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 )
33 import MkCore ( rEC_SEL_ERROR_ID )
48 import Unique ( mkBuiltinUnique )
57 %************************************************************************
59 \subsection{Type checking for type and class declarations}
61 %************************************************************************
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 -- Fails if there are any errors
72 tcTyAndClassDecls boot_details decls_s
73 = checkNoErrs $ -- The code recovers internally, but if anything gave rise to
74 -- an error we'd better stop now, to avoid a cascade
75 do { let tyclds_s = map (filterOut (isFamInstDecl . unLoc)) decls_s
76 -- Remove family instance decls altogether
77 -- They are dealt with by TcInstDcls
79 ; tyclss <- fixM $ \ rec_tyclss ->
80 tcExtendRecEnv (zipRecTyClss tyclds_s rec_tyclss) $
81 -- We must populate the environment with the loop-tied
82 -- T's right away (even before kind checking), because
83 -- the kind checker may "fault in" some type constructors
84 -- that recursively mention T
86 do { -- Kind-check in dependency order
87 -- See Note [Kind checking for type and class decls]
88 kc_decls <- kcTyClDecls tyclds_s
90 -- And now build the TyCons/Classes
91 ; let rec_flags = calcRecFlags boot_details rec_tyclss
92 ; concatMapM (tcTyClDecl rec_flags) kc_decls }
94 ; tcExtendGlobalEnv tyclss $ do
95 { -- Perform the validity check
96 -- We can do this now because we are done with the recursive knot
97 traceTc "ready for validity check" empty
98 ; mapM_ (addLocM checkValidTyCl) (concat tyclds_s)
99 ; traceTc "done" empty
101 -- Add the implicit things;
102 -- we want them in the environment because
103 -- they may be mentioned in interface files
104 -- NB: All associated types and their implicit things will be added a
105 -- second time here. This doesn't matter as the definitions are
107 ; let { implicit_things = concatMap implicitTyThings tyclss
108 ; rec_sel_binds = mkRecSelBinds [tc | ATyCon tc <- tyclss]
109 ; dm_ids = mkDefaultMethodIds tyclss }
111 ; env <- tcExtendGlobalEnv implicit_things $
112 tcExtendGlobalValEnv dm_ids $
114 ; return (env, rec_sel_binds) } }
116 zipRecTyClss :: [[LTyClDecl Name]]
117 -> [TyThing] -- Knot-tied
119 -- Build a name-TyThing mapping for the things bound by decls
120 -- being careful not to look at the [TyThing]
121 -- The TyThings in the result list must have a visible ATyCon/AClass,
122 -- because typechecking types (in, say, tcTyClDecl) looks at this outer constructor
123 zipRecTyClss decls_s rec_things
124 = [ get decl | decls <- decls_s, L _ decl <- flattenATs decls ]
126 rec_type_env :: TypeEnv
127 rec_type_env = mkTypeEnv rec_things
129 get :: TyClDecl Name -> (Name, TyThing)
130 get (ClassDecl {tcdLName = L _ name}) = (name, AClass cl)
132 Just (AClass cl) = lookupTypeEnv rec_type_env name
133 get decl = (name, ATyCon tc)
136 Just (ATyCon tc) = lookupTypeEnv rec_type_env name
140 %************************************************************************
144 %************************************************************************
146 Note [Kind checking for type and class decls]
147 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
148 Kind checking is done thus:
150 1. Make up a kind variable for each parameter of the *data* type,
151 and class, decls, and extend the kind environment (which is in
154 2. Dependency-analyse the type *synonyms* (which must be non-recursive),
155 and kind-check them in dependency order. Extend the kind envt.
157 3. Kind check the data type and class decls
159 Synonyms are treated differently to data type and classes,
160 because a type synonym can be an unboxed type
162 and a kind variable can't unify with UnboxedTypeKind
163 So we infer their kinds in dependency order
165 We need to kind check all types in the mutually recursive group
166 before we know the kind of the type variables. For example:
169 op :: D b => a -> b -> b
172 bop :: (Monad c) => ...
174 Here, the kind of the locally-polymorphic type variable "b"
175 depends on *all the uses of class D*. For example, the use of
176 Monad c in bop's type signature means that D must have kind Type->Type.
178 However type synonyms work differently. They can have kinds which don't
179 just involve (->) and *:
180 type R = Int# -- Kind #
181 type S a = Array# a -- Kind * -> #
182 type T a b = (# a,b #) -- Kind * -> * -> (# a,b #)
183 So we must infer their kinds from their right-hand sides *first* and then
184 use them, whereas for the mutually recursive data types D we bring into
185 scope kind bindings D -> k, where k is a kind variable, and do inference.
189 This treatment of type synonyms only applies to Haskell 98-style synonyms.
190 General type functions can be recursive, and hence, appear in `alg_decls'.
192 The kind of a type family is solely determinded by its kind signature;
193 hence, only kind signatures participate in the construction of the initial
194 kind environment (as constructed by `getInitialKind'). In fact, we ignore
195 instances of families altogether in the following. However, we need to
196 include the kinds of associated families into the construction of the
197 initial kind environment. (This is handled by `allDecls').
201 kcTyClDecls :: [[LTyClDecl Name]] -> TcM [LTyClDecl Name]
202 kcTyClDecls [] = return []
203 kcTyClDecls (decls : decls_s) = do { (tcl_env, kc_decls1) <- kcTyClDecls1 decls
204 ; kc_decls2 <- setLclEnv tcl_env (kcTyClDecls decls_s)
205 ; return (kc_decls1 ++ kc_decls2) }
207 kcTyClDecls1 :: [LTyClDecl Name] -> TcM (TcLclEnv, [LTyClDecl Name])
209 = do { -- Omit instances of type families; they are handled together
210 -- with the *heads* of class instances
211 ; let (syn_decls, alg_decls) = partition (isSynDecl . unLoc) decls
212 alg_at_decls = flattenATs alg_decls
215 ; traceTc "tcTyAndCl" (ptext (sLit "module") <+> ppr mod $$ vcat (map ppr decls))
217 -- First check for cyclic classes
218 ; checkClassCycleErrs alg_decls
220 -- Kind checking; see Note [Kind checking for type and class decls]
221 ; alg_kinds <- mapM getInitialKind alg_at_decls
222 ; tcExtendKindEnv alg_kinds $ do
224 { (kc_syn_decls, tcl_env) <- kcSynDecls (calcSynCycles syn_decls)
225 ; setLclEnv tcl_env $ do
226 { kc_alg_decls <- mapM (wrapLocM kcTyClDecl) alg_decls
228 -- Kind checking done for this group, so zonk the kind variables
