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, HsBang)
929 tcConArg unbox_strict bty
930 = do { arg_ty <- tcHsBangType bty
931 ; let bang = getBangStrictness bty
932 ; let 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 -> HsBang
942 chooseBoxingStrategy unbox_strict_fields arg_ty bang
945 HsUnpack -> can_unbox HsUnpackFailed arg_ty
946 HsStrict | unbox_strict_fields -> can_unbox HsStrict arg_ty
947 | otherwise -> HsStrict
948 HsUnpackFailed -> pprPanic "chooseBoxingStrategy" (ppr arg_ty)
949 -- Source code never has shtes
951 can_unbox :: HsBang -> TcType -> HsBang
952 -- Returns HsUnpack if we can unpack arg_ty
953 -- fail_bang if we know what arg_ty is but we can't unpack it
954 -- HsStrict if it's abstract, so we don't know whether or not we can unbox it
955 can_unbox fail_bang arg_ty
956 = case splitTyConApp_maybe arg_ty of
959 Just (arg_tycon, tycon_args)
960 | isAbstractTyCon arg_tycon -> HsStrict
961 -- See Note [Don't complain about UNPACK on abstract TyCons]
962 | not (isRecursiveTyCon arg_tycon) -- Note [Recusive unboxing]
963 , isProductTyCon arg_tycon
964 -- We can unbox if the type is a chain of newtypes
965 -- with a product tycon at the end
966 -> if isNewTyCon arg_tycon
967 then can_unbox fail_bang (newTyConInstRhs arg_tycon tycon_args)
970 | otherwise -> fail_bang
973 Note [Don't complain about UNPACK on abstract TyCons]
974 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
975 We are going to complain about UnpackFailed, but if we say
976 data T = MkT {-# UNPACK #-} !Wobble
977 and Wobble is a newtype imported from a module that was compiled
978 without optimisation, we don't want to complain. Because it might
979 be fine when optimsation is on. I think this happens when Haddock
980 is working over (say) GHC souce files.
982 Note [Recursive unboxing]
983 ~~~~~~~~~~~~~~~~~~~~~~~~~
984 Be careful not to try to unbox this!
986 But it's the *argument* type that matters. This is fine:
988 because Int is non-recursive.
991 %************************************************************************
995 %************************************************************************
997 Validity checking is done once the mutually-recursive knot has been
998 tied, so we can look at things freely.
1001 checkCycleErrs :: [LTyClDecl Name] -> TcM ()
1002 checkCycleErrs tyclss
1006 = do { mapM_ recClsErr cls_cycles
1007 ; failM } -- Give up now, because later checkValidTyCl
1008 -- will loop if the synonym is recursive
1010 cls_cycles = calcClassCycles tyclss
1012 checkValidTyCl :: TyClDecl Name -> TcM ()
1013 -- We do the validity check over declarations, rather than TyThings
1014 -- only so that we can add a nice context with tcAddDeclCtxt
1016 = tcAddDeclCtxt decl $
1017 do { thing <- tcLookupLocatedGlobal (tcdLName decl)
1018 ; traceTc (text "Validity of" <+> ppr thing)
1020 ATyCon tc -> checkValidTyCon tc
1021 AClass cl -> checkValidClass cl
1022 _ -> panic "checkValidTyCl"
1023 ; traceTc (text "Done validity of" <+> ppr thing)
1026 -------------------------
1027 -- For data types declared with record syntax, we require
1028 -- that each constructor that has a field 'f'
1029 -- (a) has the same result type
1030 -- (b) has the same type for 'f'
1031 -- module alpha conversion of the quantified type variables
1032 -- of the constructor.
