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, mkAuxBinds
13 #include "HsVersions.h"
26 import TysWiredIn ( unitTy )
33 import MkId ( rEC_SEL_ERROR_ID )
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 -- Fails if there are any errors
142 tcTyAndClassDecls boot_details allDecls
143 = checkNoErrs $ -- The code recovers internally, but if anything gave rise to
144 -- an error we'd better stop now, to avoid a cascade
145 do { -- Omit instances of type families; they are handled together
146 -- with the *heads* of class instances
147 ; let decls = filter (not . isFamInstDecl . unLoc) allDecls
149 -- First check for cyclic type synonysm or classes
150 -- See notes with checkCycleErrs
151 ; checkCycleErrs decls
153 ; traceTc (text "tcTyAndCl" <+> ppr mod)
154 ; (syn_tycons, alg_tyclss) <- fixM (\ ~(_rec_syn_tycons, rec_alg_tyclss) ->
155 do { let { -- Seperate ordinary synonyms from all other type and
156 -- class declarations and add all associated type
157 -- declarations from type classes. The latter is
158 -- required so that the temporary environment for the
159 -- knot includes all associated family declarations.
160 ; (syn_decls, alg_decls) = partition (isSynDecl . unLoc)
162 ; alg_at_decls = concatMap addATs alg_decls
164 -- Extend the global env with the knot-tied results
165 -- for data types and classes
167 -- We must populate the environment with the loop-tied
168 -- T's right away, because the kind checker may "fault
169 -- in" some type constructors that recursively
171 ; let gbl_things = mkGlobalThings alg_at_decls rec_alg_tyclss
172 ; tcExtendRecEnv gbl_things $ do
174 -- Kind-check the declarations
175 { (kc_syn_decls, kc_alg_decls) <- kcTyClDecls syn_decls alg_decls
177 ; let { -- Calculate rec-flag
178 ; calc_rec = calcRecFlags boot_details rec_alg_tyclss
179 ; tc_decl = addLocM (tcTyClDecl calc_rec) }
181 -- Type-check the type synonyms, and extend the envt
182 ; syn_tycons <- tcSynDecls kc_syn_decls
183 ; tcExtendGlobalEnv syn_tycons $ do
185 -- Type-check the data types and classes
186 { alg_tyclss <- mapM tc_decl kc_alg_decls
187 ; return (syn_tycons, concat alg_tyclss)
189 -- Finished with knot-tying now
190 -- Extend the environment with the finished things
191 ; tcExtendGlobalEnv (syn_tycons ++ alg_tyclss) $ do
193 -- Perform the validity check
194 { traceTc (text "ready for validity check")
195 ; mapM_ (addLocM checkValidTyCl) decls
196 ; traceTc (text "done")
198 -- Add the implicit things;
199 -- we want them in the environment because
200 -- they may be mentioned in interface files
201 -- NB: All associated types and their implicit things will be added a
202 -- second time here. This doesn't matter as the definitions are
204 ; let { implicit_things = concatMap implicitTyThings alg_tyclss
205 ; aux_binds = mkAuxBinds alg_tyclss }
206 ; traceTc ((text "Adding" <+> ppr alg_tyclss)
207 $$ (text "and" <+> ppr implicit_things))
208 ; env <- tcExtendGlobalEnv implicit_things getGblEnv
209 ; return (env, aux_binds) }
212 -- Pull associated types out of class declarations, to tie them into the
214 -- NB: We put them in the same place in the list as `tcTyClDecl' will
215 -- eventually put the matching `TyThing's. That's crucial; otherwise,
216 -- the two argument lists of `mkGlobalThings' don't match up.
217 addATs decl@(L _ (ClassDecl {tcdATs = ats})) = decl : ats
220 mkGlobalThings :: [LTyClDecl Name] -- The decls
221 -> [TyThing] -- Knot-tied, in 1-1 correspondence with the decls
223 -- Driven by the Decls, and treating the TyThings lazily
224 -- make a TypeEnv for the new things
225 mkGlobalThings decls things
226 = map mk_thing (decls `zipLazy` things)
228 mk_thing (L _ (ClassDecl {tcdLName = L _ name}), ~(AClass cl))
230 mk_thing (L _ decl, ~(ATyCon tc))
231 = (tcdName decl, ATyCon tc)
235 %************************************************************************
237 Type checking family instances
239 %************************************************************************
241 Family instances are somewhat of a hybrid. They are processed together with
242 class instance heads, but can contain data constructors and hence they share a
243 lot of kinding and type checking code with ordinary algebraic data types (and
247 tcFamInstDecl :: LTyClDecl Name -> TcM TyThing
248 tcFamInstDecl (L loc decl)
249 = -- Prime error recovery, set source location
252 do { -- type family instances require -XTypeFamilies
253 -- and can't (currently) be in an hs-boot file
254 ; type_families <- doptM Opt_TypeFamilies
255 ; is_boot <- tcIsHsBoot -- Are we compiling an hs-boot file?
256 ; checkTc type_families $ badFamInstDecl (tcdLName decl)
257 ; checkTc (not is_boot) $ badBootFamInstDeclErr
259 -- Perform kind and type checking
260 ; tc <- tcFamInstDecl1 decl
261 ; checkValidTyCon tc -- Remember to check validity;
262 -- no recursion to worry about here
263 ; return (ATyCon tc) }
265 tcFamInstDecl1 :: TyClDecl Name -> TcM TyCon
268 tcFamInstDecl1 (decl@TySynonym {tcdLName = L loc tc_name})
269 = kcIdxTyPats decl $ \k_tvs k_typats resKind family ->
270 do { -- check that the family declaration is for a synonym
271 checkTc (isOpenTyCon family) (notFamily family)
272 ; checkTc (isSynTyCon family) (wrongKindOfFamily family)
274 ; -- (1) kind check the right-hand side of the type equation
275 ; k_rhs <- kcCheckLHsType (tcdSynRhs decl) (EK resKind EkUnk)
276 -- ToDo: the ExpKind could be better
278 -- we need the exact same number of type parameters as the family
280 ; let famArity = tyConArity family
281 ; checkTc (length k_typats == famArity) $
282 wrongNumberOfParmsErr famArity
284 -- (2) type check type equation
285 ; tcTyVarBndrs k_tvs $ \t_tvs -> do { -- turn kinded into proper tyvars
286 ; t_typats <- mapM tcHsKindedType k_typats
287 ; t_rhs <- tcHsKindedType k_rhs
289 -- (3) check the well-formedness of the instance
290 ; checkValidTypeInst t_typats t_rhs
292 -- (4) construct representation tycon
293 ; rep_tc_name <- newFamInstTyConName tc_name t_typats loc
294 ; buildSynTyCon rep_tc_name t_tvs (SynonymTyCon t_rhs)
295 (typeKind t_rhs) (Just (family, t_typats))
298 -- "newtype instance" and "data instance"
299 tcFamInstDecl1 (decl@TyData {tcdND = new_or_data, tcdLName = L loc tc_name,
301 = kcIdxTyPats decl $ \k_tvs k_typats resKind fam_tycon ->
302 do { -- check that the family declaration is for the right kind
303 checkTc (isOpenTyCon fam_tycon) (notFamily fam_tycon)
304 ; checkTc (isAlgTyCon fam_tycon) (wrongKindOfFamily fam_tycon)
306 ; -- (1) kind check the data declaration as usual
307 ; k_decl <- kcDataDecl decl k_tvs
308 ; let k_ctxt = tcdCtxt k_decl
309 k_cons = tcdCons k_decl
311 -- result kind must be '*' (otherwise, we have too few patterns)
312 ; checkTc (isLiftedTypeKind resKind) $ tooFewParmsErr (tyConArity fam_tycon)
314 -- (2) type check indexed data type declaration
315 ; tcTyVarBndrs k_tvs $ \t_tvs -> do { -- turn kinded into proper tyvars
316 ; unbox_strict <- doptM Opt_UnboxStrictFields
318 -- kind check the type indexes and the context
319 ; t_typats <- mapM tcHsKindedType k_typats
320 ; stupid_theta <- tcHsKindedContext k_ctxt
323 -- (a) left-hand side contains no type family applications
324 -- (vanilla synonyms are fine, though, and we checked for
326 ; mapM_ checkTyFamFreeness t_typats
328 -- Check that we don't use GADT syntax in H98 world
329 ; gadt_ok <- doptM Opt_GADTs
330 ; checkTc (gadt_ok || consUseH98Syntax cons) (badGadtDecl tc_name)
332 -- (b) a newtype has exactly one constructor
333 ; checkTc (new_or_data == DataType || isSingleton k_cons) $
334 newtypeConError tc_name (length k_cons)
336 -- (4) construct representation tycon
337 ; rep_tc_name <- newFamInstTyConName tc_name t_typats loc
338 ; let ex_ok = True -- Existentials ok for type families!
