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"
27 import TysWiredIn ( unitTy )
35 import MkId ( rEC_SEL_ERROR_ID )
51 import Unique ( mkBuiltinUnique )
56 import Control.Monad ( mplus )
60 %************************************************************************
62 \subsection{Type checking for type and class declarations}
64 %************************************************************************
68 Consider a mutually-recursive group, binding
69 a type constructor T and a class C.
71 Step 1: getInitialKind
72 Construct a KindEnv by binding T and C to a kind variable
75 In that environment, do a kind check
77 Step 3: Zonk the kinds
79 Step 4: buildTyConOrClass
80 Construct an environment binding T to a TyCon and C to a Class.
81 a) Their kinds comes from zonking the relevant kind variable
82 b) Their arity (for synonyms) comes direct from the decl
83 c) The funcional dependencies come from the decl
84 d) The rest comes a knot-tied binding of T and C, returned from Step 4
85 e) The variances of the tycons in the group is calculated from
89 In this environment, walk over the decls, constructing the TyCons and Classes.
90 This uses in a strict way items (a)-(c) above, which is why they must
91 be constructed in Step 4. Feed the results back to Step 4.
92 For this step, pass the is-recursive flag as the wimp-out flag
96 Step 6: Extend environment
97 We extend the type environment with bindings not only for the TyCons and Classes,
98 but also for their "implicit Ids" like data constructors and class selectors
100 Step 7: checkValidTyCl
101 For a recursive group only, check all the decls again, just
102 to check all the side conditions on validity. We could not
103 do this before because we were in a mutually recursive knot.
105 Identification of recursive TyCons
106 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
107 The knot-tying parameters: @rec_details_list@ is an alist mapping @Name@s to
110 Identifying a TyCon as recursive serves two purposes
112 1. Avoid infinite types. Non-recursive newtypes are treated as
113 "transparent", like type synonyms, after the type checker. If we did
114 this for all newtypes, we'd get infinite types. So we figure out for
115 each newtype whether it is "recursive", and add a coercion if so. In
116 effect, we are trying to "cut the loops" by identifying a loop-breaker.
118 2. Avoid infinite unboxing. This is nothing to do with newtypes.
122 Well, this function diverges, but we don't want the strictness analyser
123 to diverge. But the strictness analyser will diverge because it looks
124 deeper and deeper into the structure of T. (I believe there are
125 examples where the function does something sane, and the strictness
126 analyser still diverges, but I can't see one now.)
128 Now, concerning (1), the FC2 branch currently adds a coercion for ALL
129 newtypes. I did this as an experiment, to try to expose cases in which
130 the coercions got in the way of optimisations. If it turns out that we
131 can indeed always use a coercion, then we don't risk recursive types,
132 and don't need to figure out what the loop breakers are.
134 For newtype *families* though, we will always have a coercion, so they
135 are always loop breakers! So you can easily adjust the current
136 algorithm by simply treating all newtype families as loop breakers (and
137 indeed type families). I think.
140 tcTyAndClassDecls :: ModDetails -> [LTyClDecl Name]
141 -> TcM (TcGblEnv, -- Input env extended by types and classes
142 -- and their implicit Ids,DataCons
143 HsValBinds Name) -- Renamed bindings for record selectors
144 -- Fails if there are any errors
146 tcTyAndClassDecls boot_details allDecls
147 = checkNoErrs $ -- The code recovers internally, but if anything gave rise to
148 -- an error we'd better stop now, to avoid a cascade
149 do { -- Omit instances of type families; they are handled together
150 -- with the *heads* of class instances
151 ; let decls = filter (not . isFamInstDecl . unLoc) allDecls
153 -- First check for cyclic type synonysm or classes
154 -- See notes with checkCycleErrs
155 ; checkCycleErrs decls
157 ; traceTc (text "tcTyAndCl" <+> ppr mod)
158 ; (syn_tycons, alg_tyclss) <- fixM (\ ~(_rec_syn_tycons, rec_alg_tyclss) ->
159 do { let { -- Seperate ordinary synonyms from all other type and
160 -- class declarations and add all associated type
161 -- declarations from type classes. The latter is
162 -- required so that the temporary environment for the
163 -- knot includes all associated family declarations.
164 ; (syn_decls, alg_decls) = partition (isSynDecl . unLoc)
166 ; alg_at_decls = concatMap addATs alg_decls
168 -- Extend the global env with the knot-tied results
169 -- for data types and classes
171 -- We must populate the environment with the loop-tied
172 -- T's right away, because the kind checker may "fault
173 -- in" some type constructors that recursively
175 ; let gbl_things = mkGlobalThings alg_at_decls rec_alg_tyclss
176 ; tcExtendRecEnv gbl_things $ do
178 -- Kind-check the declarations
179 { (kc_syn_decls, kc_alg_decls) <- kcTyClDecls syn_decls alg_decls
181 ; let { -- Calculate rec-flag
182 ; calc_rec = calcRecFlags boot_details rec_alg_tyclss
183 ; tc_decl = addLocM (tcTyClDecl calc_rec) }
185 -- Type-check the type synonyms, and extend the envt
186 ; syn_tycons <- tcSynDecls kc_syn_decls
187 ; tcExtendGlobalEnv syn_tycons $ do
189 -- Type-check the data types and classes
190 { alg_tyclss <- mapM tc_decl kc_alg_decls
191 ; return (syn_tycons, concat alg_tyclss)
193 -- Finished with knot-tying now
194 -- Extend the environment with the finished things
195 ; tcExtendGlobalEnv (syn_tycons ++ alg_tyclss) $ do
197 -- Perform the validity check
198 { traceTc (text "ready for validity check")
199 ; mapM_ (addLocM checkValidTyCl) decls
200 ; traceTc (text "done")
202 -- Add the implicit things;
203 -- we want them in the environment because
204 -- they may be mentioned in interface files
205 -- NB: All associated types and their implicit things will be added a
206 -- second time here. This doesn't matter as the definitions are
208 ; let { implicit_things = concatMap implicitTyThings alg_tyclss
209 ; aux_binds = mkAuxBinds alg_tyclss }
210 ; traceTc ((text "Adding" <+> ppr alg_tyclss)
211 $$ (text "and" <+> ppr implicit_things))
212 ; env <- tcExtendGlobalEnv implicit_things getGblEnv
213 ; return (env, aux_binds) }
216 -- Pull associated types out of class declarations, to tie them into the
218 -- NB: We put them in the same place in the list as `tcTyClDecl' will
219 -- eventually put the matching `TyThing's. That's crucial; otherwise,
220 -- the two argument lists of `mkGlobalThings' don't match up.
221 addATs decl@(L _ (ClassDecl {tcdATs = ats})) = decl : ats
224 mkGlobalThings :: [LTyClDecl Name] -- The decls
225 -> [TyThing] -- Knot-tied, in 1-1 correspondence with the decls
227 -- Driven by the Decls, and treating the TyThings lazily
228 -- make a TypeEnv for the new things
229 mkGlobalThings decls things
230 = map mk_thing (decls `zipLazy` things)
232 mk_thing (L _ (ClassDecl {tcdLName = L _ name}), ~(AClass cl))
234 mk_thing (L _ decl, ~(ATyCon tc))
235 = (tcdName decl, ATyCon tc)
239 %************************************************************************
241 Type checking family instances
243 %************************************************************************
245 Family instances are somewhat of a hybrid. They are processed together with
246 class instance heads, but can contain data constructors and hence they share a
247 lot of kinding and type checking code with ordinary algebraic data types (and
251 tcFamInstDecl :: LTyClDecl Name -> TcM TyThing
252 tcFamInstDecl (L loc decl)
253 = -- Prime error recovery, set source location
256 do { -- type families require -XTypeFamilies and can't be in an
258 ; type_families <- doptM Opt_TypeFamilies
259 ; is_boot <- tcIsHsBoot -- Are we compiling an hs-boot file?