1034 -- Note that we allow existentials to match becuase the
1035 -- fields can never meet. E.g
1037 -- T1 { f1 :: b, f2 :: a, f3 ::Int } :: T
1038 -- T2 { f1 :: c, f2 :: c, f3 ::Int } :: T
1039 -- Here we do not complain about f1,f2 because they are existential
1041 checkValidTyCon :: TyCon -> TcM ()
1044 = case synTyConRhs tc of
1045 OpenSynTyCon _ _ -> return ()
1046 SynonymTyCon ty -> checkValidType syn_ctxt ty
1048 = do -- Check the context on the data decl
1049 checkValidTheta (DataTyCtxt name) (tyConStupidTheta tc)
1051 -- Check arg types of data constructors
1052 mapM_ (checkValidDataCon tc) data_cons
1054 -- Check that fields with the same name share a type
1055 mapM_ check_fields groups
1058 syn_ctxt = TySynCtxt name
1060 data_cons = tyConDataCons tc
1062 groups = equivClasses cmp_fld (concatMap get_fields data_cons)
1063 cmp_fld (f1,_) (f2,_) = f1 `compare` f2
1064 get_fields con = dataConFieldLabels con `zip` repeat con
1065 -- dataConFieldLabels may return the empty list, which is fine
1067 -- See Note [GADT record selectors] in MkId.lhs
1068 -- We must check (a) that the named field has the same
1069 -- type in each constructor
1070 -- (b) that those constructors have the same result type
1072 -- However, the constructors may have differently named type variable
1073 -- and (worse) we don't know how the correspond to each other. E.g.
1074 -- C1 :: forall a b. { f :: a, g :: b } -> T a b
1075 -- C2 :: forall d c. { f :: c, g :: c } -> T c d
1077 -- So what we do is to ust Unify.tcMatchTys to compare the first candidate's
1078 -- result type against other candidates' types BOTH WAYS ROUND.
1079 -- If they magically agrees, take the substitution and
1080 -- apply them to the latter ones, and see if they match perfectly.
1081 check_fields ((label, con1) : other_fields)
1082 -- These fields all have the same name, but are from
1083 -- different constructors in the data type
1084 = recoverM (return ()) $ mapM_ checkOne other_fields
1085 -- Check that all the fields in the group have the same type
1086 -- NB: this check assumes that all the constructors of a given
1087 -- data type use the same type variables
1089 (tvs1, _, _, res1) = dataConSig con1
1091 fty1 = dataConFieldType con1 label
1093 checkOne (_, con2) -- Do it bothways to ensure they are structurally identical
1094 = do { checkFieldCompat label con1 con2 ts1 res1 res2 fty1 fty2
1095 ; checkFieldCompat label con2 con1 ts2 res2 res1 fty2 fty1 }
1097 (tvs2, _, _, res2) = dataConSig con2
1099 fty2 = dataConFieldType con2 label
1100 check_fields [] = panic "checkValidTyCon/check_fields []"
1102 checkFieldCompat :: Name -> DataCon -> DataCon -> TyVarSet
1103 -> Type -> Type -> Type -> Type -> TcM ()
1104 checkFieldCompat fld con1 con2 tvs1 res1 res2 fty1 fty2
1105 = do { checkTc (isJust mb_subst1) (resultTypeMisMatch fld con1 con2)
1106 ; checkTc (isJust mb_subst2) (fieldTypeMisMatch fld con1 con2) }
1108 mb_subst1 = tcMatchTy tvs1 res1 res2
1109 mb_subst2 = tcMatchTyX tvs1 (expectJust "checkFieldCompat" mb_subst1) fty1 fty2
1111 -------------------------------
1112 checkValidDataCon :: TyCon -> DataCon -> TcM ()
1113 checkValidDataCon tc con
1114 = setSrcSpan (srcLocSpan (getSrcLoc con)) $
1115 addErrCtxt (dataConCtxt con) $
1116 do { traceTc (ptext (sLit "Validity of data con") <+> ppr con)
1117 ; let tc_tvs = tyConTyVars tc
1118 res_ty_tmpl = mkFamilyTyConApp tc (mkTyVarTys tc_tvs)
1119 actual_res_ty = dataConOrigResTy con
1120 ; checkTc (isJust (tcMatchTy (mkVarSet tc_tvs)
1123 (badDataConTyCon con res_ty_tmpl actual_res_ty)
1124 ; checkValidMonoType (dataConOrigResTy con)
1125 -- Disallow MkT :: T (forall a. a->a)
1126 -- Reason: it's really the argument of an equality constraint
1127 ; checkValidType ctxt (dataConUserType con)
1128 ; when (isNewTyCon tc) (checkNewDataCon con)
1129 ; mapM_ check_bang (dataConStrictMarks con `zip` [1..])
