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 . kindedTyVarKind) 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 kindedTyVarKind :: LHsTyVarBndr Name -> Kind
525 kindedTyVarKind (L _ (KindedTyVar _ k)) = k
526 kindedTyVarKind x = pprPanic "kindedTyVarKind" (ppr x)
528 ------------------------------------------------------------------------
529 kcTyClDecl :: TyClDecl Name -> TcM (TyClDecl Name)
530 -- Not used for type synonyms (see kcSynDecl)
532 kcTyClDecl decl@(TyData {})
533 = ASSERT( not . isFamInstDecl $ decl ) -- must not be a family instance
534 kcTyClDeclBody decl $
537 kcTyClDecl decl@(TyFamily {})
538 = kcFamilyDecl [] decl -- the empty list signals a toplevel decl
540 kcTyClDecl decl@(ClassDecl {tcdCtxt = ctxt, tcdSigs = sigs, tcdATs = ats})
541 = kcTyClDeclBody decl $ \ tvs' ->
542 do { ctxt' <- kcHsContext ctxt
543 ; ats' <- mapM (wrapLocM (kcFamilyDecl tvs')) ats
544 ; sigs' <- mapM (wrapLocM kc_sig) sigs
545 ; return (decl {tcdTyVars = tvs', tcdCtxt = ctxt', tcdSigs = sigs',
548 kc_sig (TypeSig nm op_ty) = do { op_ty' <- kcHsLiftedSigType op_ty
549 ; return (TypeSig nm op_ty') }
550 kc_sig other_sig = return other_sig
552 kcTyClDecl decl@(ForeignType {})
555 kcTyClDecl (TySynonym {}) = panic "kcTyClDecl TySynonym"
557 kcTyClDeclBody :: TyClDecl Name
558 -> ([LHsTyVarBndr Name] -> TcM a)
560 -- getInitialKind has made a suitably-shaped kind for the type or class
561 -- Unpack it, and attribute those kinds to the type variables
562 -- Extend the env with bindings for the tyvars, taken from
563 -- the kind of the tycon/class. Give it to the thing inside, and
564 -- check the result kind matches
565 kcTyClDeclBody decl thing_inside
566 = tcAddDeclCtxt decl $
567 do { tc_ty_thing <- tcLookupLocated (tcdLName decl)
568 ; let tc_kind = case tc_ty_thing of
570 _ -> pprPanic "kcTyClDeclBody" (ppr tc_ty_thing)
571 (kinds, _) = splitKindFunTys tc_kind
572 hs_tvs = tcdTyVars decl
573 kinded_tvs = ASSERT( length kinds >= length hs_tvs )
574 [ L loc (KindedTyVar (hsTyVarName tv) k)
575 | (L loc tv, k) <- zip hs_tvs kinds]
576 ; tcExtendKindEnvTvs kinded_tvs (thing_inside kinded_tvs) }
578 -- Kind check a data declaration, assuming that we already extended the
579 -- kind environment with the type variables of the left-hand side (these
580 -- kinded type variables are also passed as the second parameter).
582 kcDataDecl :: TyClDecl Name -> [LHsTyVarBndr Name] -> TcM (TyClDecl Name)
583 kcDataDecl decl@(TyData {tcdND = new_or_data, tcdCtxt = ctxt, tcdCons = cons})
585 = do { ctxt' <- kcHsContext ctxt
586 ; cons' <- mapM (wrapLocM kc_con_decl) cons
587 ; return (decl {tcdTyVars = tvs, tcdCtxt = ctxt', tcdCons = cons'}) }
589 -- doc comments are typechecked to Nothing here
590 kc_con_decl con_decl@(ConDecl { con_name = name, con_qvars = ex_tvs
591 , con_cxt = ex_ctxt, con_details = details, con_res = res })
592 = addErrCtxt (dataConCtxt name) $
593 kcHsTyVars ex_tvs $ \ex_tvs' -> do
594 do { ex_ctxt' <- kcHsContext ex_ctxt
595 ; details' <- kc_con_details details
596 ; res' <- case res of
597 ResTyH98 -> return ResTyH98
598 ResTyGADT ty -> do { ty' <- kcHsSigType ty; return (ResTyGADT ty') }
599 ; return (con_decl { con_qvars = ex_tvs', con_cxt = ex_ctxt'
600 , con_details = details', con_res = res' }) }
602 kc_con_details (PrefixCon btys)
603 = do { btys' <- mapM kc_larg_ty btys
604 ; return (PrefixCon btys') }
605 kc_con_details (InfixCon bty1 bty2)
606 = do { bty1' <- kc_larg_ty bty1
607 ; bty2' <- kc_larg_ty bty2
608 ; return (InfixCon bty1' bty2') }
609 kc_con_details (RecCon fields)
610 = do { fields' <- mapM kc_field fields
611 ; return (RecCon fields') }
613 kc_field (ConDeclField fld bty d) = do { bty' <- kc_larg_ty bty
614 ; return (ConDeclField fld bty' d) }
616 kc_larg_ty bty = case new_or_data of
617 DataType -> kcHsSigType bty
618 NewType -> kcHsLiftedSigType bty
619 -- Can't allow an unlifted type for newtypes, because we're effectively
620 -- going to remove the constructor while coercing it to a lifted type.
