_kvs = filterOut (`elemVarSet` all_mentioned_tvs)
1274 scoped_kvs
1275 ; reportFloatingKvs name all_tc_tvs unmentioned_kvs
1276
1277 ; let final_binders = map (mkNamedTyConBinder Specified) good_tvs
1278 ++ tc_binders
1279 mk_tctc unsat = mkTcTyCon name final_binders res_kind
1280 unsat (scoped_kvs ++ tc_tvs)
1281 -- the tvs contain the binders already
1282 -- in scope from an enclosing class, but
1283 -- re-adding tvs to the env't doesn't cause
1284 -- harm
1285 ; return ( mk_tctc, stuff ) }}
1286
1287 | otherwise
1288 = do { kv_kinds <- mk_kv_kinds
1289 ; scoped_kvs <- zipWithM newSigTyVar kv_ns kv_kinds
1290 -- the names must line up in splitTelescopeTvs
1291 ; (binders, res_kind, stuff)
1292 <- tcExtendTyVarEnv2 (kv_ns `zip` scoped_kvs) $
1293 bind_telescope hs_tvs thing_inside
1294 ; let -- NB: Don't add scoped_kvs to tyConTyVars, because they
1295 -- must remain lined up with the binders
1296 mk_tctc unsat = mkTcTyCon name binders res_kind unsat
1297 (scoped_kvs ++ binderVars binders)
1298 ; return (mk_tctc, stuff) }
1299 where
1300 -- if -XNoTypeInType and we know all the implicits are kind vars,
1301 -- just give the kind *. This prevents test
1302 -- dependent/should_fail/KindLevelsB from compiling, as it should
1303 mk_kv_kinds :: TcM [Kind]
1304 mk_kv_kinds = do { typeintype <- xoptM LangExt.TypeInType
1305 ; if not typeintype && all_kind_vars
1306 then return (map (const liftedTypeKind) kv_ns)
1307 else mapM (const newMetaKindVar) kv_ns }
1308
1309 -- there may be dependency between the explicit "ty" vars. So, we have
1310 -- to handle them one at a time.
1311 bind_telescope :: [LHsTyVarBndr Name]
1312 -> TcM (Kind, r)
1313 -> TcM ([TyConBinder], TcKind, r)
1314 bind_telescope [] thing
1315 = do { (res_kind, stuff) <- thing
1316 ; return ([], res_kind, stuff) }
1317 bind_telescope (L _ hs_tv : hs_tvs) thing
1318 = do { tv_pair@(tv, _) <- kc_hs_tv hs_tv
1319 -- NB: Bring all tvs into scope, even non-dependent ones,
1320 -- as they're needed in type synonyms, data constructors, etc.
1321 ; (binders, res_kind, stuff) <- bind_unless_scoped tv_pair $
1322 bind_telescope hs_tvs $
1323 thing
1324 -- See Note [Dependent LHsQTyVars]
1325 ; let new_binder | hsTyVarName hs_tv `elemNameSet` dep_names
1326 = mkNamedTyConBinder Required tv
1327 | otherwise
1328 = mkAnonTyConBinder tv
1329 ; return ( new_binder : binders
1330 , res_kind, stuff ) }
1331
1332 -- | Bind the tyvar in the env't unless the bool is True
1333 bind_unless_scoped :: (TcTyVar, Bool) -> TcM a -> TcM a
1334 bind_unless_scoped (_, True) thing_inside = thing_inside
1335 bind_unless_scoped (tv, False) thing_inside
1336 = tcExtendTyVarEnv [tv] thing_inside
1337
1338 kc_hs_tv :: HsTyVarBndr Name -> TcM (TcTyVar, Bool)
1339 kc_hs_tv (UserTyVar (L _ name))
1340 = do { tv_pair@(tv, scoped) <- tcHsTyVarName Nothing name
1341
1342 -- Open type/data families default their variables to kind *.
1343 ; when (open_fam && not scoped) $ -- (don't default class tyvars)
1344 discardResult $ unifyKind (Just (mkTyVarTy tv)) liftedTypeKind
1345 (tyVarKind tv)
1346
1347 ; return tv_pair }
1348
1349 kc_hs_tv (KindedTyVar (L _ name) lhs_kind)
1350 = do { kind <- tcLHsKind lhs_kind
1351 ; tcHsTyVarName (Just kind) name }
1352
1353 report_non_cusk_tvs all_tvs
1354 = do { all_tvs <- mapM zonkTyCoVarKind all_tvs
1355 ; let (_, tidy_tvs) = tidyOpenTyCoVars emptyTidyEnv all_tvs
1356 (meta_tvs, other_tvs) = partition isMetaTyVar tidy_tvs
1357
1358 ; addErr $
1359 vcat [ text "You have written a *complete user-suppled kind signature*,"
1360 , hang (text "but the following variable" <> plural meta_tvs <+>
1361 isOrAre meta_tvs <+> text "undetermined:")
1362 2 (vcat (map pp_tv meta_tvs))
1363 , text "Perhaps add a kind signature."
