2 % (c) The University of Glasgow 2006
3 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
6 Handles @deriving@ clauses on @data@ declarations.
9 module TcDeriv ( tcDeriving ) where
11 #include "HsVersions.h"
19 import TcClassDcl( tcAddDeclCtxt ) -- Small helper
20 import TcGenDeriv -- Deriv stuff
59 %************************************************************************
63 %************************************************************************
67 1. Convert the decls (i.e. data/newtype deriving clauses,
68 plus standalone deriving) to [EarlyDerivSpec]
70 2. Infer the missing contexts for the Left DerivSpecs
72 3. Add the derived bindings, generating InstInfos
76 -- DerivSpec is purely local to this module
77 data DerivSpec = DS { ds_loc :: SrcSpan
81 , ds_theta :: ThetaType
85 , ds_tc_args :: [Type]
86 , ds_newtype :: Bool }
87 -- This spec implies a dfun declaration of the form
88 -- df :: forall tvs. theta => C tys
89 -- The Name is the name for the DFun we'll build
90 -- The tyvars bind all the variables in the theta
91 -- For type families, the tycon in
92 -- in ds_tys is the *family* tycon
93 -- in ds_tc, ds_tc_args is the *representation* tycon
94 -- For non-family tycons, both are the same
96 -- ds_newtype = True <=> Newtype deriving
97 -- False <=> Vanilla deriving
102 newtype instance T [a] = MkT (Tree a) deriving( C s )
104 axiom T [a] = :RTList a
105 axiom :RTList a = Tree a
107 DS { ds_tvs = [a,s], ds_cls = C, ds_tys = [s, T [a]]
108 , ds_tc = :RTList, ds_tc_args = [a]
109 , ds_newtype = True }
112 type DerivContext = Maybe ThetaType
113 -- Nothing <=> Vanilla deriving; infer the context of the instance decl
114 -- Just theta <=> Standalone deriving: context supplied by programmer
116 type EarlyDerivSpec = Either DerivSpec DerivSpec
117 -- Left ds => the context for the instance should be inferred
118 -- In this case ds_theta is the list of all the
119 -- constraints needed, such as (Eq [a], Eq a)
120 -- The inference process is to reduce this to a
121 -- simpler form (e.g. Eq a)
123 -- Right ds => the exact context for the instance is supplied
124 -- by the programmer; it is ds_theta
126 pprDerivSpec :: DerivSpec -> SDoc
127 pprDerivSpec (DS { ds_loc = l, ds_name = n, ds_tvs = tvs,
128 ds_cls = c, ds_tys = tys, ds_theta = rhs })
129 = parens (hsep [ppr l, ppr n, ppr tvs, ppr c, ppr tys]
130 <+> equals <+> ppr rhs)
132 instance Outputable DerivSpec where
137 Inferring missing contexts
138 ~~~~~~~~~~~~~~~~~~~~~~~~~~
141 data T a b = C1 (Foo a) (Bar b)
146 [NOTE: See end of these comments for what to do with
147 data (C a, D b) => T a b = ...
150 We want to come up with an instance declaration of the form
152 instance (Ping a, Pong b, ...) => Eq (T a b) where
155 It is pretty easy, albeit tedious, to fill in the code "...". The
156 trick is to figure out what the context for the instance decl is,
157 namely @Ping@, @Pong@ and friends.
159 Let's call the context reqd for the T instance of class C at types
160 (a,b, ...) C (T a b). Thus:
162 Eq (T a b) = (Ping a, Pong b, ...)
164 Now we can get a (recursive) equation from the @data@ decl:
166 Eq (T a b) = Eq (Foo a) u Eq (Bar b) -- From C1
167 u Eq (T b a) u Eq Int -- From C2
168 u Eq (T a a) -- From C3
170 Foo and Bar may have explicit instances for @Eq@, in which case we can
171 just substitute for them. Alternatively, either or both may have
172 their @Eq@ instances given by @deriving@ clauses, in which case they
173 form part of the system of equations.
175 Now all we need do is simplify and solve the equations, iterating to
176 find the least fixpoint. Notice that the order of the arguments can
177 switch around, as here in the recursive calls to T.
179 Let's suppose Eq (Foo a) = Eq a, and Eq (Bar b) = Ping b.
183 Eq (T a b) = {} -- The empty set
186 Eq (T a b) = Eq (Foo a) u Eq (Bar b) -- From C1
187 u Eq (T b a) u Eq Int -- From C2
188 u Eq (T a a) -- From C3
190 After simplification:
191 = Eq a u Ping b u {} u {} u {}
196 Eq (T a b) = Eq (Foo a) u Eq (Bar b) -- From C1
197 u Eq (T b a) u Eq Int -- From C2
198 u Eq (T a a) -- From C3
200 After simplification:
205 = Eq a u Ping b u Eq b u Ping a
207 The next iteration gives the same result, so this is the fixpoint. We
208 need to make a canonical form of the RHS to ensure convergence. We do
209 this by simplifying the RHS to a form in which
211 - the classes constrain only tyvars
212 - the list is sorted by tyvar (major key) and then class (minor key)
213 - no duplicates, of course
215 So, here are the synonyms for the ``equation'' structures:
218 Note [Data decl contexts]
219 ~~~~~~~~~~~~~~~~~~~~~~~~~
222 data (RealFloat a) => Complex a = !a :+ !a deriving( Read )
224 We will need an instance decl like:
226 instance (Read a, RealFloat a) => Read (Complex a) where
229 The RealFloat in the context is because the read method for Complex is bound
230 to construct a Complex, and doing that requires that the argument type is
233 But this ain't true for Show, Eq, Ord, etc, since they don't construct
234 a Complex; they only take them apart.
236 Our approach: identify the offending classes, and add the data type
237 context to the instance decl. The "offending classes" are
241 FURTHER NOTE ADDED March 2002. In fact, Haskell98 now requires that
242 pattern matching against a constructor from a data type with a context
243 gives rise to the constraints for that context -- or at least the thinned
244 version. So now all classes are "offending".
246 Note [Newtype deriving]
247 ~~~~~~~~~~~~~~~~~~~~~~~
251 newtype T = T Char deriving( C [a] )
253 Notice the free 'a' in the deriving. We have to fill this out to
254 newtype T = T Char deriving( forall a. C [a] )
256 And then translate it to:
257 instance C [a] Char => C [a] T where ...
260 Note [Newtype deriving superclasses]
261 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
262 (See also Trac #1220 for an interesting exchange on newtype
263 deriving and superclasses.)
265 The 'tys' here come from the partial application in the deriving
266 clause. The last arg is the new instance type.
268 We must pass the superclasses; the newtype might be an instance
269 of them in a different way than the representation type
270 E.g. newtype Foo a = Foo a deriving( Show, Num, Eq )
271 Then the Show instance is not done via isomorphism; it shows
273 The Num instance is derived via isomorphism, but the Show superclass
274 dictionary must the Show instance for Foo, *not* the Show dictionary
275 gotten from the Num dictionary. So we must build a whole new dictionary
276 not just use the Num one. The instance we want is something like:
277 instance (Num a, Show (Foo a), Eq (Foo a)) => Num (Foo a) where
280 There may be a coercion needed which we get from the tycon for the newtype
281 when the dict is constructed in TcInstDcls.tcInstDecl2
284 Note [Unused constructors and deriving clauses]
285 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
286 See Trac #3221. Consider
287 data T = T1 | T2 deriving( Show )
288 Are T1 and T2 unused? Well, no: the deriving clause expands to mention
289 both of them. So we gather defs/uses from deriving just like anything else.
291 %************************************************************************
293 \subsection[TcDeriv-driver]{Top-level function for \tr{derivings}}
295 %************************************************************************
298 tcDeriving :: [LTyClDecl Name] -- All type constructors
299 -> [LInstDecl Name] -- All instance declarations
300 -> [LDerivDecl Name] -- All stand-alone deriving declarations
301 -> TcM ([InstInfo Name] -- The generated "instance decls"
302 ,HsValBinds Name -- Extra generated top-level bindings
304 ,[TyCon] -- Extra generated top-level types
305 ,[TyCon]) -- Extra generated type family instances
307 tcDeriving tycl_decls inst_decls deriv_decls
308 = recoverM (return ([], emptyValBindsOut, emptyDUs, [], [])) $
309 do { -- Fish the "deriving"-related information out of the TcEnv
310 -- And make the necessary "equations".