621 -- And newtypes can't be bang'd
622 kcDataDecl d _ = pprPanic "kcDataDecl" (ppr d)
624 -- Kind check a family declaration or type family default declaration.
626 kcFamilyDecl :: [LHsTyVarBndr Name] -- tyvars of enclosing class decl if any
627 -> TyClDecl Name -> TcM (TyClDecl Name)
628 kcFamilyDecl classTvs decl@(TyFamily {tcdKind = kind})
629 = kcTyClDeclBody decl $ \tvs' ->
630 do { mapM_ unifyClassParmKinds tvs'
631 ; return (decl {tcdTyVars = tvs',
632 tcdKind = kind `mplus` Just liftedTypeKind})
633 -- default result kind is '*'
636 unifyClassParmKinds (L _ (KindedTyVar n k))
637 | Just classParmKind <- lookup n classTyKinds = unifyKind k classParmKind
638 | otherwise = return ()
639 unifyClassParmKinds x = pprPanic "kcFamilyDecl/unifyClassParmKinds" (ppr x)
640 classTyKinds = [(n, k) | L _ (KindedTyVar n k) <- 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 ; return (arg_ty, chooseBoxingStrategy unbox_strict arg_ty bang) }
934 -- We attempt to unbox/unpack a strict field when either:
935 -- (i) The field is marked '!!', or
936 -- (ii) The field is marked '!', and the -funbox-strict-fields flag is on.
938 -- We have turned off unboxing of newtypes because coercions make unboxing
939 -- and reboxing more complicated
940 chooseBoxingStrategy :: Bool -> TcType -> HsBang -> StrictnessMark
941 chooseBoxingStrategy unbox_strict_fields arg_ty bang
943 HsNoBang -> NotMarkedStrict
944 HsStrict | unbox_strict_fields
945 && can_unbox arg_ty -> MarkedUnboxed
946 HsUnbox | can_unbox arg_ty -> MarkedUnboxed
949 -- we can unbox if the type is a chain of newtypes with a product tycon
951 can_unbox arg_ty = case splitTyConApp_maybe arg_ty of
953 Just (arg_tycon, tycon_args) ->
954 not (isRecursiveTyCon arg_tycon) && -- Note [Recusive unboxing]
955 isProductTyCon arg_tycon &&
956 (if isNewTyCon arg_tycon then
957 can_unbox (newTyConInstRhs arg_tycon tycon_args)
961 Note [Recursive unboxing]
962 ~~~~~~~~~~~~~~~~~~~~~~~~~
963 Be careful not to try to unbox this!
965 But it's the *argument* type that matters. This is fine:
967 because Int is non-recursive.
970 %************************************************************************
974 %************************************************************************
976 Validity checking is done once the mutually-recursive knot has been
977 tied, so we can look at things freely.
980 checkCycleErrs :: [LTyClDecl Name] -> TcM ()
981 checkCycleErrs tyclss
985 = do { mapM_ recClsErr cls_cycles
986 ; failM } -- Give up now, because later checkValidTyCl
987 -- will loop if the synonym is recursive
989 cls_cycles = calcClassCycles tyclss
991 checkValidTyCl :: TyClDecl Name -> TcM ()
992 -- We do the validity check over declarations, rather than TyThings
993 -- only so that we can add a nice context with tcAddDeclCtxt
995 = tcAddDeclCtxt decl $
996 do { thing <- tcLookupLocatedGlobal (tcdLName decl)
997 ; traceTc (text "Validity of" <+> ppr thing)
999 ATyCon tc -> checkValidTyCon tc
1000 AClass cl -> checkValidClass cl
1001 _ -> panic "checkValidTyCl"
1002 ; traceTc (text "Done validity of" <+> ppr thing)
1005 -------------------------
1006 -- For data types declared with record syntax, we require
1007 -- that each constructor that has a field 'f'
1008 -- (a) has the same result type
1009 -- (b) has the same type for 'f'
1010 -- module alpha conversion of the quantified type variables
1011 -- of the constructor.
