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 "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 "ready for validity check" empty
197 ; mapM_ (addLocM checkValidTyCl) decls
198 ; traceTc "done" empty
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 "Adding types and classes" $ vcat
211 , text "and" <+> ppr implicit_things ]
212 ; env <- tcExtendGlobalEnv implicit_things getGblEnv
213 ; return (env, rec_sel_binds, dm_ids) }
216 -- Pull associated types out of class declarations, to tie them into the
218 -- NB: We put them in the same place in the list as `tcTyClDecl' will
219 -- eventually put the matching `TyThing's. That's crucial; otherwise,
220 -- the two argument lists of `mkGlobalThings' don't match up.
221 addATs decl@(L _ (ClassDecl {tcdATs = ats})) = decl : ats
224 mkGlobalThings :: [LTyClDecl Name] -- The decls
225 -> [TyThing] -- Knot-tied, in 1-1 correspondence with the decls
227 -- Driven by the Decls, and treating the TyThings lazily
228 -- make a TypeEnv for the new things
229 mkGlobalThings decls things
230 = map mk_thing (decls `zipLazy` things)
232 mk_thing (L _ (ClassDecl {tcdLName = L _ name}), ~(AClass cl))
234 mk_thing (L _ decl, ~(ATyCon tc))
235 = (tcdName decl, ATyCon tc)
239 %************************************************************************
241 Type checking family instances
243 %************************************************************************
245 Family instances are somewhat of a hybrid. They are processed together with
246 class instance heads, but can contain data constructors and hence they share a
247 lot of kinding and type checking code with ordinary algebraic data types (and
251 tcFamInstDecl :: TopLevelFlag -> LTyClDecl Name -> TcM TyThing
252 tcFamInstDecl top_lvl (L loc decl)
253 = -- Prime error recovery, set source location
256 do { -- type family instances require -XTypeFamilies
257 -- and can't (currently) be in an hs-boot file
258 ; type_families <- doptM Opt_TypeFamilies
259 ; is_boot <- tcIsHsBoot -- Are we compiling an hs-boot file?
260 ; checkTc type_families $ badFamInstDecl (tcdLName decl)
261 ; checkTc (not is_boot) $ badBootFamInstDeclErr
263 -- Perform kind and type checking
264 ; tc <- tcFamInstDecl1 decl
265 ; checkValidTyCon tc -- Remember to check validity;
266 -- no recursion to worry about here
268 -- Check that toplevel type instances are not for associated types.
269 ; when (isTopLevel top_lvl && isAssocFamily tc)
270 (addErr $ assocInClassErr (tcdName decl))
272 ; return (ATyCon tc) }
274 isAssocFamily :: TyCon -> Bool -- Is an assocaited type
276 = case tyConFamInst_maybe tycon of
277 Nothing -> panic "isAssocFamily: no family?!?"
278 Just (fam, _) -> isTyConAssoc fam
280 assocInClassErr :: Name -> SDoc
282 = ptext (sLit "Associated type") <+> quotes (ppr name) <+>
283 ptext (sLit "must be inside a class instance")
287 tcFamInstDecl1 :: TyClDecl Name -> TcM TyCon
290 tcFamInstDecl1 (decl@TySynonym {tcdLName = L loc tc_name})
291 = kcIdxTyPats decl $ \k_tvs k_typats resKind family ->
292 do { -- check that the family declaration is for a synonym
293 checkTc (isFamilyTyCon family) (notFamily family)
294 ; checkTc (isSynTyCon family) (wrongKindOfFamily family)
296 ; -- (1) kind check the right-hand side of the type equation
297 ; k_rhs <- kcCheckLHsType (tcdSynRhs decl) (EK resKind EkUnk)
298 -- ToDo: the ExpKind could be better
300 -- we need the exact same number of type parameters as the family
302 ; let famArity = tyConArity family
303 ; checkTc (length k_typats == famArity) $
304 wrongNumberOfParmsErr famArity
306 -- (2) type check type equation
307 ; tcTyVarBndrs k_tvs $ \t_tvs -> do { -- turn kinded into proper tyvars
308 ; t_typats <- mapM tcHsKindedType k_typats
309 ; t_rhs <- tcHsKindedType k_rhs
311 -- (3) check the well-formedness of the instance
312 ; checkValidTypeInst t_typats t_rhs
314 -- (4) construct representation tycon
315 ; rep_tc_name <- newFamInstTyConName tc_name t_typats loc
316 ; buildSynTyCon rep_tc_name t_tvs (SynonymTyCon t_rhs)
318 NoParentTyCon (Just (family, t_typats))
321 -- "newtype instance" and "data instance"
322 tcFamInstDecl1 (decl@TyData {tcdND = new_or_data, tcdLName = L loc tc_name,
324 = kcIdxTyPats decl $ \k_tvs k_typats resKind fam_tycon ->
325 do { -- check that the family declaration is for the right kind
326 checkTc (isFamilyTyCon fam_tycon) (notFamily fam_tycon)
327 ; checkTc (isAlgTyCon fam_tycon) (wrongKindOfFamily fam_tycon)
329 ; -- (1) kind check the data declaration as usual
330 ; k_decl <- kcDataDecl decl k_tvs
331 ; let k_ctxt = tcdCtxt k_decl
332 k_cons = tcdCons k_decl
334 -- result kind must be '*' (otherwise, we have too few patterns)
335 ; checkTc (isLiftedTypeKind resKind) $ tooFewParmsErr (tyConArity fam_tycon)
337 -- (2) type check indexed data type declaration
338 ; tcTyVarBndrs k_tvs $ \t_tvs -> do { -- turn kinded into proper tyvars
339 ; unbox_strict <- doptM Opt_UnboxStrictFields
341 -- kind check the type indexes and the context
342 ; t_typats <- mapM tcHsKindedType k_typats
343 ; stupid_theta <- tcHsKindedContext k_ctxt
346 -- (a) left-hand side contains no type family applications
347 -- (vanilla synonyms are fine, though, and we checked for
349 ; mapM_ checkTyFamFreeness t_typats
351 -- Check that we don't use GADT syntax in H98 world
352 ; gadt_ok <- doptM Opt_GADTs
353 ; checkTc (gadt_ok || consUseH98Syntax cons) (badGadtDecl tc_name)
355 -- (b) a newtype has exactly one constructor
356 ; checkTc (new_or_data == DataType || isSingleton k_cons) $
357 newtypeConError tc_name (length k_cons)
359 -- (4) construct representation tycon
360 ; rep_tc_name <- newFamInstTyConName tc_name t_typats loc
361 ; let ex_ok = True -- Existentials ok for type families!
362 ; fixM (\ rep_tycon -> do
363 { let orig_res_ty = mkTyConApp fam_tycon t_typats
364 ; data_cons <- tcConDecls unbox_strict ex_ok rep_tycon
365 (t_tvs, orig_res_ty) k_cons
368 DataType -> return (mkDataTyConRhs data_cons)
369 NewType -> ASSERT( not (null data_cons) )
370 mkNewTyConRhs rep_tc_name rep_tycon (head data_cons)
371 ; buildAlgTyCon rep_tc_name t_tvs stupid_theta tc_rhs Recursive
372 False h98_syntax NoParentTyCon (Just (fam_tycon, t_typats))
373 -- We always assume that indexed types are recursive. Why?
374 -- (1) Due to their open nature, we can never be sure that a
375 -- further instance might not introduce a new recursive
376 -- dependency. (2) They are always valid loop breakers as
377 -- they involve a coercion.
381 h98_syntax = case cons of -- All constructors have same shape
382 L _ (ConDecl { con_res = ResTyGADT _ }) : _ -> False
385 tcFamInstDecl1 d = pprPanic "tcFamInstDecl1" (ppr d)
387 -- Kind checking of indexed types
390 -- Kind check type patterns and kind annotate the embedded type variables.
392 -- * Here we check that a type instance matches its kind signature, but we do
393 -- not check whether there is a pattern for each type index; the latter
394 -- check is only required for type synonym instances.
