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 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
219 prags = prag_fn sel_name
221 ; dm_id_w_inline <- addInlinePrags dm_id prags
222 ; spec_prags <- tcSpecPrags dm_id prags
224 ; warnTc (not (null spec_prags))
225 (ptext (sLit "Ignoring SPECIALISE pragmas on default method")
226 <+> quotes (ppr sel_name))
229 tcInstanceMethodBody (ClsSkol clas)
233 dm_id_w_inline local_dm_id
234 dm_sig_fn IsDefaultMethod meth_bind }
237 tcInstanceMethodBody :: SkolemInfo -> [TcTyVar] -> [EvVar]
240 -> SigFun -> TcSpecPrags -> LHsBind Name
242 tcInstanceMethodBody skol_info tyvars dfun_ev_vars
243 this_dict meth_id local_meth_id
246 = do { -- Typecheck the binding, first extending the envt
247 -- so that when tcInstSig looks up the local_meth_id to find
248 -- its signature, we'll find it in the environment
249 let full_given = case this_dict of
250 Nothing -> dfun_ev_vars
251 Just (EvBind dict _) -> dict : dfun_ev_vars
252 lm_bind = L loc (bind { fun_id = L loc (idName local_meth_id) })
253 -- Substitue the local_meth_name for the binder
254 -- NB: the binding is always a FunBind
256 ; (ev_binds, (tc_bind, _))
257 <- checkConstraints skol_info tyvars full_given $
258 tcExtendIdEnv [local_meth_id] $
259 tcPolyBinds TopLevel meth_sig_fn no_prag_fn
260 NonRecursive NonRecursive
263 -- Add the binding for this_dict, if we have one
264 ; ev_binds' <- case this_dict of
265 Nothing -> return ev_binds
266 Just (EvBind self rhs) -> extendTcEvBinds ev_binds self rhs
268 ; let full_bind = AbsBinds { abs_tvs = tyvars, abs_ev_vars = dfun_ev_vars
269 , abs_exports = [(tyvars, meth_id, local_meth_id, specs)]
270 , abs_ev_binds = ev_binds'
271 , abs_binds = tc_bind }
273 ; return (L loc full_bind) }
275 no_prag_fn _ = [] -- No pragmas for local_meth_id;
276 -- they are all for meth_id
280 instantiateMethod :: Class -> Id -> [TcType] -> TcType
281 -- Take a class operation, say
282 -- op :: forall ab. C a => forall c. Ix c => (b,c) -> a
283 -- Instantiate it at [ty1,ty2]
284 -- Return the "local method type":
285 -- forall c. Ix x => (ty2,c) -> ty1
286 instantiateMethod clas sel_id inst_tys
287 = ASSERT( ok_first_pred ) local_meth_ty
289 (sel_tyvars,sel_rho) = tcSplitForAllTys (idType sel_id)
290 rho_ty = ASSERT( length sel_tyvars == length inst_tys )
291 substTyWith sel_tyvars inst_tys sel_rho
293 (first_pred, local_meth_ty) = tcSplitPredFunTy_maybe rho_ty
294 `orElse` pprPanic "tcInstanceMethod" (ppr sel_id)
296 ok_first_pred = case getClassPredTys_maybe first_pred of
297 Just (clas1, _tys) -> clas == clas1
299 -- The first predicate should be of form (C a b)
300 -- where C is the class in question
303 ---------------------------
304 findMethodBind :: Name -- Selector name
305 -> LHsBinds Name -- A group of bindings
306 -> Maybe (LHsBind Name) -- The binding
307 findMethodBind sel_name binds
308 = foldlBag mplus Nothing (mapBag f binds)
310 f bind@(L _ (FunBind { fun_id = L _ op_name }))
311 | op_name == sel_name
316 Note [Polymorphic methods]
317 ~~~~~~~~~~~~~~~~~~~~~~~~~~
320 op :: forall b. Ord b => a -> b -> b -> b
321 instance Foo c => Foo [c] where
324 When typechecking the binding 'op = e', we'll have a meth_id for op
326 op :: forall c. Foo c => forall b. Ord b => [c] -> b -> b -> b
328 So tcPolyBinds must be capable of dealing with nested polytypes;
329 and so it is. See TcBinds.tcMonoBinds (with type-sig case).
