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 ( rEC_SEL_ERROR_ID, mkDefaultMethodId )
47 import Unique ( mkBuiltinUnique )
56 %************************************************************************
58 \subsection{Type checking for type and class declarations}
60 %************************************************************************
64 Consider a mutually-recursive group, binding
65 a type constructor T and a class C.
67 Step 1: getInitialKind
68 Construct a KindEnv by binding T and C to a kind variable
71 In that environment, do a kind check
73 Step 3: Zonk the kinds
75 Step 4: buildTyConOrClass
76 Construct an environment binding T to a TyCon and C to a Class.
77 a) Their kinds comes from zonking the relevant kind variable
78 b) Their arity (for synonyms) comes direct from the decl
79 c) The funcional dependencies come from the decl
80 d) The rest comes a knot-tied binding of T and C, returned from Step 4
81 e) The variances of the tycons in the group is calculated from
85 In this environment, walk over the decls, constructing the TyCons and Classes.
86 This uses in a strict way items (a)-(c) above, which is why they must
87 be constructed in Step 4. Feed the results back to Step 4.
88 For this step, pass the is-recursive flag as the wimp-out flag
92 Step 6: Extend environment
93 We extend the type environment with bindings not only for the TyCons and Classes,
94 but also for their "implicit Ids" like data constructors and class selectors
96 Step 7: checkValidTyCl
97 For a recursive group only, check all the decls again, just
98 to check all the side conditions on validity. We could not
99 do this before because we were in a mutually recursive knot.
101 Identification of recursive TyCons
102 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
103 The knot-tying parameters: @rec_details_list@ is an alist mapping @Name@s to
106 Identifying a TyCon as recursive serves two purposes
108 1. Avoid infinite types. Non-recursive newtypes are treated as
109 "transparent", like type synonyms, after the type checker. If we did
110 this for all newtypes, we'd get infinite types. So we figure out for
111 each newtype whether it is "recursive", and add a coercion if so. In
112 effect, we are trying to "cut the loops" by identifying a loop-breaker.
114 2. Avoid infinite unboxing. This is nothing to do with newtypes.
118 Well, this function diverges, but we don't want the strictness analyser
119 to diverge. But the strictness analyser will diverge because it looks
120 deeper and deeper into the structure of T. (I believe there are
121 examples where the function does something sane, and the strictness
122 analyser still diverges, but I can't see one now.)
124 Now, concerning (1), the FC2 branch currently adds a coercion for ALL
125 newtypes. I did this as an experiment, to try to expose cases in which
126 the coercions got in the way of optimisations. If it turns out that we
127 can indeed always use a coercion, then we don't risk recursive types,
128 and don't need to figure out what the loop breakers are.
130 For newtype *families* though, we will always have a coercion, so they
131 are always loop breakers! So you can easily adjust the current
132 algorithm by simply treating all newtype families as loop breakers (and
133 indeed type families). I think.
136 tcTyAndClassDecls :: ModDetails -> [LTyClDecl Name]
137 -> TcM (TcGblEnv, -- Input env extended by types and classes
138 -- and their implicit Ids,DataCons
139 HsValBinds Name, -- Renamed bindings for record selectors
140 [Id]) -- Default method ids
142 -- Fails if there are any errors
144 tcTyAndClassDecls boot_details allDecls
145 = checkNoErrs $ -- The code recovers internally, but if anything gave rise to
146 -- an error we'd better stop now, to avoid a cascade
147 do { -- Omit instances of type families; they are handled together
148 -- with the *heads* of class instances
149 ; let decls = filter (not . isFamInstDecl . unLoc) allDecls
151 -- First check for cyclic type synonysm or classes
152 -- See notes with checkCycleErrs
153 ; checkCycleErrs decls
155 ; traceTc (text "tcTyAndCl" <+> ppr mod)
156 ; (syn_tycons, alg_tyclss) <- fixM (\ ~(_rec_syn_tycons, rec_alg_tyclss) ->
157 do { let { -- Seperate ordinary synonyms from all other type and
158 -- class declarations and add all associated type
159 -- declarations from type classes. The latter is
160 -- required so that the temporary environment for the
161 -- knot includes all associated family declarations.
162 ; (syn_decls, alg_decls) = partition (isSynDecl . unLoc)
164 ; alg_at_decls = concatMap addATs alg_decls
166 -- Extend the global env with the knot-tied results
167 -- for data types and classes
169 -- We must populate the environment with the loop-tied
170 -- T's right away, because the kind checker may "fault
171 -- in" some type constructors that recursively
173 ; let gbl_things = mkGlobalThings alg_at_decls rec_alg_tyclss
174 ; tcExtendRecEnv gbl_things $ do
176 -- Kind-check the declarations
177 { (kc_syn_decls, kc_alg_decls) <- kcTyClDecls syn_decls alg_decls
179 ; let { -- Calculate rec-flag
180 ; calc_rec = calcRecFlags boot_details rec_alg_tyclss
181 ; tc_decl = addLocM (tcTyClDecl calc_rec) }
183 -- Type-check the type synonyms, and extend the envt
184 ; syn_tycons <- tcSynDecls kc_syn_decls
185 ; tcExtendGlobalEnv syn_tycons $ do
187 -- Type-check the data types and classes
188 { alg_tyclss <- mapM tc_decl kc_alg_decls
189 ; return (syn_tycons, concat alg_tyclss)
191 -- Finished with knot-tying now
192 -- Extend the environment with the finished things
193 ; tcExtendGlobalEnv (syn_tycons ++ alg_tyclss) $ do
195 -- Perform the validity check
196 { traceTc (text "ready for validity check")
197 ; mapM_ (addLocM checkValidTyCl) decls
198 ; traceTc (text "done")
200 -- Add the implicit things;
201 -- we want them in the environment because
202 -- they may be mentioned in interface files
203 -- NB: All associated types and their implicit things will be added a
204 -- second time here. This doesn't matter as the definitions are
206 ; let { implicit_things = concatMap implicitTyThings alg_tyclss
207 ; rec_sel_binds = mkRecSelBinds alg_tyclss
208 ; dm_ids = mkDefaultMethodIds alg_tyclss }
209 ; traceTc ((text "Adding" <+> ppr alg_tyclss)
210 $$ (text "and" <+> ppr implicit_things))
211 ; env <- tcExtendGlobalEnv implicit_things getGblEnv
212 ; return (env, rec_sel_binds, dm_ids) }
215 -- Pull associated types out of class declarations, to tie them into the
217 -- NB: We put them in the same place in the list as `tcTyClDecl' will
218 -- eventually put the matching `TyThing's. That's crucial; otherwise,
219 -- the two argument lists of `mkGlobalThings' don't match up.
220 addATs decl@(L _ (ClassDecl {tcdATs = ats})) = decl : ats
223 mkGlobalThings :: [LTyClDecl Name] -- The decls
224 -> [TyThing] -- Knot-tied, in 1-1 correspondence with the decls
226 -- Driven by the Decls, and treating the TyThings lazily
227 -- make a TypeEnv for the new things
228 mkGlobalThings decls things
229 = map mk_thing (decls `zipLazy` things)
231 mk_thing (L _ (ClassDecl {tcdLName = L _ name}), ~(AClass cl))
233 mk_thing (L _ decl, ~(ATyCon tc))
234 = (tcdName decl, ATyCon tc)
238 %************************************************************************
240 Type checking family instances
242 %************************************************************************
244 Family instances are somewhat of a hybrid. They are processed together with
245 class instance heads, but can contain data constructors and hence they share a
246 lot of kinding and type checking code with ordinary algebraic data types (and
250 tcFamInstDecl :: TopLevelFlag -> LTyClDecl Name -> TcM TyThing
251 tcFamInstDecl top_lvl (L loc decl)
252 = -- Prime error recovery, set source location
255 do { -- type family instances require -XTypeFamilies
256 -- and can't (currently) be in an hs-boot file
257 ; type_families <- doptM Opt_TypeFamilies
258 ; is_boot <- tcIsHsBoot -- Are we compiling an hs-boot file?
259 ; checkTc type_families $ badFamInstDecl (tcdLName decl)
260 ; checkTc (not is_boot) $ badBootFamInstDeclErr
262 -- Perform kind and type checking
263 ; tc <- tcFamInstDecl1 decl
264 ; checkValidTyCon tc -- Remember to check validity;
265 -- no recursion to worry about here
267 -- Check that toplevel type instances are not for associated types.
