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
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 prag_fn = mkPragFun sigs default_binds
172 sig_fn = mkSigFun sigs
173 clas_tyvars = tcSuperSkolTyVars tyvars
174 pred = mkClassPred clas (mkTyVarTys clas_tyvars)
175 ; this_dict <- newEvVar pred
177 ; let tc_dm = tcDefMeth clas clas_tyvars
178 this_dict default_binds
181 ; dm_binds <- tcExtendTyVarEnv clas_tyvars $
184 ; return (listToBag (catMaybes dm_binds)) }
186 tcClassDecl2 d = pprPanic "tcClassDecl2" (ppr d)
188 tcDefMeth :: Class -> [TyVar] -> EvVar -> LHsBinds Name
189 -> SigFun -> PragFun -> ClassOpItem
190 -> TcM (Maybe (LHsBind Id))
191 -- Generate code for polymorphic default methods only (hence DefMeth)
192 -- (Generic default methods have turned into instance decls by now.)
193 -- This is incompatible with Hugs, which expects a polymorphic
194 -- default method for every class op, regardless of whether or not
195 -- the programmer supplied an explicit default decl for the class.
196 -- (If necessary we can fix that, but we don't have a convenient Id to hand.)
197 tcDefMeth clas tyvars this_dict binds_in sig_fn prag_fn (sel_id, dm_info)
199 NoDefMeth -> return Nothing
200 GenDefMeth -> return Nothing
201 DefMeth dm_name -> do
202 { let sel_name = idName sel_id
203 ; local_dm_name <- newLocalName sel_name
204 -- Base the local_dm_name on the selector name, because
205 -- type errors from tcInstanceMethodBody come from here
207 -- See Note [Silly default-method bind]
208 -- (possibly out of date)
210 ; let meth_bind = findMethodBind sel_name binds_in
211 `orElse` pprPanic "tcDefMeth" (ppr sel_id)
212 -- dm_info = DefMeth dm_name only if there is a binding in binds_in
214 dm_sig_fn _ = sig_fn sel_name
215 dm_id = mkDefaultMethodId sel_id dm_name
216 local_dm_type = instantiateMethod clas sel_id (mkTyVarTys tyvars)
217 local_dm_id = mkLocalId local_dm_name local_dm_type
218 prags = prag_fn sel_name
220 ; dm_id_w_inline <- addInlinePrags dm_id prags
221 ; spec_prags <- tcSpecPrags dm_id prags
223 ; warnTc (not (null spec_prags))
224 (ptext (sLit "Ignoring SPECIALISE pragmas on default method")
225 <+> quotes (ppr sel_name))
228 tcInstanceMethodBody (ClsSkol clas)
231 dm_id_w_inline local_dm_id
232 dm_sig_fn IsDefaultMethod meth_bind }
235 tcInstanceMethodBody :: SkolemInfo -> [TcTyVar] -> [EvVar]
237 -> SigFun -> TcSpecPrags -> LHsBind Name
239 tcInstanceMethodBody skol_info tyvars dfun_ev_vars
240 meth_id local_meth_id
243 = do { -- Typecheck the binding, first extending the envt
244 -- so that when tcInstSig looks up the local_meth_id to find
245 -- its signature, we'll find it in the environment
246 let lm_bind = L loc (bind { fun_id = L loc (idName local_meth_id) })
247 -- Substitute the local_meth_name for the binder
248 -- NB: the binding is always a FunBind
250 ; (ev_binds, (tc_bind, _))
251 <- checkConstraints skol_info tyvars dfun_ev_vars $
252 tcExtendIdEnv [local_meth_id] $
253 tcPolyBinds TopLevel meth_sig_fn no_prag_fn
254 NonRecursive NonRecursive
257 ; let full_bind = AbsBinds { abs_tvs = tyvars, abs_ev_vars = dfun_ev_vars
258 , abs_exports = [(tyvars, meth_id, local_meth_id, specs)]
259 , abs_ev_binds = ev_binds
260 , abs_binds = tc_bind }
262 ; return (L loc full_bind) }
264 no_prag_fn _ = [] -- No pragmas for local_meth_id;
265 -- they are all for meth_id
269 instantiateMethod :: Class -> Id -> [TcType] -> TcType
270 -- Take a class operation, say
271 -- op :: forall ab. C a => forall c. Ix c => (b,c) -> a
272 -- Instantiate it at [ty1,ty2]
273 -- Return the "local method type":
274 -- forall c. Ix x => (ty2,c) -> ty1
275 instantiateMethod clas sel_id inst_tys
276 = ASSERT( ok_first_pred ) local_meth_ty
278 (sel_tyvars,sel_rho) = tcSplitForAllTys (idType sel_id)
279 rho_ty = ASSERT( length sel_tyvars == length inst_tys )
280 substTyWith sel_tyvars inst_tys sel_rho
282 (first_pred, local_meth_ty) = tcSplitPredFunTy_maybe rho_ty
283 `orElse` pprPanic "tcInstanceMethod" (ppr sel_id)
285 ok_first_pred = case getClassPredTys_maybe first_pred of
286 Just (clas1, _tys) -> clas == clas1
288 -- The first predicate should be of form (C a b)
289 -- where C is the class in question
292 ---------------------------
293 findMethodBind :: Name -- Selector name
