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"
22 import TcPat( addInlinePrags )
30 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
100 -> TcM [TcMethInfo] -- One for each method
102 tcClassSigs clas sigs def_methods
103 = do { -- Check that all def_methods are in the class
104 ; op_info <- mapM (addLocM tc_sig) [sig | sig@(L _ (TypeSig _ _)) <- sigs]
105 ; let op_names = [ n | (n,_,_) <- op_info ]
107 ; sequence [ failWithTc (badMethodErr clas n)
108 | n <- dm_bind_names, not (n `elem` op_names) ]
109 -- Value binding for non class-method (ie no TypeSig)
111 ; sequence [ failWithTc (badGenericMethod clas n)
112 | n <- genop_names, not (n `elem` dm_bind_names) ]
113 -- Generic signature without value binding
117 dm_bind_names :: [Name] -- These ones have a value binding in the class decl
118 dm_bind_names = [op | L _ (FunBind {fun_id = L _ op}) <- bagToList def_methods]
120 genop_names :: [Name] -- These ones have a generic signature
121 genop_names = [n | L _ (GenericSig (L _ n) _) <- sigs]
123 tc_sig (TypeSig (L _ op_name) op_hs_ty)
124 = do { op_ty <- tcHsKindedType op_hs_ty -- Class tyvars already in scope
125 ; let dm | op_name `elem` genop_names = GenericDM
126 | op_name `elem` dm_bind_names = VanillaDM
128 ; return (op_name, dm, op_ty) }
129 tc_sig sig = pprPanic "tc_cls_sig" (ppr sig)
133 %************************************************************************
137 %************************************************************************
140 tcClassDecl2 :: LTyClDecl Name -- The class declaration
143 tcClassDecl2 (L loc (ClassDecl {tcdLName = class_name, tcdSigs = sigs,
144 tcdMeths = default_binds}))
145 = recoverM (return emptyLHsBinds) $
147 do { clas <- tcLookupLocatedClass class_name
149 -- We make a separate binding for each default method.
150 -- At one time I used a single AbsBinds for all of them, thus
151 -- AbsBind [d] [dm1, dm2, dm3] { dm1 = ...; dm2 = ...; dm3 = ... }
152 -- But that desugars into
153 -- ds = \d -> (..., ..., ...)
154 -- dm1 = \d -> case ds d of (a,b,c) -> a
155 -- And since ds is big, it doesn't get inlined, so we don't get good
156 -- default methods. Better to make separate AbsBinds for each
158 (tyvars, _, _, op_items) = classBigSig clas
159 prag_fn = mkPragFun sigs default_binds
160 sig_fn = mkSigFun sigs
161 clas_tyvars = tcSuperSkolTyVars tyvars
162 pred = mkClassPred clas (mkTyVarTys clas_tyvars)
163 ; this_dict <- newEvVar pred
165 ; traceTc "TIM2" (ppr sigs)
166 ; let tc_dm = tcDefMeth clas clas_tyvars
167 this_dict default_binds sigs
170 ; dm_binds <- tcExtendTyVarEnv clas_tyvars $
173 ; return (unionManyBags dm_binds) }
175 tcClassDecl2 d = pprPanic "tcClassDecl2" (ppr d)
177 tcDefMeth :: Class -> [TyVar] -> EvVar -> LHsBinds Name -> [LSig Name]
178 -> SigFun -> PragFun -> ClassOpItem
179 -> TcM (LHsBinds TcId)
180 -- Generate code for polymorphic default methods only (hence DefMeth)
181 -- (Generic default methods have turned into instance decls by now.)
182 -- This is incompatible with Hugs, which expects a polymorphic
183 -- default method for every class op, regardless of whether or not
184 -- the programmer supplied an explicit default decl for the class.
185 -- (If necessary we can fix that, but we don't have a convenient Id to hand.)