1013 -- Note that we allow existentials to match becuase the
1014 -- fields can never meet. E.g
1016 -- T1 { f1 :: b, f2 :: a, f3 ::Int } :: T
1017 -- T2 { f1 :: c, f2 :: c, f3 ::Int } :: T
1018 -- Here we do not complain about f1,f2 because they are existential
1020 checkValidTyCon :: TyCon -> TcM ()
1023 = case synTyConRhs tc of
1024 OpenSynTyCon _ _ -> return ()
1025 SynonymTyCon ty -> checkValidType syn_ctxt ty
1027 = do -- Check the context on the data decl
1028 checkValidTheta (DataTyCtxt name) (tyConStupidTheta tc)
1030 -- Check arg types of data constructors
1031 mapM_ (checkValidDataCon tc) data_cons
1033 -- Check that fields with the same name share a type
1034 mapM_ check_fields groups
1037 syn_ctxt = TySynCtxt name
1039 data_cons = tyConDataCons tc
1041 groups = equivClasses cmp_fld (concatMap get_fields data_cons)
1042 cmp_fld (f1,_) (f2,_) = f1 `compare` f2
1043 get_fields con = dataConFieldLabels con `zip` repeat con
1044 -- dataConFieldLabels may return the empty list, which is fine
1046 -- See Note [GADT record selectors] in MkId.lhs
1047 -- We must check (a) that the named field has the same
1048 -- type in each constructor
1049 -- (b) that those constructors have the same result type
1051 -- However, the constructors may have differently named type variable
1052 -- and (worse) we don't know how the correspond to each other. E.g.
1053 -- C1 :: forall a b. { f :: a, g :: b } -> T a b
1054 -- C2 :: forall d c. { f :: c, g :: c } -> T c d
1056 -- So what we do is to ust Unify.tcMatchTys to compare the first candidate's
1057 -- result type against other candidates' types BOTH WAYS ROUND.
1058 -- If they magically agrees, take the substitution and
1059 -- apply them to the latter ones, and see if they match perfectly.
1060 check_fields ((label, con1) : other_fields)
1061 -- These fields all have the same name, but are from
1062 -- different constructors in the data type
1063 = recoverM (return ()) $ mapM_ checkOne other_fields
1064 -- Check that all the fields in the group have the same type
1065 -- NB: this check assumes that all the constructors of a given
1066 -- data type use the same type variables
1068 (tvs1, _, _, res1) = dataConSig con1
1070 fty1 = dataConFieldType con1 label
1072 checkOne (_, con2) -- Do it bothways to ensure they are structurally identical
1073 = do { checkFieldCompat label con1 con2 ts1 res1 res2 fty1 fty2
1074 ; checkFieldCompat label con2 con1 ts2 res2 res1 fty2 fty1 }
1076 (tvs2, _, _, res2) = dataConSig con2
1078 fty2 = dataConFieldType con2 label
1079 check_fields [] = panic "checkValidTyCon/check_fields []"
1081 checkFieldCompat :: Name -> DataCon -> DataCon -> TyVarSet
1082 -> Type -> Type -> Type -> Type -> TcM ()
1083 checkFieldCompat fld con1 con2 tvs1 res1 res2 fty1 fty2
1084 = do { checkTc (isJust mb_subst1) (resultTypeMisMatch fld con1 con2)
1085 ; checkTc (isJust mb_subst2) (fieldTypeMisMatch fld con1 con2) }
1087 mb_subst1 = tcMatchTy tvs1 res1 res2
1088 mb_subst2 = tcMatchTyX tvs1 (expectJust "checkFieldCompat" mb_subst1) fty1 fty2
1090 -------------------------------
1091 checkValidDataCon :: TyCon -> DataCon -> TcM ()
1092 checkValidDataCon tc con
1093 = setSrcSpan (srcLocSpan (getSrcLoc con)) $
1094 addErrCtxt (dataConCtxt con) $
1095 do { traceTc (ptext (sLit "Validity of data con") <+> ppr con)
1096 ; let tc_tvs = tyConTyVars tc
1097 res_ty_tmpl = mkFamilyTyConApp tc (mkTyVarTys tc_tvs)
1098 actual_res_ty = dataConOrigResTy con
1099 ; checkTc (isJust (tcMatchTy (mkVarSet tc_tvs)
1102 (badDataConTyCon con res_ty_tmpl actual_res_ty)
1103 ; checkValidMonoType (dataConOrigResTy con)