331 Note [Silly default-method bind]
332 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
333 When we pass the default method binding to the type checker, it must
336 otherwise the "$dm" stuff comes out error messages. But we want the
337 "$dm" to come out in the interface file. So we typecheck the former,
338 and wrap it in a let, thus
339 $dmop2 = let op2 = e in op2
340 This makes the error messages right.
343 %************************************************************************
345 Extracting generic instance declaration from class declarations
347 %************************************************************************
349 @getGenericInstances@ extracts the generic instance declarations from a class
350 declaration. For exmaple
355 op{ x+y } (Inl v) = ...
356 op{ x+y } (Inr v) = ...
357 op{ x*y } (v :*: w) = ...
360 gives rise to the instance declarations
362 instance C (x+y) where
366 instance C (x*y) where
373 mkGenericDefMethBind :: Class -> [Type] -> Id -> TcM (LHsBind Name)
374 mkGenericDefMethBind clas inst_tys sel_id
375 = -- A generic default method
376 -- If the method is defined generically, we can only do the job if the
377 -- instance declaration is for a single-parameter type class with
378 -- a type constructor applied to type arguments in the instance decl
379 -- (checkTc, so False provokes the error)
380 do { checkTc (isJust maybe_tycon)
381 (badGenericInstance sel_id (notSimple inst_tys))
382 ; checkTc (tyConHasGenerics tycon)
383 (badGenericInstance sel_id (notGeneric tycon))
386 ; liftIO (dumpIfSet_dyn dflags Opt_D_dump_deriv "Filling in method body"
387 (vcat [ppr clas <+> ppr inst_tys,
388 nest 2 (ppr sel_id <+> equals <+> ppr rhs)]))
390 -- Rename it before returning it
391 ; (rn_rhs, _) <- rnLExpr rhs
392 ; return (noLoc $ mkFunBind (noLoc (idName sel_id))
393 [mkSimpleMatch [] rn_rhs]) }
395 rhs = mkGenericRhs sel_id clas_tyvar tycon
397 -- The tycon is only used in the generic case, and in that
398 -- case we require that the instance decl is for a single-parameter
399 -- type class with type variable arguments:
400 -- instance (...) => C (T a b)
401 clas_tyvar = ASSERT (not (null (classTyVars clas))) head (classTyVars clas)
402 Just tycon = maybe_tycon
403 maybe_tycon = case inst_tys of
404 [ty] -> case tcSplitTyConApp_maybe ty of
405 Just (tycon, arg_tys) | all tcIsTyVarTy arg_tys -> Just tycon
410 ---------------------------
411 getGenericInstances :: [LTyClDecl Name] -> TcM [InstInfo Name]
412 getGenericInstances class_decls
413 = do { gen_inst_infos <- mapM (addLocM get_generics) class_decls
414 ; let { gen_inst_info = concat gen_inst_infos }
416 -- Return right away if there is no generic stuff
417 ; if null gen_inst_info then return []
420 -- Otherwise print it out
422 ; liftIO (dumpIfSet_dyn dflags Opt_D_dump_deriv "Generic instances"
423 (vcat (map pprInstInfoDetails gen_inst_info)))
424 ; return gen_inst_info }}
426 get_generics :: TyClDecl Name -> TcM [InstInfo Name]
427 get_generics decl@(ClassDecl {tcdLName = class_name, tcdMeths = def_methods})
429 = return [] -- The comon case: no generic default methods
431 | otherwise -- A source class decl with generic default methods
432 = recoverM (return []) $
433 tcAddDeclCtxt decl $ do
434 clas <- tcLookupLocatedClass class_name
436 -- Group by type, and
437 -- make an InstInfo out of each group
439 groups = groupWith listToBag generic_binds
441 inst_infos <- mapM (mkGenericInstance clas) groups
443 -- Check that there is only one InstInfo for each type constructor
444 -- The main way this can fail is if you write
445 -- f {| a+b |} ... = ...