268 ; when (isTopLevel top_lvl && isAssocFamily tc)
269 (addErr $ assocInClassErr (tcdName decl))
271 ; return (ATyCon tc) }
273 isAssocFamily :: TyCon -> Bool -- Is an assocaited type
275 = case tyConFamInst_maybe tycon of
276 Nothing -> panic "isAssocFamily: no family?!?"
277 Just (fam, _) -> isTyConAssoc fam
279 assocInClassErr :: Name -> SDoc
281 = ptext (sLit "Associated type") <+> quotes (ppr name) <+>
282 ptext (sLit "must be inside a class instance")
286 tcFamInstDecl1 :: TyClDecl Name -> TcM TyCon
289 tcFamInstDecl1 (decl@TySynonym {tcdLName = L loc tc_name})
290 = kcIdxTyPats decl $ \k_tvs k_typats resKind family ->
291 do { -- check that the family declaration is for a synonym
292 checkTc (isOpenTyCon family) (notFamily family)
293 ; checkTc (isSynTyCon family) (wrongKindOfFamily family)
295 ; -- (1) kind check the right-hand side of the type equation
296 ; k_rhs <- kcCheckLHsType (tcdSynRhs decl) (EK resKind EkUnk)
297 -- ToDo: the ExpKind could be better
299 -- we need the exact same number of type parameters as the family
301 ; let famArity = tyConArity family
302 ; checkTc (length k_typats == famArity) $
303 wrongNumberOfParmsErr famArity
305 -- (2) type check type equation
306 ; tcTyVarBndrs k_tvs $ \t_tvs -> do { -- turn kinded into proper tyvars
307 ; t_typats <- mapM tcHsKindedType k_typats
308 ; t_rhs <- tcHsKindedType k_rhs
310 -- (3) check the well-formedness of the instance
311 ; checkValidTypeInst t_typats t_rhs
313 -- (4) construct representation tycon
314 ; rep_tc_name <- newFamInstTyConName tc_name t_typats loc
315 ; buildSynTyCon rep_tc_name t_tvs (SynonymTyCon t_rhs)
316 (typeKind t_rhs) (Just (family, t_typats))
319 -- "newtype instance" and "data instance"
320 tcFamInstDecl1 (decl@TyData {tcdND = new_or_data, tcdLName = L loc tc_name,
322 = kcIdxTyPats decl $ \k_tvs k_typats resKind fam_tycon ->
323 do { -- check that the family declaration is for the right kind
324 checkTc (isOpenTyCon fam_tycon) (notFamily fam_tycon)
325 ; checkTc (isAlgTyCon fam_tycon) (wrongKindOfFamily fam_tycon)
327 ; -- (1) kind check the data declaration as usual
328 ; k_decl <- kcDataDecl decl k_tvs
329 ; let k_ctxt = tcdCtxt k_decl
330 k_cons = tcdCons k_decl
332 -- result kind must be '*' (otherwise, we have too few patterns)
333 ; checkTc (isLiftedTypeKind resKind) $ tooFewParmsErr (tyConArity fam_tycon)
335 -- (2) type check indexed data type declaration
336 ; tcTyVarBndrs k_tvs $ \t_tvs -> do { -- turn kinded into proper tyvars
337 ; unbox_strict <- doptM Opt_UnboxStrictFields
339 -- kind check the type indexes and the context
340 ; t_typats <- mapM tcHsKindedType k_typats
341 ; stupid_theta <- tcHsKindedContext k_ctxt
344 -- (a) left-hand side contains no type family applications
345 -- (vanilla synonyms are fine, though, and we checked for
347 ; mapM_ checkTyFamFreeness t_typats
349 -- Check that we don't use GADT syntax in H98 world
350 ; gadt_ok <- doptM Opt_GADTs
351 ; checkTc (gadt_ok || consUseH98Syntax cons) (badGadtDecl tc_name)
353 -- (b) a newtype has exactly one constructor
354 ; checkTc (new_or_data == DataType || isSingleton k_cons) $
355 newtypeConError tc_name (length k_cons)
357 -- (4) construct representation tycon
358 ; rep_tc_name <- newFamInstTyConName tc_name t_typats loc
359 ; let ex_ok = True -- Existentials ok for type families!
360 ; fixM (\ rep_tycon -> do
361 { let orig_res_ty = mkTyConApp fam_tycon t_typats
362 ; data_cons <- tcConDecls unbox_strict ex_ok rep_tycon
363 (t_tvs, orig_res_ty) k_cons
366 DataType -> return (mkDataTyConRhs data_cons)
367 NewType -> ASSERT( not (null data_cons) )
368 mkNewTyConRhs rep_tc_name rep_tycon (head data_cons)
369 ; buildAlgTyCon rep_tc_name t_tvs stupid_theta tc_rhs Recursive
370 False h98_syntax (Just (fam_tycon, t_typats))
371 -- We always assume that indexed types are recursive. Why?
372 -- (1) Due to their open nature, we can never be sure that a
373 -- further instance might not introduce a new recursive
374 -- dependency. (2) They are always valid loop breakers as
375 -- they involve a coercion.
379 h98_syntax = case cons of -- All constructors have same shape
380 L _ (ConDecl { con_res = ResTyGADT _ }) : _ -> False
383 tcFamInstDecl1 d = pprPanic "tcFamInstDecl1" (ppr d)
385 -- Kind checking of indexed types
388 -- Kind check type patterns and kind annotate the embedded type variables.
390 -- * Here we check that a type instance matches its kind signature, but we do
391 -- not check whether there is a pattern for each type index; the latter
392 -- check is only required for type synonym instances.
394 kcIdxTyPats :: TyClDecl Name
395 -> ([LHsTyVarBndr Name] -> [LHsType Name] -> Kind -> TyCon -> TcM a)
396 -- ^^kinded tvs ^^kinded ty pats ^^res kind
398 kcIdxTyPats decl thing_inside
399 = kcHsTyVars (tcdTyVars decl) $ \tvs ->
400 do { let tc_name = tcdLName decl
401 ; fam_tycon <- tcLookupLocatedTyCon tc_name
402 ; let { (kinds, resKind) = splitKindFunTys (tyConKind fam_tycon)
403 ; hs_typats = fromJust $ tcdTyPats decl }
405 -- we may not have more parameters than the kind indicates
406 ; checkTc (length kinds >= length hs_typats) $
407 tooManyParmsErr (tcdLName decl)
409 -- type functions can have a higher-kinded result
410 ; let resultKind = mkArrowKinds (drop (length hs_typats) kinds) resKind
411 ; typats <- zipWithM kcCheckLHsType hs_typats
412 [ EK kind (EkArg (ppr tc_name) n)
413 | (kind,n) <- kinds `zip` [1..]]
414 ; thing_inside tvs typats resultKind fam_tycon
419 %************************************************************************
423 %************************************************************************
425 We need to kind check all types in the mutually recursive group
426 before we know the kind of the type variables. For example:
429 op :: D b => a -> b -> b
432 bop :: (Monad c) => ...
434 Here, the kind of the locally-polymorphic type variable "b"
435 depends on *all the uses of class D*. For example, the use of
436 Monad c in bop's type signature means that D must have kind Type->Type.
438 However type synonyms work differently. They can have kinds which don't
439 just involve (->) and *:
440 type R = Int# -- Kind #
441 type S a = Array# a -- Kind * -> #
442 type T a b = (# a,b #) -- Kind * -> * -> (# a,b #)
443 So we must infer their kinds from their right-hand sides *first* and then
444 use them, whereas for the mutually recursive data types D we bring into
445 scope kind bindings D -> k, where k is a kind variable, and do inference.
449 This treatment of type synonyms only applies to Haskell 98-style synonyms.
450 General type functions can be recursive, and hence, appear in `alg_decls'.
452 The kind of a type family is solely determinded by its kind signature;
453 hence, only kind signatures participate in the construction of the initial
454 kind environment (as constructed by `getInitialKind'). In fact, we ignore
455 instances of families altogether in the following. However, we need to
456 include the kinds of associated families into the construction of the
457 initial kind environment. (This is handled by `allDecls').