1364 , hang (text "Inferred kinds of user-written variables:")
1365 2 (vcat (map pp_tv other_tvs)) ] }
1366 where
1367 pp_tv tv = ppr tv <+> dcolon <+> ppr (tyVarKind tv)
1368
1369
1370 tcImplicitTKBndrs :: [Name]
1371 -> TcM (a, TyVarSet) -- vars are bound somewhere in the scope
1372 -- see Note [Scope-check inferred kinds]
1373 -> TcM ([TcTyVar], a)
1374 tcImplicitTKBndrs = tcImplicitTKBndrsX (tcHsTyVarName Nothing)
1375
1376 -- | Convenient specialization
1377 tcImplicitTKBndrsType :: [Name]
1378 -> TcM Type
1379 -> TcM ([TcTyVar], Type)
1380 tcImplicitTKBndrsType var_ns thing_inside
1381 = tcImplicitTKBndrs var_ns $
1382 do { res_ty <- thing_inside
1383 ; return (res_ty, allBoundVariables res_ty) }
1384
1385 -- this more general variant is needed in tcHsPatSigType.
1386 -- See Note [Pattern signature binders]
1387 tcImplicitTKBndrsX :: (Name -> TcM (TcTyVar, Bool)) -- new_tv function
1388 -> [Name]
1389 -> TcM (a, TyVarSet)
1390 -> TcM ([TcTyVar], a)
1391 -- Returned TcTyVars have the supplied Names
1392 -- i.e. no cloning of fresh names
1393 tcImplicitTKBndrsX new_tv var_ns thing_inside
1394 = do { tkvs_pairs <- mapM new_tv var_ns
1395 ; let must_scope_tkvs = [ tkv | (tkv, False) <- tkvs_pairs ]
1396 tkvs = map fst tkvs_pairs
1397 ; (result, bound_tvs) <- tcExtendTyVarEnv must_scope_tkvs $
1398 thing_inside
1399
1400 -- it's possible that we guessed the ordering of variables
1401 -- wrongly. Adjust.
1402 ; tkvs <- mapM zonkTyCoVarKind tkvs
1403 ; let extra = text "NB: Implicitly-bound variables always come" <+>
1404 text "before other ones."
1405 ; checkValidInferredKinds tkvs bound_tvs extra
1406
1407 ; let final_tvs = toposortTyVars tkvs
1408 ; traceTc "tcImplicitTKBndrs" (ppr var_ns $$ ppr final_tvs)
1409
1410 ; return (final_tvs, result) }
1411
1412 tcExplicitTKBndrs :: [LHsTyVarBndr Name]
1413 -> ([TyVar] -> TcM (a, TyVarSet))
1414 -- ^ Thing inside returns the set of variables bound
1415 -- in the scope. See Note [Scope-check inferred kinds]
1416 -> TcM (a, TyVarSet) -- ^ returns augmented bound vars
1417 -- No cloning: returned TyVars have the same Name as the incoming LHsTyVarBndrs
1418 tcExplicitTKBndrs orig_hs_tvs thing_inside
1419 = tcExplicitTKBndrsX newSkolemTyVar orig_hs_tvs thing_inside
1420
1421 tcExplicitTKBndrsX :: (Name -> Kind -> TcM TyVar)
1422 -> [LHsTyVarBndr Name]
1423 -> ([TyVar] -> TcM (a, TyVarSet))
1424 -- ^ Thing inside returns the set of variables bound
1425 -- in the scope. See Note [Scope-check inferred kinds]
1426 -> TcM (a, TyVarSet) -- ^ returns augmented bound vars
1427 tcExplicitTKBndrsX new_tv orig_hs_tvs thing_inside
1428 = go orig_hs_tvs $ \ tvs ->
1429 do { (result, bound_tvs) <- thing_inside tvs
1430
1431 -- Issue an error if the ordering is bogus.
1432 -- See Note [Bad telescopes] in TcValidity.
1433 ; tvs <- checkZonkValidTelescope (interppSP orig_hs_tvs) tvs empty
1434 ; checkValidInferredKinds tvs bound_tvs empty
1435
1436 ; traceTc "tcExplicitTKBndrs" $
1437 vcat [ text "Hs vars:" <+> ppr orig_hs_tvs
1438 , text "tvs:" <+> sep (map pprTvBndr tvs) ]
1439
1440 ; return (result, bound_tvs `unionVarSet` mkVarSet tvs)
1441 }
1442 where
1443 go [] thing = thing []
1444 go (L _ hs_tv : hs_tvs) thing
1445 = do { tv <- tcHsTyVarBndr new_tv hs_tv
1446 ; tcExtendTyVarEnv [tv] $
1447 go hs_tvs $ \ tvs ->
1448 thing (tv : tvs) }
1449
1450 tcHsTyVarBndr :: (Name -> Kind -> TcM TyVar)
1451 -> HsTyVarBndr Name -> TcM TcTyVar
1452 -- Return a SkolemTv TcTyVar, initialised with a kind variable.
