2 % (c) The University of Glasgow 2006
3 % (c) The AQUA Project, Glasgow University, 1996-1998
6 TcTyClsDecls: Typecheck type and class declarations
10 tcTyAndClassDecls, tcFamInstDecl, mkRecSelBinds
13 #include "HsVersions.h"
26 import TysWiredIn ( unitTy )
33 import MkId ( rEC_SEL_ERROR_ID, mkDefaultMethodId )
47 import Unique ( mkBuiltinUnique )
56 %************************************************************************
58 \subsection{Type checking for type and class declarations}
60 %************************************************************************
64 Consider a mutually-recursive group, binding
65 a type constructor T and a class C.
67 Step 1: getInitialKind
68 Construct a KindEnv by binding T and C to a kind variable
71 In that environment, do a kind check
73 Step 3: Zonk the kinds
75 Step 4: buildTyConOrClass
76 Construct an environment binding T to a TyCon and C to a Class.
77 a) Their kinds comes from zonking the relevant kind variable
78 b) Their arity (for synonyms) comes direct from the decl
79 c) The funcional dependencies come from the decl
80 d) The rest comes a knot-tied binding of T and C, returned from Step 4
81 e) The variances of the tycons in the group is calculated from
85 In this environment, walk over the decls, constructing the TyCons and Classes.
86 This uses in a strict way items (a)-(c) above, which is why they must
87 be constructed in Step 4. Feed the results back to Step 4.
88 For this step, pass the is-recursive flag as the wimp-out flag
92 Step 6: Extend environment
93 We extend the type environment with bindings not only for the TyCons and Classes,
94 but also for their "implicit Ids" like data constructors and class selectors
96 Step 7: checkValidTyCl
97 For a recursive group only, check all the decls again, just
98 to check all the side conditions on validity. We could not
99 do this before because we were in a mutually recursive knot.
101 Identification of recursive TyCons
102 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
103 The knot-tying parameters: @rec_details_list@ is an alist mapping @Name@s to
106 Identifying a TyCon as recursive serves two purposes
108 1. Avoid infinite types. Non-recursive newtypes are treated as
109 "transparent", like type synonyms, after the type checker. If we did
110 this for all newtypes, we'd get infinite types. So we figure out for
111 each newtype whether it is "recursive", and add a coercion if so. In
112 effect, we are trying to "cut the loops" by identifying a loop-breaker.
114 2. Avoid infinite unboxing. This is nothing to do with newtypes.
118 Well, this function diverges, but we don't want the strictness analyser
119 to diverge. But the strictness analyser will diverge because it looks
120 deeper and deeper into the structure of T. (I believe there are
121 examples where the function does something sane, and the strictness
122 analyser still diverges, but I can't see one now.)
124 Now, concerning (1), the FC2 branch currently adds a coercion for ALL
125 newtypes. I did this as an experiment, to try to expose cases in which
126 the coercions got in the way of optimisations. If it turns out that we
127 can indeed always use a coercion, then we don't risk recursive types,
128 and don't need to figure out what the loop breakers are.
130 For newtype *families* though, we will always have a coercion, so they
131 are always loop breakers! So you can easily adjust the current
132 algorithm by simply treating all newtype families as loop breakers (and
133 indeed type families). I think.
136 tcTyAndClassDecls :: ModDetails -> [LTyClDecl Name]
137 -> TcM (TcGblEnv, -- Input env extended by types and classes
138 -- and their implicit Ids,DataCons
139 HsValBinds Name, -- Renamed bindings for record selectors
140 [Id]) -- Default method ids
142 -- Fails if there are any errors
144 tcTyAndClassDecls boot_details allDecls
145 = checkNoErrs $ -- The code recovers internally, but if anything gave rise to
146 -- an error we'd better stop now, to avoid a cascade
147 do { -- Omit instances of type families; they are handled together
148 -- with the *heads* of class instances
149 ; let decls = filter (not . isFamInstDecl . unLoc) allDecls
151 -- First check for cyclic type synonysm or classes
152 -- See notes with checkCycleErrs
153 ; checkCycleErrs decls
155 ; traceTc (text "tcTyAndCl" <+> ppr mod)
156 ; (syn_tycons, alg_tyclss) <- fixM (\ ~(_rec_syn_tycons, rec_alg_tyclss) ->
157 do { let { -- Seperate ordinary synonyms from all other type and
158 -- class declarations and add all associated type
159 -- declarations from type classes. The latter is
160 -- required so that the temporary environment for the
161 -- knot includes all associated family declarations.
162 ; (syn_decls, alg_decls) = partition (isSynDecl . unLoc)
164 ; alg_at_decls = concatMap addATs alg_decls
166 -- Extend the global env with the knot-tied results
167 -- for data types and classes
169 -- We must populate the environment with the loop-tied
170 -- T's right away, because the kind checker may "fault
171 -- in" some type constructors that recursively
173 ; let gbl_things = mkGlobalThings alg_at_decls rec_alg_tyclss
174 ; tcExtendRecEnv gbl_things $ do
176 -- Kind-check the declarations
177 { (kc_syn_decls, kc_alg_decls) <- kcTyClDecls syn_decls alg_decls
179 ; let { -- Calculate rec-flag
180 ; calc_rec = calcRecFlags boot_details rec_alg_tyclss
181 ; tc_decl = addLocM (tcTyClDecl calc_rec) }
183 -- Type-check the type synonyms, and extend the envt
184 ; syn_tycons <- tcSynDecls kc_syn_decls
185 ; tcExtendGlobalEnv syn_tycons $ do
187 -- Type-check the data types and classes
188 { alg_tyclss <- mapM tc_decl kc_alg_decls
189 ; return (syn_tycons, concat alg_tyclss)
191 -- Finished with knot-tying now
192 -- Extend the environment with the finished things
193 ; tcExtendGlobalEnv (syn_tycons ++ alg_tyclss) $ do
195 -- Perform the validity check
196 { traceTc (text "ready for validity check")
197 ; mapM_ (addLocM checkValidTyCl) decls
198 ; traceTc (text "done")
200 -- Add the implicit things;
201 -- we want them in the environment because
202 -- they may be mentioned in interface files
203 -- NB: All associated types and their implicit things will be added a
204 -- second time here. This doesn't matter as the definitions are
206 ; let { implicit_things = concatMap implicitTyThings alg_tyclss
207 ; rec_sel_binds = mkRecSelBinds alg_tyclss
208 ; dm_ids = mkDefaultMethodIds alg_tyclss }
209 ; traceTc ((text "Adding" <+> ppr alg_tyclss)
210 $$ (text "and" <+> ppr implicit_things))
211 ; env <- tcExtendGlobalEnv implicit_things getGblEnv
212 ; return (env, rec_sel_binds, dm_ids) }
215 -- Pull associated types out of class declarations, to tie them into the
217 -- NB: We put them in the same place in the list as `tcTyClDecl' will
218 -- eventually put the matching `TyThing's. That's crucial; otherwise,
219 -- the two argument lists of `mkGlobalThings' don't match up.
220 addATs decl@(L _ (ClassDecl {tcdATs = ats})) = decl : ats
223 mkGlobalThings :: [LTyClDecl Name] -- The decls
224 -> [TyThing] -- Knot-tied, in 1-1 correspondence with the decls
226 -- Driven by the Decls, and treating the TyThings lazily
227 -- make a TypeEnv for the new things
228 mkGlobalThings decls things
229 = map mk_thing (decls `zipLazy` things)
231 mk_thing (L _ (ClassDecl {tcdLName = L _ name}), ~(AClass cl))
233 mk_thing (L _ decl, ~(ATyCon tc))
234 = (tcdName decl, ATyCon tc)
238 %************************************************************************
240 Type checking family instances
242 %************************************************************************
244 Family instances are somewhat of a hybrid. They are processed together with
245 class instance heads, but can contain data constructors and hence they share a
246 lot of kinding and type checking code with ordinary algebraic data types (and
250 tcFamInstDecl :: LTyClDecl Name -> TcM TyThing
251 tcFamInstDecl (L loc decl)
252 = -- Prime error recovery, set source location
255 do { -- type family instances require -XTypeFamilies
256 -- and can't (currently) be in an hs-boot file
257 ; type_families <- doptM Opt_TypeFamilies
258 ; is_boot <- tcIsHsBoot -- Are we compiling an hs-boot file?