294 -> LHsBinds Name -- A group of bindings
295 -> Maybe (LHsBind Name) -- The binding
296 findMethodBind sel_name binds
297 = foldlBag mplus Nothing (mapBag f binds)
299 f bind@(L _ (FunBind { fun_id = L _ op_name }))
300 | op_name == sel_name
305 Note [Polymorphic methods]
306 ~~~~~~~~~~~~~~~~~~~~~~~~~~
309 op :: forall b. Ord b => a -> b -> b -> b
310 instance Foo c => Foo [c] where
313 When typechecking the binding 'op = e', we'll have a meth_id for op
315 op :: forall c. Foo c => forall b. Ord b => [c] -> b -> b -> b
317 So tcPolyBinds must be capable of dealing with nested polytypes;
318 and so it is. See TcBinds.tcMonoBinds (with type-sig case).
320 Note [Silly default-method bind]
321 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
322 When we pass the default method binding to the type checker, it must
325 otherwise the "$dm" stuff comes out error messages. But we want the
326 "$dm" to come out in the interface file. So we typecheck the former,
327 and wrap it in a let, thus
328 $dmop2 = let op2 = e in op2
329 This makes the error messages right.
332 %************************************************************************
334 Extracting generic instance declaration from class declarations
336 %************************************************************************
338 @getGenericInstances@ extracts the generic instance declarations from a class
339 declaration. For exmaple
344 op{ x+y } (Inl v) = ...
345 op{ x+y } (Inr v) = ...
346 op{ x*y } (v :*: w) = ...
349 gives rise to the instance declarations
351 instance C (x+y) where
355 instance C (x*y) where
362 mkGenericDefMethBind :: Class -> [Type] -> Id -> TcM (LHsBind Name)
363 mkGenericDefMethBind clas inst_tys sel_id
364 = -- A generic default method
365 -- If the method is defined generically, we can only do the job if the
366 -- instance declaration is for a single-parameter type class with
367 -- a type constructor applied to type arguments in the instance decl
368 -- (checkTc, so False provokes the error)
369 do { checkTc (isJust maybe_tycon)
370 (badGenericInstance sel_id (notSimple inst_tys))
371 ; checkTc (tyConHasGenerics tycon)
372 (badGenericInstance sel_id (notGeneric tycon))
375 ; liftIO (dumpIfSet_dyn dflags Opt_D_dump_deriv "Filling in method body"
376 (vcat [ppr clas <+> ppr inst_tys,
377 nest 2 (ppr sel_id <+> equals <+> ppr rhs)]))
379 -- Rename it before returning it
380 ; (rn_rhs, _) <- rnLExpr rhs
381 ; return (noLoc $ mkFunBind (noLoc (idName sel_id))
382 [mkSimpleMatch [] rn_rhs]) }
384 rhs = mkGenericRhs sel_id clas_tyvar tycon
386 -- The tycon is only used in the generic case, and in that
387 -- case we require that the instance decl is for a single-parameter
388 -- type class with type variable arguments:
389 -- instance (...) => C (T a b)
390 clas_tyvar = ASSERT (not (null (classTyVars clas))) head (classTyVars clas)
391 Just tycon = maybe_tycon
392 maybe_tycon = case inst_tys of
393 [ty] -> case tcSplitTyConApp_maybe ty of
394 Just (tycon, arg_tys) | all tcIsTyVarTy arg_tys -> Just tycon
399 ---------------------------
400 getGenericInstances :: [LTyClDecl Name] -> TcM [InstInfo Name]
401 getGenericInstances class_decls
402 = do { gen_inst_infos <- mapM (addLocM get_generics) class_decls
403 ; let { gen_inst_info = concat gen_inst_infos }
405 -- Return right away if there is no generic stuff
406 ; if null gen_inst_info then return []
409 -- Otherwise print it out
410 { dumpDerivingInfo $ hang (ptext (sLit "Generic instances"))
411 2 (vcat (map pprInstInfoDetails gen_inst_info))
412 ; return gen_inst_info }}
414 get_generics :: TyClDecl Name -> TcM [InstInfo Name]
415 get_generics decl@(ClassDecl {tcdLName = class_name, tcdMeths = def_methods})
417 = return [] -- The comon case: no generic default methods
419 | otherwise -- A source class decl with generic default methods
420 = recoverM (return []) $
421 tcAddDeclCtxt decl $ do
422 clas <- tcLookupLocatedClass class_name
424 -- Group by type, and
425 -- make an InstInfo out of each group
427 groups = groupWith listToBag generic_binds
429 inst_infos <- mapM (mkGenericInstance clas) groups
431 -- Check that there is only one InstInfo for each type constructor
432 -- The main way this can fail is if you write
433 -- f {| a+b |} ... = ...