1453 -- Typically the Kind inside the HsTyVarBndr will be a tyvar
1454 -- with a mutable kind in it.
1455 -- NB: These variables must not be in scope. This function
1456 -- is not appropriate for use with associated types, for example.
1457 --
1458 -- Returned TcTyVar has the same name; no cloning
1459 --
1460 -- See also Note [Associated type tyvar names] in Class
1461 --
1462 tcHsTyVarBndr new_tv (UserTyVar (L _ name))
1463 = do { kind <- newMetaKindVar
1464 ; new_tv name kind }
1465
1466 tcHsTyVarBndr new_tv (KindedTyVar (L _ name) kind)
1467 = do { kind <- tcLHsKind kind
1468 ; new_tv name kind }
1469
1470 newWildTyVar :: Name -> TcM TcTyVar
1471 -- ^ New unification variable for a wildcard
1472 newWildTyVar _name
1473 = do { kind <- newMetaKindVar
1474 ; uniq <- newUnique
1475 ; details <- newMetaDetails TauTv
1476 ; let name = mkSysTvName uniq (fsLit "w")
1477 ; return (mkTcTyVar name kind details) }
1478
1479 -- | Produce a tyvar of the given name (with the kind provided, or
1480 -- otherwise a meta-var kind). If
1481 -- the name is already in scope, return the scoped variable, checking
1482 -- to make sure the known kind matches any kind provided. The
1483 -- second return value says whether the variable is in scope (True)
1484 -- or not (False). (Use this for associated types, for example.)
1485 tcHsTyVarName :: Maybe Kind -> Name -> TcM (TcTyVar, Bool)
1486 tcHsTyVarName m_kind name
1487 = do { mb_tv <- tcLookupLcl_maybe name
1488 ; case mb_tv of
1489 Just (ATyVar _ tv)
1490 -> do { whenIsJust m_kind $ \ kind ->
1491 discardResult $
1492 unifyKind (Just (mkTyVarTy tv)) kind (tyVarKind tv)
1493 ; return (tv, True) }
1494 _ -> do { kind <- case m_kind of
1495 Just kind -> return kind
1496 Nothing -> newMetaKindVar
1497 ; return (mk_skolem_tv name kind, False) }}
1498
1499 -- makes a new skolem tv
1500 newSkolemTyVar :: Name -> Kind -> TcM TcTyVar
1501 newSkolemTyVar name kind = return (mk_skolem_tv name kind)
1502
1503 mk_skolem_tv :: Name -> Kind -> TcTyVar
1504 mk_skolem_tv n k = mkTcTyVar n k vanillaSkolemTv
1505
1506 ------------------
1507 kindGeneralizeType :: Type -> TcM Type
1508 -- Result is zonked
1509 kindGeneralizeType ty
1510 = do { kvs <- kindGeneralize ty
1511 ; zonkTcType (mkInvForAllTys kvs ty) }
1512
1513 kindGeneralize :: TcType -> TcM [KindVar]
1514 -- Quantify the free kind variables of a kind or type
1515 -- In the latter case the type is closed, so it has no free
1516 -- type variables. So in both cases, all the free vars are kind vars
1517 kindGeneralize kind_or_type
1518 = do { kvs <- zonkTcTypeAndFV kind_or_type
1519 ; let dvs = DV { dv_kvs = kvs, dv_tvs = emptyDVarSet }
1520 ; gbl_tvs <- tcGetGlobalTyCoVars -- Already zonked
1521 ; quantifyZonkedTyVars gbl_tvs dvs }
1522
1523 {-
1524 Note [Kind generalisation]
1525 ~~~~~~~~~~~~~~~~~~~~~~~~~~
1526 We do kind generalisation only at the outer level of a type signature.
1527 For example, consider
1528 T :: forall k. k -> *
1529 f :: (forall a. T a -> Int) -> Int
1530 When kind-checking f's type signature we generalise the kind at
1531 the outermost level, thus:
1532 f1 :: forall k. (forall (a:k). T k a -> Int) -> Int -- YES!
1533 and *not* at the inner forall:
1534 f2 :: (forall k. forall (a:k). T k a -> Int) -> Int -- NO!
1535 Reason: same as for HM inference on value level declarations,
1536 we want to infer the most general type. The f2 type signature
1537 would be *less applicable* than f1, because it requires a more
1538 polymorphic argument.
1539
1540 NB: There are no explicit kind variables written in f's signature.
1541 When there are, the renamer adds these kind variables to the list of
1542 variables bound by the forall, so you can indeed have a type that's
1543 higher-rank in its kind. But only by explicit request.
1544
1545 Note [Kinds of quantified type variables]
1546 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1547 tcTyVarBndrsGen quantifies over a specified list of type variables,
1548 *and* over the kind variables mentioned in the kinds of those tyvars.