259 ; checkTc type_families $ badFamInstDecl (tcdLName decl)
260 ; checkTc (not is_boot) $ badBootFamInstDeclErr
262 -- Perform kind and type checking
263 ; tc <- tcFamInstDecl1 decl
264 ; checkValidTyCon tc -- Remember to check validity;
265 -- no recursion to worry about here
266 ; return (ATyCon tc) }
268 tcFamInstDecl1 :: TyClDecl Name -> TcM TyCon
271 tcFamInstDecl1 (decl@TySynonym {tcdLName = L loc tc_name})
272 = kcIdxTyPats decl $ \k_tvs k_typats resKind family ->
273 do { -- check that the family declaration is for a synonym
274 checkTc (isOpenTyCon family) (notFamily family)
275 ; checkTc (isSynTyCon family) (wrongKindOfFamily family)
277 ; -- (1) kind check the right-hand side of the type equation
278 ; k_rhs <- kcCheckLHsType (tcdSynRhs decl) (EK resKind EkUnk)
279 -- ToDo: the ExpKind could be better
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 t_typats 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 checkTc (isOpenTyCon fam_tycon) (notFamily fam_tycon)
307 ; checkTc (isAlgTyCon fam_tycon) (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 t_typats 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 { let tc_name = tcdLName decl
383 ; fam_tycon <- tcLookupLocatedTyCon tc_name
384 ; let { (kinds, resKind) = splitKindFunTys (tyConKind fam_tycon)
385 ; hs_typats = fromJust $ tcdTyPats decl }
387 -- we may not have more parameters than the kind indicates
388 ; checkTc (length kinds >= length hs_typats) $
389 tooManyParmsErr (tcdLName decl)
391 -- type functions can have a higher-kinded result
392 ; let resultKind = mkArrowKinds (drop (length hs_typats) kinds) resKind
393 ; typats <- zipWithM kcCheckLHsType hs_typats
394 [ EK kind (EkArg (ppr tc_name) n)
395 | (kind,n) <- kinds `zip` [1..]]
396 ; thing_inside tvs typats resultKind fam_tycon
401 %************************************************************************
405 %************************************************************************
407 We need to kind check all types in the mutually recursive group
408 before we know the kind of the type variables. For example:
411 op :: D b => a -> b -> b
414 bop :: (Monad c) => ...
416 Here, the kind of the locally-polymorphic type variable "b"
417 depends on *all the uses of class D*. For example, the use of
418 Monad c in bop's type signature means that D must have kind Type->Type.
420 However type synonyms work differently. They can have kinds which don't
421 just involve (->) and *:
422 type R = Int# -- Kind #
423 type S a = Array# a -- Kind * -> #
424 type T a b = (# a,b #) -- Kind * -> * -> (# a,b #)
425 So we must infer their kinds from their right-hand sides *first* and then
426 use them, whereas for the mutually recursive data types D we bring into
427 scope kind bindings D -> k, where k is a kind variable, and do inference.
431 This treatment of type synonyms only applies to Haskell 98-style synonyms.
432 General type functions can be recursive, and hence, appear in `alg_decls'.
434 The kind of a type family is solely determinded by its kind signature;
435 hence, only kind signatures participate in the construction of the initial
436 kind environment (as constructed by `getInitialKind'). In fact, we ignore
437 instances of families altogether in the following. However, we need to
438 include the kinds of associated families into the construction of the
439 initial kind environment. (This is handled by `allDecls').
442 kcTyClDecls :: [LTyClDecl Name] -> [Located (TyClDecl Name)]
443 -> TcM ([LTyClDecl Name], [Located (TyClDecl Name)])
444 kcTyClDecls syn_decls alg_decls
445 = do { -- First extend the kind env with each data type, class, and
446 -- indexed type, mapping them to a type variable
447 let initialKindDecls = concat [allDecls decl | L _ decl <- alg_decls]
448 ; alg_kinds <- mapM getInitialKind initialKindDecls
449 ; tcExtendKindEnv alg_kinds $ do
451 -- Now kind-check the type synonyms, in dependency order
452 -- We do these differently to data type and classes,
453 -- because a type synonym can be an unboxed type
455 -- and a kind variable can't unify with UnboxedTypeKind
456 -- So we infer their kinds in dependency order
457 { (kc_syn_decls, syn_kinds) <- kcSynDecls (calcSynCycles syn_decls)
458 ; tcExtendKindEnv syn_kinds $ do
460 -- Now kind-check the data type, class, and kind signatures,
461 -- returning kind-annotated decls; we don't kind-check
462 -- instances of indexed types yet, but leave this to
464 { kc_alg_decls <- mapM (wrapLocM kcTyClDecl)
465 (filter (not . isFamInstDecl . unLoc) alg_decls)
467 ; return (kc_syn_decls, kc_alg_decls) }}}
469 -- get all declarations relevant for determining the initial kind
471 allDecls (decl@ClassDecl {tcdATs = ats}) = decl : [ at
474 allDecls decl | isFamInstDecl decl = []
477 ------------------------------------------------------------------------
478 getInitialKind :: TyClDecl Name -> TcM (Name, TcKind)
479 -- Only for data type, class, and indexed type declarations
480 -- Get as much info as possible from the data, class, or indexed type decl,
481 -- so as to maximise usefulness of error messages
483 = do { arg_kinds <- mapM (mk_arg_kind . unLoc) (tyClDeclTyVars decl)
484 ; res_kind <- mk_res_kind decl
485 ; return (tcdName decl, mkArrowKinds arg_kinds res_kind) }
487 mk_arg_kind (UserTyVar _ _) = newKindVar
488 mk_arg_kind (KindedTyVar _ kind) = return kind
490 mk_res_kind (TyFamily { tcdKind = Just kind }) = return kind
491 mk_res_kind (TyData { tcdKindSig = Just kind }) = return kind
492 -- On GADT-style declarations we allow a kind signature
493 -- data T :: *->* where { ... }
494 mk_res_kind _ = return liftedTypeKind
498 kcSynDecls :: [SCC (LTyClDecl Name)]
499 -> TcM ([LTyClDecl Name], -- Kind-annotated decls
500 [(Name,TcKind)]) -- Kind bindings
503 kcSynDecls (group : groups)
504 = do { (decl, nk) <- kcSynDecl group
505 ; (decls, nks) <- tcExtendKindEnv [nk] (kcSynDecls groups)
506 ; return (decl:decls, nk:nks) }
509 kcSynDecl :: SCC (LTyClDecl Name)
510 -> TcM (LTyClDecl Name, -- Kind-annotated decls
511 (Name,TcKind)) -- Kind bindings
512 kcSynDecl (AcyclicSCC (L loc decl))
513 = tcAddDeclCtxt decl $
514 kcHsTyVars (tcdTyVars decl) (\ k_tvs ->
515 do { traceTc (text "kcd1" <+> ppr (unLoc (tcdLName decl)) <+> brackets (ppr (tcdTyVars decl))
516 <+> brackets (ppr k_tvs))
517 ; (k_rhs, rhs_kind) <- kcLHsType (tcdSynRhs decl)
518 ; traceTc (text "kcd2" <+> ppr (unLoc (tcdLName decl)))
519 ; let tc_kind = foldr (mkArrowKind . hsTyVarKind . unLoc) rhs_kind k_tvs
520 ; return (L loc (decl { tcdTyVars = k_tvs, tcdSynRhs = k_rhs }),
521 (unLoc (tcdLName decl), tc_kind)) })
523 kcSynDecl (CyclicSCC decls)
524 = do { recSynErr decls; failM } -- Fail here to avoid error cascade
525 -- of out-of-scope tycons
527 ------------------------------------------------------------------------
528 kcTyClDecl :: TyClDecl Name -> TcM (TyClDecl Name)
529 -- Not used for type synonyms (see kcSynDecl)
531 kcTyClDecl decl@(TyData {})
532 = ASSERT( not . isFamInstDecl $ decl ) -- must not be a family instance