460 kcTyClDecls :: [LTyClDecl Name] -> [Located (TyClDecl Name)]
461 -> TcM ([LTyClDecl Name], [Located (TyClDecl Name)])
462 kcTyClDecls syn_decls alg_decls
463 = do { -- First extend the kind env with each data type, class, and
464 -- indexed type, mapping them to a type variable
465 let initialKindDecls = concat [allDecls decl | L _ decl <- alg_decls]
466 ; alg_kinds <- mapM getInitialKind initialKindDecls
467 ; tcExtendKindEnv alg_kinds $ do
469 -- Now kind-check the type synonyms, in dependency order
470 -- We do these differently to data type and classes,
471 -- because a type synonym can be an unboxed type
473 -- and a kind variable can't unify with UnboxedTypeKind
474 -- So we infer their kinds in dependency order
475 { (kc_syn_decls, syn_kinds) <- kcSynDecls (calcSynCycles syn_decls)
476 ; tcExtendKindEnv syn_kinds $ do
478 -- Now kind-check the data type, class, and kind signatures,
479 -- returning kind-annotated decls; we don't kind-check
480 -- instances of indexed types yet, but leave this to
482 { kc_alg_decls <- mapM (wrapLocM kcTyClDecl)
483 (filter (not . isFamInstDecl . unLoc) alg_decls)
485 ; return (kc_syn_decls, kc_alg_decls) }}}
487 -- get all declarations relevant for determining the initial kind
489 allDecls (decl@ClassDecl {tcdATs = ats}) = decl : [ at
492 allDecls decl | isFamInstDecl decl = []
495 ------------------------------------------------------------------------
496 getInitialKind :: TyClDecl Name -> TcM (Name, TcKind)
497 -- Only for data type, class, and indexed type declarations
498 -- Get as much info as possible from the data, class, or indexed type decl,
499 -- so as to maximise usefulness of error messages
501 = do { arg_kinds <- mapM (mk_arg_kind . unLoc) (tyClDeclTyVars decl)
502 ; res_kind <- mk_res_kind decl
503 ; return (tcdName decl, mkArrowKinds arg_kinds res_kind) }
505 mk_arg_kind (UserTyVar _ _) = newKindVar
506 mk_arg_kind (KindedTyVar _ kind) = return kind
508 mk_res_kind (TyFamily { tcdKind = Just kind }) = return kind
509 mk_res_kind (TyData { tcdKindSig = Just kind }) = return kind
510 -- On GADT-style declarations we allow a kind signature
511 -- data T :: *->* where { ... }
512 mk_res_kind _ = return liftedTypeKind
516 kcSynDecls :: [SCC (LTyClDecl Name)]
517 -> TcM ([LTyClDecl Name], -- Kind-annotated decls
518 [(Name,TcKind)]) -- Kind bindings
521 kcSynDecls (group : groups)
522 = do { (decl, nk) <- kcSynDecl group
523 ; (decls, nks) <- tcExtendKindEnv [nk] (kcSynDecls groups)
524 ; return (decl:decls, nk:nks) }
527 kcSynDecl :: SCC (LTyClDecl Name)
528 -> TcM (LTyClDecl Name, -- Kind-annotated decls
529 (Name,TcKind)) -- Kind bindings
530 kcSynDecl (AcyclicSCC (L loc decl))
531 = tcAddDeclCtxt decl $
532 kcHsTyVars (tcdTyVars decl) (\ k_tvs ->
533 do { traceTc (text "kcd1" <+> ppr (unLoc (tcdLName decl)) <+> brackets (ppr (tcdTyVars decl))
534 <+> brackets (ppr k_tvs))
535 ; (k_rhs, rhs_kind) <- kcLHsType (tcdSynRhs decl)
536 ; traceTc (text "kcd2" <+> ppr (unLoc (tcdLName decl)))
537 ; let tc_kind = foldr (mkArrowKind . hsTyVarKind . unLoc) rhs_kind k_tvs
538 ; return (L loc (decl { tcdTyVars = k_tvs, tcdSynRhs = k_rhs }),
539 (unLoc (tcdLName decl), tc_kind)) })
541 kcSynDecl (CyclicSCC decls)
542 = do { recSynErr decls; failM } -- Fail here to avoid error cascade
543 -- of out-of-scope tycons
545 ------------------------------------------------------------------------
546 kcTyClDecl :: TyClDecl Name -> TcM (TyClDecl Name)
547 -- Not used for type synonyms (see kcSynDecl)
549 kcTyClDecl decl@(TyData {})
550 = ASSERT( not . isFamInstDecl $ decl ) -- must not be a family instance
551 kcTyClDeclBody decl $
554 kcTyClDecl decl@(TyFamily {})
555 = kcFamilyDecl [] decl -- the empty list signals a toplevel decl
557 kcTyClDecl decl@(ClassDecl {tcdCtxt = ctxt, tcdSigs = sigs, tcdATs = ats})
558 = kcTyClDeclBody decl $ \ tvs' ->
559 do { ctxt' <- kcHsContext ctxt
560 ; ats' <- mapM (wrapLocM (kcFamilyDecl tvs')) ats
561 ; sigs' <- mapM (wrapLocM kc_sig) sigs
562 ; return (decl {tcdTyVars = tvs', tcdCtxt = ctxt', tcdSigs = sigs',
565 kc_sig (TypeSig nm op_ty) = do { op_ty' <- kcHsLiftedSigType op_ty
566 ; return (TypeSig nm op_ty') }
567 kc_sig other_sig = return other_sig
569 kcTyClDecl decl@(ForeignType {})
572 kcTyClDecl (TySynonym {}) = panic "kcTyClDecl TySynonym"
574 kcTyClDeclBody :: TyClDecl Name
575 -> ([LHsTyVarBndr Name] -> TcM a)
577 -- getInitialKind has made a suitably-shaped kind for the type or class
578 -- Unpack it, and attribute those kinds to the type variables
579 -- Extend the env with bindings for the tyvars, taken from
580 -- the kind of the tycon/class. Give it to the thing inside, and
581 -- check the result kind matches
582 kcTyClDeclBody decl thing_inside
583 = tcAddDeclCtxt decl $
584 do { tc_ty_thing <- tcLookupLocated (tcdLName decl)
585 ; let tc_kind = case tc_ty_thing of
587 _ -> pprPanic "kcTyClDeclBody" (ppr tc_ty_thing)
588 (kinds, _) = splitKindFunTys tc_kind
589 hs_tvs = tcdTyVars decl
590 kinded_tvs = ASSERT( length kinds >= length hs_tvs )
591 zipWith add_kind hs_tvs kinds
592 ; tcExtendKindEnvTvs kinded_tvs thing_inside }
594 add_kind (L loc (UserTyVar n _)) k = L loc (UserTyVar n k)
595 add_kind (L loc (KindedTyVar n _)) k = L loc (KindedTyVar n k)
597 -- Kind check a data declaration, assuming that we already extended the
598 -- kind environment with the type variables of the left-hand side (these
599 -- kinded type variables are also passed as the second parameter).
601 kcDataDecl :: TyClDecl Name -> [LHsTyVarBndr Name] -> TcM (TyClDecl Name)
602 kcDataDecl decl@(TyData {tcdND = new_or_data, tcdCtxt = ctxt, tcdCons = cons})
604 = do { ctxt' <- kcHsContext ctxt
605 ; cons' <- mapM (wrapLocM kc_con_decl) cons
606 ; return (decl {tcdTyVars = tvs, tcdCtxt = ctxt', tcdCons = cons'}) }
608 -- doc comments are typechecked to Nothing here
609 kc_con_decl con_decl@(ConDecl { con_name = name, con_qvars = ex_tvs
610 , con_cxt = ex_ctxt, con_details = details, con_res = res })
611 = addErrCtxt (dataConCtxt name) $
612 kcHsTyVars ex_tvs $ \ex_tvs' -> do
613 do { ex_ctxt' <- kcHsContext ex_ctxt
614 ; details' <- kc_con_details details
615 ; res' <- case res of
616 ResTyH98 -> return ResTyH98
617 ResTyGADT ty -> do { ty' <- kcHsSigType ty; return (ResTyGADT ty') }
618 ; return (con_decl { con_qvars = ex_tvs', con_cxt = ex_ctxt'
619 , con_details = details', con_res = res' }) }
621 kc_con_details (PrefixCon btys)
622 = do { btys' <- mapM kc_larg_ty btys
623 ; return (PrefixCon btys') }
624 kc_con_details (InfixCon bty1 bty2)
625 = do { bty1' <- kc_larg_ty bty1
626 ; bty2' <- kc_larg_ty bty2
627 ; return (InfixCon bty1' bty2') }
628 kc_con_details (RecCon fields)
629 = do { fields' <- mapM kc_field fields
630 ; return (RecCon fields') }
632 kc_field (ConDeclField fld bty d) = do { bty' <- kc_larg_ty bty
633 ; return (ConDeclField fld bty' d) }
635 kc_larg_ty bty = case new_or_data of
636 DataType -> kcHsSigType bty
637 NewType -> kcHsLiftedSigType bty
638 -- Can't allow an unlifted type for newtypes, because we're effectively
639 -- going to remove the constructor while coercing it to a lifted type.
640 -- And newtypes can't be bang'd
641 kcDataDecl d _ = pprPanic "kcDataDecl" (ppr d)
643 -- Kind check a family declaration or type family default declaration.
