X-Git-Url: http://git.megacz.com/?p=ghc-hetmet.git;a=blobdiff_plain;f=compiler%2Ftypecheck%2FTcDeriv.lhs;h=44ea1fc4caa2e69adc898878b2f8ac117f867220;hp=2563b0979dcf9b116e297244868e27d88f3f658d;hb=5f8d93baa07271687825458e01c187081bcb1ddc;hpb=5e0ea427646a5474dd7c659b0713c6a62d8c99c7 diff --git a/compiler/typecheck/TcDeriv.lhs b/compiler/typecheck/TcDeriv.lhs index 2563b09..44ea1fc 100644 --- a/compiler/typecheck/TcDeriv.lhs +++ b/compiler/typecheck/TcDeriv.lhs @@ -1,7 +1,7 @@ % +% (c) The University of Glasgow 2006 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998 % -\section[TcDeriv]{Deriving} Handles @deriving@ clauses on @data@ declarations. @@ -11,58 +11,103 @@ module TcDeriv ( tcDeriving ) where #include "HsVersions.h" import HsSyn -import DynFlags ( DynFlag(..) ) +import DynFlags -import Generics ( mkTyConGenericBinds ) +import Generics import TcRnMonad -import TcMType ( checkValidInstance ) -import TcEnv ( newDFunName, pprInstInfoDetails, - InstInfo(..), InstBindings(..), simpleInstInfoClsTy, - tcLookupClass, tcLookupTyCon, tcExtendTyVarEnv - ) -import TcGenDeriv -- Deriv stuff -import InstEnv ( Instance, OverlapFlag, mkLocalInstance, instanceHead, extendInstEnvList ) -import Inst ( getOverlapFlag ) -import TcHsType ( tcHsDeriv ) -import TcSimplify ( tcSimplifyDeriv ) - -import RnBinds ( rnMethodBinds, rnTopBinds ) -import RnEnv ( bindLocalNames ) -import HscTypes ( FixityEnv ) - -import Class ( className, classArity, classKey, classTyVars, classSCTheta, Class ) -import Type ( zipOpenTvSubst, substTheta, pprThetaArrow, pprClassPred, mkTyVarTy ) -import ErrUtils ( dumpIfSet_dyn ) -import MkId ( mkDictFunId ) -import DataCon ( isNullarySrcDataCon, isVanillaDataCon, dataConOrigArgTys, dataConInstOrigArgTys ) -import Maybes ( catMaybes ) -import RdrName ( RdrName ) -import Name ( Name, getSrcLoc ) -import NameSet ( duDefs ) -import Type ( splitKindFunTys ) -import TyCon ( tyConTyVars, tyConDataCons, tyConArity, tyConHasGenerics, - tyConStupidTheta, isProductTyCon, isDataTyCon, newTyConRhs, - isEnumerationTyCon, isRecursiveTyCon, TyCon, isNewTyCon - ) -import TcType ( TcType, ThetaType, mkTyVarTys, mkTyConApp, tcTyConAppTyCon, - isUnLiftedType, mkClassPred, tyVarsOfType, - isSubArgTypeKind, tcEqTypes, tcSplitAppTys, mkAppTys ) -import Var ( TyVar, tyVarKind, varName ) -import VarSet ( mkVarSet, subVarSet ) +import TcEnv +import TcClassDcl( tcAddDeclCtxt ) -- Small helper +import TcGenDeriv -- Deriv stuff +import InstEnv +import Inst +import TcHsType +import TcMType +import TcSimplify + +import RnBinds +import RnEnv +import HscTypes + +import Class +import Type +import ErrUtils +import MkId +import DataCon +import Maybes +import RdrName +import Name +import NameSet +import TyCon +import TcType +import Var +import VarSet import PrelNames -import SrcLoc ( srcLocSpan, Located(..) ) -import Util ( zipWithEqual, sortLe, notNull ) -import ListSetOps ( removeDups, assocMaybe ) +import SrcLoc +import Util +import ListSetOps import Outputable +import FastString import Bag \end{code} %************************************************************************ %* * -\subsection[TcDeriv-intro]{Introduction to how we do deriving} + Overview %* * %************************************************************************ +Overall plan +~~~~~~~~~~~~ +1. Convert the decls (i.e. data/newtype deriving clauses, + plus standalone deriving) to [EarlyDerivSpec] + +2. Infer the missing contexts for the Left DerivSpecs + +3. Add the derived bindings, generating InstInfos + +\begin{code} +-- DerivSpec is purely local to this module +data DerivSpec = DS { ds_loc :: SrcSpan + , ds_orig :: InstOrigin + , ds_name :: Name + , ds_tvs :: [TyVar] + , ds_theta :: ThetaType + , ds_cls :: Class + , ds_tys :: [Type] + , ds_tc :: TyCon + , ds_newtype :: Bool } + -- This spec implies a dfun declaration of the form + -- df :: forall tvs. theta => C tys + -- The Name is the name for the DFun we'll build + -- The tyvars bind all the variables in the theta + -- For family indexes, the tycon in + -- in ds_tys is the *family* tycon + -- in ds_tc is the *representation* tycon + -- For non-family tycons, both are the same + + -- ds_newtype = True <=> Newtype deriving + -- False <=> Vanilla deriving + +type EarlyDerivSpec = Either DerivSpec DerivSpec + -- Left ds => the context for the instance should be inferred + -- In this case ds_theta is the list of all the + -- constraints needed, such as (Eq [a], Eq a) + -- The inference process is to reduce this to a + -- simpler form (e.g. Eq a) + -- + -- Right ds => the exact context for the instance is supplied + -- by the programmer; it is ds_theta + +pprDerivSpec :: DerivSpec -> SDoc +pprDerivSpec (DS { ds_loc = l, ds_name = n, ds_tvs = tvs, + ds_cls = c, ds_tys = tys, ds_theta = rhs }) + = parens (hsep [ppr l, ppr n, ppr tvs, ppr c, ppr tys] + <+> equals <+> ppr rhs) +\end{code} + + +Inferring missing contexts +~~~~~~~~~~~~~~~~~~~~~~~~~~ Consider data T a b = C1 (Foo a) (Bar b) @@ -141,21 +186,9 @@ this by simplifying the RHS to a form in which So, here are the synonyms for the ``equation'' structures: -\begin{code} -type DerivEqn = (Name, Class, TyCon, [TyVar], DerivRhs) - -- The Name is the name for the DFun we'll build - -- The tyvars bind all the variables in the RHS - -pprDerivEqn (n,c,tc,tvs,rhs) - = parens (hsep [ppr n, ppr c, ppr tc, ppr tvs] <+> equals <+> ppr rhs) -type DerivRhs = ThetaType -type DerivSoln = DerivRhs -\end{code} - - -[Data decl contexts] A note about contexts on data decls -~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +Note [Data decl contexts] +~~~~~~~~~~~~~~~~~~~~~~~~~ Consider data (RealFloat a) => Complex a = !a :+ !a deriving( Read ) @@ -182,8 +215,8 @@ pattern matching against a constructor from a data type with a context gives rise to the constraints for that context -- or at least the thinned version. So now all classes are "offending". -[Newtype deriving] -~~~~~~~~~~~~~~~~~~ +Note [Newtype deriving] +~~~~~~~~~~~~~~~~~~~~~~~ Consider this: class C a b instance C [a] Char @@ -196,6 +229,30 @@ And then translate it to: instance C [a] Char => C [a] T where ... +Note [Newtype deriving superclasses] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +(See also Trac #1220 for an interesting exchange on newtype +deriving and superclasses.) + +The 'tys' here come from the partial application in the deriving +clause. The last arg is the new instance type. + +We must pass the superclasses; the newtype might be an instance +of them in a different way than the representation type +E.g. newtype Foo a = Foo a deriving( Show, Num, Eq ) +Then the Show instance is not done via isomorphism; it shows + Foo 3 as "Foo 3" +The Num instance is derived via isomorphism, but the Show superclass +dictionary must the Show instance for Foo, *not* the Show dictionary +gotten from the Num dictionary. So we must build a whole new dictionary +not just use the Num one. The instance we want is something like: + instance (Num a, Show (Foo a), Eq (Foo a)) => Num (Foo a) where + (+) = ((+)@a) + ...etc... +There may be a coercion needed which we get from the tycon for the newtype +when the dict is constructed in TcInstDcls.tcInstDecl2 + + %************************************************************************ @@ -205,357 +262,383 @@ And then translate