339 ; fixM (\ rep_tycon -> do
340 { let orig_res_ty = mkTyConApp fam_tycon t_typats
341 ; data_cons <- tcConDecls unbox_strict ex_ok rep_tycon
342 (t_tvs, orig_res_ty) k_cons
345 DataType -> return (mkDataTyConRhs data_cons)
346 NewType -> ASSERT( not (null data_cons) )
347 mkNewTyConRhs rep_tc_name rep_tycon (head data_cons)
348 ; buildAlgTyCon rep_tc_name t_tvs stupid_theta tc_rhs Recursive
349 False h98_syntax (Just (fam_tycon, t_typats))
350 -- We always assume that indexed types are recursive. Why?
351 -- (1) Due to their open nature, we can never be sure that a
352 -- further instance might not introduce a new recursive
353 -- dependency. (2) They are always valid loop breakers as
354 -- they involve a coercion.
358 h98_syntax = case cons of -- All constructors have same shape
359 L _ (ConDecl { con_res = ResTyGADT _ }) : _ -> False
362 tcFamInstDecl1 d = pprPanic "tcFamInstDecl1" (ppr d)
364 -- Kind checking of indexed types
367 -- Kind check type patterns and kind annotate the embedded type variables.
369 -- * Here we check that a type instance matches its kind signature, but we do
370 -- not check whether there is a pattern for each type index; the latter
371 -- check is only required for type synonym instances.
373 kcIdxTyPats :: TyClDecl Name
374 -> ([LHsTyVarBndr Name] -> [LHsType Name] -> Kind -> TyCon -> TcM a)
375 -- ^^kinded tvs ^^kinded ty pats ^^res kind
377 kcIdxTyPats decl thing_inside
378 = kcHsTyVars (tcdTyVars decl) $ \tvs ->
379 do { let tc_name = tcdLName decl
380 ; fam_tycon <- tcLookupLocatedTyCon tc_name
381 ; let { (kinds, resKind) = splitKindFunTys (tyConKind fam_tycon)
382 ; hs_typats = fromJust $ tcdTyPats decl }
384 -- we may not have more parameters than the kind indicates
385 ; checkTc (length kinds >= length hs_typats) $
386 tooManyParmsErr (tcdLName decl)
388 -- type functions can have a higher-kinded result
389 ; let resultKind = mkArrowKinds (drop (length hs_typats) kinds) resKind
390 ; typats <- zipWithM kcCheckLHsType hs_typats
391 [ EK kind (EkArg (ppr tc_name) n)
392 | (kind,n) <- kinds `zip` [1..]]
393 ; thing_inside tvs typats resultKind fam_tycon
398 %************************************************************************
402 %************************************************************************
404 We need to kind check all types in the mutually recursive group
405 before we know the kind of the type variables. For example:
408 op :: D b => a -> b -> b
411 bop :: (Monad c) => ...
413 Here, the kind of the locally-polymorphic type variable "b"
414 depends on *all the uses of class D*. For example, the use of
415 Monad c in bop's type signature means that D must have kind Type->Type.
417 However type synonyms work differently. They can have kinds which don't
418 just involve (->) and *:
419 type R = Int# -- Kind #
420 type S a = Array# a -- Kind * -> #
421 type T a b = (# a,b #) -- Kind * -> * -> (# a,b #)
422 So we must infer their kinds from their right-hand sides *first* and then
423 use them, whereas for the mutually recursive data types D we bring into
424 scope kind bindings D -> k, where k is a kind variable, and do inference.
428 This treatment of type synonyms only applies to Haskell 98-style synonyms.
429 General type functions can be recursive, and hence, appear in `alg_decls'.
431 The kind of a type family is solely determinded by its kind signature;
432 hence, only kind signatures participate in the construction of the initial
433 kind environment (as constructed by `getInitialKind'). In fact, we ignore
434 instances of families altogether in the following. However, we need to
435 include the kinds of associated families into the construction of the
436 initial kind environment. (This is handled by `allDecls').
439 kcTyClDecls :: [LTyClDecl Name] -> [Located (TyClDecl Name)]
440 -> TcM ([LTyClDecl Name], [Located (TyClDecl Name)])
441 kcTyClDecls syn_decls alg_decls
442 = do { -- First extend the kind env with each data type, class, and
443 -- indexed type, mapping them to a type variable
444 let initialKindDecls = concat [allDecls decl | L _ decl <- alg_decls]
445 ; alg_kinds <- mapM getInitialKind initialKindDecls
446 ; tcExtendKindEnv alg_kinds $ do
448 -- Now kind-check the type synonyms, in dependency order
449 -- We do these differently to data type and classes,
450 -- because a type synonym can be an unboxed type
452 -- and a kind variable can't unify with UnboxedTypeKind
453 -- So we infer their kinds in dependency order
454 { (kc_syn_decls, syn_kinds) <- kcSynDecls (calcSynCycles syn_decls)
455 ; tcExtendKindEnv syn_kinds $ do
457 -- Now kind-check the data type, class, and kind signatures,
458 -- returning kind-annotated decls; we don't kind-check
459 -- instances of indexed types yet, but leave this to
461 { kc_alg_decls <- mapM (wrapLocM kcTyClDecl)
462 (filter (not . isFamInstDecl . unLoc) alg_decls)
464 ; return (kc_syn_decls, kc_alg_decls) }}}
466 -- get all declarations relevant for determining the initial kind
468 allDecls (decl@ClassDecl {tcdATs = ats}) = decl : [ at
471 allDecls decl | isFamInstDecl decl = []
474 ------------------------------------------------------------------------
475 getInitialKind :: TyClDecl Name -> TcM (Name, TcKind)
476 -- Only for data type, class, and indexed type declarations
477 -- Get as much info as possible from the data, class, or indexed type decl,
478 -- so as to maximise usefulness of error messages
480 = do { arg_kinds <- mapM (mk_arg_kind . unLoc) (tyClDeclTyVars decl)
481 ; res_kind <- mk_res_kind decl
482 ; return (tcdName decl, mkArrowKinds arg_kinds res_kind) }
484 mk_arg_kind (UserTyVar _ _) = newKindVar
485 mk_arg_kind (KindedTyVar _ kind) = return kind
487 mk_res_kind (TyFamily { tcdKind = Just kind }) = return kind
488 mk_res_kind (TyData { tcdKindSig = Just kind }) = return kind
489 -- On GADT-style declarations we allow a kind signature
490 -- data T :: *->* where { ... }
491 mk_res_kind _ = return liftedTypeKind
495 kcSynDecls :: [SCC (LTyClDecl Name)]
496 -> TcM ([LTyClDecl Name], -- Kind-annotated decls
497 [(Name,TcKind)]) -- Kind bindings
500 kcSynDecls (group : groups)
501 = do { (decl, nk) <- kcSynDecl group
502 ; (decls, nks) <- tcExtendKindEnv [nk] (kcSynDecls groups)
503 ; return (decl:decls, nk:nks) }
506 kcSynDecl :: SCC (LTyClDecl Name)
507 -> TcM (LTyClDecl Name, -- Kind-annotated decls
508 (Name,TcKind)) -- Kind bindings
509 kcSynDecl (AcyclicSCC (L loc decl))
510 = tcAddDeclCtxt decl $
