2 % (c) The University of Glasgow 2006
3 % (c) The AQUA Project, Glasgow University, 1996-1998
6 TcTyClsDecls: Typecheck type and class declarations
10 tcTyAndClassDecls, kcDataDecl, tcConDecls, mkRecSelBinds,
11 checkValidTyCon, dataDeclChecks, badFamInstDecl
14 #include "HsVersions.h"
27 import TysWiredIn ( unitTy )
34 import MkId ( mkDefaultMethodId )
35 import MkCore ( rEC_SEL_ERROR_ID )
49 import Unique ( mkBuiltinUnique )
58 %************************************************************************
60 \subsection{Type checking for type and class declarations}
62 %************************************************************************
65 tcTyAndClassDecls :: ModDetails
66 -> [[LTyClDecl Name]] -- Mutually-recursive groups in dependency order
67 -> TcM (TcGblEnv, -- Input env extended by types and classes
68 -- and their implicit Ids,DataCons
69 HsValBinds Name, -- Renamed bindings for record selectors
70 [Id]) -- Default method ids
71 -- Fails if there are any errors
73 tcTyAndClassDecls boot_details decls_s
74 = checkNoErrs $ -- The code recovers internally, but if anything gave rise to
75 -- an error we'd better stop now, to avoid a cascade
76 do { let tyclds_s = map (filterOut (isFamInstDecl . unLoc)) decls_s
77 -- Remove family instance decls altogether
78 -- They are dealt with by TcInstDcls
80 ; tyclss <- fixM $ \ rec_tyclss ->
81 tcExtendRecEnv (zipRecTyClss tyclds_s rec_tyclss) $
82 -- We must populate the environment with the loop-tied
83 -- T's right away (even before kind checking), because
84 -- the kind checker may "fault in" some type constructors
85 -- that recursively mention T
87 do { -- Kind-check in dependency order
88 -- See Note [Kind checking for type and class decls]
89 kc_decls <- kcTyClDecls tyclds_s
91 -- And now build the TyCons/Classes
92 ; let rec_flags = calcRecFlags boot_details rec_tyclss
93 ; concatMapM (tcTyClDecl rec_flags) kc_decls }
95 ; tcExtendGlobalEnv tyclss $ do
96 { -- Perform the validity check
97 -- We can do this now because we are done with the recursive knot
98 traceTc "ready for validity check" empty
99 ; mapM_ (addLocM checkValidTyCl) (concat tyclds_s)
100 ; traceTc "done" empty
102 -- Add the implicit things;
103 -- we want them in the environment because
104 -- they may be mentioned in interface files
105 -- NB: All associated types and their implicit things will be added a
106 -- second time here. This doesn't matter as the definitions are
108 ; let { implicit_things = concatMap implicitTyThings tyclss
109 ; rec_sel_binds = mkRecSelBinds tyclss
110 ; dm_ids = mkDefaultMethodIds tyclss }
112 ; env <- tcExtendGlobalEnv implicit_things getGblEnv
113 ; return (env, rec_sel_binds, dm_ids) } }
115 zipRecTyClss :: [[LTyClDecl Name]]
116 -> [TyThing] -- Knot-tied
118 -- Build a name-TyThing mapping for the things bound by decls
119 -- being careful not to look at the [TyThing]
120 -- The TyThings in the result list must have a visible ATyCon/AClass,
121 -- because typechecking types (in, say, tcTyClDecl) looks at this outer constructor
122 zipRecTyClss decls_s rec_things
123 = [ get decl | decls <- decls_s, L _ decl <- flattenATs decls ]
125 rec_type_env :: TypeEnv
126 rec_type_env = mkTypeEnv rec_things
128 get :: TyClDecl Name -> (Name, TyThing)
129 get (ClassDecl {tcdLName = L _ name}) = (name, AClass cl)
131 Just (AClass cl) = lookupTypeEnv rec_type_env name
132 get decl = (name, ATyCon tc)
135 Just (ATyCon tc) = lookupTypeEnv rec_type_env name
139 %************************************************************************
143 %************************************************************************
145 Note [Kind checking for type and class decls]
146 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
147 Kind checking is done thus:
149 1. Make up a kind variable for each parameter of the *data* type,
150 and class, decls, and extend the kind environment (which is in
153 2. Dependency-analyse the type *synonyms* (which must be non-recursive),
154 and kind-check them in dependency order. Extend the kind envt.
156 3. Kind check the data type and class decls
158 Synonyms are treated differently to data type and classes,
159 because a type synonym can be an unboxed type
161 and a kind variable can't unify with UnboxedTypeKind
162 So we infer their kinds in dependency order
164 We need to kind check all types in the mutually recursive group
165 before we know the kind of the type variables. For example:
168 op :: D b => a -> b -> b
171 bop :: (Monad c) => ...
173 Here, the kind of the locally-polymorphic type variable "b"
174 depends on *all the uses of class D*. For example, the use of
175 Monad c in bop's type signature means that D must have kind Type->Type.
177 However type synonyms work differently. They can have kinds which don't
178 just involve (->) and *:
179 type R = Int# -- Kind #
180 type S a = Array# a -- Kind * -> #
181 type T a b = (# a,b #) -- Kind * -> * -> (# a,b #)
182 So we must infer their kinds from their right-hand sides *first* and then
183 use them, whereas for the mutually recursive data types D we bring into
184 scope kind bindings D -> k, where k is a kind variable, and do inference.
188 This treatment of type synonyms only applies to Haskell 98-style synonyms.
189 General type functions can be recursive, and hence, appear in `alg_decls'.
191 The kind of a type family is solely determinded by its kind signature;
192 hence, only kind signatures participate in the construction of the initial
193 kind environment (as constructed by `getInitialKind'). In fact, we ignore
194 instances of families altogether in the following. However, we need to
195 include the kinds of associated families into the construction of the
196 initial kind environment. (This is handled by `allDecls').