1104 -- Disallow MkT :: T (forall a. a->a)
1105 -- Reason: it's really the argument of an equality constraint
1106 ; checkValidType ctxt (dataConUserType con)
1107 ; when (isNewTyCon tc) (checkNewDataCon con)
1110 ctxt = ConArgCtxt (dataConName con)
1112 -------------------------------
1113 checkNewDataCon :: DataCon -> TcM ()
1114 -- Checks for the data constructor of a newtype
1116 = do { checkTc (isSingleton arg_tys) (newtypeFieldErr con (length arg_tys))
1118 ; checkTc (null eq_spec) (newtypePredError con)
1119 -- Return type is (T a b c)
1120 ; checkTc (null ex_tvs && null eq_theta && null dict_theta) (newtypeExError con)
1122 ; checkTc (not (any isMarkedStrict (dataConStrictMarks con)))
1123 (newtypeStrictError con)
1127 (_univ_tvs, ex_tvs, eq_spec, eq_theta, dict_theta, arg_tys, _res_ty) = dataConFullSig con
1129 -------------------------------
1130 checkValidClass :: Class -> TcM ()
1132 = do { constrained_class_methods <- doptM Opt_ConstrainedClassMethods
1133 ; multi_param_type_classes <- doptM Opt_MultiParamTypeClasses
1134 ; fundep_classes <- doptM Opt_FunctionalDependencies
1136 -- Check that the class is unary, unless GlaExs
1137 ; checkTc (notNull tyvars) (nullaryClassErr cls)
1138 ; checkTc (multi_param_type_classes || unary) (classArityErr cls)
1139 ; checkTc (fundep_classes || null fundeps) (classFunDepsErr cls)
1141 -- Check the super-classes
1142 ; checkValidTheta (ClassSCCtxt (className cls)) theta
1144 -- Check the class operations
1145 ; mapM_ (check_op constrained_class_methods) op_stuff
1147 -- Check that if the class has generic methods, then the
1148 -- class has only one parameter. We can't do generic
1149 -- multi-parameter type classes!
1150 ; checkTc (unary || no_generics) (genericMultiParamErr cls)
1153 (tyvars, fundeps, theta, _, _, op_stuff) = classExtraBigSig cls
1154 unary = isSingleton tyvars
1155 no_generics = null [() | (_, GenDefMeth) <- op_stuff]
1157 check_op constrained_class_methods (sel_id, dm)
1158 = addErrCtxt (classOpCtxt sel_id tau) $ do
1159 { checkValidTheta SigmaCtxt (tail theta)
1160 -- The 'tail' removes the initial (C a) from the
1161 -- class itself, leaving just the method type
1163 ; traceTc (text "class op type" <+> ppr op_ty <+> ppr tau)
1164 ; checkValidType (FunSigCtxt op_name) tau
1166 -- Check that the type mentions at least one of
1167 -- the class type variables...or at least one reachable
1168 -- from one of the class variables. Example: tc223
1169 -- class Error e => Game b mv e | b -> mv e where
1170 -- newBoard :: MonadState b m => m ()
1171 -- Here, MonadState has a fundep m->b, so newBoard is fine
1172 ; let grown_tyvars = growThetaTyVars theta (mkVarSet tyvars)
1173 ; checkTc (tyVarsOfType tau `intersectsVarSet` grown_tyvars)
1174 (noClassTyVarErr cls sel_id)
1176 -- Check that for a generic method, the type of
1177 -- the method is sufficiently simple
1178 ; checkTc (dm /= GenDefMeth || validGenericMethodType tau)
1179 (badGenericMethodType op_name op_ty)
1182 op_name = idName sel_id
1183 op_ty = idType sel_id
1184 (_,theta1,tau1) = tcSplitSigmaTy op_ty
1185 (_,theta2,tau2) = tcSplitSigmaTy tau1
1186 (theta,tau) | constrained_class_methods = (theta1 ++ theta2, tau2)
1187 | otherwise = (theta1, mkPhiTy (tail theta1) tau1)
1188 -- Ugh! The function might have a type like
1189 -- op :: forall a. C a => forall b. (Eq b, Eq a) => tau2
1190 -- With -XConstrainedClassMethods, we want to allow this, even though the inner
1191 -- forall has an (Eq a) constraint. Whereas in general, each constraint
1192 -- in the context of a for-all must mention at least one quantified
1193 -- type variable. What a mess!