396 kcIdxTyPats :: TyClDecl Name
397 -> ([LHsTyVarBndr Name] -> [LHsType Name] -> Kind -> TyCon -> TcM a)
398 -- ^^kinded tvs ^^kinded ty pats ^^res kind
400 kcIdxTyPats decl thing_inside
401 = kcHsTyVars (tcdTyVars decl) $ \tvs ->
402 do { let tc_name = tcdLName decl
403 ; fam_tycon <- tcLookupLocatedTyCon tc_name
404 ; let { (kinds, resKind) = splitKindFunTys (tyConKind fam_tycon)
405 ; hs_typats = fromJust $ tcdTyPats decl }
407 -- we may not have more parameters than the kind indicates
408 ; checkTc (length kinds >= length hs_typats) $
409 tooManyParmsErr (tcdLName decl)
411 -- type functions can have a higher-kinded result
412 ; let resultKind = mkArrowKinds (drop (length hs_typats) kinds) resKind
413 ; typats <- zipWithM kcCheckLHsType hs_typats
414 [ EK kind (EkArg (ppr tc_name) n)
415 | (kind,n) <- kinds `zip` [1..]]
416 ; thing_inside tvs typats resultKind fam_tycon
421 %************************************************************************
425 %************************************************************************
427 We need to kind check all types in the mutually recursive group
428 before we know the kind of the type variables. For example:
431 op :: D b => a -> b -> b
434 bop :: (Monad c) => ...
436 Here, the kind of the locally-polymorphic type variable "b"
437 depends on *all the uses of class D*. For example, the use of
438 Monad c in bop's type signature means that D must have kind Type->Type.
440 However type synonyms work differently. They can have kinds which don't
441 just involve (->) and *:
442 type R = Int# -- Kind #
443 type S a = Array# a -- Kind * -> #
444 type T a b = (# a,b #) -- Kind * -> * -> (# a,b #)
445 So we must infer their kinds from their right-hand sides *first* and then
446 use them, whereas for the mutually recursive data types D we bring into
447 scope kind bindings D -> k, where k is a kind variable, and do inference.
451 This treatment of type synonyms only applies to Haskell 98-style synonyms.
452 General type functions can be recursive, and hence, appear in `alg_decls'.
454 The kind of a type family is solely determinded by its kind signature;
455 hence, only kind signatures participate in the construction of the initial
456 kind environment (as constructed by `getInitialKind'). In fact, we ignore
457 instances of families altogether in the following. However, we need to
458 include the kinds of associated families into the construction of the
459 initial kind environment. (This is handled by `allDecls').
462 kcTyClDecls :: [LTyClDecl Name] -> [Located (TyClDecl Name)]
463 -> TcM ([LTyClDecl Name], [Located (TyClDecl Name)])
464 kcTyClDecls syn_decls alg_decls
465 = do { -- First extend the kind env with each data type, class, and
466 -- indexed type, mapping them to a type variable
467 let initialKindDecls = concat [allDecls decl | L _ decl <- alg_decls]
468 ; alg_kinds <- mapM getInitialKind initialKindDecls
469 ; tcExtendKindEnv alg_kinds $ do
471 -- Now kind-check the type synonyms, in dependency order
472 -- We do these differently to data type and classes,
473 -- because a type synonym can be an unboxed type
475 -- and a kind variable can't unify with UnboxedTypeKind
476 -- So we infer their kinds in dependency order
477 { (kc_syn_decls, syn_kinds) <- kcSynDecls (calcSynCycles syn_decls)
478 ; tcExtendKindEnv syn_kinds $ do
480 -- Now kind-check the data type, class, and kind signatures,
481 -- returning kind-annotated decls; we don't kind-check
482 -- instances of indexed types yet, but leave this to
484 { kc_alg_decls <- mapM (wrapLocM kcTyClDecl)
485 (filter (not . isFamInstDecl . unLoc) alg_decls)
487 ; return (kc_syn_decls, kc_alg_decls) }}}
489 -- get all declarations relevant for determining the initial kind
491 allDecls (decl@ClassDecl {tcdATs = ats}) = decl : [ at
494 allDecls decl | isFamInstDecl decl = []
497 ------------------------------------------------------------------------
498 getInitialKind :: TyClDecl Name -> TcM (Name, TcKind)
499 -- Only for data type, class, and indexed type declarations
500 -- Get as much info as possible from the data, class, or indexed type decl,
501 -- so as to maximise usefulness of error messages
503 = do { arg_kinds <- mapM (mk_arg_kind . unLoc) (tyClDeclTyVars decl)
504 ; res_kind <- mk_res_kind decl
505 ; return (tcdName decl, mkArrowKinds arg_kinds res_kind) }
507 mk_arg_kind (UserTyVar _ _) = newKindVar
508 mk_arg_kind (KindedTyVar _ kind) = return kind
510 mk_res_kind (TyFamily { tcdKind = Just kind }) = return kind
511 mk_res_kind (TyData { tcdKindSig = Just kind }) = return kind
512 -- On GADT-style declarations we allow a kind signature
513 -- data T :: *->* where { ... }
514 mk_res_kind _ = return liftedTypeKind
518 kcSynDecls :: [SCC (LTyClDecl Name)]
519 -> TcM ([LTyClDecl Name], -- Kind-annotated decls
520 [(Name,TcKind)]) -- Kind bindings
523 kcSynDecls (group : groups)
524 = do { (decl, nk) <- kcSynDecl group
525 ; (decls, nks) <- tcExtendKindEnv [nk] (kcSynDecls groups)
526 ; return (decl:decls, nk:nks) }
529 kcSynDecl :: SCC (LTyClDecl Name)
530 -> TcM (LTyClDecl Name, -- Kind-annotated decls
531 (Name,TcKind)) -- Kind bindings
532 kcSynDecl (AcyclicSCC (L loc decl))
533 = tcAddDeclCtxt decl $
534 kcHsTyVars (tcdTyVars decl) (\ k_tvs ->
535 do { traceTc "kcd1" (ppr (unLoc (tcdLName decl)) <+> brackets (ppr (tcdTyVars decl))
536 <+> brackets (ppr k_tvs))
537 ; (k_rhs, rhs_kind) <- kcLHsType (tcdSynRhs decl)
538 ; traceTc "kcd2" (ppr (unLoc (tcdLName decl)))
539 ; let tc_kind = foldr (mkArrowKind . hsTyVarKind . unLoc) rhs_kind k_tvs
540 ; return (L loc (decl { tcdTyVars = k_tvs, tcdSynRhs = k_rhs }),
541 (unLoc (tcdLName decl), tc_kind)) })
543 kcSynDecl (CyclicSCC decls)
544 = do { recSynErr decls; failM } -- Fail here to avoid error cascade
545 -- of out-of-scope tycons
547 ------------------------------------------------------------------------
548 kcTyClDecl :: TyClDecl Name -> TcM (TyClDecl Name)
549 -- Not used for type synonyms (see kcSynDecl)
551 kcTyClDecl decl@(TyData {})
552 = ASSERT( not . isFamInstDecl $ decl ) -- must not be a family instance
553 kcTyClDeclBody decl $
556 kcTyClDecl decl@(TyFamily {})
557 = kcFamilyDecl [] decl -- the empty list signals a toplevel decl
559 kcTyClDecl decl@(ClassDecl {tcdCtxt = ctxt, tcdSigs = sigs, tcdATs = ats})
560 = kcTyClDeclBody decl $ \ tvs' ->
561 do { ctxt' <- kcHsContext ctxt
562 ; ats' <- mapM (wrapLocM (kcFamilyDecl tvs')) ats
563 ; sigs' <- mapM (wrapLocM kc_sig) sigs
564 ; return (decl {tcdTyVars = tvs', tcdCtxt = ctxt', tcdSigs = sigs',
567 kc_sig (TypeSig nm op_ty) = do { op_ty' <- kcHsLiftedSigType op_ty
568 ; return (TypeSig nm op_ty') }
569 kc_sig other_sig = return other_sig
571 kcTyClDecl decl@(ForeignType {})
574 kcTyClDecl (TySynonym {}) = panic "kcTyClDecl TySynonym"
576 kcTyClDeclBody :: TyClDecl Name
577 -> ([LHsTyVarBndr Name] -> TcM a)
579 -- getInitialKind has made a suitably-shaped kind for the type or class
580 -- Unpack it, and attribute those kinds to the type variables
581 -- Extend the env with bindings for the tyvars, taken from
582 -- the kind of the tycon/class. Give it to the thing inside, and
583 -- check the result kind matches
584 kcTyClDeclBody decl thing_inside
585 = tcAddDeclCtxt decl $
586 do { tc_ty_thing <- tcLookupLocated (tcdLName decl)
587 ; let tc_kind = case tc_ty_thing of
589 _ -> pprPanic "kcTyClDeclBody" (ppr tc_ty_thing)
590 (kinds, _) = splitKindFunTys tc_kind
591 hs_tvs = tcdTyVars decl
592 kinded_tvs = ASSERT( length kinds >= length hs_tvs )
593 zipWith add_kind hs_tvs kinds
594 ; tcExtendKindEnvTvs kinded_tvs thing_inside }
596 add_kind (L loc (UserTyVar n _)) k = L loc (UserTyVar n k)
597 add_kind (L loc (KindedTyVar n _)) k = L loc (KindedTyVar n k)
599 -- Kind check a data declaration, assuming that we already extended the
600 -- kind environment with the type variables of the left-hand side (these
601 -- kinded type variables are also passed as the second parameter).