229 -- See Note [Kind checking for type and class decls]
230 ; mapM_ (zonkTcKindToKind . snd) alg_kinds
232 ; return (tcl_env, kc_syn_decls ++ kc_alg_decls) } } }
234 flattenATs :: [LTyClDecl Name] -> [LTyClDecl Name]
235 flattenATs decls = concatMap flatten decls
237 flatten decl@(L _ (ClassDecl {tcdATs = ats})) = decl : ats
238 flatten decl = [decl]
240 getInitialKind :: LTyClDecl Name -> TcM (Name, TcKind)
241 -- Only for data type, class, and indexed type declarations
242 -- Get as much info as possible from the data, class, or indexed type decl,
243 -- so as to maximise usefulness of error messages
244 getInitialKind (L _ decl)
245 = do { arg_kinds <- mapM (mk_arg_kind . unLoc) (tyClDeclTyVars decl)
246 ; res_kind <- mk_res_kind decl
247 ; return (tcdName decl, mkArrowKinds arg_kinds res_kind) }
249 mk_arg_kind (UserTyVar _ _) = newKindVar
250 mk_arg_kind (KindedTyVar _ kind) = return kind
252 mk_res_kind (TyFamily { tcdKind = Just kind }) = return kind
253 mk_res_kind (TyData { tcdKindSig = Just kind }) = return kind
254 -- On GADT-style declarations we allow a kind signature
255 -- data T :: *->* where { ... }
256 mk_res_kind _ = return liftedTypeKind
260 kcSynDecls :: [SCC (LTyClDecl Name)]
261 -> TcM ([LTyClDecl Name], -- Kind-annotated decls
262 TcLclEnv) -- Kind bindings
264 = do { tcl_env <- getLclEnv; return ([], tcl_env) }
265 kcSynDecls (group : groups)
266 = do { (decl, nk) <- kcSynDecl group
267 ; (decls, tcl_env) <- tcExtendKindEnv [nk] (kcSynDecls groups)
268 ; return (decl:decls, tcl_env) }
271 kcSynDecl :: SCC (LTyClDecl Name)
272 -> TcM (LTyClDecl Name, -- Kind-annotated decls
273 (Name,TcKind)) -- Kind bindings
274 kcSynDecl (AcyclicSCC (L loc decl))
275 = tcAddDeclCtxt decl $
276 kcHsTyVars (tcdTyVars decl) (\ k_tvs ->
277 do { traceTc "kcd1" (ppr (unLoc (tcdLName decl)) <+> brackets (ppr (tcdTyVars decl))
278 <+> brackets (ppr k_tvs))
279 ; (k_rhs, rhs_kind) <- kcLHsType (tcdSynRhs decl)
280 ; traceTc "kcd2" (ppr (unLoc (tcdLName decl)))
281 ; let tc_kind = foldr (mkArrowKind . hsTyVarKind . unLoc) rhs_kind k_tvs
282 ; return (L loc (decl { tcdTyVars = k_tvs, tcdSynRhs = k_rhs }),
283 (unLoc (tcdLName decl), tc_kind)) })
285 kcSynDecl (CyclicSCC decls)
286 = do { recSynErr decls; failM } -- Fail here to avoid error cascade
287 -- of out-of-scope tycons
289 ------------------------------------------------------------------------
290 kcTyClDecl :: TyClDecl Name -> TcM (TyClDecl Name)
291 -- Not used for type synonyms (see kcSynDecl)
293 kcTyClDecl decl@(TyData {})
294 = ASSERT( not . isFamInstDecl $ decl ) -- must not be a family instance
295 kcTyClDeclBody decl $
298 kcTyClDecl decl@(TyFamily {})
299 = kcFamilyDecl [] decl -- the empty list signals a toplevel decl
301 kcTyClDecl decl@(ClassDecl {tcdCtxt = ctxt, tcdSigs = sigs, tcdATs = ats})
302 = kcTyClDeclBody decl $ \ tvs' ->
303 do { ctxt' <- kcHsContext ctxt
304 ; ats' <- mapM (wrapLocM (kcFamilyDecl tvs')) ats
305 ; sigs' <- mapM (wrapLocM kc_sig) sigs
306 ; return (decl {tcdTyVars = tvs', tcdCtxt = ctxt', tcdSigs = sigs',
309 kc_sig (TypeSig nm op_ty) = do { op_ty' <- kcHsLiftedSigType op_ty
310 ; return (TypeSig nm op_ty') }
311 kc_sig (GenericSig nm op_ty) = do { op_ty' <- kcHsLiftedSigType op_ty
312 ; return (GenericSig nm op_ty') }
313 kc_sig other_sig = return other_sig
315 kcTyClDecl decl@(ForeignType {})
318 kcTyClDecl (TySynonym {}) = panic "kcTyClDecl TySynonym"
320 kcTyClDeclBody :: TyClDecl Name
321 -> ([LHsTyVarBndr Name] -> TcM a)
323 -- getInitialKind has made a suitably-shaped kind for the type or class
324 -- Unpack it, and attribute those kinds to the type variables
325 -- Extend the env with bindings for the tyvars, taken from
326 -- the kind of the tycon/class. Give it to the thing inside, and
327 -- check the result kind matches
328 kcTyClDeclBody decl thing_inside
329 = tcAddDeclCtxt decl $
330 do { tc_ty_thing <- tcLookupLocated (tcdLName decl)
331 ; let tc_kind = case tc_ty_thing of
333 _ -> pprPanic "kcTyClDeclBody" (ppr tc_ty_thing)
334 (kinds, _) = splitKindFunTys tc_kind
335 hs_tvs = tcdTyVars decl
336 kinded_tvs = ASSERT( length kinds >= length hs_tvs )
337 zipWith add_kind hs_tvs kinds
338 ; tcExtendKindEnvTvs kinded_tvs thing_inside }
340 add_kind (L loc (UserTyVar n _)) k = L loc (UserTyVar n k)
341 add_kind (L loc (KindedTyVar n _)) k = L loc (KindedTyVar n k)
343 -- Kind check a data declaration, assuming that we already extended the
344 -- kind environment with the type variables of the left-hand side (these
345 -- kinded type variables are also passed as the second parameter).
347 kcDataDecl :: TyClDecl Name -> [LHsTyVarBndr Name] -> TcM (TyClDecl Name)
348 kcDataDecl decl@(TyData {tcdND = new_or_data, tcdCtxt = ctxt, tcdCons = cons})
350 = do { ctxt' <- kcHsContext ctxt
351 ; cons' <- mapM (wrapLocM kc_con_decl) cons
352 ; return (decl {tcdTyVars = tvs, tcdCtxt = ctxt', tcdCons = cons'}) }
354 -- doc comments are typechecked to Nothing here
355 kc_con_decl con_decl@(ConDecl { con_name = name, con_qvars = ex_tvs
356 , con_cxt = ex_ctxt, con_details = details, con_res = res })
357 = addErrCtxt (dataConCtxt name) $
358 kcHsTyVars ex_tvs $ \ex_tvs' -> do
359 do { ex_ctxt' <- kcHsContext ex_ctxt
360 ; details' <- kc_con_details details
361 ; res' <- case res of
362 ResTyH98 -> return ResTyH98
363 ResTyGADT ty -> do { ty' <- kcHsSigType ty; return (ResTyGADT ty') }
364 ; return (con_decl { con_qvars = ex_tvs', con_cxt = ex_ctxt'
365 , con_details = details', con_res = res' }) }
367 kc_con_details (PrefixCon btys)
368 = do { btys' <- mapM kc_larg_ty btys
369 ; return (PrefixCon btys') }
370 kc_con_details (InfixCon bty1 bty2)
371 = do { bty1' <- kc_larg_ty bty1
372 ; bty2' <- kc_larg_ty bty2
373 ; return (InfixCon bty1' bty2') }
374 kc_con_details (RecCon fields)
375 = do { fields' <- mapM kc_field fields
376 ; return (RecCon fields') }
378 kc_field (ConDeclField fld bty d) = do { bty' <- kc_larg_ty bty
379 ; return (ConDeclField fld bty' d) }
381 kc_larg_ty bty = case new_or_data of
382 DataType -> kcHsSigType bty
383 NewType -> kcHsLiftedSigType bty
384 -- Can't allow an unlifted type for newtypes, because we're effectively
385 -- going to remove the constructor while coercing it to a lifted type.
386 -- And newtypes can't be bang'd
387 kcDataDecl d _ = pprPanic "kcDataDecl" (ppr d)
389 -- Kind check a family declaration or type family default declaration.