260 ; checkTc type_families $ badFamInstDecl (tcdLName decl)
261 ; checkTc (not is_boot) $ badBootFamInstDeclErr
263 -- Perform kind and type checking
264 ; tc <- tcFamInstDecl1 decl
265 ; checkValidTyCon tc -- Remember to check validity;
266 -- no recursion to worry about here
267 ; return (ATyCon tc) }
269 tcFamInstDecl1 :: TyClDecl Name -> TcM TyCon
272 tcFamInstDecl1 (decl@TySynonym {tcdLName = L loc tc_name})
273 = kcIdxTyPats decl $ \k_tvs k_typats resKind family ->
274 do { -- check that the family declaration is for a synonym
275 unless (isSynTyCon family) $
276 addErr (wrongKindOfFamily family)
278 ; -- (1) kind check the right-hand side of the type equation
279 ; k_rhs <- kcCheckLHsType (tcdSynRhs decl) resKind
281 -- we need the exact same number of type parameters as the family
283 ; let famArity = tyConArity family
284 ; checkTc (length k_typats == famArity) $
285 wrongNumberOfParmsErr famArity
287 -- (2) type check type equation
288 ; tcTyVarBndrs k_tvs $ \t_tvs -> do { -- turn kinded into proper tyvars
289 ; t_typats <- mapM tcHsKindedType k_typats
290 ; t_rhs <- tcHsKindedType k_rhs
292 -- (3) check the well-formedness of the instance
293 ; checkValidTypeInst t_typats t_rhs
295 -- (4) construct representation tycon
296 ; rep_tc_name <- newFamInstTyConName tc_name loc
297 ; buildSynTyCon rep_tc_name t_tvs (SynonymTyCon t_rhs)
298 (typeKind t_rhs) (Just (family, t_typats))
301 -- "newtype instance" and "data instance"
302 tcFamInstDecl1 (decl@TyData {tcdND = new_or_data, tcdLName = L loc tc_name,
304 = kcIdxTyPats decl $ \k_tvs k_typats resKind fam_tycon ->
305 do { -- check that the family declaration is for the right kind
306 unless (isAlgTyCon fam_tycon) $
307 addErr (wrongKindOfFamily fam_tycon)
309 ; -- (1) kind check the data declaration as usual
310 ; k_decl <- kcDataDecl decl k_tvs
311 ; let k_ctxt = tcdCtxt k_decl
312 k_cons = tcdCons k_decl
314 -- result kind must be '*' (otherwise, we have too few patterns)
315 ; checkTc (isLiftedTypeKind resKind) $ tooFewParmsErr (tyConArity fam_tycon)
317 -- (2) type check indexed data type declaration
318 ; tcTyVarBndrs k_tvs $ \t_tvs -> do { -- turn kinded into proper tyvars
319 ; unbox_strict <- doptM Opt_UnboxStrictFields
321 -- kind check the type indexes and the context
322 ; t_typats <- mapM tcHsKindedType k_typats
323 ; stupid_theta <- tcHsKindedContext k_ctxt
326 -- (a) left-hand side contains no type family applications
327 -- (vanilla synonyms are fine, though, and we checked for
329 ; mapM_ checkTyFamFreeness t_typats
331 -- Check that we don't use GADT syntax in H98 world
332 ; gadt_ok <- doptM Opt_GADTs
333 ; checkTc (gadt_ok || consUseH98Syntax cons) (badGadtDecl tc_name)
335 -- (b) a newtype has exactly one constructor
336 ; checkTc (new_or_data == DataType || isSingleton k_cons) $
337 newtypeConError tc_name (length k_cons)
339 -- (4) construct representation tycon
340 ; rep_tc_name <- newFamInstTyConName tc_name loc
341 ; let ex_ok = True -- Existentials ok for type families!
342 ; fixM (\ rep_tycon -> do
343 { let orig_res_ty = mkTyConApp fam_tycon t_typats
344 ; data_cons <- tcConDecls unbox_strict ex_ok rep_tycon
345 (t_tvs, orig_res_ty) k_cons
348 DataType -> return (mkDataTyConRhs data_cons)
349 NewType -> ASSERT( not (null data_cons) )
350 mkNewTyConRhs rep_tc_name rep_tycon (head data_cons)
351 ; buildAlgTyCon rep_tc_name t_tvs stupid_theta tc_rhs Recursive
352 False h98_syntax (Just (fam_tycon, t_typats))
353 -- We always assume that indexed types are recursive. Why?
354 -- (1) Due to their open nature, we can never be sure that a
355 -- further instance might not introduce a new recursive
356 -- dependency. (2) They are always valid loop breakers as
357 -- they involve a coercion.
361 h98_syntax = case cons of -- All constructors have same shape
362 L _ (ConDecl { con_res = ResTyGADT _ }) : _ -> False
365 tcFamInstDecl1 d = pprPanic "tcFamInstDecl1" (ppr d)
367 -- Kind checking of indexed types
370 -- Kind check type patterns and kind annotate the embedded type variables.
372 -- * Here we check that a type instance matches its kind signature, but we do
373 -- not check whether there is a pattern for each type index; the latter
374 -- check is only required for type synonym instances.
376 kcIdxTyPats :: TyClDecl Name
377 -> ([LHsTyVarBndr Name] -> [LHsType Name] -> Kind -> TyCon -> TcM a)
378 -- ^^kinded tvs ^^kinded ty pats ^^res kind
380 kcIdxTyPats decl thing_inside
381 = kcHsTyVars (tcdTyVars decl) $ \tvs ->
382 do { fam_tycon <- tcLookupLocatedTyCon (tcdLName decl)
383 ; let { (kinds, resKind) = splitKindFunTys (tyConKind fam_tycon)
384 ; hs_typats = fromJust $ tcdTyPats decl }
386 -- we may not have more parameters than the kind indicates
387 ; checkTc (length kinds >= length hs_typats) $
388 tooManyParmsErr (tcdLName decl)
390 -- type functions can have a higher-kinded result
391 ; let resultKind = mkArrowKinds (drop (length hs_typats) kinds) resKind
392 ; typats <- zipWithM kcCheckLHsType hs_typats kinds
393 ; thing_inside tvs typats resultKind fam_tycon
399 %************************************************************************
403 %************************************************************************
405 We need to kind check all types in the mutually recursive group
406 before we know the kind of the type variables. For example:
409 op :: D b => a -> b -> b
412 bop :: (Monad c) => ...
414 Here, the kind of the locally-polymorphic type variable "b"
415 depends on *all the uses of class D*. For example, the use of
416 Monad c in bop's type signature means that D must have kind Type->Type.
418 However type synonyms work differently. They can have kinds which don't
419 just involve (->) and *:
420 type R = Int# -- Kind #
421 type S a = Array# a -- Kind * -> #
422 type T a b = (# a,b #) -- Kind * -> * -> (# a,b #)
423 So we must infer their kinds from their right-hand sides *first* and then
424 use them, whereas for the mutually recursive data types D we bring into
425 scope kind bindings D -> k, where k is a kind variable, and do inference.
429 This treatment of type synonyms only applies to Haskell 98-style synonyms.
430 General type functions can be recursive, and hence, appear in `alg_decls'.
432 The kind of a type family is solely determinded by its kind signature;
433 hence, only kind signatures participate in the construction of the initial
434 kind environment (as constructed by `getInitialKind'). In fact, we ignore
435 instances of families altogether in the following. However, we need to
436 include the kinds of associated families into the construction of the
437 initial kind environment. (This is handled by `allDecls').
