2 % (c) The University of Glasgow 2006
3 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
6 Typechecking class declarations
9 module TcClassDcl ( tcClassSigs, tcClassDecl2,
10 findMethodBind, instantiateMethod, tcInstanceMethodBody,
11 mkGenericDefMethBind, getGenericInstances,
12 tcAddDeclCtxt, badMethodErr, badATErr, omittedATWarn
15 #include "HsVersions.h"
29 import BuildTyCl( TcMethInfo )
59 Every class implicitly declares a new data type, corresponding to dictionaries
60 of that class. So, for example:
62 class (D a) => C a where
64 op2 :: forall b. Ord b => a -> b -> b
66 would implicitly declare
68 data CDict a = CDict (D a)
70 (forall b. Ord b => a -> b -> b)
72 (We could use a record decl, but that means changing more of the existing apparatus.
75 For classes with just one superclass+method, we use a newtype decl instead:
78 op :: forallb. a -> b -> b
82 newtype CDict a = CDict (forall b. a -> b -> b)
84 Now DictTy in Type is just a form of type synomym:
85 DictTy c t = TyConTy CDict `AppTy` t
87 Death to "ExpandingDicts".
90 %************************************************************************
92 Type-checking the class op signatures
94 %************************************************************************
97 tcClassSigs :: Name -- Name of the class
102 tcClassSigs clas sigs def_methods
103 = do { dm_env <- mapM (addLocM (checkDefaultBind clas op_names))
104 (bagToList def_methods)
105 ; mapM (tcClassSig (mkNameEnv dm_env)) op_sigs }
107 op_sigs = [sig | sig@(L _ (TypeSig _ _)) <- sigs]
108 op_names = [n | (L _ (TypeSig (L _ n) _)) <- op_sigs]
110 checkDefaultBind :: Name -> [Name] -> HsBindLR Name Name -> TcM (Name, DefMethSpec)
111 -- Check default bindings
112 -- a) must be for a class op for this class
113 -- b) must be all generic or all non-generic
114 checkDefaultBind clas ops (FunBind {fun_id = L _ op, fun_matches = MatchGroup matches _ })
115 = do { -- Check that the op is from this class
116 checkTc (op `elem` ops) (badMethodErr clas op)
118 -- Check that all the defns ar generic, or none are
119 ; case (none_generic, all_generic) of
120 (True, _) -> return (op, VanillaDM)
121 (_, True) -> return (op, GenericDM)
122 _ -> failWith (mixedGenericErr op)
125 n_generic = count (isJust . maybeGenericMatch) matches
126 none_generic = n_generic == 0
127 all_generic = matches `lengthIs` n_generic
129 checkDefaultBind _ _ b = pprPanic "checkDefaultBind" (ppr b)
132 tcClassSig :: NameEnv DefMethSpec -- Info about default methods;
136 tcClassSig dm_env (L loc (TypeSig (L _ op_name) op_hs_ty))
137 = setSrcSpan loc $ do
138 { op_ty <- tcHsKindedType op_hs_ty -- Class tyvars already in scope
139 ; let dm = lookupNameEnv dm_env op_name `orElse` NoDM
140 ; return (op_name, dm, op_ty) }
141 tcClassSig _ s = pprPanic "tcClassSig" (ppr s)
145 %************************************************************************
149 %************************************************************************
152 tcClassDecl2 :: LTyClDecl Name -- The class declaration
155 tcClassDecl2 (L loc (ClassDecl {tcdLName = class_name, tcdSigs = sigs,
156 tcdMeths = default_binds}))
157 = recoverM (return emptyLHsBinds) $
159 do { clas <- tcLookupLocatedClass class_name
161 -- We make a separate binding for each default method.
162 -- At one time I used a single AbsBinds for all of them, thus
163 -- AbsBind [d] [dm1, dm2, dm3] { dm1 = ...; dm2 = ...; dm3 = ... }
164 -- But that desugars into
165 -- ds = \d -> (..., ..., ...)