511 kcHsTyVars (tcdTyVars decl) (\ k_tvs ->
512 do { traceTc (text "kcd1" <+> ppr (unLoc (tcdLName decl)) <+> brackets (ppr (tcdTyVars decl))
513 <+> brackets (ppr k_tvs))
514 ; (k_rhs, rhs_kind) <- kcLHsType (tcdSynRhs decl)
515 ; traceTc (text "kcd2" <+> ppr (unLoc (tcdLName decl)))
516 ; let tc_kind = foldr (mkArrowKind . hsTyVarKind . unLoc) rhs_kind k_tvs
517 ; return (L loc (decl { tcdTyVars = k_tvs, tcdSynRhs = k_rhs }),
518 (unLoc (tcdLName decl), tc_kind)) })
520 kcSynDecl (CyclicSCC decls)
521 = do { recSynErr decls; failM } -- Fail here to avoid error cascade
522 -- of out-of-scope tycons
524 ------------------------------------------------------------------------
525 kcTyClDecl :: TyClDecl Name -> TcM (TyClDecl Name)
526 -- Not used for type synonyms (see kcSynDecl)
528 kcTyClDecl decl@(TyData {})
529 = ASSERT( not . isFamInstDecl $ decl ) -- must not be a family instance
530 kcTyClDeclBody decl $
533 kcTyClDecl decl@(TyFamily {})
534 = kcFamilyDecl [] decl -- the empty list signals a toplevel decl
536 kcTyClDecl decl@(ClassDecl {tcdCtxt = ctxt, tcdSigs = sigs, tcdATs = ats})
537 = kcTyClDeclBody decl $ \ tvs' ->
538 do { ctxt' <- kcHsContext ctxt
539 ; ats' <- mapM (wrapLocM (kcFamilyDecl tvs')) ats
540 ; sigs' <- mapM (wrapLocM kc_sig) sigs
541 ; return (decl {tcdTyVars = tvs', tcdCtxt = ctxt', tcdSigs = sigs',
544 kc_sig (TypeSig nm op_ty) = do { op_ty' <- kcHsLiftedSigType op_ty
545 ; return (TypeSig nm op_ty') }
546 kc_sig other_sig = return other_sig
548 kcTyClDecl decl@(ForeignType {})
551 kcTyClDecl (TySynonym {}) = panic "kcTyClDecl TySynonym"
553 kcTyClDeclBody :: TyClDecl Name
554 -> ([LHsTyVarBndr Name] -> TcM a)
556 -- getInitialKind has made a suitably-shaped kind for the type or class
557 -- Unpack it, and attribute those kinds to the type variables
558 -- Extend the env with bindings for the tyvars, taken from
559 -- the kind of the tycon/class. Give it to the thing inside, and
560 -- check the result kind matches
561 kcTyClDeclBody decl thing_inside
562 = tcAddDeclCtxt decl $
563 do { tc_ty_thing <- tcLookupLocated (tcdLName decl)
564 ; let tc_kind = case tc_ty_thing of
566 _ -> pprPanic "kcTyClDeclBody" (ppr tc_ty_thing)
567 (kinds, _) = splitKindFunTys tc_kind
568 hs_tvs = tcdTyVars decl
569 kinded_tvs = ASSERT( length kinds >= length hs_tvs )
570 zipWith add_kind hs_tvs kinds
571 ; tcExtendKindEnvTvs kinded_tvs thing_inside }
573 add_kind (L loc (UserTyVar n _)) k = L loc (UserTyVar n k)
574 add_kind (L loc (KindedTyVar n _)) k = L loc (KindedTyVar n k)
576 -- Kind check a data declaration, assuming that we already extended the
577 -- kind environment with the type variables of the left-hand side (these
578 -- kinded type variables are also passed as the second parameter).
580 kcDataDecl :: TyClDecl Name -> [LHsTyVarBndr Name] -> TcM (TyClDecl Name)
581 kcDataDecl decl@(TyData {tcdND = new_or_data, tcdCtxt = ctxt, tcdCons = cons})
583 = do { ctxt' <- kcHsContext ctxt
584 ; cons' <- mapM (wrapLocM kc_con_decl) cons
585 ; return (decl {tcdTyVars = tvs, tcdCtxt = ctxt', tcdCons = cons'}) }
587 -- doc comments are typechecked to Nothing here
588 kc_con_decl con_decl@(ConDecl { con_name = name, con_qvars = ex_tvs
589 , con_cxt = ex_ctxt, con_details = details, con_res = res })
590 = addErrCtxt (dataConCtxt name) $
591 kcHsTyVars ex_tvs $ \ex_tvs' -> do
592 do { ex_ctxt' <- kcHsContext ex_ctxt
593 ; details' <- kc_con_details details
594 ; res' <- case res of
595 ResTyH98 -> return ResTyH98
596 ResTyGADT ty -> do { ty' <- kcHsSigType ty; return (ResTyGADT ty') }
597 ; return (con_decl { con_qvars = ex_tvs', con_cxt = ex_ctxt'
598 , con_details = details', con_res = res' }) }
600 kc_con_details (PrefixCon btys)
601 = do { btys' <- mapM kc_larg_ty btys
602 ; return (PrefixCon btys') }
603 kc_con_details (InfixCon bty1 bty2)
604 = do { bty1' <- kc_larg_ty bty1
605 ; bty2' <- kc_larg_ty bty2
606 ; return (InfixCon bty1' bty2') }
607 kc_con_details (RecCon fields)
608 = do { fields' <- mapM kc_field fields
609 ; return (RecCon fields') }
611 kc_field (ConDeclField fld bty d) = do { bty' <- kc_larg_ty bty
612 ; return (ConDeclField fld bty' d) }
614 kc_larg_ty bty = case new_or_data of
615 DataType -> kcHsSigType bty
616 NewType -> kcHsLiftedSigType bty
617 -- Can't allow an unlifted type for newtypes, because we're effectively
618 -- going to remove the constructor while coercing it to a lifted type.
619 -- And newtypes can't be bang'd
620 kcDataDecl d _ = pprPanic "kcDataDecl" (ppr d)
622 -- Kind check a family declaration or type family default declaration.
624 kcFamilyDecl :: [LHsTyVarBndr Name] -- tyvars of enclosing class decl if any
625 -> TyClDecl Name -> TcM (TyClDecl Name)
626 kcFamilyDecl classTvs decl@(TyFamily {tcdKind = kind})
627 = kcTyClDeclBody decl $ \tvs' ->
628 do { mapM_ unifyClassParmKinds tvs'
629 ; return (decl {tcdTyVars = tvs',
630 tcdKind = kind `mplus` Just liftedTypeKind})
631 -- default result kind is '*'
634 unifyClassParmKinds (L _ tv)
635 | (n,k) <- hsTyVarNameKind tv
636 , Just classParmKind <- lookup n classTyKinds
637 = unifyKind k classParmKind
638 | otherwise = return ()
639 classTyKinds = [hsTyVarNameKind tv | L _ tv <- classTvs]
641 kcFamilyDecl _ (TySynonym {}) -- type family defaults
642 = panic "TcTyClsDecls.kcFamilyDecl: not implemented yet"
643 kcFamilyDecl _ d = pprPanic "kcFamilyDecl" (ppr d)
647 %************************************************************************
649 \subsection{Type checking}
651 %************************************************************************
654 tcSynDecls :: [LTyClDecl Name] -> TcM [TyThing]
655 tcSynDecls [] = return []
656 tcSynDecls (decl : decls)
657 = do { syn_tc <- addLocM tcSynDecl decl
658 ; syn_tcs <- tcExtendGlobalEnv [syn_tc] (tcSynDecls decls)
659 ; return (syn_tc : syn_tcs) }
662 tcSynDecl :: TyClDecl Name -> TcM TyThing
664 (TySynonym {tcdLName = L _ tc_name, tcdTyVars = tvs, tcdSynRhs = rhs_ty})
665 = tcTyVarBndrs tvs $ \ tvs' -> do
666 { traceTc (text "tcd1" <+> ppr tc_name)
667 ; rhs_ty' <- tcHsKindedType rhs_ty
668 ; tycon <- buildSynTyCon tc_name tvs' (SynonymTyCon rhs_ty')
669 (typeKind rhs_ty') Nothing
670 ; return (ATyCon tycon)
672 tcSynDecl d = pprPanic "tcSynDecl" (ppr d)
675 tcTyClDecl :: (Name -> RecFlag) -> TyClDecl Name -> TcM [TyThing]
677 tcTyClDecl calc_isrec decl
678 = tcAddDeclCtxt decl (tcTyClDecl1 calc_isrec decl)
680 -- "type family" declarations
681 tcTyClDecl1 :: (Name -> RecFlag) -> TyClDecl Name -> TcM [TyThing]