1132 ctxt = ConArgCtxt (dataConName con)
1133 check_bang (HsUnpackFailed, n) = addWarnTc (cant_unbox_msg n)
1134 check_bang _ = return ()
1136 cant_unbox_msg n = sep [ ptext (sLit "Ignoring unusable UNPACK pragma on the")
1137 , speakNth n <+> ptext (sLit "argument of") <+> quotes (ppr con)]
1139 -------------------------------
1140 checkNewDataCon :: DataCon -> TcM ()
1141 -- Checks for the data constructor of a newtype
1143 = do { checkTc (isSingleton arg_tys) (newtypeFieldErr con (length arg_tys))
1145 ; checkTc (null eq_spec) (newtypePredError con)
1146 -- Return type is (T a b c)
1147 ; checkTc (null ex_tvs && null eq_theta && null dict_theta) (newtypeExError con)
1149 ; checkTc (not (any isBanged (dataConStrictMarks con)))
1150 (newtypeStrictError con)
1154 (_univ_tvs, ex_tvs, eq_spec, eq_theta, dict_theta, arg_tys, _res_ty) = dataConFullSig con
1156 -------------------------------
1157 checkValidClass :: Class -> TcM ()
1159 = do { constrained_class_methods <- doptM Opt_ConstrainedClassMethods
1160 ; multi_param_type_classes <- doptM Opt_MultiParamTypeClasses
1161 ; fundep_classes <- doptM Opt_FunctionalDependencies
1163 -- Check that the class is unary, unless GlaExs
1164 ; checkTc (notNull tyvars) (nullaryClassErr cls)
1165 ; checkTc (multi_param_type_classes || unary) (classArityErr cls)
1166 ; checkTc (fundep_classes || null fundeps) (classFunDepsErr cls)
1168 -- Check the super-classes
1169 ; checkValidTheta (ClassSCCtxt (className cls)) theta
1171 -- Check the class operations
1172 ; mapM_ (check_op constrained_class_methods) op_stuff
1174 -- Check that if the class has generic methods, then the
1175 -- class has only one parameter. We can't do generic
1176 -- multi-parameter type classes!
1177 ; checkTc (unary || no_generics) (genericMultiParamErr cls)
1180 (tyvars, fundeps, theta, _, _, op_stuff) = classExtraBigSig cls
1181 unary = isSingleton tyvars
1182 no_generics = null [() | (_, GenDefMeth) <- op_stuff]
1184 check_op constrained_class_methods (sel_id, dm)
1185 = addErrCtxt (classOpCtxt sel_id tau) $ do
1186 { checkValidTheta SigmaCtxt (tail theta)
1187 -- The 'tail' removes the initial (C a) from the
1188 -- class itself, leaving just the method type
1190 ; traceTc (text "class op type" <+> ppr op_ty <+> ppr tau)
1191 ; checkValidType (FunSigCtxt op_name) tau
1193 -- Check that the type mentions at least one of
1194 -- the class type variables...or at least one reachable
1195 -- from one of the class variables. Example: tc223
1196 -- class Error e => Game b mv e | b -> mv e where
1197 -- newBoard :: MonadState b m => m ()
1198 -- Here, MonadState has a fundep m->b, so newBoard is fine
1199 ; let grown_tyvars = growThetaTyVars theta (mkVarSet tyvars)
1200 ; checkTc (tyVarsOfType tau `intersectsVarSet` grown_tyvars)
1201 (noClassTyVarErr cls sel_id)
1203 -- Check that for a generic method, the type of
1204 -- the method is sufficiently simple
1205 ; checkTc (dm /= GenDefMeth || validGenericMethodType tau)
1206 (badGenericMethodType op_name op_ty)
1209 op_name = idName sel_id
1210 op_ty = idType sel_id
1211 (_,theta1,tau1) = tcSplitSigmaTy op_ty
1212 (_,theta2,tau2) = tcSplitSigmaTy tau1
1213 (theta,tau) | constrained_class_methods = (theta1 ++ theta2, tau2)
1214 | otherwise = (theta1, mkPhiTy (tail theta1) tau1)
1215 -- Ugh! The function might have a type like
1216 -- op :: forall a. C a => forall b. (Eq b, Eq a) => tau2
1217 -- With -XConstrainedClassMethods, we want to allow this, even though the inner
1218 -- forall has an (Eq a) constraint. Whereas in general, each constraint
1219 -- in the context of a for-all must mention at least one quantified
1220 -- type variable. What a mess!