603 kcDataDecl :: TyClDecl Name -> [LHsTyVarBndr Name] -> TcM (TyClDecl Name)
604 kcDataDecl decl@(TyData {tcdND = new_or_data, tcdCtxt = ctxt, tcdCons = cons})
606 = do { ctxt' <- kcHsContext ctxt
607 ; cons' <- mapM (wrapLocM kc_con_decl) cons
608 ; return (decl {tcdTyVars = tvs, tcdCtxt = ctxt', tcdCons = cons'}) }
610 -- doc comments are typechecked to Nothing here
611 kc_con_decl con_decl@(ConDecl { con_name = name, con_qvars = ex_tvs
612 , con_cxt = ex_ctxt, con_details = details, con_res = res })
613 = addErrCtxt (dataConCtxt name) $
614 kcHsTyVars ex_tvs $ \ex_tvs' -> do
615 do { ex_ctxt' <- kcHsContext ex_ctxt
616 ; details' <- kc_con_details details
617 ; res' <- case res of
618 ResTyH98 -> return ResTyH98
619 ResTyGADT ty -> do { ty' <- kcHsSigType ty; return (ResTyGADT ty') }
620 ; return (con_decl { con_qvars = ex_tvs', con_cxt = ex_ctxt'
621 , con_details = details', con_res = res' }) }
623 kc_con_details (PrefixCon btys)
624 = do { btys' <- mapM kc_larg_ty btys
625 ; return (PrefixCon btys') }
626 kc_con_details (InfixCon bty1 bty2)
627 = do { bty1' <- kc_larg_ty bty1
628 ; bty2' <- kc_larg_ty bty2
629 ; return (InfixCon bty1' bty2') }
630 kc_con_details (RecCon fields)
631 = do { fields' <- mapM kc_field fields
632 ; return (RecCon fields') }
634 kc_field (ConDeclField fld bty d) = do { bty' <- kc_larg_ty bty
635 ; return (ConDeclField fld bty' d) }
637 kc_larg_ty bty = case new_or_data of
638 DataType -> kcHsSigType bty
639 NewType -> kcHsLiftedSigType bty
640 -- Can't allow an unlifted type for newtypes, because we're effectively
641 -- going to remove the constructor while coercing it to a lifted type.
642 -- And newtypes can't be bang'd
643 kcDataDecl d _ = pprPanic "kcDataDecl" (ppr d)
645 -- Kind check a family declaration or type family default declaration.
647 kcFamilyDecl :: [LHsTyVarBndr Name] -- tyvars of enclosing class decl if any
648 -> TyClDecl Name -> TcM (TyClDecl Name)
649 kcFamilyDecl classTvs decl@(TyFamily {tcdKind = kind})
650 = kcTyClDeclBody decl $ \tvs' ->
651 do { mapM_ unifyClassParmKinds tvs'
652 ; return (decl {tcdTyVars = tvs',
653 tcdKind = kind `mplus` Just liftedTypeKind})
654 -- default result kind is '*'
657 unifyClassParmKinds (L _ tv)
658 | (n,k) <- hsTyVarNameKind tv
659 , Just classParmKind <- lookup n classTyKinds
660 = unifyKind k classParmKind
661 | otherwise = return ()
662 classTyKinds = [hsTyVarNameKind tv | L _ tv <- classTvs]
664 kcFamilyDecl _ (TySynonym {}) -- type family defaults
665 = panic "TcTyClsDecls.kcFamilyDecl: not implemented yet"
666 kcFamilyDecl _ d = pprPanic "kcFamilyDecl" (ppr d)
670 %************************************************************************
672 \subsection{Type checking}
674 %************************************************************************
677 tcSynDecls :: [LTyClDecl Name] -> TcM [TyThing]
678 tcSynDecls [] = return []
679 tcSynDecls (decl : decls)
680 = do { syn_tc <- addLocM tcSynDecl decl
681 ; syn_tcs <- tcExtendGlobalEnv [syn_tc] (tcSynDecls decls)
682 ; return (syn_tc : syn_tcs) }
685 tcSynDecl :: TyClDecl Name -> TcM TyThing
687 (TySynonym {tcdLName = L _ tc_name, tcdTyVars = tvs, tcdSynRhs = rhs_ty})
688 = tcTyVarBndrs tvs $ \ tvs' -> do
689 { traceTc "tcd1" (ppr tc_name)
690 ; rhs_ty' <- tcHsKindedType rhs_ty
691 ; tycon <- buildSynTyCon tc_name tvs' (SynonymTyCon rhs_ty')
692 (typeKind rhs_ty') NoParentTyCon Nothing
693 ; return (ATyCon tycon)
695 tcSynDecl d = pprPanic "tcSynDecl" (ppr d)
698 tcTyClDecl :: (Name -> RecFlag) -> TyClDecl Name -> TcM [TyThing]
700 tcTyClDecl calc_isrec decl
701 = tcAddDeclCtxt decl (tcTyClDecl1 NoParentTyCon calc_isrec decl)
703 -- "type family" declarations
704 tcTyClDecl1 :: TyConParent -> (Name -> RecFlag) -> TyClDecl Name -> TcM [TyThing]
705 tcTyClDecl1 parent _calc_isrec
706 (TyFamily {tcdFlavour = TypeFamily,
707 tcdLName = L _ tc_name, tcdTyVars = tvs,
708 tcdKind = Just kind}) -- NB: kind at latest added during kind checking
709 = tcTyVarBndrs tvs $ \ tvs' -> do
710 { traceTc "type family:" (ppr tc_name)
712 -- Check that we don't use families without -XTypeFamilies
713 ; idx_tys <- doptM Opt_TypeFamilies
714 ; checkTc idx_tys $ badFamInstDecl tc_name
716 ; tycon <- buildSynTyCon tc_name tvs' SynFamilyTyCon kind parent Nothing
717 ; return [ATyCon tycon]
720 -- "data family" declaration
721 tcTyClDecl1 parent _calc_isrec
722 (TyFamily {tcdFlavour = DataFamily,
723 tcdLName = L _ tc_name, tcdTyVars = tvs, tcdKind = mb_kind})
724 = tcTyVarBndrs tvs $ \ tvs' -> do
725 { traceTc "data family:" (ppr tc_name)
726 ; extra_tvs <- tcDataKindSig mb_kind
727 ; let final_tvs = tvs' ++ extra_tvs -- we may not need these
730 -- Check that we don't use families without -XTypeFamilies
731 ; idx_tys <- doptM Opt_TypeFamilies
732 ; checkTc idx_tys $ badFamInstDecl tc_name
734 ; tycon <- buildAlgTyCon tc_name final_tvs []
735 DataFamilyTyCon Recursive False True
737 ; return [ATyCon tycon]
740 -- "newtype" and "data"
741 -- NB: not used for newtype/data instances (whether associated or not)
742 tcTyClDecl1 parent calc_isrec
743 (TyData {tcdND = new_or_data, tcdCtxt = ctxt, tcdTyVars = tvs,
744 tcdLName = L _ tc_name, tcdKindSig = mb_ksig, tcdCons = cons})
745 = tcTyVarBndrs tvs $ \ tvs' -> do
746 { extra_tvs <- tcDataKindSig mb_ksig
747 ; let final_tvs = tvs' ++ extra_tvs
748 ; stupid_theta <- tcHsKindedContext ctxt
749 ; want_generic <- doptM Opt_Generics
750 ; unbox_strict <- doptM Opt_UnboxStrictFields
751 ; empty_data_decls <- doptM Opt_EmptyDataDecls
752 ; kind_signatures <- doptM Opt_KindSignatures
753 ; existential_ok <- doptM Opt_ExistentialQuantification
754 ; gadt_ok <- doptM Opt_GADTs
755 ; is_boot <- tcIsHsBoot -- Are we compiling an hs-boot file?