166 -- dm1 = \d -> case ds d of (a,b,c) -> a
167 -- And since ds is big, it doesn't get inlined, so we don't get good
168 -- default methods. Better to make separate AbsBinds for each
170 (tyvars, _, _, op_items) = classBigSig clas
171 rigid_info = ClsSkol clas
172 prag_fn = mkPragFun sigs default_binds
173 sig_fn = mkSigFun sigs
174 clas_tyvars = tcSkolSigTyVars rigid_info tyvars
175 pred = mkClassPred clas (mkTyVarTys clas_tyvars)
176 ; this_dict <- newEvVar pred
178 ; let tc_dm = tcDefMeth clas clas_tyvars
179 this_dict default_binds
182 ; dm_binds <- tcExtendTyVarEnv clas_tyvars $
185 ; return (listToBag (catMaybes dm_binds)) }
187 tcClassDecl2 d = pprPanic "tcClassDecl2" (ppr d)
189 tcDefMeth :: Class -> [TyVar] -> EvVar -> LHsBinds Name
190 -> SigFun -> PragFun -> ClassOpItem
191 -> TcM (Maybe (LHsBind Id))
192 -- Generate code for polymorphic default methods only (hence DefMeth)
193 -- (Generic default methods have turned into instance decls by now.)
194 -- This is incompatible with Hugs, which expects a polymorphic
195 -- default method for every class op, regardless of whether or not
196 -- the programmer supplied an explicit default decl for the class.
197 -- (If necessary we can fix that, but we don't have a convenient Id to hand.)
198 tcDefMeth clas tyvars this_dict binds_in sig_fn prag_fn (sel_id, dm_info)
200 NoDefMeth -> return Nothing
201 GenDefMeth -> return Nothing
202 DefMeth dm_name -> do
203 { let sel_name = idName sel_id
204 ; local_dm_name <- newLocalName sel_name
205 -- Base the local_dm_name on the selector name, because
206 -- type errors from tcInstanceMethodBody come from here
208 -- See Note [Silly default-method bind]
209 -- (possibly out of date)
211 ; let meth_bind = findMethodBind sel_name binds_in
212 `orElse` pprPanic "tcDefMeth" (ppr sel_id)
213 -- dm_info = DefMeth dm_name only if there is a binding in binds_in
215 dm_sig_fn _ = sig_fn sel_name
216 dm_id = mkDefaultMethodId sel_id dm_name
217 local_dm_type = instantiateMethod clas sel_id (mkTyVarTys tyvars)
218 local_dm_id = mkLocalId local_dm_name local_dm_type
220 ; (dm_id_w_inline, spec_prags)
221 <- tcPrags NonRecursive False True dm_id (prag_fn sel_name)
223 ; warnTc (not (null spec_prags))
224 (ptext (sLit "Ignoring SPECIALISE pragmas on default method")
225 <+> quotes (ppr sel_name))
228 tcInstanceMethodBody (ClsSkol clas)
232 dm_id_w_inline local_dm_id
233 dm_sig_fn IsDefaultMethod meth_bind }
236 tcInstanceMethodBody :: SkolemInfo -> [TcTyVar] -> [EvVar]
239 -> SigFun -> TcSpecPrags -> LHsBind Name
241 tcInstanceMethodBody skol_info tyvars dfun_ev_vars
242 this_dict meth_id local_meth_id
245 = do { -- Typecheck the binding, first extending the envt
246 -- so that when tcInstSig looks up the local_meth_id to find
247 -- its signature, we'll find it in the environment
248 let full_given = case this_dict of
249 Nothing -> dfun_ev_vars
250 Just (EvBind dict _) -> dict : dfun_ev_vars
251 lm_bind = L loc (bind { fun_id = L loc (idName local_meth_id) })
252 -- Substitue the local_meth_name for the binder
253 -- NB: the binding is always a FunBind
255 ; (ev_binds, (tc_bind, _))
256 <- checkConstraints skol_info emptyVarSet tyvars full_given $
257 tcExtendIdEnv [local_meth_id] $
258 tcPolyBinds TopLevel meth_sig_fn no_prag_fn
259 NonRecursive NonRecursive
262 -- Add the binding for this_dict, if we have one
263 ; ev_binds' <- case this_dict of
264 Nothing -> return ev_binds
265 Just (EvBind self rhs) -> extendTcEvBinds ev_binds self rhs
267 ; let full_bind = AbsBinds { abs_tvs = tyvars, abs_ev_vars = dfun_ev_vars
268 , abs_exports = [(tyvars, meth_id, local_meth_id, specs)]
269 , abs_ev_binds = ev_binds'
270 , abs_binds = tc_bind }
272 ; return (L loc full_bind) }
274 no_prag_fn _ = [] -- No pragmas for local_meth_id;
275 -- they are all for meth_id
279 instantiateMethod :: Class -> Id -> [TcType] -> TcType
280 -- Take a class operation, say
281 -- op :: forall ab. C a => forall c. Ix c => (b,c) -> a
282 -- Instantiate it at [ty1,ty2]
283 -- Return the "local method type":
284 -- forall c. Ix x => (ty2,c) -> ty1
285 instantiateMethod clas sel_id inst_tys
286 = ASSERT( ok_first_pred ) local_meth_ty
288 (sel_tyvars,sel_rho) = tcSplitForAllTys (idType sel_id)
289 rho_ty = ASSERT( length sel_tyvars == length inst_tys )
290 substTyWith sel_tyvars inst_tys sel_rho
292 (first_pred, local_meth_ty) = tcSplitPredFunTy_maybe rho_ty
293 `orElse` pprPanic "tcInstanceMethod" (ppr sel_id)
295 ok_first_pred = case getClassPredTys_maybe first_pred of