1197 %************************************************************************
1199 Building record selectors
1201 %************************************************************************
1204 mkAuxBinds :: [TyThing] -> HsValBinds Name
1205 -- NB We produce *un-typechecked* bindings, rather like 'deriving'
1206 -- This makes life easier, because the later type checking will add
1207 -- all necessary type abstractions and applications
1208 mkAuxBinds ty_things
1209 = ValBindsOut [(NonRecursive, b) | b <- binds] sigs
1211 (sigs, binds) = unzip rec_sels
1212 rec_sels = map mkRecSelBind [ (tc,fld)
1213 | ATyCon tc <- ty_things
1214 , fld <- tyConFields tc ]
1216 mkRecSelBind :: (TyCon, FieldLabel) -> (LSig Name, LHsBinds Name)
1217 mkRecSelBind (tycon, sel_name)
1218 = (L loc (IdSig sel_id), unitBag (L loc sel_bind))
1220 loc = getSrcSpan tycon
1221 sel_id = Var.mkLocalVar rec_details sel_name sel_ty vanillaIdInfo
1222 rec_details = RecSelId { sel_tycon = tycon, sel_naughty = is_naughty }
1224 -- Find a representative constructor, con1
1225 all_cons = tyConDataCons tycon
1226 cons_w_field = [ con | con <- all_cons
1227 , sel_name `elem` dataConFieldLabels con ]
1228 con1 = ASSERT( not (null cons_w_field) ) head cons_w_field
1230 -- Selector type; Note [Polymorphic selectors]
1231 field_ty = dataConFieldType con1 sel_name
1232 data_ty = dataConOrigResTy con1
1233 data_tvs = tyVarsOfType data_ty
1234 is_naughty = not (tyVarsOfType field_ty `subVarSet` data_tvs)
1235 (field_tvs, field_theta, field_tau) = tcSplitSigmaTy field_ty
1236 sel_ty | is_naughty = unitTy -- See Note [Naughty record selectors]
1237 | otherwise = mkForAllTys (varSetElems data_tvs ++ field_tvs) $
1238 mkPhiTy (dataConStupidTheta con1) $ -- Urgh!
1239 mkPhiTy field_theta $ -- Urgh!
1240 mkFunTy data_ty field_tau
1242 -- Make the binding: sel (C2 { fld = x }) = x
1243 -- sel (C7 { fld = x }) = x
1244 -- where cons_w_field = [C2,C7]
1245 sel_bind | is_naughty = mkFunBind sel_lname [mkSimpleMatch [] unit_rhs]
1246 | otherwise = mkFunBind sel_lname (map mk_match cons_w_field ++ deflt)
1247 mk_match con = mkSimpleMatch [L loc (mk_sel_pat con)]
1248 (L loc (HsVar field_var))
1249 mk_sel_pat con = ConPatIn (L loc (getName con)) (RecCon rec_fields)
1250 rec_fields = HsRecFields { rec_flds = [rec_field], rec_dotdot = Nothing }
1251 rec_field = HsRecField { hsRecFieldId = sel_lname
1252 , hsRecFieldArg = nlVarPat field_var
1253 , hsRecPun = False }
1254 sel_lname = L loc sel_name
1255 field_var = mkInternalName (mkBuiltinUnique 1) (getOccName sel_name) loc
1257 -- Add catch-all default case unless the case is exhaustive
1258 -- We do this explicitly so that we get a nice error message that
1259 -- mentions this particular record selector
1260 deflt | not (any is_unused all_cons) = []
1261 | otherwise = [mkSimpleMatch [nlWildPat]
1262 (nlHsApp (nlHsVar (getName rEC_SEL_ERROR_ID))
1265 -- Do not add a default case unless there are unmatched
1266 -- constructors. We must take account of GADTs, else we
1267 -- get overlap warning messages from the pattern-match checker
1268 is_unused con = not (con `elem` cons_w_field
1269 || dataConCannotMatch inst_tys con)
1270 inst_tys = tyConAppArgs data_ty
1272 unit_rhs = mkLHsTupleExpr []
1273 msg_lit = HsStringPrim $ mkFastString $
1274 occNameString (getOccName sel_name)
1277 tyConFields :: TyCon -> [FieldLabel]
1279 | isAlgTyCon tc = nub (concatMap dataConFieldLabels (tyConDataCons tc))
1283 Note [Polymorphic selectors]
1284 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1285 When a record has a polymorphic field, we pull the foralls out to the front.