311 is_boot <- tcIsHsBoot
312 ; traceTc "tcDeriving" (ppr is_boot)
313 ; (early_specs, genericsExtras)
314 <- makeDerivSpecs is_boot tycl_decls inst_decls deriv_decls
315 ; let (repMetaTys, repTyCons, metaInsts) = unzip3 genericsExtras
317 ; overlap_flag <- getOverlapFlag
318 ; let (infer_specs, given_specs) = splitEithers early_specs
319 ; insts1 <- mapM (genInst True overlap_flag) given_specs
321 ; final_specs <- extendLocalInstEnv (map (iSpec . fst) insts1) $
322 inferInstanceContexts overlap_flag infer_specs
324 ; insts2 <- mapM (genInst False overlap_flag) final_specs
326 -- We no longer generate the old generic to/from functions
327 -- from each type declaration, so this is emptyBag
328 ; gen_binds <- return emptyBag -- mkGenericBinds is_boot tycl_decls
331 -- Generate the Generic instances
332 -- from each type declaration
333 ; repInstsMeta <- genGenericAlls is_boot tycl_decls
335 ; let repInsts = concat (map (\(a,_,_) -> a) repInstsMeta)
336 repMetaTys = map (\(_,b,_) -> b) repInstsMeta
337 repTyCons = map (\(_,_,c) -> c) repInstsMeta
339 ; (inst_info, rn_binds, rn_dus)
340 <- renameDeriv is_boot gen_binds (insts1 ++ insts2 ++ concat metaInsts {- ++ repInsts -})
343 ; liftIO (dumpIfSet_dyn dflags Opt_D_dump_deriv "Derived instances"
344 (ddump_deriving inst_info rn_binds))
346 ; when (not (null inst_info)) $
347 dumpDerivingInfo (ddump_deriving inst_info rn_binds)
349 ; return ( inst_info, rn_binds, rn_dus
350 , concat (map metaTyCons2TyCons repMetaTys), repTyCons) }
352 ddump_deriving :: [InstInfo Name] -> HsValBinds Name -> SDoc
353 ddump_deriving inst_infos extra_binds
354 = hang (ptext (sLit "Derived instances"))
355 2 (vcat (map (\i -> pprInstInfoDetails i $$ text "") inst_infos)
359 renameDeriv :: Bool -> LHsBinds RdrName
360 -> [(InstInfo RdrName, DerivAuxBinds)]
361 -> TcM ([InstInfo Name], HsValBinds Name, DefUses)
362 renameDeriv is_boot gen_binds insts
363 | is_boot -- If we are compiling a hs-boot file, don't generate any derived bindings
364 -- The inst-info bindings will all be empty, but it's easier to
365 -- just use rn_inst_info to change the type appropriately
366 = do { (rn_inst_infos, fvs) <- mapAndUnzipM rn_inst_info inst_infos
367 ; return (rn_inst_infos, emptyValBindsOut, usesOnly (plusFVs fvs)) }
370 = discardWarnings $ -- Discard warnings about unused bindings etc
371 do { (rn_gen, dus_gen) <- setOptM Opt_ScopedTypeVariables $ -- Type signatures in patterns
372 -- are used in the generic binds
373 rnTopBinds (ValBindsIn gen_binds [])
374 ; keepAliveSetTc (duDefs dus_gen) -- Mark these guys to be kept alive
376 -- Generate and rename any extra not-one-inst-decl-specific binds,
377 -- notably "con2tag" and/or "tag2con" functions.
378 -- Bring those names into scope before renaming the instances themselves
379 ; loc <- getSrcSpanM -- Generic loc for shared bindings
380 ; let (aux_binds, aux_sigs) = unzip $ map (genAuxBind loc) $
381 rm_dups [] $ concat deriv_aux_binds
382 aux_val_binds = ValBindsIn (listToBag aux_binds) aux_sigs
383 ; rn_aux_lhs <- rnTopBindsLHS emptyFsEnv aux_val_binds
384 ; bindLocalNames (collectHsValBinders rn_aux_lhs) $
385 do { (rn_aux, dus_aux) <- rnTopBindsRHS rn_aux_lhs
386 ; (rn_inst_infos, fvs_insts) <- mapAndUnzipM rn_inst_info inst_infos
387 ; return (rn_inst_infos, rn_aux `plusHsValBinds` rn_gen,
388 dus_gen `plusDU` dus_aux `plusDU` usesOnly (plusFVs fvs_insts)) } }
391 (inst_infos, deriv_aux_binds) = unzip insts
393 -- Remove duplicate requests for auxilliary bindings
395 rm_dups acc (b:bs) | any (isDupAux b) acc = rm_dups acc bs
396 | otherwise = rm_dups (b:acc) bs
399 rn_inst_info :: InstInfo RdrName -> TcM (InstInfo Name, FreeVars)
400 rn_inst_info info@(InstInfo { iBinds = NewTypeDerived coi tc })
401 = return ( info { iBinds = NewTypeDerived coi tc }
402 , mkFVs (map dataConName (tyConDataCons tc)))
403 -- See Note [Newtype deriving and unused constructors]
405 rn_inst_info inst_info@(InstInfo { iSpec = inst, iBinds = VanillaInst binds sigs standalone_deriv })
406 = -- Bring the right type variables into
407 -- scope (yuk), and rename the method binds
409 bindLocalNames (map Var.varName tyvars) $
410 do { (rn_binds, fvs) <- rnMethodBinds clas_nm (\_ -> []) binds
411 ; let binds' = VanillaInst rn_binds [] standalone_deriv
412 ; return (inst_info { iBinds = binds' }, fvs) }
414 (tyvars,_, clas,_) = instanceHead inst
415 clas_nm = className clas
417 -----------------------------------------
419 mkGenericBinds :: Bool -> [LTyClDecl Name] -> TcM (LHsBinds RdrName)
420 mkGenericBinds is_boot tycl_decls
424 = do { tcs <- mapM tcLookupTyCon [ tcdName d
425 | L _ d <- tycl_decls, isDataDecl d ]
426 ; return (unionManyBags [ mkTyConGenericBinds tc
427 | tc <- tcs, tyConHasGenerics tc ]) }
428 -- We are only interested in the data type declarations,
429 -- and then only in the ones whose 'has-generics' flag is on
430 -- The predicate tyConHasGenerics finds both of these
434 Note [Newtype deriving and unused constructors]
435 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
436 Consider this (see Trac #1954):
439 newtype P a = MkP (IO a) deriving Monad
441 If you compile with -fwarn-unused-binds you do not expect the warning
442 "Defined but not used: data consructor MkP". Yet the newtype deriving
443 code does not explicitly mention MkP, but it should behave as if you
445 instance Monad P where
446 return x = MkP (return x)
449 So we want to signal a user of the data constructor 'MkP'. That's
450 what we do in rn_inst_info, and it's the only reason we have the TyCon
451 stored in NewTypeDerived.
454 %************************************************************************
456 From HsSyn to DerivSpec
458 %************************************************************************
460 @makeDerivSpecs@ fishes around to find the info about needed derived instances.
464 -- Make the EarlyDerivSpec for Generic
465 mkGenDerivSpec :: TyCon -> TcRn (EarlyDerivSpec)
466 mkGenDerivSpec tc = do
467 { cls <- tcLookupClass genClassName
468 ; let tc_tvs = tyConTyVars tc
469 ; let tc_app = mkTyConApp tc (mkTyVarTys tc_tvs)
471 ; let mtheta = Just []
472 ; ds <- mkEqnHelp StandAloneDerivOrigin tc_tvs cls cls_tys tc_app mtheta
473 -- JPM TODO: StandAloneDerivOrigin?...
476 -- Make the "extras" for the generic representation
477 mkGenDerivExtras :: TyCon
478 -> TcRn (MetaTyCons, TyCon, [(InstInfo RdrName, DerivAuxBinds)])
479 mkGenDerivExtras tc = do
480 { (metaTyCons, rep0TyInst) <- genGenericRepExtras tc
481 ; metaInsts <- genDtMeta (tc, metaTyCons)
482 ; return (metaTyCons, rep0TyInst, metaInsts) }
484 makeDerivSpecs :: Bool
488 -> TcM ( [EarlyDerivSpec]
489 , [(MetaTyCons, TyCon, [(InstInfo RdrName, DerivAuxBinds)])])
490 makeDerivSpecs is_boot tycl_decls inst_decls deriv_decls
491 | is_boot -- No 'deriving' at all in hs-boot files
492 = do { mapM_ add_deriv_err deriv_locs
495 = do { eqns1 <- mapAndRecoverM deriveTyData all_tydata
496 ; eqns2 <- mapAndRecoverM deriveStandalone deriv_decls
497 -- Generate EarlyDerivSpec's for Generic, if asked for
498 -- ; (xGenerics, xDerRep) <- genericsFlags
499 ; xDerRep <- genericsFlag
500 ; let allTyNames = [ tcdName d | L _ d <- tycl_decls, isDataDecl d ]
501 -- ; allTyDecls <- mapM tcLookupTyCon allTyNames
502 -- Select only those types that derive Generic
503 ; let sel_tydata = [ tcdName t | (L _ c, L _ t) <- all_tydata
504 , getClassName c == Just genClassName ]
505 ; let sel_deriv_decls = catMaybes [ getTypeName t
506 | L _ (DerivDecl (L _ t)) <- deriv_decls
507 , getClassName t == Just genClassName ]
508 ; derTyDecls <- mapM tcLookupTyCon $
509 filter (needsExtras xDerRep
510 (sel_tydata ++ sel_deriv_decls)) allTyNames
511 -- We need to generate the extras to add to what has
512 -- already been derived
513 ; generic_extras_deriv <- mapM mkGenDerivExtras derTyDecls
514 -- For the remaining types, if Generics is on, we need to
515 -- generate both the instances and the extras, but only for the
516 -- types we can represent.
