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, tcFamInstDecl, mkRecSelBinds
13 #include "HsVersions.h"
26 import TysWiredIn ( unitTy )
33 import MkId ( mkDefaultMethodId )
34 import MkCore ( rEC_SEL_ERROR_ID )
48 import Unique ( mkBuiltinUnique )
57 %************************************************************************
59 \subsection{Type checking for type and class declarations}
61 %************************************************************************
64 tcTyAndClassDecls :: ModDetails
65 -> [[LTyClDecl Name]] -- Mutually-recursive groups in dependency order
66 -> TcM (TcGblEnv, -- Input env extended by types and classes
67 -- and their implicit Ids,DataCons
68 HsValBinds Name, -- Renamed bindings for record selectors
69 [Id]) -- Default method ids
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 tyclss
109 ; dm_ids = mkDefaultMethodIds tyclss }
111 ; env <- tcExtendGlobalEnv implicit_things getGblEnv
112 ; return (env, rec_sel_binds, dm_ids) } }
114 zipRecTyClss :: [[LTyClDecl Name]]
115 -> [TyThing] -- Knot-tied
117 -- Build a name-TyThing mapping for the things bound by decls
118 -- being careful not to look at the [TyThing]
119 -- The TyThings in the result list must have a visible ATyCon/AClass,
120 -- because typechecking types (in, say, tcTyClDecl) looks at this outer constructor
121 zipRecTyClss decls_s rec_things
122 = [ get decl | decls <- decls_s, L _ decl <- flattenATs decls ]
124 rec_type_env :: TypeEnv
125 rec_type_env = mkTypeEnv rec_things
127 get :: TyClDecl Name -> (Name, TyThing)
128 get (ClassDecl {tcdLName = L _ name}) = (name, AClass cl)
130 Just (AClass cl) = lookupTypeEnv rec_type_env name
131 get decl = (name, ATyCon tc)
134 Just (ATyCon tc) = lookupTypeEnv rec_type_env name
138 %************************************************************************
140 Type checking family instances
142 %************************************************************************
144 Family instances are somewhat of a hybrid. They are processed together with
145 class instance heads, but can contain data constructors and hence they share a
146 lot of kinding and type checking code with ordinary algebraic data types (and
150 tcFamInstDecl :: TopLevelFlag -> LTyClDecl Name -> TcM TyThing
151 tcFamInstDecl top_lvl (L loc decl)
152 = -- Prime error recovery, set source location
155 do { -- type family instances require -XTypeFamilies
156 -- and can't (currently) be in an hs-boot file
157 ; type_families <- xoptM Opt_TypeFamilies
158 ; is_boot <- tcIsHsBoot -- Are we compiling an hs-boot file?
159 ; checkTc type_families $ badFamInstDecl (tcdLName decl)
160 ; checkTc (not is_boot) $ badBootFamInstDeclErr
162 -- Perform kind and type checking
163 ; tc <- tcFamInstDecl1 decl
164 ; checkValidTyCon tc -- Remember to check validity;
165 -- no recursion to worry about here
167 -- Check that toplevel type instances are not for associated types.
168 ; when (isTopLevel top_lvl && isAssocFamily tc)
169 (addErr $ assocInClassErr (tcdName decl))
171 ; return (ATyCon tc) }
173 isAssocFamily :: TyCon -> Bool -- Is an assocaited type
175 = case tyConFamInst_maybe tycon of
176 Nothing -> panic "isAssocFamily: no family?!?"
177 Just (fam, _) -> isTyConAssoc fam
179 assocInClassErr :: Name -> SDoc
181 = ptext (sLit "Associated type") <+> quotes (ppr name) <+>
182 ptext (sLit "must be inside a class instance")
186 tcFamInstDecl1 :: TyClDecl Name -> TcM TyCon
189 tcFamInstDecl1 (decl@TySynonym {tcdLName = L loc tc_name})
190 = kcIdxTyPats decl $ \k_tvs k_typats resKind family ->
191 do { -- check that the family declaration is for a synonym
192 checkTc (isFamilyTyCon family) (notFamily family)
193 ; checkTc (isSynTyCon family) (wrongKindOfFamily family)
195 ; -- (1) kind check the right-hand side of the type equation
196 ; k_rhs <- kcCheckLHsType (tcdSynRhs decl) (EK resKind EkUnk)
197 -- ToDo: the ExpKind could be better
199 -- we need the exact same number of type parameters as the family
201 ; let famArity = tyConArity family
202 ; checkTc (length k_typats == famArity) $
203 wrongNumberOfParmsErr famArity
205 -- (2) type check type equation
206 ; tcTyVarBndrs k_tvs $ \t_tvs -> do { -- turn kinded into proper tyvars
207 ; t_typats <- mapM tcHsKindedType k_typats
208 ; t_rhs <- tcHsKindedType k_rhs
210 -- (3) check the well-formedness of the instance
211 ; checkValidTypeInst t_typats t_rhs
213 -- (4) construct representation tycon
214 ; rep_tc_name <- newFamInstTyConName tc_name t_typats loc
215 ; buildSynTyCon rep_tc_name t_tvs (SynonymTyCon t_rhs)
217 NoParentTyCon (Just (family, t_typats))
220 -- "newtype instance" and "data instance"
221 tcFamInstDecl1 (decl@TyData {tcdND = new_or_data, tcdLName = L loc tc_name,
223 = kcIdxTyPats decl $ \k_tvs k_typats resKind fam_tycon ->
224 do { -- check that the family declaration is for the right kind
225 checkTc (isFamilyTyCon fam_tycon) (notFamily fam_tycon)
226 ; checkTc (isAlgTyCon fam_tycon) (wrongKindOfFamily fam_tycon)
228 ; -- (1) kind check the data declaration as usual
229 ; k_decl <- kcDataDecl decl k_tvs
230 ; let k_ctxt = tcdCtxt k_decl
231 k_cons = tcdCons k_decl
233 -- result kind must be '*' (otherwise, we have too few patterns)
234 ; checkTc (isLiftedTypeKind resKind) $ tooFewParmsErr (tyConArity fam_tycon)
236 -- (2) type check indexed data type declaration
237 ; tcTyVarBndrs k_tvs $ \t_tvs -> do { -- turn kinded into proper tyvars
238 ; unbox_strict <- doptM Opt_UnboxStrictFields
240 -- kind check the type indexes and the context
241 ; t_typats <- mapM tcHsKindedType k_typats
242 ; stupid_theta <- tcHsKindedContext k_ctxt
245 -- (a) left-hand side contains no type family applications
246 -- (vanilla synonyms are fine, though, and we checked for
248 ; mapM_ checkTyFamFreeness t_typats
250 -- Check that we don't use GADT syntax in H98 world
251 ; gadt_ok <- xoptM Opt_GADTs
252 ; checkTc (gadt_ok || consUseH98Syntax cons) (badGadtDecl tc_name)
254 -- (b) a newtype has exactly one constructor
255 ; checkTc (new_or_data == DataType || isSingleton k_cons) $
256 newtypeConError tc_name (length k_cons)
258 -- (4) construct representation tycon
259 ; rep_tc_name <- newFamInstTyConName tc_name t_typats loc
260 ; let ex_ok = True -- Existentials ok for type families!
261 ; fixM (\ rep_tycon -> do
262 { let orig_res_ty = mkTyConApp fam_tycon t_typats
263 ; data_cons <- tcConDecls unbox_strict ex_ok rep_tycon
264 (t_tvs, orig_res_ty) k_cons
267 DataType -> return (mkDataTyConRhs data_cons)
268 NewType -> ASSERT( not (null data_cons) )
269 mkNewTyConRhs rep_tc_name rep_tycon (head data_cons)
270 ; buildAlgTyCon rep_tc_name t_tvs stupid_theta tc_rhs Recursive
271 False h98_syntax NoParentTyCon (Just (fam_tycon, t_typats))
272 -- We always assume that indexed types are recursive. Why?
273 -- (1) Due to their open nature, we can never be sure that a
274 -- further instance might not introduce a new recursive
275 -- dependency. (2) They are always valid loop breakers as
276 -- they involve a coercion.
280 h98_syntax = case cons of -- All constructors have same shape
281 L _ (ConDecl { con_res = ResTyGADT _ }) : _ -> False
284 tcFamInstDecl1 d = pprPanic "tcFamInstDecl1" (ppr d)
286 -- Kind checking of indexed types
289 -- Kind check type patterns and kind annotate the embedded type variables.