391 kcFamilyDecl :: [LHsTyVarBndr Name] -- tyvars of enclosing class decl if any
392 -> TyClDecl Name -> TcM (TyClDecl Name)
393 kcFamilyDecl classTvs decl@(TyFamily {tcdKind = kind})
394 = kcTyClDeclBody decl $ \tvs' ->
395 do { mapM_ unifyClassParmKinds tvs'
396 ; return (decl {tcdTyVars = tvs',
397 tcdKind = kind `mplus` Just liftedTypeKind})
398 -- default result kind is '*'
401 unifyClassParmKinds (L _ tv)
402 | (n,k) <- hsTyVarNameKind tv
403 , Just classParmKind <- lookup n classTyKinds
404 = unifyKind k classParmKind
405 | otherwise = return ()
406 classTyKinds = [hsTyVarNameKind tv | L _ tv <- classTvs]
408 kcFamilyDecl _ (TySynonym {}) -- type family defaults
409 = panic "TcTyClsDecls.kcFamilyDecl: not implemented yet"
410 kcFamilyDecl _ d = pprPanic "kcFamilyDecl" (ppr d)
414 %************************************************************************
416 \subsection{Type checking}
418 %************************************************************************
421 tcTyClDecl :: (Name -> RecFlag) -> LTyClDecl Name -> TcM [TyThing]
423 tcTyClDecl calc_isrec (L loc decl)
424 = setSrcSpan loc $ tcAddDeclCtxt decl $
425 tcTyClDecl1 NoParentTyCon calc_isrec decl
427 -- "type family" declarations
428 tcTyClDecl1 :: TyConParent -> (Name -> RecFlag) -> TyClDecl Name -> TcM [TyThing]
429 tcTyClDecl1 parent _calc_isrec
430 (TyFamily {tcdFlavour = TypeFamily,
431 tcdLName = L _ tc_name, tcdTyVars = tvs,
432 tcdKind = Just kind}) -- NB: kind at latest added during kind checking
433 = tcTyVarBndrs tvs $ \ tvs' -> do
434 { traceTc "type family:" (ppr tc_name)
436 -- Check that we don't use families without -XTypeFamilies
437 ; idx_tys <- xoptM Opt_TypeFamilies
438 ; checkTc idx_tys $ badFamInstDecl tc_name
440 ; tycon <- buildSynTyCon tc_name tvs' SynFamilyTyCon kind parent Nothing
441 ; return [ATyCon tycon]
444 -- "data family" declaration
445 tcTyClDecl1 parent _calc_isrec
446 (TyFamily {tcdFlavour = DataFamily,
447 tcdLName = L _ tc_name, tcdTyVars = tvs, tcdKind = mb_kind})
448 = tcTyVarBndrs tvs $ \ tvs' -> do
449 { traceTc "data family:" (ppr tc_name)
450 ; extra_tvs <- tcDataKindSig mb_kind
451 ; let final_tvs = tvs' ++ extra_tvs -- we may not need these
454 -- Check that we don't use families without -XTypeFamilies
455 ; idx_tys <- xoptM Opt_TypeFamilies
456 ; checkTc idx_tys $ badFamInstDecl tc_name
458 ; tycon <- buildAlgTyCon tc_name final_tvs []
459 DataFamilyTyCon Recursive True
461 ; return [ATyCon tycon]
465 tcTyClDecl1 _parent _calc_isrec
466 (TySynonym {tcdLName = L _ tc_name, tcdTyVars = tvs, tcdSynRhs = rhs_ty})
467 = ASSERT( isNoParent _parent )
468 tcTyVarBndrs tvs $ \ tvs' -> do
469 { traceTc "tcd1" (ppr tc_name)
470 ; rhs_ty' <- tcHsKindedType rhs_ty
471 ; tycon <- buildSynTyCon tc_name tvs' (SynonymTyCon rhs_ty')
472 (typeKind rhs_ty') NoParentTyCon Nothing
473 ; return [ATyCon tycon] }
475 -- "newtype" and "data"
476 -- NB: not used for newtype/data instances (whether associated or not)
477 tcTyClDecl1 _parent calc_isrec
478 (TyData {tcdND = new_or_data, tcdCtxt = ctxt, tcdTyVars = tvs,
479 tcdLName = L _ tc_name, tcdKindSig = mb_ksig, tcdCons = cons})
480 = ASSERT( isNoParent _parent )
481 tcTyVarBndrs tvs $ \ tvs' -> do
482 { extra_tvs <- tcDataKindSig mb_ksig
483 ; let final_tvs = tvs' ++ extra_tvs
484 ; stupid_theta <- tcHsKindedContext ctxt
485 ; unbox_strict <- doptM Opt_UnboxStrictFields
486 ; kind_signatures <- xoptM Opt_KindSignatures
487 ; existential_ok <- xoptM Opt_ExistentialQuantification
488 ; gadt_ok <- xoptM Opt_GADTs
489 ; is_boot <- tcIsHsBoot -- Are we compiling an hs-boot file?
490 ; let ex_ok = existential_ok || gadt_ok -- Data cons can have existential context
492 -- Check that we don't use kind signatures without Glasgow extensions
493 ; checkTc (kind_signatures || isNothing mb_ksig) (badSigTyDecl tc_name)
495 ; dataDeclChecks tc_name new_or_data stupid_theta cons
497 ; tycon <- fixM (\ tycon -> do
498 { let res_ty = mkTyConApp tycon (mkTyVarTys final_tvs)
499 ; data_cons <- tcConDecls unbox_strict ex_ok
500 tycon (final_tvs, res_ty) cons
502 if null cons && is_boot -- In a hs-boot file, empty cons means
503 then return AbstractTyCon -- "don't know"; hence Abstract
504 else case new_or_data of
505 DataType -> return (mkDataTyConRhs data_cons)
506 NewType -> ASSERT( not (null data_cons) )
507 mkNewTyConRhs tc_name tycon (head data_cons)
508 ; buildAlgTyCon tc_name final_tvs stupid_theta tc_rhs is_rec
509 (not h98_syntax) NoParentTyCon Nothing
511 ; return [ATyCon tycon]
514 is_rec = calc_isrec tc_name
515 h98_syntax = consUseH98Syntax cons
517 tcTyClDecl1 _parent calc_isrec
518 (ClassDecl {tcdLName = L _ class_name, tcdTyVars = tvs,
519 tcdCtxt = ctxt, tcdMeths = meths,
520 tcdFDs = fundeps, tcdSigs = sigs, tcdATs = ats} )
521 = ASSERT( isNoParent _parent )
522 tcTyVarBndrs tvs $ \ tvs' -> do
523 { ctxt' <- tcHsKindedContext ctxt
524 ; fds' <- mapM (addLocM tc_fundep) fundeps
525 ; (sig_stuff, gen_dm_env) <- tcClassSigs class_name sigs meths
526 ; clas <- fixM $ \ clas -> do
527 { let -- This little knot is just so we can get
528 -- hold of the name of the class TyCon, which we
529 -- need to look up its recursiveness
530 tycon_name = tyConName (classTyCon clas)
531 tc_isrec = calc_isrec tycon_name
532 ; atss' <- mapM (addLocM $ tcTyClDecl1 (AssocFamilyTyCon clas) (const Recursive)) ats
533 -- NB: 'ats' only contains "type family" and "data family"
534 -- declarations as well as type family defaults
535 ; buildClass False {- Must include unfoldings for selectors -}
536 class_name tvs' ctxt' fds' (concat atss')
539 ; let gen_dm_ids = [ AnId (mkExportedLocalId gen_dm_name gen_dm_ty)
540 | (sel_id, GenDefMeth gen_dm_name) <- classOpItems clas
541 , let gen_dm_tau = expectJust "tcTyClDecl1" $
542 lookupNameEnv gen_dm_env (idName sel_id)
543 , let gen_dm_ty = mkSigmaTy tvs'
544 [mkClassPred clas (mkTyVarTys tvs')]
547 class_ats = map ATyCon (classATs clas)
549 ; return (AClass clas : gen_dm_ids ++ class_ats )
550 -- NB: Order is important due to the call to `mkGlobalThings' when
551 -- tying the the type and class declaration type checking knot.