518 ; let repTyDecls = filter canDoGenerics allTyDecls
519 ; let remTyDecls = filter (\x -> not (x `elem` derTyDecls)) repTyDecls
520 ; generic_instances <- if xGenerics
521 then mapM mkGenDerivSpec remTyDecls
523 ; generic_extras_flag <- if xGenerics
524 then mapM mkGenDerivExtras remTyDecls
527 -- Merge and return everything
528 ; return ( eqns1 ++ eqns2 -- ++ generic_instances
529 , generic_extras_deriv {- ++ generic_extras_flag -}) }
531 -- We need extras if the flag DeriveGeneric is on and this type is
533 needsExtras xDerRep tydata tc_name = xDerRep && tc_name `elem` tydata
535 -- Extracts the name of the class in the deriving
536 getClassName :: HsType Name -> Maybe Name
537 getClassName (HsPredTy (HsClassP n _)) = Just n
538 getClassName _ = Nothing
540 -- Extracts the name of the type in the deriving
541 getTypeName :: HsType Name -> Maybe Name
542 getTypeName (HsTyVar n) = Just n
543 getTypeName (HsOpTy _ (L _ n) _) = Just n
544 getTypeName (HsPredTy (HsClassP _ [L _ n])) = getTypeName n
545 getTypeName _ = Nothing
547 extractTyDataPreds decls
548 = [(p, d) | d@(L _ (TyData {tcdDerivs = Just preds})) <- decls, p <- preds]
550 all_tydata :: [(LHsType Name, LTyClDecl Name)]
551 -- Derived predicate paired with its data type declaration
552 all_tydata = extractTyDataPreds (instDeclATs inst_decls ++ tycl_decls)
554 deriv_locs = map (getLoc . snd) all_tydata
555 ++ map getLoc deriv_decls
557 add_deriv_err loc = setSrcSpan loc $
558 addErr (hang (ptext (sLit "Deriving not permitted in hs-boot file"))
559 2 (ptext (sLit "Use an instance declaration instead")))
561 genericsFlag :: TcM Bool
562 genericsFlag = do dOpts <- getDOpts
563 return ( xopt Opt_Generics dOpts
564 || xopt Opt_DeriveGeneric dOpts)
566 ------------------------------------------------------------------
567 deriveStandalone :: LDerivDecl Name -> TcM EarlyDerivSpec
568 -- Standalone deriving declarations
569 -- e.g. deriving instance Show a => Show (T a)
570 -- Rather like tcLocalInstDecl
571 deriveStandalone (L loc (DerivDecl deriv_ty))
573 addErrCtxt (standaloneCtxt deriv_ty) $
574 do { traceTc "Standalone deriving decl for" (ppr deriv_ty)
575 ; (tvs, theta, cls, inst_tys) <- tcHsInstHead deriv_ty
576 ; traceTc "Standalone deriving;" $ vcat
577 [ text "tvs:" <+> ppr tvs
578 , text "theta:" <+> ppr theta
579 , text "cls:" <+> ppr cls
580 , text "tys:" <+> ppr inst_tys ]
581 ; checkValidInstance deriv_ty tvs theta cls inst_tys
582 -- C.f. TcInstDcls.tcLocalInstDecl1
584 ; let cls_tys = take (length inst_tys - 1) inst_tys
585 inst_ty = last inst_tys
586 ; traceTc "Standalone deriving:" $ vcat
587 [ text "class:" <+> ppr cls
588 , text "class types:" <+> ppr cls_tys
589 , text "type:" <+> ppr inst_ty ]
590 ; mkEqnHelp StandAloneDerivOrigin tvs cls cls_tys inst_ty
593 ------------------------------------------------------------------
594 deriveTyData :: (LHsType Name, LTyClDecl Name) -> TcM EarlyDerivSpec
595 deriveTyData (L loc deriv_pred, L _ decl@(TyData { tcdLName = L _ tycon_name,
596 tcdTyVars = tv_names,
597 tcdTyPats = ty_pats }))
598 = setSrcSpan loc $ -- Use the location of the 'deriving' item
600 do { (tvs, tc, tc_args) <- get_lhs ty_pats
601 ; tcExtendTyVarEnv tvs $ -- Deriving preds may (now) mention
602 -- the type variables for the type constructor
604 do { (deriv_tvs, cls, cls_tys) <- tcHsDeriv deriv_pred
605 -- The "deriv_pred" is a LHsType to take account of the fact that for
606 -- newtype deriving we allow deriving (forall a. C [a]).
608 -- Given data T a b c = ... deriving( C d ),
609 -- we want to drop type variables from T so that (C d (T a)) is well-kinded
610 ; let cls_tyvars = classTyVars cls
611 kind = tyVarKind (last cls_tyvars)
612 (arg_kinds, _) = splitKindFunTys kind
613 n_args_to_drop = length arg_kinds
614 n_args_to_keep = tyConArity tc - n_args_to_drop
615 args_to_drop = drop n_args_to_keep tc_args
616 inst_ty = mkTyConApp tc (take n_args_to_keep tc_args)
617 inst_ty_kind = typeKind inst_ty
618 dropped_tvs = mkVarSet (mapCatMaybes getTyVar_maybe args_to_drop)
619 univ_tvs = (mkVarSet tvs `extendVarSetList` deriv_tvs)
620 `minusVarSet` dropped_tvs
622 -- Check that the result really is well-kinded
623 ; checkTc (n_args_to_keep >= 0 && (inst_ty_kind `eqKind` kind))
624 (derivingKindErr tc cls cls_tys kind)
626 ; checkTc (sizeVarSet dropped_tvs == n_args_to_drop && -- (a)
627 tyVarsOfTypes (inst_ty:cls_tys) `subVarSet` univ_tvs) -- (b)
628 (derivingEtaErr cls cls_tys inst_ty)
630 -- (a) The data type can be eta-reduced; eg reject:
631 -- data instance T a a = ... deriving( Monad )
632 -- (b) The type class args do not mention any of the dropped type
634 -- newtype T a s = ... deriving( ST s )
636 -- Type families can't be partially applied
637 -- e.g. newtype instance T Int a = MkT [a] deriving( Monad )
638 -- Note [Deriving, type families, and partial applications]
639 ; checkTc (not (isFamilyTyCon tc) || n_args_to_drop == 0)
640 (typeFamilyPapErr tc cls cls_tys inst_ty)
642 ; mkEqnHelp DerivOrigin (varSetElems univ_tvs) cls cls_tys inst_ty Nothing } }
644 -- Tiresomely we must figure out the "lhs", which is awkward for type families
645 -- E.g. data T a b = .. deriving( Eq )
646 -- Here, the lhs is (T a b)
647 -- data instance TF Int b = ... deriving( Eq )
648 -- Here, the lhs is (TF Int b)
649 -- But if we just look up the tycon_name, we get is the *family*
650 -- tycon, but not pattern types -- they are in the *rep* tycon.
651 get_lhs Nothing = do { tc <- tcLookupTyCon tycon_name
652 ; let tvs = tyConTyVars tc
653 ; return (tvs, tc, mkTyVarTys tvs) }
654 get_lhs (Just pats) = do { let hs_app = nlHsTyConApp tycon_name pats
655 ; (tvs, tc_app) <- tcHsQuantifiedType tv_names hs_app
656 ; let (tc, tc_args) = tcSplitTyConApp tc_app
657 ; return (tvs, tc, tc_args) }
660 = panic "derivTyData" -- Caller ensures that only TyData can happen
663 Note [Deriving, type families, and partial applications]
664 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
665 When there are no type families, it's quite easy:
667 newtype S a = MkS [a]
668 -- :CoS :: S ~ [] -- Eta-reduced
670 instance Eq [a] => Eq (S a) -- by coercion sym (Eq (:CoS a)) : Eq [a] ~ Eq (S a)
671 instance Monad [] => Monad S -- by coercion sym (Monad :CoS) : Monad [] ~ Monad S
673 When type familes are involved it's trickier:
676 newtype instance T Int a = MkT [a] deriving( Eq, Monad )
677 -- :RT is the representation type for (T Int a)
678 -- :CoF:R1T a :: T Int a ~ :RT a -- Not eta reduced
679 -- :Co:R1T :: :RT ~ [] -- Eta-reduced
681 instance Eq [a] => Eq (T Int a) -- easy by coercion
682 instance Monad [] => Monad (T Int) -- only if we can eta reduce???
684 The "???" bit is that we don't build the :CoF thing in eta-reduced form
685 Henc the current typeFamilyPapErr, even though the instance makes sense.
686 After all, we can write it out
687 instance Monad [] => Monad (T Int) -- only if we can eta reduce???
692 mkEqnHelp :: CtOrigin -> [TyVar] -> Class -> [Type] -> Type
693 -> DerivContext -- Just => context supplied (standalone deriving)
694 -- Nothing => context inferred (deriving on data decl)
695 -> TcRn EarlyDerivSpec
696 -- Make the EarlyDerivSpec for an instance
697 -- forall tvs. theta => cls (tys ++ [ty])
698 -- where the 'theta' is optional (that's the Maybe part)
699 -- Assumes that this declaration is well-kinded
701 mkEqnHelp orig tvs cls cls_tys tc_app mtheta
702 | Just (tycon, tc_args) <- tcSplitTyConApp_maybe tc_app
703 , isAlgTyCon tycon -- Check for functions, primitive types etc
704 = mk_alg_eqn tycon tc_args
706 = failWithTc (derivingThingErr False cls cls_tys tc_app
707 (ptext (sLit "The last argument of the instance must be a data or newtype application")))
710 bale_out msg = failWithTc (derivingThingErr False cls cls_tys tc_app msg)
712 mk_alg_eqn tycon tc_args
713 | className cls `elem` typeableClassNames
714 = do { dflags <- getDOpts
715 ; case checkTypeableConditions (dflags, tycon) of
716 Just err -> bale_out err
717 Nothing -> mk_typeable_eqn orig tvs cls tycon tc_args mtheta }
719 | isDataFamilyTyCon tycon
720 , length tc_args /= tyConArity tycon
721 = bale_out (ptext (sLit "Unsaturated data family application"))
724 = do { (rep_tc, rep_tc_args) <- tcLookupDataFamInst tycon tc_args
725 -- Be careful to test rep_tc here: in the case of families,
726 -- we want to check the instance tycon, not the family tycon
728 -- For standalone deriving (mtheta /= Nothing),
729 -- check that all the data constructors are in scope.