200 kcTyClDecls :: [[LTyClDecl Name]] -> TcM [LTyClDecl Name]
201 kcTyClDecls [] = return []
202 kcTyClDecls (decls : decls_s) = do { (tcl_env, kc_decls1) <- kcTyClDecls1 decls
203 ; kc_decls2 <- setLclEnv tcl_env (kcTyClDecls decls_s)
204 ; return (kc_decls1 ++ kc_decls2) }
206 kcTyClDecls1 :: [LTyClDecl Name] -> TcM (TcLclEnv, [LTyClDecl Name])
208 = do { -- Omit instances of type families; they are handled together
209 -- with the *heads* of class instances
210 ; let (syn_decls, alg_decls) = partition (isSynDecl . unLoc) decls
211 alg_at_decls = flattenATs alg_decls
214 ; traceTc "tcTyAndCl" (ptext (sLit "module") <+> ppr mod $$ vcat (map ppr decls))
216 -- First check for cyclic classes
217 ; checkClassCycleErrs alg_decls
219 -- Kind checking; see Note [Kind checking for type and class decls]
220 ; alg_kinds <- mapM getInitialKind alg_at_decls
221 ; tcExtendKindEnv alg_kinds $ do
223 { (kc_syn_decls, tcl_env) <- kcSynDecls (calcSynCycles syn_decls)
224 ; setLclEnv tcl_env $ do
225 { kc_alg_decls <- mapM (wrapLocM kcTyClDecl) alg_decls
227 -- Kind checking done for this group, so zonk the kind variables
228 -- See Note [Kind checking for type and class decls]
229 ; mapM_ (zonkTcKindToKind . snd) alg_kinds
231 ; return (tcl_env, kc_syn_decls ++ kc_alg_decls) } } }
233 flattenATs :: [LTyClDecl Name] -> [LTyClDecl Name]
234 flattenATs decls = concatMap flatten decls
236 flatten decl@(L _ (ClassDecl {tcdATs = ats})) = decl : ats
237 flatten decl = [decl]
239 getInitialKind :: LTyClDecl Name -> TcM (Name, TcKind)
240 -- Only for data type, class, and indexed type declarations
241 -- Get as much info as possible from the data, class, or indexed type decl,
242 -- so as to maximise usefulness of error messages
243 getInitialKind (L _ decl)
244 = do { arg_kinds <- mapM (mk_arg_kind . unLoc) (tyClDeclTyVars decl)
245 ; res_kind <- mk_res_kind decl
246 ; return (tcdName decl, mkArrowKinds arg_kinds res_kind) }
248 mk_arg_kind (UserTyVar _ _) = newKindVar
249 mk_arg_kind (KindedTyVar _ kind) = return kind
251 mk_res_kind (TyFamily { tcdKind = Just kind }) = return kind
252 mk_res_kind (TyData { tcdKindSig = Just kind }) = return kind
253 -- On GADT-style declarations we allow a kind signature
254 -- data T :: *->* where { ... }
255 mk_res_kind _ = return liftedTypeKind
259 kcSynDecls :: [SCC (LTyClDecl Name)]
260 -> TcM ([LTyClDecl Name], -- Kind-annotated decls
261 TcLclEnv) -- Kind bindings
263 = do { tcl_env <- getLclEnv; return ([], tcl_env) }
264 kcSynDecls (group : groups)
265 = do { (decl, nk) <- kcSynDecl group
266 ; (decls, tcl_env) <- tcExtendKindEnv [nk] (kcSynDecls groups)
267 ; return (decl:decls, tcl_env) }
270 kcSynDecl :: SCC (LTyClDecl Name)
271 -> TcM (LTyClDecl Name, -- Kind-annotated decls
272 (Name,TcKind)) -- Kind bindings
273 kcSynDecl (AcyclicSCC (L loc decl))
274 = tcAddDeclCtxt decl $
275 kcHsTyVars (tcdTyVars decl) (\ k_tvs ->
276 do { traceTc "kcd1" (ppr (unLoc (tcdLName decl)) <+> brackets (ppr (tcdTyVars decl))
277 <+> brackets (ppr k_tvs))
278 ; (k_rhs, rhs_kind) <- kcLHsType (tcdSynRhs decl)
279 ; traceTc "kcd2" (ppr (unLoc (tcdLName decl)))
280 ; let tc_kind = foldr (mkArrowKind . hsTyVarKind . unLoc) rhs_kind k_tvs
281 ; return (L loc (decl { tcdTyVars = k_tvs, tcdSynRhs = k_rhs }),
282 (unLoc (tcdLName decl), tc_kind)) })
284 kcSynDecl (CyclicSCC decls)
285 = do { recSynErr decls; failM } -- Fail here to avoid error cascade
286 -- of out-of-scope tycons
288 ------------------------------------------------------------------------
289 kcTyClDecl :: TyClDecl Name -> TcM (TyClDecl Name)
290 -- Not used for type synonyms (see kcSynDecl)
292 kcTyClDecl decl@(TyData {})
293 = ASSERT( not . isFamInstDecl $ decl ) -- must not be a family instance
294 kcTyClDeclBody decl $
297 kcTyClDecl decl@(TyFamily {})
298 = kcFamilyDecl [] decl -- the empty list signals a toplevel decl
300 kcTyClDecl decl@(ClassDecl {tcdCtxt = ctxt, tcdSigs = sigs, tcdATs = ats})
301 = kcTyClDeclBody decl $ \ tvs' ->
302 do { ctxt' <- kcHsContext ctxt
303 ; ats' <- mapM (wrapLocM (kcFamilyDecl tvs')) ats
304 ; sigs' <- mapM (wrapLocM kc_sig) sigs
305 ; return (decl {tcdTyVars = tvs', tcdCtxt = ctxt', tcdSigs = sigs',
308 kc_sig (TypeSig nm op_ty) = do { op_ty' <- kcHsLiftedSigType op_ty
309 ; return (TypeSig nm op_ty') }
310 kc_sig other_sig = return other_sig
312 kcTyClDecl decl@(ForeignType {})
315 kcTyClDecl (TySynonym {}) = panic "kcTyClDecl TySynonym"
317 kcTyClDeclBody :: TyClDecl Name
318 -> ([LHsTyVarBndr Name] -> TcM a)
320 -- getInitialKind has made a suitably-shaped kind for the type or class
321 -- Unpack it, and attribute those kinds to the type variables
322 -- Extend the env with bindings for the tyvars, taken from
323 -- the kind of the tycon/class. Give it to the thing inside, and
324 -- check the result kind matches
325 kcTyClDeclBody decl thing_inside
326 = tcAddDeclCtxt decl $
327 do { tc_ty_thing <- tcLookupLocated (tcdLName decl)
328 ; let tc_kind = case tc_ty_thing of
330 _ -> pprPanic "kcTyClDeclBody" (ppr tc_ty_thing)
331 (kinds, _) = splitKindFunTys tc_kind
332 hs_tvs = tcdTyVars decl
333 kinded_tvs = ASSERT( length kinds >= length hs_tvs )
334 zipWith add_kind hs_tvs kinds
335 ; tcExtendKindEnvTvs kinded_tvs thing_inside }
337 add_kind (L loc (UserTyVar n _)) k = L loc (UserTyVar n k)
338 add_kind (L loc (KindedTyVar n _)) k = L loc (KindedTyVar n k)
340 -- Kind check a data declaration, assuming that we already extended the
341 -- kind environment with the type variables of the left-hand side (these
342 -- kinded type variables are also passed as the second parameter).
344 kcDataDecl :: TyClDecl Name -> [LHsTyVarBndr Name] -> TcM (TyClDecl Name)
345 kcDataDecl decl@(TyData {tcdND = new_or_data, tcdCtxt = ctxt, tcdCons = cons})
347 = do { ctxt' <- kcHsContext ctxt
348 ; cons' <- mapM (wrapLocM kc_con_decl) cons
349 ; return (decl {tcdTyVars = tvs, tcdCtxt = ctxt', tcdCons = cons'}) }
351 -- doc comments are typechecked to Nothing here
352 kc_con_decl con_decl@(ConDecl { con_name = name, con_qvars = ex_tvs
353 , con_cxt = ex_ctxt, con_details = details, con_res = res })
354 = addErrCtxt (dataConCtxt name) $
355 kcHsTyVars ex_tvs $ \ex_tvs' -> do
356 do { ex_ctxt' <- kcHsContext ex_ctxt
357 ; details' <- kc_con_details details
358 ; res' <- case res of
359 ResTyH98 -> return ResTyH98
360 ResTyGADT ty -> do { ty' <- kcHsSigType ty; return (ResTyGADT ty') }
361 ; return (con_decl { con_qvars = ex_tvs', con_cxt = ex_ctxt'
362 , con_details = details', con_res = res' }) }
364 kc_con_details (PrefixCon btys)
365 = do { btys' <- mapM kc_larg_ty btys
366 ; return (PrefixCon btys') }
367 kc_con_details (InfixCon bty1 bty2)
368 = do { bty1' <- kc_larg_ty bty1
369 ; bty2' <- kc_larg_ty bty2
370 ; return (InfixCon bty1' bty2') }
371 kc_con_details (RecCon fields)
372 = do { fields' <- mapM kc_field fields
373 ; return (RecCon fields') }
375 kc_field (ConDeclField fld bty d) = do { bty' <- kc_larg_ty bty
376 ; return (ConDeclField fld bty' d) }
378 kc_larg_ty bty = case new_or_data of
379 DataType -> kcHsSigType bty
380 NewType -> kcHsLiftedSigType bty
381 -- Can't allow an unlifted type for newtypes, because we're effectively
382 -- going to remove the constructor while coercing it to a lifted type.