291 -- * Here we check that a type instance matches its kind signature, but we do
292 -- not check whether there is a pattern for each type index; the latter
293 -- check is only required for type synonym instances.
295 kcIdxTyPats :: TyClDecl Name
296 -> ([LHsTyVarBndr Name] -> [LHsType Name] -> Kind -> TyCon -> TcM a)
297 -- ^^kinded tvs ^^kinded ty pats ^^res kind
299 kcIdxTyPats decl thing_inside
300 = kcHsTyVars (tcdTyVars decl) $ \tvs ->
301 do { let tc_name = tcdLName decl
302 ; fam_tycon <- tcLookupLocatedTyCon tc_name
303 ; let { (kinds, resKind) = splitKindFunTys (tyConKind fam_tycon)
304 ; hs_typats = fromJust $ tcdTyPats decl }
306 -- we may not have more parameters than the kind indicates
307 ; checkTc (length kinds >= length hs_typats) $
308 tooManyParmsErr (tcdLName decl)
310 -- type functions can have a higher-kinded result
311 ; let resultKind = mkArrowKinds (drop (length hs_typats) kinds) resKind
312 ; typats <- zipWithM kcCheckLHsType hs_typats
313 [ EK kind (EkArg (ppr tc_name) n)
314 | (kind,n) <- kinds `zip` [1..]]
315 ; thing_inside tvs typats resultKind fam_tycon
320 %************************************************************************
324 %************************************************************************
326 Note [Kind checking for type and class decls]
327 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
328 Kind checking is done thus:
330 1. Make up a kind variable for each parameter of the *data* type,
331 and class, decls, and extend the kind environment (which is in
334 2. Dependency-analyse the type *synonyms* (which must be non-recursive),
335 and kind-check them in dependency order. Extend the kind envt.
337 3. Kind check the data type and class decls
339 Synonyms are treated differently to data type and classes,
340 because a type synonym can be an unboxed type
342 and a kind variable can't unify with UnboxedTypeKind
343 So we infer their kinds in dependency order
345 We need to kind check all types in the mutually recursive group
346 before we know the kind of the type variables. For example:
349 op :: D b => a -> b -> b
352 bop :: (Monad c) => ...
354 Here, the kind of the locally-polymorphic type variable "b"
355 depends on *all the uses of class D*. For example, the use of
356 Monad c in bop's type signature means that D must have kind Type->Type.
358 However type synonyms work differently. They can have kinds which don't
359 just involve (->) and *:
360 type R = Int# -- Kind #
361 type S a = Array# a -- Kind * -> #
362 type T a b = (# a,b #) -- Kind * -> * -> (# a,b #)
363 So we must infer their kinds from their right-hand sides *first* and then
364 use them, whereas for the mutually recursive data types D we bring into
365 scope kind bindings D -> k, where k is a kind variable, and do inference.
369 This treatment of type synonyms only applies to Haskell 98-style synonyms.
370 General type functions can be recursive, and hence, appear in `alg_decls'.
372 The kind of a type family is solely determinded by its kind signature;
373 hence, only kind signatures participate in the construction of the initial
374 kind environment (as constructed by `getInitialKind'). In fact, we ignore
375 instances of families altogether in the following. However, we need to
376 include the kinds of associated families into the construction of the
377 initial kind environment. (This is handled by `allDecls').
381 kcTyClDecls :: [[LTyClDecl Name]] -> TcM [LTyClDecl Name]
382 kcTyClDecls [] = return []
383 kcTyClDecls (decls : decls_s) = do { (tcl_env, kc_decls1) <- kcTyClDecls1 decls
384 ; kc_decls2 <- setLclEnv tcl_env (kcTyClDecls decls_s)
385 ; return (kc_decls1 ++ kc_decls2) }
387 kcTyClDecls1 :: [LTyClDecl Name] -> TcM (TcLclEnv, [LTyClDecl Name])
389 = do { -- Omit instances of type families; they are handled together
390 -- with the *heads* of class instances
391 ; let (syn_decls, alg_decls) = partition (isSynDecl . unLoc) decls
392 alg_at_decls = flattenATs alg_decls
395 ; traceTc "tcTyAndCl" (ptext (sLit "module") <+> ppr mod $$ vcat (map ppr decls))
397 -- First check for cyclic classes
398 ; checkClassCycleErrs alg_decls
400 -- Kind checking; see Note [Kind checking for type and class decls]
401 ; alg_kinds <- mapM getInitialKind alg_at_decls
402 ; tcExtendKindEnv alg_kinds $ do
404 { (kc_syn_decls, tcl_env) <- kcSynDecls (calcSynCycles syn_decls)
405 ; setLclEnv tcl_env $ do
406 { kc_alg_decls <- mapM (wrapLocM kcTyClDecl) alg_decls
408 -- Kind checking done for this group, so zonk the kind variables
409 -- See Note [Kind checking for type and class decls]
410 ; mapM_ (zonkTcKindToKind . snd) alg_kinds
412 ; return (tcl_env, kc_syn_decls ++ kc_alg_decls) } } }
414 flattenATs :: [LTyClDecl Name] -> [LTyClDecl Name]
415 flattenATs decls = concatMap flatten decls
417 flatten decl@(L _ (ClassDecl {tcdATs = ats})) = decl : ats
418 flatten decl = [decl]
420 getInitialKind :: LTyClDecl Name -> TcM (Name, TcKind)
421 -- Only for data type, class, and indexed type declarations
422 -- Get as much info as possible from the data, class, or indexed type decl,
423 -- so as to maximise usefulness of error messages
424 getInitialKind (L _ decl)
425 = do { arg_kinds <- mapM (mk_arg_kind . unLoc) (tyClDeclTyVars decl)
426 ; res_kind <- mk_res_kind decl
427 ; return (tcdName decl, mkArrowKinds arg_kinds res_kind) }
429 mk_arg_kind (UserTyVar _ _) = newKindVar
430 mk_arg_kind (KindedTyVar _ kind) = return kind
432 mk_res_kind (TyFamily { tcdKind = Just kind }) = return kind
433 mk_res_kind (TyData { tcdKindSig = Just kind }) = return kind
434 -- On GADT-style declarations we allow a kind signature
435 -- data T :: *->* where { ... }
436 mk_res_kind _ = return liftedTypeKind
440 kcSynDecls :: [SCC (LTyClDecl Name)]
441 -> TcM ([LTyClDecl Name], -- Kind-annotated decls
442 TcLclEnv) -- Kind bindings
444 = do { tcl_env <- getLclEnv; return ([], tcl_env) }
445 kcSynDecls (group : groups)
446 = do { (decl, nk) <- kcSynDecl group
447 ; (decls, tcl_env) <- tcExtendKindEnv [nk] (kcSynDecls groups)
448 ; return (decl:decls, tcl_env) }
451 kcSynDecl :: SCC (LTyClDecl Name)
452 -> TcM (LTyClDecl Name, -- Kind-annotated decls
453 (Name,TcKind)) -- Kind bindings
454 kcSynDecl (AcyclicSCC (L loc decl))
455 = tcAddDeclCtxt decl $
456 kcHsTyVars (tcdTyVars decl) (\ k_tvs ->
457 do { traceTc "kcd1" (ppr (unLoc (tcdLName decl)) <+> brackets (ppr (tcdTyVars decl))
458 <+> brackets (ppr k_tvs))
459 ; (k_rhs, rhs_kind) <- kcLHsType (tcdSynRhs decl)
460 ; traceTc "kcd2" (ppr (unLoc (tcdLName decl)))
461 ; let tc_kind = foldr (mkArrowKind . hsTyVarKind . unLoc) rhs_kind k_tvs
462 ; return (L loc (decl { tcdTyVars = k_tvs, tcdSynRhs = k_rhs }),
463 (unLoc (tcdLName decl), tc_kind)) })
465 kcSynDecl (CyclicSCC decls)
466 = do { recSynErr decls; failM } -- Fail here to avoid error cascade
467 -- of out-of-scope tycons
469 ------------------------------------------------------------------------
470 kcTyClDecl :: TyClDecl Name -> TcM (TyClDecl Name)
471 -- Not used for type synonyms (see kcSynDecl)
473 kcTyClDecl decl@(TyData {})
474 = ASSERT( not . isFamInstDecl $ decl ) -- must not be a family instance
475 kcTyClDeclBody decl $
478 kcTyClDecl decl@(TyFamily {})
479 = kcFamilyDecl [] decl -- the empty list signals a toplevel decl
481 kcTyClDecl decl@(ClassDecl {tcdCtxt = ctxt, tcdSigs = sigs, tcdATs = ats})
482 = kcTyClDeclBody decl $ \ tvs' ->
483 do { ctxt' <- kcHsContext ctxt
484 ; ats' <- mapM (wrapLocM (kcFamilyDecl tvs')) ats
485 ; sigs' <- mapM (wrapLocM kc_sig) sigs
486 ; return (decl {tcdTyVars = tvs', tcdCtxt = ctxt', tcdSigs = sigs',
489 kc_sig (TypeSig nm op_ty) = do { op_ty' <- kcHsLiftedSigType op_ty
490 ; return (TypeSig nm op_ty') }
491 kc_sig other_sig = return other_sig
493 kcTyClDecl decl@(ForeignType {})
496 kcTyClDecl (TySynonym {}) = panic "kcTyClDecl TySynonym"
498 kcTyClDeclBody :: TyClDecl Name
499 -> ([LHsTyVarBndr Name] -> TcM a)
501 -- getInitialKind has made a suitably-shaped kind for the type or class
502 -- Unpack it, and attribute those kinds to the type variables
503 -- Extend the env with bindings for the tyvars, taken from
504 -- the kind of the tycon/class. Give it to the thing inside, and
505 -- check the result kind matches
506 kcTyClDeclBody decl thing_inside
507 = tcAddDeclCtxt decl $
508 do { tc_ty_thing <- tcLookupLocated (tcdLName decl)
509 ; let tc_kind = case tc_ty_thing of
511 _ -> pprPanic "kcTyClDeclBody" (ppr tc_ty_thing)
512 (kinds, _) = splitKindFunTys tc_kind
513 hs_tvs = tcdTyVars decl
514 kinded_tvs = ASSERT( length kinds >= length hs_tvs )
515 zipWith add_kind hs_tvs kinds
516 ; tcExtendKindEnvTvs kinded_tvs thing_inside }
518 add_kind (L loc (UserTyVar n _)) k = L loc (UserTyVar n k)
519 add_kind (L loc (KindedTyVar n _)) k = L loc (KindedTyVar n k)
521 -- Kind check a data declaration, assuming that we already extended the
522 -- kind environment with the type variables of the left-hand side (these
523 -- kinded type variables are also passed as the second parameter).