554 tc_fundep (tvs1, tvs2) = do { tvs1' <- mapM tcLookupTyVar tvs1 ;
555 ; tvs2' <- mapM tcLookupTyVar tvs2 ;
556 ; return (tvs1', tvs2') }
559 (ForeignType {tcdLName = L _ tc_name, tcdExtName = tc_ext_name})
560 = return [ATyCon (mkForeignTyCon tc_name tc_ext_name liftedTypeKind 0)]
562 tcTyClDecl1 _ _ d = pprPanic "tcTyClDecl1" (ppr d)
564 dataDeclChecks :: Name -> NewOrData -> ThetaType -> [LConDecl Name] -> TcM ()
565 dataDeclChecks tc_name new_or_data stupid_theta cons
566 = do { -- Check that we don't use GADT syntax in H98 world
567 gadtSyntax_ok <- xoptM Opt_GADTSyntax
568 ; let h98_syntax = consUseH98Syntax cons
569 ; checkTc (gadtSyntax_ok || h98_syntax) (badGadtDecl tc_name)
571 -- Check that the stupid theta is empty for a GADT-style declaration
572 ; checkTc (null stupid_theta || h98_syntax) (badStupidTheta tc_name)
574 -- Check that a newtype has exactly one constructor
575 -- Do this before checking for empty data decls, so that
576 -- we don't suggest -XEmptyDataDecls for newtypes
577 ; checkTc (new_or_data == DataType || isSingleton cons)
578 (newtypeConError tc_name (length cons))
580 -- Check that there's at least one condecl,
581 -- or else we're reading an hs-boot file, or -XEmptyDataDecls
582 ; empty_data_decls <- xoptM Opt_EmptyDataDecls
583 ; is_boot <- tcIsHsBoot -- Are we compiling an hs-boot file?
584 ; checkTc (not (null cons) || empty_data_decls || is_boot)
585 (emptyConDeclsErr tc_name) }
587 -----------------------------------
588 tcConDecls :: Bool -> Bool -> TyCon -> ([TyVar], Type)
589 -> [LConDecl Name] -> TcM [DataCon]
590 tcConDecls unbox ex_ok rep_tycon res_tmpl cons
591 = mapM (addLocM (tcConDecl unbox ex_ok rep_tycon res_tmpl)) cons
593 tcConDecl :: Bool -- True <=> -funbox-strict_fields
594 -> Bool -- True <=> -XExistentialQuantificaton or -XGADTs
595 -> TyCon -- Representation tycon
596 -> ([TyVar], Type) -- Return type template (with its template tyvars)
600 tcConDecl unbox_strict existential_ok rep_tycon res_tmpl -- Data types
601 con@(ConDecl {con_name = name, con_qvars = tvs, con_cxt = ctxt
602 , con_details = details, con_res = res_ty })
603 = addErrCtxt (dataConCtxt name) $
604 tcTyVarBndrs tvs $ \ tvs' -> do
605 { ctxt' <- tcHsKindedContext ctxt
606 ; checkTc (existential_ok || conRepresentibleWithH98Syntax con)
607 (badExistential name)
608 ; (univ_tvs, ex_tvs, eq_preds, res_ty') <- tcResultType res_tmpl tvs' res_ty
610 tc_datacon is_infix field_lbls btys
611 = do { (arg_tys, stricts) <- mapAndUnzipM (tcConArg unbox_strict) btys
612 ; buildDataCon (unLoc name) is_infix
614 univ_tvs ex_tvs eq_preds ctxt' arg_tys
616 -- NB: we put data_tc, the type constructor gotten from the
617 -- constructor type signature into the data constructor;
618 -- that way checkValidDataCon can complain if it's wrong.
621 PrefixCon btys -> tc_datacon False [] btys
622 InfixCon bty1 bty2 -> tc_datacon True [] [bty1,bty2]
623 RecCon fields -> tc_datacon False field_names btys
625 field_names = map (unLoc . cd_fld_name) fields
626 btys = map cd_fld_type fields
630 -- data instance T (b,c) where
631 -- TI :: forall e. e -> T (e,e)
633 -- The representation tycon looks like this:
634 -- data :R7T b c where
635 -- TI :: forall b1 c1. (b1 ~ c1) => b1 -> :R7T b1 c1
636 -- In this case orig_res_ty = T (e,e)
638 tcResultType :: ([TyVar], Type) -- Template for result type; e.g.
639 -- data instance T [a] b c = ...
640 -- gives template ([a,b,c], T [a] b c)
641 -> [TyVar] -- where MkT :: forall x y z. ...
643 -> TcM ([TyVar], -- Universal
644 [TyVar], -- Existential (distinct OccNames from univs)
645 [(TyVar,Type)], -- Equality predicates
646 Type) -- Typechecked return type
647 -- We don't check that the TyCon given in the ResTy is
648 -- the same as the parent tycon, becuase we are in the middle
649 -- of a recursive knot; so it's postponed until checkValidDataCon
651 tcResultType (tmpl_tvs, res_ty) dc_tvs ResTyH98
652 = return (tmpl_tvs, dc_tvs, [], res_ty)
653 -- In H98 syntax the dc_tvs are the existential ones
654 -- data T a b c = forall d e. MkT ...