383 -- And newtypes can't be bang'd
384 kcDataDecl d _ = pprPanic "kcDataDecl" (ppr d)
386 -- Kind check a family declaration or type family default declaration.
388 kcFamilyDecl :: [LHsTyVarBndr Name] -- tyvars of enclosing class decl if any
389 -> TyClDecl Name -> TcM (TyClDecl Name)
390 kcFamilyDecl classTvs decl@(TyFamily {tcdKind = kind})
391 = kcTyClDeclBody decl $ \tvs' ->
392 do { mapM_ unifyClassParmKinds tvs'
393 ; return (decl {tcdTyVars = tvs',
394 tcdKind = kind `mplus` Just liftedTypeKind})
395 -- default result kind is '*'
398 unifyClassParmKinds (L _ tv)
399 | (n,k) <- hsTyVarNameKind tv
400 , Just classParmKind <- lookup n classTyKinds
401 = unifyKind k classParmKind
402 | otherwise = return ()
403 classTyKinds = [hsTyVarNameKind tv | L _ tv <- classTvs]
405 kcFamilyDecl _ (TySynonym {}) -- type family defaults
406 = panic "TcTyClsDecls.kcFamilyDecl: not implemented yet"
407 kcFamilyDecl _ d = pprPanic "kcFamilyDecl" (ppr d)
411 %************************************************************************
413 \subsection{Type checking}
415 %************************************************************************
418 tcTyClDecl :: (Name -> RecFlag) -> LTyClDecl Name -> TcM [TyThing]
420 tcTyClDecl calc_isrec (L loc decl)
421 = setSrcSpan loc $ tcAddDeclCtxt decl $
422 tcTyClDecl1 NoParentTyCon calc_isrec decl
424 -- "type family" declarations
425 tcTyClDecl1 :: TyConParent -> (Name -> RecFlag) -> TyClDecl Name -> TcM [TyThing]
426 tcTyClDecl1 parent _calc_isrec
427 (TyFamily {tcdFlavour = TypeFamily,
428 tcdLName = L _ tc_name, tcdTyVars = tvs,
429 tcdKind = Just kind}) -- NB: kind at latest added during kind checking
430 = tcTyVarBndrs tvs $ \ tvs' -> do
431 { traceTc "type family:" (ppr tc_name)
433 -- Check that we don't use families without -XTypeFamilies
434 ; idx_tys <- xoptM Opt_TypeFamilies
435 ; checkTc idx_tys $ badFamInstDecl tc_name
437 ; tycon <- buildSynTyCon tc_name tvs' SynFamilyTyCon kind parent Nothing
438 ; return [ATyCon tycon]
441 -- "data family" declaration
442 tcTyClDecl1 parent _calc_isrec
443 (TyFamily {tcdFlavour = DataFamily,
444 tcdLName = L _ tc_name, tcdTyVars = tvs, tcdKind = mb_kind})
445 = tcTyVarBndrs tvs $ \ tvs' -> do
446 { traceTc "data family:" (ppr tc_name)
447 ; extra_tvs <- tcDataKindSig mb_kind
448 ; let final_tvs = tvs' ++ extra_tvs -- we may not need these
451 -- Check that we don't use families without -XTypeFamilies
452 ; idx_tys <- xoptM Opt_TypeFamilies
453 ; checkTc idx_tys $ badFamInstDecl tc_name
455 ; tycon <- buildAlgTyCon tc_name final_tvs []
456 DataFamilyTyCon Recursive False True
458 ; return [ATyCon tycon]
462 tcTyClDecl1 _parent _calc_isrec
463 (TySynonym {tcdLName = L _ tc_name, tcdTyVars = tvs, tcdSynRhs = rhs_ty})
464 = ASSERT( isNoParent _parent )
465 tcTyVarBndrs tvs $ \ tvs' -> do
466 { traceTc "tcd1" (ppr tc_name)
467 ; rhs_ty' <- tcHsKindedType rhs_ty
468 ; tycon <- buildSynTyCon tc_name tvs' (SynonymTyCon rhs_ty')
469 (typeKind rhs_ty') NoParentTyCon Nothing
470 ; return [ATyCon tycon] }
472 -- "newtype" and "data"
473 -- NB: not used for newtype/data instances (whether associated or not)
474 tcTyClDecl1 _parent calc_isrec
475 (TyData {tcdND = new_or_data, tcdCtxt = ctxt, tcdTyVars = tvs,
476 tcdLName = L _ tc_name, tcdKindSig = mb_ksig, tcdCons = cons})
477 = ASSERT( isNoParent _parent )
478 tcTyVarBndrs tvs $ \ tvs' -> do
479 { extra_tvs <- tcDataKindSig mb_ksig
480 ; let final_tvs = tvs' ++ extra_tvs
481 ; stupid_theta <- tcHsKindedContext ctxt
482 ; want_generic <- xoptM Opt_Generics
483 ; unbox_strict <- doptM Opt_UnboxStrictFields
484 ; kind_signatures <- xoptM Opt_KindSignatures
485 ; existential_ok <- xoptM Opt_ExistentialQuantification
486 ; gadt_ok <- xoptM Opt_GADTs
487 ; is_boot <- tcIsHsBoot -- Are we compiling an hs-boot file?
488 ; let ex_ok = existential_ok || gadt_ok -- Data cons can have existential context
490 -- Check that we don't use kind signatures without Glasgow extensions
491 ; checkTc (kind_signatures || isNothing mb_ksig) (badSigTyDecl tc_name)
493 ; dataDeclChecks tc_name new_or_data stupid_theta cons
495 ; tycon <- fixM (\ tycon -> do
496 { let res_ty = mkTyConApp tycon (mkTyVarTys final_tvs)
497 ; data_cons <- tcConDecls unbox_strict ex_ok
498 tycon (final_tvs, res_ty) cons
500 if null cons && is_boot -- In a hs-boot file, empty cons means
501 then return AbstractTyCon -- "don't know"; hence Abstract
502 else case new_or_data of
503 DataType -> return (mkDataTyConRhs data_cons)
504 NewType -> ASSERT( not (null data_cons) )
505 mkNewTyConRhs tc_name tycon (head data_cons)
506 ; buildAlgTyCon tc_name final_tvs stupid_theta tc_rhs is_rec
507 (want_generic && canDoGenerics data_cons) (not h98_syntax)
508 NoParentTyCon Nothing
510 ; return [ATyCon tycon]
513 is_rec = calc_isrec tc_name
514 h98_syntax = consUseH98Syntax cons
516 tcTyClDecl1 _parent calc_isrec
517 (ClassDecl {tcdLName = L _ class_name, tcdTyVars = tvs,
518 tcdCtxt = ctxt, tcdMeths = meths,
519 tcdFDs = fundeps, tcdSigs = sigs, tcdATs = ats} )
520 = ASSERT( isNoParent _parent )
521 tcTyVarBndrs tvs $ \ tvs' -> do
522 { ctxt' <- tcHsKindedContext ctxt
523 ; fds' <- mapM (addLocM tc_fundep) fundeps
524 ; sig_stuff <- tcClassSigs class_name sigs meths
525 ; clas <- fixM $ \ clas -> do
526 { let -- This little knot is just so we can get
527 -- hold of the name of the class TyCon, which we
528 -- need to look up its recursiveness
529 tycon_name = tyConName (classTyCon clas)
530 tc_isrec = calc_isrec tycon_name
531 ; atss' <- mapM (addLocM $ tcTyClDecl1 (AssocFamilyTyCon clas) (const Recursive)) ats
532 -- NB: 'ats' only contains "type family" and "data family"
533 -- declarations as well as type family defaults
534 ; buildClass False {- Must include unfoldings for selectors -}
535 class_name tvs' ctxt' fds' (concat atss')
537 ; return (AClass clas : map ATyCon (classATs clas))
538 -- NB: Order is important due to the call to `mkGlobalThings' when
539 -- tying the the type and class declaration type checking knot.