1549
1550 Note that we must zonk those kinds (obviously) but less obviously, we
1551 must return type variables whose kinds are zonked too. Example
1552 (a :: k7) where k7 := k9 -> k9
1553 We must return
1554 [k9, a:k9->k9]
1555 and NOT
1556 [k9, a:k7]
1557 Reason: we're going to turn this into a for-all type,
1558 forall k9. forall (a:k7). blah
1559 which the type checker will then instantiate, and instantiate does not
1560 look through unification variables!
1561
1562 Hence using zonked_kinds when forming tvs'.
1563
1564 Note [Free-floating kind vars]
1565 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1566 Consider
1567
1568 data T = MkT (forall (a :: k). Proxy a)
1569 -- from test ghci/scripts/T7873
1570
1571 This is not an existential datatype, but a higher-rank one. Note that
1572 the forall to the right of MkT. Also consider
1573
1574 data S a = MkS (Proxy (a :: k))
1575
1576 According to the rules around implicitly-bound kind variables, those
1577 k's scope over the whole declarations. The renamer grabs it and adds it
1578 to the hsq_implicits field of the HsQTyVars of the tycon. So it must
1579 be in scope during type-checking, but we want to reject T while accepting
1580 S.
1581
1582 Why reject T? Because the kind variable isn't fixed by anything. For
1583 a variable like k to be implicit, it needs to be mentioned in the kind
1584 of a tycon tyvar. But it isn't.
1585
1586 Why accept S? Because kind inference tells us that a has kind k, so it's
1587 all OK.
1588
1589 Our approach depends on whether or not the datatype has a CUSK.
1590
1591 Non-CUSK: In the first pass (kcTyClTyVars) we just bring
1592 k into scope. In the second pass (tcTyClTyVars),
1593 we check to make sure that k has been unified with some other variable
1594 (or generalized over, making k into a skolem). If it hasn't been, then
1595 it must be a free-floating kind var. Error.
1596
1597 CUSK: When we determine the tycon's final, never-to-be-changed kind
1598 in kcHsTyVarBndrs, we check to make sure all implicitly-bound kind
1599 vars are indeed mentioned in a kind somewhere. If not, error.
1600
1601 -}
1602
1603 --------------------
1604 -- getInitialKind has made a suitably-shaped kind for the type or class
1605 -- Look it up in the local environment. This is used only for tycons
1606 -- that we're currently type-checking, so we're sure to find a TcTyCon.
1607 kcLookupTcTyCon :: Name -> TcM TcTyCon
1608 kcLookupTcTyCon nm
1609 = do { tc_ty_thing <- tcLookup nm
1610 ; return $ case tc_ty_thing of
1611 ATcTyCon tc -> tc
1612 _ -> pprPanic "kcLookupTcTyCon" (ppr tc_ty_thing) }
1613
1614 -----------------------
1615 -- | Bring tycon tyvars into scope. This is used during the "kind-checking"
1616 -- pass in TcTyClsDecls. (Never in getInitialKind, never in the
1617 -- "type-checking"/desugaring pass.)
1618 -- Never emits constraints, though the thing_inside might.
1619 kcTyClTyVars :: Name -> TcM a -> TcM a
1620 kcTyClTyVars tycon_name thing_inside
1621 = do { tycon <- kcLookupTcTyCon tycon_name
1622 ; tcExtendTyVarEnv (tcTyConScopedTyVars tycon) $ thing_inside }
1623
1624 tcTyClTyVars :: Name
1625 -> ([TyConBinder] -> Kind -> TcM a) -> TcM a
1626 -- ^ Used for the type variables of a type or class decl
1627 -- on the second full pass (type-checking/desugaring) in TcTyClDecls.
1628 -- This is *not* used in the initial-kind run, nor in the "kind-checking" pass.
1629 -- Accordingly, everything passed to the continuation is fully zonked.
1630 --
1631 -- (tcTyClTyVars T [a,b] thing_inside)
1632 -- where T : forall k1 k2 (a:k1 -> *) (b:k1). k2 -> *
1633 -- calls thing_inside with arguments
1634 -- [k1,k2,a,b] [k1:*, k2:*, Anon (k1 -> *), Anon k1] (k2 -> *)
1635 -- having also extended the type environment with bindings
1636 -- for k1,k2,a,b
1637 --
1638 -- Never emits constraints.
1639 --
1640 -- The LHsTyVarBndrs is always user-written, and the full, generalised
1641 -- kind of the tycon is available in the local env.
1642 tcTyClTyVars tycon_name thing_inside
1643 = do { tycon <- kcLookupTcTyCon tycon_name
1644
1645 ; let scoped_tvs = tcTyConScopedTyVars tycon
1646 -- these are all zonked:
1647 binders = tyConBinders tycon
1648 res_kind = tyConResKind tycon
1649
1650 -- See Note [Free-floating kind vars]
1651 ; zonked_scoped_tvs <- mapM zonkTcTyVarToTyVar scoped_tvs
1652 ; let still_sig_tvs = filter isSigTyVar zonked_scoped_tvs
1653 ; checkNoErrs $ reportFloatingKvs tycon_name
1654 zonked_scoped_tvs still_sig_tvs
1655
1656 -- Add the *unzonked* tyvars to the env't, because those
1657 -- are the ones mentioned in the source.