434 -- f {| x+y |} ... = ...
435 -- Then at this point we'll have an InstInfo for each
437 -- The class should be unary, which is why simpleInstInfoTyCon should be ok
439 tc_inst_infos :: [(TyCon, InstInfo Name)]
440 tc_inst_infos = [(simpleInstInfoTyCon i, i) | i <- inst_infos]
442 bad_groups = [group | group <- equivClassesByUniq get_uniq tc_inst_infos,
443 group `lengthExceeds` 1]
444 get_uniq (tc,_) = getUnique tc
446 mapM_ (addErrTc . dupGenericInsts) bad_groups
448 -- Check that there is an InstInfo for each generic type constructor
450 missing = genericTyConNames `minusList` [tyConName tc | (tc,_) <- tc_inst_infos]
452 checkTc (null missing) (missingGenericInstances missing)
456 generic_binds :: [(HsType Name, LHsBind Name)]
457 generic_binds = getGenericBinds def_methods
458 get_generics decl = pprPanic "get_generics" (ppr decl)
461 ---------------------------------
462 getGenericBinds :: LHsBinds Name -> [(HsType Name, LHsBind Name)]
463 -- Takes a group of method bindings, finds the generic ones, and returns
464 -- them in finite map indexed by the type parameter in the definition.
465 getGenericBinds binds = concat (map getGenericBind (bagToList binds))
467 getGenericBind :: LHsBindLR Name Name -> [(HsType Name, LHsBindLR Name Name)]
468 getGenericBind (L loc bind@(FunBind { fun_matches = MatchGroup matches ty }))
469 = groupWith wrap (mapCatMaybes maybeGenericMatch matches)
471 wrap ms = L loc (bind { fun_matches = MatchGroup ms ty })
475 groupWith :: ([a] -> b) -> [(HsType Name, a)] -> [(HsType Name, b)]
477 groupWith op ((t,v):prs) = (t, op (v:vs)) : groupWith op rest
480 (this,rest) = partition same_t prs
481 same_t (t', _v) = t `eqPatType` t'
483 eqPatLType :: LHsType Name -> LHsType Name -> Bool
484 eqPatLType t1 t2 = unLoc t1 `eqPatType` unLoc t2
486 eqPatType :: HsType Name -> HsType Name -> Bool
487 -- A very simple equality function, only for
488 -- type patterns in generic function definitions.