296 Just (clas1, _tys) -> clas == clas1
298 -- The first predicate should be of form (C a b)
299 -- where C is the class in question
302 ---------------------------
303 findMethodBind :: Name -- Selector name
304 -> LHsBinds Name -- A group of bindings
305 -> Maybe (LHsBind Name) -- The binding
306 findMethodBind sel_name binds
307 = foldlBag mplus Nothing (mapBag f binds)
309 f bind@(L _ (FunBind { fun_id = L _ op_name }))
310 | op_name == sel_name
315 Note [Polymorphic methods]
316 ~~~~~~~~~~~~~~~~~~~~~~~~~~
319 op :: forall b. Ord b => a -> b -> b -> b
320 instance Foo c => Foo [c] where
323 When typechecking the binding 'op = e', we'll have a meth_id for op
325 op :: forall c. Foo c => forall b. Ord b => [c] -> b -> b -> b
327 So tcPolyBinds must be capable of dealing with nested polytypes;
328 and so it is. See TcBinds.tcMonoBinds (with type-sig case).
330 Note [Silly default-method bind]
331 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
332 When we pass the default method binding to the type checker, it must
335 otherwise the "$dm" stuff comes out error messages. But we want the
336 "$dm" to come out in the interface file. So we typecheck the former,
337 and wrap it in a let, thus
338 $dmop2 = let op2 = e in op2
339 This makes the error messages right.
342 %************************************************************************
344 Extracting generic instance declaration from class declarations
346 %************************************************************************
348 @getGenericInstances@ extracts the generic instance declarations from a class
349 declaration. For exmaple
354 op{ x+y } (Inl v) = ...
355 op{ x+y } (Inr v) = ...
356 op{ x*y } (v :*: w) = ...
359 gives rise to the instance declarations
361 instance C (x+y) where
365 instance C (x*y) where
372 mkGenericDefMethBind :: Class -> [Type] -> Id -> TcM (LHsBind Name)
373 mkGenericDefMethBind clas inst_tys sel_id
374 = -- A generic default method
375 -- If the method is defined generically, we can only do the job if the
376 -- instance declaration is for a single-parameter type class with
377 -- a type constructor applied to type arguments in the instance decl
378 -- (checkTc, so False provokes the error)
379 do { checkTc (isJust maybe_tycon)
380 (badGenericInstance sel_id (notSimple inst_tys))
381 ; checkTc (tyConHasGenerics tycon)
382 (badGenericInstance sel_id (notGeneric tycon))
385 ; liftIO (dumpIfSet_dyn dflags Opt_D_dump_deriv "Filling in method body"
386 (vcat [ppr clas <+> ppr inst_tys,
387 nest 2 (ppr sel_id <+> equals <+> ppr rhs)]))
389 -- Rename it before returning it
390 ; (rn_rhs, _) <- rnLExpr rhs
391 ; return (noLoc $ mkFunBind (noLoc (idName sel_id))
392 [mkSimpleMatch [] rn_rhs]) }
394 rhs = mkGenericRhs sel_id clas_tyvar tycon
396 -- The tycon is only used in the generic case, and in that
397 -- case we require that the instance decl is for a single-parameter
398 -- type class with type variable arguments:
399 -- instance (...) => C (T a b)
400 clas_tyvar = ASSERT (not (null (classTyVars clas))) head (classTyVars clas)
401 Just tycon = maybe_tycon
402 maybe_tycon = case inst_tys of
403 [ty] -> case tcSplitTyConApp_maybe ty of
404 Just (tycon, arg_tys) | all tcIsTyVarTy arg_tys -> Just tycon
409 ---------------------------
410 getGenericInstances :: [LTyClDecl Name] -> TcM [InstInfo Name]
411 getGenericInstances class_decls
412 = do { gen_inst_infos <- mapM (addLocM get_generics) class_decls
413 ; let { gen_inst_info = concat gen_inst_infos }
415 -- Return right away if there is no generic stuff
416 ; if null gen_inst_info then return []
419 -- Otherwise print it out
421 ; liftIO (dumpIfSet_dyn dflags Opt_D_dump_deriv "Generic instances"
422 (vcat (map pprInstInfoDetails gen_inst_info)))
423 ; return gen_inst_info }}
425 get_generics :: TyClDecl Name -> TcM [InstInfo Name]
426 get_generics decl@(ClassDecl {tcdLName = class_name, tcdMeths = def_methods})
428 = return [] -- The comon case: no generic default methods
430 | otherwise -- A source class decl with generic default methods
431 = recoverM (return []) $
432 tcAddDeclCtxt decl $ do
433 clas <- tcLookupLocatedClass class_name
435 -- Group by type, and
436 -- make an InstInfo out of each group
438 groups = groupWith listToBag generic_binds
440 inst_infos <- mapM (mkGenericInstance clas) groups
442 -- Check that there is only one InstInfo for each type constructor
443 -- The main way this can fail is if you write
444 -- f {| a+b |} ... = ...