1658 ; tcExtendTyVarEnv scoped_tvs $
1659 thing_inside binders res_kind }
1660 where
1661
1662 -----------------------------------
1663 tcDataKindSig :: Kind -> TcM ([TyConBinder], Kind)
1664 -- GADT decls can have a (perhaps partial) kind signature
1665 -- e.g. data T :: * -> * -> * where ...
1666 -- This function makes up suitable (kinded) type variables for
1667 -- the argument kinds, and checks that the result kind is indeed *.
1668 -- We use it also to make up argument type variables for for data instances.
1669 -- Never emits constraints.
1670 -- Returns the new TyVars, the extracted TyBinders, and the new, reduced
1671 -- result kind (which should always be Type or a synonym thereof)
1672 tcDataKindSig kind
1673 = do { checkTc (isLiftedTypeKind res_kind) (badKindSig kind)
1674 ; span <- getSrcSpanM
1675 ; us <- newUniqueSupply
1676 ; rdr_env <- getLocalRdrEnv
1677 ; let uniqs = uniqsFromSupply us
1678 occs = [ occ | str <- allNameStrings
1679 , let occ = mkOccName tvName str
1680 , isNothing (lookupLocalRdrOcc rdr_env occ) ]
1681 -- Note [Avoid name clashes for associated data types]
1682
1683 -- NB: Use the tv from a binder if there is one. Otherwise,
1684 -- we end up inventing a new Unique for it, and any other tv
1685 -- that mentions the first ends up with the wrong kind.
1686 extra_bndrs = zipWith4 mkTyBinderTyConBinder
1687 tv_bndrs (repeat span) uniqs occs
1688
1689 ; return (extra_bndrs, res_kind) }
1690 where
1691 (tv_bndrs, res_kind) = splitPiTys kind
1692
1693 badKindSig :: Kind -> SDoc
1694 badKindSig kind
1695 = hang (text "Kind signature on data type declaration has non-* return kind")
1696 2 (ppr kind)
1697
1698 {-
1699 Note [Avoid name clashes for associated data types]
1700 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1701 Consider class C a b where
1702 data D b :: * -> *
1703 When typechecking the decl for D, we'll invent an extra type variable
1704 for D, to fill out its kind. Ideally we don't want this type variable
1705 to be 'a', because when pretty printing we'll get
1706 class C a b where
1707 data D b a0
1708 (NB: the tidying happens in the conversion to IfaceSyn, which happens
1709 as part of pretty-printing a TyThing.)
1710
1711 That's why we look in the LocalRdrEnv to see what's in scope. This is
1712 important only to get nice-looking output when doing ":info C" in GHCi.
1713 It isn't essential for correctness.
1714
1715
1716 ************************************************************************
1717 * *
1718 Partial signatures and pattern signatures
1719 * *
1720 ************************************************************************
1721
1722
1723 Note [Solving equalities in partial type signatures]
1724 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1725 We treat a partial type signature as a "shape constraint" to impose on
1726 the term:
1727 * We make no attempt to kind-generalise it
1728 * We instantiate the explicit and implicit foralls with SigTvs
1729 * We instantiate the wildcards with meta tyvars
1730
1731 We /do/ call solveEqualities, and then zonk to propage the result of
1732 solveEqualities, mainly so that functions like matchExpectedFunTys will
1733 be able to decompose the type, and hence higher-rank signatures will
1734 work. Ugh! For example
1735 f :: (forall a. a->a) -> _
1736 f x = (x True, x 'c')
1737
1738 -}
1739
1740 tcHsPartialSigType
1741 :: UserTypeCtxt
1742 -> LHsSigWcType Name -- The type signature
1743 -> TcM ( [(Name, TcTyVar)] -- Wildcards
1744 , Maybe TcTyVar -- Extra-constraints wildcard
1745 , [TcTyVar] -- Implicitly and explicitly bound type varialbes
1746 , TcThetaType -- Theta part
1747 , TcType ) -- Tau part
1748 tcHsPartialSigType ctxt sig_ty
1749 | HsWC { hswc_wcs = sig_wcs, hswc_body = ib_ty } <- sig_ty
1750 , HsIB { hsib_vars = implicit_hs_tvs, hsib_body = hs_ty } <- ib_ty
1751 , (explicit_hs_tvs, L _ hs_ctxt, hs_tau) <- splitLHsSigmaTy hs_ty
1752 = addSigCtxt ctxt hs_ty $
1753 do { (implicit_tvs, (wcs, wcx, explicit_tvs, theta, tau))
1754 <- -- See Note [Solving equalities in partial type signatures]
1755 solveEqualities $
1756 tcWildCardBindersX newWildTyVar sig_wcs $ \ wcs ->
1757 tcImplicitTKBndrsX new_implicit_tv implicit_hs_tvs $
1758 tcExplicitTKBndrsX newSigTyVar explicit_hs_tvs $ \ explicit_tvs ->
1759 do { -- Instantiate the type-class context; but if there