756 ; let ex_ok = existential_ok || gadt_ok -- Data cons can have existential context
758 -- Check that we don't use GADT syntax in H98 world
759 ; checkTc (gadt_ok || h98_syntax) (badGadtDecl tc_name)
761 -- Check that we don't use kind signatures without Glasgow extensions
762 ; checkTc (kind_signatures || isNothing mb_ksig) (badSigTyDecl tc_name)
764 -- Check that the stupid theta is empty for a GADT-style declaration
765 ; checkTc (null stupid_theta || h98_syntax) (badStupidTheta tc_name)
767 -- Check that a newtype has exactly one constructor
768 -- Do this before checking for empty data decls, so that
769 -- we don't suggest -XEmptyDataDecls for newtypes
770 ; checkTc (new_or_data == DataType || isSingleton cons)
771 (newtypeConError tc_name (length cons))
773 -- Check that there's at least one condecl,
774 -- or else we're reading an hs-boot file, or -XEmptyDataDecls
775 ; checkTc (not (null cons) || empty_data_decls || is_boot)
776 (emptyConDeclsErr tc_name)
778 ; tycon <- fixM (\ tycon -> do
779 { let res_ty = mkTyConApp tycon (mkTyVarTys final_tvs)
780 ; data_cons <- tcConDecls unbox_strict ex_ok
781 tycon (final_tvs, res_ty) cons
783 if null cons && is_boot -- In a hs-boot file, empty cons means
784 then return AbstractTyCon -- "don't know"; hence Abstract
785 else case new_or_data of
786 DataType -> return (mkDataTyConRhs data_cons)
787 NewType -> ASSERT( not (null data_cons) )
788 mkNewTyConRhs tc_name tycon (head data_cons)
789 ; buildAlgTyCon tc_name final_tvs stupid_theta tc_rhs is_rec
790 (want_generic && canDoGenerics data_cons) (not h98_syntax)
793 ; return [ATyCon tycon]
796 is_rec = calc_isrec tc_name
797 h98_syntax = consUseH98Syntax cons
799 tcTyClDecl1 _parent calc_isrec
800 (ClassDecl {tcdLName = L _ class_name, tcdTyVars = tvs,
801 tcdCtxt = ctxt, tcdMeths = meths,
802 tcdFDs = fundeps, tcdSigs = sigs, tcdATs = ats} )
803 = tcTyVarBndrs tvs $ \ tvs' -> do
804 { ctxt' <- tcHsKindedContext ctxt
805 ; fds' <- mapM (addLocM tc_fundep) fundeps
806 ; sig_stuff <- tcClassSigs class_name sigs meths
807 ; clas <- fixM $ \ clas -> do
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
813 ; atss' <- mapM (addLocM $ tcTyClDecl1 (AssocFamilyTyCon clas) (const Recursive)) ats
814 -- NB: 'ats' only contains "type family" and "data family"
815 -- declarations as well as type family defaults
816 ; buildClass False {- Must include unfoldings for selectors -}
817 class_name tvs' ctxt' fds' (concat atss')
819 ; return (AClass clas : map ATyCon (classATs clas))
820 -- NB: Order is important due to the call to `mkGlobalThings' when
821 -- tying the the type and class declaration type checking knot.
824 tc_fundep (tvs1, tvs2) = do { tvs1' <- mapM tcLookupTyVar tvs1 ;
825 ; tvs2' <- mapM tcLookupTyVar tvs2 ;
826 ; return (tvs1', tvs2') }
829 (ForeignType {tcdLName = L _ tc_name, tcdExtName = tc_ext_name})
830 = return [ATyCon (mkForeignTyCon tc_name tc_ext_name liftedTypeKind 0)]
832 tcTyClDecl1 _ _ d = pprPanic "tcTyClDecl1" (ppr d)
834 -----------------------------------
835 tcConDecls :: Bool -> Bool -> TyCon -> ([TyVar], Type)
836 -> [LConDecl Name] -> TcM [DataCon]
837 tcConDecls unbox ex_ok rep_tycon res_tmpl cons
838 = mapM (addLocM (tcConDecl unbox ex_ok rep_tycon res_tmpl)) cons
840 tcConDecl :: Bool -- True <=> -funbox-strict_fields
841 -> Bool -- True <=> -XExistentialQuantificaton or -XGADTs
842 -> TyCon -- Representation tycon
843 -> ([TyVar], Type) -- Return type template (with its template tyvars)
847 tcConDecl unbox_strict existential_ok rep_tycon res_tmpl -- Data types
848 (ConDecl {con_name =name, con_qvars = tvs, con_cxt = ctxt
849 , con_details = details, con_res = res_ty })
850 = addErrCtxt (dataConCtxt name) $
851 tcTyVarBndrs tvs $ \ tvs' -> do
852 { ctxt' <- tcHsKindedContext ctxt
853 ; checkTc (existential_ok || (null tvs && null (unLoc ctxt)))
854 (badExistential name)
855 ; (univ_tvs, ex_tvs, eq_preds, res_ty') <- tcResultType res_tmpl tvs' res_ty
857 tc_datacon is_infix field_lbls btys
858 = do { (arg_tys, stricts) <- mapAndUnzipM (tcConArg unbox_strict) btys
859 ; buildDataCon (unLoc name) is_infix
861 univ_tvs ex_tvs eq_preds ctxt' arg_tys
863 -- NB: we put data_tc, the type constructor gotten from the
864 -- constructor type signature into the data constructor;
865 -- that way checkValidDataCon can complain if it's wrong.
868 PrefixCon btys -> tc_datacon False [] btys
869 InfixCon bty1 bty2 -> tc_datacon True [] [bty1,bty2]
870 RecCon fields -> tc_datacon False field_names btys
872 field_names = map (unLoc . cd_fld_name) fields
873 btys = map cd_fld_type fields
877 -- data instance T (b,c) where
878 -- TI :: forall e. e -> T (e,e)
880 -- The representation tycon looks like this:
881 -- data :R7T b c where
882 -- TI :: forall b1 c1. (b1 ~ c1) => b1 -> :R7T b1 c1
883 -- In this case orig_res_ty = T (e,e)
885 tcResultType :: ([TyVar], Type) -- Template for result type; e.g.
886 -- data instance T [a] b c = ...
887 -- gives template ([a,b,c], T [a] b c)
888 -> [TyVar] -- where MkT :: forall x y z. ...
890 -> TcM ([TyVar], -- Universal
891 [TyVar], -- Existential (distinct OccNames from univs)
892 [(TyVar,Type)], -- Equality predicates
893 Type) -- Typechecked return type
894 -- We don't check that the TyCon given in the ResTy is
895 -- the same as the parent tycon, becuase we are in the middle
896 -- of a recursive knot; so it's postponed until checkValidDataCon
898 tcResultType (tmpl_tvs, res_ty) dc_tvs ResTyH98
899 = return (tmpl_tvs, dc_tvs, [], res_ty)
900 -- In H98 syntax the dc_tvs are the existential ones
901 -- data T a b c = forall d e. MkT ...