645 kcFamilyDecl :: [LHsTyVarBndr Name] -- tyvars of enclosing class decl if any
646 -> TyClDecl Name -> TcM (TyClDecl Name)
647 kcFamilyDecl classTvs decl@(TyFamily {tcdKind = kind})
648 = kcTyClDeclBody decl $ \tvs' ->
649 do { mapM_ unifyClassParmKinds tvs'
650 ; return (decl {tcdTyVars = tvs',
651 tcdKind = kind `mplus` Just liftedTypeKind})
652 -- default result kind is '*'
655 unifyClassParmKinds (L _ tv)
656 | (n,k) <- hsTyVarNameKind tv
657 , Just classParmKind <- lookup n classTyKinds
658 = unifyKind k classParmKind
659 | otherwise = return ()
660 classTyKinds = [hsTyVarNameKind tv | L _ tv <- classTvs]
662 kcFamilyDecl _ (TySynonym {}) -- type family defaults
663 = panic "TcTyClsDecls.kcFamilyDecl: not implemented yet"
664 kcFamilyDecl _ d = pprPanic "kcFamilyDecl" (ppr d)
668 %************************************************************************
670 \subsection{Type checking}
672 %************************************************************************
675 tcSynDecls :: [LTyClDecl Name] -> TcM [TyThing]
676 tcSynDecls [] = return []
677 tcSynDecls (decl : decls)
678 = do { syn_tc <- addLocM tcSynDecl decl
679 ; syn_tcs <- tcExtendGlobalEnv [syn_tc] (tcSynDecls decls)
680 ; return (syn_tc : syn_tcs) }
683 tcSynDecl :: TyClDecl Name -> TcM TyThing
685 (TySynonym {tcdLName = L _ tc_name, tcdTyVars = tvs, tcdSynRhs = rhs_ty})
686 = tcTyVarBndrs tvs $ \ tvs' -> do
687 { traceTc (text "tcd1" <+> ppr tc_name)
688 ; rhs_ty' <- tcHsKindedType rhs_ty
689 ; tycon <- buildSynTyCon tc_name tvs' (SynonymTyCon rhs_ty')
690 (typeKind rhs_ty') Nothing
691 ; return (ATyCon tycon)
693 tcSynDecl d = pprPanic "tcSynDecl" (ppr d)
696 tcTyClDecl :: (Name -> RecFlag) -> TyClDecl Name -> TcM [TyThing]
698 tcTyClDecl calc_isrec decl
699 = tcAddDeclCtxt decl (tcTyClDecl1 calc_isrec decl)
701 -- "type family" declarations
702 tcTyClDecl1 :: (Name -> RecFlag) -> TyClDecl Name -> TcM [TyThing]
703 tcTyClDecl1 _calc_isrec
704 (TyFamily {tcdFlavour = TypeFamily,
705 tcdLName = L _ tc_name, tcdTyVars = tvs,
706 tcdKind = Just kind}) -- NB: kind at latest added during kind checking
707 = tcTyVarBndrs tvs $ \ tvs' -> do
708 { traceTc (text "type family: " <+> ppr tc_name)
710 -- Check that we don't use families without -XTypeFamilies
711 ; idx_tys <- doptM Opt_TypeFamilies
712 ; checkTc idx_tys $ badFamInstDecl tc_name
714 ; tycon <- buildSynTyCon tc_name tvs' (OpenSynTyCon kind Nothing) kind Nothing
715 ; return [ATyCon tycon]
718 -- "data family" declaration
719 tcTyClDecl1 _calc_isrec
720 (TyFamily {tcdFlavour = DataFamily,
721 tcdLName = L _ tc_name, tcdTyVars = tvs, tcdKind = mb_kind})
722 = tcTyVarBndrs tvs $ \ tvs' -> do
723 { traceTc (text "data family: " <+> ppr tc_name)
724 ; extra_tvs <- tcDataKindSig mb_kind
725 ; let final_tvs = tvs' ++ extra_tvs -- we may not need these
728 -- Check that we don't use families without -XTypeFamilies
729 ; idx_tys <- doptM Opt_TypeFamilies
730 ; checkTc idx_tys $ badFamInstDecl tc_name
732 ; tycon <- buildAlgTyCon tc_name final_tvs []
733 mkOpenDataTyConRhs Recursive False True Nothing
734 ; return [ATyCon tycon]
737 -- "newtype" and "data"
738 -- NB: not used for newtype/data instances (whether associated or not)
739 tcTyClDecl1 calc_isrec
740 (TyData {tcdND = new_or_data, tcdCtxt = ctxt, tcdTyVars = tvs,
741 tcdLName = L _ tc_name, tcdKindSig = mb_ksig, tcdCons = cons})
742 = tcTyVarBndrs tvs $ \ tvs' -> do
743 { extra_tvs <- tcDataKindSig mb_ksig
744 ; let final_tvs = tvs' ++ extra_tvs
745 ; stupid_theta <- tcHsKindedContext ctxt
746 ; want_generic <- doptM Opt_Generics
747 ; unbox_strict <- doptM Opt_UnboxStrictFields
748 ; empty_data_decls <- doptM Opt_EmptyDataDecls
749 ; kind_signatures <- doptM Opt_KindSignatures
750 ; existential_ok <- doptM Opt_ExistentialQuantification
751 ; gadt_ok <- doptM Opt_GADTs
752 ; is_boot <- tcIsHsBoot -- Are we compiling an hs-boot file?
753 ; let ex_ok = existential_ok || gadt_ok -- Data cons can have existential context
755 -- Check that we don't use GADT syntax in H98 world
756 ; checkTc (gadt_ok || h98_syntax) (badGadtDecl tc_name)
758 -- Check that we don't use kind signatures without Glasgow extensions
759 ; checkTc (kind_signatures || isNothing mb_ksig) (badSigTyDecl tc_name)
761 -- Check that the stupid theta is empty for a GADT-style declaration
762 ; checkTc (null stupid_theta || h98_syntax) (badStupidTheta tc_name)
764 -- Check that a newtype has exactly one constructor
765 -- Do this before checking for empty data decls, so that
766 -- we don't suggest -XEmptyDataDecls for newtypes
767 ; checkTc (new_or_data == DataType || isSingleton cons)
768 (newtypeConError tc_name (length cons))
770 -- Check that there's at least one condecl,
771 -- or else we're reading an hs-boot file, or -XEmptyDataDecls
772 ; checkTc (not (null cons) || empty_data_decls || is_boot)
773 (emptyConDeclsErr tc_name)
775 ; tycon <- fixM (\ tycon -> do
776 { let res_ty = mkTyConApp tycon (mkTyVarTys final_tvs)
777 ; data_cons <- tcConDecls unbox_strict ex_ok
778 tycon (final_tvs, res_ty) cons
780 if null cons && is_boot -- In a hs-boot file, empty cons means
781 then return AbstractTyCon -- "don't know"; hence Abstract
782 else case new_or_data of
783 DataType -> return (mkDataTyConRhs data_cons)
784 NewType -> ASSERT( not (null data_cons) )
785 mkNewTyConRhs tc_name tycon (head data_cons)
786 ; buildAlgTyCon tc_name final_tvs stupid_theta tc_rhs is_rec
787 (want_generic && canDoGenerics data_cons) (not h98_syntax) Nothing
789 ; return [ATyCon tycon]
792 is_rec = calc_isrec tc_name
793 h98_syntax = consUseH98Syntax cons
795 tcTyClDecl1 calc_isrec
796 (ClassDecl {tcdLName = L _ class_name, tcdTyVars = tvs,
797 tcdCtxt = ctxt, tcdMeths = meths,
798 tcdFDs = fundeps, tcdSigs = sigs, tcdATs = ats} )
799 = tcTyVarBndrs tvs $ \ tvs' -> do
800 { ctxt' <- tcHsKindedContext ctxt
801 ; fds' <- mapM (addLocM tc_fundep) fundeps
802 ; atss <- mapM (addLocM (tcTyClDecl1 (const Recursive))) ats
803 -- NB: 'ats' only contains "type family" and "data family"
804 -- declarations as well as type family defaults
805 ; let ats' = map (setAssocFamilyPermutation tvs') (concat atss)
806 ; sig_stuff <- tcClassSigs class_name sigs meths
807 ; clas <- fixM (\ clas ->
808 let -- This little knot is just so we can get
809 -- hold of the name of the class TyCon, which we
810 -- need to look up its recursiveness
811 tycon_name = tyConName (classTyCon clas)
812 tc_isrec = calc_isrec tycon_name
814 buildClass False {- Must include unfoldings for selectors -}
815 class_name tvs' ctxt' fds' ats'
817 ; return (AClass clas : ats')
818 -- NB: Order is important due to the call to `mkGlobalThings' when
819 -- tying the the type and class declaration type checking knot.