1224 %************************************************************************
1226 Building record selectors
1228 %************************************************************************
1231 mkAuxBinds :: [TyThing] -> HsValBinds Name
1232 -- NB We produce *un-typechecked* bindings, rather like 'deriving'
1233 -- This makes life easier, because the later type checking will add
1234 -- all necessary type abstractions and applications
1235 mkAuxBinds ty_things
1236 = ValBindsOut [(NonRecursive, b) | b <- binds] sigs
1238 (sigs, binds) = unzip rec_sels
1239 rec_sels = map mkRecSelBind [ (tc,fld)
1240 | ATyCon tc <- ty_things
1241 , fld <- tyConFields tc ]
1243 mkRecSelBind :: (TyCon, FieldLabel) -> (LSig Name, LHsBinds Name)
1244 mkRecSelBind (tycon, sel_name)
1245 = (L loc (IdSig sel_id), unitBag (L loc sel_bind))
1247 loc = getSrcSpan tycon
1248 sel_id = Var.mkLocalVar rec_details sel_name sel_ty vanillaIdInfo
1249 rec_details = RecSelId { sel_tycon = tycon, sel_naughty = is_naughty }
1251 -- Find a representative constructor, con1
1252 all_cons = tyConDataCons tycon
1253 cons_w_field = [ con | con <- all_cons
1254 , sel_name `elem` dataConFieldLabels con ]
1255 con1 = ASSERT( not (null cons_w_field) ) head cons_w_field
1257 -- Selector type; Note [Polymorphic selectors]
1258 field_ty = dataConFieldType con1 sel_name
1259 data_ty = dataConOrigResTy con1
1260 data_tvs = tyVarsOfType data_ty
1261 is_naughty = not (tyVarsOfType field_ty `subVarSet` data_tvs)
1262 (field_tvs, field_theta, field_tau) = tcSplitSigmaTy field_ty
1263 sel_ty | is_naughty = unitTy -- See Note [Naughty record selectors]
1264 | otherwise = mkForAllTys (varSetElems data_tvs ++ field_tvs) $
1265 mkPhiTy (dataConStupidTheta con1) $ -- Urgh!
1266 mkPhiTy field_theta $ -- Urgh!
1267 mkFunTy data_ty field_tau
1269 -- Make the binding: sel (C2 { fld = x }) = x
1270 -- sel (C7 { fld = x }) = x
1271 -- where cons_w_field = [C2,C7]
1272 sel_bind | is_naughty = mkFunBind sel_lname [mkSimpleMatch [] unit_rhs]
1273 | otherwise = mkFunBind sel_lname (map mk_match cons_w_field ++ deflt)
1274 mk_match con = mkSimpleMatch [L loc (mk_sel_pat con)]
1275 (L loc (HsVar field_var))
1276 mk_sel_pat con = ConPatIn (L loc (getName con)) (RecCon rec_fields)
1277 rec_fields = HsRecFields { rec_flds = [rec_field], rec_dotdot = Nothing }
1278 rec_field = HsRecField { hsRecFieldId = sel_lname
1279 , hsRecFieldArg = nlVarPat field_var
1280 , hsRecPun = False }
1281 sel_lname = L loc sel_name
1282 field_var = mkInternalName (mkBuiltinUnique 1) (getOccName sel_name) loc
1284 -- Add catch-all default case unless the case is exhaustive
1285 -- We do this explicitly so that we get a nice error message that
1286 -- mentions this particular record selector
1287 deflt | not (any is_unused all_cons) = []
1288 | otherwise = [mkSimpleMatch [nlWildPat]
1289 (nlHsApp (nlHsVar (getName rEC_SEL_ERROR_ID))
1292 -- Do not add a default case unless there are unmatched
1293 -- constructors. We must take account of GADTs, else we
1294 -- get overlap warning messages from the pattern-match checker
1295 is_unused con = not (con `elem` cons_w_field
1296 || dataConCannotMatch inst_tys con)
1297 inst_tys = tyConAppArgs data_ty
1299 unit_rhs = mkLHsTupleExpr []
1300 msg_lit = HsStringPrim $ mkFastString $
1301 occNameString (getOccName sel_name)
1304 tyConFields :: TyCon -> [FieldLabel]
1306 | isAlgTyCon tc = nub (concatMap dataConFieldLabels (tyConDataCons tc))
1310 Note [Polymorphic selectors]
1311 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1312 When a record has a polymorphic field, we pull the foralls out to the front.