1760 -- is an extra-constraints wildcard, just discard it here
1761 (theta, wcx) <- tcPartialContext hs_ctxt
1762
1763 ; tau <- tcHsOpenType hs_tau
1764
1765 ; let bound_tvs = unionVarSets [ allBoundVariables tau
1766 , mkVarSet explicit_tvs
1767 , mkVarSet (map snd wcs) ]
1768
1769 ; return ( (wcs, wcx, explicit_tvs, theta, tau)
1770 , bound_tvs) }
1771
1772 ; emitWildCardHoleConstraints wcs
1773
1774 -- See Note [Solving equalities in partial type signatures]
1775 ; all_tvs <- mapM (updateTyVarKindM zonkTcType)
1776 (implicit_tvs ++ explicit_tvs)
1777 ; theta <- mapM zonkTcType theta
1778 ; tau <- zonkTcType tau
1779 ; checkValidType ctxt (mkSpecForAllTys all_tvs $ mkPhiTy theta tau)
1780
1781 ; traceTc "tcHsPatSigType" (ppr all_tvs)
1782 ; return (wcs, wcx, all_tvs, theta, tau) }
1783 where
1784 new_implicit_tv name = do { kind <- newMetaKindVar
1785 ; tv <- newSigTyVar name kind
1786 ; return (tv, False) }
1787
1788 tcPartialContext :: HsContext Name -> TcM (TcThetaType, Maybe TcTyVar)
1789 tcPartialContext hs_theta
1790 | Just (hs_theta1, hs_ctxt_last) <- snocView hs_theta
1791 , L _ (HsWildCardTy wc) <- ignoreParens hs_ctxt_last
1792 = do { wc_tv <- tcWildCardOcc wc constraintKind
1793 ; theta <- mapM tcLHsPredType hs_theta1
1794 ; return (theta, Just wc_tv) }
1795 | otherwise
1796 = do { theta <- mapM tcLHsPredType hs_theta
1797 ; return (theta, Nothing) }
1798
1799 tcHsPatSigType :: UserTypeCtxt
1800 -> LHsSigWcType Name -- The type signature
1801 -> TcM ( [(Name, TcTyVar)] -- Wildcards
1802 , [TcTyVar] -- The new bit of type environment, binding
1803 -- the scoped type variables
1804 , TcType) -- The type
1805 -- Used for type-checking type signatures in
1806 -- (a) patterns e.g f (x::Int) = e
1807 -- (b) RULE forall bndrs e.g. forall (x::Int). f x = x
1808 --
1809 -- This may emit constraints
1810
1811 tcHsPatSigType ctxt sig_ty
1812 | HsWC { hswc_wcs = sig_wcs, hswc_body = ib_ty } <- sig_ty
1813 , HsIB { hsib_vars = sig_vars, hsib_body = hs_ty } <- ib_ty
1814 = addSigCtxt ctxt hs_ty $
1815 do { (implicit_tvs, (wcs, sig_ty))
1816 <- -- See Note [Solving equalities in partial type signatures]
1817 solveEqualities $
1818 tcWildCardBindersX newWildTyVar sig_wcs $ \ wcs ->
1819 tcImplicitTKBndrsX new_implicit_tv sig_vars $
1820 do { sig_ty <- tcHsOpenType hs_ty
1821 ; return ((wcs, sig_ty), allBoundVariables sig_ty) }
1822
1823 ; emitWildCardHoleConstraints wcs
1824
1825 ; sig_ty <- zonkTcType sig_ty
1826 ; checkValidType ctxt sig_ty
1827
1828 ; traceTc "tcHsPatSigType" (ppr sig_vars)
1829 ; return (wcs, implicit_tvs, sig_ty) }
1830 where
1831 new_implicit_tv name = do { kind <- newMetaKindVar
1832 ; tv <- new_tv name kind
1833 ; return (tv, False) }
1834 -- "False" means that these tyvars aren't yet in scope
1835 new_tv = case ctxt of
1836 RuleSigCtxt {} -> newSkolemTyVar
1837 _ -> newSigTyVar
1838 -- See Note [Pattern signature binders]
1839 -- See Note [Unifying SigTvs]
1840
1841
1842 tcPatSig :: Bool -- True <=> pattern binding
1843 -> LHsSigWcType Name
1844 -> ExpSigmaType
1845 -> TcM (TcType, -- The type to use for "inside" the signature
1846 [TcTyVar], -- The new bit of type environment, binding
1847 -- the scoped type variables
1848 [(Name,TcTyVar)], -- The wildcards
1849 HsWrapper) -- Coercion due to unification with actual ty
1850 -- Of shape: res_ty ~ sig_ty
1851 tcPatSig in_pat_bind sig res_ty
1852 = do { (sig_wcs, sig_tvs, sig_ty) <- tcHsPatSigType PatSigCtxt sig
1853 -- sig_tvs are the type variables free in 'sig',
1854 -- and not already in scope. These are the ones
1855 -- that should be brought into scope
1856
1857 ; if null sig_tvs then do {
1858 -- Just do the subsumption check and return
1859 wrap <- addErrCtxtM (mk_msg sig_ty) $
1860 tcSubTypeET_NC PatSigCtxt res_ty sig_ty
1861 ; return (sig_ty, [], sig_wcs, wrap)
1862 } else do
1863 -- Type signature binds at least one scoped type variable
1864
1865 -- A pattern binding cannot bind scoped type variables
1866 -- It is more convenient to make the test here
1867 -- than in the renamer
1868 { when in_pat_bind (addErr (patBindSigErr sig_tvs))
1869
1870 -- Check that all newly-in-scope tyvars are in fact
1871 -- constrained by the pattern. This catches tiresome
1872 -- cases like
1873 -- type T a = Int
1874 -- f :: Int -> Int
1875 -- f (x :: T a) = ...