822 tc_fundep (tvs1, tvs2) = do { tvs1' <- mapM tcLookupTyVar tvs1 ;
823 ; tvs2' <- mapM tcLookupTyVar tvs2 ;
824 ; return (tvs1', tvs2') }
827 (ForeignType {tcdLName = L _ tc_name, tcdExtName = tc_ext_name})
828 = return [ATyCon (mkForeignTyCon tc_name tc_ext_name liftedTypeKind 0)]
830 tcTyClDecl1 _ d = pprPanic "tcTyClDecl1" (ppr d)
832 -----------------------------------
833 tcConDecls :: Bool -> Bool -> TyCon -> ([TyVar], Type)
834 -> [LConDecl Name] -> TcM [DataCon]
835 tcConDecls unbox ex_ok rep_tycon res_tmpl cons
836 = mapM (addLocM (tcConDecl unbox ex_ok rep_tycon res_tmpl)) cons
838 tcConDecl :: Bool -- True <=> -funbox-strict_fields
839 -> Bool -- True <=> -XExistentialQuantificaton or -XGADTs
840 -> TyCon -- Representation tycon
841 -> ([TyVar], Type) -- Return type template (with its template tyvars)
845 tcConDecl unbox_strict existential_ok rep_tycon res_tmpl -- Data types
846 (ConDecl {con_name =name, con_qvars = tvs, con_cxt = ctxt
847 , con_details = details, con_res = res_ty })
848 = addErrCtxt (dataConCtxt name) $
849 tcTyVarBndrs tvs $ \ tvs' -> do
850 { ctxt' <- tcHsKindedContext ctxt
851 ; checkTc (existential_ok || (null tvs && null (unLoc ctxt)))
852 (badExistential name)
853 ; (univ_tvs, ex_tvs, eq_preds, res_ty') <- tcResultType res_tmpl tvs' res_ty
855 tc_datacon is_infix field_lbls btys
856 = do { (arg_tys, stricts) <- mapAndUnzipM (tcConArg unbox_strict) btys
857 ; buildDataCon (unLoc name) is_infix
859 univ_tvs ex_tvs eq_preds ctxt' arg_tys
861 -- NB: we put data_tc, the type constructor gotten from the
862 -- constructor type signature into the data constructor;
863 -- that way checkValidDataCon can complain if it's wrong.
866 PrefixCon btys -> tc_datacon False [] btys
867 InfixCon bty1 bty2 -> tc_datacon True [] [bty1,bty2]
868 RecCon fields -> tc_datacon False field_names btys
870 field_names = map (unLoc . cd_fld_name) fields
871 btys = map cd_fld_type fields
875 -- data instance T (b,c) where
876 -- TI :: forall e. e -> T (e,e)
878 -- The representation tycon looks like this:
879 -- data :R7T b c where
880 -- TI :: forall b1 c1. (b1 ~ c1) => b1 -> :R7T b1 c1
881 -- In this case orig_res_ty = T (e,e)
883 tcResultType :: ([TyVar], Type) -- Template for result type; e.g.
884 -- data instance T [a] b c = ...
885 -- gives template ([a,b,c], T [a] b c)
886 -> [TyVar] -- where MkT :: forall x y z. ...
888 -> TcM ([TyVar], -- Universal
889 [TyVar], -- Existential (distinct OccNames from univs)
890 [(TyVar,Type)], -- Equality predicates
891 Type) -- Typechecked return type
892 -- We don't check that the TyCon given in the ResTy is
893 -- the same as the parent tycon, becuase we are in the middle
894 -- of a recursive knot; so it's postponed until checkValidDataCon
896 tcResultType (tmpl_tvs, res_ty) dc_tvs ResTyH98
897 = return (tmpl_tvs, dc_tvs, [], res_ty)
898 -- In H98 syntax the dc_tvs are the existential ones
899 -- data T a b c = forall d e. MkT ...
900 -- The {a,b,c} are tc_tvs, and {d,e} are dc_tvs
902 tcResultType (tmpl_tvs, res_tmpl) dc_tvs (ResTyGADT res_ty)
903 -- E.g. data T [a] b c where
904 -- MkT :: forall x y z. T [(x,y)] z z
906 -- Univ tyvars Eq-spec
910 -- Existentials are the leftover type vars: [x,y]
911 -- So we return ([a,b,z], [x,y], [a~(x,y),b~z], T [(x,y)] z z)
912 = do { res_ty' <- tcHsKindedType res_ty
913 ; let Just subst = tcMatchTy (mkVarSet tmpl_tvs) res_tmpl res_ty'
915 -- /Lazily/ figure out the univ_tvs etc
916 -- Each univ_tv is either a dc_tv or a tmpl_tv
917 (univ_tvs, eq_spec) = foldr choose ([], []) tidy_tmpl_tvs
918 choose tmpl (univs, eqs)
919 | Just ty <- lookupTyVar subst tmpl
920 = case tcGetTyVar_maybe ty of
921 Just tv | not (tv `elem` univs)
923 _other -> (tmpl:univs, (tmpl,ty):eqs)
924 | otherwise = pprPanic "tcResultType" (ppr res_ty)
925 ex_tvs = dc_tvs `minusList` univ_tvs
927 ; return (univ_tvs, ex_tvs, eq_spec, res_ty') }
929 -- NB: tmpl_tvs and dc_tvs are distinct, but
930 -- we want them to be *visibly* distinct, both for
931 -- interface files and general confusion. So rename
932 -- the tc_tvs, since they are not used yet (no
933 -- consequential renaming needed)
934 (_, tidy_tmpl_tvs) = mapAccumL tidy_one init_occ_env tmpl_tvs
935 init_occ_env = initTidyOccEnv (map getOccName dc_tvs)
936 tidy_one env tv = (env', setTyVarName tv (tidyNameOcc name occ'))
939 (env', occ') = tidyOccName env (getOccName name)
941 consUseH98Syntax :: [LConDecl a] -> Bool
942 consUseH98Syntax (L _ (ConDecl { con_res = ResTyGADT _ }) : _) = False
943 consUseH98Syntax _ = True
944 -- All constructors have same shape
947 tcConArg :: Bool -- True <=> -funbox-strict_fields
949 -> TcM (TcType, HsBang)
950 tcConArg unbox_strict bty
951 = do { arg_ty <- tcHsBangType bty
952 ; let bang = getBangStrictness bty
953 ; let strict_mark = chooseBoxingStrategy unbox_strict arg_ty bang
954 ; return (arg_ty, strict_mark) }
956 -- We attempt to unbox/unpack a strict field when either:
957 -- (i) The field is marked '!!', or
958 -- (ii) The field is marked '!', and the -funbox-strict-fields flag is on.
960 -- We have turned off unboxing of newtypes because coercions make unboxing
961 -- and reboxing more complicated
962 chooseBoxingStrategy :: Bool -> TcType -> HsBang -> HsBang
963 chooseBoxingStrategy unbox_strict_fields arg_ty bang
966 HsUnpack -> can_unbox HsUnpackFailed arg_ty
967 HsStrict | unbox_strict_fields -> can_unbox HsStrict arg_ty
968 | otherwise -> HsStrict
969 HsUnpackFailed -> pprPanic "chooseBoxingStrategy" (ppr arg_ty)
970 -- Source code never has shtes
972 can_unbox :: HsBang -> TcType -> HsBang
973 -- Returns HsUnpack if we can unpack arg_ty
974 -- fail_bang if we know what arg_ty is but we can't unpack it
975 -- HsStrict if it's abstract, so we don't know whether or not we can unbox it
976 can_unbox fail_bang arg_ty
977 = case splitTyConApp_maybe arg_ty of
980 Just (arg_tycon, tycon_args)
981 | isAbstractTyCon arg_tycon -> HsStrict
982 -- See Note [Don't complain about UNPACK on abstract TyCons]
983 | not (isRecursiveTyCon arg_tycon) -- Note [Recusive unboxing]
984 , isProductTyCon arg_tycon
985 -- We can unbox if the type is a chain of newtypes
986 -- with a product tycon at the end
987 -> if isNewTyCon arg_tycon
988 then can_unbox fail_bang (newTyConInstRhs arg_tycon tycon_args)
991 | otherwise -> fail_bang
994 Note [Don't complain about UNPACK on abstract TyCons]
995 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
996 We are going to complain about UnpackFailed, but if we say
997 data T = MkT {-# UNPACK #-} !Wobble
998 and Wobble is a newtype imported from a module that was compiled
999 without optimisation, we don't want to complain. Because it might
1000 be fine when optimsation is on. I think this happens when Haddock
1001 is working over (say) GHC souce files.
1003 Note [Recursive unboxing]
1004 ~~~~~~~~~~~~~~~~~~~~~~~~~
1005 Be careful not to try to unbox this!
1007 But it's the *argument* type that matters. This is fine:
1009 because Int is non-recursive.
1012 %************************************************************************
1016 %************************************************************************
1018 Validity checking is done once the mutually-recursive knot has been
1019 tied, so we can look at things freely.
1022 checkCycleErrs :: [LTyClDecl Name] -> TcM ()
1023 checkCycleErrs tyclss
1027 = do { mapM_ recClsErr cls_cycles
1028 ; failM } -- Give up now, because later checkValidTyCl
1029 -- will loop if the synonym is recursive
1031 cls_cycles = calcClassCycles tyclss
1033 checkValidTyCl :: TyClDecl Name -> TcM ()
1034 -- We do the validity check over declarations, rather than TyThings
1035 -- only so that we can add a nice context with tcAddDeclCtxt
1037 = tcAddDeclCtxt decl $
1038 do { thing <- tcLookupLocatedGlobal (tcdLName decl)
1039 ; traceTc (text "Validity of" <+> ppr thing)
1041 ATyCon tc -> checkValidTyCon tc
1042 AClass cl -> checkValidClass cl
1043 _ -> panic "checkValidTyCl"
1044 ; traceTc (text "Done validity of" <+> ppr thing)
1047 -------------------------
1048 -- For data types declared with record syntax, we require
1049 -- that each constructor that has a field 'f'
1050 -- (a) has the same result type
1051 -- (b) has the same type for 'f'
1052 -- module alpha conversion of the quantified type variables
1053 -- of the constructor.