440 kcTyClDecls :: [LTyClDecl Name] -> [Located (TyClDecl Name)]
441 -> TcM ([LTyClDecl Name], [Located (TyClDecl Name)])
442 kcTyClDecls syn_decls alg_decls
443 = do { -- First extend the kind env with each data type, class, and
444 -- indexed type, mapping them to a type variable
445 let initialKindDecls = concat [allDecls decl | L _ decl <- alg_decls]
446 ; alg_kinds <- mapM getInitialKind initialKindDecls
447 ; tcExtendKindEnv alg_kinds $ do
449 -- Now kind-check the type synonyms, in dependency order
450 -- We do these differently to data type and classes,
451 -- because a type synonym can be an unboxed type
453 -- and a kind variable can't unify with UnboxedTypeKind
454 -- So we infer their kinds in dependency order
455 { (kc_syn_decls, syn_kinds) <- kcSynDecls (calcSynCycles syn_decls)
456 ; tcExtendKindEnv syn_kinds $ do
458 -- Now kind-check the data type, class, and kind signatures,
459 -- returning kind-annotated decls; we don't kind-check
460 -- instances of indexed types yet, but leave this to
462 { kc_alg_decls <- mapM (wrapLocM kcTyClDecl)
463 (filter (not . isFamInstDecl . unLoc) alg_decls)
465 ; return (kc_syn_decls, kc_alg_decls) }}}
467 -- get all declarations relevant for determining the initial kind
469 allDecls (decl@ClassDecl {tcdATs = ats}) = decl : [ at
472 allDecls decl | isFamInstDecl decl = []
475 ------------------------------------------------------------------------
476 getInitialKind :: TyClDecl Name -> TcM (Name, TcKind)
477 -- Only for data type, class, and indexed type declarations
478 -- Get as much info as possible from the data, class, or indexed type decl,
479 -- so as to maximise usefulness of error messages
481 = do { arg_kinds <- mapM (mk_arg_kind . unLoc) (tyClDeclTyVars decl)
482 ; res_kind <- mk_res_kind decl
483 ; return (tcdName decl, mkArrowKinds arg_kinds res_kind) }
485 mk_arg_kind (UserTyVar _) = newKindVar
486 mk_arg_kind (KindedTyVar _ kind) = return kind
488 mk_res_kind (TyFamily { tcdKind = Just kind }) = return kind
489 mk_res_kind (TyData { tcdKindSig = Just kind }) = return kind
490 -- On GADT-style declarations we allow a kind signature
491 -- data T :: *->* where { ... }
492 mk_res_kind _ = return liftedTypeKind
496 kcSynDecls :: [SCC (LTyClDecl Name)]
497 -> TcM ([LTyClDecl Name], -- Kind-annotated decls
498 [(Name,TcKind)]) -- Kind bindings
501 kcSynDecls (group : groups)
502 = do { (decl, nk) <- kcSynDecl group
503 ; (decls, nks) <- tcExtendKindEnv [nk] (kcSynDecls groups)
504 ; return (decl:decls, nk:nks) }
507 kcSynDecl :: SCC (LTyClDecl Name)
508 -> TcM (LTyClDecl Name, -- Kind-annotated decls
509 (Name,TcKind)) -- Kind bindings
510 kcSynDecl (AcyclicSCC (L loc decl))
511 = tcAddDeclCtxt decl $
512 kcHsTyVars (tcdTyVars decl) (\ k_tvs ->
513 do { traceTc (text "kcd1" <+> ppr (unLoc (tcdLName decl)) <+> brackets (ppr (tcdTyVars decl))
514 <+> brackets (ppr k_tvs))
515 ; (k_rhs, rhs_kind) <- kcLHsType (tcdSynRhs decl)
516 ; traceTc (text "kcd2" <+> ppr (unLoc (tcdLName decl)))
517 ; let tc_kind = foldr (mkArrowKind . kindedTyVarKind) rhs_kind k_tvs
518 ; return (L loc (decl { tcdTyVars = k_tvs, tcdSynRhs = k_rhs }),
519 (unLoc (tcdLName decl), tc_kind)) })
521 kcSynDecl (CyclicSCC decls)
522 = do { recSynErr decls; failM } -- Fail here to avoid error cascade
523 -- of out-of-scope tycons
525 kindedTyVarKind :: LHsTyVarBndr Name -> Kind
526 kindedTyVarKind (L _ (KindedTyVar _ k)) = k
527 kindedTyVarKind x = pprPanic "kindedTyVarKind" (ppr x)
529 ------------------------------------------------------------------------
530 kcTyClDecl :: TyClDecl Name -> TcM (TyClDecl Name)
531 -- Not used for type synonyms (see kcSynDecl)
533 kcTyClDecl decl@(TyData {})
534 = ASSERT( not . isFamInstDecl $ decl ) -- must not be a family instance
535 kcTyClDeclBody decl $
538 kcTyClDecl decl@(TyFamily {})
539 = kcFamilyDecl [] decl -- the empty list signals a toplevel decl
541 kcTyClDecl decl@(ClassDecl {tcdCtxt = ctxt, tcdSigs = sigs, tcdATs = ats})
542 = kcTyClDeclBody decl $ \ tvs' ->
543 do { ctxt' <- kcHsContext ctxt
544 ; ats' <- mapM (wrapLocM (kcFamilyDecl tvs')) ats
545 ; sigs' <- mapM (wrapLocM kc_sig) sigs
546 ; return (decl {tcdTyVars = tvs', tcdCtxt = ctxt', tcdSigs = sigs',
549 kc_sig (TypeSig nm op_ty) = do { op_ty' <- kcHsLiftedSigType op_ty
550 ; return (TypeSig nm op_ty') }
551 kc_sig other_sig = return other_sig
553 kcTyClDecl decl@(ForeignType {})
556 kcTyClDecl (TySynonym {}) = panic "kcTyClDecl TySynonym"
558 kcTyClDeclBody :: TyClDecl Name
559 -> ([LHsTyVarBndr Name] -> TcM a)
561 -- getInitialKind has made a suitably-shaped kind for the type or class
562 -- Unpack it, and attribute those kinds to the type variables
563 -- Extend the env with bindings for the tyvars, taken from
564 -- the kind of the tycon/class. Give it to the thing inside, and
565 -- check the result kind matches
566 kcTyClDeclBody decl thing_inside
567 = tcAddDeclCtxt decl $
568 do { tc_ty_thing <- tcLookupLocated (tcdLName decl)
569 ; let tc_kind = case tc_ty_thing of
571 _ -> pprPanic "kcTyClDeclBody" (ppr tc_ty_thing)
572 (kinds, _) = splitKindFunTys tc_kind
573 hs_tvs = tcdTyVars decl
574 kinded_tvs = ASSERT( length kinds >= length hs_tvs )
575 [ L loc (KindedTyVar (hsTyVarName tv) k)
576 | (L loc tv, k) <- zip hs_tvs kinds]
577 ; tcExtendKindEnvTvs kinded_tvs (thing_inside kinded_tvs) }
579 -- Kind check a data declaration, assuming that we already extended the
580 -- kind environment with the type variables of the left-hand side (these
581 -- kinded type variables are also passed as the second parameter).
583 kcDataDecl :: TyClDecl Name -> [LHsTyVarBndr Name] -> TcM (TyClDecl Name)
584 kcDataDecl decl@(TyData {tcdND = new_or_data, tcdCtxt = ctxt, tcdCons = cons})
586 = do { ctxt' <- kcHsContext ctxt
587 ; cons' <- mapM (wrapLocM kc_con_decl) cons
588 ; return (decl {tcdTyVars = tvs, tcdCtxt = ctxt', tcdCons = cons'}) }
590 -- doc comments are typechecked to Nothing here
591 kc_con_decl (ConDecl name expl ex_tvs ex_ctxt details 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 (ConDecl name expl ex_tvs' ex_ctxt' details' res' Nothing) }
601 kc_con_details (PrefixCon btys)
602 = do { btys' <- mapM kc_larg_ty btys
603 ; return (PrefixCon btys') }
604 kc_con_details (InfixCon bty1 bty2)
605 = do { bty1' <- kc_larg_ty bty1
606 ; bty2' <- kc_larg_ty bty2
607 ; return (InfixCon bty1' bty2') }
608 kc_con_details (RecCon fields)
609 = do { fields' <- mapM kc_field fields
610 ; return (RecCon fields') }
612 kc_field (ConDeclField fld bty d) = do { bty' <- kc_larg_ty bty
613 ; return (ConDeclField fld bty' d) }
615 kc_larg_ty bty = case new_or_data of
616 DataType -> kcHsSigType bty
617 NewType -> kcHsLiftedSigType bty
618 -- Can't allow an unlifted type for newtypes, because we're effectively
619 -- going to remove the constructor while coercing it to a lifted type.
620 -- And newtypes can't be bang'd
621 kcDataDecl d _ = pprPanic "kcDataDecl" (ppr d)
623 -- Kind check a family declaration or type family default declaration.