730 ; rdr_env <- getGlobalRdrEnv
731 ; let hidden_data_cons = isAbstractTyCon rep_tc ||
732 any not_in_scope (tyConDataCons rep_tc)
733 not_in_scope dc = null (lookupGRE_Name rdr_env (dataConName dc))
734 ; unless (isNothing mtheta || not hidden_data_cons)
735 (bale_out (derivingHiddenErr tycon))
738 ; if isDataTyCon rep_tc then
739 mkDataTypeEqn orig dflags tvs cls cls_tys
740 tycon tc_args rep_tc rep_tc_args mtheta
742 mkNewTypeEqn orig dflags tvs cls cls_tys
743 tycon tc_args rep_tc rep_tc_args mtheta }
747 %************************************************************************
751 %************************************************************************
754 mkDataTypeEqn :: CtOrigin
756 -> [Var] -- Universally quantified type variables in the instance
757 -> Class -- Class for which we need to derive an instance
758 -> [Type] -- Other parameters to the class except the last
759 -> TyCon -- Type constructor for which the instance is requested
760 -- (last parameter to the type class)
761 -> [Type] -- Parameters to the type constructor
762 -> TyCon -- rep of the above (for type families)
763 -> [Type] -- rep of the above
764 -> DerivContext -- Context of the instance, for standalone deriving
765 -> TcRn EarlyDerivSpec -- Return 'Nothing' if error
767 mkDataTypeEqn orig dflags tvs cls cls_tys
768 tycon tc_args rep_tc rep_tc_args mtheta
769 = case checkSideConditions dflags mtheta cls cls_tys rep_tc of
770 -- NB: pass the *representation* tycon to checkSideConditions
771 CanDerive -> go_for_it
772 NonDerivableClass -> bale_out (nonStdErr cls)
773 DerivableClassError msg -> bale_out msg
775 go_for_it = mk_data_eqn orig tvs cls tycon tc_args rep_tc rep_tc_args mtheta
776 bale_out msg = failWithTc (derivingThingErr False cls cls_tys (mkTyConApp tycon tc_args) msg)
778 mk_data_eqn :: CtOrigin -> [TyVar] -> Class
779 -> TyCon -> [TcType] -> TyCon -> [TcType] -> DerivContext
780 -> TcM EarlyDerivSpec
781 mk_data_eqn orig tvs cls tycon tc_args rep_tc rep_tc_args mtheta
782 = do { dfun_name <- new_dfun_name cls tycon
784 ; let inst_tys = [mkTyConApp tycon tc_args]
785 inferred_constraints = inferConstraints tvs cls inst_tys rep_tc rep_tc_args
786 spec = DS { ds_loc = loc, ds_orig = orig
787 , ds_name = dfun_name, ds_tvs = tvs
788 , ds_cls = cls, ds_tys = inst_tys
789 , ds_tc = rep_tc, ds_tc_args = rep_tc_args
790 , ds_theta = mtheta `orElse` inferred_constraints
791 , ds_newtype = False }
793 ; return (if isJust mtheta then Right spec -- Specified context
794 else Left spec) } -- Infer context
796 ----------------------
797 mk_typeable_eqn :: CtOrigin -> [TyVar] -> Class
798 -> TyCon -> [TcType] -> DerivContext
799 -> TcM EarlyDerivSpec
800 mk_typeable_eqn orig tvs cls tycon tc_args mtheta
801 -- The Typeable class is special in several ways
802 -- data T a b = ... deriving( Typeable )
804 -- instance Typeable2 T where ...
806 -- 1. There are no constraints in the instance
807 -- 2. There are no type variables either
808 -- 3. The actual class we want to generate isn't necessarily
809 -- Typeable; it depends on the arity of the type
810 | isNothing mtheta -- deriving on a data type decl
811 = do { checkTc (cls `hasKey` typeableClassKey)
812 (ptext (sLit "Use deriving( Typeable ) on a data type declaration"))
813 ; real_cls <- tcLookupClass (typeableClassNames !! tyConArity tycon)
814 ; mk_typeable_eqn orig tvs real_cls tycon [] (Just []) }
816 | otherwise -- standaone deriving
817 = do { checkTc (null tc_args)
818 (ptext (sLit "Derived typeable instance must be of form (Typeable")
819 <> int (tyConArity tycon) <+> ppr tycon <> rparen)
820 ; dfun_name <- new_dfun_name cls tycon
823 DS { ds_loc = loc, ds_orig = orig, ds_name = dfun_name, ds_tvs = []
824 , ds_cls = cls, ds_tys = [mkTyConApp tycon []]
825 , ds_tc = tycon, ds_tc_args = []
826 , ds_theta = mtheta `orElse` [], ds_newtype = False }) }
828 ----------------------
829 inferConstraints :: [TyVar] -> Class -> [TcType] -> TyCon -> [TcType] -> ThetaType
830 -- Generate a sufficiently large set of constraints that typechecking the
831 -- generated method definitions should succeed. This set will be simplified
832 -- before being used in the instance declaration
833 inferConstraints _ cls inst_tys rep_tc rep_tc_args
834 -- Generic constraints are easy
835 | cls `hasKey` genClassKey
837 -- The others are a bit more complicated
839 = ASSERT2( equalLength rep_tc_tvs all_rep_tc_args, ppr cls <+> ppr rep_tc )
840 stupid_constraints ++ extra_constraints
841 ++ sc_constraints ++ con_arg_constraints
843 -- Constraints arising from the arguments of each constructor
845 = [ mkClassPred cls [arg_ty]
846 | data_con <- tyConDataCons rep_tc,
847 arg_ty <- ASSERT( isVanillaDataCon data_con )
848 get_constrained_tys $
849 dataConInstOrigArgTys data_con all_rep_tc_args,
850 not (isUnLiftedType arg_ty) ]
851 -- No constraints for unlifted types
852 -- Where they are legal we generate specilised function calls
854 -- For functor-like classes, two things are different
855 -- (a) We recurse over argument types to generate constraints
856 -- See Functor examples in TcGenDeriv
857 -- (b) The rep_tc_args will be one short
858 is_functor_like = getUnique cls `elem` functorLikeClassKeys
860 get_constrained_tys :: [Type] -> [Type]
861 get_constrained_tys tys
862 | is_functor_like = concatMap (deepSubtypesContaining last_tv) tys
865 rep_tc_tvs = tyConTyVars rep_tc
866 last_tv = last rep_tc_tvs
867 all_rep_tc_args | is_functor_like = rep_tc_args ++ [mkTyVarTy last_tv]
868 | otherwise = rep_tc_args
870 -- Constraints arising from superclasses
871 -- See Note [Superclasses of derived instance]
872 sc_constraints = substTheta (zipOpenTvSubst (classTyVars cls) inst_tys)
875 -- Stupid constraints
876 stupid_constraints = substTheta subst (tyConStupidTheta rep_tc)
877 subst = zipTopTvSubst rep_tc_tvs all_rep_tc_args
879 -- Extra Data constraints
880 -- The Data class (only) requires that for
881 -- instance (...) => Data (T t1 t2)
883 -- THEN (Data t1, Data t2) are among the (...) constraints
884 -- Reason: when the IF holds, we generate a method
885 -- dataCast2 f = gcast2 f
886 -- and we need the Data constraints to typecheck the method
888 | cls `hasKey` dataClassKey
889 , all (isLiftedTypeKind . typeKind) rep_tc_args
890 = [mkClassPred cls [ty] | ty <- rep_tc_args]
894 ------------------------------------------------------------------
895 -- Check side conditions that dis-allow derivability for particular classes
896 -- This is *apart* from the newtype-deriving mechanism
898 -- Here we get the representation tycon in case of family instances as it has
899 -- the data constructors - but we need to be careful to fall back to the
900 -- family tycon (with indexes) in error messages.
902 data DerivStatus = CanDerive
903 | DerivableClassError SDoc -- Standard class, but can't do it
904 | NonDerivableClass -- Non-standard class
906 checkSideConditions :: DynFlags -> DerivContext -> Class -> [TcType] -> TyCon -> DerivStatus
907 checkSideConditions dflags mtheta cls cls_tys rep_tc
908 | Just cond <- sideConditions mtheta cls
909 = case (cond (dflags, rep_tc)) of
910 Just err -> DerivableClassError err -- Class-specific error
911 Nothing | null cls_tys -> CanDerive -- All derivable classes are unary, so
912 -- cls_tys (the type args other than last)
914 | otherwise -> DerivableClassError ty_args_why -- e.g. deriving( Eq s )
915 | otherwise = NonDerivableClass -- Not a standard class
917 ty_args_why = quotes (ppr (mkClassPred cls cls_tys)) <+> ptext (sLit "is not a class")
919 checkTypeableConditions :: Condition
920 checkTypeableConditions = checkFlag Opt_DeriveDataTypeable `andCond` cond_typeableOK
922 nonStdErr :: Class -> SDoc
923 nonStdErr cls = quotes (ppr cls) <+> ptext (sLit "is not a derivable class")
925 sideConditions :: DerivContext -> Class -> Maybe Condition
926 sideConditions mtheta cls
927 | cls_key == eqClassKey = Just cond_std
928 | cls_key == ordClassKey = Just cond_std
929 | cls_key == showClassKey = Just cond_std
930 | cls_key == readClassKey = Just (cond_std `andCond` cond_noUnliftedArgs)
931 | cls_key == enumClassKey = Just (cond_std `andCond` cond_isEnumeration)
932 | cls_key == ixClassKey = Just (cond_std `andCond` cond_enumOrProduct)
933 | cls_key == boundedClassKey = Just (cond_std `andCond` cond_enumOrProduct)
934 | cls_key == dataClassKey = Just (checkFlag Opt_DeriveDataTypeable `andCond`
935 cond_std `andCond` cond_noUnliftedArgs)
936 | cls_key == functorClassKey = Just (checkFlag Opt_DeriveFunctor `andCond`
937 cond_functorOK True) -- NB: no cond_std!