655 -- The {a,b,c} are tc_tvs, and {d,e} are dc_tvs
657 tcResultType (tmpl_tvs, res_tmpl) dc_tvs (ResTyGADT res_ty)
658 -- E.g. data T [a] b c where
659 -- MkT :: forall x y z. T [(x,y)] z z
661 -- Univ tyvars Eq-spec
665 -- Existentials are the leftover type vars: [x,y]
666 -- So we return ([a,b,z], [x,y], [a~(x,y),b~z], T [(x,y)] z z)
667 = do { res_ty' <- tcHsKindedType res_ty
668 ; let Just subst = tcMatchTy (mkVarSet tmpl_tvs) res_tmpl res_ty'
670 -- /Lazily/ figure out the univ_tvs etc
671 -- Each univ_tv is either a dc_tv or a tmpl_tv
672 (univ_tvs, eq_spec) = foldr choose ([], []) tidy_tmpl_tvs
673 choose tmpl (univs, eqs)
674 | Just ty <- lookupTyVar subst tmpl
675 = case tcGetTyVar_maybe ty of
676 Just tv | not (tv `elem` univs)
678 _other -> (tmpl:univs, (tmpl,ty):eqs)
679 | otherwise = pprPanic "tcResultType" (ppr res_ty)
680 ex_tvs = dc_tvs `minusList` univ_tvs
682 ; return (univ_tvs, ex_tvs, eq_spec, res_ty') }
684 -- NB: tmpl_tvs and dc_tvs are distinct, but
685 -- we want them to be *visibly* distinct, both for
686 -- interface files and general confusion. So rename
687 -- the tc_tvs, since they are not used yet (no
688 -- consequential renaming needed)
689 (_, tidy_tmpl_tvs) = mapAccumL tidy_one init_occ_env tmpl_tvs
690 init_occ_env = initTidyOccEnv (map getOccName dc_tvs)
691 tidy_one env tv = (env', setTyVarName tv (tidyNameOcc name occ'))
694 (env', occ') = tidyOccName env (getOccName name)
696 consUseH98Syntax :: [LConDecl a] -> Bool
697 consUseH98Syntax (L _ (ConDecl { con_res = ResTyGADT _ }) : _) = False
698 consUseH98Syntax _ = True
699 -- All constructors have same shape
701 conRepresentibleWithH98Syntax :: ConDecl Name -> Bool
702 conRepresentibleWithH98Syntax
703 (ConDecl {con_qvars = tvs, con_cxt = ctxt, con_res = ResTyH98 })
704 = null tvs && null (unLoc ctxt)
705 conRepresentibleWithH98Syntax
706 (ConDecl {con_qvars = tvs, con_cxt = ctxt, con_res = ResTyGADT (L _ t) })
707 = null (unLoc ctxt) && f t (map (hsTyVarName . unLoc) tvs)
708 where -- Each type variable should be used exactly once in the
709 -- result type, and the result type must just be the type
710 -- constructor applied to type variables
711 f (HsAppTy (L _ t1) (L _ (HsTyVar v2))) vs
712 = (v2 `elem` vs) && f t1 (delete v2 vs)
713 f (HsTyVar _) [] = True
717 tcConArg :: Bool -- True <=> -funbox-strict_fields
719 -> TcM (TcType, HsBang)
720 tcConArg unbox_strict bty
721 = do { arg_ty <- tcHsBangType bty
722 ; let bang = getBangStrictness bty
723 ; let strict_mark = chooseBoxingStrategy unbox_strict arg_ty bang
724 ; return (arg_ty, strict_mark) }
726 -- We attempt to unbox/unpack a strict field when either:
727 -- (i) The field is marked '!!', or
728 -- (ii) The field is marked '!', and the -funbox-strict-fields flag is on.
730 -- We have turned off unboxing of newtypes because coercions make unboxing
731 -- and reboxing more complicated
732 chooseBoxingStrategy :: Bool -> TcType -> HsBang -> HsBang
733 chooseBoxingStrategy unbox_strict_fields arg_ty bang
736 HsUnpack -> can_unbox HsUnpackFailed arg_ty
737 HsStrict | unbox_strict_fields -> can_unbox HsStrict arg_ty
738 | otherwise -> HsStrict
739 HsUnpackFailed -> pprPanic "chooseBoxingStrategy" (ppr arg_ty)
740 -- Source code never has shtes
742 can_unbox :: HsBang -> TcType -> HsBang
743 -- Returns HsUnpack if we can unpack arg_ty
744 -- fail_bang if we know what arg_ty is but we can't unpack it
745 -- HsStrict if it's abstract, so we don't know whether or not we can unbox it
746 can_unbox fail_bang arg_ty
747 = case splitTyConApp_maybe arg_ty of
750 Just (arg_tycon, tycon_args)
751 | isAbstractTyCon arg_tycon -> HsStrict
752 -- See Note [Don't complain about UNPACK on abstract TyCons]
753 | not (isRecursiveTyCon arg_tycon) -- Note [Recusive unboxing]
754 , isProductTyCon arg_tycon
755 -- We can unbox if the type is a chain of newtypes
756 -- with a product tycon at the end
757 -> if isNewTyCon arg_tycon
758 then can_unbox fail_bang (newTyConInstRhs arg_tycon tycon_args)
761 | otherwise -> fail_bang
764 Note [Don't complain about UNPACK on abstract TyCons]
765 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
766 We are going to complain about UnpackFailed, but if we say
767 data T = MkT {-# UNPACK #-} !Wobble
768 and Wobble is a newtype imported from a module that was compiled
769 without optimisation, we don't want to complain. Because it might
770 be fine when optimsation is on. I think this happens when Haddock
771 is working over (say) GHC souce files.
773 Note [Recursive unboxing]
774 ~~~~~~~~~~~~~~~~~~~~~~~~~
775 Be careful not to try to unbox this!
777 But it's the *argument* type that matters. This is fine:
779 because Int is non-recursive.
782 %************************************************************************
786 %************************************************************************
788 Validity checking is done once the mutually-recursive knot has been
789 tied, so we can look at things freely.
792 checkClassCycleErrs :: [LTyClDecl Name] -> TcM ()
793 checkClassCycleErrs tyclss
797 = do { mapM_ recClsErr cls_cycles
798 ; failM } -- Give up now, because later checkValidTyCl
799 -- will loop if the synonym is recursive
801 cls_cycles = calcClassCycles tyclss
803 checkValidTyCl :: TyClDecl Name -> TcM ()
804 -- We do the validity check over declarations, rather than TyThings
805 -- only so that we can add a nice context with tcAddDeclCtxt
807 = tcAddDeclCtxt decl $
808 do { thing <- tcLookupLocatedGlobal (tcdLName decl)
809 ; traceTc "Validity of" (ppr thing)
811 ATyCon tc -> checkValidTyCon tc
812 AClass cl -> do { checkValidClass cl
813 ; mapM_ (addLocM checkValidTyCl) (tcdATs decl) }
814 AnId _ -> return () -- Generic default methods are checked
815 -- with their parent class
816 _ -> panic "checkValidTyCl"
817 ; traceTc "Done validity of" (ppr thing)
820 -------------------------
821 -- For data types declared with record syntax, we require
822 -- that each constructor that has a field 'f'
823 -- (a) has the same result type
824 -- (b) has the same type for 'f'
825 -- module alpha conversion of the quantified type variables
826 -- of the constructor.
828 -- Note that we allow existentials to match becuase the
829 -- fields can never meet. E.g
831 -- T1 { f1 :: b, f2 :: a, f3 ::Int } :: T
832 -- T2 { f1 :: c, f2 :: c, f3 ::Int } :: T
833 -- Here we do not complain about f1,f2 because they are existential
835 checkValidTyCon :: TyCon -> TcM ()
838 = case synTyConRhs tc of
839 SynFamilyTyCon {} -> return ()
840 SynonymTyCon ty -> checkValidType syn_ctxt ty
842 = do -- Check the context on the data decl
843 checkValidTheta (DataTyCtxt name) (tyConStupidTheta tc)
845 -- Check arg types of data constructors
846 mapM_ (checkValidDataCon tc) data_cons
848 -- Check that fields with the same name share a type
849 mapM_ check_fields groups
852 syn_ctxt = TySynCtxt name
854 data_cons = tyConDataCons tc
856 groups = equivClasses cmp_fld (concatMap get_fields data_cons)
857 cmp_fld (f1,_) (f2,_) = f1 `compare` f2
858 get_fields con = dataConFieldLabels con `zip` repeat con
859 -- dataConFieldLabels may return the empty list, which is fine
861 -- See Note [GADT record selectors] in MkId.lhs
862 -- We must check (a) that the named field has the same
863 -- type in each constructor
864 -- (b) that those constructors have the same result type
866 -- However, the constructors may have differently named type variable
867 -- and (worse) we don't know how the correspond to each other. E.g.
868 -- C1 :: forall a b. { f :: a, g :: b } -> T a b
869 -- C2 :: forall d c. { f :: c, g :: c } -> T c d
871 -- So what we do is to ust Unify.tcMatchTys to compare the first candidate's
872 -- result type against other candidates' types BOTH WAYS ROUND.
873 -- If they magically agrees, take the substitution and
874 -- apply them to the latter ones, and see if they match perfectly.