525 kcDataDecl :: TyClDecl Name -> [LHsTyVarBndr Name] -> TcM (TyClDecl Name)
526 kcDataDecl decl@(TyData {tcdND = new_or_data, tcdCtxt = ctxt, tcdCons = cons})
528 = do { ctxt' <- kcHsContext ctxt
529 ; cons' <- mapM (wrapLocM kc_con_decl) cons
530 ; return (decl {tcdTyVars = tvs, tcdCtxt = ctxt', tcdCons = cons'}) }
532 -- doc comments are typechecked to Nothing here
533 kc_con_decl con_decl@(ConDecl { con_name = name, con_qvars = ex_tvs
534 , con_cxt = ex_ctxt, con_details = details, con_res = res })
535 = addErrCtxt (dataConCtxt name) $
536 kcHsTyVars ex_tvs $ \ex_tvs' -> do
537 do { ex_ctxt' <- kcHsContext ex_ctxt
538 ; details' <- kc_con_details details
539 ; res' <- case res of
540 ResTyH98 -> return ResTyH98
541 ResTyGADT ty -> do { ty' <- kcHsSigType ty; return (ResTyGADT ty') }
542 ; return (con_decl { con_qvars = ex_tvs', con_cxt = ex_ctxt'
543 , con_details = details', con_res = res' }) }
545 kc_con_details (PrefixCon btys)
546 = do { btys' <- mapM kc_larg_ty btys
547 ; return (PrefixCon btys') }
548 kc_con_details (InfixCon bty1 bty2)
549 = do { bty1' <- kc_larg_ty bty1
550 ; bty2' <- kc_larg_ty bty2
551 ; return (InfixCon bty1' bty2') }
552 kc_con_details (RecCon fields)
553 = do { fields' <- mapM kc_field fields
554 ; return (RecCon fields') }
556 kc_field (ConDeclField fld bty d) = do { bty' <- kc_larg_ty bty
557 ; return (ConDeclField fld bty' d) }
559 kc_larg_ty bty = case new_or_data of
560 DataType -> kcHsSigType bty
561 NewType -> kcHsLiftedSigType bty
562 -- Can't allow an unlifted type for newtypes, because we're effectively
563 -- going to remove the constructor while coercing it to a lifted type.
564 -- And newtypes can't be bang'd
565 kcDataDecl d _ = pprPanic "kcDataDecl" (ppr d)
567 -- Kind check a family declaration or type family default declaration.
569 kcFamilyDecl :: [LHsTyVarBndr Name] -- tyvars of enclosing class decl if any
570 -> TyClDecl Name -> TcM (TyClDecl Name)
571 kcFamilyDecl classTvs decl@(TyFamily {tcdKind = kind})
572 = kcTyClDeclBody decl $ \tvs' ->
573 do { mapM_ unifyClassParmKinds tvs'
574 ; return (decl {tcdTyVars = tvs',
575 tcdKind = kind `mplus` Just liftedTypeKind})
576 -- default result kind is '*'
579 unifyClassParmKinds (L _ tv)
580 | (n,k) <- hsTyVarNameKind tv
581 , Just classParmKind <- lookup n classTyKinds
582 = unifyKind k classParmKind
583 | otherwise = return ()
584 classTyKinds = [hsTyVarNameKind tv | L _ tv <- classTvs]
586 kcFamilyDecl _ (TySynonym {}) -- type family defaults
587 = panic "TcTyClsDecls.kcFamilyDecl: not implemented yet"
588 kcFamilyDecl _ d = pprPanic "kcFamilyDecl" (ppr d)
592 %************************************************************************
594 \subsection{Type checking}
596 %************************************************************************
599 tcTyClDecl :: (Name -> RecFlag) -> LTyClDecl Name -> TcM [TyThing]
601 tcTyClDecl calc_isrec (L loc decl)
602 = setSrcSpan loc $ tcAddDeclCtxt decl $
603 tcTyClDecl1 NoParentTyCon calc_isrec decl
605 -- "type family" declarations
606 tcTyClDecl1 :: TyConParent -> (Name -> RecFlag) -> TyClDecl Name -> TcM [TyThing]
607 tcTyClDecl1 parent _calc_isrec
608 (TyFamily {tcdFlavour = TypeFamily,
609 tcdLName = L _ tc_name, tcdTyVars = tvs,
610 tcdKind = Just kind}) -- NB: kind at latest added during kind checking
611 = tcTyVarBndrs tvs $ \ tvs' -> do
612 { traceTc "type family:" (ppr tc_name)
614 -- Check that we don't use families without -XTypeFamilies
615 ; idx_tys <- xoptM Opt_TypeFamilies
616 ; checkTc idx_tys $ badFamInstDecl tc_name
618 ; tycon <- buildSynTyCon tc_name tvs' SynFamilyTyCon kind parent Nothing
619 ; return [ATyCon tycon]
622 -- "data family" declaration
623 tcTyClDecl1 parent _calc_isrec
624 (TyFamily {tcdFlavour = DataFamily,
625 tcdLName = L _ tc_name, tcdTyVars = tvs, tcdKind = mb_kind})
626 = tcTyVarBndrs tvs $ \ tvs' -> do
627 { traceTc "data family:" (ppr tc_name)
628 ; extra_tvs <- tcDataKindSig mb_kind
629 ; let final_tvs = tvs' ++ extra_tvs -- we may not need these
632 -- Check that we don't use families without -XTypeFamilies
633 ; idx_tys <- xoptM Opt_TypeFamilies
634 ; checkTc idx_tys $ badFamInstDecl tc_name
636 ; tycon <- buildAlgTyCon tc_name final_tvs []
637 DataFamilyTyCon Recursive False True
639 ; return [ATyCon tycon]
643 tcTyClDecl1 _parent _calc_isrec
644 (TySynonym {tcdLName = L _ tc_name, tcdTyVars = tvs, tcdSynRhs = rhs_ty})
645 = ASSERT( isNoParent _parent )
646 tcTyVarBndrs tvs $ \ tvs' -> do
647 { traceTc "tcd1" (ppr tc_name)
648 ; rhs_ty' <- tcHsKindedType rhs_ty
649 ; tycon <- buildSynTyCon tc_name tvs' (SynonymTyCon rhs_ty')
650 (typeKind rhs_ty') NoParentTyCon Nothing
651 ; return [ATyCon tycon] }
653 -- "newtype" and "data"
654 -- NB: not used for newtype/data instances (whether associated or not)
655 tcTyClDecl1 _parent calc_isrec
656 (TyData {tcdND = new_or_data, tcdCtxt = ctxt, tcdTyVars = tvs,
657 tcdLName = L _ tc_name, tcdKindSig = mb_ksig, tcdCons = cons})
658 = ASSERT( isNoParent _parent )
659 tcTyVarBndrs tvs $ \ tvs' -> do
660 { extra_tvs <- tcDataKindSig mb_ksig
661 ; let final_tvs = tvs' ++ extra_tvs
662 ; stupid_theta <- tcHsKindedContext ctxt
663 ; want_generic <- xoptM Opt_Generics
664 ; unbox_strict <- doptM Opt_UnboxStrictFields
665 ; empty_data_decls <- xoptM Opt_EmptyDataDecls
666 ; kind_signatures <- xoptM Opt_KindSignatures
667 ; existential_ok <- xoptM Opt_ExistentialQuantification
668 ; gadt_ok <- xoptM Opt_GADTs
669 ; gadtSyntax_ok <- xoptM Opt_GADTSyntax
670 ; is_boot <- tcIsHsBoot -- Are we compiling an hs-boot file?