682 tcTyClDecl1 _calc_isrec
683 (TyFamily {tcdFlavour = TypeFamily,
684 tcdLName = L _ tc_name, tcdTyVars = tvs,
685 tcdKind = Just kind}) -- NB: kind at latest added during kind checking
686 = tcTyVarBndrs tvs $ \ tvs' -> do
687 { traceTc (text "type family: " <+> ppr tc_name)
689 -- Check that we don't use families without -XTypeFamilies
690 ; idx_tys <- doptM Opt_TypeFamilies
691 ; checkTc idx_tys $ badFamInstDecl tc_name
693 ; tycon <- buildSynTyCon tc_name tvs' (OpenSynTyCon kind Nothing) kind Nothing
694 ; return [ATyCon tycon]
697 -- "data family" declaration
698 tcTyClDecl1 _calc_isrec
699 (TyFamily {tcdFlavour = DataFamily,
700 tcdLName = L _ tc_name, tcdTyVars = tvs, tcdKind = mb_kind})
701 = tcTyVarBndrs tvs $ \ tvs' -> do
702 { traceTc (text "data family: " <+> ppr tc_name)
703 ; extra_tvs <- tcDataKindSig mb_kind
704 ; let final_tvs = tvs' ++ extra_tvs -- we may not need these
707 -- Check that we don't use families without -XTypeFamilies
708 ; idx_tys <- doptM Opt_TypeFamilies
709 ; checkTc idx_tys $ badFamInstDecl tc_name
711 ; tycon <- buildAlgTyCon tc_name final_tvs []
712 mkOpenDataTyConRhs Recursive False True Nothing
713 ; return [ATyCon tycon]
716 -- "newtype" and "data"
717 -- NB: not used for newtype/data instances (whether associated or not)
718 tcTyClDecl1 calc_isrec
719 (TyData {tcdND = new_or_data, tcdCtxt = ctxt, tcdTyVars = tvs,
720 tcdLName = L _ tc_name, tcdKindSig = mb_ksig, tcdCons = cons})
721 = tcTyVarBndrs tvs $ \ tvs' -> do
722 { extra_tvs <- tcDataKindSig mb_ksig
723 ; let final_tvs = tvs' ++ extra_tvs
724 ; stupid_theta <- tcHsKindedContext ctxt
725 ; want_generic <- doptM Opt_Generics
726 ; unbox_strict <- doptM Opt_UnboxStrictFields
727 ; empty_data_decls <- doptM Opt_EmptyDataDecls
728 ; kind_signatures <- doptM Opt_KindSignatures
729 ; existential_ok <- doptM Opt_ExistentialQuantification
730 ; gadt_ok <- doptM Opt_GADTs
731 ; is_boot <- tcIsHsBoot -- Are we compiling an hs-boot file?
732 ; let ex_ok = existential_ok || gadt_ok -- Data cons can have existential context
734 -- Check that we don't use GADT syntax in H98 world
735 ; checkTc (gadt_ok || h98_syntax) (badGadtDecl tc_name)
737 -- Check that we don't use kind signatures without Glasgow extensions
738 ; checkTc (kind_signatures || isNothing mb_ksig) (badSigTyDecl tc_name)
740 -- Check that the stupid theta is empty for a GADT-style declaration
741 ; checkTc (null stupid_theta || h98_syntax) (badStupidTheta tc_name)
743 -- Check that a newtype has exactly one constructor
744 -- Do this before checking for empty data decls, so that
745 -- we don't suggest -XEmptyDataDecls for newtypes
746 ; checkTc (new_or_data == DataType || isSingleton cons)
747 (newtypeConError tc_name (length cons))
749 -- Check that there's at least one condecl,
750 -- or else we're reading an hs-boot file, or -XEmptyDataDecls
751 ; checkTc (not (null cons) || empty_data_decls || is_boot)
752 (emptyConDeclsErr tc_name)
754 ; tycon <- fixM (\ tycon -> do
755 { let res_ty = mkTyConApp tycon (mkTyVarTys final_tvs)
756 ; data_cons <- tcConDecls unbox_strict ex_ok
757 tycon (final_tvs, res_ty) cons
759 if null cons && is_boot -- In a hs-boot file, empty cons means
760 then return AbstractTyCon -- "don't know"; hence Abstract
761 else case new_or_data of
762 DataType -> return (mkDataTyConRhs data_cons)
763 NewType -> ASSERT( not (null data_cons) )
764 mkNewTyConRhs tc_name tycon (head data_cons)
765 ; buildAlgTyCon tc_name final_tvs stupid_theta tc_rhs is_rec
766 (want_generic && canDoGenerics data_cons) h98_syntax Nothing
768 ; return [ATyCon tycon]
771 is_rec = calc_isrec tc_name
772 h98_syntax = consUseH98Syntax cons
774 tcTyClDecl1 calc_isrec
775 (ClassDecl {tcdLName = L _ class_name, tcdTyVars = tvs,
776 tcdCtxt = ctxt, tcdMeths = meths,
777 tcdFDs = fundeps, tcdSigs = sigs, tcdATs = ats} )
778 = tcTyVarBndrs tvs $ \ tvs' -> do
779 { ctxt' <- tcHsKindedContext ctxt
780 ; fds' <- mapM (addLocM tc_fundep) fundeps
781 ; atss <- mapM (addLocM (tcTyClDecl1 (const Recursive))) ats
782 -- NB: 'ats' only contains "type family" and "data family"
783 -- declarations as well as type family defaults
784 ; let ats' = map (setAssocFamilyPermutation tvs') (concat atss)
785 ; sig_stuff <- tcClassSigs class_name sigs meths
786 ; clas <- fixM (\ clas ->
787 let -- This little knot is just so we can get
788 -- hold of the name of the class TyCon, which we
789 -- need to look up its recursiveness
790 tycon_name = tyConName (classTyCon clas)
791 tc_isrec = calc_isrec tycon_name
793 buildClass False {- Must include unfoldings for selectors -}
794 class_name tvs' ctxt' fds' ats'
796 ; return (AClass clas : ats')
797 -- NB: Order is important due to the call to `mkGlobalThings' when
798 -- tying the the type and class declaration type checking knot.
801 tc_fundep (tvs1, tvs2) = do { tvs1' <- mapM tcLookupTyVar tvs1 ;
802 ; tvs2' <- mapM tcLookupTyVar tvs2 ;
803 ; return (tvs1', tvs2') }
806 (ForeignType {tcdLName = L _ tc_name, tcdExtName = tc_ext_name})
807 = return [ATyCon (mkForeignTyCon tc_name tc_ext_name liftedTypeKind 0)]
809 tcTyClDecl1 _ d = pprPanic "tcTyClDecl1" (ppr d)
811 -----------------------------------
812 tcConDecls :: Bool -> Bool -> TyCon -> ([TyVar], Type)
813 -> [LConDecl Name] -> TcM [DataCon]
814 tcConDecls unbox ex_ok rep_tycon res_tmpl cons
815 = mapM (addLocM (tcConDecl unbox ex_ok rep_tycon res_tmpl)) cons
817 tcConDecl :: Bool -- True <=> -funbox-strict_fields
818 -> Bool -- True <=> -XExistentialQuantificaton or -XGADTs
819 -> TyCon -- Representation tycon
820 -> ([TyVar], Type) -- Return type template (with its template tyvars)
824 tcConDecl unbox_strict existential_ok rep_tycon res_tmpl -- Data types
825 (ConDecl {con_name =name, con_qvars = tvs, con_cxt = ctxt
826 , con_details = details, con_res = res_ty })
827 = addErrCtxt (dataConCtxt name) $
828 tcTyVarBndrs tvs $ \ tvs' -> do
829 { ctxt' <- tcHsKindedContext ctxt
830 ; checkTc (existential_ok || (null tvs && null (unLoc ctxt)))
831 (badExistential name)
832 ; (univ_tvs, ex_tvs, eq_preds, res_ty') <- tcResultType res_tmpl tvs' res_ty
834 tc_datacon is_infix field_lbls btys
835 = do { (arg_tys, stricts) <- mapAndUnzipM (tcConArg unbox_strict) btys
836 ; buildDataCon (unLoc name) is_infix
838 univ_tvs ex_tvs eq_preds ctxt' arg_tys
840 -- NB: we put data_tc, the type constructor gotten from the
841 -- constructor type signature into the data constructor;
842 -- that way checkValidDataCon can complain if it's wrong.