902 -- The {a,b,c} are tc_tvs, and {d,e} are dc_tvs
904 tcResultType (tmpl_tvs, res_tmpl) dc_tvs (ResTyGADT res_ty)
905 -- E.g. data T [a] b c where
906 -- MkT :: forall x y z. T [(x,y)] z z
908 -- Univ tyvars Eq-spec
912 -- Existentials are the leftover type vars: [x,y]
913 -- So we return ([a,b,z], [x,y], [a~(x,y),b~z], T [(x,y)] z z)
914 = do { res_ty' <- tcHsKindedType res_ty
915 ; let Just subst = tcMatchTy (mkVarSet tmpl_tvs) res_tmpl res_ty'
917 -- /Lazily/ figure out the univ_tvs etc
918 -- Each univ_tv is either a dc_tv or a tmpl_tv
919 (univ_tvs, eq_spec) = foldr choose ([], []) tidy_tmpl_tvs
920 choose tmpl (univs, eqs)
921 | Just ty <- lookupTyVar subst tmpl
922 = case tcGetTyVar_maybe ty of
923 Just tv | not (tv `elem` univs)
925 _other -> (tmpl:univs, (tmpl,ty):eqs)
926 | otherwise = pprPanic "tcResultType" (ppr res_ty)
927 ex_tvs = dc_tvs `minusList` univ_tvs
929 ; return (univ_tvs, ex_tvs, eq_spec, res_ty') }
931 -- NB: tmpl_tvs and dc_tvs are distinct, but
932 -- we want them to be *visibly* distinct, both for
933 -- interface files and general confusion. So rename
934 -- the tc_tvs, since they are not used yet (no
935 -- consequential renaming needed)
936 (_, tidy_tmpl_tvs) = mapAccumL tidy_one init_occ_env tmpl_tvs
937 init_occ_env = initTidyOccEnv (map getOccName dc_tvs)
938 tidy_one env tv = (env', setTyVarName tv (tidyNameOcc name occ'))
941 (env', occ') = tidyOccName env (getOccName name)
943 consUseH98Syntax :: [LConDecl a] -> Bool
944 consUseH98Syntax (L _ (ConDecl { con_res = ResTyGADT _ }) : _) = False
945 consUseH98Syntax _ = True
946 -- All constructors have same shape
949 tcConArg :: Bool -- True <=> -funbox-strict_fields
951 -> TcM (TcType, HsBang)
952 tcConArg unbox_strict bty
953 = do { arg_ty <- tcHsBangType bty
954 ; let bang = getBangStrictness bty
955 ; let strict_mark = chooseBoxingStrategy unbox_strict arg_ty bang
956 ; return (arg_ty, strict_mark) }
958 -- We attempt to unbox/unpack a strict field when either:
959 -- (i) The field is marked '!!', or
960 -- (ii) The field is marked '!', and the -funbox-strict-fields flag is on.
962 -- We have turned off unboxing of newtypes because coercions make unboxing
963 -- and reboxing more complicated
964 chooseBoxingStrategy :: Bool -> TcType -> HsBang -> HsBang
965 chooseBoxingStrategy unbox_strict_fields arg_ty bang
968 HsUnpack -> can_unbox HsUnpackFailed arg_ty
969 HsStrict | unbox_strict_fields -> can_unbox HsStrict arg_ty
970 | otherwise -> HsStrict
971 HsUnpackFailed -> pprPanic "chooseBoxingStrategy" (ppr arg_ty)
972 -- Source code never has shtes
974 can_unbox :: HsBang -> TcType -> HsBang
975 -- Returns HsUnpack if we can unpack arg_ty
976 -- fail_bang if we know what arg_ty is but we can't unpack it
977 -- HsStrict if it's abstract, so we don't know whether or not we can unbox it
978 can_unbox fail_bang arg_ty
979 = case splitTyConApp_maybe arg_ty of
982 Just (arg_tycon, tycon_args)
983 | isAbstractTyCon arg_tycon -> HsStrict
984 -- See Note [Don't complain about UNPACK on abstract TyCons]
985 | not (isRecursiveTyCon arg_tycon) -- Note [Recusive unboxing]
986 , isProductTyCon arg_tycon
987 -- We can unbox if the type is a chain of newtypes
988 -- with a product tycon at the end
989 -> if isNewTyCon arg_tycon
990 then can_unbox fail_bang (newTyConInstRhs arg_tycon tycon_args)
993 | otherwise -> fail_bang
996 Note [Don't complain about UNPACK on abstract TyCons]
997 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
998 We are going to complain about UnpackFailed, but if we say
999 data T = MkT {-# UNPACK #-} !Wobble
1000 and Wobble is a newtype imported from a module that was compiled
1001 without optimisation, we don't want to complain. Because it might
1002 be fine when optimsation is on. I think this happens when Haddock
1003 is working over (say) GHC souce files.
1005 Note [Recursive unboxing]
1006 ~~~~~~~~~~~~~~~~~~~~~~~~~
1007 Be careful not to try to unbox this!
1009 But it's the *argument* type that matters. This is fine:
1011 because Int is non-recursive.
1014 %************************************************************************
1018 %************************************************************************
1020 Validity checking is done once the mutually-recursive knot has been
1021 tied, so we can look at things freely.
1024 checkCycleErrs :: [LTyClDecl Name] -> TcM ()
1025 checkCycleErrs tyclss
1029 = do { mapM_ recClsErr cls_cycles
1030 ; failM } -- Give up now, because later checkValidTyCl
1031 -- will loop if the synonym is recursive
1033 cls_cycles = calcClassCycles tyclss
1035 checkValidTyCl :: TyClDecl Name -> TcM ()
1036 -- We do the validity check over declarations, rather than TyThings
1037 -- only so that we can add a nice context with tcAddDeclCtxt
1039 = tcAddDeclCtxt decl $
1040 do { thing <- tcLookupLocatedGlobal (tcdLName decl)
1041 ; traceTc "Validity of" (ppr thing)
1043 ATyCon tc -> checkValidTyCon tc
1044 AClass cl -> checkValidClass cl
1045 _ -> panic "checkValidTyCl"
1046 ; traceTc "Done validity of" (ppr thing)
1049 -------------------------
1050 -- For data types declared with record syntax, we require
1051 -- that each constructor that has a field 'f'
1052 -- (a) has the same result type
1053 -- (b) has the same type for 'f'
1054 -- module alpha conversion of the quantified type variables
1055 -- of the constructor.
1057 -- Note that we allow existentials to match becuase the
1058 -- fields can never meet. E.g
1060 -- T1 { f1 :: b, f2 :: a, f3 ::Int } :: T
1061 -- T2 { f1 :: c, f2 :: c, f3 ::Int } :: T
1062 -- Here we do not complain about f1,f2 because they are existential
1064 checkValidTyCon :: TyCon -> TcM ()
1067 = case synTyConRhs tc of
1068 SynFamilyTyCon {} -> return ()
1069 SynonymTyCon ty -> checkValidType syn_ctxt ty
1071 = do -- Check the context on the data decl
1072 checkValidTheta (DataTyCtxt name) (tyConStupidTheta tc)
1074 -- Check arg types of data constructors
1075 mapM_ (checkValidDataCon tc) data_cons
1077 -- Check that fields with the same name share a type
1078 mapM_ check_fields groups
1081 syn_ctxt = TySynCtxt name
1083 data_cons = tyConDataCons tc
1085 groups = equivClasses cmp_fld (concatMap get_fields data_cons)
1086 cmp_fld (f1,_) (f2,_) = f1 `compare` f2
1087 get_fields con = dataConFieldLabels con `zip` repeat con
1088 -- dataConFieldLabels may return the empty list, which is fine
1090 -- See Note [GADT record selectors] in MkId.lhs
1091 -- We must check (a) that the named field has the same
1092 -- type in each constructor
1093 -- (b) that those constructors have the same result type
1095 -- However, the constructors may have differently named type variable
1096 -- and (worse) we don't know how the correspond to each other. E.g.
1097 -- C1 :: forall a b. { f :: a, g :: b } -> T a b
1098 -- C2 :: forall d c. { f :: c, g :: c } -> T c d
1100 -- So what we do is to ust Unify.tcMatchTys to compare the first candidate's
1101 -- result type against other candidates' types BOTH WAYS ROUND.
1102 -- If they magically agrees, take the substitution and
1103 -- apply them to the latter ones, and see if they match perfectly.