671 ; let ex_ok = existential_ok || gadt_ok -- Data cons can have existential context
673 -- Check that we don't use GADT syntax in H98 world
674 ; checkTc (gadtSyntax_ok || h98_syntax) (badGadtDecl tc_name)
676 -- Check that we don't use kind signatures without Glasgow extensions
677 ; checkTc (kind_signatures || isNothing mb_ksig) (badSigTyDecl tc_name)
679 -- Check that the stupid theta is empty for a GADT-style declaration
680 ; checkTc (null stupid_theta || h98_syntax) (badStupidTheta tc_name)
682 -- Check that a newtype has exactly one constructor
683 -- Do this before checking for empty data decls, so that
684 -- we don't suggest -XEmptyDataDecls for newtypes
685 ; checkTc (new_or_data == DataType || isSingleton cons)
686 (newtypeConError tc_name (length cons))
688 -- Check that there's at least one condecl,
689 -- or else we're reading an hs-boot file, or -XEmptyDataDecls
690 ; checkTc (not (null cons) || empty_data_decls || is_boot)
691 (emptyConDeclsErr tc_name)
693 ; tycon <- fixM (\ tycon -> do
694 { let res_ty = mkTyConApp tycon (mkTyVarTys final_tvs)
695 ; data_cons <- tcConDecls unbox_strict ex_ok
696 tycon (final_tvs, res_ty) cons
698 if null cons && is_boot -- In a hs-boot file, empty cons means
699 then return AbstractTyCon -- "don't know"; hence Abstract
700 else case new_or_data of
701 DataType -> return (mkDataTyConRhs data_cons)
702 NewType -> ASSERT( not (null data_cons) )
703 mkNewTyConRhs tc_name tycon (head data_cons)
704 ; buildAlgTyCon tc_name final_tvs stupid_theta tc_rhs is_rec
705 (want_generic && canDoGenerics data_cons) (not h98_syntax)
706 NoParentTyCon Nothing
708 ; return [ATyCon tycon]
711 is_rec = calc_isrec tc_name
712 h98_syntax = consUseH98Syntax cons
714 tcTyClDecl1 _parent calc_isrec
715 (ClassDecl {tcdLName = L _ class_name, tcdTyVars = tvs,
716 tcdCtxt = ctxt, tcdMeths = meths,
717 tcdFDs = fundeps, tcdSigs = sigs, tcdATs = ats} )
718 = ASSERT( isNoParent _parent )
719 tcTyVarBndrs tvs $ \ tvs' -> do
720 { ctxt' <- tcHsKindedContext ctxt
721 ; fds' <- mapM (addLocM tc_fundep) fundeps
722 ; sig_stuff <- tcClassSigs class_name sigs meths
723 ; clas <- fixM $ \ clas -> do
724 { let -- This little knot is just so we can get
725 -- hold of the name of the class TyCon, which we
726 -- need to look up its recursiveness
727 tycon_name = tyConName (classTyCon clas)
728 tc_isrec = calc_isrec tycon_name
729 ; atss' <- mapM (addLocM $ tcTyClDecl1 (AssocFamilyTyCon clas) (const Recursive)) ats
730 -- NB: 'ats' only contains "type family" and "data family"
731 -- declarations as well as type family defaults
732 ; buildClass False {- Must include unfoldings for selectors -}
733 class_name tvs' ctxt' fds' (concat atss')
735 ; return (AClass clas : map ATyCon (classATs clas))
736 -- NB: Order is important due to the call to `mkGlobalThings' when
737 -- tying the the type and class declaration type checking knot.
740 tc_fundep (tvs1, tvs2) = do { tvs1' <- mapM tcLookupTyVar tvs1 ;
741 ; tvs2' <- mapM tcLookupTyVar tvs2 ;
742 ; return (tvs1', tvs2') }
745 (ForeignType {tcdLName = L _ tc_name, tcdExtName = tc_ext_name})
746 = return [ATyCon (mkForeignTyCon tc_name tc_ext_name liftedTypeKind 0)]
748 tcTyClDecl1 _ _ d = pprPanic "tcTyClDecl1" (ppr d)
750 -----------------------------------
751 tcConDecls :: Bool -> Bool -> TyCon -> ([TyVar], Type)
752 -> [LConDecl Name] -> TcM [DataCon]
753 tcConDecls unbox ex_ok rep_tycon res_tmpl cons
754 = mapM (addLocM (tcConDecl unbox ex_ok rep_tycon res_tmpl)) cons
756 tcConDecl :: Bool -- True <=> -funbox-strict_fields
757 -> Bool -- True <=> -XExistentialQuantificaton or -XGADTs
758 -> TyCon -- Representation tycon
759 -> ([TyVar], Type) -- Return type template (with its template tyvars)
763 tcConDecl unbox_strict existential_ok rep_tycon res_tmpl -- Data types
764 con@(ConDecl {con_name = name, con_qvars = tvs, con_cxt = ctxt
765 , con_details = details, con_res = res_ty })
766 = addErrCtxt (dataConCtxt name) $
767 tcTyVarBndrs tvs $ \ tvs' -> do
768 { ctxt' <- tcHsKindedContext ctxt
769 ; checkTc (existential_ok || conRepresentibleWithH98Syntax con)
770 (badExistential name)
771 ; (univ_tvs, ex_tvs, eq_preds, res_ty') <- tcResultType res_tmpl tvs' res_ty
773 tc_datacon is_infix field_lbls btys
774 = do { (arg_tys, stricts) <- mapAndUnzipM (tcConArg unbox_strict) btys
775 ; buildDataCon (unLoc name) is_infix
777 univ_tvs ex_tvs eq_preds ctxt' arg_tys
779 -- NB: we put data_tc, the type constructor gotten from the
780 -- constructor type signature into the data constructor;
781 -- that way checkValidDataCon can complain if it's wrong.
784 PrefixCon btys -> tc_datacon False [] btys
785 InfixCon bty1 bty2 -> tc_datacon True [] [bty1,bty2]
786 RecCon fields -> tc_datacon False field_names btys
788 field_names = map (unLoc . cd_fld_name) fields
789 btys = map cd_fld_type fields
793 -- data instance T (b,c) where
794 -- TI :: forall e. e -> T (e,e)
796 -- The representation tycon looks like this:
797 -- data :R7T b c where
798 -- TI :: forall b1 c1. (b1 ~ c1) => b1 -> :R7T b1 c1
799 -- In this case orig_res_ty = T (e,e)
801 tcResultType :: ([TyVar], Type) -- Template for result type; e.g.
802 -- data instance T [a] b c = ...
803 -- gives template ([a,b,c], T [a] b c)
804 -> [TyVar] -- where MkT :: forall x y z. ...
806 -> TcM ([TyVar], -- Universal
807 [TyVar], -- Existential (distinct OccNames from univs)
808 [(TyVar,Type)], -- Equality predicates
809 Type) -- Typechecked return type
810 -- We don't check that the TyCon given in the ResTy is
811 -- the same as the parent tycon, becuase we are in the middle
812 -- of a recursive knot; so it's postponed until checkValidDataCon
814 tcResultType (tmpl_tvs, res_ty) dc_tvs ResTyH98
815 = return (tmpl_tvs, dc_tvs, [], res_ty)
816 -- In H98 syntax the dc_tvs are the existential ones
817 -- data T a b c = forall d e. MkT ...