542 tc_fundep (tvs1, tvs2) = do { tvs1' <- mapM tcLookupTyVar tvs1 ;
543 ; tvs2' <- mapM tcLookupTyVar tvs2 ;
544 ; return (tvs1', tvs2') }
547 (ForeignType {tcdLName = L _ tc_name, tcdExtName = tc_ext_name})
548 = return [ATyCon (mkForeignTyCon tc_name tc_ext_name liftedTypeKind 0)]
550 tcTyClDecl1 _ _ d = pprPanic "tcTyClDecl1" (ppr d)
552 dataDeclChecks :: Name -> NewOrData -> ThetaType -> [LConDecl Name] -> TcM ()
553 dataDeclChecks tc_name new_or_data stupid_theta cons
554 = do { -- Check that we don't use GADT syntax in H98 world
555 gadtSyntax_ok <- xoptM Opt_GADTSyntax
556 ; let h98_syntax = consUseH98Syntax cons
557 ; checkTc (gadtSyntax_ok || h98_syntax) (badGadtDecl tc_name)
559 -- Check that the stupid theta is empty for a GADT-style declaration
560 ; checkTc (null stupid_theta || h98_syntax) (badStupidTheta tc_name)
562 -- Check that a newtype has exactly one constructor
563 -- Do this before checking for empty data decls, so that
564 -- we don't suggest -XEmptyDataDecls for newtypes
565 ; checkTc (new_or_data == DataType || isSingleton cons)
566 (newtypeConError tc_name (length cons))
568 -- Check that there's at least one condecl,
569 -- or else we're reading an hs-boot file, or -XEmptyDataDecls
570 ; empty_data_decls <- xoptM Opt_EmptyDataDecls
571 ; is_boot <- tcIsHsBoot -- Are we compiling an hs-boot file?
572 ; checkTc (not (null cons) || empty_data_decls || is_boot)
573 (emptyConDeclsErr tc_name) }
575 -----------------------------------
576 tcConDecls :: Bool -> Bool -> TyCon -> ([TyVar], Type)
577 -> [LConDecl Name] -> TcM [DataCon]
578 tcConDecls unbox ex_ok rep_tycon res_tmpl cons
579 = mapM (addLocM (tcConDecl unbox ex_ok rep_tycon res_tmpl)) cons
581 tcConDecl :: Bool -- True <=> -funbox-strict_fields
582 -> Bool -- True <=> -XExistentialQuantificaton or -XGADTs
583 -> TyCon -- Representation tycon
584 -> ([TyVar], Type) -- Return type template (with its template tyvars)
588 tcConDecl unbox_strict existential_ok rep_tycon res_tmpl -- Data types
589 con@(ConDecl {con_name = name, con_qvars = tvs, con_cxt = ctxt
590 , con_details = details, con_res = res_ty })
591 = addErrCtxt (dataConCtxt name) $
592 tcTyVarBndrs tvs $ \ tvs' -> do
593 { ctxt' <- tcHsKindedContext ctxt
594 ; checkTc (existential_ok || conRepresentibleWithH98Syntax con)
595 (badExistential name)
596 ; (univ_tvs, ex_tvs, eq_preds, res_ty') <- tcResultType res_tmpl tvs' res_ty
598 tc_datacon is_infix field_lbls btys
599 = do { (arg_tys, stricts) <- mapAndUnzipM (tcConArg unbox_strict) btys
600 ; buildDataCon (unLoc name) is_infix
602 univ_tvs ex_tvs eq_preds ctxt' arg_tys
604 -- NB: we put data_tc, the type constructor gotten from the
605 -- constructor type signature into the data constructor;
606 -- that way checkValidDataCon can complain if it's wrong.
609 PrefixCon btys -> tc_datacon False [] btys
610 InfixCon bty1 bty2 -> tc_datacon True [] [bty1,bty2]
611 RecCon fields -> tc_datacon False field_names btys
613 field_names = map (unLoc . cd_fld_name) fields
614 btys = map cd_fld_type fields
618 -- data instance T (b,c) where
619 -- TI :: forall e. e -> T (e,e)
621 -- The representation tycon looks like this:
622 -- data :R7T b c where
623 -- TI :: forall b1 c1. (b1 ~ c1) => b1 -> :R7T b1 c1
624 -- In this case orig_res_ty = T (e,e)
626 tcResultType :: ([TyVar], Type) -- Template for result type; e.g.
627 -- data instance T [a] b c = ...
628 -- gives template ([a,b,c], T [a] b c)
629 -> [TyVar] -- where MkT :: forall x y z. ...
631 -> TcM ([TyVar], -- Universal
632 [TyVar], -- Existential (distinct OccNames from univs)
633 [(TyVar,Type)], -- Equality predicates
634 Type) -- Typechecked return type
635 -- We don't check that the TyCon given in the ResTy is
636 -- the same as the parent tycon, becuase we are in the middle
637 -- of a recursive knot; so it's postponed until checkValidDataCon
639 tcResultType (tmpl_tvs, res_ty) dc_tvs ResTyH98
640 = return (tmpl_tvs, dc_tvs, [], res_ty)
641 -- In H98 syntax the dc_tvs are the existential ones
642 -- data T a b c = forall d e. MkT ...