1055 -- Note that we allow existentials to match becuase the
1056 -- fields can never meet. E.g
1058 -- T1 { f1 :: b, f2 :: a, f3 ::Int } :: T
1059 -- T2 { f1 :: c, f2 :: c, f3 ::Int } :: T
1060 -- Here we do not complain about f1,f2 because they are existential
1062 checkValidTyCon :: TyCon -> TcM ()
1065 = case synTyConRhs tc of
1066 OpenSynTyCon _ _ -> return ()
1067 SynonymTyCon ty -> checkValidType syn_ctxt ty
1069 = do -- Check the context on the data decl
1070 checkValidTheta (DataTyCtxt name) (tyConStupidTheta tc)
1072 -- Check arg types of data constructors
1073 mapM_ (checkValidDataCon tc) data_cons
1075 -- Check that fields with the same name share a type
1076 mapM_ check_fields groups
1079 syn_ctxt = TySynCtxt name
1081 data_cons = tyConDataCons tc
1083 groups = equivClasses cmp_fld (concatMap get_fields data_cons)
1084 cmp_fld (f1,_) (f2,_) = f1 `compare` f2
1085 get_fields con = dataConFieldLabels con `zip` repeat con
1086 -- dataConFieldLabels may return the empty list, which is fine
1088 -- See Note [GADT record selectors] in MkId.lhs
1089 -- We must check (a) that the named field has the same
1090 -- type in each constructor
1091 -- (b) that those constructors have the same result type
1093 -- However, the constructors may have differently named type variable
1094 -- and (worse) we don't know how the correspond to each other. E.g.
1095 -- C1 :: forall a b. { f :: a, g :: b } -> T a b
1096 -- C2 :: forall d c. { f :: c, g :: c } -> T c d
1098 -- So what we do is to ust Unify.tcMatchTys to compare the first candidate's
1099 -- result type against other candidates' types BOTH WAYS ROUND.
1100 -- If they magically agrees, take the substitution and
1101 -- apply them to the latter ones, and see if they match perfectly.
1102 check_fields ((label, con1) : other_fields)
1103 -- These fields all have the same name, but are from
1104 -- different constructors in the data type
1105 = recoverM (return ()) $ mapM_ checkOne other_fields
1106 -- Check that all the fields in the group have the same type
1107 -- NB: this check assumes that all the constructors of a given
1108 -- data type use the same type variables
1110 (tvs1, _, _, res1) = dataConSig con1
1112 fty1 = dataConFieldType con1 label
1114 checkOne (_, con2) -- Do it bothways to ensure they are structurally identical
1115 = do { checkFieldCompat label con1 con2 ts1 res1 res2 fty1 fty2
1116 ; checkFieldCompat label con2 con1 ts2 res2 res1 fty2 fty1 }
1118 (tvs2, _, _, res2) = dataConSig con2
1120 fty2 = dataConFieldType con2 label
1121 check_fields [] = panic "checkValidTyCon/check_fields []"
1123 checkFieldCompat :: Name -> DataCon -> DataCon -> TyVarSet
1124 -> Type -> Type -> Type -> Type -> TcM ()
1125 checkFieldCompat fld con1 con2 tvs1 res1 res2 fty1 fty2
1126 = do { checkTc (isJust mb_subst1) (resultTypeMisMatch fld con1 con2)
1127 ; checkTc (isJust mb_subst2) (fieldTypeMisMatch fld con1 con2) }
1129 mb_subst1 = tcMatchTy tvs1 res1 res2
1130 mb_subst2 = tcMatchTyX tvs1 (expectJust "checkFieldCompat" mb_subst1) fty1 fty2
1132 -------------------------------
1133 checkValidDataCon :: TyCon -> DataCon -> TcM ()
1134 checkValidDataCon tc con
1135 = setSrcSpan (srcLocSpan (getSrcLoc con)) $
1136 addErrCtxt (dataConCtxt con) $
1137 do { traceTc (ptext (sLit "Validity of data con") <+> ppr con)
1138 ; let tc_tvs = tyConTyVars tc
1139 res_ty_tmpl = mkFamilyTyConApp tc (mkTyVarTys tc_tvs)
1140 actual_res_ty = dataConOrigResTy con
1141 ; checkTc (isJust (tcMatchTy (mkVarSet tc_tvs)
1144 (badDataConTyCon con res_ty_tmpl actual_res_ty)
1145 ; checkValidMonoType (dataConOrigResTy con)
1146 -- Disallow MkT :: T (forall a. a->a)
1147 -- Reason: it's really the argument of an equality constraint
1148 ; checkValidType ctxt (dataConUserType con)
1149 ; when (isNewTyCon tc) (checkNewDataCon con)
1150 ; mapM_ check_bang (dataConStrictMarks con `zip` [1..])
1153 ctxt = ConArgCtxt (dataConName con)
1154 check_bang (HsUnpackFailed, n) = addWarnTc (cant_unbox_msg n)
1155 check_bang _ = return ()
1157 cant_unbox_msg n = sep [ ptext (sLit "Ignoring unusable UNPACK pragma on the")
1158 , speakNth n <+> ptext (sLit "argument of") <+> quotes (ppr con)]
1160 -------------------------------
1161 checkNewDataCon :: DataCon -> TcM ()
1162 -- Checks for the data constructor of a newtype
1164 = do { checkTc (isSingleton arg_tys) (newtypeFieldErr con (length arg_tys))
1166 ; checkTc (null eq_spec) (newtypePredError con)
1167 -- Return type is (T a b c)
1168 ; checkTc (null ex_tvs && null eq_theta && null dict_theta) (newtypeExError con)
1170 ; checkTc (not (any isBanged (dataConStrictMarks con)))
1171 (newtypeStrictError con)
1175 (_univ_tvs, ex_tvs, eq_spec, eq_theta, dict_theta, arg_tys, _res_ty) = dataConFullSig con
1177 -------------------------------
1178 checkValidClass :: Class -> TcM ()
1180 = do { constrained_class_methods <- doptM Opt_ConstrainedClassMethods
1181 ; multi_param_type_classes <- doptM Opt_MultiParamTypeClasses
1182 ; fundep_classes <- doptM Opt_FunctionalDependencies
1184 -- Check that the class is unary, unless GlaExs
1185 ; checkTc (notNull tyvars) (nullaryClassErr cls)
1186 ; checkTc (multi_param_type_classes || unary) (classArityErr cls)
1187 ; checkTc (fundep_classes || null fundeps) (classFunDepsErr cls)
1189 -- Check the super-classes
1190 ; checkValidTheta (ClassSCCtxt (className cls)) theta
1192 -- Check the class operations
1193 ; mapM_ (check_op constrained_class_methods) op_stuff
1195 -- Check that if the class has generic methods, then the
1196 -- class has only one parameter. We can't do generic
1197 -- multi-parameter type classes!
1198 ; checkTc (unary || no_generics) (genericMultiParamErr cls)
1201 (tyvars, fundeps, theta, _, _, op_stuff) = classExtraBigSig cls
1202 unary = isSingleton tyvars
1203 no_generics = null [() | (_, GenDefMeth) <- op_stuff]
1205 check_op constrained_class_methods (sel_id, dm)
1206 = addErrCtxt (classOpCtxt sel_id tau) $ do
1207 { checkValidTheta SigmaCtxt (tail theta)
1208 -- The 'tail' removes the initial (C a) from the
1209 -- class itself, leaving just the method type
1211 ; traceTc (text "class op type" <+> ppr op_ty <+> ppr tau)
1212 ; checkValidType (FunSigCtxt op_name) tau
1214 -- Check that the type mentions at least one of
1215 -- the class type variables...or at least one reachable
1216 -- from one of the class variables. Example: tc223
1217 -- class Error e => Game b mv e | b -> mv e where
1218 -- newBoard :: MonadState b m => m ()
1219 -- Here, MonadState has a fundep m->b, so newBoard is fine
1220 ; let grown_tyvars = growThetaTyVars theta (mkVarSet tyvars)
1221 ; checkTc (tyVarsOfType tau `intersectsVarSet` grown_tyvars)
1222 (noClassTyVarErr cls sel_id)
1224 -- Check that for a generic method, the type of
1225 -- the method is sufficiently simple
1226 ; checkTc (dm /= GenDefMeth || validGenericMethodType tau)
1227 (badGenericMethodType op_name op_ty)
1230 op_name = idName sel_id
1231 op_ty = idType sel_id
1232 (_,theta1,tau1) = tcSplitSigmaTy op_ty
1233 (_,theta2,tau2) = tcSplitSigmaTy tau1
1234 (theta,tau) | constrained_class_methods = (theta1 ++ theta2, tau2)
1235 | otherwise = (theta1, mkPhiTy (tail theta1) tau1)
1236 -- Ugh! The function might have a type like
1237 -- op :: forall a. C a => forall b. (Eq b, Eq a) => tau2
1238 -- With -XConstrainedClassMethods, we want to allow this, even though the inner
1239 -- forall has an (Eq a) constraint. Whereas in general, each constraint
1240 -- in the context of a for-all must mention at least one quantified
1241 -- type variable. What a mess!