818 -- The {a,b,c} are tc_tvs, and {d,e} are dc_tvs
820 tcResultType (tmpl_tvs, res_tmpl) dc_tvs (ResTyGADT res_ty)
821 -- E.g. data T [a] b c where
822 -- MkT :: forall x y z. T [(x,y)] z z
824 -- Univ tyvars Eq-spec
828 -- Existentials are the leftover type vars: [x,y]
829 -- So we return ([a,b,z], [x,y], [a~(x,y),b~z], T [(x,y)] z z)
830 = do { res_ty' <- tcHsKindedType res_ty
831 ; let Just subst = tcMatchTy (mkVarSet tmpl_tvs) res_tmpl res_ty'
833 -- /Lazily/ figure out the univ_tvs etc
834 -- Each univ_tv is either a dc_tv or a tmpl_tv
835 (univ_tvs, eq_spec) = foldr choose ([], []) tidy_tmpl_tvs
836 choose tmpl (univs, eqs)
837 | Just ty <- lookupTyVar subst tmpl
838 = case tcGetTyVar_maybe ty of
839 Just tv | not (tv `elem` univs)
841 _other -> (tmpl:univs, (tmpl,ty):eqs)
842 | otherwise = pprPanic "tcResultType" (ppr res_ty)
843 ex_tvs = dc_tvs `minusList` univ_tvs
845 ; return (univ_tvs, ex_tvs, eq_spec, res_ty') }
847 -- NB: tmpl_tvs and dc_tvs are distinct, but
848 -- we want them to be *visibly* distinct, both for
849 -- interface files and general confusion. So rename
850 -- the tc_tvs, since they are not used yet (no
851 -- consequential renaming needed)
852 (_, tidy_tmpl_tvs) = mapAccumL tidy_one init_occ_env tmpl_tvs
853 init_occ_env = initTidyOccEnv (map getOccName dc_tvs)
854 tidy_one env tv = (env', setTyVarName tv (tidyNameOcc name occ'))
857 (env', occ') = tidyOccName env (getOccName name)
859 consUseH98Syntax :: [LConDecl a] -> Bool
860 consUseH98Syntax (L _ (ConDecl { con_res = ResTyGADT _ }) : _) = False
861 consUseH98Syntax _ = True
862 -- All constructors have same shape
864 conRepresentibleWithH98Syntax :: ConDecl Name -> Bool
865 conRepresentibleWithH98Syntax
866 (ConDecl {con_qvars = tvs, con_cxt = ctxt, con_res = ResTyH98 })
867 = null tvs && null (unLoc ctxt)
868 conRepresentibleWithH98Syntax
869 (ConDecl {con_qvars = tvs, con_cxt = ctxt, con_res = ResTyGADT (L _ t) })
870 = null (unLoc ctxt) && f t (map (hsTyVarName . unLoc) tvs)
871 where -- Each type variable should be used exactly once in the
872 -- result type, and the result type must just be the type
873 -- constructor applied to type variables
874 f (HsAppTy (L _ t1) (L _ (HsTyVar v2))) vs
875 = (v2 `elem` vs) && f t1 (delete v2 vs)
876 f (HsTyVar _) [] = True
880 tcConArg :: Bool -- True <=> -funbox-strict_fields
882 -> TcM (TcType, HsBang)
883 tcConArg unbox_strict bty
884 = do { arg_ty <- tcHsBangType bty
885 ; let bang = getBangStrictness bty
886 ; let strict_mark = chooseBoxingStrategy unbox_strict arg_ty bang
887 ; return (arg_ty, strict_mark) }
889 -- We attempt to unbox/unpack a strict field when either:
890 -- (i) The field is marked '!!', or
891 -- (ii) The field is marked '!', and the -funbox-strict-fields flag is on.
893 -- We have turned off unboxing of newtypes because coercions make unboxing
894 -- and reboxing more complicated
895 chooseBoxingStrategy :: Bool -> TcType -> HsBang -> HsBang
896 chooseBoxingStrategy unbox_strict_fields arg_ty bang
899 HsUnpack -> can_unbox HsUnpackFailed arg_ty
900 HsStrict | unbox_strict_fields -> can_unbox HsStrict arg_ty
901 | otherwise -> HsStrict
902 HsUnpackFailed -> pprPanic "chooseBoxingStrategy" (ppr arg_ty)
903 -- Source code never has shtes
905 can_unbox :: HsBang -> TcType -> HsBang
906 -- Returns HsUnpack if we can unpack arg_ty
907 -- fail_bang if we know what arg_ty is but we can't unpack it
908 -- HsStrict if it's abstract, so we don't know whether or not we can unbox it
909 can_unbox fail_bang arg_ty
910 = case splitTyConApp_maybe arg_ty of
913 Just (arg_tycon, tycon_args)
914 | isAbstractTyCon arg_tycon -> HsStrict
915 -- See Note [Don't complain about UNPACK on abstract TyCons]
916 | not (isRecursiveTyCon arg_tycon) -- Note [Recusive unboxing]
917 , isProductTyCon arg_tycon
918 -- We can unbox if the type is a chain of newtypes
919 -- with a product tycon at the end
920 -> if isNewTyCon arg_tycon
921 then can_unbox fail_bang (newTyConInstRhs arg_tycon tycon_args)
924 | otherwise -> fail_bang
927 Note [Don't complain about UNPACK on abstract TyCons]
928 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
929 We are going to complain about UnpackFailed, but if we say
930 data T = MkT {-# UNPACK #-} !Wobble
931 and Wobble is a newtype imported from a module that was compiled
932 without optimisation, we don't want to complain. Because it might
933 be fine when optimsation is on. I think this happens when Haddock
934 is working over (say) GHC souce files.
936 Note [Recursive unboxing]
937 ~~~~~~~~~~~~~~~~~~~~~~~~~
938 Be careful not to try to unbox this!
940 But it's the *argument* type that matters. This is fine:
942 because Int is non-recursive.
945 %************************************************************************
949 %************************************************************************
951 Validity checking is done once the mutually-recursive knot has been
952 tied, so we can look at things freely.
955 checkClassCycleErrs :: [LTyClDecl Name] -> TcM ()
956 checkClassCycleErrs tyclss
960 = do { mapM_ recClsErr cls_cycles
961 ; failM } -- Give up now, because later checkValidTyCl
962 -- will loop if the synonym is recursive
964 cls_cycles = calcClassCycles tyclss
966 checkValidTyCl :: TyClDecl Name -> TcM ()
967 -- We do the validity check over declarations, rather than TyThings
968 -- only so that we can add a nice context with tcAddDeclCtxt
970 = tcAddDeclCtxt decl $
971 do { thing <- tcLookupLocatedGlobal (tcdLName decl)
972 ; traceTc "Validity of" (ppr thing)
974 ATyCon tc -> checkValidTyCon tc
975 AClass cl -> do { checkValidClass cl
976 ; mapM_ (addLocM checkValidTyCl) (tcdATs decl) }
977 _ -> panic "checkValidTyCl"
978 ; traceTc "Done validity of" (ppr thing)
981 -------------------------
982 -- For data types declared with record syntax, we require
983 -- that each constructor that has a field 'f'
984 -- (a) has the same result type
985 -- (b) has the same type for 'f'
986 -- module alpha conversion of the quantified type variables
987 -- of the constructor.
989 -- Note that we allow existentials to match becuase the
990 -- fields can never meet. E.g
992 -- T1 { f1 :: b, f2 :: a, f3 ::Int } :: T
993 -- T2 { f1 :: c, f2 :: c, f3 ::Int } :: T
994 -- Here we do not complain about f1,f2 because they are existential
996 checkValidTyCon :: TyCon -> TcM ()
999 = case synTyConRhs tc of
1000 SynFamilyTyCon {} -> return ()
1001 SynonymTyCon ty -> checkValidType syn_ctxt ty
1003 = do -- Check the context on the data decl
1004 checkValidTheta (DataTyCtxt name) (tyConStupidTheta tc)
1006 -- Check arg types of data constructors
1007 mapM_ (checkValidDataCon tc) data_cons
1009 -- Check that fields with the same name share a type
1010 mapM_ check_fields groups
1013 syn_ctxt = TySynCtxt name
1015 data_cons = tyConDataCons tc
1017 groups = equivClasses cmp_fld (concatMap get_fields data_cons)
1018 cmp_fld (f1,_) (f2,_) = f1 `compare` f2
1019 get_fields con = dataConFieldLabels con `zip` repeat con
1020 -- dataConFieldLabels may return the empty list, which is fine
1022 -- See Note [GADT record selectors] in MkId.lhs
1023 -- We must check (a) that the named field has the same
1024 -- type in each constructor
1025 -- (b) that those constructors have the same result type
1027 -- However, the constructors may have differently named type variable
1028 -- and (worse) we don't know how the correspond to each other. E.g.