445 -- f {| x+y |} ... = ...
446 -- Then at this point we'll have an InstInfo for each
448 -- The class should be unary, which is why simpleInstInfoTyCon should be ok
450 tc_inst_infos :: [(TyCon, InstInfo Name)]
451 tc_inst_infos = [(simpleInstInfoTyCon i, i) | i <- inst_infos]
453 bad_groups = [group | group <- equivClassesByUniq get_uniq tc_inst_infos,
454 group `lengthExceeds` 1]
455 get_uniq (tc,_) = getUnique tc
457 mapM_ (addErrTc . dupGenericInsts) bad_groups
459 -- Check that there is an InstInfo for each generic type constructor
461 missing = genericTyConNames `minusList` [tyConName tc | (tc,_) <- tc_inst_infos]
463 checkTc (null missing) (missingGenericInstances missing)
467 generic_binds :: [(HsType Name, LHsBind Name)]
468 generic_binds = getGenericBinds def_methods
469 get_generics decl = pprPanic "get_generics" (ppr decl)
472 ---------------------------------
473 getGenericBinds :: LHsBinds Name -> [(HsType Name, LHsBind Name)]
474 -- Takes a group of method bindings, finds the generic ones, and returns
475 -- them in finite map indexed by the type parameter in the definition.
476 getGenericBinds binds = concat (map getGenericBind (bagToList binds))
478 getGenericBind :: LHsBindLR Name Name -> [(HsType Name, LHsBindLR Name Name)]
479 getGenericBind (L loc bind@(FunBind { fun_matches = MatchGroup matches ty }))
480 = groupWith wrap (mapCatMaybes maybeGenericMatch matches)
482 wrap ms = L loc (bind { fun_matches = MatchGroup ms ty })
486 groupWith :: ([a] -> b) -> [(HsType Name, a)] -> [(HsType Name, b)]
488 groupWith op ((t,v):prs) = (t, op (v:vs)) : groupWith op rest
491 (this,rest) = partition same_t prs
492 same_t (t', _v) = t `eqPatType` t'
494 eqPatLType :: LHsType Name -> LHsType Name -> Bool
495 eqPatLType t1 t2 = unLoc t1 `eqPatType` unLoc t2
497 eqPatType :: HsType Name -> HsType Name -> Bool
498 -- A very simple equality function, only for
499 -- type patterns in generic function definitions.
