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 )
58 Every class implicitly declares a new data type, corresponding to dictionaries
59 of that class. So, for example:
61 class (D a) => C a where
63 op2 :: forall b. Ord b => a -> b -> b
65 would implicitly declare
67 data CDict a = CDict (D a)
69 (forall b. Ord b => a -> b -> b)
71 (We could use a record decl, but that means changing more of the existing apparatus.
74 For classes with just one superclass+method, we use a newtype decl instead:
77 op :: forallb. a -> b -> b
81 newtype CDict a = CDict (forall b. a -> b -> b)
83 Now DictTy in Type is just a form of type synomym:
84 DictTy c t = TyConTy CDict `AppTy` t
86 Death to "ExpandingDicts".
89 %************************************************************************
91 Type-checking the class op signatures
93 %************************************************************************
96 tcClassSigs :: Name -- Name of the class
101 tcClassSigs clas sigs def_methods
102 = do { dm_env <- mapM (addLocM (checkDefaultBind clas op_names))
103 (bagToList def_methods)
104 ; mapM (tcClassSig (mkNameEnv dm_env)) op_sigs }
106 op_sigs = [sig | sig@(L _ (TypeSig _ _)) <- sigs]
107 op_names = [n | (L _ (TypeSig (L _ n) _)) <- op_sigs]
109 checkDefaultBind :: Name -> [Name] -> HsBindLR Name Name -> TcM (Name, DefMethSpec)
110 -- Check default bindings
111 -- a) must be for a class op for this class
112 -- b) must be all generic or all non-generic
113 checkDefaultBind clas ops (FunBind {fun_id = L _ op, fun_matches = MatchGroup matches _ })
114 = do { -- Check that the op is from this class
115 checkTc (op `elem` ops) (badMethodErr clas op)
117 -- Check that all the defns ar generic, or none are
118 ; case (none_generic, all_generic) of
119 (True, _) -> return (op, VanillaDM)
120 (_, True) -> return (op, GenericDM)
121 _ -> failWith (mixedGenericErr op)
124 n_generic = count (isJust . maybeGenericMatch) matches
125 none_generic = n_generic == 0
126 all_generic = matches `lengthIs` n_generic
128 checkDefaultBind _ _ b = pprPanic "checkDefaultBind" (ppr b)
131 tcClassSig :: NameEnv DefMethSpec -- Info about default methods;
135 tcClassSig dm_env (L loc (TypeSig (L _ op_name) op_hs_ty))
136 = setSrcSpan loc $ do
137 { op_ty <- tcHsKindedType op_hs_ty -- Class tyvars already in scope
138 ; let dm = lookupNameEnv dm_env op_name `orElse` NoDM
139 ; return (op_name, dm, op_ty) }
140 tcClassSig _ s = pprPanic "tcClassSig" (ppr s)
144 %************************************************************************
148 %************************************************************************
151 tcClassDecl2 :: LTyClDecl Name -- The class declaration
152 -> TcM ([Id], LHsBinds Id)
154 tcClassDecl2 (L loc (ClassDecl {tcdLName = class_name, tcdSigs = sigs,
155 tcdMeths = default_binds}))
156 = recoverM (return ([], emptyLHsBinds)) $
158 do { clas <- tcLookupLocatedClass class_name
160 -- We make a separate binding for each default method.
161 -- At one time I used a single AbsBinds for all of them, thus
162 -- AbsBind [d] [dm1, dm2, dm3] { dm1 = ...; dm2 = ...; dm3 = ... }
163 -- But that desugars into
164 -- ds = \d -> (..., ..., ...)