446 -- f {| x+y |} ... = ...
447 -- Then at this point we'll have an InstInfo for each
449 -- The class should be unary, which is why simpleInstInfoTyCon should be ok
451 tc_inst_infos :: [(TyCon, InstInfo Name)]
452 tc_inst_infos = [(simpleInstInfoTyCon i, i) | i <- inst_infos]
454 bad_groups = [group | group <- equivClassesByUniq get_uniq tc_inst_infos,
455 group `lengthExceeds` 1]
456 get_uniq (tc,_) = getUnique tc
458 mapM_ (addErrTc . dupGenericInsts) bad_groups
460 -- Check that there is an InstInfo for each generic type constructor
462 missing = genericTyConNames `minusList` [tyConName tc | (tc,_) <- tc_inst_infos]
464 checkTc (null missing) (missingGenericInstances missing)
468 generic_binds :: [(HsType Name, LHsBind Name)]
469 generic_binds = getGenericBinds def_methods
470 get_generics decl = pprPanic "get_generics" (ppr decl)
473 ---------------------------------
474 getGenericBinds :: LHsBinds Name -> [(HsType Name, LHsBind Name)]
475 -- Takes a group of method bindings, finds the generic ones, and returns
476 -- them in finite map indexed by the type parameter in the definition.
477 getGenericBinds binds = concat (map getGenericBind (bagToList binds))
479 getGenericBind :: LHsBindLR Name Name -> [(HsType Name, LHsBindLR Name Name)]
480 getGenericBind (L loc bind@(FunBind { fun_matches = MatchGroup matches ty }))
481 = groupWith wrap (mapCatMaybes maybeGenericMatch matches)
483 wrap ms = L loc (bind { fun_matches = MatchGroup ms ty })
487 groupWith :: ([a] -> b) -> [(HsType Name, a)] -> [(HsType Name, b)]
489 groupWith op ((t,v):prs) = (t, op (v:vs)) : groupWith op rest
492 (this,rest) = partition same_t prs
493 same_t (t', _v) = t `eqPatType` t'
495 eqPatLType :: LHsType Name -> LHsType Name -> Bool
496 eqPatLType t1 t2 = unLoc t1 `eqPatType` unLoc t2
498 eqPatType :: HsType Name -> HsType Name -> Bool
499 -- A very simple equality function, only for
500 -- type patterns in generic function definitions.
501 eqPatType (HsTyVar v1) (HsTyVar v2) = v1==v2
502 eqPatType (HsAppTy s1 t1) (HsAppTy s2 t2) = s1 `eqPatLType` s2 && t1 `eqPatLType` t2
503 eqPatType (HsOpTy s1 op1 t1) (HsOpTy s2 op2 t2) = s1 `eqPatLType` s2 && t1 `eqPatLType` t2 && unLoc op1 == unLoc op2
504 eqPatType (HsNumTy n1) (HsNumTy n2) = n1 == n2
505 eqPatType (HsParTy t1) t2 = unLoc t1 `eqPatType` t2
506 eqPatType t1 (HsParTy t2) = t1 `eqPatType` unLoc t2
507 eqPatType _ _ = False
509 ---------------------------------
510 mkGenericInstance :: Class
511 -> (HsType Name, LHsBinds Name)
512 -> TcM (InstInfo Name)
514 mkGenericInstance clas (hs_ty, binds) = do
515 -- Make a generic instance declaration
516 -- For example: instance (C a, C b) => C (a+b) where { binds }
518 -- Extract the universally quantified type variables
519 -- and wrap them as forall'd tyvars, so that kind inference
520 -- works in the standard way
522 sig_tvs = userHsTyVarBndrs $ map noLoc $ nameSetToList $
523 extractHsTyVars (noLoc hs_ty)
524 hs_forall_ty = noLoc $ mkExplicitHsForAllTy sig_tvs (noLoc []) (noLoc hs_ty)
526 -- Type-check the instance type, and check its form
527 forall_inst_ty <- tcHsSigType GenPatCtxt hs_forall_ty
529 (tyvars, inst_ty) = tcSplitForAllTys forall_inst_ty
531 checkTc (validGenericInstanceType inst_ty)
532 (badGenericInstanceType binds)
534 -- Make the dictionary function.