1313 data T = MkT { f :: forall a. [a] -> a }
1314 Then f :: forall a. T -> [a] -> a
1315 NOT f :: T -> forall a. [a] -> a
1317 This is horrid. It's only needed in deeply obscure cases, which I hate.
1318 The only case I know is test tc163, which is worth looking at. It's far
1319 from clear that this test should succeed at all!
1321 Note [Naughty record selectors]
1322 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1323 A "naughty" field is one for which we can't define a record
1324 selector, because an existential type variable would escape. For example:
1325 data T = forall a. MkT { x,y::a }
1326 We obviously can't define
1328 Nevertheless we *do* put a RecSelId into the type environment
1329 so that if the user tries to use 'x' as a selector we can bleat
1330 helpfully, rather than saying unhelpfully that 'x' is not in scope.
1331 Hence the sel_naughty flag, to identify record selectors that don't really exist.
1333 In general, a field is "naughty" if its type mentions a type variable that
1334 isn't in the result type of the constructor. Note that this *allows*
1335 GADT record selectors (Note [GADT record selectors]) whose types may look
1336 like sel :: T [a] -> a
1338 For naughty selectors we make a dummy binding
1340 for naughty selectors, so that the later type-check will add them to the
1341 environment, and they'll be exported. The function is never called, because
1342 the tyepchecker spots the sel_naughty field.
1344 Note [GADT record selectors]
1345 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1346 For GADTs, we require that all constructors with a common field 'f' have the same
1347 result type (modulo alpha conversion). [Checked in TcTyClsDecls.checkValidTyCon]
1350 T1 { f :: Maybe a } :: T [a]
1351 T2 { f :: Maybe a, y :: b } :: T [a]
1353 and now the selector takes that result type as its argument:
1354 f :: forall a. T [a] -> Maybe a
1356 Details: the "real" types of T1,T2 are:
1357 T1 :: forall r a. (r~[a]) => a -> T r
1358 T2 :: forall r a b. (r~[a]) => a -> b -> T r
1360 So the selector loooks like this:
1361 f :: forall a. T [a] -> Maybe a
1364 T1 c (g:[a]~[c]) (v:Maybe c) -> v `cast` Maybe (right (sym g))
1365 T2 c d (g:[a]~[c]) (v:Maybe c) (w:d) -> v `cast` Maybe (right (sym g))
1367 Note the forall'd tyvars of the selector are just the free tyvars
1368 of the result type; there may be other tyvars in the constructor's
1369 type (e.g. 'b' in T2).
1371 Note the need for casts in the result!
1373 Note [Selector running example]
1374 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1375 It's OK to combine GADTs and type families. Here's a running example:
1377 data instance T [a] where
1378 T1 { fld :: b } :: T [Maybe b]
1380 The representation type looks like this
1382 T1 { fld :: b } :: :R7T (Maybe b)
1384 and there's coercion from the family type to the representation type
1385 :CoR7T a :: T [a] ~ :R7T a
1387 The selector we want for fld looks like this:
1389 fld :: forall b. T [Maybe b] -> b
1390 fld = /\b. \(d::T [Maybe b]).
1391 case d `cast` :CoR7T (Maybe b) of
1394 The scrutinee of the case has type :R7T (Maybe b), which can be
1395 gotten by appying the eq_spec to the univ_tvs of the data con.