186 tcDefMeth clas tyvars this_dict binds_in sigs sig_fn prag_fn (sel_id, dm_info)
187 | NoDefMeth <- dm_info = return emptyBag
189 = do { (dm_id, tvs, sig_loc) <- tc_dm_id dm_info
190 ; let L loc meth_bind = findMethodBind sel_name binds_in
191 `orElse` pprPanic "tcDefMeth" (ppr sel_id)
192 dm_bind = L loc (meth_bind { fun_id = L loc (idName dm_id) })
193 -- Substitute the meth_name for the binder
194 -- NB: the binding is always a FunBind
196 dm_sig_fn _ = Just (clas_tv_names ++ tvs, sig_loc)
197 dm_prag_fn _ = prag_fn sel_name
199 ; (binds,_) <- tcExtendIdEnv [dm_id] $
200 tcPolyBinds TopLevel dm_sig_fn dm_prag_fn
201 NonRecursive NonRecursive
205 sel_name = idName sel_id
206 clas_tv_names = map getName tyvars
208 -- Find the 'generic op :: ty' signature among the sigs
209 -- If dm_info is GenDefMeth, the corresponding signature
210 -- should jolly well exist! Hence the panic
211 genop_lhs_ty = case [lty | L _ (GenericSig (L _ n) lty) <- sigs
214 _ -> pprPanic "tcDefMeth" (ppr sel_name $$ ppr sigs)
216 tc_dm_id :: DefMeth -> TcM (Id, [Name], SrcSpan)
217 -- Make a default-method Id of the appropriate type
218 -- That may entail getting the generic-default signature
219 -- from the type signatures.
220 -- Also return the in-scope tyvars for the default method, and their binding site
221 tc_dm_id NoDefMeth = panic "tc_dm_id"
222 tc_dm_id (DefMeth dm_name)
223 | Just (tvs, loc) <- sig_fn sel_name
224 = return (mkDefaultMethodId sel_id dm_name, tvs, loc)
226 = pprPanic "No sig for" (ppr sel_name)
227 tc_dm_id (GenDefMeth dm_name)
229 do { tau <- tcHsKindedType genop_lhs_ty
230 ; checkValidType (FunSigCtxt sel_name) tau
231 ; return ( mkExportedLocalId dm_name (mkForAllTys tyvars tau)
232 , hsExplicitTvs genop_lhs_ty, loc ) }
234 loc = getLoc genop_lhs_ty
237 tcInstanceMethodBody :: SkolemInfo -> [TcTyVar] -> [EvVar]
239 -> SigFun -> TcSpecPrags -> LHsBind Name
241 tcInstanceMethodBody skol_info tyvars dfun_ev_vars
242 meth_id local_meth_id
245 = do { -- Typecheck the binding, first extending the envt
246 -- so that when tcInstSig looks up the local_meth_id to find
247 -- its signature, we'll find it in the environment
248 let lm_bind = L loc (bind { fun_id = L loc (idName local_meth_id) })
249 -- Substitute the local_meth_name for the binder
250 -- NB: the binding is always a FunBind
251 ; traceTc "TIM" (ppr local_meth_id $$ ppr (meth_sig_fn (idName local_meth_id)))
252 ; (ev_binds, (tc_bind, _))
253 <- checkConstraints skol_info tyvars dfun_ev_vars $
254 tcExtendIdEnv [local_meth_id] $
255 tcPolyBinds TopLevel meth_sig_fn no_prag_fn
256 NonRecursive NonRecursive
259 ; let full_bind = AbsBinds { abs_tvs = tyvars, abs_ev_vars = dfun_ev_vars
260 , abs_exports = [(tyvars, meth_id, local_meth_id, specs)]
261 , abs_ev_binds = ev_binds
262 , abs_binds = tc_bind }
264 ; return (L loc full_bind) }
266 no_prag_fn _ = [] -- No pragmas for local_meth_id;
267 -- they are all for meth_id
271 instantiateMethod :: Class -> Id -> [TcType] -> TcType
272 -- Take a class operation, say
273 -- op :: forall ab. C a => forall c. Ix c => (b,c) -> a
274 -- Instantiate it at [ty1,ty2]
275 -- Return the "local method type":
276 -- forall c. Ix x => (ty2,c) -> ty1
277 instantiateMethod clas sel_id inst_tys
278 = ASSERT( ok_first_pred ) local_meth_ty
280 (sel_tyvars,sel_rho) = tcSplitForAllTys (idType sel_id)
281 rho_ty = ASSERT( length sel_tyvars == length inst_tys )
282 substTyWith sel_tyvars inst_tys sel_rho
284 (first_pred, local_meth_ty) = tcSplitPredFunTy_maybe rho_ty
285 `orElse` pprPanic "tcInstanceMethod" (ppr sel_id)
287 ok_first_pred = case getClassPredTys_maybe first_pred of
288 Just (clas1, _tys) -> clas == clas1
290 -- The first predicate should be of form (C a b)
291 -- where C is the class in question
294 ---------------------------
295 findMethodBind :: Name -- Selector name
296 -> LHsBinds Name -- A group of bindings
297 -> Maybe (LHsBind Name) -- The binding
298 findMethodBind sel_name binds
299 = foldlBag mplus Nothing (mapBag f binds)
301 f bind@(L _ (FunBind { fun_id = L _ op_name }))
302 | op_name == sel_name
307 Note [Polymorphic methods]
308 ~~~~~~~~~~~~~~~~~~~~~~~~~~
311 op :: forall b. Ord b => a -> b -> b -> b
312 instance Foo c => Foo [c] where
315 When typechecking the binding 'op = e', we'll have a meth_id for op
317 op :: forall c. Foo c => forall b. Ord b => [c] -> b -> b -> b
319 So tcPolyBinds must be capable of dealing with nested polytypes;
320 and so it is. See TcBinds.tcMonoBinds (with type-sig case).