1245 %************************************************************************
1247 Building record selectors
1249 %************************************************************************
1252 mkDefaultMethodIds :: [TyThing] -> [Id]
1253 -- See Note [Default method Ids and Template Haskell]
1254 mkDefaultMethodIds things
1255 = [ mkDefaultMethodId sel_id dm_name
1256 | AClass cls <- things
1257 , (sel_id, DefMeth dm_name) <- classOpItems cls ]
1260 Note [Default method Ids and Template Haskell]
1261 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1262 Consider this (Trac #4169):
1263 class Numeric a where
1265 fromIntegerNum = ...
1268 ast = [d| instance Numeric Int |]
1270 When we typecheck 'ast' we have done the first pass over the class decl
1271 (in tcTyClDecls), but we have not yet typechecked the default-method
1272 declarations (becuase they can mention value declarations). So we
1273 must bring the default method Ids into scope first (so they can be seen
1274 when typechecking the [d| .. |] quote, and typecheck them later.
1277 mkRecSelBinds :: [TyThing] -> HsValBinds Name
1278 -- NB We produce *un-typechecked* bindings, rather like 'deriving'
1279 -- This makes life easier, because the later type checking will add
1280 -- all necessary type abstractions and applications
1281 mkRecSelBinds ty_things
1282 = ValBindsOut [(NonRecursive, b) | b <- binds] sigs
1284 (sigs, binds) = unzip rec_sels
1285 rec_sels = map mkRecSelBind [ (tc,fld)
1286 | ATyCon tc <- ty_things
1287 , fld <- tyConFields tc ]
1289 mkRecSelBind :: (TyCon, FieldLabel) -> (LSig Name, LHsBinds Name)
1290 mkRecSelBind (tycon, sel_name)
1291 = (L loc (IdSig sel_id), unitBag (L loc sel_bind))
1293 loc = getSrcSpan tycon
1294 sel_id = Var.mkLocalVar rec_details sel_name sel_ty vanillaIdInfo
1295 rec_details = RecSelId { sel_tycon = tycon, sel_naughty = is_naughty }
1297 -- Find a representative constructor, con1
1298 all_cons = tyConDataCons tycon
1299 cons_w_field = [ con | con <- all_cons
1300 , sel_name `elem` dataConFieldLabels con ]
1301 con1 = ASSERT( not (null cons_w_field) ) head cons_w_field
1303 -- Selector type; Note [Polymorphic selectors]
1304 field_ty = dataConFieldType con1 sel_name
1305 data_ty = dataConOrigResTy con1
1306 data_tvs = tyVarsOfType data_ty
1307 is_naughty = not (tyVarsOfType field_ty `subVarSet` data_tvs)
1308 (field_tvs, field_theta, field_tau) = tcSplitSigmaTy field_ty
1309 sel_ty | is_naughty = unitTy -- See Note [Naughty record selectors]
1310 | otherwise = mkForAllTys (varSetElems data_tvs ++ field_tvs) $
1311 mkPhiTy (dataConStupidTheta con1) $ -- Urgh!
1312 mkPhiTy field_theta $ -- Urgh!
1313 mkFunTy data_ty field_tau
1315 -- Make the binding: sel (C2 { fld = x }) = x
1316 -- sel (C7 { fld = x }) = x
1317 -- where cons_w_field = [C2,C7]
1318 sel_bind | is_naughty = mkFunBind sel_lname [mkSimpleMatch [] unit_rhs]
1319 | otherwise = mkFunBind sel_lname (map mk_match cons_w_field ++ deflt)
1320 mk_match con = mkSimpleMatch [L loc (mk_sel_pat con)]
1321 (L loc (HsVar field_var))
1322 mk_sel_pat con = ConPatIn (L loc (getName con)) (RecCon rec_fields)
1323 rec_fields = HsRecFields { rec_flds = [rec_field], rec_dotdot = Nothing }
1324 rec_field = HsRecField { hsRecFieldId = sel_lname
1325 , hsRecFieldArg = nlVarPat field_var
1326 , hsRecPun = False }
1327 sel_lname = L loc sel_name
1328 field_var = mkInternalName (mkBuiltinUnique 1) (getOccName sel_name) loc
1330 -- Add catch-all default case unless the case is exhaustive
1331 -- We do this explicitly so that we get a nice error message that
1332 -- mentions this particular record selector
1333 deflt | not (any is_unused all_cons) = []
1334 | otherwise = [mkSimpleMatch [nlWildPat]
1335 (nlHsApp (nlHsVar (getName rEC_SEL_ERROR_ID))
1338 -- Do not add a default case unless there are unmatched
1339 -- constructors. We must take account of GADTs, else we
1340 -- get overlap warning messages from the pattern-match checker
1341 is_unused con = not (con `elem` cons_w_field
1342 || dataConCannotMatch inst_tys con)
1343 inst_tys = tyConAppArgs data_ty
1345 unit_rhs = mkLHsTupleExpr []
1346 msg_lit = HsStringPrim $ mkFastString $
1347 occNameString (getOccName sel_name)
1350 tyConFields :: TyCon -> [FieldLabel]
1352 | isAlgTyCon tc = nub (concatMap dataConFieldLabels (tyConDataCons tc))
1356 Note [Polymorphic selectors]
1357 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1358 When a record has a polymorphic field, we pull the foralls out to the front.
1359 data T = MkT { f :: forall a. [a] -> a }
1360 Then f :: forall a. T -> [a] -> a
1361 NOT f :: T -> forall a. [a] -> a
1363 This is horrid. It's only needed in deeply obscure cases, which I hate.
1364 The only case I know is test tc163, which is worth looking at. It's far
1365 from clear that this test should succeed at all!
1367 Note [Naughty record selectors]
1368 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1369 A "naughty" field is one for which we can't define a record
1370 selector, because an existential type variable would escape. For example:
1371 data T = forall a. MkT { x,y::a }
1372 We obviously can't define
1374 Nevertheless we *do* put a RecSelId into the type environment
1375 so that if the user tries to use 'x' as a selector we can bleat
1376 helpfully, rather than saying unhelpfully that 'x' is not in scope.
1377 Hence the sel_naughty flag, to identify record selectors that don't really exist.
1379 In general, a field is "naughty" if its type mentions a type variable that
1380 isn't in the result type of the constructor. Note that this *allows*
1381 GADT record selectors (Note [GADT record selectors]) whose types may look
1382 like sel :: T [a] -> a
1384 For naughty selectors we make a dummy binding
1386 for naughty selectors, so that the later type-check will add them to the
1387 environment, and they'll be exported. The function is never called, because
1388 the tyepchecker spots the sel_naughty field.
1390 Note [GADT record selectors]
1391 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1392 For GADTs, we require that all constructors with a common field 'f' have the same
1393 result type (modulo alpha conversion). [Checked in TcTyClsDecls.checkValidTyCon]
1396 T1 { f :: Maybe a } :: T [a]
1397 T2 { f :: Maybe a, y :: b } :: T [a]
1399 and now the selector takes that result type as its argument:
1400 f :: forall a. T [a] -> Maybe a
1402 Details: the "real" types of T1,T2 are:
1403 T1 :: forall r a. (r~[a]) => a -> T r
1404 T2 :: forall r a b. (r~[a]) => a -> b -> T r
1406 So the selector loooks like this:
1407 f :: forall a. T [a] -> Maybe a
1410 T1 c (g:[a]~[c]) (v:Maybe c) -> v `cast` Maybe (right (sym g))
1411 T2 c d (g:[a]~[c]) (v:Maybe c) (w:d) -> v `cast` Maybe (right (sym g))
1413 Note the forall'd tyvars of the selector are just the free tyvars
1414 of the result type; there may be other tyvars in the constructor's
1415 type (e.g. 'b' in T2).
1417 Note the need for casts in the result!
1419 Note [Selector running example]
1420 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1421 It's OK to combine GADTs and type families. Here's a running example:
1423 data instance T [a] where
1424 T1 { fld :: b } :: T [Maybe b]
1426 The representation type looks like this
1428 T1 { fld :: b } :: :R7T (Maybe b)
1430 and there's coercion from the family type to the representation type
1431 :CoR7T a :: T [a] ~ :R7T a
1433 The selector we want for fld looks like this:
1435 fld :: forall b. T [Maybe b] -> b
1436 fld = /\b. \(d::T [Maybe b]).
1437 case d `cast` :CoR7T (Maybe b) of
1440 The scrutinee of the case has type :R7T (Maybe b), which can be
1441 gotten by appying the eq_spec to the univ_tvs of the data con.