643 -- The {a,b,c} are tc_tvs, and {d,e} are dc_tvs
645 tcResultType (tmpl_tvs, res_tmpl) dc_tvs (ResTyGADT res_ty)
646 -- E.g. data T [a] b c where
647 -- MkT :: forall x y z. T [(x,y)] z z
649 -- Univ tyvars Eq-spec
653 -- Existentials are the leftover type vars: [x,y]
654 -- So we return ([a,b,z], [x,y], [a~(x,y),b~z], T [(x,y)] z z)
655 = do { res_ty' <- tcHsKindedType res_ty
656 ; let Just subst = tcMatchTy (mkVarSet tmpl_tvs) res_tmpl res_ty'
658 -- /Lazily/ figure out the univ_tvs etc
659 -- Each univ_tv is either a dc_tv or a tmpl_tv
660 (univ_tvs, eq_spec) = foldr choose ([], []) tidy_tmpl_tvs
661 choose tmpl (univs, eqs)
662 | Just ty <- lookupTyVar subst tmpl
663 = case tcGetTyVar_maybe ty of
664 Just tv | not (tv `elem` univs)
666 _other -> (tmpl:univs, (tmpl,ty):eqs)
667 | otherwise = pprPanic "tcResultType" (ppr res_ty)
668 ex_tvs = dc_tvs `minusList` univ_tvs
670 ; return (univ_tvs, ex_tvs, eq_spec, res_ty') }
672 -- NB: tmpl_tvs and dc_tvs are distinct, but
673 -- we want them to be *visibly* distinct, both for
674 -- interface files and general confusion. So rename
675 -- the tc_tvs, since they are not used yet (no
676 -- consequential renaming needed)
677 (_, tidy_tmpl_tvs) = mapAccumL tidy_one init_occ_env tmpl_tvs
678 init_occ_env = initTidyOccEnv (map getOccName dc_tvs)
679 tidy_one env tv = (env', setTyVarName tv (tidyNameOcc name occ'))
682 (env', occ') = tidyOccName env (getOccName name)
684 consUseH98Syntax :: [LConDecl a] -> Bool
685 consUseH98Syntax (L _ (ConDecl { con_res = ResTyGADT _ }) : _) = False
686 consUseH98Syntax _ = True
687 -- All constructors have same shape
689 conRepresentibleWithH98Syntax :: ConDecl Name -> Bool
690 conRepresentibleWithH98Syntax
691 (ConDecl {con_qvars = tvs, con_cxt = ctxt, con_res = ResTyH98 })
692 = null tvs && null (unLoc ctxt)
693 conRepresentibleWithH98Syntax
694 (ConDecl {con_qvars = tvs, con_cxt = ctxt, con_res = ResTyGADT (L _ t) })
695 = null (unLoc ctxt) && f t (map (hsTyVarName . unLoc) tvs)
696 where -- Each type variable should be used exactly once in the
697 -- result type, and the result type must just be the type
698 -- constructor applied to type variables
699 f (HsAppTy (L _ t1) (L _ (HsTyVar v2))) vs
700 = (v2 `elem` vs) && f t1 (delete v2 vs)
701 f (HsTyVar _) [] = True
705 tcConArg :: Bool -- True <=> -funbox-strict_fields
707 -> TcM (TcType, HsBang)
708 tcConArg unbox_strict bty
709 = do { arg_ty <- tcHsBangType bty
710 ; let bang = getBangStrictness bty
711 ; let strict_mark = chooseBoxingStrategy unbox_strict arg_ty bang
712 ; return (arg_ty, strict_mark) }
714 -- We attempt to unbox/unpack a strict field when either:
715 -- (i) The field is marked '!!', or
716 -- (ii) The field is marked '!', and the -funbox-strict-fields flag is on.
718 -- We have turned off unboxing of newtypes because coercions make unboxing
719 -- and reboxing more complicated
720 chooseBoxingStrategy :: Bool -> TcType -> HsBang -> HsBang
721 chooseBoxingStrategy unbox_strict_fields arg_ty bang
724 HsUnpack -> can_unbox HsUnpackFailed arg_ty
725 HsStrict | unbox_strict_fields -> can_unbox HsStrict arg_ty
726 | otherwise -> HsStrict
727 HsUnpackFailed -> pprPanic "chooseBoxingStrategy" (ppr arg_ty)
728 -- Source code never has shtes
730 can_unbox :: HsBang -> TcType -> HsBang
731 -- Returns HsUnpack if we can unpack arg_ty
732 -- fail_bang if we know what arg_ty is but we can't unpack it
733 -- HsStrict if it's abstract, so we don't know whether or not we can unbox it
734 can_unbox fail_bang arg_ty
735 = case splitTyConApp_maybe arg_ty of
738 Just (arg_tycon, tycon_args)
739 | isAbstractTyCon arg_tycon -> HsStrict
740 -- See Note [Don't complain about UNPACK on abstract TyCons]
741 | not (isRecursiveTyCon arg_tycon) -- Note [Recusive unboxing]
742 , isProductTyCon arg_tycon
743 -- We can unbox if the type is a chain of newtypes
744 -- with a product tycon at the end
745 -> if isNewTyCon arg_tycon
746 then can_unbox fail_bang (newTyConInstRhs arg_tycon tycon_args)
749 | otherwise -> fail_bang
752 Note [Don't complain about UNPACK on abstract TyCons]
753 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
754 We are going to complain about UnpackFailed, but if we say
755 data T = MkT {-# UNPACK #-} !Wobble
756 and Wobble is a newtype imported from a module that was compiled
757 without optimisation, we don't want to complain. Because it might
758 be fine when optimsation is on. I think this happens when Haddock
759 is working over (say) GHC souce files.
761 Note [Recursive unboxing]
762 ~~~~~~~~~~~~~~~~~~~~~~~~~
763 Be careful not to try to unbox this!
765 But it's the *argument* type that matters. This is fine:
767 because Int is non-recursive.
770 %************************************************************************
774 %************************************************************************
776 Validity checking is done once the mutually-recursive knot has been
777 tied, so we can look at things freely.
780 checkClassCycleErrs :: [LTyClDecl Name] -> TcM ()
781 checkClassCycleErrs tyclss
785 = do { mapM_ recClsErr cls_cycles
786 ; failM } -- Give up now, because later checkValidTyCl
787 -- will loop if the synonym is recursive
789 cls_cycles = calcClassCycles tyclss
791 checkValidTyCl :: TyClDecl Name -> TcM ()
792 -- We do the validity check over declarations, rather than TyThings
793 -- only so that we can add a nice context with tcAddDeclCtxt
795 = tcAddDeclCtxt decl $
796 do { thing <- tcLookupLocatedGlobal (tcdLName decl)
797 ; traceTc "Validity of" (ppr thing)
799 ATyCon tc -> checkValidTyCon tc
800 AClass cl -> do { checkValidClass cl
801 ; mapM_ (addLocM checkValidTyCl) (tcdATs decl) }
802 _ -> panic "checkValidTyCl"
803 ; traceTc "Done validity of" (ppr thing)
806 -------------------------
807 -- For data types declared with record syntax, we require
808 -- that each constructor that has a field 'f'
809 -- (a) has the same result type
810 -- (b) has the same type for 'f'
811 -- module alpha conversion of the quantified type variables
812 -- of the constructor.
814 -- Note that we allow existentials to match becuase the
815 -- fields can never meet. E.g
817 -- T1 { f1 :: b, f2 :: a, f3 ::Int } :: T
818 -- T2 { f1 :: c, f2 :: c, f3 ::Int } :: T
819 -- Here we do not complain about f1,f2 because they are existential
821 checkValidTyCon :: TyCon -> TcM ()
824 = case synTyConRhs tc of
825 SynFamilyTyCon {} -> return ()
826 SynonymTyCon ty -> checkValidType syn_ctxt ty
828 = do -- Check the context on the data decl
829 checkValidTheta (DataTyCtxt name) (tyConStupidTheta tc)
831 -- Check arg types of data constructors
832 mapM_ (checkValidDataCon tc) data_cons
834 -- Check that fields with the same name share a type
835 mapM_ check_fields groups
838 syn_ctxt = TySynCtxt name
840 data_cons = tyConDataCons tc
842 groups = equivClasses cmp_fld (concatMap get_fields data_cons)
843 cmp_fld (f1,_) (f2,_) = f1 `compare` f2
844 get_fields con = dataConFieldLabels con `zip` repeat con
845 -- dataConFieldLabels may return the empty list, which is fine
847 -- See Note [GADT record selectors] in MkId.lhs
848 -- We must check (a) that the named field has the same
849 -- type in each constructor
850 -- (b) that those constructors have the same result type
852 -- However, the constructors may have differently named type variable
853 -- and (worse) we don't know how the correspond to each other. E.g.
854 -- C1 :: forall a b. { f :: a, g :: b } -> T a b
855 -- C2 :: forall d c. { f :: c, g :: c } -> T c d
857 -- So what we do is to ust Unify.tcMatchTys to compare the first candidate's
858 -- result type against other candidates' types BOTH WAYS ROUND.
859 -- If they magically agrees, take the substitution and
860 -- apply them to the latter ones, and see if they match perfectly.