625 kcFamilyDecl :: [LHsTyVarBndr Name] -- tyvars of enclosing class decl if any
626 -> TyClDecl Name -> TcM (TyClDecl Name)
627 kcFamilyDecl classTvs decl@(TyFamily {tcdKind = kind})
628 = kcTyClDeclBody decl $ \tvs' ->
629 do { mapM_ unifyClassParmKinds tvs'
630 ; return (decl {tcdTyVars = tvs',
631 tcdKind = kind `mplus` Just liftedTypeKind})
632 -- default result kind is '*'
635 unifyClassParmKinds (L _ (KindedTyVar n k))
636 | Just classParmKind <- lookup n classTyKinds = unifyKind k classParmKind
637 | otherwise = return ()
638 unifyClassParmKinds x = pprPanic "kcFamilyDecl/unifyClassParmKinds" (ppr x)
639 classTyKinds = [(n, k) | L _ (KindedTyVar n k) <- classTvs]
640 kcFamilyDecl _ (TySynonym {}) -- type family defaults
641 = panic "TcTyClsDecls.kcFamilyDecl: not implemented yet"
642 kcFamilyDecl _ d = pprPanic "kcFamilyDecl" (ppr d)
646 %************************************************************************
648 \subsection{Type checking}
650 %************************************************************************
653 tcSynDecls :: [LTyClDecl Name] -> TcM [TyThing]
654 tcSynDecls [] = return []
655 tcSynDecls (decl : decls)
656 = do { syn_tc <- addLocM tcSynDecl decl
657 ; syn_tcs <- tcExtendGlobalEnv [syn_tc] (tcSynDecls decls)
658 ; return (syn_tc : syn_tcs) }
661 tcSynDecl :: TyClDecl Name -> TcM TyThing
663 (TySynonym {tcdLName = L _ tc_name, tcdTyVars = tvs, tcdSynRhs = rhs_ty})
664 = tcTyVarBndrs tvs $ \ tvs' -> do
665 { traceTc (text "tcd1" <+> ppr tc_name)
666 ; rhs_ty' <- tcHsKindedType rhs_ty
667 ; tycon <- buildSynTyCon tc_name tvs' (SynonymTyCon rhs_ty')
668 (typeKind rhs_ty') Nothing
669 ; return (ATyCon tycon)
671 tcSynDecl d = pprPanic "tcSynDecl" (ppr d)
674 tcTyClDecl :: (Name -> RecFlag) -> TyClDecl Name -> TcM [TyThing]
676 tcTyClDecl calc_isrec decl
677 = tcAddDeclCtxt decl (tcTyClDecl1 calc_isrec decl)
679 -- "type family" declarations
680 tcTyClDecl1 :: (Name -> RecFlag) -> TyClDecl Name -> TcM [TyThing]
681 tcTyClDecl1 _calc_isrec
682 (TyFamily {tcdFlavour = TypeFamily,
683 tcdLName = L _ tc_name, tcdTyVars = tvs,
684 tcdKind = Just kind}) -- NB: kind at latest added during kind checking
685 = tcTyVarBndrs tvs $ \ tvs' -> do
686 { traceTc (text "type family: " <+> ppr tc_name)
688 -- Check that we don't use families without -XTypeFamilies
689 ; idx_tys <- doptM Opt_TypeFamilies
690 ; checkTc idx_tys $ badFamInstDecl tc_name
692 -- Check for no type indices
693 ; checkTc (not (null tvs)) (noIndexTypes tc_name)
695 ; tycon <- buildSynTyCon tc_name tvs' (OpenSynTyCon kind Nothing) kind Nothing
696 ; return [ATyCon tycon]
699 -- "data family" declaration
700 tcTyClDecl1 _calc_isrec
701 (TyFamily {tcdFlavour = DataFamily,
702 tcdLName = L _ tc_name, tcdTyVars = tvs, tcdKind = mb_kind})
703 = tcTyVarBndrs tvs $ \ tvs' -> do
704 { traceTc (text "data family: " <+> ppr tc_name)
705 ; extra_tvs <- tcDataKindSig mb_kind
706 ; let final_tvs = tvs' ++ extra_tvs -- we may not need these
709 -- Check that we don't use families without -XTypeFamilies
710 ; idx_tys <- doptM Opt_TypeFamilies
711 ; checkTc idx_tys $ badFamInstDecl tc_name
713 -- Check for no type indices
714 ; checkTc (not (null tvs)) (noIndexTypes tc_name)
716 ; tycon <- buildAlgTyCon tc_name final_tvs []
717 mkOpenDataTyConRhs Recursive False True Nothing
718 ; return [ATyCon tycon]
721 -- "newtype" and "data"
722 -- NB: not used for newtype/data instances (whether associated or not)
723 tcTyClDecl1 calc_isrec
724 (TyData {tcdND = new_or_data, tcdCtxt = ctxt, tcdTyVars = tvs,
725 tcdLName = L _ tc_name, tcdKindSig = mb_ksig, tcdCons = cons})
726 = tcTyVarBndrs tvs $ \ tvs' -> do
727 { extra_tvs <- tcDataKindSig mb_ksig
728 ; let final_tvs = tvs' ++ extra_tvs
729 ; stupid_theta <- tcHsKindedContext ctxt
730 ; want_generic <- doptM Opt_Generics
731 ; unbox_strict <- doptM Opt_UnboxStrictFields
732 ; empty_data_decls <- doptM Opt_EmptyDataDecls
733 ; kind_signatures <- doptM Opt_KindSignatures
734 ; existential_ok <- doptM Opt_ExistentialQuantification
735 ; gadt_ok <- doptM Opt_GADTs
736 ; is_boot <- tcIsHsBoot -- Are we compiling an hs-boot file?
737 ; let ex_ok = existential_ok || gadt_ok -- Data cons can have existential context
739 -- Check that we don't use GADT syntax in H98 world
740 ; checkTc (gadt_ok || h98_syntax) (badGadtDecl tc_name)
742 -- Check that we don't use kind signatures without Glasgow extensions
743 ; checkTc (kind_signatures || isNothing mb_ksig) (badSigTyDecl tc_name)
745 -- Check that the stupid theta is empty for a GADT-style declaration
746 ; checkTc (null stupid_theta || h98_syntax) (badStupidTheta tc_name)
748 -- Check that a newtype has exactly one constructor
749 -- Do this before checking for empty data decls, so that
750 -- we don't suggest -XEmptyDataDecls for newtypes
751 ; checkTc (new_or_data == DataType || isSingleton cons)
752 (newtypeConError tc_name (length cons))
754 -- Check that there's at least one condecl,
755 -- or else we're reading an hs-boot file, or -XEmptyDataDecls
756 ; checkTc (not (null cons) || empty_data_decls || is_boot)
757 (emptyConDeclsErr tc_name)
759 ; tycon <- fixM (\ tycon -> do
760 { let res_ty = mkTyConApp tycon (mkTyVarTys final_tvs)
761 ; data_cons <- tcConDecls unbox_strict ex_ok
762 tycon (final_tvs, res_ty) cons
764 if null cons && is_boot -- In a hs-boot file, empty cons means
765 then return AbstractTyCon -- "don't know"; hence Abstract
766 else case new_or_data of
767 DataType -> return (mkDataTyConRhs data_cons)
768 NewType -> ASSERT( not (null data_cons) )
769 mkNewTyConRhs tc_name tycon (head data_cons)
770 ; buildAlgTyCon tc_name final_tvs stupid_theta tc_rhs is_rec
771 (want_generic && canDoGenerics data_cons) h98_syntax Nothing
773 ; return [ATyCon tycon]
776 is_rec = calc_isrec tc_name
777 h98_syntax = consUseH98Syntax cons
779 tcTyClDecl1 calc_isrec
780 (ClassDecl {tcdLName = L _ class_name, tcdTyVars = tvs,
781 tcdCtxt = ctxt, tcdMeths = meths,
782 tcdFDs = fundeps, tcdSigs = sigs, tcdATs = ats} )
783 = tcTyVarBndrs tvs $ \ tvs' -> do
784 { ctxt' <- tcHsKindedContext ctxt
785 ; fds' <- mapM (addLocM tc_fundep) fundeps
786 ; atss <- mapM (addLocM (tcTyClDecl1 (const Recursive))) ats
787 -- NB: 'ats' only contains "type family" and "data family"
788 -- declarations as well as type family defaults
789 ; let ats' = map (setAssocFamilyPermutation tvs') (concat atss)
790 ; sig_stuff <- tcClassSigs class_name sigs meths
791 ; clas <- fixM (\ clas ->
792 let -- This little knot is just so we can get
793 -- hold of the name of the class TyCon, which we
794 -- need to look up its recursiveness
795 tycon_name = tyConName (classTyCon clas)
796 tc_isrec = calc_isrec tycon_name
798 buildClass False {- Must include unfoldings for selectors -}
799 class_name tvs' ctxt' fds' ats'
801 ; return (AClass clas : ats')
802 -- NB: Order is important due to the call to `mkGlobalThings' when
803 -- tying the the type and class declaration type checking knot.