1397 %************************************************************************
1401 %************************************************************************
1404 resultTypeMisMatch :: Name -> DataCon -> DataCon -> SDoc
1405 resultTypeMisMatch field_name con1 con2
1406 = vcat [sep [ptext (sLit "Constructors") <+> ppr con1 <+> ptext (sLit "and") <+> ppr con2,
1407 ptext (sLit "have a common field") <+> quotes (ppr field_name) <> comma],
1408 nest 2 $ ptext (sLit "but have different result types")]
1410 fieldTypeMisMatch :: Name -> DataCon -> DataCon -> SDoc
1411 fieldTypeMisMatch field_name con1 con2
1412 = sep [ptext (sLit "Constructors") <+> ppr con1 <+> ptext (sLit "and") <+> ppr con2,
1413 ptext (sLit "give different types for field"), quotes (ppr field_name)]
1415 dataConCtxt :: Outputable a => a -> SDoc
1416 dataConCtxt con = ptext (sLit "In the definition of data constructor") <+> quotes (ppr con)
1418 classOpCtxt :: Var -> Type -> SDoc
1419 classOpCtxt sel_id tau = sep [ptext (sLit "When checking the class method:"),
1420 nest 2 (ppr sel_id <+> dcolon <+> ppr tau)]
1422 nullaryClassErr :: Class -> SDoc
1424 = ptext (sLit "No parameters for class") <+> quotes (ppr cls)
1426 classArityErr :: Class -> SDoc
1428 = vcat [ptext (sLit "Too many parameters for class") <+> quotes (ppr cls),
1429 parens (ptext (sLit "Use -XMultiParamTypeClasses to allow multi-parameter classes"))]
1431 classFunDepsErr :: Class -> SDoc
1433 = vcat [ptext (sLit "Fundeps in class") <+> quotes (ppr cls),
1434 parens (ptext (sLit "Use -XFunctionalDependencies to allow fundeps"))]
1436 noClassTyVarErr :: Class -> Var -> SDoc
1437 noClassTyVarErr clas op
1438 = sep [ptext (sLit "The class method") <+> quotes (ppr op),
1439 ptext (sLit "mentions none of the type variables of the class") <+>
1440 ppr clas <+> hsep (map ppr (classTyVars clas))]
1442 genericMultiParamErr :: Class -> SDoc
1443 genericMultiParamErr clas
1444 = ptext (sLit "The multi-parameter class") <+> quotes (ppr clas) <+>
1445 ptext (sLit "cannot have generic methods")
1447 badGenericMethodType :: Name -> Kind -> SDoc
1448 badGenericMethodType op op_ty
1449 = hang (ptext (sLit "Generic method type is too complex"))
1450 4 (vcat [ppr op <+> dcolon <+> ppr op_ty,
1451 ptext (sLit "You can only use type variables, arrows, lists, and tuples")])
1453 recSynErr :: [LTyClDecl Name] -> TcRn ()
1455 = setSrcSpan (getLoc (head sorted_decls)) $
1456 addErr (sep [ptext (sLit "Cycle in type synonym declarations:"),
1457 nest 2 (vcat (map ppr_decl sorted_decls))])
1459 sorted_decls = sortLocated syn_decls
1460 ppr_decl (L loc decl) = ppr loc <> colon <+> ppr decl
1462 recClsErr :: [Located (TyClDecl Name)] -> TcRn ()
1464 = setSrcSpan (getLoc (head sorted_decls)) $
1465 addErr (sep [ptext (sLit "Cycle in class declarations (via superclasses):"),
1466 nest 2 (vcat (map ppr_decl sorted_decls))])
1468 sorted_decls = sortLocated cls_decls
1469 ppr_decl (L loc decl) = ppr loc <> colon <+> ppr (decl { tcdSigs = [] })
1471 sortLocated :: [Located a] -> [Located a]
1472 sortLocated things = sortLe le things
1474 le (L l1 _) (L l2 _) = l1 <= l2
1476 badDataConTyCon :: DataCon -> Type -> Type -> SDoc
1477 badDataConTyCon data_con res_ty_tmpl actual_res_ty
1478 = hang (ptext (sLit "Data constructor") <+> quotes (ppr data_con) <+>
1479 ptext (sLit "returns type") <+> quotes (ppr actual_res_ty))
1480 2 (ptext (sLit "instead of an instance of its parent type") <+> quotes (ppr res_ty_tmpl))
1482 badGadtDecl :: Name -> SDoc
1484 = vcat [ ptext (sLit "Illegal generalised algebraic data declaration for") <+> quotes (ppr tc_name)