500 eqPatType (HsTyVar v1) (HsTyVar v2) = v1==v2
501 eqPatType (HsAppTy s1 t1) (HsAppTy s2 t2) = s1 `eqPatLType` s2 && t1 `eqPatLType` t2
502 eqPatType (HsOpTy s1 op1 t1) (HsOpTy s2 op2 t2) = s1 `eqPatLType` s2 && t1 `eqPatLType` t2 && unLoc op1 == unLoc op2
503 eqPatType (HsNumTy n1) (HsNumTy n2) = n1 == n2
504 eqPatType (HsParTy t1) t2 = unLoc t1 `eqPatType` t2
505 eqPatType t1 (HsParTy t2) = t1 `eqPatType` unLoc t2
506 eqPatType _ _ = False
508 ---------------------------------
509 mkGenericInstance :: Class
510 -> (HsType Name, LHsBinds Name)
511 -> TcM (InstInfo Name)
513 mkGenericInstance clas (hs_ty, binds) = do
514 -- Make a generic instance declaration
515 -- For example: instance (C a, C b) => C (a+b) where { binds }
517 -- Extract the universally quantified type variables
518 -- and wrap them as forall'd tyvars, so that kind inference
519 -- works in the standard way
521 sig_tvs = userHsTyVarBndrs $ map noLoc $ nameSetToList $
522 extractHsTyVars (noLoc hs_ty)
523 hs_forall_ty = noLoc $ mkExplicitHsForAllTy sig_tvs (noLoc []) (noLoc hs_ty)
525 -- Type-check the instance type, and check its form
526 forall_inst_ty <- tcHsSigType GenPatCtxt hs_forall_ty
528 (tyvars, inst_ty) = tcSplitForAllTys forall_inst_ty
530 checkTc (validGenericInstanceType inst_ty)
531 (badGenericInstanceType binds)
533 -- Make the dictionary function.
535 overlap_flag <- getOverlapFlag
536 dfun_name <- newDFunName clas [inst_ty] span
538 inst_theta = [mkClassPred clas [mkTyVarTy tv] | tv <- tyvars]
539 dfun_id = mkDictFunId dfun_name tyvars inst_theta clas [inst_ty]
540 ispec = mkLocalInstance dfun_id overlap_flag
542 return (InstInfo { iSpec = ispec, iBinds = VanillaInst binds [] False })
546 %************************************************************************
550 %************************************************************************
553 tcAddDeclCtxt :: TyClDecl Name -> TcM a -> TcM a
554 tcAddDeclCtxt decl thing_inside
555 = addErrCtxt ctxt thing_inside
557 thing | isClassDecl decl = "class"
558 | isTypeDecl decl = "type synonym" ++ maybeInst
559 | isDataDecl decl = if tcdND decl == NewType
560 then "newtype" ++ maybeInst
561 else "data type" ++ maybeInst
562 | isFamilyDecl decl = "family"
563 | otherwise = panic "tcAddDeclCtxt/thing"
565 maybeInst | isFamInstDecl decl = " instance"
568 ctxt = hsep [ptext (sLit "In the"), text thing,
569 ptext (sLit "declaration for"), quotes (ppr (tcdName decl))]
571 badMethodErr :: Outputable a => a -> Name -> SDoc
573 = hsep [ptext (sLit "Class"), quotes (ppr clas),
574 ptext (sLit "does not have a method"), quotes (ppr op)]
576 badATErr :: Class -> Name -> SDoc
578 = hsep [ptext (sLit "Class"), quotes (ppr clas),
579 ptext (sLit "does not have an associated type"), quotes (ppr at)]
581 omittedATWarn :: Name -> SDoc
583 = ptext (sLit "No explicit AT declaration for") <+> quotes (ppr at)
585 badGenericInstance :: Var -> SDoc -> SDoc
586 badGenericInstance sel_id because
587 = sep [ptext (sLit "Can't derive generic code for") <+> quotes (ppr sel_id),
590 notSimple :: [Type] -> SDoc
592 = vcat [ptext (sLit "because the instance type(s)"),
593 nest 2 (ppr inst_tys),
594 ptext (sLit "is not a simple type of form (T a1 ... an)")]
596 notGeneric :: TyCon -> SDoc
598 = vcat [ptext (sLit "because the instance type constructor") <+> quotes (ppr tycon) <+>
599 ptext (sLit "was not compiled with -XGenerics")]
601 badGenericInstanceType :: LHsBinds Name -> SDoc
602 badGenericInstanceType binds
603 = vcat [ptext (sLit "Illegal type pattern in the generic bindings"),
606 missingGenericInstances :: [Name] -> SDoc
607 missingGenericInstances missing
608 = ptext (sLit "Missing type patterns for") <+> pprQuotedList missing
610 dupGenericInsts :: [(TyCon, InstInfo a)] -> SDoc
611 dupGenericInsts tc_inst_infos
612 = vcat [ptext (sLit "More than one type pattern for a single generic type constructor:"),
613 nest 2 (vcat (map ppr_inst_ty tc_inst_infos)),
614 ptext (sLit "All the type patterns for a generic type constructor must be identical")
617 ppr_inst_ty (_,inst) = ppr (simpleInstInfoTy inst)
619 mixedGenericErr :: Name -> SDoc
621 = ptext (sLit "Can't mix generic and non-generic equations for class method") <+> quotes (ppr op)