533 kcTyClDeclBody decl $
536 kcTyClDecl decl@(TyFamily {})
537 = kcFamilyDecl [] decl -- the empty list signals a toplevel decl
539 kcTyClDecl decl@(ClassDecl {tcdCtxt = ctxt, tcdSigs = sigs, tcdATs = ats})
540 = kcTyClDeclBody decl $ \ tvs' ->
541 do { ctxt' <- kcHsContext ctxt
542 ; ats' <- mapM (wrapLocM (kcFamilyDecl tvs')) ats
543 ; sigs' <- mapM (wrapLocM kc_sig) sigs
544 ; return (decl {tcdTyVars = tvs', tcdCtxt = ctxt', tcdSigs = sigs',
547 kc_sig (TypeSig nm op_ty) = do { op_ty' <- kcHsLiftedSigType op_ty
548 ; return (TypeSig nm op_ty') }
549 kc_sig other_sig = return other_sig
551 kcTyClDecl decl@(ForeignType {})
554 kcTyClDecl (TySynonym {}) = panic "kcTyClDecl TySynonym"
556 kcTyClDeclBody :: TyClDecl Name
557 -> ([LHsTyVarBndr Name] -> TcM a)
559 -- getInitialKind has made a suitably-shaped kind for the type or class
560 -- Unpack it, and attribute those kinds to the type variables
561 -- Extend the env with bindings for the tyvars, taken from
562 -- the kind of the tycon/class. Give it to the thing inside, and
563 -- check the result kind matches
564 kcTyClDeclBody decl thing_inside
565 = tcAddDeclCtxt decl $
566 do { tc_ty_thing <- tcLookupLocated (tcdLName decl)
567 ; let tc_kind = case tc_ty_thing of
569 _ -> pprPanic "kcTyClDeclBody" (ppr tc_ty_thing)
570 (kinds, _) = splitKindFunTys tc_kind
571 hs_tvs = tcdTyVars decl
572 kinded_tvs = ASSERT( length kinds >= length hs_tvs )
573 zipWith add_kind hs_tvs kinds
574 ; tcExtendKindEnvTvs kinded_tvs thing_inside }
576 add_kind (L loc (UserTyVar n _)) k = L loc (UserTyVar n k)
577 add_kind (L loc (KindedTyVar n _)) k = L loc (KindedTyVar n k)
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 con_decl@(ConDecl { con_name = name, con_qvars = ex_tvs
592 , con_cxt = ex_ctxt, con_details = details, con_res = res })
593 = addErrCtxt (dataConCtxt name) $
594 kcHsTyVars ex_tvs $ \ex_tvs' -> do
595 do { ex_ctxt' <- kcHsContext ex_ctxt
596 ; details' <- kc_con_details details
597 ; res' <- case res of
598 ResTyH98 -> return ResTyH98
599 ResTyGADT ty -> do { ty' <- kcHsSigType ty; return (ResTyGADT ty') }
600 ; return (con_decl { con_qvars = ex_tvs', con_cxt = ex_ctxt'
601 , con_details = details', con_res = res' }) }
603 kc_con_details (PrefixCon btys)
604 = do { btys' <- mapM kc_larg_ty btys
605 ; return (PrefixCon btys') }
606 kc_con_details (InfixCon bty1 bty2)
607 = do { bty1' <- kc_larg_ty bty1
608 ; bty2' <- kc_larg_ty bty2
609 ; return (InfixCon bty1' bty2') }
610 kc_con_details (RecCon fields)
611 = do { fields' <- mapM kc_field fields
612 ; return (RecCon fields') }
614 kc_field (ConDeclField fld bty d) = do { bty' <- kc_larg_ty bty
615 ; return (ConDeclField fld bty' d) }
617 kc_larg_ty bty = case new_or_data of
618 DataType -> kcHsSigType bty
619 NewType -> kcHsLiftedSigType bty
620 -- Can't allow an unlifted type for newtypes, because we're effectively
621 -- going to remove the constructor while coercing it to a lifted type.
622 -- And newtypes can't be bang'd
623 kcDataDecl d _ = pprPanic "kcDataDecl" (ppr d)
625 -- Kind check a family declaration or type family default declaration.
627 kcFamilyDecl :: [LHsTyVarBndr Name] -- tyvars of enclosing class decl if any
628 -> TyClDecl Name -> TcM (TyClDecl Name)
629 kcFamilyDecl classTvs decl@(TyFamily {tcdKind = kind})
630 = kcTyClDeclBody decl $ \tvs' ->
631 do { mapM_ unifyClassParmKinds tvs'
632 ; return (decl {tcdTyVars = tvs',
633 tcdKind = kind `mplus` Just liftedTypeKind})
634 -- default result kind is '*'
637 unifyClassParmKinds (L _ tv)
638 | (n,k) <- hsTyVarNameKind tv
639 , Just classParmKind <- lookup n classTyKinds
640 = unifyKind k classParmKind
641 | otherwise = return ()
642 classTyKinds = [hsTyVarNameKind tv | L _ tv <- classTvs]
644 kcFamilyDecl _ (TySynonym {}) -- type family defaults
645 = panic "TcTyClsDecls.kcFamilyDecl: not implemented yet"
646 kcFamilyDecl _ d = pprPanic "kcFamilyDecl" (ppr d)
650 %************************************************************************
652 \subsection{Type checking}
654 %************************************************************************
657 tcSynDecls :: [LTyClDecl Name] -> TcM [TyThing]
658 tcSynDecls [] = return []
659 tcSynDecls (decl : decls)
660 = do { syn_tc <- addLocM tcSynDecl decl
661 ; syn_tcs <- tcExtendGlobalEnv [syn_tc] (tcSynDecls decls)
662 ; return (syn_tc : syn_tcs) }
665 tcSynDecl :: TyClDecl Name -> TcM TyThing
667 (TySynonym {tcdLName = L _ tc_name, tcdTyVars = tvs, tcdSynRhs = rhs_ty})
668 = tcTyVarBndrs tvs $ \ tvs' -> do
669 { traceTc (text "tcd1" <+> ppr tc_name)
670 ; rhs_ty' <- tcHsKindedType rhs_ty
671 ; tycon <- buildSynTyCon tc_name tvs' (SynonymTyCon rhs_ty')
672 (typeKind rhs_ty') Nothing
673 ; return (ATyCon tycon)
675 tcSynDecl d = pprPanic "tcSynDecl" (ppr d)
678 tcTyClDecl :: (Name -> RecFlag) -> TyClDecl Name -> TcM [TyThing]
680 tcTyClDecl calc_isrec decl
681 = tcAddDeclCtxt decl (tcTyClDecl1 calc_isrec decl)
683 -- "type family" declarations
684 tcTyClDecl1 :: (Name -> RecFlag) -> TyClDecl Name -> TcM [TyThing]
685 tcTyClDecl1 _calc_isrec
686 (TyFamily {tcdFlavour = TypeFamily,
687 tcdLName = L _ tc_name, tcdTyVars = tvs,
688 tcdKind = Just kind}) -- NB: kind at latest added during kind checking
689 = tcTyVarBndrs tvs $ \ tvs' -> do
690 { traceTc (text "type family: " <+> ppr tc_name)
692 -- Check that we don't use families without -XTypeFamilies
693 ; idx_tys <- doptM Opt_TypeFamilies
694 ; checkTc idx_tys $ badFamInstDecl tc_name
696 ; tycon <- buildSynTyCon tc_name tvs' (OpenSynTyCon kind Nothing) kind Nothing
697 ; return [ATyCon tycon]
700 -- "data family" declaration
701 tcTyClDecl1 _calc_isrec
702 (TyFamily {tcdFlavour = DataFamily,
703 tcdLName = L _ tc_name, tcdTyVars = tvs, tcdKind = mb_kind})
704 = tcTyVarBndrs tvs $ \ tvs' -> do
705 { traceTc (text "data family: " <+> ppr tc_name)
706 ; extra_tvs <- tcDataKindSig mb_kind
707 ; let final_tvs = tvs' ++ extra_tvs -- we may not need these
710 -- Check that we don't use families without -XTypeFamilies
711 ; idx_tys <- doptM Opt_TypeFamilies
712 ; checkTc idx_tys $ badFamInstDecl tc_name
714 ; tycon <- buildAlgTyCon tc_name final_tvs []
715 mkOpenDataTyConRhs Recursive False True Nothing
716 ; return [ATyCon tycon]
719 -- "newtype" and "data"
720 -- NB: not used for newtype/data instances (whether associated or not)
721 tcTyClDecl1 calc_isrec
722 (TyData {tcdND = new_or_data, tcdCtxt = ctxt, tcdTyVars = tvs,
723 tcdLName = L _ tc_name, tcdKindSig = mb_ksig, tcdCons = cons})
724 = tcTyVarBndrs tvs $ \ tvs' -> do
725 { extra_tvs <- tcDataKindSig mb_ksig
726 ; let final_tvs = tvs' ++ extra_tvs
727 ; stupid_theta <- tcHsKindedContext ctxt
728 ; want_generic <- doptM Opt_Generics
729 ; unbox_strict <- doptM Opt_UnboxStrictFields
730 ; empty_data_decls <- doptM Opt_EmptyDataDecls
731 ; kind_signatures <- doptM Opt_KindSignatures
732 ; existential_ok <- doptM Opt_ExistentialQuantification
733 ; gadt_ok <- doptM Opt_GADTs
734 ; is_boot <- tcIsHsBoot -- Are we compiling an hs-boot file?