1485 , nest 2 (parens $ ptext (sLit "Use -XGADTs to allow GADTs")) ]
1487 badExistential :: Located Name -> SDoc
1488 badExistential con_name
1489 = hang (ptext (sLit "Data constructor") <+> quotes (ppr con_name) <+>
1490 ptext (sLit "has existential type variables, or a context"))
1491 2 (parens $ ptext (sLit "Use -XExistentialQuantification or -XGADTs to allow this"))
1493 badStupidTheta :: Name -> SDoc
1494 badStupidTheta tc_name
1495 = ptext (sLit "A data type declared in GADT style cannot have a context:") <+> quotes (ppr tc_name)
1497 newtypeConError :: Name -> Int -> SDoc
1498 newtypeConError tycon n
1499 = sep [ptext (sLit "A newtype must have exactly one constructor,"),
1500 nest 2 $ ptext (sLit "but") <+> quotes (ppr tycon) <+> ptext (sLit "has") <+> speakN n ]
1502 newtypeExError :: DataCon -> SDoc
1504 = sep [ptext (sLit "A newtype constructor cannot have an existential context,"),
1505 nest 2 $ ptext (sLit "but") <+> quotes (ppr con) <+> ptext (sLit "does")]
1507 newtypeStrictError :: DataCon -> SDoc
1508 newtypeStrictError con
1509 = sep [ptext (sLit "A newtype constructor cannot have a strictness annotation,"),
1510 nest 2 $ ptext (sLit "but") <+> quotes (ppr con) <+> ptext (sLit "does")]
1512 newtypePredError :: DataCon -> SDoc
1513 newtypePredError con
1514 = sep [ptext (sLit "A newtype constructor must have a return type of form T a1 ... an"),
1515 nest 2 $ ptext (sLit "but") <+> quotes (ppr con) <+> ptext (sLit "does not")]
1517 newtypeFieldErr :: DataCon -> Int -> SDoc
1518 newtypeFieldErr con_name n_flds
1519 = sep [ptext (sLit "The constructor of a newtype must have exactly one field"),
1520 nest 2 $ ptext (sLit "but") <+> quotes (ppr con_name) <+> ptext (sLit "has") <+> speakN n_flds]
1522 badSigTyDecl :: Name -> SDoc
1523 badSigTyDecl tc_name
1524 = vcat [ ptext (sLit "Illegal kind signature") <+>
1525 quotes (ppr tc_name)
1526 , nest 2 (parens $ ptext (sLit "Use -XKindSignatures to allow kind signatures")) ]
1528 badFamInstDecl :: Outputable a => a -> SDoc
1529 badFamInstDecl tc_name
1530 = vcat [ ptext (sLit "Illegal family instance for") <+>
1531 quotes (ppr tc_name)
1532 , nest 2 (parens $ ptext (sLit "Use -XTypeFamilies to allow indexed type families")) ]
1534 tooManyParmsErr :: Located Name -> SDoc
1535 tooManyParmsErr tc_name
1536 = ptext (sLit "Family instance has too many parameters:") <+>
1537 quotes (ppr tc_name)
1539 tooFewParmsErr :: Arity -> SDoc
1540 tooFewParmsErr arity
1541 = ptext (sLit "Family instance has too few parameters; expected") <+>
1544 wrongNumberOfParmsErr :: Arity -> SDoc
1545 wrongNumberOfParmsErr exp_arity
1546 = ptext (sLit "Number of parameters must match family declaration; expected")
1549 badBootFamInstDeclErr :: SDoc
1550 badBootFamInstDeclErr
1551 = ptext (sLit "Illegal family instance in hs-boot file")
1553 notFamily :: TyCon -> SDoc
1555 = vcat [ ptext (sLit "Illegal family instance for") <+> quotes (ppr tycon)
1556 , nest 2 $ parens (ppr tycon <+> ptext (sLit "is not an indexed type family"))]
1558 wrongKindOfFamily :: TyCon -> SDoc
1559 wrongKindOfFamily family
1560 = ptext (sLit "Wrong category of family instance; declaration was for a")
1563 kindOfFamily | isSynTyCon family = ptext (sLit "type synonym")
1564 | isAlgTyCon family = ptext (sLit "data type")
1565 | otherwise = pprPanic "wrongKindOfFamily" (ppr family)
1567 emptyConDeclsErr :: Name -> SDoc
1568 emptyConDeclsErr tycon
1569 = sep [quotes (ppr tycon) <+> ptext (sLit "has no constructors"),
1570 nest 2 $ ptext (sLit "(-XEmptyDataDecls permits this)")]