1876 -- Here 'a' doesn't get a binding. Sigh
1877 ; let bad_tvs = [ tv | tv <- sig_tvs
1878 , not (tv `elemVarSet` exactTyCoVarsOfType sig_ty) ]
1879 ; checkTc (null bad_tvs) (badPatSigTvs sig_ty bad_tvs)
1880
1881 -- Now do a subsumption check of the pattern signature against res_ty
1882 ; wrap <- addErrCtxtM (mk_msg sig_ty) $
1883 tcSubTypeET_NC PatSigCtxt res_ty sig_ty
1884
1885 -- Phew!
1886 ; return (sig_ty, sig_tvs, sig_wcs, wrap)
1887 } }
1888 where
1889 mk_msg sig_ty tidy_env
1890 = do { (tidy_env, sig_ty) <- zonkTidyTcType tidy_env sig_ty
1891 ; res_ty <- readExpType res_ty -- should be filled in by now
1892 ; (tidy_env, res_ty) <- zonkTidyTcType tidy_env res_ty
1893 ; let msg = vcat [ hang (text "When checking that the pattern signature:")
1894 4 (ppr sig_ty)
1895 , nest 2 (hang (text "fits the type of its context:")
1896 2 (ppr res_ty)) ]
1897 ; return (tidy_env, msg) }
1898
1899 patBindSigErr :: [TcTyVar] -> SDoc
1900 patBindSigErr sig_tvs
1901 = hang (text "You cannot bind scoped type variable" <> plural sig_tvs
1902 <+> pprQuotedList sig_tvs)
1903 2 (text "in a pattern binding signature")
1904
1905 {-
1906 Note [Pattern signature binders]
1907 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1908 Consider
1909 data T = forall a. T a (a->Int)
1910 f (T x (f :: a->Int) = blah)
1911
1912 Here
1913 * The pattern (T p1 p2) creates a *skolem* type variable 'a_sk',
1914 It must be a skolem so that that it retains its identity, and
1915 TcErrors.getSkolemInfo can thereby find the binding site for the skolem.
1916
1917 * The type signature pattern (f :: a->Int) binds "a" -> a_sig in the envt
1918
1919 * Then unification makes a_sig := a_sk
1920
1921 That's why we must make a_sig a MetaTv (albeit a SigTv),
1922 not a SkolemTv, so that it can unify to a_sk.
1923
1924 For RULE binders, though, things are a bit different (yuk).
1925 RULE "foo" forall (x::a) (y::[a]). f x y = ...
1926 Here this really is the binding site of the type variable so we'd like
1927 to use a skolem, so that we get a complaint if we unify two of them
1928 together.
1929
1930 Note [Unifying SigTvs]
1931 ~~~~~~~~~~~~~~~~~~~~~~
1932 ALAS we have no decent way of avoiding two SigTvs getting unified.
1933 Consider
1934 f (x::(a,b)) (y::c)) = [fst x, y]
1935 Here we'd really like to complain that 'a' and 'c' are unified. But
1936 for the reasons above we can't make a,b,c into skolems, so they
1937 are just SigTvs that can unify. And indeed, this would be ok,
1938 f x (y::c) = case x of
1939 (x1 :: a1, True) -> [x,y]
1940 (x1 :: a2, False) -> [x,y,y]
1941 Here the type of x's first component is called 'a1' in one branch and
1942 'a2' in the other. We could try insisting on the same OccName, but
1943 they definitely won't have the sane lexical Name.
1944
1945 I think we could solve this by recording in a SigTv a list of all the
1946 in-scope variables that it should not unify with, but it's fiddly.
1947
1948
1949 ************************************************************************
1950 * *
1951 Checking kinds
1952 * *
1953 ************************************************************************
1954
1955 -}
1956
1957 -- | Produce an 'TcKind' suitable for a checking a type that can be * or #.