938 | cls_key == foldableClassKey = Just (checkFlag Opt_DeriveFoldable `andCond`
939 cond_functorOK False) -- Functor/Fold/Trav works ok for rank-n types
940 | cls_key == traversableClassKey = Just (checkFlag Opt_DeriveTraversable `andCond`
941 cond_functorOK False)
942 | cls_key == genClassKey = Just (cond_RepresentableOk `andCond`
943 checkFlag Opt_DeriveGeneric)
944 | otherwise = Nothing
946 cls_key = getUnique cls
947 cond_std = cond_stdOK mtheta
949 type Condition = (DynFlags, TyCon) -> Maybe SDoc
950 -- first Bool is whether or not we are allowed to derive Data and Typeable
951 -- second Bool is whether or not we are allowed to derive Functor
952 -- TyCon is the *representation* tycon if the
953 -- data type is an indexed one
956 orCond :: Condition -> Condition -> Condition
959 Nothing -> Nothing -- c1 succeeds
960 Just x -> case c2 tc of -- c1 fails
962 Just y -> Just (x $$ ptext (sLit " or") $$ y)
965 andCond :: Condition -> Condition -> Condition
966 andCond c1 c2 tc = case c1 tc of
967 Nothing -> c2 tc -- c1 succeeds
968 Just x -> Just x -- c1 fails
970 cond_stdOK :: DerivContext -> Condition
971 cond_stdOK (Just _) _
972 = Nothing -- Don't check these conservative conditions for
973 -- standalone deriving; just generate the code
974 -- and let the typechecker handle the result
975 cond_stdOK Nothing (_, rep_tc)
976 | null data_cons = Just (no_cons_why rep_tc $$ suggestion)
977 | not (null con_whys) = Just (vcat con_whys $$ suggestion)
978 | otherwise = Nothing
980 suggestion = ptext (sLit "Possible fix: use a standalone deriving declaration instead")
981 data_cons = tyConDataCons rep_tc
982 con_whys = mapCatMaybes check_con data_cons
984 check_con :: DataCon -> Maybe SDoc
986 | isVanillaDataCon con
987 , all isTauTy (dataConOrigArgTys con) = Nothing
988 | otherwise = Just (badCon con (ptext (sLit "must have a Haskell-98 type")))
990 no_cons_why :: TyCon -> SDoc
991 no_cons_why rep_tc = quotes (pprSourceTyCon rep_tc) <+>
992 ptext (sLit "must have at least one data constructor")
994 -- JPM TODO: should give better error message
995 cond_RepresentableOk :: Condition
997 cond_RepresentableOk (_,t) | canDoGenerics t = Nothing
998 | otherwise = Just (ptext (sLit "Cannot derive Generic for type") <+> ppr t)
1000 cond_RepresentableOk (_,t) = canDoGenerics t
1002 cond_enumOrProduct :: Condition
1003 cond_enumOrProduct = cond_isEnumeration `orCond`
1004 (cond_isProduct `andCond` cond_noUnliftedArgs)
1006 cond_noUnliftedArgs :: Condition
1007 -- For some classes (eg Eq, Ord) we allow unlifted arg types
1008 -- by generating specilaised code. For others (eg Data) we don't.
1009 cond_noUnliftedArgs (_, tc)
1010 | null bad_cons = Nothing
1011 | otherwise = Just why
1013 bad_cons = [ con | con <- tyConDataCons tc
1014 , any isUnLiftedType (dataConOrigArgTys con) ]
1015 why = badCon (head bad_cons) (ptext (sLit "must have only arguments of lifted type"))
1017 cond_isEnumeration :: Condition
1018 cond_isEnumeration (_, rep_tc)
1019 | isEnumerationTyCon rep_tc = Nothing
1020 | otherwise = Just why
1022 why = sep [ quotes (pprSourceTyCon rep_tc) <+>
1023 ptext (sLit "must be an enumeration type")
1024 , ptext (sLit "(an enumeration consists of one or more nullary, non-GADT constructors)") ]
1025 -- See Note [Enumeration types] in TyCon
1027 cond_isProduct :: Condition
1028 cond_isProduct (_, rep_tc)
1029 | isProductTyCon rep_tc = Nothing
1030 | otherwise = Just why
1032 why = quotes (pprSourceTyCon rep_tc) <+>
1033 ptext (sLit "must have precisely one constructor")
1035 cond_typeableOK :: Condition
1036 -- OK for Typeable class
1037 -- Currently: (a) args all of kind *
1038 -- (b) 7 or fewer args
1039 cond_typeableOK (_, tc)
1040 | tyConArity tc > 7 = Just too_many
1041 | not (all (isSubArgTypeKind . tyVarKind) (tyConTyVars tc))
1043 | otherwise = Nothing
1045 too_many = quotes (pprSourceTyCon tc) <+>
1046 ptext (sLit "must have 7 or fewer arguments")
1047 bad_kind = quotes (pprSourceTyCon tc) <+>
1048 ptext (sLit "must only have arguments of kind `*'")
1050 functorLikeClassKeys :: [Unique]
1051 functorLikeClassKeys = [functorClassKey, foldableClassKey, traversableClassKey]
1053 cond_functorOK :: Bool -> Condition
1054 -- OK for Functor/Foldable/Traversable class
1055 -- Currently: (a) at least one argument
1056 -- (b) don't use argument contravariantly
1057 -- (c) don't use argument in the wrong place, e.g. data T a = T (X a a)
1058 -- (d) optionally: don't use function types
1059 -- (e) no "stupid context" on data type
1060 cond_functorOK allowFunctions (_, rep_tc)
1062 = Just (ptext (sLit "Data type") <+> quotes (ppr rep_tc)
1063 <+> ptext (sLit "must have some type parameters"))
1065 | not (null bad_stupid_theta)
1066 = Just (ptext (sLit "Data type") <+> quotes (ppr rep_tc)
1067 <+> ptext (sLit "must not have a class context") <+> pprTheta bad_stupid_theta)
1070 = msum (map check_con data_cons) -- msum picks the first 'Just', if any
1072 tc_tvs = tyConTyVars rep_tc
1073 Just (_, last_tv) = snocView tc_tvs
1074 bad_stupid_theta = filter is_bad (tyConStupidTheta rep_tc)
1075 is_bad pred = last_tv `elemVarSet` tyVarsOfPred pred
1077 data_cons = tyConDataCons rep_tc
1078 check_con con = msum (check_vanilla con : foldDataConArgs (ft_check con) con)
1080 check_vanilla :: DataCon -> Maybe SDoc
1081 check_vanilla con | isVanillaDataCon con = Nothing
1082 | otherwise = Just (badCon con existential)
1084 ft_check :: DataCon -> FFoldType (Maybe SDoc)
1085 ft_check con = FT { ft_triv = Nothing, ft_var = Nothing
1086 , ft_co_var = Just (badCon con covariant)
1087 , ft_fun = \x y -> if allowFunctions then x `mplus` y
1088 else Just (badCon con functions)
1089 , ft_tup = \_ xs -> msum xs
1090 , ft_ty_app = \_ x -> x
1091 , ft_bad_app = Just (badCon con wrong_arg)
1092 , ft_forall = \_ x -> x }
1094 existential = ptext (sLit "must not have existential arguments")
1095 covariant = ptext (sLit "must not use the type variable in a function argument")
1096 functions = ptext (sLit "must not contain function types")
1097 wrong_arg = ptext (sLit "must not use the type variable in an argument other than the last")
1099 checkFlag :: ExtensionFlag -> Condition
1100 checkFlag flag (dflags, _)
1101 | xopt flag dflags = Nothing
1102 | otherwise = Just why
1104 why = ptext (sLit "You need -X") <> text flag_str
1105 <+> ptext (sLit "to derive an instance for this class")
1106 flag_str = case [ s | (s, f, _) <- xFlags, f==flag ] of
1108 other -> pprPanic "checkFlag" (ppr other)
1110 std_class_via_iso :: Class -> Bool
1111 -- These standard classes can be derived for a newtype
1112 -- using the isomorphism trick *even if no -XGeneralizedNewtypeDeriving
1113 -- because giving so gives the same results as generating the boilerplate
1114 std_class_via_iso clas
1115 = classKey clas `elem` [eqClassKey, ordClassKey, ixClassKey, boundedClassKey]
1116 -- Not Read/Show because they respect the type
1117 -- Not Enum, because newtypes are never in Enum
1120 non_iso_class :: Class -> Bool
1121 -- *Never* derive Read, Show, Typeable, Data, Generic by isomorphism,
1122 -- even with -XGeneralizedNewtypeDeriving
1124 = classKey cls `elem` ([ readClassKey, showClassKey, dataClassKey
1125 , genClassKey] ++ typeableClassKeys)
1127 typeableClassKeys :: [Unique]
1128 typeableClassKeys = map getUnique typeableClassNames
1130 new_dfun_name :: Class -> TyCon -> TcM Name
1131 new_dfun_name clas tycon -- Just a simple wrapper
1132 = do { loc <- getSrcSpanM -- The location of the instance decl, not of the tycon
1133 ; newDFunName clas [mkTyConApp tycon []] loc }
1134 -- The type passed to newDFunName is only used to generate
1135 -- a suitable string; hence the empty type arg list
1137 badCon :: DataCon -> SDoc -> SDoc
1138 badCon con msg = ptext (sLit "Constructor") <+> quotes (ppr con) <+> msg
1141 Note [Superclasses of derived instance]
1142 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1143 In general, a derived instance decl needs the superclasses of the derived
1144 class too. So if we have
1145 data T a = ...deriving( Ord )
1146 then the initial context for Ord (T a) should include Eq (T a). Often this is
1147 redundant; we'll also generate an Ord constraint for each constructor argument,
1148 and that will probably generate enough constraints to make the Eq (T a) constraint
1149 be satisfied too. But not always; consider:
1155 data T a = MkT (S a) deriving( Ord )
1156 instance Num a => Eq (T a)
1158 The derived instance for (Ord (T a)) must have a (Num a) constraint!
1160 data T a = MkT deriving( Data, Typeable )
1161 Here there *is* no argument field, but we must nevertheless generate
1162 a context for the Data instances:
1163 instance Typable a => Data (T a) where ...