806 tc_fundep (tvs1, tvs2) = do { tvs1' <- mapM tcLookupTyVar tvs1 ;
807 ; tvs2' <- mapM tcLookupTyVar tvs2 ;
808 ; return (tvs1', tvs2') }
811 (ForeignType {tcdLName = L _ tc_name, tcdExtName = tc_ext_name})
812 = return [ATyCon (mkForeignTyCon tc_name tc_ext_name liftedTypeKind 0)]
814 tcTyClDecl1 _ d = pprPanic "tcTyClDecl1" (ppr d)
816 -----------------------------------
817 tcConDecls :: Bool -> Bool -> TyCon -> ([TyVar], Type)
818 -> [LConDecl Name] -> TcM [DataCon]
819 tcConDecls unbox ex_ok rep_tycon res_tmpl cons
820 = mapM (addLocM (tcConDecl unbox ex_ok rep_tycon res_tmpl)) cons
822 tcConDecl :: Bool -- True <=> -funbox-strict_fields
823 -> Bool -- True <=> -XExistentialQuantificaton or -XGADTs
824 -> TyCon -- Representation tycon
825 -> ([TyVar], Type) -- Return type template (with its template tyvars)
829 tcConDecl unbox_strict existential_ok rep_tycon res_tmpl -- Data types
830 (ConDecl name _ tvs ctxt details res_ty _)
831 = addErrCtxt (dataConCtxt name) $
832 tcTyVarBndrs tvs $ \ tvs' -> do
833 { ctxt' <- tcHsKindedContext ctxt
834 ; checkTc (existential_ok || (null tvs && null (unLoc ctxt)))
835 (badExistential name)
836 ; (univ_tvs, ex_tvs, eq_preds, res_ty') <- tcResultType res_tmpl tvs' res_ty
838 tc_datacon is_infix field_lbls btys
839 = do { (arg_tys, stricts) <- mapAndUnzipM (tcConArg unbox_strict) btys
840 ; buildDataCon (unLoc name) is_infix
842 univ_tvs ex_tvs eq_preds ctxt' arg_tys
844 -- NB: we put data_tc, the type constructor gotten from the
845 -- constructor type signature into the data constructor;
846 -- that way checkValidDataCon can complain if it's wrong.
849 PrefixCon btys -> tc_datacon False [] btys
850 InfixCon bty1 bty2 -> tc_datacon True [] [bty1,bty2]
851 RecCon fields -> tc_datacon False field_names btys
853 field_names = map (unLoc . cd_fld_name) fields
854 btys = map cd_fld_type fields
858 -- data instance T (b,c) where
859 -- TI :: forall e. e -> T (e,e)
861 -- The representation tycon looks like this:
862 -- data :R7T b c where
863 -- TI :: forall b1 c1. (b1 ~ c1) => b1 -> :R7T b1 c1
864 -- In this case orig_res_ty = T (e,e)
866 tcResultType :: ([TyVar], Type) -- Template for result type; e.g.
867 -- data instance T [a] b c = ...
868 -- gives template ([a,b,c], T [a] b c)
869 -> [TyVar] -- where MkT :: forall x y z. ...
871 -> TcM ([TyVar], -- Universal
872 [TyVar], -- Existential (distinct OccNames from univs)
873 [(TyVar,Type)], -- Equality predicates
874 Type) -- Typechecked return type
875 -- We don't check that the TyCon given in the ResTy is
876 -- the same as the parent tycon, becuase we are in the middle
877 -- of a recursive knot; so it's postponed until checkValidDataCon
879 tcResultType (tmpl_tvs, res_ty) dc_tvs ResTyH98
880 = return (tmpl_tvs, dc_tvs, [], res_ty)
881 -- In H98 syntax the dc_tvs are the existential ones
882 -- data T a b c = forall d e. MkT ...
883 -- The {a,b,c} are tc_tvs, and {d,e} are dc_tvs
885 tcResultType (tmpl_tvs, res_tmpl) dc_tvs (ResTyGADT res_ty)
886 -- E.g. data T [a] b c where
887 -- MkT :: forall x y z. T [(x,y)] z z
889 -- Univ tyvars Eq-spec
893 -- Existentials are the leftover type vars: [x,y]
894 -- So we return ([a,b,z], [x,y], [a~(x,y),b~z], T [(x,y)] z z)
895 = do { res_ty' <- tcHsKindedType res_ty
896 ; let Just subst = tcMatchTy (mkVarSet tmpl_tvs) res_tmpl res_ty'
898 -- /Lazily/ figure out the univ_tvs etc
899 -- Each univ_tv is either a dc_tv or a tmpl_tv
900 (univ_tvs, eq_spec) = foldr choose ([], []) tidy_tmpl_tvs
901 choose tmpl (univs, eqs)
902 | Just ty <- lookupTyVar subst tmpl
903 = case tcGetTyVar_maybe ty of
904 Just tv | not (tv `elem` univs)
906 _other -> (tmpl:univs, (tmpl,ty):eqs)
907 | otherwise = pprPanic "tcResultType" (ppr res_ty)
908 ex_tvs = dc_tvs `minusList` univ_tvs
910 ; return (univ_tvs, ex_tvs, eq_spec, res_ty') }
912 -- NB: tmpl_tvs and dc_tvs are distinct, but
913 -- we want them to be *visibly* distinct, both for
914 -- interface files and general confusion. So rename
915 -- the tc_tvs, since they are not used yet (no
916 -- consequential renaming needed)
917 (_, tidy_tmpl_tvs) = mapAccumL tidy_one init_occ_env tmpl_tvs
918 init_occ_env = initTidyOccEnv (map getOccName dc_tvs)
919 tidy_one env tv = (env', setTyVarName tv (tidyNameOcc name occ'))
922 (env', occ') = tidyOccName env (getOccName name)
924 consUseH98Syntax :: [LConDecl a] -> Bool
925 consUseH98Syntax (L _ (ConDecl { con_res = ResTyGADT _ }) : _) = False
926 consUseH98Syntax _ = True
927 -- All constructors have same shape
930 tcConArg :: Bool -- True <=> -funbox-strict_fields
932 -> TcM (TcType, StrictnessMark)
933 tcConArg unbox_strict bty
934 = do { arg_ty <- tcHsBangType bty
935 ; let bang = getBangStrictness bty
936 ; return (arg_ty, chooseBoxingStrategy unbox_strict arg_ty bang) }
938 -- We attempt to unbox/unpack a strict field when either:
939 -- (i) The field is marked '!!', or
940 -- (ii) The field is marked '!', and the -funbox-strict-fields flag is on.
942 -- We have turned off unboxing of newtypes because coercions make unboxing
943 -- and reboxing more complicated
944 chooseBoxingStrategy :: Bool -> TcType -> HsBang -> StrictnessMark
945 chooseBoxingStrategy unbox_strict_fields arg_ty bang
947 HsNoBang -> NotMarkedStrict
948 HsStrict | unbox_strict_fields
949 && can_unbox arg_ty -> MarkedUnboxed
950 HsUnbox | can_unbox arg_ty -> MarkedUnboxed
953 -- we can unbox if the type is a chain of newtypes with a product tycon
955 can_unbox arg_ty = case splitTyConApp_maybe arg_ty of
957 Just (arg_tycon, tycon_args) ->
958 not (isRecursiveTyCon arg_tycon) && -- Note [Recusive unboxing]
959 isProductTyCon arg_tycon &&
960 (if isNewTyCon arg_tycon then
961 can_unbox (newTyConInstRhs arg_tycon tycon_args)
965 Note [Recursive unboxing]
966 ~~~~~~~~~~~~~~~~~~~~~~~~~
967 Be careful not to try to unbox this!
969 But it's the *argument* type that matters. This is fine:
971 because Int is non-recursive.
974 %************************************************************************
978 %************************************************************************
980 Validity checking is done once the mutually-recursive knot has been
981 tied, so we can look at things freely.