735 ; let ex_ok = existential_ok || gadt_ok -- Data cons can have existential context
737 -- Check that we don't use GADT syntax in H98 world
738 ; checkTc (gadt_ok || h98_syntax) (badGadtDecl tc_name)
740 -- Check that we don't use kind signatures without Glasgow extensions
741 ; checkTc (kind_signatures || isNothing mb_ksig) (badSigTyDecl tc_name)
743 -- Check that the stupid theta is empty for a GADT-style declaration
744 ; checkTc (null stupid_theta || h98_syntax) (badStupidTheta tc_name)
746 -- Check that a newtype has exactly one constructor
747 -- Do this before checking for empty data decls, so that
748 -- we don't suggest -XEmptyDataDecls for newtypes
749 ; checkTc (new_or_data == DataType || isSingleton cons)
750 (newtypeConError tc_name (length cons))
752 -- Check that there's at least one condecl,
753 -- or else we're reading an hs-boot file, or -XEmptyDataDecls
754 ; checkTc (not (null cons) || empty_data_decls || is_boot)
755 (emptyConDeclsErr tc_name)
757 ; tycon <- fixM (\ tycon -> do
758 { let res_ty = mkTyConApp tycon (mkTyVarTys final_tvs)
759 ; data_cons <- tcConDecls unbox_strict ex_ok
760 tycon (final_tvs, res_ty) cons
762 if null cons && is_boot -- In a hs-boot file, empty cons means
763 then return AbstractTyCon -- "don't know"; hence Abstract
764 else case new_or_data of
765 DataType -> return (mkDataTyConRhs data_cons)
766 NewType -> ASSERT( not (null data_cons) )
767 mkNewTyConRhs tc_name tycon (head data_cons)
768 ; buildAlgTyCon tc_name final_tvs stupid_theta tc_rhs is_rec
769 (want_generic && canDoGenerics data_cons) h98_syntax Nothing
771 ; return [ATyCon tycon]
774 is_rec = calc_isrec tc_name
775 h98_syntax = consUseH98Syntax cons
777 tcTyClDecl1 calc_isrec
778 (ClassDecl {tcdLName = L _ class_name, tcdTyVars = tvs,
779 tcdCtxt = ctxt, tcdMeths = meths,
780 tcdFDs = fundeps, tcdSigs = sigs, tcdATs = ats} )
781 = tcTyVarBndrs tvs $ \ tvs' -> do
782 { ctxt' <- tcHsKindedContext ctxt
783 ; fds' <- mapM (addLocM tc_fundep) fundeps
784 ; atss <- mapM (addLocM (tcTyClDecl1 (const Recursive))) ats
785 -- NB: 'ats' only contains "type family" and "data family"
786 -- declarations as well as type family defaults
787 ; let ats' = map (setAssocFamilyPermutation tvs') (concat atss)
788 ; sig_stuff <- tcClassSigs class_name sigs meths
789 ; clas <- fixM (\ clas ->
790 let -- This little knot is just so we can get
791 -- hold of the name of the class TyCon, which we
792 -- need to look up its recursiveness
793 tycon_name = tyConName (classTyCon clas)
794 tc_isrec = calc_isrec tycon_name
796 buildClass False {- Must include unfoldings for selectors -}
797 class_name tvs' ctxt' fds' ats'
799 ; return (AClass clas : ats')
800 -- NB: Order is important due to the call to `mkGlobalThings' when
801 -- tying the the type and class declaration type checking knot.
804 tc_fundep (tvs1, tvs2) = do { tvs1' <- mapM tcLookupTyVar tvs1 ;
805 ; tvs2' <- mapM tcLookupTyVar tvs2 ;
806 ; return (tvs1', tvs2') }
809 (ForeignType {tcdLName = L _ tc_name, tcdExtName = tc_ext_name})
810 = return [ATyCon (mkForeignTyCon tc_name tc_ext_name liftedTypeKind 0)]
812 tcTyClDecl1 _ d = pprPanic "tcTyClDecl1" (ppr d)
814 -----------------------------------
815 tcConDecls :: Bool -> Bool -> TyCon -> ([TyVar], Type)
816 -> [LConDecl Name] -> TcM [DataCon]
817 tcConDecls unbox ex_ok rep_tycon res_tmpl cons
818 = mapM (addLocM (tcConDecl unbox ex_ok rep_tycon res_tmpl)) cons
820 tcConDecl :: Bool -- True <=> -funbox-strict_fields
821 -> Bool -- True <=> -XExistentialQuantificaton or -XGADTs
822 -> TyCon -- Representation tycon
823 -> ([TyVar], Type) -- Return type template (with its template tyvars)
827 tcConDecl unbox_strict existential_ok rep_tycon res_tmpl -- Data types
828 (ConDecl {con_name =name, con_qvars = tvs, con_cxt = ctxt
829 , con_details = details, con_res = res_ty })
830 = addErrCtxt (dataConCtxt name) $
831 tcTyVarBndrs tvs $ \ tvs' -> do
832 { ctxt' <- tcHsKindedContext ctxt
833 ; checkTc (existential_ok || (null tvs && null (unLoc ctxt)))
834 (badExistential name)
835 ; (univ_tvs, ex_tvs, eq_preds, res_ty') <- tcResultType res_tmpl tvs' res_ty
837 tc_datacon is_infix field_lbls btys
838 = do { (arg_tys, stricts) <- mapAndUnzipM (tcConArg unbox_strict) btys
839 ; buildDataCon (unLoc name) is_infix
841 univ_tvs ex_tvs eq_preds ctxt' arg_tys
843 -- NB: we put data_tc, the type constructor gotten from the
844 -- constructor type signature into the data constructor;
845 -- that way checkValidDataCon can complain if it's wrong.
848 PrefixCon btys -> tc_datacon False [] btys
849 InfixCon bty1 bty2 -> tc_datacon True [] [bty1,bty2]
850 RecCon fields -> tc_datacon False field_names btys
852 field_names = map (unLoc . cd_fld_name) fields
853 btys = map cd_fld_type fields
857 -- data instance T (b,c) where
858 -- TI :: forall e. e -> T (e,e)
860 -- The representation tycon looks like this:
861 -- data :R7T b c where
862 -- TI :: forall b1 c1. (b1 ~ c1) => b1 -> :R7T b1 c1
863 -- In this case orig_res_ty = T (e,e)
865 tcResultType :: ([TyVar], Type) -- Template for result type; e.g.
866 -- data instance T [a] b c = ...
867 -- gives template ([a,b,c], T [a] b c)
868 -> [TyVar] -- where MkT :: forall x y z. ...
870 -> TcM ([TyVar], -- Universal
871 [TyVar], -- Existential (distinct OccNames from univs)
872 [(TyVar,Type)], -- Equality predicates
873 Type) -- Typechecked return type
874 -- We don't check that the TyCon given in the ResTy is
875 -- the same as the parent tycon, becuase we are in the middle
876 -- of a recursive knot; so it's postponed until checkValidDataCon
878 tcResultType (tmpl_tvs, res_ty) dc_tvs ResTyH98
879 = return (tmpl_tvs, dc_tvs, [], res_ty)
880 -- In H98 syntax the dc_tvs are the existential ones
881 -- data T a b c = forall d e. MkT ...