1166 %************************************************************************
1170 %************************************************************************
1173 mkNewTypeEqn :: CtOrigin -> DynFlags -> [Var] -> Class
1174 -> [Type] -> TyCon -> [Type] -> TyCon -> [Type]
1176 -> TcRn EarlyDerivSpec
1177 mkNewTypeEqn orig dflags tvs
1178 cls cls_tys tycon tc_args rep_tycon rep_tc_args mtheta
1179 -- Want: instance (...) => cls (cls_tys ++ [tycon tc_args]) where ...
1180 | can_derive_via_isomorphism && (newtype_deriving || std_class_via_iso cls)
1181 = do { traceTc "newtype deriving:" (ppr tycon <+> ppr rep_tys <+> ppr all_preds)
1182 ; dfun_name <- new_dfun_name cls tycon
1183 ; loc <- getSrcSpanM
1184 ; let spec = DS { ds_loc = loc, ds_orig = orig
1185 , ds_name = dfun_name, ds_tvs = varSetElems dfun_tvs
1186 , ds_cls = cls, ds_tys = inst_tys
1187 , ds_tc = rep_tycon, ds_tc_args = rep_tc_args
1188 , ds_theta = mtheta `orElse` all_preds
1189 , ds_newtype = True }
1190 ; return (if isJust mtheta then Right spec
1194 = case checkSideConditions dflags mtheta cls cls_tys rep_tycon of
1195 CanDerive -> go_for_it -- Use the standard H98 method
1196 DerivableClassError msg -- Error with standard class
1197 | can_derive_via_isomorphism -> bale_out (msg $$ suggest_nd)
1198 | otherwise -> bale_out msg
1199 NonDerivableClass -- Must use newtype deriving
1200 | newtype_deriving -> bale_out cant_derive_err -- Too hard, even with newtype deriving
1201 | can_derive_via_isomorphism -> bale_out (non_std $$ suggest_nd) -- Try newtype deriving!
1202 | otherwise -> bale_out non_std
1204 newtype_deriving = xopt Opt_GeneralizedNewtypeDeriving dflags
1205 go_for_it = mk_data_eqn orig tvs cls tycon tc_args rep_tycon rep_tc_args mtheta
1206 bale_out msg = failWithTc (derivingThingErr newtype_deriving cls cls_tys inst_ty msg)
1208 non_std = nonStdErr cls
1209 suggest_nd = ptext (sLit "Try -XGeneralizedNewtypeDeriving for GHC's newtype-deriving extension")
1211 -- Here is the plan for newtype derivings. We see
1212 -- newtype T a1...an = MkT (t ak+1...an) deriving (.., C s1 .. sm, ...)
1213 -- where t is a type,
1214 -- ak+1...an is a suffix of a1..an, and are all tyars
1215 -- ak+1...an do not occur free in t, nor in the s1..sm
1216 -- (C s1 ... sm) is a *partial applications* of class C
1217 -- with the last parameter missing
1218 -- (T a1 .. ak) matches the kind of C's last argument
1219 -- (and hence so does t)
1220 -- The latter kind-check has been done by deriveTyData already,
1221 -- and tc_args are already trimmed
1223 -- We generate the instance
1224 -- instance forall ({a1..ak} u fvs(s1..sm)).
1225 -- C s1 .. sm t => C s1 .. sm (T a1...ak)
1226 -- where T a1...ap is the partial application of
1227 -- the LHS of the correct kind and p >= k
1229 -- NB: the variables below are:
1230 -- tc_tvs = [a1, ..., an]
1231 -- tyvars_to_keep = [a1, ..., ak]
1232 -- rep_ty = t ak .. an
1233 -- deriv_tvs = fvs(s1..sm) \ tc_tvs
1234 -- tys = [s1, ..., sm]
1237 -- Running example: newtype T s a = MkT (ST s a) deriving( Monad )
1238 -- We generate the instance
1239 -- instance Monad (ST s) => Monad (T s) where
1241 nt_eta_arity = length (fst (newTyConEtadRhs rep_tycon))
1242 -- For newtype T a b = MkT (S a a b), the TyCon machinery already
1243 -- eta-reduces the representation type, so we know that
1245 -- That's convenient here, because we may have to apply
1246 -- it to fewer than its original complement of arguments
1248 -- Note [Newtype representation]
1249 -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1250 -- Need newTyConRhs (*not* a recursive representation finder)
1251 -- to get the representation type. For example
1252 -- newtype B = MkB Int
1253 -- newtype A = MkA B deriving( Num )
1254 -- We want the Num instance of B, *not* the Num instance of Int,
1255 -- when making the Num instance of A!
1256 rep_inst_ty = newTyConInstRhs rep_tycon rep_tc_args
1257 rep_tys = cls_tys ++ [rep_inst_ty]
1258 rep_pred = mkClassPred cls rep_tys
1259 -- rep_pred is the representation dictionary, from where
1260 -- we are gong to get all the methods for the newtype
1264 -- Next we figure out what superclass dictionaries to use
1265 -- See Note [Newtype deriving superclasses] above
1267 cls_tyvars = classTyVars cls
1268 dfun_tvs = tyVarsOfTypes inst_tys
1269 inst_ty = mkTyConApp tycon tc_args
1270 inst_tys = cls_tys ++ [inst_ty]
1271 sc_theta = substTheta (zipOpenTvSubst cls_tyvars inst_tys)
1274 -- If there are no tyvars, there's no need
1275 -- to abstract over the dictionaries we need
1276 -- Example: newtype T = MkT Int deriving( C )
1277 -- We get the derived instance
1280 -- instance C Int => C T
1281 all_preds = rep_pred : sc_theta -- NB: rep_pred comes first
1283 -------------------------------------------------------------------
1284 -- Figuring out whether we can only do this newtype-deriving thing
1286 can_derive_via_isomorphism
1287 = not (non_iso_class cls)
1291 -- && not (isRecursiveTyCon tycon) -- Note [Recursive newtypes]
1293 arity_ok = length cls_tys + 1 == classArity cls
1294 -- Well kinded; eg not: newtype T ... deriving( ST )
1295 -- because ST needs *2* type params
1297 -- Check that eta reduction is OK
1298 eta_ok = nt_eta_arity <= length rep_tc_args
1299 -- The newtype can be eta-reduced to match the number
1300 -- of type argument actually supplied
1301 -- newtype T a b = MkT (S [a] b) deriving( Monad )
1302 -- Here the 'b' must be the same in the rep type (S [a] b)
1303 -- And the [a] must not mention 'b'. That's all handled
1306 ats_ok = null (classATs cls)
1307 -- No associated types for the class, because we don't
1308 -- currently generate type 'instance' decls; and cannot do
1309 -- so for 'data' instance decls
1312 = vcat [ ppUnless arity_ok arity_msg
1313 , ppUnless eta_ok eta_msg
1314 , ppUnless ats_ok ats_msg ]
1315 arity_msg = quotes (ppr (mkClassPred cls cls_tys)) <+> ptext (sLit "does not have arity 1")
1316 eta_msg = ptext (sLit "cannot eta-reduce the representation type enough")
1317 ats_msg = ptext (sLit "the class has associated types")
1320 Note [Recursive newtypes]
1321 ~~~~~~~~~~~~~~~~~~~~~~~~~
1322 Newtype deriving works fine, even if the newtype is recursive.
1323 e.g. newtype S1 = S1 [T1 ()]
1324 newtype T1 a = T1 (StateT S1 IO a ) deriving( Monad )
1325 Remember, too, that type families are curretly (conservatively) given
1326 a recursive flag, so this also allows newtype deriving to work
1329 We used to exclude recursive types, because we had a rather simple
1330 minded way of generating the instance decl:
1332 instance Eq [A] => Eq A -- Makes typechecker loop!
1333 But now we require a simple context, so it's ok.
1336 %************************************************************************
1338 \subsection[TcDeriv-fixpoint]{Finding the fixed point of \tr{deriving} equations}
1340 %************************************************************************
1342 A ``solution'' (to one of the equations) is a list of (k,TyVarTy tv)
1343 terms, which is the final correct RHS for the corresponding original
1347 Each (k,TyVarTy tv) in a solution constrains only a type
1351 The (k,TyVarTy tv) pairs in a solution are canonically
1352 ordered by sorting on type varible, tv, (major key) and then class, k,
1357 inferInstanceContexts :: OverlapFlag -> [DerivSpec] -> TcM [DerivSpec]
1359 inferInstanceContexts _ [] = return []
1361 inferInstanceContexts oflag infer_specs
1362 = do { traceTc "inferInstanceContexts" $ vcat (map pprDerivSpec infer_specs)
1363 ; iterate_deriv 1 initial_solutions }
1365 ------------------------------------------------------------------
1366 -- The initial solutions for the equations claim that each
1367 -- instance has an empty context; this solution is certainly
1368 -- in canonical form.