322 Note [Silly default-method bind]
323 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
324 When we pass the default method binding to the type checker, it must
327 otherwise the "$dm" stuff comes out error messages. But we want the
328 "$dm" to come out in the interface file. So we typecheck the former,
329 and wrap it in a let, thus
330 $dmop2 = let op2 = e in op2
331 This makes the error messages right.
334 %************************************************************************
336 Extracting generic instance declaration from class declarations
338 %************************************************************************
340 @getGenericInstances@ extracts the generic instance declarations from a class
341 declaration. For exmaple
346 op{ x+y } (Inl v) = ...
347 op{ x+y } (Inr v) = ...
348 op{ x*y } (v :*: w) = ...
351 gives rise to the instance declarations
353 instance C (x+y) where
357 instance C (x*y) where
364 mkGenericDefMethBind :: Class -> [Type] -> Id -> TcM (LHsBind Name)
365 mkGenericDefMethBind clas inst_tys sel_id
366 = -- A generic default method
367 -- If the method is defined generically, we can only do the job if the
368 -- instance declaration is for a single-parameter type class with
369 -- a type constructor applied to type arguments in the instance decl
370 -- (checkTc, so False provokes the error)
371 do { checkTc (isJust maybe_tycon)
372 (badGenericInstance sel_id (notSimple inst_tys))
373 ; checkTc (tyConHasGenerics tycon)
374 (badGenericInstance sel_id (notGeneric tycon))
377 ; liftIO (dumpIfSet_dyn dflags Opt_D_dump_deriv "Filling in method body"
378 (vcat [ppr clas <+> ppr inst_tys,
379 nest 2 (ppr sel_id <+> equals <+> ppr rhs)]))
381 -- Rename it before returning it
382 ; (rn_rhs, _) <- rnLExpr rhs
383 ; return (noLoc $ mkFunBind (noLoc (idName sel_id))
384 [mkSimpleMatch [] rn_rhs]) }
386 rhs = mkGenericRhs sel_id clas_tyvar tycon
388 -- The tycon is only used in the generic case, and in that
389 -- case we require that the instance decl is for a single-parameter
390 -- type class with type variable arguments:
391 -- instance (...) => C (T a b)
392 clas_tyvar = ASSERT (not (null (classTyVars clas))) head (classTyVars clas)
393 Just tycon = maybe_tycon
394 maybe_tycon = case inst_tys of
395 [ty] -> case tcSplitTyConApp_maybe ty of
396 Just (tycon, arg_tys) | all tcIsTyVarTy arg_tys -> Just tycon
401 ---------------------------
402 getGenericInstances :: [LTyClDecl Name] -> TcM [InstInfo Name]
403 getGenericInstances class_decls
404 = do { gen_inst_infos <- mapM (addLocM get_generics) class_decls
405 ; let { gen_inst_info = concat gen_inst_infos }
407 -- Return right away if there is no generic stuff
408 ; if null gen_inst_info then return []
411 -- Otherwise print it out
412 { dumpDerivingInfo $ hang (ptext (sLit "Generic instances"))
413 2 (vcat (map pprInstInfoDetails gen_inst_info))
414 ; return gen_inst_info }}
416 get_generics :: TyClDecl Name -> TcM [InstInfo Name]
417 get_generics decl@(ClassDecl {tcdLName = class_name, tcdMeths = def_methods})
419 = return [] -- The comon case: no generic default methods
421 | otherwise -- A source class decl with generic default methods
422 = recoverM (return []) $
423 tcAddDeclCtxt decl $ do
424 clas <- tcLookupLocatedClass class_name
426 -- Group by type, and
427 -- make an InstInfo out of each group
429 groups = groupWith listToBag generic_binds
431 inst_infos <- mapM (mkGenericInstance clas) groups
433 -- Check that there is only one InstInfo for each type constructor
434 -- The main way this can fail is if you write
435 -- f {| a+b |} ... = ...