1029 -- C1 :: forall a b. { f :: a, g :: b } -> T a b
1030 -- C2 :: forall d c. { f :: c, g :: c } -> T c d
1032 -- So what we do is to ust Unify.tcMatchTys to compare the first candidate's
1033 -- result type against other candidates' types BOTH WAYS ROUND.
1034 -- If they magically agrees, take the substitution and
1035 -- apply them to the latter ones, and see if they match perfectly.
1036 check_fields ((label, con1) : other_fields)
1037 -- These fields all have the same name, but are from
1038 -- different constructors in the data type
1039 = recoverM (return ()) $ mapM_ checkOne other_fields
1040 -- Check that all the fields in the group have the same type
1041 -- NB: this check assumes that all the constructors of a given
1042 -- data type use the same type variables
1044 (tvs1, _, _, res1) = dataConSig con1
1046 fty1 = dataConFieldType con1 label
1048 checkOne (_, con2) -- Do it bothways to ensure they are structurally identical
1049 = do { checkFieldCompat label con1 con2 ts1 res1 res2 fty1 fty2
1050 ; checkFieldCompat label con2 con1 ts2 res2 res1 fty2 fty1 }
1052 (tvs2, _, _, res2) = dataConSig con2
1054 fty2 = dataConFieldType con2 label
1055 check_fields [] = panic "checkValidTyCon/check_fields []"
1057 checkFieldCompat :: Name -> DataCon -> DataCon -> TyVarSet
1058 -> Type -> Type -> Type -> Type -> TcM ()
1059 checkFieldCompat fld con1 con2 tvs1 res1 res2 fty1 fty2
1060 = do { checkTc (isJust mb_subst1) (resultTypeMisMatch fld con1 con2)
1061 ; checkTc (isJust mb_subst2) (fieldTypeMisMatch fld con1 con2) }
1063 mb_subst1 = tcMatchTy tvs1 res1 res2
1064 mb_subst2 = tcMatchTyX tvs1 (expectJust "checkFieldCompat" mb_subst1) fty1 fty2
1066 -------------------------------
1067 checkValidDataCon :: TyCon -> DataCon -> TcM ()
1068 checkValidDataCon tc con
1069 = setSrcSpan (srcLocSpan (getSrcLoc con)) $
1070 addErrCtxt (dataConCtxt con) $
1071 do { traceTc "Validity of data con" (ppr con)
1072 ; let tc_tvs = tyConTyVars tc
1073 res_ty_tmpl = mkFamilyTyConApp tc (mkTyVarTys tc_tvs)
1074 actual_res_ty = dataConOrigResTy con
1075 ; checkTc (isJust (tcMatchTy (mkVarSet tc_tvs)
1078 (badDataConTyCon con res_ty_tmpl actual_res_ty)
1079 ; checkValidMonoType (dataConOrigResTy con)
1080 -- Disallow MkT :: T (forall a. a->a)
1081 -- Reason: it's really the argument of an equality constraint
1082 ; checkValidType ctxt (dataConUserType con)
1083 ; when (isNewTyCon tc) (checkNewDataCon con)
1084 ; mapM_ check_bang (dataConStrictMarks con `zip` [1..])
1087 ctxt = ConArgCtxt (dataConName con)
1088 check_bang (HsUnpackFailed, n) = addWarnTc (cant_unbox_msg n)
1089 check_bang _ = return ()
1091 cant_unbox_msg n = sep [ ptext (sLit "Ignoring unusable UNPACK pragma on the")
1092 , speakNth n <+> ptext (sLit "argument of") <+> quotes (ppr con)]
1094 -------------------------------
1095 checkNewDataCon :: DataCon -> TcM ()
1096 -- Checks for the data constructor of a newtype
1098 = do { checkTc (isSingleton arg_tys) (newtypeFieldErr con (length arg_tys))
1100 ; checkTc (null eq_spec) (newtypePredError con)
1101 -- Return type is (T a b c)
1102 ; checkTc (null ex_tvs && null eq_theta && null dict_theta) (newtypeExError con)
1104 ; checkTc (not (any isBanged (dataConStrictMarks con)))
1105 (newtypeStrictError con)
1109 (_univ_tvs, ex_tvs, eq_spec, eq_theta, dict_theta, arg_tys, _res_ty) = dataConFullSig con
1111 -------------------------------
1112 checkValidClass :: Class -> TcM ()
1114 = do { constrained_class_methods <- xoptM Opt_ConstrainedClassMethods
1115 ; multi_param_type_classes <- xoptM Opt_MultiParamTypeClasses
1116 ; fundep_classes <- xoptM Opt_FunctionalDependencies
1118 -- Check that the class is unary, unless GlaExs
1119 ; checkTc (notNull tyvars) (nullaryClassErr cls)
1120 ; checkTc (multi_param_type_classes || unary) (classArityErr cls)
1121 ; checkTc (fundep_classes || null fundeps) (classFunDepsErr cls)
1123 -- Check the super-classes
1124 ; checkValidTheta (ClassSCCtxt (className cls)) theta
1126 -- Check the class operations
1127 ; mapM_ (check_op constrained_class_methods) op_stuff
1129 -- Check that if the class has generic methods, then the
1130 -- class has only one parameter. We can't do generic
1131 -- multi-parameter type classes!
1132 ; checkTc (unary || no_generics) (genericMultiParamErr cls)
1135 (tyvars, fundeps, theta, _, _, op_stuff) = classExtraBigSig cls
1136 unary = isSingleton tyvars
1137 no_generics = null [() | (_, GenDefMeth) <- op_stuff]
1139 check_op constrained_class_methods (sel_id, dm)
1140 = addErrCtxt (classOpCtxt sel_id tau) $ do
1141 { checkValidTheta SigmaCtxt (tail theta)
1142 -- The 'tail' removes the initial (C a) from the
1143 -- class itself, leaving just the method type
1145 ; traceTc "class op type" (ppr op_ty <+> ppr tau)
1146 ; checkValidType (FunSigCtxt op_name) tau
1148 -- Check that the type mentions at least one of
1149 -- the class type variables...or at least one reachable
1150 -- from one of the class variables. Example: tc223
1151 -- class Error e => Game b mv e | b -> mv e where
1152 -- newBoard :: MonadState b m => m ()
1153 -- Here, MonadState has a fundep m->b, so newBoard is fine
1154 ; let grown_tyvars = growThetaTyVars theta (mkVarSet tyvars)
1155 ; checkTc (tyVarsOfType tau `intersectsVarSet` grown_tyvars)
1156 (noClassTyVarErr cls sel_id)
1158 -- Check that for a generic method, the type of
1159 -- the method is sufficiently simple
1160 ; checkTc (dm /= GenDefMeth || validGenericMethodType tau)
1161 (badGenericMethodType op_name op_ty)
1164 op_name = idName sel_id
1165 op_ty = idType sel_id
1166 (_,theta1,tau1) = tcSplitSigmaTy op_ty
1167 (_,theta2,tau2) = tcSplitSigmaTy tau1
1168 (theta,tau) | constrained_class_methods = (theta1 ++ theta2, tau2)
1169 | otherwise = (theta1, mkPhiTy (tail theta1) tau1)
1170 -- Ugh! The function might have a type like
1171 -- op :: forall a. C a => forall b. (Eq b, Eq a) => tau2
1172 -- With -XConstrainedClassMethods, we want to allow this, even though the inner
1173 -- forall has an (Eq a) constraint. Whereas in general, each constraint
1174 -- in the context of a for-all must mention at least one quantified
1175 -- type variable. What a mess!
1179 %************************************************************************
1181 Building record selectors
1183 %************************************************************************
1186 mkDefaultMethodIds :: [TyThing] -> [Id]
1187 -- See Note [Default method Ids and Template Haskell]
1188 mkDefaultMethodIds things
1189 = [ mkDefaultMethodId sel_id dm_name
1190 | AClass cls <- things
1191 , (sel_id, DefMeth dm_name) <- classOpItems cls ]
1194 Note [Default method Ids and Template Haskell]
1195 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1196 Consider this (Trac #4169):
1197 class Numeric a where
1199 fromIntegerNum = ...