875 check_fields ((label, con1) : other_fields)
876 -- These fields all have the same name, but are from
877 -- different constructors in the data type
878 = recoverM (return ()) $ mapM_ checkOne other_fields
879 -- Check that all the fields in the group have the same type
880 -- NB: this check assumes that all the constructors of a given
881 -- data type use the same type variables
883 (tvs1, _, _, res1) = dataConSig con1
885 fty1 = dataConFieldType con1 label
887 checkOne (_, con2) -- Do it bothways to ensure they are structurally identical
888 = do { checkFieldCompat label con1 con2 ts1 res1 res2 fty1 fty2
889 ; checkFieldCompat label con2 con1 ts2 res2 res1 fty2 fty1 }
891 (tvs2, _, _, res2) = dataConSig con2
893 fty2 = dataConFieldType con2 label
894 check_fields [] = panic "checkValidTyCon/check_fields []"
896 checkFieldCompat :: Name -> DataCon -> DataCon -> TyVarSet
897 -> Type -> Type -> Type -> Type -> TcM ()
898 checkFieldCompat fld con1 con2 tvs1 res1 res2 fty1 fty2
899 = do { checkTc (isJust mb_subst1) (resultTypeMisMatch fld con1 con2)
900 ; checkTc (isJust mb_subst2) (fieldTypeMisMatch fld con1 con2) }
902 mb_subst1 = tcMatchTy tvs1 res1 res2
903 mb_subst2 = tcMatchTyX tvs1 (expectJust "checkFieldCompat" mb_subst1) fty1 fty2
905 -------------------------------
906 checkValidDataCon :: TyCon -> DataCon -> TcM ()
907 checkValidDataCon tc con
908 = setSrcSpan (srcLocSpan (getSrcLoc con)) $
909 addErrCtxt (dataConCtxt con) $
910 do { traceTc "Validity of data con" (ppr con)
911 ; let tc_tvs = tyConTyVars tc
912 res_ty_tmpl = mkFamilyTyConApp tc (mkTyVarTys tc_tvs)
913 actual_res_ty = dataConOrigResTy con
914 ; checkTc (isJust (tcMatchTy (mkVarSet tc_tvs)
917 (badDataConTyCon con res_ty_tmpl actual_res_ty)
918 ; checkValidMonoType (dataConOrigResTy con)
919 -- Disallow MkT :: T (forall a. a->a)
920 -- Reason: it's really the argument of an equality constraint
921 ; checkValidType ctxt (dataConUserType con)
922 ; when (isNewTyCon tc) (checkNewDataCon con)
923 ; mapM_ check_bang (dataConStrictMarks con `zip` [1..])
926 ctxt = ConArgCtxt (dataConName con)
927 check_bang (HsUnpackFailed, n) = addWarnTc (cant_unbox_msg n)
928 check_bang _ = return ()
930 cant_unbox_msg n = sep [ ptext (sLit "Ignoring unusable UNPACK pragma on the")
931 , speakNth n <+> ptext (sLit "argument of") <+> quotes (ppr con)]
933 -------------------------------
934 checkNewDataCon :: DataCon -> TcM ()
935 -- Checks for the data constructor of a newtype
937 = do { checkTc (isSingleton arg_tys) (newtypeFieldErr con (length arg_tys))
939 ; checkTc (null eq_spec) (newtypePredError con)
940 -- Return type is (T a b c)
941 ; checkTc (null ex_tvs && null theta) (newtypeExError con)
943 ; checkTc (not (any isBanged (dataConStrictMarks con)))
944 (newtypeStrictError con)
948 (_univ_tvs, ex_tvs, eq_spec, theta, arg_tys, _res_ty) = dataConFullSig con
950 -------------------------------
951 checkValidClass :: Class -> TcM ()
953 = do { constrained_class_methods <- xoptM Opt_ConstrainedClassMethods
954 ; multi_param_type_classes <- xoptM Opt_MultiParamTypeClasses
955 ; fundep_classes <- xoptM Opt_FunctionalDependencies
957 -- Check that the class is unary, unless GlaExs
958 ; checkTc (notNull tyvars) (nullaryClassErr cls)
959 ; checkTc (multi_param_type_classes || unary) (classArityErr cls)
960 ; checkTc (fundep_classes || null fundeps) (classFunDepsErr cls)
962 -- Check the super-classes
963 ; checkValidTheta (ClassSCCtxt (className cls)) theta
965 -- Check the class operations
966 ; mapM_ (check_op constrained_class_methods) op_stuff
968 -- Check that if the class has generic methods, then the
969 -- class has only one parameter. We can't do generic
970 -- multi-parameter type classes!
971 ; checkTc (unary || no_generics) (genericMultiParamErr cls)
974 (tyvars, fundeps, theta, _, _, op_stuff) = classExtraBigSig cls
975 unary = isSingleton tyvars
976 no_generics = null [() | (_, (GenDefMeth _)) <- op_stuff]
978 check_op constrained_class_methods (sel_id, dm)
979 = addErrCtxt (classOpCtxt sel_id tau) $ do
980 { checkValidTheta SigmaCtxt (tail theta)
981 -- The 'tail' removes the initial (C a) from the
982 -- class itself, leaving just the method type
984 ; traceTc "class op type" (ppr op_ty <+> ppr tau)
985 ; checkValidType (FunSigCtxt op_name) tau
987 -- Check that the type mentions at least one of
988 -- the class type variables...or at least one reachable
989 -- from one of the class variables. Example: tc223
990 -- class Error e => Game b mv e | b -> mv e where
991 -- newBoard :: MonadState b m => m ()
992 -- Here, MonadState has a fundep m->b, so newBoard is fine
993 ; let grown_tyvars = growThetaTyVars theta (mkVarSet tyvars)
994 ; checkTc (tyVarsOfType tau `intersectsVarSet` grown_tyvars)
995 (noClassTyVarErr cls sel_id)
998 GenDefMeth dm_name -> do { dm_id <- tcLookupId dm_name
999 ; checkValidType (FunSigCtxt op_name) (idType dm_id) }
1003 op_name = idName sel_id
1004 op_ty = idType sel_id
1005 (_,theta1,tau1) = tcSplitSigmaTy op_ty
1006 (_,theta2,tau2) = tcSplitSigmaTy tau1
1007 (theta,tau) | constrained_class_methods = (theta1 ++ theta2, tau2)
1008 | otherwise = (theta1, mkPhiTy (tail theta1) tau1)
1009 -- Ugh! The function might have a type like
1010 -- op :: forall a. C a => forall b. (Eq b, Eq a) => tau2
1011 -- With -XConstrainedClassMethods, we want to allow this, even though the inner
1012 -- forall has an (Eq a) constraint. Whereas in general, each constraint
1013 -- in the context of a for-all must mention at least one quantified
1014 -- type variable. What a mess!
1018 %************************************************************************
1020 Building record selectors
1022 %************************************************************************
1025 mkDefaultMethodIds :: [TyThing] -> [Id]
1026 -- See Note [Default method Ids and Template Haskell]
1027 mkDefaultMethodIds things
1028 = [ mkExportedLocalId dm_name (idType sel_id)
1029 | AClass cls <- things
1030 , (sel_id, DefMeth dm_name) <- classOpItems cls ]
1033 Note [Default method Ids and Template Haskell]
1034 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1035 Consider this (Trac #4169):
1036 class Numeric a where
1038 fromIntegerNum = ...