1369 initial_solutions :: [ThetaType]
1370 initial_solutions = [ [] | _ <- infer_specs ]
1372 ------------------------------------------------------------------
1373 -- iterate_deriv calculates the next batch of solutions,
1374 -- compares it with the current one; finishes if they are the
1375 -- same, otherwise recurses with the new solutions.
1376 -- It fails if any iteration fails
1377 iterate_deriv :: Int -> [ThetaType] -> TcM [DerivSpec]
1378 iterate_deriv n current_solns
1379 | n > 20 -- Looks as if we are in an infinite loop
1380 -- This can happen if we have -XUndecidableInstances
1381 -- (See TcSimplify.tcSimplifyDeriv.)
1382 = pprPanic "solveDerivEqns: probable loop"
1383 (vcat (map pprDerivSpec infer_specs) $$ ppr current_solns)
1385 = do { -- Extend the inst info from the explicit instance decls
1386 -- with the current set of solutions, and simplify each RHS
1387 let inst_specs = zipWithEqual "add_solns" (mkInstance oflag)
1388 current_solns infer_specs
1389 ; new_solns <- checkNoErrs $
1390 extendLocalInstEnv inst_specs $
1391 mapM gen_soln infer_specs
1393 ; if (current_solns == new_solns) then
1394 return [ spec { ds_theta = soln }
1395 | (spec, soln) <- zip infer_specs current_solns ]
1397 iterate_deriv (n+1) new_solns }
1399 ------------------------------------------------------------------
1400 gen_soln :: DerivSpec -> TcM [PredType]
1401 gen_soln (DS { ds_loc = loc, ds_orig = orig, ds_tvs = tyvars
1402 , ds_cls = clas, ds_tys = inst_tys, ds_theta = deriv_rhs })
1404 addErrCtxt (derivInstCtxt the_pred) $
1405 do { -- Check for a bizarre corner case, when the derived instance decl should
1406 -- have form instance C a b => D (T a) where ...
1407 -- Note that 'b' isn't a parameter of T. This gives rise to all sorts
1408 -- of problems; in particular, it's hard to compare solutions for
1409 -- equality when finding the fixpoint. Moreover, simplifyDeriv
1410 -- has an assert failure because it finds a TyVar when it expects
1411 -- only TcTyVars. So I just rule it out for now. I'm not
1412 -- even sure how it can arise.
1414 ; let tv_set = mkVarSet tyvars
1415 weird_preds = [pred | pred <- deriv_rhs
1416 , not (tyVarsOfPred pred `subVarSet` tv_set)]
1417 ; mapM_ (addErrTc . badDerivedPred) weird_preds
1419 ; theta <- simplifyDeriv orig the_pred tyvars deriv_rhs
1420 -- checkValidInstance tyvars theta clas inst_tys
1421 -- Not necessary; see Note [Exotic derived instance contexts]
1424 ; traceTc "TcDeriv" (ppr deriv_rhs $$ ppr theta)
1425 -- Claim: the result instance declaration is guaranteed valid
1426 -- Hence no need to call:
1427 -- checkValidInstance tyvars theta clas inst_tys
1428 ; return (sortLe (<=) theta) } -- Canonicalise before returning the solution
1430 the_pred = mkClassPred clas inst_tys
1432 ------------------------------------------------------------------
1433 mkInstance :: OverlapFlag -> ThetaType -> DerivSpec -> Instance
1434 mkInstance overlap_flag theta
1435 (DS { ds_name = dfun_name
1436 , ds_tvs = tyvars, ds_cls = clas, ds_tys = tys })
1437 = mkLocalInstance dfun overlap_flag
1439 dfun = mkDictFunId dfun_name tyvars theta clas tys
1442 extendLocalInstEnv :: [Instance] -> TcM a -> TcM a
1443 -- Add new locally-defined instances; don't bother to check
1444 -- for functional dependency errors -- that'll happen in TcInstDcls
1445 extendLocalInstEnv dfuns thing_inside
1446 = do { env <- getGblEnv
1447 ; let inst_env' = extendInstEnvList (tcg_inst_env env) dfuns
1448 env' = env { tcg_inst_env = inst_env' }
1449 ; setGblEnv env' thing_inside }
1453 %************************************************************************
1455 \subsection[TcDeriv-normal-binds]{Bindings for the various classes}
1457 %************************************************************************
1459 After all the trouble to figure out the required context for the
1460 derived instance declarations, all that's left is to chug along to
1461 produce them. They will then be shoved into @tcInstDecls2@, which
1462 will do all its usual business.
1464 There are lots of possibilities for code to generate. Here are
1465 various general remarks.
1470 We want derived instances of @Eq@ and @Ord@ (both v common) to be
1471 ``you-couldn't-do-better-by-hand'' efficient.
1474 Deriving @Show@---also pretty common--- should also be reasonable good code.
1477 Deriving for the other classes isn't that common or that big a deal.
1484 Deriving @Ord@ is done mostly with the 1.3 @compare@ method.
1487 Deriving @Eq@ also uses @compare@, if we're deriving @Ord@, too.
1490 We {\em normally} generate code only for the non-defaulted methods;
1491 there are some exceptions for @Eq@ and (especially) @Ord@...
1494 Sometimes we use a @_con2tag_<tycon>@ function, which returns a data
1495 constructor's numeric (@Int#@) tag. These are generated by
1496 @gen_tag_n_con_binds@, and the heuristic for deciding if one of
1497 these is around is given by @hasCon2TagFun@.
1499 The examples under the different sections below will make this
1503 Much less often (really just for deriving @Ix@), we use a
1504 @_tag2con_<tycon>@ function. See the examples.
1507 We use the renamer!!! Reason: we're supposed to be
1508 producing @LHsBinds Name@ for the methods, but that means
1509 producing correctly-uniquified code on the fly. This is entirely
1510 possible (the @TcM@ monad has a @UniqueSupply@), but it is painful.
1511 So, instead, we produce @MonoBinds RdrName@ then heave 'em through
1512 the renamer. What a great hack!
1516 -- Generate the InstInfo for the required instance paired with the
1517 -- *representation* tycon for that instance,
1518 -- plus any auxiliary bindings required
1520 -- Representation tycons differ from the tycon in the instance signature in
1521 -- case of instances for indexed families.
1523 genInst :: Bool -- True <=> standalone deriving
1525 -> DerivSpec -> TcM (InstInfo RdrName, DerivAuxBinds)
1526 genInst standalone_deriv oflag
1527 spec@(DS { ds_tc = rep_tycon, ds_tc_args = rep_tc_args
1528 , ds_theta = theta, ds_newtype = is_newtype
1529 , ds_name = name, ds_cls = clas })
1531 = return (InstInfo { iSpec = inst_spec
1532 , iBinds = NewTypeDerived co rep_tycon }, [])
1535 = do { fix_env <- getFixityEnv
1536 ; let loc = getSrcSpan name
1537 (meth_binds, aux_binds) = genDerivBinds loc fix_env clas rep_tycon
1538 -- In case of a family instance, we need to use the representation
1539 -- tycon (after all, it has the data constructors)
1541 ; return (InstInfo { iSpec = inst_spec
1542 , iBinds = VanillaInst meth_binds [] standalone_deriv }
1545 inst_spec = mkInstance oflag theta spec
1546 co1 = case tyConFamilyCoercion_maybe rep_tycon of
1547 Just co_con -> ACo (mkTyConApp co_con rep_tc_args)
1549 -- Not a family => rep_tycon = main tycon
1550 co2 = case newTyConCo_maybe rep_tycon of
1551 Just co_con -> ACo (mkTyConApp co_con rep_tc_args)
1552 Nothing -> id_co -- The newtype is transparent; no need for a cast
1553 co = co1 `mkTransCoI` co2
1554 id_co = IdCo (mkTyConApp rep_tycon rep_tc_args)
1556 -- Example: newtype instance N [a] = N1 (Tree a)
1557 -- deriving instance Eq b => Eq (N [(b,b)])
1558 -- From the instance, we get an implicit newtype R1:N a = N1 (Tree a)
1559 -- When dealing with the deriving clause
1560 -- co1 : N [(b,b)] ~ R1:N (b,b)
1561 -- co2 : R1:N (b,b) ~ Tree (b,b)
1562 -- co : N [(b,b)] ~ Tree (b,b)
1564 genDerivBinds :: SrcSpan -> FixityEnv -> Class -> TyCon -> (LHsBinds RdrName, DerivAuxBinds)
1565 genDerivBinds loc fix_env clas tycon
1566 | className clas `elem` typeableClassNames
1567 = (gen_Typeable_binds loc tycon, [])
1570 = case assocMaybe gen_list (getUnique clas) of
1571 Just gen_fn -> gen_fn loc tycon
1572 Nothing -> pprPanic "genDerivBinds: bad derived class" (ppr clas)