436 -- f {| x+y |} ... = ...
437 -- Then at this point we'll have an InstInfo for each
439 -- The class should be unary, which is why simpleInstInfoTyCon should be ok
441 tc_inst_infos :: [(TyCon, InstInfo Name)]
442 tc_inst_infos = [(simpleInstInfoTyCon i, i) | i <- inst_infos]
444 bad_groups = [group | group <- equivClassesByUniq get_uniq tc_inst_infos,
445 group `lengthExceeds` 1]
446 get_uniq (tc,_) = getUnique tc
448 mapM_ (addErrTc . dupGenericInsts) bad_groups
450 -- Check that there is an InstInfo for each generic type constructor
452 missing = genericTyConNames `minusList` [tyConName tc | (tc,_) <- tc_inst_infos]
454 checkTc (null missing) (missingGenericInstances missing)
458 generic_binds :: [(HsType Name, LHsBind Name)]
459 generic_binds = getGenericBinds def_methods
460 get_generics decl = pprPanic "get_generics" (ppr decl)
463 ---------------------------------
464 getGenericBinds :: LHsBinds Name -> [(HsType Name, LHsBind Name)]
465 -- Takes a group of method bindings, finds the generic ones, and returns
466 -- them in finite map indexed by the type parameter in the definition.
467 getGenericBinds binds = concat (map getGenericBind (bagToList binds))
469 getGenericBind :: LHsBindLR Name Name -> [(HsType Name, LHsBindLR Name Name)]
470 getGenericBind (L loc bind@(FunBind { fun_matches = MatchGroup matches ty }))
471 = groupWith wrap (mapCatMaybes maybeGenericMatch matches)
473 wrap ms = L loc (bind { fun_matches = MatchGroup ms ty })
477 groupWith :: ([a] -> b) -> [(HsType Name, a)] -> [(HsType Name, b)]
479 groupWith op ((t,v):prs) = (t, op (v:vs)) : groupWith op rest
482 (this,rest) = partition same_t prs
483 same_t (t', _v) = t `eqPatType` t'
485 eqPatLType :: LHsType Name -> LHsType Name -> Bool
486 eqPatLType t1 t2 = unLoc t1 `eqPatType` unLoc t2
488 eqPatType :: HsType Name -> HsType Name -> Bool
489 -- A very simple equality function, only for
490 -- type patterns in generic function definitions.
491 eqPatType (HsTyVar v1) (HsTyVar v2) = v1==v2
492 eqPatType (HsAppTy s1 t1) (HsAppTy s2 t2) = s1 `eqPatLType` s2 && t1 `eqPatLType` t2
493 eqPatType (HsOpTy s1 op1 t1) (HsOpTy s2 op2 t2) = s1 `eqPatLType` s2 && t1 `eqPatLType` t2 && unLoc op1 == unLoc op2
494 eqPatType (HsNumTy n1) (HsNumTy n2) = n1 == n2
495 eqPatType (HsParTy t1) t2 = unLoc t1 `eqPatType` t2
496 eqPatType t1 (HsParTy t2) = t1 `eqPatType` unLoc t2
497 eqPatType _ _ = False
499 ---------------------------------
500 mkGenericInstance :: Class
501 -> (HsType Name, LHsBinds Name)
502 -> TcM (InstInfo Name)
504 mkGenericInstance clas (hs_ty, binds) = do
505 -- Make a generic instance declaration
506 -- For example: instance (C a, C b) => C (a+b) where { binds }
508 -- Extract the universally quantified type variables
509 -- and wrap them as forall'd tyvars, so that kind inference
510 -- works in the standard way
512 sig_tvs = userHsTyVarBndrs $ map noLoc $ nameSetToList $
513 extractHsTyVars (noLoc hs_ty)
514 hs_forall_ty = noLoc $ mkExplicitHsForAllTy sig_tvs (noLoc []) (noLoc hs_ty)
516 -- Type-check the instance type, and check its form
517 forall_inst_ty <- tcHsSigType GenPatCtxt hs_forall_ty
519 (tyvars, inst_ty) = tcSplitForAllTys forall_inst_ty
521 checkTc (validGenericInstanceType inst_ty)
522 (badGenericInstanceType binds)
524 -- Make the dictionary function.