1286 data T = MkT { f :: forall a. [a] -> a }
1287 Then f :: forall a. T -> [a] -> a
1288 NOT f :: T -> forall a. [a] -> a
1290 This is horrid. It's only needed in deeply obscure cases, which I hate.
1291 The only case I know is test tc163, which is worth looking at. It's far
1292 from clear that this test should succeed at all!
1294 Note [Naughty record selectors]
1295 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1296 A "naughty" field is one for which we can't define a record
1297 selector, because an existential type variable would escape. For example:
1298 data T = forall a. MkT { x,y::a }
1299 We obviously can't define
1301 Nevertheless we *do* put a RecSelId into the type environment
1302 so that if the user tries to use 'x' as a selector we can bleat
1303 helpfully, rather than saying unhelpfully that 'x' is not in scope.
1304 Hence the sel_naughty flag, to identify record selectors that don't really exist.
1306 In general, a field is "naughty" if its type mentions a type variable that
1307 isn't in the result type of the constructor. Note that this *allows*
1308 GADT record selectors (Note [GADT record selectors]) whose types may look
1309 like sel :: T [a] -> a
1311 For naughty selectors we make a dummy binding
1313 for naughty selectors, so that the later type-check will add them to the
1314 environment, and they'll be exported. The function is never called, because
1315 the tyepchecker spots the sel_naughty field.
1317 Note [GADT record selectors]
1318 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1319 For GADTs, we require that all constructors with a common field 'f' have the same
1320 result type (modulo alpha conversion). [Checked in TcTyClsDecls.checkValidTyCon]
1323 T1 { f :: Maybe a } :: T [a]
1324 T2 { f :: Maybe a, y :: b } :: T [a]
1326 and now the selector takes that result type as its argument:
1327 f :: forall a. T [a] -> Maybe a
1329 Details: the "real" types of T1,T2 are:
1330 T1 :: forall r a. (r~[a]) => a -> T r
1331 T2 :: forall r a b. (r~[a]) => a -> b -> T r
1333 So the selector loooks like this:
1334 f :: forall a. T [a] -> Maybe a
1337 T1 c (g:[a]~[c]) (v:Maybe c) -> v `cast` Maybe (right (sym g))
1338 T2 c d (g:[a]~[c]) (v:Maybe c) (w:d) -> v `cast` Maybe (right (sym g))
1340 Note the forall'd tyvars of the selector are just the free tyvars
1341 of the result type; there may be other tyvars in the constructor's
1342 type (e.g. 'b' in T2).
1344 Note the need for casts in the result!
1346 Note [Selector running example]
1347 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1348 It's OK to combine GADTs and type families. Here's a running example:
1350 data instance T [a] where
1351 T1 { fld :: b } :: T [Maybe b]
1353 The representation type looks like this
1355 T1 { fld :: b } :: :R7T (Maybe b)
1357 and there's coercion from the family type to the representation type
1358 :CoR7T a :: T [a] ~ :R7T a
1360 The selector we want for fld looks like this:
1362 fld :: forall b. T [Maybe b] -> b
1363 fld = /\b. \(d::T [Maybe b]).
1364 case d `cast` :CoR7T (Maybe b) of
1367 The scrutinee of the case has type :R7T (Maybe b), which can be
1368 gotten by appying the eq_spec to the univ_tvs of the data con.