1574 gen_list :: [(Unique, SrcSpan -> TyCon -> (LHsBinds RdrName, DerivAuxBinds))]
1575 gen_list = [(eqClassKey, gen_Eq_binds)
1576 ,(ordClassKey, gen_Ord_binds)
1577 ,(enumClassKey, gen_Enum_binds)
1578 ,(boundedClassKey, gen_Bounded_binds)
1579 ,(ixClassKey, gen_Ix_binds)
1580 ,(showClassKey, gen_Show_binds fix_env)
1581 ,(readClassKey, gen_Read_binds fix_env)
1582 ,(dataClassKey, gen_Data_binds)
1583 ,(functorClassKey, gen_Functor_binds)
1584 ,(foldableClassKey, gen_Foldable_binds)
1585 ,(traversableClassKey, gen_Traversable_binds)
1586 ,(genClassKey, genGenericBinds)
1590 %************************************************************************
1592 \subsection[TcDeriv-generic-binds]{Bindings for the new generic deriving mechanism}
1594 %************************************************************************
1596 For the generic representation we need to generate:
1598 \item A Generic instance
1599 \item A Rep type instance
1600 \item Many auxiliary datatypes and instances for them (for the meta-information)
1603 @genGenericBinds@ does (1)
1604 @genGenericRepExtras@ does (2) and (3)
1605 @genGenericAll@ does all of them
1608 genGenericBinds :: SrcSpan -> TyCon -> (LHsBinds RdrName, DerivAuxBinds)
1609 genGenericBinds _ tc = (mkBindsRep tc, [ {- No DerivAuxBinds -} ])
1611 genGenericRepExtras :: TyCon -> TcM (MetaTyCons, TyCon)
1612 genGenericRepExtras tc =
1613 do uniqS <- newUniqueSupply
1615 -- Uniques for everyone
1616 (uniqD:uniqs) = uniqsFromSupply uniqS
1617 (uniqsC,us) = splitAt (length tc_cons) uniqs
1618 uniqsS :: [[Unique]] -- Unique supply for the S datatypes
1619 uniqsS = mkUniqsS tc_arits us
1621 mkUniqsS (n:t) us = case splitAt n us of
1622 (us1,us2) -> us1 : mkUniqsS t us2
1624 tc_name = tyConName tc
1625 tc_cons = tyConDataCons tc
1626 tc_arits = map dataConSourceArity tc_cons
1628 tc_occ = nameOccName tc_name
1629 d_occ = mkGenD tc_occ
1630 c_occ m = mkGenC tc_occ m
1631 s_occ m n = mkGenS tc_occ m n
1632 mod_name = nameModule (tyConName tc)
1633 d_name = mkExternalName uniqD mod_name d_occ wiredInSrcSpan
1634 c_names = [ mkExternalName u mod_name (c_occ m) wiredInSrcSpan
1635 | (u,m) <- zip uniqsC [0..] ]
1636 s_names = [ [ mkExternalName u mod_name (s_occ m n) wiredInSrcSpan
1637 | (u,n) <- zip us [0..] ] | (us,m) <- zip uniqsS [0..] ]
1639 mkTyCon name = ASSERT( isExternalName name )
1640 buildAlgTyCon name [] [] mkAbstractTyConRhs
1641 NonRecursive False NoParentTyCon Nothing
1643 metaDTyCon <- mkTyCon d_name
1644 metaCTyCons <- sequence [ mkTyCon c_name | c_name <- c_names ]
1645 metaSTyCons <- mapM sequence
1647 | s_name <- s_namesC ] | s_namesC <- s_names ]
1649 let metaDts = MetaTyCons metaDTyCon metaCTyCons metaSTyCons
1651 rep0_tycon <- tc_mkRepTyCon tc metaDts
1653 return (metaDts, rep0_tycon)
1655 genGenericAll :: TyCon
1656 -> TcM ((InstInfo RdrName, DerivAuxBinds), MetaTyCons, TyCon)
1658 do (metaDts, rep0_tycon) <- genGenericRepExtras tc
1659 clas <- tcLookupClass genClassName
1660 dfun_name <- new_dfun_name clas tc
1662 mkInstRep = (InstInfo { iSpec = inst, iBinds = binds }
1663 , [ {- No DerivAuxBinds -} ])
1664 inst = mkLocalInstance dfun NoOverlap
1665 binds = VanillaInst (mkBindsRep tc) [] False
1667 tvs = tyConTyVars tc
1668 tc_ty = mkTyConApp tc (mkTyVarTys tvs)
1670 dfun = mkDictFunId dfun_name (tyConTyVars tc) [] clas [tc_ty]
1671 return (mkInstRep, metaDts, rep0_tycon)
1673 genDtMeta :: (TyCon, MetaTyCons) -> TcM [(InstInfo RdrName, DerivAuxBinds)]
1674 genDtMeta (tc,metaDts) =
1675 do dClas <- tcLookupClass datatypeClassName
1676 d_dfun_name <- new_dfun_name dClas tc
1677 cClas <- tcLookupClass constructorClassName
1678 c_dfun_names <- sequence [ new_dfun_name cClas tc | _ <- metaC metaDts ]
1679 sClas <- tcLookupClass selectorClassName
1680 s_dfun_names <- sequence (map sequence [ [ new_dfun_name sClas tc
1682 | x <- metaS metaDts ])
1683 fix_env <- getFixityEnv
1686 (dBinds,cBinds,sBinds) = mkBindsMetaD fix_env tc
1689 d_metaTycon = metaD metaDts
1690 d_inst = mkLocalInstance d_dfun NoOverlap
1691 d_binds = VanillaInst dBinds [] False
1692 d_dfun = mkDictFunId d_dfun_name (tyConTyVars tc) [] dClas
1693 [ mkTyConTy d_metaTycon ]
1694 d_mkInst = (InstInfo { iSpec = d_inst, iBinds = d_binds }, [])
1697 c_metaTycons = metaC metaDts
1698 c_insts = [ mkLocalInstance (c_dfun c ds) NoOverlap
1699 | (c, ds) <- myZip1 c_metaTycons c_dfun_names ]
1700 c_binds = [ VanillaInst c [] False | c <- cBinds ]
1701 c_dfun c dfun_name = mkDictFunId dfun_name (tyConTyVars tc) [] cClas
1703 c_mkInst = [ (InstInfo { iSpec = is, iBinds = bs }, [])
1704 | (is,bs) <- myZip1 c_insts c_binds ]
1707 s_metaTycons = metaS metaDts
1708 s_insts = map (map (\(s,ds) -> mkLocalInstance (s_dfun s ds) NoOverlap))
1709 (myZip2 s_metaTycons s_dfun_names)
1710 s_binds = [ [ VanillaInst s [] False | s <- ss ] | ss <- sBinds ]
1711 s_dfun s dfun_name = mkDictFunId dfun_name (tyConTyVars tc) [] sClas
1713 s_mkInst = map (map (\(is,bs) -> (InstInfo {iSpec=is, iBinds=bs}, [])))
1714 (myZip2 s_insts s_binds)
1716 myZip1 :: [a] -> [b] -> [(a,b)]
1717 myZip1 l1 l2 = ASSERT (length l1 == length l2) zip l1 l2
1719 myZip2 :: [[a]] -> [[b]] -> [[(a,b)]]
1721 ASSERT (and (zipWith (>=) (map length l1) (map length l2)))
1722 [ zip x1 x2 | (x1,x2) <- zip l1 l2 ]
1724 return (d_mkInst : c_mkInst ++ concat s_mkInst)
1728 %************************************************************************
1730 \subsection[TcDeriv-taggery-Names]{What con2tag/tag2con functions are available?}
1732 %************************************************************************
1735 derivingKindErr :: TyCon -> Class -> [Type] -> Kind -> Message
1736 derivingKindErr tc cls cls_tys cls_kind
1737 = hang (ptext (sLit "Cannot derive well-kinded instance of form")
1738 <+> quotes (pprClassPred cls cls_tys <+> parens (ppr tc <+> ptext (sLit "..."))))
1739 2 (ptext (sLit "Class") <+> quotes (ppr cls)
1740 <+> ptext (sLit "expects an argument of kind") <+> quotes (pprKind cls_kind))
1742 derivingEtaErr :: Class -> [Type] -> Type -> Message
1743 derivingEtaErr cls cls_tys inst_ty
1744 = sep [ptext (sLit "Cannot eta-reduce to an instance of form"),
1745 nest 2 (ptext (sLit "instance (...) =>")
1746 <+> pprClassPred cls (cls_tys ++ [inst_ty]))]
1748 typeFamilyPapErr :: TyCon -> Class -> [Type] -> Type -> Message
1749 typeFamilyPapErr tc cls cls_tys inst_ty
1750 = hang (ptext (sLit "Derived instance") <+> quotes (pprClassPred cls (cls_tys ++ [inst_ty])))
1751 2 (ptext (sLit "requires illegal partial application of data type family") <+> ppr tc)
1753 derivingThingErr :: Bool -> Class -> [Type] -> Type -> Message -> Message
1754 derivingThingErr newtype_deriving clas tys ty why
1755 = sep [(hang (ptext (sLit "Can't make a derived instance of"))
1756 2 (quotes (ppr pred))
1757 $$ nest 2 extra) <> colon,
1760 extra | newtype_deriving = ptext (sLit "(even with cunning newtype deriving)")
1762 pred = mkClassPred clas (tys ++ [ty])
1764 derivingHiddenErr :: TyCon -> SDoc
1765 derivingHiddenErr tc
1766 = hang (ptext (sLit "The data constructors of") <+> quotes (ppr tc) <+> ptext (sLit "are not all in scope"))
1767 2 (ptext (sLit "so you cannot derive an instance for it"))
1769 standaloneCtxt :: LHsType Name -> SDoc
1770 standaloneCtxt ty = hang (ptext (sLit "In the stand-alone deriving instance for"))
1773 derivInstCtxt :: PredType -> Message
1775 = ptext (sLit "When deriving the instance for") <+> parens (ppr pred)
1777 badDerivedPred :: PredType -> Message
1779 = vcat [ptext (sLit "Can't derive instances where the instance context mentions"),
1780 ptext (sLit "type variables that are not data type parameters"),
1781 nest 2 (ptext (sLit "Offending constraint:") <+> ppr pred)]