1104 check_fields ((label, con1) : other_fields)
1105 -- These fields all have the same name, but are from
1106 -- different constructors in the data type
1107 = recoverM (return ()) $ mapM_ checkOne other_fields
1108 -- Check that all the fields in the group have the same type
1109 -- NB: this check assumes that all the constructors of a given
1110 -- data type use the same type variables
1112 (tvs1, _, _, res1) = dataConSig con1
1114 fty1 = dataConFieldType con1 label
1116 checkOne (_, con2) -- Do it bothways to ensure they are structurally identical
1117 = do { checkFieldCompat label con1 con2 ts1 res1 res2 fty1 fty2
1118 ; checkFieldCompat label con2 con1 ts2 res2 res1 fty2 fty1 }
1120 (tvs2, _, _, res2) = dataConSig con2
1122 fty2 = dataConFieldType con2 label
1123 check_fields [] = panic "checkValidTyCon/check_fields []"
1125 checkFieldCompat :: Name -> DataCon -> DataCon -> TyVarSet
1126 -> Type -> Type -> Type -> Type -> TcM ()
1127 checkFieldCompat fld con1 con2 tvs1 res1 res2 fty1 fty2
1128 = do { checkTc (isJust mb_subst1) (resultTypeMisMatch fld con1 con2)
1129 ; checkTc (isJust mb_subst2) (fieldTypeMisMatch fld con1 con2) }
1131 mb_subst1 = tcMatchTy tvs1 res1 res2
1132 mb_subst2 = tcMatchTyX tvs1 (expectJust "checkFieldCompat" mb_subst1) fty1 fty2
1134 -------------------------------
1135 checkValidDataCon :: TyCon -> DataCon -> TcM ()
1136 checkValidDataCon tc con
1137 = setSrcSpan (srcLocSpan (getSrcLoc con)) $
1138 addErrCtxt (dataConCtxt con) $
1139 do { traceTc "Validity of data con" (ppr con)
1140 ; let tc_tvs = tyConTyVars tc
1141 res_ty_tmpl = mkFamilyTyConApp tc (mkTyVarTys tc_tvs)
1142 actual_res_ty = dataConOrigResTy con
1143 ; checkTc (isJust (tcMatchTy (mkVarSet tc_tvs)
1146 (badDataConTyCon con res_ty_tmpl actual_res_ty)
1147 ; checkValidMonoType (dataConOrigResTy con)
1148 -- Disallow MkT :: T (forall a. a->a)
1149 -- Reason: it's really the argument of an equality constraint
1150 ; checkValidType ctxt (dataConUserType con)
1151 ; when (isNewTyCon tc) (checkNewDataCon con)
1152 ; mapM_ check_bang (dataConStrictMarks con `zip` [1..])
1155 ctxt = ConArgCtxt (dataConName con)
1156 check_bang (HsUnpackFailed, n) = addWarnTc (cant_unbox_msg n)
1157 check_bang _ = return ()
1159 cant_unbox_msg n = sep [ ptext (sLit "Ignoring unusable UNPACK pragma on the")
1160 , speakNth n <+> ptext (sLit "argument of") <+> quotes (ppr con)]
1162 -------------------------------
1163 checkNewDataCon :: DataCon -> TcM ()
1164 -- Checks for the data constructor of a newtype
1166 = do { checkTc (isSingleton arg_tys) (newtypeFieldErr con (length arg_tys))
1168 ; checkTc (null eq_spec) (newtypePredError con)
1169 -- Return type is (T a b c)
1170 ; checkTc (null ex_tvs && null eq_theta && null dict_theta) (newtypeExError con)
1172 ; checkTc (not (any isBanged (dataConStrictMarks con)))
1173 (newtypeStrictError con)
1177 (_univ_tvs, ex_tvs, eq_spec, eq_theta, dict_theta, arg_tys, _res_ty) = dataConFullSig con
1179 -------------------------------
1180 checkValidClass :: Class -> TcM ()
1182 = do { constrained_class_methods <- doptM Opt_ConstrainedClassMethods
1183 ; multi_param_type_classes <- doptM Opt_MultiParamTypeClasses
1184 ; fundep_classes <- doptM Opt_FunctionalDependencies
1186 -- Check that the class is unary, unless GlaExs
1187 ; checkTc (notNull tyvars) (nullaryClassErr cls)
1188 ; checkTc (multi_param_type_classes || unary) (classArityErr cls)
1189 ; checkTc (fundep_classes || null fundeps) (classFunDepsErr cls)
1191 -- Check the super-classes
1192 ; checkValidTheta (ClassSCCtxt (className cls)) theta
1194 -- Check the class operations
1195 ; mapM_ (check_op constrained_class_methods) op_stuff
1197 -- Check that if the class has generic methods, then the
1198 -- class has only one parameter. We can't do generic
1199 -- multi-parameter type classes!
1200 ; checkTc (unary || no_generics) (genericMultiParamErr cls)
1203 (tyvars, fundeps, theta, _, _, op_stuff) = classExtraBigSig cls
1204 unary = isSingleton tyvars
1205 no_generics = null [() | (_, GenDefMeth) <- op_stuff]
1207 check_op constrained_class_methods (sel_id, dm)
1208 = addErrCtxt (classOpCtxt sel_id tau) $ do
1209 { checkValidTheta SigmaCtxt (tail theta)
1210 -- The 'tail' removes the initial (C a) from the
1211 -- class itself, leaving just the method type
1213 ; traceTc "class op type" (ppr op_ty <+> ppr tau)
1214 ; checkValidType (FunSigCtxt op_name) tau
1216 -- Check that the type mentions at least one of
1217 -- the class type variables...or at least one reachable
1218 -- from one of the class variables. Example: tc223
1219 -- class Error e => Game b mv e | b -> mv e where
1220 -- newBoard :: MonadState b m => m ()
1221 -- Here, MonadState has a fundep m->b, so newBoard is fine
1222 ; let grown_tyvars = growThetaTyVars theta (mkVarSet tyvars)
1223 ; checkTc (tyVarsOfType tau `intersectsVarSet` grown_tyvars)
1224 (noClassTyVarErr cls sel_id)
1226 -- Check that for a generic method, the type of
1227 -- the method is sufficiently simple
1228 ; checkTc (dm /= GenDefMeth || validGenericMethodType tau)
1229 (badGenericMethodType op_name op_ty)
1232 op_name = idName sel_id
1233 op_ty = idType sel_id
1234 (_,theta1,tau1) = tcSplitSigmaTy op_ty
1235 (_,theta2,tau2) = tcSplitSigmaTy tau1
1236 (theta,tau) | constrained_class_methods = (theta1 ++ theta2, tau2)
1237 | otherwise = (theta1, mkPhiTy (tail theta1) tau1)
1238 -- Ugh! The function might have a type like
1239 -- op :: forall a. C a => forall b. (Eq b, Eq a) => tau2
1240 -- With -XConstrainedClassMethods, we want to allow this, even though the inner
1241 -- forall has an (Eq a) constraint. Whereas in general, each constraint
1242 -- in the context of a for-all must mention at least one quantified
1243 -- type variable. What a mess!
1247 %************************************************************************
1249 Building record selectors
1251 %************************************************************************
1254 mkDefaultMethodIds :: [TyThing] -> [Id]
1255 -- See Note [Default method Ids and Template Haskell]
1256 mkDefaultMethodIds things
1257 = [ mkDefaultMethodId sel_id dm_name
1258 | AClass cls <- things
1259 , (sel_id, DefMeth dm_name) <- classOpItems cls ]
1262 Note [Default method Ids and Template Haskell]
1263 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1264 Consider this (Trac #4169):
1265 class Numeric a where
1267 fromIntegerNum = ...
1270 ast = [d| instance Numeric Int |]
1272 When we typecheck 'ast' we have done the first pass over the class decl
1273 (in tcTyClDecls), but we have not yet typechecked the default-method
1274 declarations (becuase they can mention value declarations). So we
1275 must bring the default method Ids into scope first (so they can be seen
1276 when typechecking the [d| .. |] quote, and typecheck them later.