165 -- dm1 = \d -> case ds d of (a,b,c) -> a
166 -- And since ds is big, it doesn't get inlined, so we don't get good
167 -- default methods. Better to make separate AbsBinds for each
169 (tyvars, _, _, op_items) = classBigSig clas
170 rigid_info = ClsSkol clas
171 prag_fn = mkPragFun sigs default_binds
172 sig_fn = mkTcSigFun sigs
173 clas_tyvars = tcSkolSigTyVars rigid_info tyvars
174 pred = mkClassPred clas (mkTyVarTys clas_tyvars)
175 ; inst_loc <- getInstLoc (SigOrigin rigid_info)
176 ; this_dict <- newDictBndr inst_loc pred
178 ; let tc_dm = tcDefMeth clas clas_tyvars
179 this_dict default_binds
182 ; dm_stuff <- tcExtendTyVarEnv clas_tyvars $
184 ; let (dm_ids, defm_binds) = unzip (catMaybes dm_stuff)
186 ; return (dm_ids, listToBag defm_binds) }
188 tcClassDecl2 d = pprPanic "tcClassDecl2" (ppr d)
190 tcDefMeth :: Class -> [TyVar] -> Inst -> LHsBinds Name
191 -> TcSigFun -> TcPragFun -> ClassOpItem
192 -> TcM (Maybe (Id, LHsBind Id))
193 -- Generate code for polymorphic default methods only (hence DefMeth)
194 -- (Generic default methods have turned into instance decls by now.)
195 -- This is incompatible with Hugs, which expects a polymorphic
196 -- default method for every class op, regardless of whether or not
197 -- the programmer supplied an explicit default decl for the class.
198 -- (If necessary we can fix that, but we don't have a convenient Id to hand.)
199 tcDefMeth clas tyvars this_dict binds_in sig_fn prag_fn (sel_id, dm_info)
201 NoDefMeth -> return Nothing
202 GenDefMeth -> return Nothing
203 DefMeth dm_name -> do
204 { let sel_name = idName sel_id
205 ; local_dm_name <- newLocalName sel_name
206 -- Base the local_dm_name on the selector name, because
207 -- type errors from tcInstanceMethodBody come from here
209 -- See Note [Silly default-method bind]
210 -- (possibly out of date)
212 ; let meth_bind = findMethodBind sel_name local_dm_name binds_in
213 `orElse` pprPanic "tcDefMeth" (ppr sel_id)
214 -- dm_info = DefMeth dm_name only if there is a binding in binds_in
216 dm_sig_fn _ = sig_fn sel_name
217 dm_ty = idType sel_id
218 dm_id = mkDefaultMethodId dm_name dm_ty
219 local_dm_type = instantiateMethod clas sel_id (mkTyVarTys tyvars)
220 local_dm_id = mkLocalId local_dm_name local_dm_type
222 ; (dm_id_w_inline, spec_prags)
223 <- tcPrags NonRecursive False True dm_id (prag_fn sel_name)
225 ; warnTc (not (null spec_prags))
226 (ptext (sLit "Ignoring SPECIALISE pragmas on default method")
227 <+> quotes (ppr sel_name))
230 tcInstanceMethodBody (instLoc this_dict)
233 dm_id_w_inline local_dm_id
234 dm_sig_fn IsDefaultMethod meth_bind }
237 tcInstanceMethodBody :: InstLoc -> [TcTyVar] -> [Inst]
238 -> ([Inst], LHsBinds Id) -> Id -> Id
239 -> TcSigFun -> TcSpecPrags -> LHsBind Name
240 -> TcM (Id, LHsBind Id)
241 tcInstanceMethodBody inst_loc tyvars dfun_dicts
242 (this_dict, this_bind) meth_id local_meth_id
243 meth_sig_fn spec_prags bind@(L loc _)
244 = do { -- Typecheck the binding, first extending the envt
245 -- so that when tcInstSig looks up the local_meth_id to find
246 -- its signature, we'll find it in the environment
247 ; ((tc_bind, _), lie) <- getLIE $
248 tcExtendIdEnv [local_meth_id] $
249 tcPolyBinds TopLevel meth_sig_fn no_prag_fn
250 NonRecursive NonRecursive
253 ; let avails = this_dict ++ dfun_dicts