882 -- The {a,b,c} are tc_tvs, and {d,e} are dc_tvs
884 tcResultType (tmpl_tvs, res_tmpl) dc_tvs (ResTyGADT res_ty)
885 -- E.g. data T [a] b c where
886 -- MkT :: forall x y z. T [(x,y)] z z
888 -- Univ tyvars Eq-spec
892 -- Existentials are the leftover type vars: [x,y]
893 -- So we return ([a,b,z], [x,y], [a~(x,y),b~z], T [(x,y)] z z)
894 = do { res_ty' <- tcHsKindedType res_ty
895 ; let Just subst = tcMatchTy (mkVarSet tmpl_tvs) res_tmpl res_ty'
897 -- /Lazily/ figure out the univ_tvs etc
898 -- Each univ_tv is either a dc_tv or a tmpl_tv
899 (univ_tvs, eq_spec) = foldr choose ([], []) tidy_tmpl_tvs
900 choose tmpl (univs, eqs)
901 | Just ty <- lookupTyVar subst tmpl
902 = case tcGetTyVar_maybe ty of
903 Just tv | not (tv `elem` univs)
905 _other -> (tmpl:univs, (tmpl,ty):eqs)
906 | otherwise = pprPanic "tcResultType" (ppr res_ty)
907 ex_tvs = dc_tvs `minusList` univ_tvs
909 ; return (univ_tvs, ex_tvs, eq_spec, res_ty') }
911 -- NB: tmpl_tvs and dc_tvs are distinct, but
912 -- we want them to be *visibly* distinct, both for
913 -- interface files and general confusion. So rename
914 -- the tc_tvs, since they are not used yet (no
915 -- consequential renaming needed)
916 (_, tidy_tmpl_tvs) = mapAccumL tidy_one init_occ_env tmpl_tvs
917 init_occ_env = initTidyOccEnv (map getOccName dc_tvs)
918 tidy_one env tv = (env', setTyVarName tv (tidyNameOcc name occ'))
921 (env', occ') = tidyOccName env (getOccName name)
923 consUseH98Syntax :: [LConDecl a] -> Bool
924 consUseH98Syntax (L _ (ConDecl { con_res = ResTyGADT _ }) : _) = False
925 consUseH98Syntax _ = True
926 -- All constructors have same shape
929 tcConArg :: Bool -- True <=> -funbox-strict_fields
931 -> TcM (TcType, HsBang)
932 tcConArg unbox_strict bty
933 = do { arg_ty <- tcHsBangType bty
934 ; let bang = getBangStrictness bty
935 ; let strict_mark = chooseBoxingStrategy unbox_strict arg_ty bang
936 ; return (arg_ty, strict_mark) }
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 -> HsBang
945 chooseBoxingStrategy unbox_strict_fields arg_ty bang
948 HsUnpack -> can_unbox HsUnpackFailed arg_ty
949 HsStrict | unbox_strict_fields -> can_unbox HsStrict arg_ty
950 | otherwise -> HsStrict
951 HsUnpackFailed -> pprPanic "chooseBoxingStrategy" (ppr arg_ty)
952 -- Source code never has shtes
954 can_unbox :: HsBang -> TcType -> HsBang
955 -- Returns HsUnpack if we can unpack arg_ty
956 -- fail_bang if we know what arg_ty is but we can't unpack it
957 -- HsStrict if it's abstract, so we don't know whether or not we can unbox it
958 can_unbox fail_bang arg_ty
959 = case splitTyConApp_maybe arg_ty of
962 Just (arg_tycon, tycon_args)
963 | isAbstractTyCon arg_tycon -> HsStrict
964 -- See Note [Don't complain about UNPACK on abstract TyCons]
965 | not (isRecursiveTyCon arg_tycon) -- Note [Recusive unboxing]
966 , isProductTyCon arg_tycon
967 -- We can unbox if the type is a chain of newtypes
968 -- with a product tycon at the end
969 -> if isNewTyCon arg_tycon
970 then can_unbox fail_bang (newTyConInstRhs arg_tycon tycon_args)
973 | otherwise -> fail_bang
976 Note [Don't complain about UNPACK on abstract TyCons]
977 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
978 We are going to complain about UnpackFailed, but if we say
979 data T = MkT {-# UNPACK #-} !Wobble
980 and Wobble is a newtype imported from a module that was compiled
981 without optimisation, we don't want to complain. Because it might
982 be fine when optimsation is on. I think this happens when Haddock
983 is working over (say) GHC souce files.
985 Note [Recursive unboxing]
986 ~~~~~~~~~~~~~~~~~~~~~~~~~
987 Be careful not to try to unbox this!
989 But it's the *argument* type that matters. This is fine:
991 because Int is non-recursive.
994 %************************************************************************
998 %************************************************************************
1000 Validity checking is done once the mutually-recursive knot has been
1001 tied, so we can look at things freely.
1004 checkCycleErrs :: [LTyClDecl Name] -> TcM ()
1005 checkCycleErrs tyclss
1009 = do { mapM_ recClsErr cls_cycles
1010 ; failM } -- Give up now, because later checkValidTyCl
1011 -- will loop if the synonym is recursive
1013 cls_cycles = calcClassCycles tyclss
1015 checkValidTyCl :: TyClDecl Name -> TcM ()
1016 -- We do the validity check over declarations, rather than TyThings
1017 -- only so that we can add a nice context with tcAddDeclCtxt
1019 = tcAddDeclCtxt decl $
1020 do { thing <- tcLookupLocatedGlobal (tcdLName decl)
1021 ; traceTc (text "Validity of" <+> ppr thing)
1023 ATyCon tc -> checkValidTyCon tc
1024 AClass cl -> checkValidClass cl
1025 _ -> panic "checkValidTyCl"
1026 ; traceTc (text "Done validity of" <+> ppr thing)
1029 -------------------------
1030 -- For data types declared with record syntax, we require
1031 -- that each constructor that has a field 'f'
1032 -- (a) has the same result type
1033 -- (b) has the same type for 'f'
1034 -- module alpha conversion of the quantified type variables
1035 -- of the constructor.
1037 -- Note that we allow existentials to match becuase the
1038 -- fields can never meet. E.g
1040 -- T1 { f1 :: b, f2 :: a, f3 ::Int } :: T
1041 -- T2 { f1 :: c, f2 :: c, f3 ::Int } :: T
1042 -- Here we do not complain about f1,f2 because they are existential
1044 checkValidTyCon :: TyCon -> TcM ()
1047 = case synTyConRhs tc of
1048 OpenSynTyCon _ _ -> return ()
1049 SynonymTyCon ty -> checkValidType syn_ctxt ty
1051 = do -- Check the context on the data decl
1052 checkValidTheta (DataTyCtxt name) (tyConStupidTheta tc)
1054 -- Check arg types of data constructors
1055 mapM_ (checkValidDataCon tc) data_cons
1057 -- Check that fields with the same name share a type
1058 mapM_ check_fields groups
1061 syn_ctxt = TySynCtxt name
1063 data_cons = tyConDataCons tc
1065 groups = equivClasses cmp_fld (concatMap get_fields data_cons)
1066 cmp_fld (f1,_) (f2,_) = f1 `compare` f2
1067 get_fields con = dataConFieldLabels con `zip` repeat con
1068 -- dataConFieldLabels may return the empty list, which is fine
1070 -- See Note [GADT record selectors] in MkId.lhs
1071 -- We must check (a) that the named field has the same
1072 -- type in each constructor
1073 -- (b) that those constructors have the same result type
1075 -- However, the constructors may have differently named type variable
1076 -- and (worse) we don't know how the correspond to each other. E.g.
1077 -- C1 :: forall a b. { f :: a, g :: b } -> T a b
1078 -- C2 :: forall d c. { f :: c, g :: c } -> T c d
1080 -- So what we do is to ust Unify.tcMatchTys to compare the first candidate's
1081 -- result type against other candidates' types BOTH WAYS ROUND.
1082 -- If they magically agrees, take the substitution and
1083 -- apply them to the latter ones, and see if they match perfectly.