984 checkCycleErrs :: [LTyClDecl Name] -> TcM ()
985 checkCycleErrs tyclss
989 = do { mapM_ recClsErr cls_cycles
990 ; failM } -- Give up now, because later checkValidTyCl
991 -- will loop if the synonym is recursive
993 cls_cycles = calcClassCycles tyclss
995 checkValidTyCl :: TyClDecl Name -> TcM ()
996 -- We do the validity check over declarations, rather than TyThings
997 -- only so that we can add a nice context with tcAddDeclCtxt
999 = tcAddDeclCtxt decl $
1000 do { thing <- tcLookupLocatedGlobal (tcdLName decl)
1001 ; traceTc (text "Validity of" <+> ppr thing)
1003 ATyCon tc -> checkValidTyCon tc
1004 AClass cl -> checkValidClass cl
1005 _ -> panic "checkValidTyCl"
1006 ; traceTc (text "Done validity of" <+> ppr thing)
1009 -------------------------
1010 -- For data types declared with record syntax, we require
1011 -- that each constructor that has a field 'f'
1012 -- (a) has the same result type
1013 -- (b) has the same type for 'f'
1014 -- module alpha conversion of the quantified type variables
1015 -- of the constructor.
1017 -- Note that we allow existentials to match becuase the
1018 -- fields can never meet. E.g
1020 -- T1 { f1 :: b, f2 :: a, f3 ::Int } :: T
1021 -- T2 { f1 :: c, f2 :: c, f3 ::Int } :: T
1022 -- Here we do not complain about f1,f2 because they are existential
1024 checkValidTyCon :: TyCon -> TcM ()
1027 = case synTyConRhs tc of
1028 OpenSynTyCon _ _ -> return ()
1029 SynonymTyCon ty -> checkValidType syn_ctxt ty
1031 = do -- Check the context on the data decl
1032 checkValidTheta (DataTyCtxt name) (tyConStupidTheta tc)
1034 -- Check arg types of data constructors
1035 mapM_ (checkValidDataCon tc) data_cons
1037 -- Check that fields with the same name share a type
1038 mapM_ check_fields groups
1041 syn_ctxt = TySynCtxt name
1043 data_cons = tyConDataCons tc
1045 groups = equivClasses cmp_fld (concatMap get_fields data_cons)
1046 cmp_fld (f1,_) (f2,_) = f1 `compare` f2
1047 get_fields con = dataConFieldLabels con `zip` repeat con
1048 -- dataConFieldLabels may return the empty list, which is fine
1050 -- See Note [GADT record selectors] in MkId.lhs
1051 -- We must check (a) that the named field has the same
1052 -- type in each constructor
1053 -- (b) that those constructors have the same result type
1055 -- However, the constructors may have differently named type variable
1056 -- and (worse) we don't know how the correspond to each other. E.g.
1057 -- C1 :: forall a b. { f :: a, g :: b } -> T a b
1058 -- C2 :: forall d c. { f :: c, g :: c } -> T c d
1060 -- So what we do is to ust Unify.tcMatchTys to compare the first candidate's
1061 -- result type against other candidates' types BOTH WAYS ROUND.
1062 -- If they magically agrees, take the substitution and
1063 -- apply them to the latter ones, and see if they match perfectly.
1064 check_fields ((label, con1) : other_fields)
1065 -- These fields all have the same name, but are from
1066 -- different constructors in the data type
1067 = recoverM (return ()) $ mapM_ checkOne other_fields
1068 -- Check that all the fields in the group have the same type
1069 -- NB: this check assumes that all the constructors of a given
1070 -- data type use the same type variables
1072 (tvs1, _, _, res1) = dataConSig con1
1074 fty1 = dataConFieldType con1 label
1076 checkOne (_, con2) -- Do it bothways to ensure they are structurally identical
1077 = do { checkFieldCompat label con1 con2 ts1 res1 res2 fty1 fty2
1078 ; checkFieldCompat label con2 con1 ts2 res2 res1 fty2 fty1 }
1080 (tvs2, _, _, res2) = dataConSig con2
1082 fty2 = dataConFieldType con2 label
1083 check_fields [] = panic "checkValidTyCon/check_fields []"
1085 checkFieldCompat :: Name -> DataCon -> DataCon -> TyVarSet
1086 -> Type -> Type -> Type -> Type -> TcM ()
1087 checkFieldCompat fld con1 con2 tvs1 res1 res2 fty1 fty2
1088 = do { checkTc (isJust mb_subst1) (resultTypeMisMatch fld con1 con2)
1089 ; checkTc (isJust mb_subst2) (fieldTypeMisMatch fld con1 con2) }
1091 mb_subst1 = tcMatchTy tvs1 res1 res2
1092 mb_subst2 = tcMatchTyX tvs1 (expectJust "checkFieldCompat" mb_subst1) fty1 fty2
1094 -------------------------------
1095 checkValidDataCon :: TyCon -> DataCon -> TcM ()
1096 checkValidDataCon tc con
1097 = setSrcSpan (srcLocSpan (getSrcLoc con)) $
1098 addErrCtxt (dataConCtxt con) $
1099 do { let tc_tvs = tyConTyVars tc
1100 res_ty_tmpl = mkFamilyTyConApp tc (mkTyVarTys tc_tvs)
1101 actual_res_ty = dataConOrigResTy con
1102 ; checkTc (isJust (tcMatchTy (mkVarSet tc_tvs)
1105 (badDataConTyCon con res_ty_tmpl actual_res_ty)
1106 ; checkValidMonoType (dataConOrigResTy con)
1107 -- Disallow MkT :: T (forall a. a->a)
1108 -- Reason: it's really the argument of an equality constraint
1109 ; checkValidType ctxt (dataConUserType con)
1110 ; when (isNewTyCon tc) (checkNewDataCon con)
1113 ctxt = ConArgCtxt (dataConName con)
1115 -------------------------------
1116 checkNewDataCon :: DataCon -> TcM ()
1117 -- Checks for the data constructor of a newtype
1119 = do { checkTc (isSingleton arg_tys) (newtypeFieldErr con (length arg_tys))
1121 ; checkTc (null eq_spec) (newtypePredError con)
1122 -- Return type is (T a b c)
1123 ; checkTc (null ex_tvs && null eq_theta && null dict_theta) (newtypeExError con)
1125 ; checkTc (not (any isMarkedStrict (dataConStrictMarks con)))
1126 (newtypeStrictError con)
1130 (_univ_tvs, ex_tvs, eq_spec, eq_theta, dict_theta, arg_tys, _res_ty) = dataConFullSig con
1132 -------------------------------
1133 checkValidClass :: Class -> TcM ()
1135 = do { constrained_class_methods <- doptM Opt_ConstrainedClassMethods
1136 ; multi_param_type_classes <- doptM Opt_MultiParamTypeClasses
1137 ; fundep_classes <- doptM Opt_FunctionalDependencies
1139 -- Check that the class is unary, unless GlaExs
1140 ; checkTc (notNull tyvars) (nullaryClassErr cls)
1141 ; checkTc (multi_param_type_classes || unary) (classArityErr cls)
1142 ; checkTc (fundep_classes || null fundeps) (classFunDepsErr cls)
1144 -- Check the super-classes
1145 ; checkValidTheta (ClassSCCtxt (className cls)) theta
1147 -- Check the class operations
1148 ; mapM_ (check_op constrained_class_methods) op_stuff
1150 -- Check that if the class has generic methods, then the
1151 -- class has only one parameter. We can't do generic
1152 -- multi-parameter type classes!
1153 ; checkTc (unary || no_generics) (genericMultiParamErr cls)
1156 (tyvars, fundeps, theta, _, _, op_stuff) = classExtraBigSig cls
1157 unary = isSingleton tyvars
1158 no_generics = null [() | (_, GenDefMeth) <- op_stuff]
1160 check_op constrained_class_methods (sel_id, dm)
1161 = addErrCtxt (classOpCtxt sel_id tau) $ do
1162 { checkValidTheta SigmaCtxt (tail theta)
1163 -- The 'tail' removes the initial (C a) from the
1164 -- class itself, leaving just the method type
1166 ; traceTc (text "class op type" <+> ppr op_ty <+> ppr tau)
1167 ; checkValidType (FunSigCtxt op_name) tau
1169 -- Check that the type mentions at least one of
1170 -- the class type variables...or at least one reachable
1171 -- from one of the class variables. Example: tc223
1172 -- class Error e => Game b mv e | b -> mv e where
1173 -- newBoard :: MonadState b m => m ()
1174 -- Here, MonadState has a fundep m->b, so newBoard is fine
1175 ; let grown_tyvars = grow theta (mkVarSet tyvars)
1176 ; checkTc (tyVarsOfType tau `intersectsVarSet` grown_tyvars)
1177 (noClassTyVarErr cls sel_id)
1179 -- Check that for a generic method, the type of
1180 -- the method is sufficiently simple
1181 ; checkTc (dm /= GenDefMeth || validGenericMethodType tau)
1182 (badGenericMethodType op_name op_ty)
1185 op_name = idName sel_id
1186 op_ty = idType sel_id
1187 (_,theta1,tau1) = tcSplitSigmaTy op_ty
1188 (_,theta2,tau2) = tcSplitSigmaTy tau1
1189 (theta,tau) | constrained_class_methods = (theta1 ++ theta2, tau2)
1190 | otherwise = (theta1, mkPhiTy (tail theta1) tau1)
1191 -- Ugh! The function might have a type like
1192 -- op :: forall a. C a => forall b. (Eq b, Eq a) => tau2
1193 -- With -XConstrainedClassMethods, we want to allow this, even though the inner
1194 -- forall has an (Eq a) constraint. Whereas in general, each constraint
1195 -- in the context of a for-all must mention at least one quantified
1196 -- type variable. What a mess!