254 -- Only need the this_dict stuff if there are type
255 -- variables involved; otherwise overlap is not possible
256 -- See Note [Subtle interaction of recursion and overlap]
258 ; lie_binds <- tcSimplifyCheck inst_loc tyvars avails lie
260 ; let full_bind = AbsBinds tyvars dfun_lam_vars
261 [(tyvars, meth_id, local_meth_id, spec_prags)]
262 (this_bind `unionBags` lie_binds
265 dfun_lam_vars = map instToVar dfun_dicts -- Includes equalities
267 ; return (meth_id, L loc full_bind) }
269 no_prag_fn _ = [] -- No pragmas for local_meth_id;
270 -- they are all for meth_id
274 instantiateMethod :: Class -> Id -> [TcType] -> TcType
275 -- Take a class operation, say
276 -- op :: forall ab. C a => forall c. Ix c => (b,c) -> a
277 -- Instantiate it at [ty1,ty2]
278 -- Return the "local method type":
279 -- forall c. Ix x => (ty2,c) -> ty1
280 instantiateMethod clas sel_id inst_tys
281 = ASSERT( ok_first_pred ) local_meth_ty
283 (sel_tyvars,sel_rho) = tcSplitForAllTys (idType sel_id)
284 rho_ty = ASSERT( length sel_tyvars == length inst_tys )
285 substTyWith sel_tyvars inst_tys sel_rho
287 (first_pred, local_meth_ty) = tcSplitPredFunTy_maybe rho_ty
288 `orElse` pprPanic "tcInstanceMethod" (ppr sel_id)
290 ok_first_pred = case getClassPredTys_maybe first_pred of
291 Just (clas1, _tys) -> clas == clas1
293 -- The first predicate should be of form (C a b)
294 -- where C is the class in question
297 ---------------------------
298 -- The renamer just puts the selector ID as the binder in the method binding
299 -- but we must use the method name; so we substitute it here. Crude but simple.
300 findMethodBind :: Name -> Name -- Selector and method name
301 -> LHsBinds Name -- A group of bindings
302 -> Maybe (LHsBind Name) -- The binding, with meth_name replacing sel_name
303 findMethodBind sel_name meth_name binds
304 = foldlBag mplus Nothing (mapBag f binds)
306 f (L loc1 bind@(FunBind { fun_id = L loc2 op_name }))
307 | op_name == sel_name
308 = Just (L loc1 (bind { fun_id = L loc2 meth_name }))
312 Note [Polymorphic methods]
313 ~~~~~~~~~~~~~~~~~~~~~~~~~~
316 op :: forall b. Ord b => a -> b -> b -> b
317 instance Foo c => Foo [c] where
320 When typechecking the binding 'op = e', we'll have a meth_id for op
322 op :: forall c. Foo c => forall b. Ord b => [c] -> b -> b -> b
324 So tcPolyBinds must be capable of dealing with nested polytypes;
325 and so it is. See TcBinds.tcMonoBinds (with type-sig case).
327 Note [Silly default-method bind]
328 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
329 When we pass the default method binding to the type checker, it must
332 otherwise the "$dm" stuff comes out error messages. But we want the
333 "$dm" to come out in the interface file. So we typecheck the former,
334 and wrap it in a let, thus
335 $dmop2 = let op2 = e in op2
336 This makes the error messages right.
339 %************************************************************************
341 Extracting generic instance declaration from class declarations
343 %************************************************************************
345 @getGenericInstances@ extracts the generic instance declarations from a class
346 declaration. For exmaple
351 op{ x+y } (Inl v) = ...
352 op{ x+y } (Inr v) = ...
353 op{ x*y } (v :*: w) = ...