845 PrefixCon btys -> tc_datacon False [] btys
846 InfixCon bty1 bty2 -> tc_datacon True [] [bty1,bty2]
847 RecCon fields -> tc_datacon False field_names btys
849 field_names = map (unLoc . cd_fld_name) fields
850 btys = map cd_fld_type fields
854 -- data instance T (b,c) where
855 -- TI :: forall e. e -> T (e,e)
857 -- The representation tycon looks like this:
858 -- data :R7T b c where
859 -- TI :: forall b1 c1. (b1 ~ c1) => b1 -> :R7T b1 c1
860 -- In this case orig_res_ty = T (e,e)
862 tcResultType :: ([TyVar], Type) -- Template for result type; e.g.
863 -- data instance T [a] b c = ...
864 -- gives template ([a,b,c], T [a] b c)
865 -> [TyVar] -- where MkT :: forall x y z. ...
867 -> TcM ([TyVar], -- Universal
868 [TyVar], -- Existential (distinct OccNames from univs)
869 [(TyVar,Type)], -- Equality predicates
870 Type) -- Typechecked return type
871 -- We don't check that the TyCon given in the ResTy is
872 -- the same as the parent tycon, becuase we are in the middle
873 -- of a recursive knot; so it's postponed until checkValidDataCon
875 tcResultType (tmpl_tvs, res_ty) dc_tvs ResTyH98
876 = return (tmpl_tvs, dc_tvs, [], res_ty)
877 -- In H98 syntax the dc_tvs are the existential ones
878 -- data T a b c = forall d e. MkT ...
879 -- The {a,b,c} are tc_tvs, and {d,e} are dc_tvs
881 tcResultType (tmpl_tvs, res_tmpl) dc_tvs (ResTyGADT res_ty)
882 -- E.g. data T [a] b c where
883 -- MkT :: forall x y z. T [(x,y)] z z
885 -- Univ tyvars Eq-spec
889 -- Existentials are the leftover type vars: [x,y]
890 -- So we return ([a,b,z], [x,y], [a~(x,y),b~z], T [(x,y)] z z)
891 = do { res_ty' <- tcHsKindedType res_ty
892 ; let Just subst = tcMatchTy (mkVarSet tmpl_tvs) res_tmpl res_ty'
894 -- /Lazily/ figure out the univ_tvs etc
895 -- Each univ_tv is either a dc_tv or a tmpl_tv
896 (univ_tvs, eq_spec) = foldr choose ([], []) tidy_tmpl_tvs
897 choose tmpl (univs, eqs)
898 | Just ty <- lookupTyVar subst tmpl
899 = case tcGetTyVar_maybe ty of
900 Just tv | not (tv `elem` univs)
902 _other -> (tmpl:univs, (tmpl,ty):eqs)
903 | otherwise = pprPanic "tcResultType" (ppr res_ty)
904 ex_tvs = dc_tvs `minusList` univ_tvs
906 ; return (univ_tvs, ex_tvs, eq_spec, res_ty') }
908 -- NB: tmpl_tvs and dc_tvs are distinct, but
909 -- we want them to be *visibly* distinct, both for
910 -- interface files and general confusion. So rename
911 -- the tc_tvs, since they are not used yet (no
912 -- consequential renaming needed)
913 (_, tidy_tmpl_tvs) = mapAccumL tidy_one init_occ_env tmpl_tvs
914 init_occ_env = initTidyOccEnv (map getOccName dc_tvs)
915 tidy_one env tv = (env', setTyVarName tv (tidyNameOcc name occ'))
918 (env', occ') = tidyOccName env (getOccName name)
920 consUseH98Syntax :: [LConDecl a] -> Bool
921 consUseH98Syntax (L _ (ConDecl { con_res = ResTyGADT _ }) : _) = False
922 consUseH98Syntax _ = True
923 -- All constructors have same shape
926 tcConArg :: Bool -- True <=> -funbox-strict_fields
928 -> TcM (TcType, StrictnessMark)
929 tcConArg unbox_strict bty
930 = do { arg_ty <- tcHsBangType bty
931 ; let bang = getBangStrictness bty
932 ; strict_mark <- chooseBoxingStrategy unbox_strict arg_ty bang
933 ; return (arg_ty, strict_mark) }
935 -- We attempt to unbox/unpack a strict field when either:
936 -- (i) The field is marked '!!', or
937 -- (ii) The field is marked '!', and the -funbox-strict-fields flag is on.
939 -- We have turned off unboxing of newtypes because coercions make unboxing
940 -- and reboxing more complicated
941 chooseBoxingStrategy :: Bool -> TcType -> HsBang -> TcM StrictnessMark
942 chooseBoxingStrategy unbox_strict_fields arg_ty bang
944 HsNoBang -> return NotMarkedStrict
945 HsUnbox | can_unbox arg_ty -> return MarkedUnboxed
946 | otherwise -> do { addWarnTc cant_unbox_msg
947 ; return MarkedStrict }
948 HsStrict | unbox_strict_fields
949 , can_unbox arg_ty -> return MarkedUnboxed
950 _ -> return MarkedStrict
952 -- we can unbox if the type is a chain of newtypes with a product tycon
954 can_unbox arg_ty = case splitTyConApp_maybe arg_ty of
956 Just (arg_tycon, tycon_args) ->
957 not (isRecursiveTyCon arg_tycon) && -- Note [Recusive unboxing]
958 isProductTyCon arg_tycon &&
959 (if isNewTyCon arg_tycon then
960 can_unbox (newTyConInstRhs arg_tycon tycon_args)
963 cant_unbox_msg = ptext (sLit "Ignoring unusable UNPACK pragma")
966 Note [Recursive unboxing]
967 ~~~~~~~~~~~~~~~~~~~~~~~~~
968 Be careful not to try to unbox this!
970 But it's the *argument* type that matters. This is fine:
972 because Int is non-recursive.
975 %************************************************************************
979 %************************************************************************
981 Validity checking is done once the mutually-recursive knot has been
982 tied, so we can look at things freely.
985 checkCycleErrs :: [LTyClDecl Name] -> TcM ()
986 checkCycleErrs tyclss
990 = do { mapM_ recClsErr cls_cycles
991 ; failM } -- Give up now, because later checkValidTyCl
992 -- will loop if the synonym is recursive
994 cls_cycles = calcClassCycles tyclss
996 checkValidTyCl :: TyClDecl Name -> TcM ()
997 -- We do the validity check over declarations, rather than TyThings
998 -- only so that we can add a nice context with tcAddDeclCtxt
1000 = tcAddDeclCtxt decl $
1001 do { thing <- tcLookupLocatedGlobal (tcdLName decl)
1002 ; traceTc (text "Validity of" <+> ppr thing)
1004 ATyCon tc -> checkValidTyCon tc
1005 AClass cl -> checkValidClass cl
1006 _ -> panic "checkValidTyCl"
1007 ; traceTc (text "Done validity of" <+> ppr thing)
1010 -------------------------
1011 -- For data types declared with record syntax, we require
1012 -- that each constructor that has a field 'f'
1013 -- (a) has the same result type
1014 -- (b) has the same type for 'f'
1015 -- module alpha conversion of the quantified type variables
1016 -- of the constructor.