1279 mkRecSelBinds :: [TyThing] -> HsValBinds Name
1280 -- NB We produce *un-typechecked* bindings, rather like 'deriving'
1281 -- This makes life easier, because the later type checking will add
1282 -- all necessary type abstractions and applications
1283 mkRecSelBinds ty_things
1284 = ValBindsOut [(NonRecursive, b) | b <- binds] sigs
1286 (sigs, binds) = unzip rec_sels
1287 rec_sels = map mkRecSelBind [ (tc,fld)
1288 | ATyCon tc <- ty_things
1289 , fld <- tyConFields tc ]
1291 mkRecSelBind :: (TyCon, FieldLabel) -> (LSig Name, LHsBinds Name)
1292 mkRecSelBind (tycon, sel_name)
1293 = (L loc (IdSig sel_id), unitBag (L loc sel_bind))
1295 loc = getSrcSpan tycon
1296 sel_id = Var.mkLocalVar rec_details sel_name sel_ty vanillaIdInfo
1297 rec_details = RecSelId { sel_tycon = tycon, sel_naughty = is_naughty }
1299 -- Find a representative constructor, con1
1300 all_cons = tyConDataCons tycon
1301 cons_w_field = [ con | con <- all_cons
1302 , sel_name `elem` dataConFieldLabels con ]
1303 con1 = ASSERT( not (null cons_w_field) ) head cons_w_field
1305 -- Selector type; Note [Polymorphic selectors]
1306 field_ty = dataConFieldType con1 sel_name
1307 data_ty = dataConOrigResTy con1
1308 data_tvs = tyVarsOfType data_ty
1309 is_naughty = not (tyVarsOfType field_ty `subVarSet` data_tvs)
1310 (field_tvs, field_theta, field_tau) = tcSplitSigmaTy field_ty
1311 sel_ty | is_naughty = unitTy -- See Note [Naughty record selectors]
1312 | otherwise = mkForAllTys (varSetElems data_tvs ++ field_tvs) $
1313 mkPhiTy (dataConStupidTheta con1) $ -- Urgh!
1314 mkPhiTy field_theta $ -- Urgh!
1315 mkFunTy data_ty field_tau
1317 -- Make the binding: sel (C2 { fld = x }) = x
1318 -- sel (C7 { fld = x }) = x
1319 -- where cons_w_field = [C2,C7]
1320 sel_bind | is_naughty = mkFunBind sel_lname [mkSimpleMatch [] unit_rhs]
1321 | otherwise = mkFunBind sel_lname (map mk_match cons_w_field ++ deflt)
1322 mk_match con = mkSimpleMatch [L loc (mk_sel_pat con)]
1323 (L loc (HsVar field_var))
1324 mk_sel_pat con = ConPatIn (L loc (getName con)) (RecCon rec_fields)
1325 rec_fields = HsRecFields { rec_flds = [rec_field], rec_dotdot = Nothing }
1326 rec_field = HsRecField { hsRecFieldId = sel_lname
1327 , hsRecFieldArg = nlVarPat field_var
1328 , hsRecPun = False }
1329 sel_lname = L loc sel_name
1330 field_var = mkInternalName (mkBuiltinUnique 1) (getOccName sel_name) loc
1332 -- Add catch-all default case unless the case is exhaustive
1333 -- We do this explicitly so that we get a nice error message that
1334 -- mentions this particular record selector
1335 deflt | not (any is_unused all_cons) = []
1336 | otherwise = [mkSimpleMatch [nlWildPat]
1337 (nlHsApp (nlHsVar (getName rEC_SEL_ERROR_ID))
1340 -- Do not add a default case unless there are unmatched
1341 -- constructors. We must take account of GADTs, else we
1342 -- get overlap warning messages from the pattern-match checker
1343 is_unused con = not (con `elem` cons_w_field
1344 || dataConCannotMatch inst_tys con)
1345 inst_tys = tyConAppArgs data_ty
1347 unit_rhs = mkLHsTupleExpr []
1348 msg_lit = HsStringPrim $ mkFastString $
1349 occNameString (getOccName sel_name)
1352 tyConFields :: TyCon -> [FieldLabel]
1354 | isAlgTyCon tc = nub (concatMap dataConFieldLabels (tyConDataCons tc))
1358 Note [Polymorphic selectors]
1359 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1360 When a record has a polymorphic field, we pull the foralls out to the front.
1361 data T = MkT { f :: forall a. [a] -> a }
1362 Then f :: forall a. T -> [a] -> a
1363 NOT f :: T -> forall a. [a] -> a
1365 This is horrid. It's only needed in deeply obscure cases, which I hate.
1366 The only case I know is test tc163, which is worth looking at. It's far
1367 from clear that this test should succeed at all!
1369 Note [Naughty record selectors]
1370 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1371 A "naughty" field is one for which we can't define a record
1372 selector, because an existential type variable would escape. For example:
1373 data T = forall a. MkT { x,y::a }
1374 We obviously can't define
1376 Nevertheless we *do* put a RecSelId into the type environment
1377 so that if the user tries to use 'x' as a selector we can bleat
1378 helpfully, rather than saying unhelpfully that 'x' is not in scope.
1379 Hence the sel_naughty flag, to identify record selectors that don't really exist.
1381 In general, a field is "naughty" if its type mentions a type variable that
1382 isn't in the result type of the constructor. Note that this *allows*
1383 GADT record selectors (Note [GADT record selectors]) whose types may look
1384 like sel :: T [a] -> a
1386 For naughty selectors we make a dummy binding
1388 for naughty selectors, so that the later type-check will add them to the
1389 environment, and they'll be exported. The function is never called, because
1390 the tyepchecker spots the sel_naughty field.
1392 Note [GADT record selectors]
1393 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1394 For GADTs, we require that all constructors with a common field 'f' have the same
1395 result type (modulo alpha conversion). [Checked in TcTyClsDecls.checkValidTyCon]
1398 T1 { f :: Maybe a } :: T [a]
1399 T2 { f :: Maybe a, y :: b } :: T [a]
1401 and now the selector takes that result type as its argument:
1402 f :: forall a. T [a] -> Maybe a
1404 Details: the "real" types of T1,T2 are:
1405 T1 :: forall r a. (r~[a]) => a -> T r
1406 T2 :: forall r a b. (r~[a]) => a -> b -> T r
1408 So the selector loooks like this:
1409 f :: forall a. T [a] -> Maybe a
1412 T1 c (g:[a]~[c]) (v:Maybe c) -> v `cast` Maybe (right (sym g))
1413 T2 c d (g:[a]~[c]) (v:Maybe c) (w:d) -> v `cast` Maybe (right (sym g))
1415 Note the forall'd tyvars of the selector are just the free tyvars
1416 of the result type; there may be other tyvars in the constructor's
1417 type (e.g. 'b' in T2).
1419 Note the need for casts in the result!
1421 Note [Selector running example]
1422 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1423 It's OK to combine GADTs and type families. Here's a running example:
1425 data instance T [a] where
1426 T1 { fld :: b } :: T [Maybe b]
1428 The representation type looks like this
1430 T1 { fld :: b } :: :R7T (Maybe b)
1432 and there's coercion from the family type to the representation type
1433 :CoR7T a :: T [a] ~ :R7T a
1435 The selector we want for fld looks like this:
1437 fld :: forall b. T [Maybe b] -> b
1438 fld = /\b. \(d::T [Maybe b]).
1439 case d `cast` :CoR7T (Maybe b) of
1442 The scrutinee of the case has type :R7T (Maybe b), which can be
1443 gotten by appying the eq_spec to the univ_tvs of the data con.