526 overlap_flag <- getOverlapFlag
527 dfun_name <- newDFunName clas [inst_ty] span
529 inst_theta = [mkClassPred clas [mkTyVarTy tv] | tv <- tyvars]
530 dfun_id = mkDictFunId dfun_name tyvars inst_theta clas [inst_ty]
531 ispec = mkLocalInstance dfun_id overlap_flag
533 return (InstInfo { iSpec = ispec, iBinds = VanillaInst binds [] False })
537 %************************************************************************
541 %************************************************************************
544 tcAddDeclCtxt :: TyClDecl Name -> TcM a -> TcM a
545 tcAddDeclCtxt decl thing_inside
546 = addErrCtxt ctxt thing_inside
548 thing | isClassDecl decl = "class"
549 | isTypeDecl decl = "type synonym" ++ maybeInst
550 | isDataDecl decl = if tcdND decl == NewType
551 then "newtype" ++ maybeInst
552 else "data type" ++ maybeInst
553 | isFamilyDecl decl = "family"
554 | otherwise = panic "tcAddDeclCtxt/thing"
556 maybeInst | isFamInstDecl decl = " instance"
559 ctxt = hsep [ptext (sLit "In the"), text thing,
560 ptext (sLit "declaration for"), quotes (ppr (tcdName decl))]
562 badMethodErr :: Outputable a => a -> Name -> SDoc
564 = hsep [ptext (sLit "Class"), quotes (ppr clas),
565 ptext (sLit "does not have a method"), quotes (ppr op)]
567 badGenericMethod :: Outputable a => a -> Name -> SDoc
568 badGenericMethod clas op
569 = hsep [ptext (sLit "Class"), quotes (ppr clas),
570 ptext (sLit "has a generic-default signature without a binding"), quotes (ppr op)]
572 badATErr :: Class -> Name -> SDoc
574 = hsep [ptext (sLit "Class"), quotes (ppr clas),
575 ptext (sLit "does not have an associated type"), quotes (ppr at)]
577 omittedATWarn :: Name -> SDoc
579 = ptext (sLit "No explicit AT declaration for") <+> quotes (ppr at)
581 badGenericInstance :: Var -> SDoc -> SDoc
582 badGenericInstance sel_id because
583 = sep [ptext (sLit "Can't derive generic code for") <+> quotes (ppr sel_id),
586 notSimple :: [Type] -> SDoc
588 = vcat [ptext (sLit "because the instance type(s)"),
589 nest 2 (ppr inst_tys),
590 ptext (sLit "is not a simple type of form (T a1 ... an)")]
592 notGeneric :: TyCon -> SDoc
594 = vcat [ptext (sLit "because the instance type constructor") <+> quotes (ppr tycon) <+>
595 ptext (sLit "was not compiled with -XGenerics")]
597 badGenericInstanceType :: LHsBinds Name -> SDoc
598 badGenericInstanceType binds
599 = vcat [ptext (sLit "Illegal type pattern in the generic bindings"),
602 missingGenericInstances :: [Name] -> SDoc
603 missingGenericInstances missing
604 = ptext (sLit "Missing type patterns for") <+> pprQuotedList missing
606 dupGenericInsts :: [(TyCon, InstInfo a)] -> SDoc
607 dupGenericInsts tc_inst_infos
608 = vcat [ptext (sLit "More than one type pattern for a single generic type constructor:"),
609 nest 2 (vcat (map ppr_inst_ty tc_inst_infos)),
610 ptext (sLit "All the type patterns for a generic type constructor must be identical")
613 ppr_inst_ty (_,inst) = ppr (simpleInstInfoTy inst)
615 mixedGenericErr :: Name -> SDoc
617 = ptext (sLit "Can't mix generic and non-generic equations for class method") <+> quotes (ppr op)