1041 ast = [d| instance Numeric Int |]
1043 When we typecheck 'ast' we have done the first pass over the class decl
1044 (in tcTyClDecls), but we have not yet typechecked the default-method
1045 declarations (becuase they can mention value declarations). So we
1046 must bring the default method Ids into scope first (so they can be seen
1047 when typechecking the [d| .. |] quote, and typecheck them later.
1050 mkRecSelBinds :: [TyCon] -> HsValBinds Name
1051 -- NB We produce *un-typechecked* bindings, rather like 'deriving'
1052 -- This makes life easier, because the later type checking will add
1053 -- all necessary type abstractions and applications
1054 mkRecSelBinds tycons
1055 = ValBindsOut [(NonRecursive, b) | b <- binds] sigs
1057 (sigs, binds) = unzip rec_sels
1058 rec_sels = map mkRecSelBind [ (tc,fld)
1060 , fld <- tyConFields tc ]
1062 mkRecSelBind :: (TyCon, FieldLabel) -> (LSig Name, LHsBinds Name)
1063 mkRecSelBind (tycon, sel_name)
1064 = (L loc (IdSig sel_id), unitBag (L loc sel_bind))
1066 loc = getSrcSpan tycon
1067 sel_id = Var.mkLocalVar rec_details sel_name sel_ty vanillaIdInfo
1068 rec_details = RecSelId { sel_tycon = tycon, sel_naughty = is_naughty }
1070 -- Find a representative constructor, con1
1071 all_cons = tyConDataCons tycon
1072 cons_w_field = [ con | con <- all_cons
1073 , sel_name `elem` dataConFieldLabels con ]
1074 con1 = ASSERT( not (null cons_w_field) ) head cons_w_field
1076 -- Selector type; Note [Polymorphic selectors]
1077 field_ty = dataConFieldType con1 sel_name
1078 data_ty = dataConOrigResTy con1
1079 data_tvs = tyVarsOfType data_ty
1080 is_naughty = not (tyVarsOfType field_ty `subVarSet` data_tvs)
1081 (field_tvs, field_theta, field_tau) = tcSplitSigmaTy field_ty
1082 sel_ty | is_naughty = unitTy -- See Note [Naughty record selectors]
1083 | otherwise = mkForAllTys (varSetElems data_tvs ++ field_tvs) $
1084 mkPhiTy (dataConStupidTheta con1) $ -- Urgh!
1085 mkPhiTy field_theta $ -- Urgh!
1086 mkFunTy data_ty field_tau
1088 -- Make the binding: sel (C2 { fld = x }) = x
1089 -- sel (C7 { fld = x }) = x
1090 -- where cons_w_field = [C2,C7]
1091 sel_bind | is_naughty = mkFunBind sel_lname [mkSimpleMatch [] unit_rhs]
1092 | otherwise = mkFunBind sel_lname (map mk_match cons_w_field ++ deflt)
1093 mk_match con = mkSimpleMatch [L loc (mk_sel_pat con)]
1094 (L loc (HsVar field_var))
1095 mk_sel_pat con = ConPatIn (L loc (getName con)) (RecCon rec_fields)
1096 rec_fields = HsRecFields { rec_flds = [rec_field], rec_dotdot = Nothing }
1097 rec_field = HsRecField { hsRecFieldId = sel_lname
1098 , hsRecFieldArg = nlVarPat field_var
1099 , hsRecPun = False }
1100 sel_lname = L loc sel_name
1101 field_var = mkInternalName (mkBuiltinUnique 1) (getOccName sel_name) loc
1103 -- Add catch-all default case unless the case is exhaustive
1104 -- We do this explicitly so that we get a nice error message that
1105 -- mentions this particular record selector
1106 deflt | not (any is_unused all_cons) = []
1107 | otherwise = [mkSimpleMatch [nlWildPat]
1108 (nlHsApp (nlHsVar (getName rEC_SEL_ERROR_ID))
1111 -- Do not add a default case unless there are unmatched
1112 -- constructors. We must take account of GADTs, else we
1113 -- get overlap warning messages from the pattern-match checker
1114 is_unused con = not (con `elem` cons_w_field
1115 || dataConCannotMatch inst_tys con)
1116 inst_tys = tyConAppArgs data_ty
1118 unit_rhs = mkLHsTupleExpr []
1119 msg_lit = HsStringPrim $ mkFastString $
1120 occNameString (getOccName sel_name)
1123 tyConFields :: TyCon -> [FieldLabel]
1125 | isAlgTyCon tc = nub (concatMap dataConFieldLabels (tyConDataCons tc))
1129 Note [Polymorphic selectors]
1130 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1131 When a record has a polymorphic field, we pull the foralls out to the front.
1132 data T = MkT { f :: forall a. [a] -> a }
1133 Then f :: forall a. T -> [a] -> a
1134 NOT f :: T -> forall a. [a] -> a
1136 This is horrid. It's only needed in deeply obscure cases, which I hate.
1137 The only case I know is test tc163, which is worth looking at. It's far
1138 from clear that this test should succeed at all!
1140 Note [Naughty record selectors]
1141 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1142 A "naughty" field is one for which we can't define a record
1143 selector, because an existential type variable would escape. For example:
1144 data T = forall a. MkT { x,y::a }
1145 We obviously can't define
1147 Nevertheless we *do* put a RecSelId into the type environment
1148 so that if the user tries to use 'x' as a selector we can bleat
1149 helpfully, rather than saying unhelpfully that 'x' is not in scope.
1150 Hence the sel_naughty flag, to identify record selectors that don't really exist.
1152 In general, a field is "naughty" if its type mentions a type variable that
1153 isn't in the result type of the constructor. Note that this *allows*
1154 GADT record selectors (Note [GADT record selectors]) whose types may look
1155 like sel :: T [a] -> a
1157 For naughty selectors we make a dummy binding
1159 for naughty selectors, so that the later type-check will add them to the
1160 environment, and they'll be exported. The function is never called, because
1161 the tyepchecker spots the sel_naughty field.
1163 Note [GADT record selectors]
1164 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1165 For GADTs, we require that all constructors with a common field 'f' have the same
1166 result type (modulo alpha conversion). [Checked in TcTyClsDecls.checkValidTyCon]
1169 T1 { f :: Maybe a } :: T [a]
1170 T2 { f :: Maybe a, y :: b } :: T [a]
1172 and now the selector takes that result type as its argument:
1173 f :: forall a. T [a] -> Maybe a
1175 Details: the "real" types of T1,T2 are:
1176 T1 :: forall r a. (r~[a]) => a -> T r
1177 T2 :: forall r a b. (r~[a]) => a -> b -> T r
1179 So the selector loooks like this:
1180 f :: forall a. T [a] -> Maybe a
1183 T1 c (g:[a]~[c]) (v:Maybe c) -> v `cast` Maybe (right (sym g))
1184 T2 c d (g:[a]~[c]) (v:Maybe c) (w:d) -> v `cast` Maybe (right (sym g))
1186 Note the forall'd tyvars of the selector are just the free tyvars
1187 of the result type; there may be other tyvars in the constructor's
1188 type (e.g. 'b' in T2).
1190 Note the need for casts in the result!
1192 Note [Selector running example]
1193 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1194 It's OK to combine GADTs and type families. Here's a running example:
1196 data instance T [a] where
1197 T1 { fld :: b } :: T [Maybe b]
1199 The representation type looks like this
1201 T1 { fld :: b } :: :R7T (Maybe b)
1203 and there's coercion from the family type to the representation type
1204 :CoR7T a :: T [a] ~ :R7T a
1206 The selector we want for fld looks like this:
1208 fld :: forall b. T [Maybe b] -> b
1209 fld = /\b. \(d::T [Maybe b]).