1018 -- Note that we allow existentials to match becuase the
1019 -- fields can never meet. E.g
1021 -- T1 { f1 :: b, f2 :: a, f3 ::Int } :: T
1022 -- T2 { f1 :: c, f2 :: c, f3 ::Int } :: T
1023 -- Here we do not complain about f1,f2 because they are existential
1025 checkValidTyCon :: TyCon -> TcM ()
1028 = case synTyConRhs tc of
1029 OpenSynTyCon _ _ -> return ()
1030 SynonymTyCon ty -> checkValidType syn_ctxt ty
1032 = do -- Check the context on the data decl
1033 checkValidTheta (DataTyCtxt name) (tyConStupidTheta tc)
1035 -- Check arg types of data constructors
1036 mapM_ (checkValidDataCon tc) data_cons
1038 -- Check that fields with the same name share a type
1039 mapM_ check_fields groups
1042 syn_ctxt = TySynCtxt name
1044 data_cons = tyConDataCons tc
1046 groups = equivClasses cmp_fld (concatMap get_fields data_cons)
1047 cmp_fld (f1,_) (f2,_) = f1 `compare` f2
1048 get_fields con = dataConFieldLabels con `zip` repeat con
1049 -- dataConFieldLabels may return the empty list, which is fine
1051 -- See Note [GADT record selectors] in MkId.lhs
1052 -- We must check (a) that the named field has the same
1053 -- type in each constructor
1054 -- (b) that those constructors have the same result type
1056 -- However, the constructors may have differently named type variable
1057 -- and (worse) we don't know how the correspond to each other. E.g.
1058 -- C1 :: forall a b. { f :: a, g :: b } -> T a b
1059 -- C2 :: forall d c. { f :: c, g :: c } -> T c d
1061 -- So what we do is to ust Unify.tcMatchTys to compare the first candidate's
1062 -- result type against other candidates' types BOTH WAYS ROUND.
1063 -- If they magically agrees, take the substitution and
1064 -- apply them to the latter ones, and see if they match perfectly.
1065 check_fields ((label, con1) : other_fields)
1066 -- These fields all have the same name, but are from
1067 -- different constructors in the data type
1068 = recoverM (return ()) $ mapM_ checkOne other_fields
1069 -- Check that all the fields in the group have the same type
1070 -- NB: this check assumes that all the constructors of a given
1071 -- data type use the same type variables
1073 (tvs1, _, _, res1) = dataConSig con1
1075 fty1 = dataConFieldType con1 label
1077 checkOne (_, con2) -- Do it bothways to ensure they are structurally identical
1078 = do { checkFieldCompat label con1 con2 ts1 res1 res2 fty1 fty2
1079 ; checkFieldCompat label con2 con1 ts2 res2 res1 fty2 fty1 }
1081 (tvs2, _, _, res2) = dataConSig con2
1083 fty2 = dataConFieldType con2 label
1084 check_fields [] = panic "checkValidTyCon/check_fields []"
1086 checkFieldCompat :: Name -> DataCon -> DataCon -> TyVarSet
1087 -> Type -> Type -> Type -> Type -> TcM ()
1088 checkFieldCompat fld con1 con2 tvs1 res1 res2 fty1 fty2
1089 = do { checkTc (isJust mb_subst1) (resultTypeMisMatch fld con1 con2)
1090 ; checkTc (isJust mb_subst2) (fieldTypeMisMatch fld con1 con2) }
1092 mb_subst1 = tcMatchTy tvs1 res1 res2
1093 mb_subst2 = tcMatchTyX tvs1 (expectJust "checkFieldCompat" mb_subst1) fty1 fty2
1095 -------------------------------
1096 checkValidDataCon :: TyCon -> DataCon -> TcM ()
1097 checkValidDataCon tc con
1098 = setSrcSpan (srcLocSpan (getSrcLoc con)) $
1099 addErrCtxt (dataConCtxt con) $
1100 do { traceTc (ptext (sLit "Validity of data con") <+> ppr con)
1101 ; let tc_tvs = tyConTyVars tc
1102 res_ty_tmpl = mkFamilyTyConApp tc (mkTyVarTys tc_tvs)
1103 actual_res_ty = dataConOrigResTy con
1104 ; checkTc (isJust (tcMatchTy (mkVarSet tc_tvs)
1107 (badDataConTyCon con res_ty_tmpl actual_res_ty)
1108 ; checkValidMonoType (dataConOrigResTy con)
1109 -- Disallow MkT :: T (forall a. a->a)
1110 -- Reason: it's really the argument of an equality constraint
1111 ; checkValidType ctxt (dataConUserType con)
1112 ; when (isNewTyCon tc) (checkNewDataCon con)
1115 ctxt = ConArgCtxt (dataConName con)
1117 -------------------------------
1118 checkNewDataCon :: DataCon -> TcM ()
1119 -- Checks for the data constructor of a newtype
1121 = do { checkTc (isSingleton arg_tys) (newtypeFieldErr con (length arg_tys))
1123 ; checkTc (null eq_spec) (newtypePredError con)
1124 -- Return type is (T a b c)
1125 ; checkTc (null ex_tvs && null eq_theta && null dict_theta) (newtypeExError con)
1127 ; checkTc (not (any isMarkedStrict (dataConStrictMarks con)))
1128 (newtypeStrictError con)
1132 (_univ_tvs, ex_tvs, eq_spec, eq_theta, dict_theta, arg_tys, _res_ty) = dataConFullSig con
1134 -------------------------------
1135 checkValidClass :: Class -> TcM ()
1137 = do { constrained_class_methods <- doptM Opt_ConstrainedClassMethods
1138 ; multi_param_type_classes <- doptM Opt_MultiParamTypeClasses
1139 ; fundep_classes <- doptM Opt_FunctionalDependencies
1141 -- Check that the class is unary, unless GlaExs
1142 ; checkTc (notNull tyvars) (nullaryClassErr cls)
1143 ; checkTc (multi_param_type_classes || unary) (classArityErr cls)
1144 ; checkTc (fundep_classes || null fundeps) (classFunDepsErr cls)
1146 -- Check the super-classes
1147 ; checkValidTheta (ClassSCCtxt (className cls)) theta
1149 -- Check the class operations
1150 ; mapM_ (check_op constrained_class_methods) op_stuff
1152 -- Check that if the class has generic methods, then the
1153 -- class has only one parameter. We can't do generic
1154 -- multi-parameter type classes!
1155 ; checkTc (unary || no_generics) (genericMultiParamErr cls)
1158 (tyvars, fundeps, theta, _, _, op_stuff) = classExtraBigSig cls
1159 unary = isSingleton tyvars
1160 no_generics = null [() | (_, GenDefMeth) <- op_stuff]
1162 check_op constrained_class_methods (sel_id, dm)
1163 = addErrCtxt (classOpCtxt sel_id tau) $ do
1164 { checkValidTheta SigmaCtxt (tail theta)
1165 -- The 'tail' removes the initial (C a) from the
1166 -- class itself, leaving just the method type
1168 ; traceTc (text "class op type" <+> ppr op_ty <+> ppr tau)
1169 ; checkValidType (FunSigCtxt op_name) tau
1171 -- Check that the type mentions at least one of
1172 -- the class type variables...or at least one reachable
1173 -- from one of the class variables. Example: tc223
1174 -- class Error e => Game b mv e | b -> mv e where
1175 -- newBoard :: MonadState b m => m ()
1176 -- Here, MonadState has a fundep m->b, so newBoard is fine
1177 ; let grown_tyvars = growThetaTyVars theta (mkVarSet tyvars)
1178 ; checkTc (tyVarsOfType tau `intersectsVarSet` grown_tyvars)
1179 (noClassTyVarErr cls sel_id)
1181 -- Check that for a generic method, the type of
1182 -- the method is sufficiently simple
1183 ; checkTc (dm /= GenDefMeth || validGenericMethodType tau)
1184 (badGenericMethodType op_name op_ty)
1187 op_name = idName sel_id
1188 op_ty = idType sel_id
1189 (_,theta1,tau1) = tcSplitSigmaTy op_ty
1190 (_,theta2,tau2) = tcSplitSigmaTy tau1
1191 (theta,tau) | constrained_class_methods = (theta1 ++ theta2, tau2)
1192 | otherwise = (theta1, mkPhiTy (tail theta1) tau1)
1193 -- Ugh! The function might have a type like
1194 -- op :: forall a. C a => forall b. (Eq b, Eq a) => tau2
1195 -- With -XConstrainedClassMethods, we want to allow this, even though the inner
1196 -- forall has an (Eq a) constraint. Whereas in general, each constraint
1197 -- in the context of a for-all must mention at least one quantified
1198 -- type variable. What a mess!