356 gives rise to the instance declarations
358 instance C (x+y) where
362 instance C (x*y) where
369 mkGenericDefMethBind :: Class -> [Type] -> Id -> Name -> TcM (LHsBind Name)
370 mkGenericDefMethBind clas inst_tys sel_id meth_name
371 = -- A generic default method
372 -- If the method is defined generically, we can only do the job if the
373 -- instance declaration is for a single-parameter type class with
374 -- a type constructor applied to type arguments in the instance decl
375 -- (checkTc, so False provokes the error)
376 do { checkTc (isJust maybe_tycon)
377 (badGenericInstance sel_id (notSimple inst_tys))
378 ; checkTc (tyConHasGenerics tycon)
379 (badGenericInstance sel_id (notGeneric tycon))
382 ; liftIO (dumpIfSet_dyn dflags Opt_D_dump_deriv "Filling in method body"
383 (vcat [ppr clas <+> ppr inst_tys,
384 nest 2 (ppr sel_id <+> equals <+> ppr rhs)]))
386 -- Rename it before returning it
387 ; (rn_rhs, _) <- rnLExpr rhs
388 ; return (noLoc $ mkFunBind (noLoc meth_name) [mkSimpleMatch [] rn_rhs]) }
390 rhs = mkGenericRhs sel_id clas_tyvar tycon
392 -- The tycon is only used in the generic case, and in that
393 -- case we require that the instance decl is for a single-parameter
394 -- type class with type variable arguments:
395 -- instance (...) => C (T a b)
396 clas_tyvar = ASSERT (not (null (classTyVars clas))) head (classTyVars clas)
397 Just tycon = maybe_tycon
398 maybe_tycon = case inst_tys of
399 [ty] -> case tcSplitTyConApp_maybe ty of
400 Just (tycon, arg_tys) | all tcIsTyVarTy arg_tys -> Just tycon
405 ---------------------------
406 getGenericInstances :: [LTyClDecl Name] -> TcM [InstInfo Name]
407 getGenericInstances class_decls
408 = do { gen_inst_infos <- mapM (addLocM get_generics) class_decls
409 ; let { gen_inst_info = concat gen_inst_infos }
411 -- Return right away if there is no generic stuff
412 ; if null gen_inst_info then return []
415 -- Otherwise print it out
417 ; liftIO (dumpIfSet_dyn dflags Opt_D_dump_deriv "Generic instances"
418 (vcat (map pprInstInfoDetails gen_inst_info)))
419 ; return gen_inst_info }}
421 get_generics :: TyClDecl Name -> TcM [InstInfo Name]
422 get_generics decl@(ClassDecl {tcdLName = class_name, tcdMeths = def_methods})
424 = return [] -- The comon case: no generic default methods
426 | otherwise -- A source class decl with generic default methods
427 = recoverM (return []) $
428 tcAddDeclCtxt decl $ do
429 clas <- tcLookupLocatedClass class_name
431 -- Group by type, and
432 -- make an InstInfo out of each group
434 groups = groupWith listToBag generic_binds
436 inst_infos <- mapM (mkGenericInstance clas) groups
438 -- Check that there is only one InstInfo for each type constructor
439 -- The main way this can fail is if you write
440 -- f {| a+b |} ... = ...
441 -- f {| x+y |} ... = ...
442 -- Then at this point we'll have an InstInfo for each
444 -- The class should be unary, which is why simpleInstInfoTyCon should be ok
446 tc_inst_infos :: [(TyCon, InstInfo Name)]
447 tc_inst_infos = [(simpleInstInfoTyCon i, i) | i <- inst_infos]
449 bad_groups = [group | group <- equivClassesByUniq get_uniq tc_inst_infos,
450 group `lengthExceeds` 1]
451 get_uniq (tc,_) = getUnique tc
453 mapM_ (addErrTc . dupGenericInsts) bad_groups
455 -- Check that there is an InstInfo for each generic type constructor
457 missing = genericTyConNames `minusList` [tyConName tc | (tc,_) <- tc_inst_infos]
459 checkTc (null missing) (missingGenericInstances missing)
463 generic_binds :: [(HsType Name, LHsBind Name)]
464 generic_binds = getGenericBinds def_methods
465 get_generics decl = pprPanic "get_generics" (ppr decl)
468 ---------------------------------
469 getGenericBinds :: LHsBinds Name -> [(HsType Name, LHsBind Name)]
470 -- Takes a group of method bindings, finds the generic ones, and returns
471 -- them in finite map indexed by the type parameter in the definition.