1200 %************************************************************************
1202 Building record selectors
1204 %************************************************************************
1207 mkAuxBinds :: [TyThing] -> HsValBinds Name
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 ]
1217 mkRecSelBind :: (TyCon, FieldLabel) -> (LSig Name, LHsBinds Name)
1218 mkRecSelBind (tycon, sel_name)
1219 = (L loc (IdSig sel_id), unitBag (L loc sel_bind))
1221 loc = getSrcSpan tycon
1222 sel_id = Var.mkLocalVar rec_details sel_name sel_ty vanillaIdInfo
1223 rec_details = RecSelId { sel_tycon = tycon, sel_naughty = is_naughty }
1225 -- Find a representative constructor, con1
1226 all_cons = tyConDataCons tycon
1227 cons_w_field = [ con | con <- all_cons
1228 , sel_name `elem` dataConFieldLabels con ]
1229 con1 = ASSERT( not (null cons_w_field) ) head cons_w_field
1231 -- Selector type; Note [Polymorphic selectors]
1232 field_ty = dataConFieldType con1 sel_name
1233 (field_tvs, field_theta, field_tau)
1234 | is_naughty = ([], [], unitTy)
1235 | otherwise = tcSplitSigmaTy field_ty
1236 data_ty = dataConOrigResTy con1
1237 data_tvs = tyVarsOfType data_ty
1238 is_naughty = not (tyVarsOfType field_ty `subVarSet` data_tvs)
1239 sel_ty = mkForAllTys (varSetElems data_tvs ++ field_tvs) $
1240 mkPhiTy (dataConStupidTheta con1) $ -- Urgh!
1241 mkPhiTy field_theta $ -- Urgh!
1242 mkFunTy data_ty field_tau
1244 -- Make the binding: sel (C2 { fld = x }) = x
1245 -- sel (C7 { fld = x }) = x
1246 -- where cons_w_field = [C2,C7]
1247 sel_bind = mkFunBind sel_lname (map mk_match cons_w_field ++ deflt)
1248 mk_match con = mkSimpleMatch [L loc (mk_sel_pat con)]
1250 mk_sel_pat con = ConPatIn (L loc (getName con)) (RecCon rec_fields)
1251 rec_fields = HsRecFields { rec_flds = [rec_field], rec_dotdot = Nothing }
1252 rec_field = HsRecField { hsRecFieldId = sel_lname
1253 , hsRecFieldArg = nlVarPat field_var
1254 , hsRecPun = False }
1255 match_body | is_naughty = ExplicitTuple [] Boxed
1256 | otherwise = HsVar field_var
1257 sel_lname = L loc sel_name
1258 field_var = mkInternalName (mkBuiltinUnique 1) (getOccName sel_name) loc
1260 -- Add catch-all default case unless the case is exhaustive
1261 -- We do this explicitly so that we get a nice error message that
1262 -- mentions this particular record selector
1263 deflt | length cons_w_field == length all_cons = []
1264 | otherwise = [mkSimpleMatch [nlWildPat]
1265 (nlHsApp (nlHsVar (getName rEC_SEL_ERROR_ID))
1267 msg_lit = HsStringPrim $ mkFastString $
1268 occNameString (getOccName sel_name)
1271 tyConFields :: TyCon -> [FieldLabel]
1273 | isAlgTyCon tc = nub (concatMap dataConFieldLabels (tyConDataCons tc))
1277 Note [Polymorphic selectors]
1278 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1279 When a record has a polymorphic field, we pull the foralls out to the front.
1280 data T = MkT { f :: forall a. [a] -> a }
1281 Then f :: forall a. T -> [a] -> a
1282 NOT f :: T -> forall a. [a] -> a
1284 This is horrid. It's only needed in deeply obscure cases, which I hate.
1285 The only case I know is test tc163, which is worth looking at. It's far
1286 from clear that this test should succeed at all!
1288 Note [Naughty record selectors]
1289 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1290 A "naughty" field is one for which we can't define a record
1291 selector, because an existential type variable would escape. For example:
1292 data T = forall a. MkT { x,y::a }
1293 We obviously can't define
1295 Nevertheless we *do* put a RecSelId into the type environment
1296 so that if the user tries to use 'x' as a selector we can bleat
1297 helpfully, rather than saying unhelpfully that 'x' is not in scope.
1298 Hence the sel_naughty flag, to identify record selectors that don't really exist.
1300 In general, a field is naughty if its type mentions a type variable that
1301 isn't in the result type of the constructor.
1303 We make a dummy binding for naughty selectors, so that they can be treated
1304 uniformly, apart from their sel_naughty field. The function is never called.
1306 Note [GADT record selectors]
1307 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1308 For GADTs, we require that all constructors with a common field 'f' have the same
1309 result type (modulo alpha conversion). [Checked in TcTyClsDecls.checkValidTyCon]
1312 T1 { f :: Maybe a } :: T [a]
1313 T2 { f :: Maybe a, y :: b } :: T [a]
1315 and now the selector takes that result type as its argument:
1316 f :: forall a. T [a] -> Maybe a
1318 Details: the "real" types of T1,T2 are:
1319 T1 :: forall r a. (r~[a]) => a -> T r
1320 T2 :: forall r a b. (r~[a]) => a -> b -> T r
1322 So the selector loooks like this:
1323 f :: forall a. T [a] -> Maybe a
1326 T1 c (g:[a]~[c]) (v:Maybe c) -> v `cast` Maybe (right (sym g))
1327 T2 c d (g:[a]~[c]) (v:Maybe c) (w:d) -> v `cast` Maybe (right (sym g))
1329 Note the forall'd tyvars of the selector are just the free tyvars
1330 of the result type; there may be other tyvars in the constructor's
1331 type (e.g. 'b' in T2).
1333 Note the need for casts in the result!
1335 Note [Selector running example]
1336 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1337 It's OK to combine GADTs and type families. Here's a running example:
1339 data instance T [a] where
1340 T1 { fld :: b } :: T [Maybe b]
1342 The representation type looks like this
1344 T1 { fld :: b } :: :R7T (Maybe b)
1346 and there's coercion from the family type to the representation type
1347 :CoR7T a :: T [a] ~ :R7T a
1349 The selector we want for fld looks like this:
1351 fld :: forall b. T [Maybe b] -> b
1352 fld = /\b. \(d::T [Maybe b]).
1353 case d `cast` :CoR7T (Maybe b) of
1356 The scrutinee of the case has type :R7T (Maybe b), which can be
1357 gotten by appying the eq_spec to the univ_tvs of the data con.