861 check_fields ((label, con1) : other_fields)
862 -- These fields all have the same name, but are from
863 -- different constructors in the data type
864 = recoverM (return ()) $ mapM_ checkOne other_fields
865 -- Check that all the fields in the group have the same type
866 -- NB: this check assumes that all the constructors of a given
867 -- data type use the same type variables
869 (tvs1, _, _, res1) = dataConSig con1
871 fty1 = dataConFieldType con1 label
873 checkOne (_, con2) -- Do it bothways to ensure they are structurally identical
874 = do { checkFieldCompat label con1 con2 ts1 res1 res2 fty1 fty2
875 ; checkFieldCompat label con2 con1 ts2 res2 res1 fty2 fty1 }
877 (tvs2, _, _, res2) = dataConSig con2
879 fty2 = dataConFieldType con2 label
880 check_fields [] = panic "checkValidTyCon/check_fields []"
882 checkFieldCompat :: Name -> DataCon -> DataCon -> TyVarSet
883 -> Type -> Type -> Type -> Type -> TcM ()
884 checkFieldCompat fld con1 con2 tvs1 res1 res2 fty1 fty2
885 = do { checkTc (isJust mb_subst1) (resultTypeMisMatch fld con1 con2)
886 ; checkTc (isJust mb_subst2) (fieldTypeMisMatch fld con1 con2) }
888 mb_subst1 = tcMatchTy tvs1 res1 res2
889 mb_subst2 = tcMatchTyX tvs1 (expectJust "checkFieldCompat" mb_subst1) fty1 fty2
891 -------------------------------
892 checkValidDataCon :: TyCon -> DataCon -> TcM ()
893 checkValidDataCon tc con
894 = setSrcSpan (srcLocSpan (getSrcLoc con)) $
895 addErrCtxt (dataConCtxt con) $
896 do { traceTc "Validity of data con" (ppr con)
897 ; let tc_tvs = tyConTyVars tc
898 res_ty_tmpl = mkFamilyTyConApp tc (mkTyVarTys tc_tvs)
899 actual_res_ty = dataConOrigResTy con
900 ; checkTc (isJust (tcMatchTy (mkVarSet tc_tvs)
903 (badDataConTyCon con res_ty_tmpl actual_res_ty)
904 ; checkValidMonoType (dataConOrigResTy con)
905 -- Disallow MkT :: T (forall a. a->a)
906 -- Reason: it's really the argument of an equality constraint
907 ; checkValidType ctxt (dataConUserType con)
908 ; when (isNewTyCon tc) (checkNewDataCon con)
909 ; mapM_ check_bang (dataConStrictMarks con `zip` [1..])
912 ctxt = ConArgCtxt (dataConName con)
913 check_bang (HsUnpackFailed, n) = addWarnTc (cant_unbox_msg n)
914 check_bang _ = return ()
916 cant_unbox_msg n = sep [ ptext (sLit "Ignoring unusable UNPACK pragma on the")
917 , speakNth n <+> ptext (sLit "argument of") <+> quotes (ppr con)]
919 -------------------------------
920 checkNewDataCon :: DataCon -> TcM ()
921 -- Checks for the data constructor of a newtype
923 = do { checkTc (isSingleton arg_tys) (newtypeFieldErr con (length arg_tys))
925 ; checkTc (null eq_spec) (newtypePredError con)
926 -- Return type is (T a b c)
927 ; checkTc (null ex_tvs && null theta) (newtypeExError con)
929 ; checkTc (not (any isBanged (dataConStrictMarks con)))
930 (newtypeStrictError con)
934 (_univ_tvs, ex_tvs, eq_spec, theta, arg_tys, _res_ty) = dataConFullSig con
936 -------------------------------
937 checkValidClass :: Class -> TcM ()
939 = do { constrained_class_methods <- xoptM Opt_ConstrainedClassMethods
940 ; multi_param_type_classes <- xoptM Opt_MultiParamTypeClasses
941 ; fundep_classes <- xoptM Opt_FunctionalDependencies
943 -- Check that the class is unary, unless GlaExs
944 ; checkTc (notNull tyvars) (nullaryClassErr cls)
945 ; checkTc (multi_param_type_classes || unary) (classArityErr cls)
946 ; checkTc (fundep_classes || null fundeps) (classFunDepsErr cls)
948 -- Check the super-classes
949 ; checkValidTheta (ClassSCCtxt (className cls)) theta
951 -- Check the class operations
952 ; mapM_ (check_op constrained_class_methods) op_stuff
954 -- Check that if the class has generic methods, then the
955 -- class has only one parameter. We can't do generic
956 -- multi-parameter type classes!
957 ; checkTc (unary || no_generics) (genericMultiParamErr cls)
960 (tyvars, fundeps, theta, _, _, op_stuff) = classExtraBigSig cls
961 unary = isSingleton tyvars
962 no_generics = null [() | (_, GenDefMeth) <- op_stuff]
964 check_op constrained_class_methods (sel_id, dm)
965 = addErrCtxt (classOpCtxt sel_id tau) $ do
966 { checkValidTheta SigmaCtxt (tail theta)
967 -- The 'tail' removes the initial (C a) from the
968 -- class itself, leaving just the method type
970 ; traceTc "class op type" (ppr op_ty <+> ppr tau)
971 ; checkValidType (FunSigCtxt op_name) tau
973 -- Check that the type mentions at least one of
974 -- the class type variables...or at least one reachable
975 -- from one of the class variables. Example: tc223
976 -- class Error e => Game b mv e | b -> mv e where
977 -- newBoard :: MonadState b m => m ()
978 -- Here, MonadState has a fundep m->b, so newBoard is fine
979 ; let grown_tyvars = growThetaTyVars theta (mkVarSet tyvars)
980 ; checkTc (tyVarsOfType tau `intersectsVarSet` grown_tyvars)
981 (noClassTyVarErr cls sel_id)
983 -- Check that for a generic method, the type of
984 -- the method is sufficiently simple
985 ; checkTc (dm /= GenDefMeth || validGenericMethodType tau)
986 (badGenericMethodType op_name op_ty)
989 op_name = idName sel_id
990 op_ty = idType sel_id
991 (_,theta1,tau1) = tcSplitSigmaTy op_ty
992 (_,theta2,tau2) = tcSplitSigmaTy tau1
993 (theta,tau) | constrained_class_methods = (theta1 ++ theta2, tau2)
994 | otherwise = (theta1, mkPhiTy (tail theta1) tau1)
995 -- Ugh! The function might have a type like
996 -- op :: forall a. C a => forall b. (Eq b, Eq a) => tau2
997 -- With -XConstrainedClassMethods, we want to allow this, even though the inner
998 -- forall has an (Eq a) constraint. Whereas in general, each constraint
999 -- in the context of a for-all must mention at least one quantified
1000 -- type variable. What a mess!
1004 %************************************************************************
1006 Building record selectors
1008 %************************************************************************
1011 mkDefaultMethodIds :: [TyThing] -> [Id]
1012 -- See Note [Default method Ids and Template Haskell]
1013 mkDefaultMethodIds things
1014 = [ mkDefaultMethodId sel_id dm_name
1015 | AClass cls <- things
1016 , (sel_id, DefMeth dm_name) <- classOpItems cls ]
1019 Note [Default method Ids and Template Haskell]
1020 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1021 Consider this (Trac #4169):
1022 class Numeric a where
1024 fromIntegerNum = ...
1027 ast = [d| instance Numeric Int |]
1029 When we typecheck 'ast' we have done the first pass over the class decl
1030 (in tcTyClDecls), but we have not yet typechecked the default-method
1031 declarations (becuase they can mention value declarations). So we
1032 must bring the default method Ids into scope first (so they can be seen
1033 when typechecking the [d| .. |] quote, and typecheck them later.