it to: %************************************************************************ \begin{code} -tcDeriving :: [LTyClDecl Name] -- All type constructors - -> TcM ([InstInfo], -- The generated "instance decls" +tcDeriving :: [LTyClDecl Name] -- All type constructors + -> [LInstDecl Name] -- All instance declarations + -> [LDerivDecl Name] -- All stand-alone deriving declarations + -> TcM ([InstInfo Name], -- The generated "instance decls" HsValBinds Name) -- Extra generated top-level bindings -tcDeriving tycl_decls - = recoverM (returnM ([], emptyValBindsOut)) $ +tcDeriving tycl_decls inst_decls deriv_decls + = recoverM (return ([], emptyValBindsOut)) $ do { -- Fish the "deriving"-related information out of the TcEnv - -- and make the necessary "equations". - overlap_flag <- getOverlapFlag - ; (ordinary_eqns, newtype_inst_info) <- makeDerivEqns overlap_flag tycl_decls - - ; (ordinary_inst_info, deriv_binds) - <- extendLocalInstEnv (map iSpec newtype_inst_info) $ - deriveOrdinaryStuff overlap_flag ordinary_eqns - -- Add the newtype-derived instances to the inst env - -- before tacking the "ordinary" ones - - ; let inst_info = newtype_inst_info ++ ordinary_inst_info - - -- If we are compiling a hs-boot file, - -- don't generate any derived bindings - ; is_boot <- tcIsHsBoot - ; if is_boot then - return (inst_info, emptyValBindsOut) - else do - { - - -- Generate the generic to/from functions from each type declaration - ; gen_binds <- mkGenericBinds tycl_decls - - -- Rename these extra bindings, discarding warnings about unused bindings etc - -- Set -fglasgow exts so that we can have type signatures in patterns, - -- which is used in the generic binds - ; rn_binds - <- discardWarnings $ setOptM Opt_GlasgowExts $ do - { (rn_deriv, _dus1) <- rnTopBinds (ValBindsIn deriv_binds []) - ; (rn_gen, dus_gen) <- rnTopBinds (ValBindsIn gen_binds []) - ; keepAliveSetTc (duDefs dus_gen) -- Mark these guys to - -- be kept alive - ; return (rn_deriv `plusHsValBinds` rn_gen) } + -- And make the necessary "equations". + is_boot <- tcIsHsBoot + ; traceTc (text "tcDeriving" <+> ppr is_boot) + ; early_specs <- makeDerivSpecs is_boot tycl_decls inst_decls deriv_decls + + ; overlap_flag <- getOverlapFlag + ; let (infer_specs, given_specs) = splitEithers early_specs + ; insts1 <- mapM (genInst overlap_flag) given_specs + ; final_specs <- extendLocalInstEnv (map (iSpec . fst) insts1) $ + inferInstanceContexts overlap_flag infer_specs + + ; insts2 <- mapM (genInst overlap_flag) final_specs + + -- Generate the generic to/from functions from each type declaration + ; gen_binds <- mkGenericBinds is_boot + ; (inst_info, rn_binds) <- renameDeriv is_boot gen_binds (insts1 ++ insts2) ; dflags <- getDOpts - ; ioToTcRn (dumpIfSet_dyn dflags Opt_D_dump_deriv "Derived instances" - (ddump_deriving inst_info rn_binds)) + ; liftIO (dumpIfSet_dyn dflags Opt_D_dump_deriv "Derived instances" + (ddump_deriving inst_info rn_binds)) - ; returnM (inst_info, rn_binds) - }} + ; return (inst_info, rn_binds) } where - ddump_deriving :: [InstInfo] -> HsValBinds Name -> SDoc + ddump_deriving :: [InstInfo Name] -> HsValBinds Name -> SDoc ddump_deriving inst_infos extra_binds = vcat (map pprInstInfoDetails inst_infos) $$ ppr extra_binds ------------------------------------------ -deriveOrdinaryStuff overlap_flag [] -- Short cut - = returnM ([], emptyLHsBinds) - -deriveOrdinaryStuff overlap_flag eqns - = do { -- Take the equation list and solve it, to deliver a list of - -- solutions, a.k.a. the contexts for the instance decls - -- required for the corresponding equations. - inst_specs <- solveDerivEqns overlap_flag eqns - - -- Generate the