1202 %************************************************************************
1204 Building record selectors
1206 %************************************************************************
1209 mkAuxBinds :: [TyThing] -> HsValBinds Name
1210 -- NB We produce *un-typechecked* bindings, rather like 'deriving'
1211 -- This makes life easier, because the later type checking will add
1212 -- all necessary type abstractions and applications
1213 mkAuxBinds ty_things
1214 = ValBindsOut [(NonRecursive, b) | b <- binds] sigs
1216 (sigs, binds) = unzip rec_sels
1217 rec_sels = map mkRecSelBind [ (tc,fld)
1218 | ATyCon tc <- ty_things
1219 , fld <- tyConFields tc ]
1221 mkRecSelBind :: (TyCon, FieldLabel) -> (LSig Name, LHsBinds Name)
1222 mkRecSelBind (tycon, sel_name)
1223 = (L loc (IdSig sel_id), unitBag (L loc sel_bind))
1225 loc = getSrcSpan tycon
1226 sel_id = Var.mkLocalVar rec_details sel_name sel_ty vanillaIdInfo
1227 rec_details = RecSelId { sel_tycon = tycon, sel_naughty = is_naughty }
1229 -- Find a representative constructor, con1
1230 all_cons = tyConDataCons tycon
1231 cons_w_field = [ con | con <- all_cons
1232 , sel_name `elem` dataConFieldLabels con ]
1233 con1 = ASSERT( not (null cons_w_field) ) head cons_w_field
1235 -- Selector type; Note [Polymorphic selectors]
1236 field_ty = dataConFieldType con1 sel_name
1237 data_ty = dataConOrigResTy con1
1238 data_tvs = tyVarsOfType data_ty
1239 is_naughty = not (tyVarsOfType field_ty `subVarSet` data_tvs)
1240 (field_tvs, field_theta, field_tau) = tcSplitSigmaTy field_ty
1241 sel_ty | is_naughty = unitTy -- See Note [Naughty record selectors]
1242 | otherwise = mkForAllTys (varSetElems data_tvs ++ field_tvs) $
1243 mkPhiTy (dataConStupidTheta con1) $ -- Urgh!
1244 mkPhiTy field_theta $ -- Urgh!
1245 mkFunTy data_ty field_tau
1247 -- Make the binding: sel (C2 { fld = x }) = x
1248 -- sel (C7 { fld = x }) = x
1249 -- where cons_w_field = [C2,C7]
1250 sel_bind | is_naughty = mkFunBind sel_lname [mkSimpleMatch [] unit_rhs]
1251 | otherwise = mkFunBind sel_lname (map mk_match cons_w_field ++ deflt)
1252 mk_match con = mkSimpleMatch [L loc (mk_sel_pat con)]
1253 (L loc (HsVar field_var))
1254 mk_sel_pat con = ConPatIn (L loc (getName con)) (RecCon rec_fields)
1255 rec_fields = HsRecFields { rec_flds = [rec_field], rec_dotdot = Nothing }
1256 rec_field = HsRecField { hsRecFieldId = sel_lname
1257 , hsRecFieldArg = nlVarPat field_var
1258 , hsRecPun = False }
1259 sel_lname = L loc sel_name
1260 field_var = mkInternalName (mkBuiltinUnique 1) (getOccName sel_name) loc
1262 -- Add catch-all default case unless the case is exhaustive
1263 -- We do this explicitly so that we get a nice error message that
1264 -- mentions this particular record selector
1265 deflt | not (any is_unused all_cons) = []
1266 | otherwise = [mkSimpleMatch [nlWildPat]
1267 (nlHsApp (nlHsVar (getName rEC_SEL_ERROR_ID))
1270 -- Do not add a default case unless there are unmatched
1271 -- constructors. We must take account of GADTs, else we
1272 -- get overlap warning messages from the pattern-match checker
1273 is_unused con = not (con `elem` cons_w_field
1274 || dataConCannotMatch inst_tys con)
1275 inst_tys = tyConAppArgs data_ty
1277 unit_rhs = mkLHsTupleExpr []
1278 msg_lit = HsStringPrim $ mkFastString $
1279 occNameString (getOccName sel_name)
1282 tyConFields :: TyCon -> [FieldLabel]
1284 | isAlgTyCon tc = nub (concatMap dataConFieldLabels (tyConDataCons tc))
1288 Note [Polymorphic selectors]
1289 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1290 When a record has a polymorphic field, we pull the foralls out to the front.
1291 data T = MkT { f :: forall a. [a] -> a }
1292 Then f :: forall a. T -> [a] -> a
1293 NOT f :: T -> forall a. [a] -> a
1295 This is horrid. It's only needed in deeply obscure cases, which I hate.
1296 The only case I know is test tc163, which is worth looking at. It's far
1297 from clear that this test should succeed at all!
1299 Note [Naughty record selectors]
1300 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1301 A "naughty" field is one for which we can't define a record
1302 selector, because an existential type variable would escape. For example:
1303 data T = forall a. MkT { x,y::a }
1304 We obviously can't define
1306 Nevertheless we *do* put a RecSelId into the type environment
1307 so that if the user tries to use 'x' as a selector we can bleat
1308 helpfully, rather than saying unhelpfully that 'x' is not in scope.
1309 Hence the sel_naughty flag, to identify record selectors that don't really exist.
1311 In general, a field is "naughty" if its type mentions a type variable that
1312 isn't in the result type of the constructor. Note that this *allows*
1313 GADT record selectors (Note [GADT record selectors]) whose types may look
1314 like sel :: T [a] -> a
1316 For naughty selectors we make a dummy binding
1318 for naughty selectors, so that the later type-check will add them to the
1319 environment, and they'll be exported. The function is never called, because
1320 the tyepchecker spots the sel_naughty field.
1322 Note [GADT record selectors]
1323 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1324 For GADTs, we require that all constructors with a common field 'f' have the same
1325 result type (modulo alpha conversion). [Checked in TcTyClsDecls.checkValidTyCon]
1328 T1 { f :: Maybe a } :: T [a]
1329 T2 { f :: Maybe a, y :: b } :: T [a]
1331 and now the selector takes that result type as its argument:
1332 f :: forall a. T [a] -> Maybe a
1334 Details: the "real" types of T1,T2 are:
1335 T1 :: forall r a. (r~[a]) => a -> T r
1336 T2 :: forall r a b. (r~[a]) => a -> b -> T r
1338 So the selector loooks like this:
1339 f :: forall a. T [a] -> Maybe a
1342 T1 c (g:[a]~[c]) (v:Maybe c) -> v `cast` Maybe (right (sym g))
1343 T2 c d (g:[a]~[c]) (v:Maybe c) (w:d) -> v `cast` Maybe (right (sym g))
1345 Note the forall'd tyvars of the selector are just the free tyvars
1346 of the result type; there may be other tyvars in the constructor's
1347 type (e.g. 'b' in T2).
1349 Note the need for casts in the result!
1351 Note [Selector running example]
1352 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1353 It's OK to combine GADTs and type families. Here's a running example:
1355 data instance T [a] where
1356 T1 { fld :: b } :: T [Maybe b]
1358 The representation type looks like this
1360 T1 { fld :: b } :: :R7T (Maybe b)
1362 and there's coercion from the family type to the representation type
1363 :CoR7T a :: T [a] ~ :R7T a
1365 The selector we want for fld looks like this:
1367 fld :: forall b. T [Maybe b] -> b
1368 fld = /\b. \(d::T [Maybe b]).
1369 case d `cast` :CoR7T (Maybe b) of
1372 The scrutinee of the case has type :R7T (Maybe b), which can be
1373 gotten by appying the eq_spec to the univ_tvs of the data con.