1084 check_fields ((label, con1) : other_fields)
1085 -- These fields all have the same name, but are from
1086 -- different constructors in the data type
1087 = recoverM (return ()) $ mapM_ checkOne other_fields
1088 -- Check that all the fields in the group have the same type
1089 -- NB: this check assumes that all the constructors of a given
1090 -- data type use the same type variables
1092 (tvs1, _, _, res1) = dataConSig con1
1094 fty1 = dataConFieldType con1 label
1096 checkOne (_, con2) -- Do it bothways to ensure they are structurally identical
1097 = do { checkFieldCompat label con1 con2 ts1 res1 res2 fty1 fty2
1098 ; checkFieldCompat label con2 con1 ts2 res2 res1 fty2 fty1 }
1100 (tvs2, _, _, res2) = dataConSig con2
1102 fty2 = dataConFieldType con2 label
1103 check_fields [] = panic "checkValidTyCon/check_fields []"
1105 checkFieldCompat :: Name -> DataCon -> DataCon -> TyVarSet
1106 -> Type -> Type -> Type -> Type -> TcM ()
1107 checkFieldCompat fld con1 con2 tvs1 res1 res2 fty1 fty2
1108 = do { checkTc (isJust mb_subst1) (resultTypeMisMatch fld con1 con2)
1109 ; checkTc (isJust mb_subst2) (fieldTypeMisMatch fld con1 con2) }
1111 mb_subst1 = tcMatchTy tvs1 res1 res2
1112 mb_subst2 = tcMatchTyX tvs1 (expectJust "checkFieldCompat" mb_subst1) fty1 fty2
1114 -------------------------------
1115 checkValidDataCon :: TyCon -> DataCon -> TcM ()
1116 checkValidDataCon tc con
1117 = setSrcSpan (srcLocSpan (getSrcLoc con)) $
1118 addErrCtxt (dataConCtxt con) $
1119 do { traceTc (ptext (sLit "Validity of data con") <+> ppr con)
1120 ; let tc_tvs = tyConTyVars tc
1121 res_ty_tmpl = mkFamilyTyConApp tc (mkTyVarTys tc_tvs)
1122 actual_res_ty = dataConOrigResTy con
1123 ; checkTc (isJust (tcMatchTy (mkVarSet tc_tvs)
1126 (badDataConTyCon con res_ty_tmpl actual_res_ty)
1127 ; checkValidMonoType (dataConOrigResTy con)
1128 -- Disallow MkT :: T (forall a. a->a)
1129 -- Reason: it's really the argument of an equality constraint
1130 ; checkValidType ctxt (dataConUserType con)
1131 ; when (isNewTyCon tc) (checkNewDataCon con)
1132 ; mapM_ check_bang (dataConStrictMarks con `zip` [1..])
1135 ctxt = ConArgCtxt (dataConName con)
1136 check_bang (HsUnpackFailed, n) = addWarnTc (cant_unbox_msg n)
1137 check_bang _ = return ()
1139 cant_unbox_msg n = sep [ ptext (sLit "Ignoring unusable UNPACK pragma on the")
1140 , speakNth n <+> ptext (sLit "argument of") <+> quotes (ppr con)]
1142 -------------------------------
1143 checkNewDataCon :: DataCon -> TcM ()
1144 -- Checks for the data constructor of a newtype
1146 = do { checkTc (isSingleton arg_tys) (newtypeFieldErr con (length arg_tys))
1148 ; checkTc (null eq_spec) (newtypePredError con)
1149 -- Return type is (T a b c)
1150 ; checkTc (null ex_tvs && null eq_theta && null dict_theta) (newtypeExError con)
1152 ; checkTc (not (any isBanged (dataConStrictMarks con)))
1153 (newtypeStrictError con)
1157 (_univ_tvs, ex_tvs, eq_spec, eq_theta, dict_theta, arg_tys, _res_ty) = dataConFullSig con
1159 -------------------------------
1160 checkValidClass :: Class -> TcM ()
1162 = do { constrained_class_methods <- doptM Opt_ConstrainedClassMethods
1163 ; multi_param_type_classes <- doptM Opt_MultiParamTypeClasses
1164 ; fundep_classes <- doptM Opt_FunctionalDependencies
1166 -- Check that the class is unary, unless GlaExs
1167 ; checkTc (notNull tyvars) (nullaryClassErr cls)
1168 ; checkTc (multi_param_type_classes || unary) (classArityErr cls)
1169 ; checkTc (fundep_classes || null fundeps) (classFunDepsErr cls)
1171 -- Check the super-classes
1172 ; checkValidTheta (ClassSCCtxt (className cls)) theta
1174 -- Check the class operations
1175 ; mapM_ (check_op constrained_class_methods) op_stuff
1177 -- Check that if the class has generic methods, then the
1178 -- class has only one parameter. We can't do generic
1179 -- multi-parameter type classes!
1180 ; checkTc (unary || no_generics) (genericMultiParamErr cls)
1183 (tyvars, fundeps, theta, _, _, op_stuff) = classExtraBigSig cls
1184 unary = isSingleton tyvars
1185 no_generics = null [() | (_, GenDefMeth) <- op_stuff]
1187 check_op constrained_class_methods (sel_id, dm)
1188 = addErrCtxt (classOpCtxt sel_id tau) $ do
1189 { checkValidTheta SigmaCtxt (tail theta)
1190 -- The 'tail' removes the initial (C a) from the
1191 -- class itself, leaving just the method type
1193 ; traceTc (text "class op type" <+> ppr op_ty <+> ppr tau)
1194 ; checkValidType (FunSigCtxt op_name) tau
1196 -- Check that the type mentions at least one of
1197 -- the class type variables...or at least one reachable
1198 -- from one of the class variables. Example: tc223
1199 -- class Error e => Game b mv e | b -> mv e where
1200 -- newBoard :: MonadState b m => m ()
1201 -- Here, MonadState has a fundep m->b, so newBoard is fine
1202 ; let grown_tyvars = growThetaTyVars theta (mkVarSet tyvars)
1203 ; checkTc (tyVarsOfType tau `intersectsVarSet` grown_tyvars)
1204 (noClassTyVarErr cls sel_id)
1206 -- Check that for a generic method, the type of
1207 -- the method is sufficiently simple
1208 ; checkTc (dm /= GenDefMeth || validGenericMethodType tau)
1209 (badGenericMethodType op_name op_ty)
1212 op_name = idName sel_id
1213 op_ty = idType sel_id
1214 (_,theta1,tau1) = tcSplitSigmaTy op_ty
1215 (_,theta2,tau2) = tcSplitSigmaTy tau1
1216 (theta,tau) | constrained_class_methods = (theta1 ++ theta2, tau2)
1217 | otherwise = (theta1, mkPhiTy (tail theta1) tau1)
1218 -- Ugh! The function might have a type like
1219 -- op :: forall a. C a => forall b. (Eq b, Eq a) => tau2
1220 -- With -XConstrainedClassMethods, we want to allow this, even though the inner
1221 -- forall has an (Eq a) constraint. Whereas in general, each constraint
1222 -- in the context of a for-all must mention at least one quantified
1223 -- type variable. What a mess!
1227 %************************************************************************
1229 Building record selectors
1231 %************************************************************************
1234 mkDefaultMethodIds :: [TyThing] -> [Id]
1235 -- See Note [Default method Ids and Template Haskell]
1236 mkDefaultMethodIds things
1237 = [ mkDefaultMethodId sel_id dm_name
1238 | AClass cls <- things
1239 , (sel_id, DefMeth dm_name) <- classOpItems cls ]
1242 Note [Default method Ids and Template Haskell]
1243 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1244 Consider this (Trac #4169):
1245 class Numeric a where
1247 fromIntegerNum = ...
1250 ast = [d| instance Numeric Int |]
1252 When we typecheck 'ast' we have done the first pass over the class decl
1253 (in tcTyClDecls), but we have not yet typechecked the default-method
1254 declarations (becuase they can mention value declarations). So we
1255 must bring the default method Ids into scope first (so they can be seen
1256 when typechecking the [d| .. |] quote, and typecheck them later.