1202 ast = [d| instance Numeric Int |]
1204 When we typecheck 'ast' we have done the first pass over the class decl
1205 (in tcTyClDecls), but we have not yet typechecked the default-method
1206 declarations (becuase they can mention value declarations). So we
1207 must bring the default method Ids into scope first (so they can be seen
1208 when typechecking the [d| .. |] quote, and typecheck them later.
1211 mkRecSelBinds :: [TyThing] -> HsValBinds Name
1212 -- NB We produce *un-typechecked* bindings, rather like 'deriving'
1213 -- This makes life easier, because the later type checking will add
1214 -- all necessary type abstractions and applications
1215 mkRecSelBinds ty_things
1216 = ValBindsOut [(NonRecursive, b) | b <- binds] sigs
1218 (sigs, binds) = unzip rec_sels
1219 rec_sels = map mkRecSelBind [ (tc,fld)
1220 | ATyCon tc <- ty_things
1221 , fld <- tyConFields tc ]
1223 mkRecSelBind :: (TyCon, FieldLabel) -> (LSig Name, LHsBinds Name)
1224 mkRecSelBind (tycon, sel_name)
1225 = (L loc (IdSig sel_id), unitBag (L loc sel_bind))
1227 loc = getSrcSpan tycon
1228 sel_id = Var.mkLocalVar rec_details sel_name sel_ty vanillaIdInfo
1229 rec_details = RecSelId { sel_tycon = tycon, sel_naughty = is_naughty }
1231 -- Find a representative constructor, con1
1232 all_cons = tyConDataCons tycon
1233 cons_w_field = [ con | con <- all_cons
1234 , sel_name `elem` dataConFieldLabels con ]
1235 con1 = ASSERT( not (null cons_w_field) ) head cons_w_field
1237 -- Selector type; Note [Polymorphic selectors]
1238 field_ty = dataConFieldType con1 sel_name
1239 data_ty = dataConOrigResTy con1
1240 data_tvs = tyVarsOfType data_ty
1241 is_naughty = not (tyVarsOfType field_ty `subVarSet` data_tvs)
1242 (field_tvs, field_theta, field_tau) = tcSplitSigmaTy field_ty
1243 sel_ty | is_naughty = unitTy -- See Note [Naughty record selectors]
1244 | otherwise = mkForAllTys (varSetElems data_tvs ++ field_tvs) $
1245 mkPhiTy (dataConStupidTheta con1) $ -- Urgh!
1246 mkPhiTy field_theta $ -- Urgh!
1247 mkFunTy data_ty field_tau
1249 -- Make the binding: sel (C2 { fld = x }) = x
1250 -- sel (C7 { fld = x }) = x
1251 -- where cons_w_field = [C2,C7]
1252 sel_bind | is_naughty = mkFunBind sel_lname [mkSimpleMatch [] unit_rhs]
1253 | otherwise = mkFunBind sel_lname (map mk_match cons_w_field ++ deflt)
1254 mk_match con = mkSimpleMatch [L loc (mk_sel_pat con)]
1255 (L loc (HsVar field_var))
1256 mk_sel_pat con = ConPatIn (L loc (getName con)) (RecCon rec_fields)
1257 rec_fields = HsRecFields { rec_flds = [rec_field], rec_dotdot = Nothing }
1258 rec_field = HsRecField { hsRecFieldId = sel_lname
1259 , hsRecFieldArg = nlVarPat field_var
1260 , hsRecPun = False }
1261 sel_lname = L loc sel_name
1262 field_var = mkInternalName (mkBuiltinUnique 1) (getOccName sel_name) loc
1264 -- Add catch-all default case unless the case is exhaustive
1265 -- We do this explicitly so that we get a nice error message that
1266 -- mentions this particular record selector
1267 deflt | not (any is_unused all_cons) = []
1268 | otherwise = [mkSimpleMatch [nlWildPat]
1269 (nlHsApp (nlHsVar (getName rEC_SEL_ERROR_ID))
1272 -- Do not add a default case unless there are unmatched
1273 -- constructors. We must take account of GADTs, else we
1274 -- get overlap warning messages from the pattern-match checker
1275 is_unused con = not (con `elem` cons_w_field
1276 || dataConCannotMatch inst_tys con)
1277 inst_tys = tyConAppArgs data_ty
1279 unit_rhs = mkLHsTupleExpr []
1280 msg_lit = HsStringPrim $ mkFastString $
1281 occNameString (getOccName sel_name)
1284 tyConFields :: TyCon -> [FieldLabel]
1286 | isAlgTyCon tc = nub (concatMap dataConFieldLabels (tyConDataCons tc))
1290 Note [Polymorphic selectors]
1291 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1292 When a record has a polymorphic field, we pull the foralls out to the front.
1293 data T = MkT { f :: forall a. [a] -> a }
1294 Then f :: forall a. T -> [a] -> a
1295 NOT f :: T -> forall a. [a] -> a
1297 This is horrid. It's only needed in deeply obscure cases, which I hate.
1298 The only case I know is test tc163, which is worth looking at. It's far
1299 from clear that this test should succeed at all!
1301 Note [Naughty record selectors]
1302 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1303 A "naughty" field is one for which we can't define a record
1304 selector, because an existential type variable would escape. For example:
1305 data T = forall a. MkT { x,y::a }
1306 We obviously can't define
1308 Nevertheless we *do* put a RecSelId into the type environment
1309 so that if the user tries to use 'x' as a selector we can bleat
1310 helpfully, rather than saying unhelpfully that 'x' is not in scope.
1311 Hence the sel_naughty flag, to identify record selectors that don't really exist.
1313 In general, a field is "naughty" if its type mentions a type variable that
1314 isn't in the result type of the constructor. Note that this *allows*
1315 GADT record selectors (Note [GADT record selectors]) whose types may look
1316 like sel :: T [a] -> a
1318 For naughty selectors we make a dummy binding
1320 for naughty selectors, so that the later type-check will add them to the
1321 environment, and they'll be exported. The function is never called, because
1322 the tyepchecker spots the sel_naughty field.
1324 Note [GADT record selectors]
1325 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1326 For GADTs, we require that all constructors with a common field 'f' have the same
1327 result type (modulo alpha conversion). [Checked in TcTyClsDecls.checkValidTyCon]
1330 T1 { f :: Maybe a } :: T [a]
1331 T2 { f :: Maybe a, y :: b } :: T [a]
1333 and now the selector takes that result type as its argument:
1334 f :: forall a. T [a] -> Maybe a
1336 Details: the "real" types of T1,T2 are:
1337 T1 :: forall r a. (r~[a]) => a -> T r
1338 T2 :: forall r a b. (r~[a]) => a -> b -> T r
1340 So the selector loooks like this:
1341 f :: forall a. T [a] -> Maybe a
1344 T1 c (g:[a]~[c]) (v:Maybe c) -> v `cast` Maybe (right (sym g))
1345 T2 c d (g:[a]~[c]) (v:Maybe c) (w:d) -> v `cast` Maybe (right (sym g))
1347 Note the forall'd tyvars of the selector are just the free tyvars
1348 of the result type; there may be other tyvars in the constructor's
1349 type (e.g. 'b' in T2).
1351 Note the need for casts in the result!
1353 Note [Selector running example]
1354 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1355 It's OK to combine GADTs and type families. Here's a running example:
1357 data instance T [a] where
1358 T1 { fld :: b } :: T [Maybe b]
1360 The representation type looks like this
1362 T1 { fld :: b } :: :R7T (Maybe b)
1364 and there's coercion from the family type to the representation type
1365 :CoR7T a :: T [a] ~ :R7T a
1367 The selector we want for fld looks like this:
1369 fld :: forall b. T [Maybe b] -> b
1370 fld = /\b. \(d::T [Maybe b]).
1371 case d `cast` :CoR7T (Maybe b) of
1374 The scrutinee of the case has type :R7T (Maybe b), which can be
1375 gotten by appying the eq_spec to the univ_tvs of the data con.