472 getGenericBinds binds = concat (map getGenericBind (bagToList binds))
474 getGenericBind :: LHsBindLR Name Name -> [(HsType Name, LHsBindLR Name Name)]
475 getGenericBind (L loc bind@(FunBind { fun_matches = MatchGroup matches ty }))
476 = groupWith wrap (mapCatMaybes maybeGenericMatch matches)
478 wrap ms = L loc (bind { fun_matches = MatchGroup ms ty })
482 groupWith :: ([a] -> b) -> [(HsType Name, a)] -> [(HsType Name, b)]
484 groupWith op ((t,v):prs) = (t, op (v:vs)) : groupWith op rest
487 (this,rest) = partition same_t prs
488 same_t (t', _v) = t `eqPatType` t'
490 eqPatLType :: LHsType Name -> LHsType Name -> Bool
491 eqPatLType t1 t2 = unLoc t1 `eqPatType` unLoc t2
493 eqPatType :: HsType Name -> HsType Name -> Bool
494 -- A very simple equality function, only for
495 -- type patterns in generic function definitions.
496 eqPatType (HsTyVar v1) (HsTyVar v2) = v1==v2
497 eqPatType (HsAppTy s1 t1) (HsAppTy s2 t2) = s1 `eqPatLType` s2 && t1 `eqPatLType` t2
498 eqPatType (HsOpTy s1 op1 t1) (HsOpTy s2 op2 t2) = s1 `eqPatLType` s2 && t1 `eqPatLType` t2 && unLoc op1 == unLoc op2
499 eqPatType (HsNumTy n1) (HsNumTy n2) = n1 == n2
500 eqPatType (HsParTy t1) t2 = unLoc t1 `eqPatType` t2
501 eqPatType t1 (HsParTy t2) = t1 `eqPatType` unLoc t2
502 eqPatType _ _ = False
504 ---------------------------------
505 mkGenericInstance :: Class
506 -> (HsType Name, LHsBinds Name)
507 -> TcM (InstInfo Name)
509 mkGenericInstance clas (hs_ty, binds) = do
510 -- Make a generic instance declaration
511 -- For example: instance (C a, C b) => C (a+b) where { binds }
513 -- Extract the universally quantified type variables
514 -- and wrap them as forall'd tyvars, so that kind inference
515 -- works in the standard way
517 sig_tvs = userHsTyVarBndrs $ map noLoc $ nameSetToList $
518 extractHsTyVars (noLoc hs_ty)
519 hs_forall_ty = noLoc $ mkExplicitHsForAllTy sig_tvs (noLoc []) (noLoc hs_ty)
521 -- Type-check the instance type, and check its form
522 forall_inst_ty <- tcHsSigType GenPatCtxt hs_forall_ty
524 (tyvars, inst_ty) = tcSplitForAllTys forall_inst_ty
526 checkTc (validGenericInstanceType inst_ty)
527 (badGenericInstanceType binds)
529 -- Make the dictionary function.
531 overlap_flag <- getOverlapFlag
532 dfun_name <- newDFunName clas [inst_ty] span
534 inst_theta = [mkClassPred clas [mkTyVarTy tv] | tv <- tyvars]
535 dfun_id = mkDictFunId dfun_name tyvars inst_theta clas [inst_ty]
536 ispec = mkLocalInstance dfun_id overlap_flag
538 return (InstInfo { iSpec = ispec, iBinds = VanillaInst binds [] False })
542 %************************************************************************
546 %************************************************************************
549 tcAddDeclCtxt :: TyClDecl Name -> TcM a -> TcM a
550 tcAddDeclCtxt decl thing_inside
551 = addErrCtxt ctxt thing_inside
553 thing | isClassDecl decl = "class"
554 | isTypeDecl decl = "type synonym" ++ maybeInst
555 | isDataDecl decl = if tcdND decl == NewType
556 then "newtype" ++ maybeInst
557 else "data type" ++ maybeInst
558 | isFamilyDecl decl = "family"
559 | otherwise = panic "tcAddDeclCtxt/thing"
561 maybeInst | isFamInstDecl decl = " instance"
564 ctxt = hsep [ptext (sLit "In the"), text thing,
565 ptext (sLit "declaration for"), quotes (ppr (tcdName decl))]
567 badMethodErr :: Outputable a => a -> Name -> SDoc
569 = hsep [ptext (sLit "Class"), quotes (ppr clas),
570 ptext (sLit "does not have a method"), 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 4 (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)