1259 mkRecSelBinds :: [TyThing] -> HsValBinds Name
1260 -- NB We produce *un-typechecked* bindings, rather like 'deriving'
1261 -- This makes life easier, because the later type checking will add
1262 -- all necessary type abstractions and applications
1263 mkRecSelBinds ty_things
1264 = ValBindsOut [(NonRecursive, b) | b <- binds] sigs
1266 (sigs, binds) = unzip rec_sels
1267 rec_sels = map mkRecSelBind [ (tc,fld)
1268 | ATyCon tc <- ty_things
1269 , fld <- tyConFields tc ]
1271 mkRecSelBind :: (TyCon, FieldLabel) -> (LSig Name, LHsBinds Name)
1272 mkRecSelBind (tycon, sel_name)
1273 = (L loc (IdSig sel_id), unitBag (L loc sel_bind))
1275 loc = getSrcSpan tycon
1276 sel_id = Var.mkLocalVar rec_details sel_name sel_ty vanillaIdInfo
1277 rec_details = RecSelId { sel_tycon = tycon, sel_naughty = is_naughty }
1279 -- Find a representative constructor, con1
1280 all_cons = tyConDataCons tycon
1281 cons_w_field = [ con | con <- all_cons
1282 , sel_name `elem` dataConFieldLabels con ]
1283 con1 = ASSERT( not (null cons_w_field) ) head cons_w_field
1285 -- Selector type; Note [Polymorphic selectors]
1286 field_ty = dataConFieldType con1 sel_name
1287 data_ty = dataConOrigResTy con1
1288 data_tvs = tyVarsOfType data_ty
1289 is_naughty = not (tyVarsOfType field_ty `subVarSet` data_tvs)
1290 (field_tvs, field_theta, field_tau) = tcSplitSigmaTy field_ty
1291 sel_ty | is_naughty = unitTy -- See Note [Naughty record selectors]
1292 | otherwise = mkForAllTys (varSetElems data_tvs ++ field_tvs) $
1293 mkPhiTy (dataConStupidTheta con1) $ -- Urgh!
1294 mkPhiTy field_theta $ -- Urgh!
1295 mkFunTy data_ty field_tau
1297 -- Make the binding: sel (C2 { fld = x }) = x
1298 -- sel (C7 { fld = x }) = x
1299 -- where cons_w_field = [C2,C7]
1300 sel_bind | is_naughty = mkFunBind sel_lname [mkSimpleMatch [] unit_rhs]
1301 | otherwise = mkFunBind sel_lname (map mk_match cons_w_field ++ deflt)
1302 mk_match con = mkSimpleMatch [L loc (mk_sel_pat con)]
1303 (L loc (HsVar field_var))
1304 mk_sel_pat con = ConPatIn (L loc (getName con)) (RecCon rec_fields)
1305 rec_fields = HsRecFields { rec_flds = [rec_field], rec_dotdot = Nothing }
1306 rec_field = HsRecField { hsRecFieldId = sel_lname
1307 , hsRecFieldArg = nlVarPat field_var
1308 , hsRecPun = False }
1309 sel_lname = L loc sel_name
1310 field_var = mkInternalName (mkBuiltinUnique 1) (getOccName sel_name) loc
1312 -- Add catch-all default case unless the case is exhaustive
1313 -- We do this explicitly so that we get a nice error message that
1314 -- mentions this particular record selector
1315 deflt | not (any is_unused all_cons) = []
1316 | otherwise = [mkSimpleMatch [nlWildPat]
1317 (nlHsApp (nlHsVar (getName rEC_SEL_ERROR_ID))
1320 -- Do not add a default case unless there are unmatched
1321 -- constructors. We must take account of GADTs, else we
1322 -- get overlap warning messages from the pattern-match checker
1323 is_unused con = not (con `elem` cons_w_field
1324 || dataConCannotMatch inst_tys con)
1325 inst_tys = tyConAppArgs data_ty
1327 unit_rhs = mkLHsTupleExpr []
1328 msg_lit = HsStringPrim $ mkFastString $
1329 occNameString (getOccName sel_name)
1332 tyConFields :: TyCon -> [FieldLabel]
1334 | isAlgTyCon tc = nub (concatMap dataConFieldLabels (tyConDataCons tc))
1338 Note [Polymorphic selectors]
1339 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1340 When a record has a polymorphic field, we pull the foralls out to the front.
1341 data T = MkT { f :: forall a. [a] -> a }
1342 Then f :: forall a. T -> [a] -> a
1343 NOT f :: T -> forall a. [a] -> a
1345 This is horrid. It's only needed in deeply obscure cases, which I hate.
1346 The only case I know is test tc163, which is worth looking at. It's far
1347 from clear that this test should succeed at all!
1349 Note [Naughty record selectors]
1350 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1351 A "naughty" field is one for which we can't define a record
1352 selector, because an existential type variable would escape. For example:
1353 data T = forall a. MkT { x,y::a }
1354 We obviously can't define
1356 Nevertheless we *do* put a RecSelId into the type environment
1357 so that if the user tries to use 'x' as a selector we can bleat
1358 helpfully, rather than saying unhelpfully that 'x' is not in scope.
1359 Hence the sel_naughty flag, to identify record selectors that don't really exist.
1361 In general, a field is "naughty" if its type mentions a type variable that
1362 isn't in the result type of the constructor. Note that this *allows*
1363 GADT record selectors (Note [GADT record selectors]) whose types may look
1364 like sel :: T [a] -> a
1366 For naughty selectors we make a dummy binding
1368 for naughty selectors, so that the later type-check will add them to the
1369 environment, and they'll be exported. The function is never called, because
1370 the tyepchecker spots the sel_naughty field.
1372 Note [GADT record selectors]
1373 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1374 For GADTs, we require that all constructors with a common field 'f' have the same
1375 result type (modulo alpha conversion). [Checked in TcTyClsDecls.checkValidTyCon]
1378 T1 { f :: Maybe a } :: T [a]
1379 T2 { f :: Maybe a, y :: b } :: T [a]
1381 and now the selector takes that result type as its argument:
1382 f :: forall a. T [a] -> Maybe a
1384 Details: the "real" types of T1,T2 are:
1385 T1 :: forall r a. (r~[a]) => a -> T r
1386 T2 :: forall r a b. (r~[a]) => a -> b -> T r
1388 So the selector loooks like this:
1389 f :: forall a. T [a] -> Maybe a
1392 T1 c (g:[a]~[c]) (v:Maybe c) -> v `cast` Maybe (right (sym g))
1393 T2 c d (g:[a]~[c]) (v:Maybe c) (w:d) -> v `cast` Maybe (right (sym g))
1395 Note the forall'd tyvars of the selector are just the free tyvars
1396 of the result type; there may be other tyvars in the constructor's
1397 type (e.g. 'b' in T2).
1399 Note the need for casts in the result!
1401 Note [Selector running example]
1402 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1403 It's OK to combine GADTs and type families. Here's a running example:
1405 data instance T [a] where
1406 T1 { fld :: b } :: T [Maybe b]
1408 The representation type looks like this
1410 T1 { fld :: b } :: :R7T (Maybe b)
1412 and there's coercion from the family type to the representation type
1413 :CoR7T a :: T [a] ~ :R7T a
1415 The selector we want for fld looks like this:
1417 fld :: forall b. T [Maybe b] -> b
1418 fld = /\b. \(d::T [Maybe b]).
1419 case d `cast` :CoR7T (Maybe b) of
1422 The scrutinee of the case has type :R7T (Maybe b), which can be
1423 gotten by appying the eq_spec to the univ_tvs of the data con.