1443 %************************************************************************
1447 %************************************************************************
1450 resultTypeMisMatch :: Name -> DataCon -> DataCon -> SDoc
1451 resultTypeMisMatch field_name con1 con2
1452 = vcat [sep [ptext (sLit "Constructors") <+> ppr con1 <+> ptext (sLit "and") <+> ppr con2,
1453 ptext (sLit "have a common field") <+> quotes (ppr field_name) <> comma],
1454 nest 2 $ ptext (sLit "but have different result types")]
1456 fieldTypeMisMatch :: Name -> DataCon -> DataCon -> SDoc
1457 fieldTypeMisMatch field_name con1 con2
1458 = sep [ptext (sLit "Constructors") <+> ppr con1 <+> ptext (sLit "and") <+> ppr con2,
1459 ptext (sLit "give different types for field"), quotes (ppr field_name)]
1461 dataConCtxt :: Outputable a => a -> SDoc
1462 dataConCtxt con = ptext (sLit "In the definition of data constructor") <+> quotes (ppr con)
1464 classOpCtxt :: Var -> Type -> SDoc
1465 classOpCtxt sel_id tau = sep [ptext (sLit "When checking the class method:"),
1466 nest 2 (ppr sel_id <+> dcolon <+> ppr tau)]
1468 nullaryClassErr :: Class -> SDoc
1470 = ptext (sLit "No parameters for class") <+> quotes (ppr cls)
1472 classArityErr :: Class -> SDoc
1474 = vcat [ptext (sLit "Too many parameters for class") <+> quotes (ppr cls),
1475 parens (ptext (sLit "Use -XMultiParamTypeClasses to allow multi-parameter classes"))]
1477 classFunDepsErr :: Class -> SDoc
1479 = vcat [ptext (sLit "Fundeps in class") <+> quotes (ppr cls),
1480 parens (ptext (sLit "Use -XFunctionalDependencies to allow fundeps"))]
1482 noClassTyVarErr :: Class -> Var -> SDoc
1483 noClassTyVarErr clas op
1484 = sep [ptext (sLit "The class method") <+> quotes (ppr op),
1485 ptext (sLit "mentions none of the type variables of the class") <+>
1486 ppr clas <+> hsep (map ppr (classTyVars clas))]
1488 genericMultiParamErr :: Class -> SDoc
1489 genericMultiParamErr clas
1490 = ptext (sLit "The multi-parameter class") <+> quotes (ppr clas) <+>
1491 ptext (sLit "cannot have generic methods")
1493 badGenericMethodType :: Name -> Kind -> SDoc
1494 badGenericMethodType op op_ty
1495 = hang (ptext (sLit "Generic method type is too complex"))
1496 4 (vcat [ppr op <+> dcolon <+> ppr op_ty,
1497 ptext (sLit "You can only use type variables, arrows, lists, and tuples")])
1499 recSynErr :: [LTyClDecl Name] -> TcRn ()
1501 = setSrcSpan (getLoc (head sorted_decls)) $
1502 addErr (sep [ptext (sLit "Cycle in type synonym declarations:"),
1503 nest 2 (vcat (map ppr_decl sorted_decls))])
1505 sorted_decls = sortLocated syn_decls
1506 ppr_decl (L loc decl) = ppr loc <> colon <+> ppr decl
1508 recClsErr :: [Located (TyClDecl Name)] -> TcRn ()
1510 = setSrcSpan (getLoc (head sorted_decls)) $
1511 addErr (sep [ptext (sLit "Cycle in class declarations (via superclasses):"),
1512 nest 2 (vcat (map ppr_decl sorted_decls))])
1514 sorted_decls = sortLocated cls_decls
1515 ppr_decl (L loc decl) = ppr loc <> colon <+> ppr (decl { tcdSigs = [] })
1517 sortLocated :: [Located a] -> [Located a]
1518 sortLocated things = sortLe le things
1520 le (L l1 _) (L l2 _) = l1 <= l2
1522 badDataConTyCon :: DataCon -> Type -> Type -> SDoc
1523 badDataConTyCon data_con res_ty_tmpl actual_res_ty
1524 = hang (ptext (sLit "Data constructor") <+> quotes (ppr data_con) <+>
1525 ptext (sLit "returns type") <+> quotes (ppr actual_res_ty))
1526 2 (ptext (sLit "instead of an instance of its parent type") <+> quotes (ppr res_ty_tmpl))
1528 badGadtDecl :: Name -> SDoc
1530 = vcat [ ptext (sLit "Illegal generalised algebraic data declaration for") <+> quotes (ppr tc_name)
1531 , nest 2 (parens $ ptext (sLit "Use -XGADTs to allow GADTs")) ]
1533 badExistential :: Located Name -> SDoc
1534 badExistential con_name
1535 = hang (ptext (sLit "Data constructor") <+> quotes (ppr con_name) <+>
1536 ptext (sLit "has existential type variables, or a context"))
1537 2 (parens $ ptext (sLit "Use -XExistentialQuantification or -XGADTs to allow this"))
1539 badStupidTheta :: Name -> SDoc
1540 badStupidTheta tc_name
1541 = ptext (sLit "A data type declared in GADT style cannot have a context:") <+> quotes (ppr tc_name)
1543 newtypeConError :: Name -> Int -> SDoc
1544 newtypeConError tycon n
1545 = sep [ptext (sLit "A newtype must have exactly one constructor,"),
1546 nest 2 $ ptext (sLit "but") <+> quotes (ppr tycon) <+> ptext (sLit "has") <+> speakN n ]
1548 newtypeExError :: DataCon -> SDoc
1550 = sep [ptext (sLit "A newtype constructor cannot have an existential context,"),
1551 nest 2 $ ptext (sLit "but") <+> quotes (ppr con) <+> ptext (sLit "does")]
1553 newtypeStrictError :: DataCon -> SDoc
1554 newtypeStrictError con
1555 = sep [ptext (sLit "A newtype constructor cannot have a strictness annotation,"),
1556 nest 2 $ ptext (sLit "but") <+> quotes (ppr con) <+> ptext (sLit "does")]
1558 newtypePredError :: DataCon -> SDoc
1559 newtypePredError con
1560 = sep [ptext (sLit "A newtype constructor must have a return type of form T a1 ... an"),
1561 nest 2 $ ptext (sLit "but") <+> quotes (ppr con) <+> ptext (sLit "does not")]
1563 newtypeFieldErr :: DataCon -> Int -> SDoc
1564 newtypeFieldErr con_name n_flds
1565 = sep [ptext (sLit "The constructor of a newtype must have exactly one field"),
1566 nest 2 $ ptext (sLit "but") <+> quotes (ppr con_name) <+> ptext (sLit "has") <+> speakN n_flds]
1568 badSigTyDecl :: Name -> SDoc
1569 badSigTyDecl tc_name
1570 = vcat [ ptext (sLit "Illegal kind signature") <+>
1571 quotes (ppr tc_name)
1572 , nest 2 (parens $ ptext (sLit "Use -XKindSignatures to allow kind signatures")) ]
1574 badFamInstDecl :: Outputable a => a -> SDoc
1575 badFamInstDecl tc_name
1576 = vcat [ ptext (sLit "Illegal family instance for") <+>
1577 quotes (ppr tc_name)
1578 , nest 2 (parens $ ptext (sLit "Use -XTypeFamilies to allow indexed type families")) ]
1580 tooManyParmsErr :: Located Name -> SDoc
1581 tooManyParmsErr tc_name
1582 = ptext (sLit "Family instance has too many parameters:") <+>
1583 quotes (ppr tc_name)
1585 tooFewParmsErr :: Arity -> SDoc
1586 tooFewParmsErr arity
1587 = ptext (sLit "Family instance has too few parameters; expected") <+>
1590 wrongNumberOfParmsErr :: Arity -> SDoc
1591 wrongNumberOfParmsErr exp_arity
1592 = ptext (sLit "Number of parameters must match family declaration; expected")
1595 badBootFamInstDeclErr :: SDoc
1596 badBootFamInstDeclErr
1597 = ptext (sLit "Illegal family instance in hs-boot file")
1599 notFamily :: TyCon -> SDoc
1601 = vcat [ ptext (sLit "Illegal family instance for") <+> quotes (ppr tycon)
1602 , nest 2 $ parens (ppr tycon <+> ptext (sLit "is not an indexed type family"))]
1604 wrongKindOfFamily :: TyCon -> SDoc
1605 wrongKindOfFamily family
1606 = ptext (sLit "Wrong category of family instance; declaration was for a")
1609 kindOfFamily | isSynTyCon family = ptext (sLit "type synonym")
1610 | isAlgTyCon family = ptext (sLit "data type")
1611 | otherwise = pprPanic "wrongKindOfFamily" (ppr family)
1613 emptyConDeclsErr :: Name -> SDoc
1614 emptyConDeclsErr tycon
1615 = sep [quotes (ppr tycon) <+> ptext (sLit "has no constructors"),
1616 nest 2 $ ptext (sLit "(-XEmptyDataDecls permits this)")]