1377 %************************************************************************
1381 %************************************************************************
1384 resultTypeMisMatch :: Name -> DataCon -> DataCon -> SDoc
1385 resultTypeMisMatch field_name con1 con2
1386 = vcat [sep [ptext (sLit "Constructors") <+> ppr con1 <+> ptext (sLit "and") <+> ppr con2,
1387 ptext (sLit "have a common field") <+> quotes (ppr field_name) <> comma],
1388 nest 2 $ ptext (sLit "but have different result types")]
1390 fieldTypeMisMatch :: Name -> DataCon -> DataCon -> SDoc
1391 fieldTypeMisMatch field_name con1 con2
1392 = sep [ptext (sLit "Constructors") <+> ppr con1 <+> ptext (sLit "and") <+> ppr con2,
1393 ptext (sLit "give different types for field"), quotes (ppr field_name)]
1395 dataConCtxt :: Outputable a => a -> SDoc
1396 dataConCtxt con = ptext (sLit "In the definition of data constructor") <+> quotes (ppr con)
1398 classOpCtxt :: Var -> Type -> SDoc
1399 classOpCtxt sel_id tau = sep [ptext (sLit "When checking the class method:"),
1400 nest 2 (ppr sel_id <+> dcolon <+> ppr tau)]
1402 nullaryClassErr :: Class -> SDoc
1404 = ptext (sLit "No parameters for class") <+> quotes (ppr cls)
1406 classArityErr :: Class -> SDoc
1408 = vcat [ptext (sLit "Too many parameters for class") <+> quotes (ppr cls),
1409 parens (ptext (sLit "Use -XMultiParamTypeClasses to allow multi-parameter classes"))]
1411 classFunDepsErr :: Class -> SDoc
1413 = vcat [ptext (sLit "Fundeps in class") <+> quotes (ppr cls),
1414 parens (ptext (sLit "Use -XFunctionalDependencies to allow fundeps"))]
1416 noClassTyVarErr :: Class -> Var -> SDoc
1417 noClassTyVarErr clas op
1418 = sep [ptext (sLit "The class method") <+> quotes (ppr op),
1419 ptext (sLit "mentions none of the type variables of the class") <+>
1420 ppr clas <+> hsep (map ppr (classTyVars clas))]
1422 genericMultiParamErr :: Class -> SDoc
1423 genericMultiParamErr clas
1424 = ptext (sLit "The multi-parameter class") <+> quotes (ppr clas) <+>
1425 ptext (sLit "cannot have generic methods")
1427 badGenericMethodType :: Name -> Kind -> SDoc
1428 badGenericMethodType op op_ty
1429 = hang (ptext (sLit "Generic method type is too complex"))
1430 2 (vcat [ppr op <+> dcolon <+> ppr op_ty,
1431 ptext (sLit "You can only use type variables, arrows, lists, and tuples")])
1433 recSynErr :: [LTyClDecl Name] -> TcRn ()
1435 = setSrcSpan (getLoc (head sorted_decls)) $
1436 addErr (sep [ptext (sLit "Cycle in type synonym declarations:"),
1437 nest 2 (vcat (map ppr_decl sorted_decls))])
1439 sorted_decls = sortLocated syn_decls
1440 ppr_decl (L loc decl) = ppr loc <> colon <+> ppr decl
1442 recClsErr :: [Located (TyClDecl Name)] -> TcRn ()
1444 = setSrcSpan (getLoc (head sorted_decls)) $
1445 addErr (sep [ptext (sLit "Cycle in class declarations (via superclasses):"),
1446 nest 2 (vcat (map ppr_decl sorted_decls))])
1448 sorted_decls = sortLocated cls_decls
1449 ppr_decl (L loc decl) = ppr loc <> colon <+> ppr (decl { tcdSigs = [] })
1451 sortLocated :: [Located a] -> [Located a]
1452 sortLocated things = sortLe le things
1454 le (L l1 _) (L l2 _) = l1 <= l2
1456 badDataConTyCon :: DataCon -> Type -> Type -> SDoc
1457 badDataConTyCon data_con res_ty_tmpl actual_res_ty
1458 = hang (ptext (sLit "Data constructor") <+> quotes (ppr data_con) <+>
1459 ptext (sLit "returns type") <+> quotes (ppr actual_res_ty))
1460 2 (ptext (sLit "instead of an instance of its parent type") <+> quotes (ppr res_ty_tmpl))
1462 badGadtDecl :: Name -> SDoc
1464 = vcat [ ptext (sLit "Illegal generalised algebraic data declaration for") <+> quotes (ppr tc_name)
1465 , nest 2 (parens $ ptext (sLit "Use -XGADTs to allow GADTs")) ]
1467 badExistential :: Located Name -> SDoc
1468 badExistential con_name
1469 = hang (ptext (sLit "Data constructor") <+> quotes (ppr con_name) <+>
1470 ptext (sLit "has existential type variables, a context, or a specialised result type"))
1471 2 (parens $ ptext (sLit "Use -XExistentialQuantification or -XGADTs to allow this"))
1473 badStupidTheta :: Name -> SDoc
1474 badStupidTheta tc_name
1475 = ptext (sLit "A data type declared in GADT style cannot have a context:") <+> quotes (ppr tc_name)
1477 newtypeConError :: Name -> Int -> SDoc
1478 newtypeConError tycon n
1479 = sep [ptext (sLit "A newtype must have exactly one constructor,"),
1480 nest 2 $ ptext (sLit "but") <+> quotes (ppr tycon) <+> ptext (sLit "has") <+> speakN n ]
1482 newtypeExError :: DataCon -> SDoc
1484 = sep [ptext (sLit "A newtype constructor cannot have an existential context,"),
1485 nest 2 $ ptext (sLit "but") <+> quotes (ppr con) <+> ptext (sLit "does")]
1487 newtypeStrictError :: DataCon -> SDoc
1488 newtypeStrictError con
1489 = sep [ptext (sLit "A newtype constructor cannot have a strictness annotation,"),
1490 nest 2 $ ptext (sLit "but") <+> quotes (ppr con) <+> ptext (sLit "does")]
1492 newtypePredError :: DataCon -> SDoc
1493 newtypePredError con
1494 = sep [ptext (sLit "A newtype constructor must have a return type of form T a1 ... an"),
1495 nest 2 $ ptext (sLit "but") <+> quotes (ppr con) <+> ptext (sLit "does not")]
1497 newtypeFieldErr :: DataCon -> Int -> SDoc
1498 newtypeFieldErr con_name n_flds
1499 = sep [ptext (sLit "The constructor of a newtype must have exactly one field"),
1500 nest 2 $ ptext (sLit "but") <+> quotes (ppr con_name) <+> ptext (sLit "has") <+> speakN n_flds]
1502 badSigTyDecl :: Name -> SDoc
1503 badSigTyDecl tc_name
1504 = vcat [ ptext (sLit "Illegal kind signature") <+>
1505 quotes (ppr tc_name)
1506 , nest 2 (parens $ ptext (sLit "Use -XKindSignatures to allow kind signatures")) ]
1508 badFamInstDecl :: Outputable a => a -> SDoc
1509 badFamInstDecl tc_name
1510 = vcat [ ptext (sLit "Illegal family instance for") <+>
1511 quotes (ppr tc_name)
1512 , nest 2 (parens $ ptext (sLit "Use -XTypeFamilies to allow indexed type families")) ]
1514 tooManyParmsErr :: Located Name -> SDoc
1515 tooManyParmsErr tc_name
1516 = ptext (sLit "Family instance has too many parameters:") <+>
1517 quotes (ppr tc_name)
1519 tooFewParmsErr :: Arity -> SDoc
1520 tooFewParmsErr arity
1521 = ptext (sLit "Family instance has too few parameters; expected") <+>
1524 wrongNumberOfParmsErr :: Arity -> SDoc
1525 wrongNumberOfParmsErr exp_arity
1526 = ptext (sLit "Number of parameters must match family declaration; expected")
1529 badBootFamInstDeclErr :: SDoc
1530 badBootFamInstDeclErr
1531 = ptext (sLit "Illegal family instance in hs-boot file")
1533 notFamily :: TyCon -> SDoc
1535 = vcat [ ptext (sLit "Illegal family instance for") <+> quotes (ppr tycon)
1536 , nest 2 $ parens (ppr tycon <+> ptext (sLit "is not an indexed type family"))]
1538 wrongKindOfFamily :: TyCon -> SDoc
1539 wrongKindOfFamily family
1540 = ptext (sLit "Wrong category of family instance; declaration was for a")
1543 kindOfFamily | isSynTyCon family = ptext (sLit "type synonym")
1544 | isAlgTyCon family = ptext (sLit "data type")
1545 | otherwise = pprPanic "wrongKindOfFamily" (ppr family)
1547 emptyConDeclsErr :: Name -> SDoc
1548 emptyConDeclsErr tycon
1549 = sep [quotes (ppr tycon) <+> ptext (sLit "has no constructors"),
1550 nest 2 $ ptext (sLit "(-XEmptyDataDecls permits this)")]