1958 ekOpen :: TcM TcKind
1959 ekOpen = do { rr <- newFlexiTyVarTy runtimeRepTy
1960 ; return (tYPE rr) }
1961
1962 unifyKinds :: [(TcType, TcKind)] -> TcM ([TcType], TcKind)
1963 unifyKinds act_kinds
1964 = do { kind <- newMetaKindVar
1965 ; let check (ty, act_kind) = checkExpectedKind ty act_kind kind
1966 ; tys' <- mapM check act_kinds
1967 ; return (tys', kind) }
1968
1969 {-
1970 ************************************************************************
1971 * *
1972 Sort checking kinds
1973 * *
1974 ************************************************************************
1975
1976 tcLHsKind converts a user-written kind to an internal, sort-checked kind.
1977 It does sort checking and desugaring at the same time, in one single pass.
1978 -}
1979
1980 tcLHsKind :: LHsKind Name -> TcM Kind
1981 tcLHsKind = tc_lhs_kind kindLevelMode
1982
1983 tc_lhs_kind :: TcTyMode -> LHsKind Name -> TcM Kind
1984 tc_lhs_kind mode k
1985 = addErrCtxt (text "In the kind" <+> quotes (ppr k)) $
1986 tc_lhs_type (kindLevel mode) k liftedTypeKind
1987
1988 promotionErr :: Name -> PromotionErr -> TcM a
1989 promotionErr name err
1990 = failWithTc (hang (pprPECategory err <+> quotes (ppr name) <+> text "cannot be used here")
1991 2 (parens reason))
1992 where
1993 reason = case err of
1994 FamDataConPE -> text "it comes from a data family instance"
1995 NoDataKindsTC -> text "Perhaps you intended to use DataKinds"
1996 NoDataKindsDC -> text "Perhaps you intended to use DataKinds"
1997 NoTypeInTypeTC -> text "Perhaps you intended to use TypeInType"
1998 NoTypeInTypeDC -> text "Perhaps you intended to use TypeInType"
1999 PatSynPE -> text "Pattern synonyms cannot be promoted"
2000 _ -> text "it is defined and used in the same recursive group"
2001
2002 {-
2003 ************************************************************************
2004 * *
2005 Scoped type variables
2006 * *
2007 ************************************************************************
2008 -}
2009
2010 badPatSigTvs :: TcType -> [TyVar] -> SDoc
2011 badPatSigTvs sig_ty bad_tvs
2012 = vcat [ fsep [text "The type variable" <> plural bad_tvs,
2013 quotes (pprWithCommas ppr bad_tvs),
2014 text "should be bound by the pattern signature" <+> quotes (ppr sig_ty),
2015 text "but are actually discarded by a type synonym" ]
2016 , text "To fix this, expand the type synonym"
2017 , text "[Note: I hope to lift this restriction in due course]" ]
2018
2019 {-
2020 ************************************************************************
2021 * *
2022 Error messages and such
2023 * *
2024 ************************************************************************
2025 -}
2026
2027 -- | Make an appropriate message for an error in a function argument.
2028 -- Used for both expressions and types.
2029 funAppCtxt :: (Outputable fun, Outputable arg) => fun -> arg -> Int -> SDoc
2030 funAppCtxt fun arg arg_no
2031 = hang (hsep [ text "In the", speakNth arg_no, ptext (sLit "argument of"),
2032 quotes (ppr fun) <> text ", namely"])
2033 2 (quotes (ppr arg))
2034
2035 -- See Note [Free-floating kind vars]
2036 reportFloatingKvs :: Name -- of the tycon
2037 -> [TcTyVar] -- all tyvars, not necessarily zonked
2038 -> [TcTyVar] -- floating tyvars
2039 -> TcM ()
2040 reportFloatingKvs tycon_name all_tvs bad_tvs
2041 = unless (null bad_tvs) $ -- don't bother zonking if there's no error
2042 do { all_tvs <- mapM zonkTcTyVarToTyVar all_tvs
2043 ; bad_tvs <- mapM zonkTcTyVarToTyVar bad_tvs
2044 ; let (tidy_env, tidy_all_tvs) = tidyOpenTyCoVars emptyTidyEnv all_tvs
2045 tidy_bad_tvs = map (tidyTyVarOcc tidy_env) bad_tvs
2046 ; typeintype <- xoptM LangExt.TypeInType
2047 ; mapM_ (report typeintype tidy_all_tvs) tidy_bad_tvs }
2048 where
2049 report typeintype tidy_all_tvs tidy_bad_tv
2050 = addErr $
2051 vcat [ text "Kind variable" <+> quotes (ppr tidy_bad_tv) <+>
2052 text "is implicitly bound in datatype"
2053 , quotes (ppr tycon_name) <> comma <+>
2054 text "but does not appear as the kind of any"
2055 , text "of its type variables. Perhaps you meant"
2056 , text "to bind it" <+> ppWhen (not typeintype)
2057 (text "(with TypeInType)") <+>
2058 text "explicitly somewhere?"
2059 , ppWhen (not (null tidy_all_tvs)) $
2060 hang (text "Type variables with inferred kinds:")
2061 2 (ppr_tv_bndrs tidy_all_tvs) ]
2062
2063 ppr_tv_bndrs tvs = sep (map pp_tv tvs)
2064 pp_tv tv = parens (ppr tv <+> dcolon <+> ppr (tyVarKind tv))