1210 case d `cast` :CoR7T (Maybe b) of
1213 The scrutinee of the case has type :R7T (Maybe b), which can be
1214 gotten by appying the eq_spec to the univ_tvs of the data con.
1216 %************************************************************************
1220 %************************************************************************
1223 resultTypeMisMatch :: Name -> DataCon -> DataCon -> SDoc
1224 resultTypeMisMatch field_name con1 con2
1225 = vcat [sep [ptext (sLit "Constructors") <+> ppr con1 <+> ptext (sLit "and") <+> ppr con2,
1226 ptext (sLit "have a common field") <+> quotes (ppr field_name) <> comma],
1227 nest 2 $ ptext (sLit "but have different result types")]
1229 fieldTypeMisMatch :: Name -> DataCon -> DataCon -> SDoc
1230 fieldTypeMisMatch field_name con1 con2
1231 = sep [ptext (sLit "Constructors") <+> ppr con1 <+> ptext (sLit "and") <+> ppr con2,
1232 ptext (sLit "give different types for field"), quotes (ppr field_name)]
1234 dataConCtxt :: Outputable a => a -> SDoc
1235 dataConCtxt con = ptext (sLit "In the definition of data constructor") <+> quotes (ppr con)
1237 classOpCtxt :: Var -> Type -> SDoc
1238 classOpCtxt sel_id tau = sep [ptext (sLit "When checking the class method:"),
1239 nest 2 (ppr sel_id <+> dcolon <+> ppr tau)]
1241 nullaryClassErr :: Class -> SDoc
1243 = ptext (sLit "No parameters for class") <+> quotes (ppr cls)
1245 classArityErr :: Class -> SDoc
1247 = vcat [ptext (sLit "Too many parameters for class") <+> quotes (ppr cls),
1248 parens (ptext (sLit "Use -XMultiParamTypeClasses to allow multi-parameter classes"))]
1250 classFunDepsErr :: Class -> SDoc
1252 = vcat [ptext (sLit "Fundeps in class") <+> quotes (ppr cls),
1253 parens (ptext (sLit "Use -XFunctionalDependencies to allow fundeps"))]
1255 noClassTyVarErr :: Class -> Var -> SDoc
1256 noClassTyVarErr clas op
1257 = sep [ptext (sLit "The class method") <+> quotes (ppr op),
1258 ptext (sLit "mentions none of the type variables of the class") <+>
1259 ppr clas <+> hsep (map ppr (classTyVars clas))]
1261 genericMultiParamErr :: Class -> SDoc
1262 genericMultiParamErr clas
1263 = ptext (sLit "The multi-parameter class") <+> quotes (ppr clas) <+>
1264 ptext (sLit "cannot have generic methods")
1266 recSynErr :: [LTyClDecl Name] -> TcRn ()
1268 = setSrcSpan (getLoc (head sorted_decls)) $
1269 addErr (sep [ptext (sLit "Cycle in type synonym declarations:"),
1270 nest 2 (vcat (map ppr_decl sorted_decls))])
1272 sorted_decls = sortLocated syn_decls
1273 ppr_decl (L loc decl) = ppr loc <> colon <+> ppr decl
1275 recClsErr :: [Located (TyClDecl Name)] -> TcRn ()
1277 = setSrcSpan (getLoc (head sorted_decls)) $
1278 addErr (sep [ptext (sLit "Cycle in class declarations (via superclasses):"),
1279 nest 2 (vcat (map ppr_decl sorted_decls))])
1281 sorted_decls = sortLocated cls_decls
1282 ppr_decl (L loc decl) = ppr loc <> colon <+> ppr (decl { tcdSigs = [] })
1284 sortLocated :: [Located a] -> [Located a]
1285 sortLocated things = sortLe le things
1287 le (L l1 _) (L l2 _) = l1 <= l2
1289 badDataConTyCon :: DataCon -> Type -> Type -> SDoc
1290 badDataConTyCon data_con res_ty_tmpl actual_res_ty
1291 = hang (ptext (sLit "Data constructor") <+> quotes (ppr data_con) <+>
1292 ptext (sLit "returns type") <+> quotes (ppr actual_res_ty))
1293 2 (ptext (sLit "instead of an instance of its parent type") <+> quotes (ppr res_ty_tmpl))
1295 badGadtDecl :: Name -> SDoc
1297 = vcat [ ptext (sLit "Illegal generalised algebraic data declaration for") <+> quotes (ppr tc_name)
1298 , nest 2 (parens $ ptext (sLit "Use -XGADTs to allow GADTs")) ]
1300 badExistential :: Located Name -> SDoc
1301 badExistential con_name
1302 = hang (ptext (sLit "Data constructor") <+> quotes (ppr con_name) <+>
1303 ptext (sLit "has existential type variables, a context, or a specialised result type"))
1304 2 (parens $ ptext (sLit "Use -XExistentialQuantification or -XGADTs to allow this"))
1306 badStupidTheta :: Name -> SDoc
1307 badStupidTheta tc_name
1308 = ptext (sLit "A data type declared in GADT style cannot have a context:") <+> quotes (ppr tc_name)
1310 newtypeConError :: Name -> Int -> SDoc
1311 newtypeConError tycon n
1312 = sep [ptext (sLit "A newtype must have exactly one constructor,"),
1313 nest 2 $ ptext (sLit "but") <+> quotes (ppr tycon) <+> ptext (sLit "has") <+> speakN n ]
1315 newtypeExError :: DataCon -> SDoc
1317 = sep [ptext (sLit "A newtype constructor cannot have an existential context,"),
1318 nest 2 $ ptext (sLit "but") <+> quotes (ppr con) <+> ptext (sLit "does")]
1320 newtypeStrictError :: DataCon -> SDoc
1321 newtypeStrictError con
1322 = sep [ptext (sLit "A newtype constructor cannot have a strictness annotation,"),
1323 nest 2 $ ptext (sLit "but") <+> quotes (ppr con) <+> ptext (sLit "does")]
1325 newtypePredError :: DataCon -> SDoc
1326 newtypePredError con
1327 = sep [ptext (sLit "A newtype constructor must have a return type of form T a1 ... an"),
1328 nest 2 $ ptext (sLit "but") <+> quotes (ppr con) <+> ptext (sLit "does not")]
1330 newtypeFieldErr :: DataCon -> Int -> SDoc
1331 newtypeFieldErr con_name n_flds
1332 = sep [ptext (sLit "The constructor of a newtype must have exactly one field"),
1333 nest 2 $ ptext (sLit "but") <+> quotes (ppr con_name) <+> ptext (sLit "has") <+> speakN n_flds]
1335 badSigTyDecl :: Name -> SDoc
1336 badSigTyDecl tc_name
1337 = vcat [ ptext (sLit "Illegal kind signature") <+>
1338 quotes (ppr tc_name)
1339 , nest 2 (parens $ ptext (sLit "Use -XKindSignatures to allow kind signatures")) ]
1341 badFamInstDecl :: Outputable a => a -> SDoc
1342 badFamInstDecl tc_name
1343 = vcat [ ptext (sLit "Illegal family instance for") <+>
1344 quotes (ppr tc_name)
1345 , nest 2 (parens $ ptext (sLit "Use -XTypeFamilies to allow indexed type families")) ]
1347 emptyConDeclsErr :: Name -> SDoc
1348 emptyConDeclsErr tycon
1349 = sep [quotes (ppr tycon) <+> ptext (sLit "has no constructors"),
1350 nest 2 $ ptext (sLit "(-XEmptyDataDecls permits this)")]