1370 %************************************************************************
1374 %************************************************************************
1377 resultTypeMisMatch :: Name -> DataCon -> DataCon -> SDoc
1378 resultTypeMisMatch field_name con1 con2
1379 = vcat [sep [ptext (sLit "Constructors") <+> ppr con1 <+> ptext (sLit "and") <+> ppr con2,
1380 ptext (sLit "have a common field") <+> quotes (ppr field_name) <> comma],
1381 nest 2 $ ptext (sLit "but have different result types")]
1383 fieldTypeMisMatch :: Name -> DataCon -> DataCon -> SDoc
1384 fieldTypeMisMatch field_name con1 con2
1385 = sep [ptext (sLit "Constructors") <+> ppr con1 <+> ptext (sLit "and") <+> ppr con2,
1386 ptext (sLit "give different types for field"), quotes (ppr field_name)]
1388 dataConCtxt :: Outputable a => a -> SDoc
1389 dataConCtxt con = ptext (sLit "In the definition of data constructor") <+> quotes (ppr con)
1391 classOpCtxt :: Var -> Type -> SDoc
1392 classOpCtxt sel_id tau = sep [ptext (sLit "When checking the class method:"),
1393 nest 2 (ppr sel_id <+> dcolon <+> ppr tau)]
1395 nullaryClassErr :: Class -> SDoc
1397 = ptext (sLit "No parameters for class") <+> quotes (ppr cls)
1399 classArityErr :: Class -> SDoc
1401 = vcat [ptext (sLit "Too many parameters for class") <+> quotes (ppr cls),
1402 parens (ptext (sLit "Use -XMultiParamTypeClasses to allow multi-parameter classes"))]
1404 classFunDepsErr :: Class -> SDoc
1406 = vcat [ptext (sLit "Fundeps in class") <+> quotes (ppr cls),
1407 parens (ptext (sLit "Use -XFunctionalDependencies to allow fundeps"))]
1409 noClassTyVarErr :: Class -> Var -> SDoc
1410 noClassTyVarErr clas op
1411 = sep [ptext (sLit "The class method") <+> quotes (ppr op),
1412 ptext (sLit "mentions none of the type variables of the class") <+>
1413 ppr clas <+> hsep (map ppr (classTyVars clas))]
1415 genericMultiParamErr :: Class -> SDoc
1416 genericMultiParamErr clas
1417 = ptext (sLit "The multi-parameter class") <+> quotes (ppr clas) <+>
1418 ptext (sLit "cannot have generic methods")
1420 badGenericMethodType :: Name -> Kind -> SDoc
1421 badGenericMethodType op op_ty
1422 = hang (ptext (sLit "Generic method type is too complex"))
1423 4 (vcat [ppr op <+> dcolon <+> ppr op_ty,
1424 ptext (sLit "You can only use type variables, arrows, lists, and tuples")])
1426 recSynErr :: [LTyClDecl Name] -> TcRn ()
1428 = setSrcSpan (getLoc (head sorted_decls)) $
1429 addErr (sep [ptext (sLit "Cycle in type synonym declarations:"),
1430 nest 2 (vcat (map ppr_decl sorted_decls))])
1432 sorted_decls = sortLocated syn_decls
1433 ppr_decl (L loc decl) = ppr loc <> colon <+> ppr decl
1435 recClsErr :: [Located (TyClDecl Name)] -> TcRn ()
1437 = setSrcSpan (getLoc (head sorted_decls)) $
1438 addErr (sep [ptext (sLit "Cycle in class declarations (via superclasses):"),
1439 nest 2 (vcat (map ppr_decl sorted_decls))])
1441 sorted_decls = sortLocated cls_decls
1442 ppr_decl (L loc decl) = ppr loc <> colon <+> ppr (decl { tcdSigs = [] })
1444 sortLocated :: [Located a] -> [Located a]
1445 sortLocated things = sortLe le things
1447 le (L l1 _) (L l2 _) = l1 <= l2
1449 badDataConTyCon :: DataCon -> Type -> Type -> SDoc
1450 badDataConTyCon data_con res_ty_tmpl actual_res_ty
1451 = hang (ptext (sLit "Data constructor") <+> quotes (ppr data_con) <+>
1452 ptext (sLit "returns type") <+> quotes (ppr actual_res_ty))
1453 2 (ptext (sLit "instead of an instance of its parent type") <+> quotes (ppr res_ty_tmpl))
1455 badGadtDecl :: Name -> SDoc
1457 = vcat [ ptext (sLit "Illegal generalised algebraic data declaration for") <+> quotes (ppr tc_name)