1036 mkRecSelBinds :: [TyThing] -> HsValBinds Name
1037 -- NB We produce *un-typechecked* bindings, rather like 'deriving'
1038 -- This makes life easier, because the later type checking will add
1039 -- all necessary type abstractions and applications
1040 mkRecSelBinds ty_things
1041 = ValBindsOut [(NonRecursive, b) | b <- binds] sigs
1043 (sigs, binds) = unzip rec_sels
1044 rec_sels = map mkRecSelBind [ (tc,fld)
1045 | ATyCon tc <- ty_things
1046 , fld <- tyConFields tc ]
1048 mkRecSelBind :: (TyCon, FieldLabel) -> (LSig Name, LHsBinds Name)
1049 mkRecSelBind (tycon, sel_name)
1050 = (L loc (IdSig sel_id), unitBag (L loc sel_bind))
1052 loc = getSrcSpan tycon
1053 sel_id = Var.mkLocalVar rec_details sel_name sel_ty vanillaIdInfo
1054 rec_details = RecSelId { sel_tycon = tycon, sel_naughty = is_naughty }
1056 -- Find a representative constructor, con1
1057 all_cons = tyConDataCons tycon
1058 cons_w_field = [ con | con <- all_cons
1059 , sel_name `elem` dataConFieldLabels con ]
1060 con1 = ASSERT( not (null cons_w_field) ) head cons_w_field
1062 -- Selector type; Note [Polymorphic selectors]
1063 field_ty = dataConFieldType con1 sel_name
1064 data_ty = dataConOrigResTy con1
1065 data_tvs = tyVarsOfType data_ty
1066 is_naughty = not (tyVarsOfType field_ty `subVarSet` data_tvs)
1067 (field_tvs, field_theta, field_tau) = tcSplitSigmaTy field_ty
1068 sel_ty | is_naughty = unitTy -- See Note [Naughty record selectors]
1069 | otherwise = mkForAllTys (varSetElems data_tvs ++ field_tvs) $
1070 mkPhiTy (dataConStupidTheta con1) $ -- Urgh!
1071 mkPhiTy field_theta $ -- Urgh!
1072 mkFunTy data_ty field_tau
1074 -- Make the binding: sel (C2 { fld = x }) = x
1075 -- sel (C7 { fld = x }) = x
1076 -- where cons_w_field = [C2,C7]
1077 sel_bind | is_naughty = mkFunBind sel_lname [mkSimpleMatch [] unit_rhs]
1078 | otherwise = mkFunBind sel_lname (map mk_match cons_w_field ++ deflt)
1079 mk_match con = mkSimpleMatch [L loc (mk_sel_pat con)]
1080 (L loc (HsVar field_var))
1081 mk_sel_pat con = ConPatIn (L loc (getName con)) (RecCon rec_fields)
1082 rec_fields = HsRecFields { rec_flds = [rec_field], rec_dotdot = Nothing }
1083 rec_field = HsRecField { hsRecFieldId = sel_lname
1084 , hsRecFieldArg = nlVarPat field_var
1085 , hsRecPun = False }
1086 sel_lname = L loc sel_name
1087 field_var = mkInternalName (mkBuiltinUnique 1) (getOccName sel_name) loc
1089 -- Add catch-all default case unless the case is exhaustive
1090 -- We do this explicitly so that we get a nice error message that
1091 -- mentions this particular record selector
1092 deflt | not (any is_unused all_cons) = []
1093 | otherwise = [mkSimpleMatch [nlWildPat]
1094 (nlHsApp (nlHsVar (getName rEC_SEL_ERROR_ID))
1097 -- Do not add a default case unless there are unmatched
1098 -- constructors. We must take account of GADTs, else we
1099 -- get overlap warning messages from the pattern-match checker
1100 is_unused con = not (con `elem` cons_w_field
1101 || dataConCannotMatch inst_tys con)
1102 inst_tys = tyConAppArgs data_ty
1104 unit_rhs = mkLHsTupleExpr []
1105 msg_lit = HsStringPrim $ mkFastString $
1106 occNameString (getOccName sel_name)
1109 tyConFields :: TyCon -> [FieldLabel]
1111 | isAlgTyCon tc = nub (concatMap dataConFieldLabels (tyConDataCons tc))
1115 Note [Polymorphic selectors]
1116 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1117 When a record has a polymorphic field, we pull the foralls out to the front.
1118 data T = MkT { f :: forall a. [a] -> a }
1119 Then f :: forall a. T -> [a] -> a
1120 NOT f :: T -> forall a. [a] -> a
1122 This is horrid. It's only needed in deeply obscure cases, which I hate.
1123 The only case I know is test tc163, which is worth looking at. It's far
1124 from clear that this test should succeed at all!
1126 Note [Naughty record selectors]
1127 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1128 A "naughty" field is one for which we can't define a record
1129 selector, because an existential type variable would escape. For example:
1130 data T = forall a. MkT { x,y::a }
1131 We obviously can't define
1133 Nevertheless we *do* put a RecSelId into the type environment
1134 so that if the user tries to use 'x' as a selector we can bleat
1135 helpfully, rather than saying unhelpfully that 'x' is not in scope.
1136 Hence the sel_naughty flag, to identify record selectors that don't really exist.
1138 In general, a field is "naughty" if its type mentions a type variable that
1139 isn't in the result type of the constructor. Note that this *allows*
1140 GADT record selectors (Note [GADT record selectors]) whose types may look
1141 like sel :: T [a] -> a
1143 For naughty selectors we make a dummy binding
1145 for naughty selectors, so that the later type-check will add them to the
1146 environment, and they'll be exported. The function is never called, because
1147 the tyepchecker spots the sel_naughty field.
1149 Note [GADT record selectors]
1150 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1151 For GADTs, we require that all constructors with a common field 'f' have the same
1152 result type (modulo alpha conversion). [Checked in TcTyClsDecls.checkValidTyCon]
1155 T1 { f :: Maybe a } :: T [a]
1156 T2 { f :: Maybe a, y :: b } :: T [a]
1158 and now the selector takes that result type as its argument:
1159 f :: forall a. T [a] -> Maybe a
1161 Details: the "real" types of T1,T2 are:
1162 T1 :: forall r a. (r~[a]) => a -> T r
1163 T2 :: forall r a b. (r~[a]) => a -> b -> T r
1165 So the selector loooks like this:
1166 f :: forall a. T [a] -> Maybe a
1169 T1 c (g:[a]~[c]) (v:Maybe c) -> v `cast` Maybe (right (sym g))
1170 T2 c d (g:[a]~[c]) (v:Maybe c) (w:d) -> v `cast` Maybe (right (sym g))
1172 Note the forall'd tyvars of the selector are just the free tyvars
1173 of the result type; there may be other tyvars in the constructor's
1174 type (e.g. 'b' in T2).
1176 Note the need for casts in the result!
1178 Note [Selector running example]
1179 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1180 It's OK to combine GADTs and type families. Here's a running example:
1182 data instance T [a] where
1183 T1 { fld :: b } :: T [Maybe b]
1185 The representation type looks like this
1187 T1 { fld :: b } :: :R7T (Maybe b)
1189 and there's coercion from the family type to the representation type
1190 :CoR7T a :: T [a] ~ :R7T a
1192 The selector we want for fld looks like this:
1194 fld :: forall b. T [Maybe b] -> b
1195 fld = /\b. \(d::T [Maybe b]).
1196 case d `cast` :CoR7T (Maybe b) of
1199 The scrutinee of the case has type :R7T (Maybe b), which can be
1200 gotten by appying the eq_spec to the univ_tvs of the data con.