536 overlap_flag <- getOverlapFlag
537 dfun_name <- newDFunName clas [inst_ty] span
539 inst_theta = [mkClassPred clas [mkTyVarTy tv] | tv <- tyvars]
540 dfun_id = mkDictFunId dfun_name tyvars inst_theta clas [inst_ty]
541 ispec = mkLocalInstance dfun_id overlap_flag
543 return (InstInfo { iSpec = ispec, iBinds = VanillaInst binds [] False })
547 %************************************************************************
551 %************************************************************************
554 tcAddDeclCtxt :: TyClDecl Name -> TcM a -> TcM a
555 tcAddDeclCtxt decl thing_inside
556 = addErrCtxt ctxt thing_inside
558 thing | isClassDecl decl = "class"
559 | isTypeDecl decl = "type synonym" ++ maybeInst
560 | isDataDecl decl = if tcdND decl == NewType
561 then "newtype" ++ maybeInst
562 else "data type" ++ maybeInst
563 | isFamilyDecl decl = "family"
564 | otherwise = panic "tcAddDeclCtxt/thing"
566 maybeInst | isFamInstDecl decl = " instance"
569 ctxt = hsep [ptext (sLit "In the"), text thing,
570 ptext (sLit "declaration for"), quotes (ppr (tcdName decl))]
572 badMethodErr :: Outputable a => a -> Name -> SDoc
574 = hsep [ptext (sLit "Class"), quotes (ppr clas),
575 ptext (sLit "does not have a method"), quotes (ppr op)]
577 badATErr :: Class -> Name -> SDoc
579 = hsep [ptext (sLit "Class"), quotes (ppr clas),
580 ptext (sLit "does not have an associated type"), quotes (ppr at)]
582 omittedATWarn :: Name -> SDoc
584 = ptext (sLit "No explicit AT declaration for") <+> quotes (ppr at)
586 badGenericInstance :: Var -> SDoc -> SDoc
587 badGenericInstance sel_id because
588 = sep [ptext (sLit "Can't derive generic code for") <+> quotes (ppr sel_id),
591 notSimple :: [Type] -> SDoc
593 = vcat [ptext (sLit "because the instance type(s)"),
594 nest 2 (ppr inst_tys),
595 ptext (sLit "is not a simple type of form (T a1 ... an)")]
597 notGeneric :: TyCon -> SDoc
599 = vcat [ptext (sLit "because the instance type constructor") <+> quotes (ppr tycon) <+>
600 ptext (sLit "was not compiled with -XGenerics")]
602 badGenericInstanceType :: LHsBinds Name -> SDoc
603 badGenericInstanceType binds
604 = vcat [ptext (sLit "Illegal type pattern in the generic bindings"),
607 missingGenericInstances :: [Name] -> SDoc
608 missingGenericInstances missing
609 = ptext (sLit "Missing type patterns for") <+> pprQuotedList missing
611 dupGenericInsts :: [(TyCon, InstInfo a)] -> SDoc
612 dupGenericInsts tc_inst_infos
613 = vcat [ptext (sLit "More than one type pattern for a single generic type constructor:"),
614 nest 2 (vcat (map ppr_inst_ty tc_inst_infos)),
615 ptext (sLit "All the type patterns for a generic type constructor must be identical")
618 ppr_inst_ty (_,inst) = ppr (simpleInstInfoTy inst)
620 mixedGenericErr :: Name -> SDoc
622 = ptext (sLit "Can't mix generic and non-generic equations for class method") <+> quotes (ppr op)