489 eqPatType (HsTyVar v1) (HsTyVar v2) = v1==v2
490 eqPatType (HsAppTy s1 t1) (HsAppTy s2 t2) = s1 `eqPatLType` s2 && t1 `eqPatLType` t2
491 eqPatType (HsOpTy s1 op1 t1) (HsOpTy s2 op2 t2) = s1 `eqPatLType` s2 && t1 `eqPatLType` t2 && unLoc op1 == unLoc op2
492 eqPatType (HsNumTy n1) (HsNumTy n2) = n1 == n2
493 eqPatType (HsParTy t1) t2 = unLoc t1 `eqPatType` t2
494 eqPatType t1 (HsParTy t2) = t1 `eqPatType` unLoc t2
495 eqPatType _ _ = False
497 ---------------------------------
498 mkGenericInstance :: Class
499 -> (HsType Name, LHsBinds Name)
500 -> TcM (InstInfo Name)
502 mkGenericInstance clas (hs_ty, binds) = do
503 -- Make a generic instance declaration
504 -- For example: instance (C a, C b) => C (a+b) where { binds }
506 -- Extract the universally quantified type variables
507 -- and wrap them as forall'd tyvars, so that kind inference
508 -- works in the standard way
510 sig_tvs = userHsTyVarBndrs $ map noLoc $ nameSetToList $
511 extractHsTyVars (noLoc hs_ty)
512 hs_forall_ty = noLoc $ mkExplicitHsForAllTy sig_tvs (noLoc []) (noLoc hs_ty)
514 -- Type-check the instance type, and check its form
515 forall_inst_ty <- tcHsSigType GenPatCtxt hs_forall_ty
517 (tyvars, inst_ty) = tcSplitForAllTys forall_inst_ty
519 checkTc (validGenericInstanceType inst_ty)
520 (badGenericInstanceType binds)
522 -- Make the dictionary function.
524 overlap_flag <- getOverlapFlag
525 dfun_name <- newDFunName clas [inst_ty] span
527 inst_theta = [mkClassPred clas [mkTyVarTy tv] | tv <- tyvars]
528 dfun_id = mkDictFunId dfun_name tyvars inst_theta clas [inst_ty]
529 ispec = mkLocalInstance dfun_id overlap_flag
531 return (InstInfo { iSpec = ispec, iBinds = VanillaInst binds [] False })
535 %************************************************************************
539 %************************************************************************
542 tcAddDeclCtxt :: TyClDecl Name -> TcM a -> TcM a
543 tcAddDeclCtxt decl thing_inside
544 = addErrCtxt ctxt thing_inside
546 thing | isClassDecl decl = "class"
547 | isTypeDecl decl = "type synonym" ++ maybeInst
548 | isDataDecl decl = if tcdND decl == NewType
549 then "newtype" ++ maybeInst
550 else "data type" ++ maybeInst
551 | isFamilyDecl decl = "family"
552 | otherwise = panic "tcAddDeclCtxt/thing"
554 maybeInst | isFamInstDecl decl = " instance"
557 ctxt = hsep [ptext (sLit "In the"), text thing,
558 ptext (sLit "declaration for"), quotes (ppr (tcdName decl))]
560 badMethodErr :: Outputable a => a -> Name -> SDoc
562 = hsep [ptext (sLit "Class"), quotes (ppr clas),
563 ptext (sLit "does not have a method"), quotes (ppr op)]
565 badATErr :: Class -> Name -> SDoc
567 = hsep [ptext (sLit "Class"), quotes (ppr clas),
568 ptext (sLit "does not have an associated type"), quotes (ppr at)]
570 omittedATWarn :: Name -> SDoc
572 = ptext (sLit "No explicit AT declaration for") <+> quotes (ppr at)
574 badGenericInstance :: Var -> SDoc -> SDoc
575 badGenericInstance sel_id because
576 = sep [ptext (sLit "Can't derive generic code for") <+> quotes (ppr sel_id),
579 notSimple :: [Type] -> SDoc
581 = vcat [ptext (sLit "because the instance type(s)"),
582 nest 2 (ppr inst_tys),
583 ptext (sLit "is not a simple type of form (T a1 ... an)")]
585 notGeneric :: TyCon -> SDoc
587 = vcat [ptext (sLit "because the instance type constructor") <+> quotes (ppr tycon) <+>
588 ptext (sLit "was not compiled with -XGenerics")]
590 badGenericInstanceType :: LHsBinds Name -> SDoc
591 badGenericInstanceType binds
592 = vcat [ptext (sLit "Illegal type pattern in the generic bindings"),
595 missingGenericInstances :: [Name] -> SDoc
596 missingGenericInstances missing
597 = ptext (sLit "Missing type patterns for") <+> pprQuotedList missing
599 dupGenericInsts :: [(TyCon, InstInfo a)] -> SDoc
600 dupGenericInsts tc_inst_infos
601 = vcat [ptext (sLit "More than one type pattern for a single generic type constructor:"),
602 nest 2 (vcat (map ppr_inst_ty tc_inst_infos)),
603 ptext (sLit "All the type patterns for a generic type constructor must be identical")
606 ppr_inst_ty (_,inst) = ppr (simpleInstInfoTy inst)
608 mixedGenericErr :: Name -> SDoc
610 = ptext (sLit "Can't mix generic and non-generic equations for class method") <+> quotes (ppr op)