1202 %************************************************************************
1206 %************************************************************************
1209 resultTypeMisMatch :: Name -> DataCon -> DataCon -> SDoc
1210 resultTypeMisMatch field_name con1 con2
1211 = vcat [sep [ptext (sLit "Constructors") <+> ppr con1 <+> ptext (sLit "and") <+> ppr con2,
1212 ptext (sLit "have a common field") <+> quotes (ppr field_name) <> comma],
1213 nest 2 $ ptext (sLit "but have different result types")]
1215 fieldTypeMisMatch :: Name -> DataCon -> DataCon -> SDoc
1216 fieldTypeMisMatch field_name con1 con2
1217 = sep [ptext (sLit "Constructors") <+> ppr con1 <+> ptext (sLit "and") <+> ppr con2,
1218 ptext (sLit "give different types for field"), quotes (ppr field_name)]
1220 dataConCtxt :: Outputable a => a -> SDoc
1221 dataConCtxt con = ptext (sLit "In the definition of data constructor") <+> quotes (ppr con)
1223 classOpCtxt :: Var -> Type -> SDoc
1224 classOpCtxt sel_id tau = sep [ptext (sLit "When checking the class method:"),
1225 nest 2 (ppr sel_id <+> dcolon <+> ppr tau)]
1227 nullaryClassErr :: Class -> SDoc
1229 = ptext (sLit "No parameters for class") <+> quotes (ppr cls)
1231 classArityErr :: Class -> SDoc
1233 = vcat [ptext (sLit "Too many parameters for class") <+> quotes (ppr cls),
1234 parens (ptext (sLit "Use -XMultiParamTypeClasses to allow multi-parameter classes"))]
1236 classFunDepsErr :: Class -> SDoc
1238 = vcat [ptext (sLit "Fundeps in class") <+> quotes (ppr cls),
1239 parens (ptext (sLit "Use -XFunctionalDependencies to allow fundeps"))]
1241 noClassTyVarErr :: Class -> Var -> SDoc
1242 noClassTyVarErr clas op
1243 = sep [ptext (sLit "The class method") <+> quotes (ppr op),
1244 ptext (sLit "mentions none of the type variables of the class") <+>
1245 ppr clas <+> hsep (map ppr (classTyVars clas))]
1247 genericMultiParamErr :: Class -> SDoc
1248 genericMultiParamErr clas
1249 = ptext (sLit "The multi-parameter class") <+> quotes (ppr clas) <+>
1250 ptext (sLit "cannot have generic methods")
1252 badGenericMethodType :: Name -> Kind -> SDoc
1253 badGenericMethodType op op_ty
1254 = hang (ptext (sLit "Generic method type is too complex"))
1255 2 (vcat [ppr op <+> dcolon <+> ppr op_ty,
1256 ptext (sLit "You can only use type variables, arrows, lists, and tuples")])
1258 recSynErr :: [LTyClDecl Name] -> TcRn ()
1260 = setSrcSpan (getLoc (head sorted_decls)) $
1261 addErr (sep [ptext (sLit "Cycle in type synonym declarations:"),
1262 nest 2 (vcat (map ppr_decl sorted_decls))])
1264 sorted_decls = sortLocated syn_decls
1265 ppr_decl (L loc decl) = ppr loc <> colon <+> ppr decl
1267 recClsErr :: [Located (TyClDecl Name)] -> TcRn ()
1269 = setSrcSpan (getLoc (head sorted_decls)) $
1270 addErr (sep [ptext (sLit "Cycle in class declarations (via superclasses):"),
1271 nest 2 (vcat (map ppr_decl sorted_decls))])
1273 sorted_decls = sortLocated cls_decls
1274 ppr_decl (L loc decl) = ppr loc <> colon <+> ppr (decl { tcdSigs = [] })
1276 sortLocated :: [Located a] -> [Located a]
1277 sortLocated things = sortLe le things
1279 le (L l1 _) (L l2 _) = l1 <= l2
1281 badDataConTyCon :: DataCon -> Type -> Type -> SDoc
1282 badDataConTyCon data_con res_ty_tmpl actual_res_ty
1283 = hang (ptext (sLit "Data constructor") <+> quotes (ppr data_con) <+>
1284 ptext (sLit "returns type") <+> quotes (ppr actual_res_ty))
1285 2 (ptext (sLit "instead of an instance of its parent type") <+> quotes (ppr res_ty_tmpl))
1287 badGadtDecl :: Name -> SDoc
1289 = vcat [ ptext (sLit "Illegal generalised algebraic data declaration for") <+> quotes (ppr tc_name)
1290 , nest 2 (parens $ ptext (sLit "Use -XGADTs to allow GADTs")) ]
1292 badExistential :: Located Name -> SDoc
1293 badExistential con_name
1294 = hang (ptext (sLit "Data constructor") <+> quotes (ppr con_name) <+>
1295 ptext (sLit "has existential type variables, a context, or a specialised result type"))
1296 2 (parens $ ptext (sLit "Use -XExistentialQuantification or -XGADTs to allow this"))
1298 badStupidTheta :: Name -> SDoc
1299 badStupidTheta tc_name
1300 = ptext (sLit "A data type declared in GADT style cannot have a context:") <+> quotes (ppr tc_name)
1302 newtypeConError :: Name -> Int -> SDoc
1303 newtypeConError tycon n
1304 = sep [ptext (sLit "A newtype must have exactly one constructor,"),
1305 nest 2 $ ptext (sLit "but") <+> quotes (ppr tycon) <+> ptext (sLit "has") <+> speakN n ]
1307 newtypeExError :: DataCon -> SDoc
1309 = sep [ptext (sLit "A newtype constructor cannot have an existential context,"),
1310 nest 2 $ ptext (sLit "but") <+> quotes (ppr con) <+> ptext (sLit "does")]
1312 newtypeStrictError :: DataCon -> SDoc
1313 newtypeStrictError con
1314 = sep [ptext (sLit "A newtype constructor cannot have a strictness annotation,"),
1315 nest 2 $ ptext (sLit "but") <+> quotes (ppr con) <+> ptext (sLit "does")]
1317 newtypePredError :: DataCon -> SDoc
1318 newtypePredError con
1319 = sep [ptext (sLit "A newtype constructor must have a return type of form T a1 ... an"),
1320 nest 2 $ ptext (sLit "but") <+> quotes (ppr con) <+> ptext (sLit "does not")]
1322 newtypeFieldErr :: DataCon -> Int -> SDoc
1323 newtypeFieldErr con_name n_flds
1324 = sep [ptext (sLit "The constructor of a newtype must have exactly one field"),
1325 nest 2 $ ptext (sLit "but") <+> quotes (ppr con_name) <+> ptext (sLit "has") <+> speakN n_flds]
1327 badSigTyDecl :: Name -> SDoc
1328 badSigTyDecl tc_name
1329 = vcat [ ptext (sLit "Illegal kind signature") <+>
1330 quotes (ppr tc_name)
1331 , nest 2 (parens $ ptext (sLit "Use -XKindSignatures to allow kind signatures")) ]
1333 badFamInstDecl :: Outputable a => a -> SDoc
1334 badFamInstDecl tc_name
1335 = vcat [ ptext (sLit "Illegal family instance for") <+>
1336 quotes (ppr tc_name)
1337 , nest 2 (parens $ ptext (sLit "Use -XTypeFamilies to allow indexed type families")) ]
1339 emptyConDeclsErr :: Name -> SDoc
1340 emptyConDeclsErr tycon
1341 = sep [quotes (ppr tycon) <+> ptext (sLit "has no constructors"),
1342 nest 2 $ ptext (sLit "(-XEmptyDataDecls permits this)")]