1458 , nest 2 (parens $ ptext (sLit "Use -XGADTs to allow GADTs")) ]
1460 badExistential :: Located Name -> SDoc
1461 badExistential con_name
1462 = hang (ptext (sLit "Data constructor") <+> quotes (ppr con_name) <+>
1463 ptext (sLit "has existential type variables, or a context"))
1464 2 (parens $ ptext (sLit "Use -XExistentialQuantification or -XGADTs to allow this"))
1466 badStupidTheta :: Name -> SDoc
1467 badStupidTheta tc_name
1468 = ptext (sLit "A data type declared in GADT style cannot have a context:") <+> quotes (ppr tc_name)
1470 newtypeConError :: Name -> Int -> SDoc
1471 newtypeConError tycon n
1472 = sep [ptext (sLit "A newtype must have exactly one constructor,"),
1473 nest 2 $ ptext (sLit "but") <+> quotes (ppr tycon) <+> ptext (sLit "has") <+> speakN n ]
1475 newtypeExError :: DataCon -> SDoc
1477 = sep [ptext (sLit "A newtype constructor cannot have an existential context,"),
1478 nest 2 $ ptext (sLit "but") <+> quotes (ppr con) <+> ptext (sLit "does")]
1480 newtypeStrictError :: DataCon -> SDoc
1481 newtypeStrictError con
1482 = sep [ptext (sLit "A newtype constructor cannot have a strictness annotation,"),
1483 nest 2 $ ptext (sLit "but") <+> quotes (ppr con) <+> ptext (sLit "does")]
1485 newtypePredError :: DataCon -> SDoc
1486 newtypePredError con
1487 = sep [ptext (sLit "A newtype constructor must have a return type of form T a1 ... an"),
1488 nest 2 $ ptext (sLit "but") <+> quotes (ppr con) <+> ptext (sLit "does not")]
1490 newtypeFieldErr :: DataCon -> Int -> SDoc
1491 newtypeFieldErr con_name n_flds
1492 = sep [ptext (sLit "The constructor of a newtype must have exactly one field"),
1493 nest 2 $ ptext (sLit "but") <+> quotes (ppr con_name) <+> ptext (sLit "has") <+> speakN n_flds]
1495 badSigTyDecl :: Name -> SDoc
1496 badSigTyDecl tc_name
1497 = vcat [ ptext (sLit "Illegal kind signature") <+>
1498 quotes (ppr tc_name)
1499 , nest 2 (parens $ ptext (sLit "Use -XKindSignatures to allow kind signatures")) ]
1501 badFamInstDecl :: Outputable a => a -> SDoc
1502 badFamInstDecl tc_name
1503 = vcat [ ptext (sLit "Illegal family instance for") <+>
1504 quotes (ppr tc_name)
1505 , nest 2 (parens $ ptext (sLit "Use -XTypeFamilies to allow indexed type families")) ]
1507 tooManyParmsErr :: Located Name -> SDoc
1508 tooManyParmsErr tc_name
1509 = ptext (sLit "Family instance has too many parameters:") <+>
1510 quotes (ppr tc_name)
1512 tooFewParmsErr :: Arity -> SDoc
1513 tooFewParmsErr arity
1514 = ptext (sLit "Family instance has too few parameters; expected") <+>
1517 wrongNumberOfParmsErr :: Arity -> SDoc
1518 wrongNumberOfParmsErr exp_arity
1519 = ptext (sLit "Number of parameters must match family declaration; expected")
1522 badBootFamInstDeclErr :: SDoc
1523 badBootFamInstDeclErr
1524 = ptext (sLit "Illegal family instance in hs-boot file")
1526 notFamily :: TyCon -> SDoc
1528 = vcat [ ptext (sLit "Illegal family instance for") <+> quotes (ppr tycon)
1529 , nest 2 $ parens (ppr tycon <+> ptext (sLit "is not an indexed type family"))]
1531 wrongKindOfFamily :: TyCon -> SDoc
1532 wrongKindOfFamily family
1533 = ptext (sLit "Wrong category of family instance; declaration was for a")
1536 kindOfFamily | isSynTyCon family = ptext (sLit "type synonym")
1537 | isAlgTyCon family = ptext (sLit "data type")
1538 | otherwise = pprPanic "wrongKindOfFamily" (ppr family)
1540 emptyConDeclsErr :: Name -> SDoc
1541 emptyConDeclsErr tycon
1542 = sep [quotes (ppr tycon) <+> ptext (sLit "has no constructors"),
1543 nest 2 $ ptext (sLit "(-XEmptyDataDecls permits this)")]