1425 %************************************************************************
1429 %************************************************************************
1432 resultTypeMisMatch :: Name -> DataCon -> DataCon -> SDoc
1433 resultTypeMisMatch field_name con1 con2
1434 = vcat [sep [ptext (sLit "Constructors") <+> ppr con1 <+> ptext (sLit "and") <+> ppr con2,
1435 ptext (sLit "have a common field") <+> quotes (ppr field_name) <> comma],
1436 nest 2 $ ptext (sLit "but have different result types")]
1438 fieldTypeMisMatch :: Name -> DataCon -> DataCon -> SDoc
1439 fieldTypeMisMatch field_name con1 con2
1440 = sep [ptext (sLit "Constructors") <+> ppr con1 <+> ptext (sLit "and") <+> ppr con2,
1441 ptext (sLit "give different types for field"), quotes (ppr field_name)]
1443 dataConCtxt :: Outputable a => a -> SDoc
1444 dataConCtxt con = ptext (sLit "In the definition of data constructor") <+> quotes (ppr con)
1446 classOpCtxt :: Var -> Type -> SDoc
1447 classOpCtxt sel_id tau = sep [ptext (sLit "When checking the class method:"),
1448 nest 2 (ppr sel_id <+> dcolon <+> ppr tau)]
1450 nullaryClassErr :: Class -> SDoc
1452 = ptext (sLit "No parameters for class") <+> quotes (ppr cls)
1454 classArityErr :: Class -> SDoc
1456 = vcat [ptext (sLit "Too many parameters for class") <+> quotes (ppr cls),
1457 parens (ptext (sLit "Use -XMultiParamTypeClasses to allow multi-parameter classes"))]
1459 classFunDepsErr :: Class -> SDoc
1461 = vcat [ptext (sLit "Fundeps in class") <+> quotes (ppr cls),
1462 parens (ptext (sLit "Use -XFunctionalDependencies to allow fundeps"))]
1464 noClassTyVarErr :: Class -> Var -> SDoc
1465 noClassTyVarErr clas op
1466 = sep [ptext (sLit "The class method") <+> quotes (ppr op),
1467 ptext (sLit "mentions none of the type variables of the class") <+>
1468 ppr clas <+> hsep (map ppr (classTyVars clas))]
1470 genericMultiParamErr :: Class -> SDoc
1471 genericMultiParamErr clas
1472 = ptext (sLit "The multi-parameter class") <+> quotes (ppr clas) <+>
1473 ptext (sLit "cannot have generic methods")
1475 badGenericMethodType :: Name -> Kind -> SDoc
1476 badGenericMethodType op op_ty
1477 = hang (ptext (sLit "Generic method type is too complex"))
1478 4 (vcat [ppr op <+> dcolon <+> ppr op_ty,
1479 ptext (sLit "You can only use type variables, arrows, lists, and tuples")])
1481 recSynErr :: [LTyClDecl Name] -> TcRn ()
1483 = setSrcSpan (getLoc (head sorted_decls)) $
1484 addErr (sep [ptext (sLit "Cycle in type synonym declarations:"),
1485 nest 2 (vcat (map ppr_decl sorted_decls))])
1487 sorted_decls = sortLocated syn_decls
1488 ppr_decl (L loc decl) = ppr loc <> colon <+> ppr decl
1490 recClsErr :: [Located (TyClDecl Name)] -> TcRn ()
1492 = setSrcSpan (getLoc (head sorted_decls)) $
1493 addErr (sep [ptext (sLit "Cycle in class declarations (via superclasses):"),
1494 nest 2 (vcat (map ppr_decl sorted_decls))])
1496 sorted_decls = sortLocated cls_decls
1497 ppr_decl (L loc decl) = ppr loc <> colon <+> ppr (decl { tcdSigs = [] })
1499 sortLocated :: [Located a] -> [Located a]
1500 sortLocated things = sortLe le things
1502 le (L l1 _) (L l2 _) = l1 <= l2
1504 badDataConTyCon :: DataCon -> Type -> Type -> SDoc
1505 badDataConTyCon data_con res_ty_tmpl actual_res_ty
1506 = hang (ptext (sLit "Data constructor") <+> quotes (ppr data_con) <+>
1507 ptext (sLit "returns type") <+> quotes (ppr actual_res_ty))
1508 2 (ptext (sLit "instead of an instance of its parent type") <+> quotes (ppr res_ty_tmpl))
1510 badGadtDecl :: Name -> SDoc
1512 = vcat [ ptext (sLit "Illegal generalised algebraic data declaration for") <+> quotes (ppr tc_name)
1513 , nest 2 (parens $ ptext (sLit "Use -XGADTs to allow GADTs")) ]
1515 badExistential :: Located Name -> SDoc
1516 badExistential con_name
1517 = hang (ptext (sLit "Data constructor") <+> quotes (ppr con_name) <+>
1518 ptext (sLit "has existential type variables, or a context"))
1519 2 (parens $ ptext (sLit "Use -XExistentialQuantification or -XGADTs to allow this"))
1521 badStupidTheta :: Name -> SDoc
1522 badStupidTheta tc_name
1523 = ptext (sLit "A data type declared in GADT style cannot have a context:") <+> quotes (ppr tc_name)
1525 newtypeConError :: Name -> Int -> SDoc
1526 newtypeConError tycon n
1527 = sep [ptext (sLit "A newtype must have exactly one constructor,"),
1528 nest 2 $ ptext (sLit "but") <+> quotes (ppr tycon) <+> ptext (sLit "has") <+> speakN n ]
1530 newtypeExError :: DataCon -> SDoc
1532 = sep [ptext (sLit "A newtype constructor cannot have an existential context,"),
1533 nest 2 $ ptext (sLit "but") <+> quotes (ppr con) <+> ptext (sLit "does")]
1535 newtypeStrictError :: DataCon -> SDoc
1536 newtypeStrictError con
1537 = sep [ptext (sLit "A newtype constructor cannot have a strictness annotation,"),
1538 nest 2 $ ptext (sLit "but") <+> quotes (ppr con) <+> ptext (sLit "does")]
1540 newtypePredError :: DataCon -> SDoc
1541 newtypePredError con
1542 = sep [ptext (sLit "A newtype constructor must have a return type of form T a1 ... an"),
1543 nest 2 $ ptext (sLit "but") <+> quotes (ppr con) <+> ptext (sLit "does not")]
1545 newtypeFieldErr :: DataCon -> Int -> SDoc
1546 newtypeFieldErr con_name n_flds
1547 = sep [ptext (sLit "The constructor of a newtype must have exactly one field"),
1548 nest 2 $ ptext (sLit "but") <+> quotes (ppr con_name) <+> ptext (sLit "has") <+> speakN n_flds]
1550 badSigTyDecl :: Name -> SDoc
1551 badSigTyDecl tc_name
1552 = vcat [ ptext (sLit "Illegal kind signature") <+>
1553 quotes (ppr tc_name)
1554 , nest 2 (parens $ ptext (sLit "Use -XKindSignatures to allow kind signatures")) ]
1556 badFamInstDecl :: Outputable a => a -> SDoc
1557 badFamInstDecl tc_name
1558 = vcat [ ptext (sLit "Illegal family instance for") <+>
1559 quotes (ppr tc_name)
1560 , nest 2 (parens $ ptext (sLit "Use -XTypeFamilies to allow indexed type families")) ]
1562 tooManyParmsErr :: Located Name -> SDoc
1563 tooManyParmsErr tc_name
1564 = ptext (sLit "Family instance has too many parameters:") <+>
1565 quotes (ppr tc_name)
1567 tooFewParmsErr :: Arity -> SDoc
1568 tooFewParmsErr arity
1569 = ptext (sLit "Family instance has too few parameters; expected") <+>
1572 wrongNumberOfParmsErr :: Arity -> SDoc
1573 wrongNumberOfParmsErr exp_arity
1574 = ptext (sLit "Number of parameters must match family declaration; expected")
1577 badBootFamInstDeclErr :: SDoc
1578 badBootFamInstDeclErr
1579 = ptext (sLit "Illegal family instance in hs-boot file")
1581 notFamily :: TyCon -> SDoc
1583 = vcat [ ptext (sLit "Illegal family instance for") <+> quotes (ppr tycon)
1584 , nest 2 $ parens (ppr tycon <+> ptext (sLit "is not an indexed type family"))]
1586 wrongKindOfFamily :: TyCon -> SDoc
1587 wrongKindOfFamily family
1588 = ptext (sLit "Wrong category of family instance; declaration was for a")
1591 kindOfFamily | isSynTyCon family = ptext (sLit "type synonym")
1592 | isAlgTyCon family = ptext (sLit "data type")
1593 | otherwise = pprPanic "wrongKindOfFamily" (ppr family)
1595 emptyConDeclsErr :: Name -> SDoc
1596 emptyConDeclsErr tycon
1597 = sep [quotes (ppr tycon) <+> ptext (sLit "has no constructors"),
1598 nest 2 $ ptext (sLit "(-XEmptyDataDecls permits this)")]