1359 %************************************************************************
1363 %************************************************************************
1366 resultTypeMisMatch :: Name -> DataCon -> DataCon -> SDoc
1367 resultTypeMisMatch field_name con1 con2
1368 = vcat [sep [ptext (sLit "Constructors") <+> ppr con1 <+> ptext (sLit "and") <+> ppr con2,
1369 ptext (sLit "have a common field") <+> quotes (ppr field_name) <> comma],
1370 nest 2 $ ptext (sLit "but have different result types")]
1372 fieldTypeMisMatch :: Name -> DataCon -> DataCon -> SDoc
1373 fieldTypeMisMatch field_name con1 con2
1374 = sep [ptext (sLit "Constructors") <+> ppr con1 <+> ptext (sLit "and") <+> ppr con2,
1375 ptext (sLit "give different types for field"), quotes (ppr field_name)]
1377 dataConCtxt :: Outputable a => a -> SDoc
1378 dataConCtxt con = ptext (sLit "In the definition of data constructor") <+> quotes (ppr con)
1380 classOpCtxt :: Var -> Type -> SDoc
1381 classOpCtxt sel_id tau = sep [ptext (sLit "When checking the class method:"),
1382 nest 2 (ppr sel_id <+> dcolon <+> ppr tau)]
1384 nullaryClassErr :: Class -> SDoc
1386 = ptext (sLit "No parameters for class") <+> quotes (ppr cls)
1388 classArityErr :: Class -> SDoc
1390 = vcat [ptext (sLit "Too many parameters for class") <+> quotes (ppr cls),
1391 parens (ptext (sLit "Use -XMultiParamTypeClasses to allow multi-parameter classes"))]
1393 classFunDepsErr :: Class -> SDoc
1395 = vcat [ptext (sLit "Fundeps in class") <+> quotes (ppr cls),
1396 parens (ptext (sLit "Use -XFunctionalDependencies to allow fundeps"))]
1398 noClassTyVarErr :: Class -> Var -> SDoc
1399 noClassTyVarErr clas op
1400 = sep [ptext (sLit "The class method") <+> quotes (ppr op),
1401 ptext (sLit "mentions none of the type variables of the class") <+>
1402 ppr clas <+> hsep (map ppr (classTyVars clas))]
1404 genericMultiParamErr :: Class -> SDoc
1405 genericMultiParamErr clas
1406 = ptext (sLit "The multi-parameter class") <+> quotes (ppr clas) <+>
1407 ptext (sLit "cannot have generic methods")
1409 badGenericMethodType :: Name -> Kind -> SDoc
1410 badGenericMethodType op op_ty
1411 = hang (ptext (sLit "Generic method type is too complex"))
1412 4 (vcat [ppr op <+> dcolon <+> ppr op_ty,
1413 ptext (sLit "You can only use type variables, arrows, lists, and tuples")])
1415 recSynErr :: [LTyClDecl Name] -> TcRn ()
1417 = setSrcSpan (getLoc (head sorted_decls)) $
1418 addErr (sep [ptext (sLit "Cycle in type synonym declarations:"),
1419 nest 2 (vcat (map ppr_decl sorted_decls))])
1421 sorted_decls = sortLocated syn_decls
1422 ppr_decl (L loc decl) = ppr loc <> colon <+> ppr decl
1424 recClsErr :: [Located (TyClDecl Name)] -> TcRn ()
1426 = setSrcSpan (getLoc (head sorted_decls)) $
1427 addErr (sep [ptext (sLit "Cycle in class declarations (via superclasses):"),
1428 nest 2 (vcat (map ppr_decl sorted_decls))])
1430 sorted_decls = sortLocated cls_decls
1431 ppr_decl (L loc decl) = ppr loc <> colon <+> ppr (decl { tcdSigs = [] })
1433 sortLocated :: [Located a] -> [Located a]
1434 sortLocated things = sortLe le things
1436 le (L l1 _) (L l2 _) = l1 <= l2
1438 badDataConTyCon :: DataCon -> Type -> Type -> SDoc
1439 badDataConTyCon data_con res_ty_tmpl actual_res_ty
1440 = hang (ptext (sLit "Data constructor") <+> quotes (ppr data_con) <+>
1441 ptext (sLit "returns type") <+> quotes (ppr actual_res_ty))
1442 2 (ptext (sLit "instead of an instance of its parent type") <+> quotes (ppr res_ty_tmpl))
1444 badGadtDecl :: Name -> SDoc
1446 = vcat [ ptext (sLit "Illegal generalised algebraic data declaration for") <+> quotes (ppr tc_name)
1447 , nest 2 (parens $ ptext (sLit "Use -XGADTs to allow GADTs")) ]
1449 badExistential :: Located Name -> SDoc
1450 badExistential con_name
1451 = hang (ptext (sLit "Data constructor") <+> quotes (ppr con_name) <+>
1452 ptext (sLit "has existential type variables, or a context"))
1453 2 (parens $ ptext (sLit "Use -XExistentialQuantification or -XGADTs to allow this"))
1455 badStupidTheta :: Name -> SDoc
1456 badStupidTheta tc_name
1457 = ptext (sLit "A data type declared in GADT style cannot have a context:") <+> quotes (ppr tc_name)
1459 newtypeConError :: Name -> Int -> SDoc
1460 newtypeConError tycon n
1461 = sep [ptext (sLit "A newtype must have exactly one constructor,"),
1462 nest 2 $ ptext (sLit "but") <+> quotes (ppr tycon) <+> ptext (sLit "has") <+> speakN n ]
1464 newtypeExError :: DataCon -> SDoc
1466 = sep [ptext (sLit "A newtype constructor cannot have an existential context,"),
1467 nest 2 $ ptext (sLit "but") <+> quotes (ppr con) <+> ptext (sLit "does")]
1469 newtypeStrictError :: DataCon -> SDoc
1470 newtypeStrictError con
1471 = sep [ptext (sLit "A newtype constructor cannot have a strictness annotation,"),
1472 nest 2 $ ptext (sLit "but") <+> quotes (ppr con) <+> ptext (sLit "does")]
1474 newtypePredError :: DataCon -> SDoc
1475 newtypePredError con
1476 = sep [ptext (sLit "A newtype constructor must have a return type of form T a1 ... an"),
1477 nest 2 $ ptext (sLit "but") <+> quotes (ppr con) <+> ptext (sLit "does not")]
1479 newtypeFieldErr :: DataCon -> Int -> SDoc
1480 newtypeFieldErr con_name n_flds
1481 = sep [ptext (sLit "The constructor of a newtype must have exactly one field"),
1482 nest 2 $ ptext (sLit "but") <+> quotes (ppr con_name) <+> ptext (sLit "has") <+> speakN n_flds]
1484 badSigTyDecl :: Name -> SDoc
1485 badSigTyDecl tc_name
1486 = vcat [ ptext (sLit "Illegal kind signature") <+>
1487 quotes (ppr tc_name)
1488 , nest 2 (parens $ ptext (sLit "Use -XKindSignatures to allow kind signatures")) ]
1490 noIndexTypes :: Name -> SDoc
1491 noIndexTypes tc_name
1492 = ptext (sLit "Type family constructor") <+> quotes (ppr tc_name)
1493 <+> ptext (sLit "must have at least one type index parameter")
1495 badFamInstDecl :: Outputable a => a -> SDoc
1496 badFamInstDecl tc_name
1497 = vcat [ ptext (sLit "Illegal family instance for") <+>
1498 quotes (ppr tc_name)
1499 , nest 2 (parens $ ptext (sLit "Use -XTypeFamilies to allow indexed type families")) ]
1501 tooManyParmsErr :: Located Name -> SDoc
1502 tooManyParmsErr tc_name
1503 = ptext (sLit "Family instance has too many parameters:") <+>
1504 quotes (ppr tc_name)
1506 tooFewParmsErr :: Arity -> SDoc
1507 tooFewParmsErr arity
1508 = ptext (sLit "Family instance has too few parameters; expected") <+>
1511 wrongNumberOfParmsErr :: Arity -> SDoc
1512 wrongNumberOfParmsErr exp_arity
1513 = ptext (sLit "Number of parameters must match family declaration; expected")
1516 badBootFamInstDeclErr :: SDoc
1517 badBootFamInstDeclErr =
1518 ptext (sLit "Illegal family instance in hs-boot file")
1520 wrongKindOfFamily :: TyCon -> SDoc
1521 wrongKindOfFamily family =
1522 ptext (sLit "Wrong category of family instance; declaration was for a") <+>
1525 kindOfFamily | isSynTyCon family = ptext (sLit "type synonym")
1526 | isAlgTyCon family = ptext (sLit "data type")
1527 | otherwise = pprPanic "wrongKindOfFamily" (ppr family)
1529 emptyConDeclsErr :: Name -> SDoc
1530 emptyConDeclsErr tycon
1531 = sep [quotes (ppr tycon) <+> ptext (sLit "has no constructors"),
1532 nest 2 $ ptext (sLit "(-XEmptyDataDecls permits this)")]