1375 %************************************************************************
1379 %************************************************************************
1382 resultTypeMisMatch :: Name -> DataCon -> DataCon -> SDoc
1383 resultTypeMisMatch field_name con1 con2
1384 = vcat [sep [ptext (sLit "Constructors") <+> ppr con1 <+> ptext (sLit "and") <+> ppr con2,
1385 ptext (sLit "have a common field") <+> quotes (ppr field_name) <> comma],
1386 nest 2 $ ptext (sLit "but have different result types")]
1388 fieldTypeMisMatch :: Name -> DataCon -> DataCon -> SDoc
1389 fieldTypeMisMatch field_name con1 con2
1390 = sep [ptext (sLit "Constructors") <+> ppr con1 <+> ptext (sLit "and") <+> ppr con2,
1391 ptext (sLit "give different types for field"), quotes (ppr field_name)]
1393 dataConCtxt :: Outputable a => a -> SDoc
1394 dataConCtxt con = ptext (sLit "In the definition of data constructor") <+> quotes (ppr con)
1396 classOpCtxt :: Var -> Type -> SDoc
1397 classOpCtxt sel_id tau = sep [ptext (sLit "When checking the class method:"),
1398 nest 2 (ppr sel_id <+> dcolon <+> ppr tau)]
1400 nullaryClassErr :: Class -> SDoc
1402 = ptext (sLit "No parameters for class") <+> quotes (ppr cls)
1404 classArityErr :: Class -> SDoc
1406 = vcat [ptext (sLit "Too many parameters for class") <+> quotes (ppr cls),
1407 parens (ptext (sLit "Use -XMultiParamTypeClasses to allow multi-parameter classes"))]
1409 classFunDepsErr :: Class -> SDoc
1411 = vcat [ptext (sLit "Fundeps in class") <+> quotes (ppr cls),
1412 parens (ptext (sLit "Use -XFunctionalDependencies to allow fundeps"))]
1414 noClassTyVarErr :: Class -> Var -> SDoc
1415 noClassTyVarErr clas op
1416 = sep [ptext (sLit "The class method") <+> quotes (ppr op),
1417 ptext (sLit "mentions none of the type variables of the class") <+>
1418 ppr clas <+> hsep (map ppr (classTyVars clas))]
1420 genericMultiParamErr :: Class -> SDoc
1421 genericMultiParamErr clas
1422 = ptext (sLit "The multi-parameter class") <+> quotes (ppr clas) <+>
1423 ptext (sLit "cannot have generic methods")
1425 badGenericMethodType :: Name -> Kind -> SDoc
1426 badGenericMethodType op op_ty
1427 = hang (ptext (sLit "Generic method type is too complex"))
1428 4 (vcat [ppr op <+> dcolon <+> ppr op_ty,
1429 ptext (sLit "You can only use type variables, arrows, lists, and tuples")])
1431 recSynErr :: [LTyClDecl Name] -> TcRn ()
1433 = setSrcSpan (getLoc (head sorted_decls)) $
1434 addErr (sep [ptext (sLit "Cycle in type synonym declarations:"),
1435 nest 2 (vcat (map ppr_decl sorted_decls))])
1437 sorted_decls = sortLocated syn_decls
1438 ppr_decl (L loc decl) = ppr loc <> colon <+> ppr decl
1440 recClsErr :: [Located (TyClDecl Name)] -> TcRn ()
1442 = setSrcSpan (getLoc (head sorted_decls)) $
1443 addErr (sep [ptext (sLit "Cycle in class declarations (via superclasses):"),
1444 nest 2 (vcat (map ppr_decl sorted_decls))])
1446 sorted_decls = sortLocated cls_decls
1447 ppr_decl (L loc decl) = ppr loc <> colon <+> ppr (decl { tcdSigs = [] })
1449 sortLocated :: [Located a] -> [Located a]
1450 sortLocated things = sortLe le things
1452 le (L l1 _) (L l2 _) = l1 <= l2
1454 badDataConTyCon :: DataCon -> Type -> Type -> SDoc
1455 badDataConTyCon data_con res_ty_tmpl actual_res_ty
1456 = hang (ptext (sLit "Data constructor") <+> quotes (ppr data_con) <+>
1457 ptext (sLit "returns type") <+> quotes (ppr actual_res_ty))
1458 2 (ptext (sLit "instead of an instance of its parent type") <+> quotes (ppr res_ty_tmpl))
1460 badGadtDecl :: Name -> SDoc
1462 = vcat [ ptext (sLit "Illegal generalised algebraic data declaration for") <+> quotes (ppr tc_name)
1463 , nest 2 (parens $ ptext (sLit "Use -XGADTs to allow GADTs")) ]
1465 badExistential :: Located Name -> SDoc
1466 badExistential con_name
1467 = hang (ptext (sLit "Data constructor") <+> quotes (ppr con_name) <+>
1468 ptext (sLit "has existential type variables, or a context"))
1469 2 (parens $ ptext (sLit "Use -XExistentialQuantification or -XGADTs to allow this"))
1471 badStupidTheta :: Name -> SDoc
1472 badStupidTheta tc_name
1473 = ptext (sLit "A data type declared in GADT style cannot have a context:") <+> quotes (ppr tc_name)
1475 newtypeConError :: Name -> Int -> SDoc
1476 newtypeConError tycon n
1477 = sep [ptext (sLit "A newtype must have exactly one constructor,"),
1478 nest 2 $ ptext (sLit "but") <+> quotes (ppr tycon) <+> ptext (sLit "has") <+> speakN n ]
1480 newtypeExError :: DataCon -> SDoc
1482 = sep [ptext (sLit "A newtype constructor cannot have an existential context,"),
1483 nest 2 $ ptext (sLit "but") <+> quotes (ppr con) <+> ptext (sLit "does")]
1485 newtypeStrictError :: DataCon -> SDoc
1486 newtypeStrictError con
1487 = sep [ptext (sLit "A newtype constructor cannot have a strictness annotation,"),
1488 nest 2 $ ptext (sLit "but") <+> quotes (ppr con) <+> ptext (sLit "does")]
1490 newtypePredError :: DataCon -> SDoc
1491 newtypePredError con
1492 = sep [ptext (sLit "A newtype constructor must have a return type of form T a1 ... an"),
1493 nest 2 $ ptext (sLit "but") <+> quotes (ppr con) <+> ptext (sLit "does not")]
1495 newtypeFieldErr :: DataCon -> Int -> SDoc
1496 newtypeFieldErr con_name n_flds
1497 = sep [ptext (sLit "The constructor of a newtype must have exactly one field"),
1498 nest 2 $ ptext (sLit "but") <+> quotes (ppr con_name) <+> ptext (sLit "has") <+> speakN n_flds]
1500 badSigTyDecl :: Name -> SDoc
1501 badSigTyDecl tc_name
1502 = vcat [ ptext (sLit "Illegal kind signature") <+>
1503 quotes (ppr tc_name)
1504 , nest 2 (parens $ ptext (sLit "Use -XKindSignatures to allow kind signatures")) ]
1506 badFamInstDecl :: Outputable a => a -> SDoc
1507 badFamInstDecl tc_name
1508 = vcat [ ptext (sLit "Illegal family instance for") <+>
1509 quotes (ppr tc_name)
1510 , nest 2 (parens $ ptext (sLit "Use -XTypeFamilies to allow indexed type families")) ]
1512 tooManyParmsErr :: Located Name -> SDoc
1513 tooManyParmsErr tc_name
1514 = ptext (sLit "Family instance has too many parameters:") <+>
1515 quotes (ppr tc_name)
1517 tooFewParmsErr :: Arity -> SDoc
1518 tooFewParmsErr arity
1519 = ptext (sLit "Family instance has too few parameters; expected") <+>
1522 wrongNumberOfParmsErr :: Arity -> SDoc
1523 wrongNumberOfParmsErr exp_arity
1524 = ptext (sLit "Number of parameters must match family declaration; expected")
1527 badBootFamInstDeclErr :: SDoc
1528 badBootFamInstDeclErr
1529 = ptext (sLit "Illegal family instance in hs-boot file")
1531 notFamily :: TyCon -> SDoc
1533 = vcat [ ptext (sLit "Illegal family instance for") <+> quotes (ppr tycon)
1534 , nest 2 $ parens (ppr tycon <+> ptext (sLit "is not an indexed type family"))]
1536 wrongKindOfFamily :: TyCon -> SDoc
1537 wrongKindOfFamily family
1538 = ptext (sLit "Wrong category of family instance; declaration was for a")
1541 kindOfFamily | isSynTyCon family = ptext (sLit "type synonym")
1542 | isAlgTyCon family = ptext (sLit "data type")
1543 | otherwise = pprPanic "wrongKindOfFamily" (ppr family)
1545 emptyConDeclsErr :: Name -> SDoc
1546 emptyConDeclsErr tycon
1547 = sep [quotes (ppr tycon) <+> ptext (sLit "has no constructors"),
1548 nest 2 $ ptext (sLit "(-XEmptyDataDecls permits this)")]