1445 %************************************************************************
1449 %************************************************************************
1452 resultTypeMisMatch :: Name -> DataCon -> DataCon -> SDoc
1453 resultTypeMisMatch field_name con1 con2
1454 = vcat [sep [ptext (sLit "Constructors") <+> ppr con1 <+> ptext (sLit "and") <+> ppr con2,
1455 ptext (sLit "have a common field") <+> quotes (ppr field_name) <> comma],
1456 nest 2 $ ptext (sLit "but have different result types")]
1458 fieldTypeMisMatch :: Name -> DataCon -> DataCon -> SDoc
1459 fieldTypeMisMatch field_name con1 con2
1460 = sep [ptext (sLit "Constructors") <+> ppr con1 <+> ptext (sLit "and") <+> ppr con2,
1461 ptext (sLit "give different types for field"), quotes (ppr field_name)]
1463 dataConCtxt :: Outputable a => a -> SDoc
1464 dataConCtxt con = ptext (sLit "In the definition of data constructor") <+> quotes (ppr con)
1466 classOpCtxt :: Var -> Type -> SDoc
1467 classOpCtxt sel_id tau = sep [ptext (sLit "When checking the class method:"),
1468 nest 2 (ppr sel_id <+> dcolon <+> ppr tau)]
1470 nullaryClassErr :: Class -> SDoc
1472 = ptext (sLit "No parameters for class") <+> quotes (ppr cls)
1474 classArityErr :: Class -> SDoc
1476 = vcat [ptext (sLit "Too many parameters for class") <+> quotes (ppr cls),
1477 parens (ptext (sLit "Use -XMultiParamTypeClasses to allow multi-parameter classes"))]
1479 classFunDepsErr :: Class -> SDoc
1481 = vcat [ptext (sLit "Fundeps in class") <+> quotes (ppr cls),
1482 parens (ptext (sLit "Use -XFunctionalDependencies to allow fundeps"))]
1484 noClassTyVarErr :: Class -> Var -> SDoc
1485 noClassTyVarErr clas op
1486 = sep [ptext (sLit "The class method") <+> quotes (ppr op),
1487 ptext (sLit "mentions none of the type variables of the class") <+>
1488 ppr clas <+> hsep (map ppr (classTyVars clas))]
1490 genericMultiParamErr :: Class -> SDoc
1491 genericMultiParamErr clas
1492 = ptext (sLit "The multi-parameter class") <+> quotes (ppr clas) <+>
1493 ptext (sLit "cannot have generic methods")
1495 badGenericMethodType :: Name -> Kind -> SDoc
1496 badGenericMethodType op op_ty
1497 = hang (ptext (sLit "Generic method type is too complex"))
1498 2 (vcat [ppr op <+> dcolon <+> ppr op_ty,
1499 ptext (sLit "You can only use type variables, arrows, lists, and tuples")])
1501 recSynErr :: [LTyClDecl Name] -> TcRn ()
1503 = setSrcSpan (getLoc (head sorted_decls)) $
1504 addErr (sep [ptext (sLit "Cycle in type synonym declarations:"),
1505 nest 2 (vcat (map ppr_decl sorted_decls))])
1507 sorted_decls = sortLocated syn_decls
1508 ppr_decl (L loc decl) = ppr loc <> colon <+> ppr decl
1510 recClsErr :: [Located (TyClDecl Name)] -> TcRn ()
1512 = setSrcSpan (getLoc (head sorted_decls)) $
1513 addErr (sep [ptext (sLit "Cycle in class declarations (via superclasses):"),
1514 nest 2 (vcat (map ppr_decl sorted_decls))])
1516 sorted_decls = sortLocated cls_decls
1517 ppr_decl (L loc decl) = ppr loc <> colon <+> ppr (decl { tcdSigs = [] })
1519 sortLocated :: [Located a] -> [Located a]
1520 sortLocated things = sortLe le things
1522 le (L l1 _) (L l2 _) = l1 <= l2
1524 badDataConTyCon :: DataCon -> Type -> Type -> SDoc
1525 badDataConTyCon data_con res_ty_tmpl actual_res_ty
1526 = hang (ptext (sLit "Data constructor") <+> quotes (ppr data_con) <+>
1527 ptext (sLit "returns type") <+> quotes (ppr actual_res_ty))
1528 2 (ptext (sLit "instead of an instance of its parent type") <+> quotes (ppr res_ty_tmpl))
1530 badGadtDecl :: Name -> SDoc
1532 = vcat [ ptext (sLit "Illegal generalised algebraic data declaration for") <+> quotes (ppr tc_name)
1533 , nest 2 (parens $ ptext (sLit "Use -XGADTs to allow GADTs")) ]
1535 badExistential :: Located Name -> SDoc
1536 badExistential con_name
1537 = hang (ptext (sLit "Data constructor") <+> quotes (ppr con_name) <+>
1538 ptext (sLit "has existential type variables, or a context"))
1539 2 (parens $ ptext (sLit "Use -XExistentialQuantification or -XGADTs to allow this"))
1541 badStupidTheta :: Name -> SDoc
1542 badStupidTheta tc_name
1543 = ptext (sLit "A data type declared in GADT style cannot have a context:") <+> quotes (ppr tc_name)
1545 newtypeConError :: Name -> Int -> SDoc
1546 newtypeConError tycon n
1547 = sep [ptext (sLit "A newtype must have exactly one constructor,"),
1548 nest 2 $ ptext (sLit "but") <+> quotes (ppr tycon) <+> ptext (sLit "has") <+> speakN n ]
1550 newtypeExError :: DataCon -> SDoc
1552 = sep [ptext (sLit "A newtype constructor cannot have an existential context,"),
1553 nest 2 $ ptext (sLit "but") <+> quotes (ppr con) <+> ptext (sLit "does")]
1555 newtypeStrictError :: DataCon -> SDoc
1556 newtypeStrictError con
1557 = sep [ptext (sLit "A newtype constructor cannot have a strictness annotation,"),
1558 nest 2 $ ptext (sLit "but") <+> quotes (ppr con) <+> ptext (sLit "does")]
1560 newtypePredError :: DataCon -> SDoc
1561 newtypePredError con
1562 = sep [ptext (sLit "A newtype constructor must have a return type of form T a1 ... an"),
1563 nest 2 $ ptext (sLit "but") <+> quotes (ppr con) <+> ptext (sLit "does not")]
1565 newtypeFieldErr :: DataCon -> Int -> SDoc
1566 newtypeFieldErr con_name n_flds
1567 = sep [ptext (sLit "The constructor of a newtype must have exactly one field"),
1568 nest 2 $ ptext (sLit "but") <+> quotes (ppr con_name) <+> ptext (sLit "has") <+> speakN n_flds]
1570 badSigTyDecl :: Name -> SDoc
1571 badSigTyDecl tc_name
1572 = vcat [ ptext (sLit "Illegal kind signature") <+>
1573 quotes (ppr tc_name)
1574 , nest 2 (parens $ ptext (sLit "Use -XKindSignatures to allow kind signatures")) ]
1576 badFamInstDecl :: Outputable a => a -> SDoc
1577 badFamInstDecl tc_name
1578 = vcat [ ptext (sLit "Illegal family instance for") <+>
1579 quotes (ppr tc_name)
1580 , nest 2 (parens $ ptext (sLit "Use -XTypeFamilies to allow indexed type families")) ]
1582 tooManyParmsErr :: Located Name -> SDoc
1583 tooManyParmsErr tc_name
1584 = ptext (sLit "Family instance has too many parameters:") <+>
1585 quotes (ppr tc_name)
1587 tooFewParmsErr :: Arity -> SDoc
1588 tooFewParmsErr arity
1589 = ptext (sLit "Family instance has too few parameters; expected") <+>
1592 wrongNumberOfParmsErr :: Arity -> SDoc
1593 wrongNumberOfParmsErr exp_arity
1594 = ptext (sLit "Number of parameters must match family declaration; expected")
1597 badBootFamInstDeclErr :: SDoc
1598 badBootFamInstDeclErr
1599 = ptext (sLit "Illegal family instance in hs-boot file")
1601 notFamily :: TyCon -> SDoc
1603 = vcat [ ptext (sLit "Illegal family instance for") <+> quotes (ppr tycon)
1604 , nest 2 $ parens (ppr tycon <+> ptext (sLit "is not an indexed type family"))]
1606 wrongKindOfFamily :: TyCon -> SDoc
1607 wrongKindOfFamily family
1608 = ptext (sLit "Wrong category of family instance; declaration was for a")
1611 kindOfFamily | isSynTyCon family = ptext (sLit "type synonym")
1612 | isAlgTyCon family = ptext (sLit "data type")
1613 | otherwise = pprPanic "wrongKindOfFamily" (ppr family)
1615 emptyConDeclsErr :: Name -> SDoc
1616 emptyConDeclsErr tycon
1617 = sep [quotes (ppr tycon) <+> ptext (sLit "has no constructors"),
1618 nest 2 $ ptext (sLit "(-XEmptyDataDecls permits this)")]