InstInfo for each dfun, - -- plus any auxiliary bindings it needs - ; (inst_infos, aux_binds_s) <- mapAndUnzipM genInst inst_specs +renameDeriv :: Bool -> LHsBinds RdrName + -> [(InstInfo RdrName, DerivAuxBinds)] + -> TcM ([InstInfo Name], HsValBinds Name) +renameDeriv is_boot gen_binds insts + | is_boot -- If we are compiling a hs-boot file, don't generate any derived bindings + -- The inst-info bindings will all be empty, but it's easier to + -- just use rn_inst_info to change the type appropriately + = do { rn_inst_infos <- mapM rn_inst_info inst_infos + ; return (rn_inst_infos, emptyValBindsOut) } - -- Generate any extra not-one-inst-decl-specific binds, - -- notably "con2tag" and/or "tag2con" functions. - ; extra_binds <- genTaggeryBinds inst_infos + | otherwise + = discardWarnings $ -- Discard warnings about unused bindings etc + do { (rn_gen, dus_gen) <- setOptM Opt_ScopedTypeVariables $ -- Type signatures in patterns + -- are used in the generic binds + rnTopBinds (ValBindsIn gen_binds []) + ; keepAliveSetTc (duDefs dus_gen) -- Mark these guys to be kept alive + + -- Generate and rename any extra not-one-inst-decl-specific binds, + -- notably "con2tag" and/or "tag2con" functions. + -- Bring those names into scope before renaming the instances themselves + ; loc <- getSrcSpanM -- Generic loc for shared bindings + ; let aux_binds = listToBag $ map (genAuxBind loc) $ + rm_dups [] $ concat deriv_aux_binds + ; rn_aux_lhs <- rnTopBindsLHS emptyFsEnv (ValBindsIn aux_binds []) + ; let aux_names = map unLoc (collectHsValBinders rn_aux_lhs) + + ; bindLocalNames aux_names $ + do { (rn_aux, _dus) <- rnTopBindsRHS (mkNameSet aux_names) rn_aux_lhs + ; rn_inst_infos <- mapM rn_inst_info inst_infos + ; return (rn_inst_infos, rn_aux `plusHsValBinds` rn_gen) } } - -- Done - ; returnM (inst_infos, unionManyBags (extra_binds : aux_binds_s)) - } + where + (inst_infos, deriv_aux_binds) = unzip insts + + -- Remove duplicate requests for auxilliary bindings + rm_dups acc [] = acc + rm_dups acc (b:bs) | any (isDupAux b) acc = rm_dups acc bs + | otherwise = rm_dups (b:acc) bs + + + rn_inst_info (InstInfo { iSpec = inst, iBinds = NewTypeDerived }) + = return (InstInfo { iSpec = inst, iBinds = NewTypeDerived }) + + rn_inst_info (InstInfo { iSpec = inst, iBinds = VanillaInst binds sigs }) + = -- Bring the right type variables into + -- scope (yuk), and rename the method binds + ASSERT( null sigs ) + bindLocalNames (map Var.varName tyvars) $ + do { (rn_binds, _fvs) <- rnMethodBinds clas_nm (\_ -> []) [] binds + ; return (InstInfo { iSpec = inst, iBinds = VanillaInst rn_binds [] }) } + where + (tyvars,_,clas,_) = instanceHead inst + clas_nm = className clas ----------------------------------------- -mkGenericBinds tycl_decls - = do { tcs <- mapM tcLookupTyCon - [ tc_name | - L _ (TyData { tcdLName = L _ tc_name }) <- tycl_decls] - -- We are only interested in the data type declarations +mkGenericBinds :: Bool -> TcM (LHsBinds RdrName) +mkGenericBinds is_boot + | is_boot + = return emptyBag + | otherwise + = do { gbl_env <- getGblEnv + ; let tcs = typeEnvTyCons (tcg_type_env gbl_env) ; return (unionManyBags [ mkTyConGenericBinds tc | tc <- tcs, tyConHasGenerics tc ]) } - -- And then only in the ones whose 'has-generics' flag is on + -- We are only interested in the data type declarations, + -- and then only in the ones whose 'has-generics' flag is on + -- The predicate tyConHasGenerics finds both of these \end{code} %************************************************************************ %* * -\subsection[TcDeriv-eqns]{Forming the equations} + From HsSyn to DerivSpec %* * %************************************************************************ -@makeDerivEqns@ fishes around to find the info about needed derived -instances. Complicating factors: -\begin{itemize} -\item -We can only derive @Enum@ if the data type is an enumeration -type (all nullary data constructors). - -\item -We can only derive @Ix@ if the data type is an enumeration {\em -or} has just one data constructor (e.g., tuples). -\end{itemize} - -[See Appendix~E in the Haskell~1.2 report.] This code here deals w/ -all those. - -Note [Newtype deriving superclasses] -~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ - -The 'tys' here come from the partial application -in the deriving clause. The last arg is the new -instance type. - -We must pass the superclasses; the newtype might be an instance -of them in a different way than the representation type -E.g. newtype Foo a = Foo a deriving( Show, Num, Eq ) -Then the Show instance is not done via isomorphism; it shows - Foo 3 as "Foo 3" -The Num instance is derived via isomorphism, but the Show superclass -dictionary must the Show instance for Foo, *not* the Show dictionary -gotten from the Num dictionary. So we must build a whole new dictionary -not just use the Num one. The instance we want is something like: - instance (Num a, Show (Foo a), Eq (Foo a)) => Num (Foo a) where - (+) = ((+)@a) - ...etc... -There may be a coercion needed which we get from the tycon for the newtype -when the dict is constructed in TcInstDcls.tcInstDecl2 - +@makeDerivSpecs@ fishes around to find the info about needed derived instances. \begin{code} -makeDerivEqns :: OverlapFlag - -> [LTyClDecl Name] - -> TcM ([DerivEqn], -- Ordinary derivings - [InstInfo]) -- Special newtype derivings - -makeDerivEqns overlap_flag tycl_decls - = mapAndUnzipM mk_eqn derive_these `thenM` \ (maybe_ordinaries, maybe_newtypes) -> - returnM (catMaybes maybe_ordinaries, catMaybes maybe_newtypes) +makeDerivSpecs :: Bool + -> [LTyClDecl Name] + -> [LInstDecl Name] + -> [LDerivDecl Name] + -> TcM [EarlyDerivSpec] + +makeDerivSpecs is_boot tycl_decls inst_decls deriv_decls + | is_boot -- No 'deriving' at all in hs-boot files + = do { mapM_ add_deriv_err deriv_locs + ; return [] } + | otherwise + = do { eqns1 <- mapAndRecoverM deriveTyData all_tydata + ; eqns2 <- mapAndRecoverM deriveStandalone deriv_decls + ; return (eqns1 ++ eqns2) } where - ------------------------------------------------------------------ - derive_these :: [(NewOrData, Name, LHsType Name)] - -- Find the (nd, TyCon, Pred) pairs that must be `derived' - derive_these = [ (nd, tycon, pred) - | L _ (TyData { tcdND = nd, tcdLName = L _ tycon, - tcdDerivs = Just preds }) <- tycl_decls, - pred <- preds ] + extractTyDataPreds decls + = [(p, d) | d@(L _ (TyData {tcdDerivs = Just preds})) <- decls, p <- preds] - ------------------------------------------------------------------ - mk_eqn :: (NewOrData, Name, LHsType Name) -> TcM (Maybe DerivEqn, Maybe InstInfo) - -- We swizzle the tyvars and datacons out of the tycon - -- to make the rest of the equation - -- - -- The "deriv_ty" is a LHsType to take account of the fact that for newtype derivign - -- we allow deriving (forall a. C [a]). - - mk_eqn (new_or_data, tycon_name, hs_deriv_ty) - = tcLookupTyCon tycon_name `thenM` \ tycon -> - setSrcSpan (srcLocSpan (getSrcLoc tycon)) $ - addErrCtxt (derivCtxt tycon) $ - tcExtendTyVarEnv (tyConTyVars tycon) $ -- Deriving preds may (now) mention - -- the type variables for the type constructor - tcHsDeriv hs_deriv_ty `thenM` \ (deriv_tvs, clas, tys) -> - doptM Opt_GlasgowExts `thenM` \ gla_exts -> - mk_eqn_help gla_exts new_or_data tycon deriv_tvs clas tys + all_tydata :: [(LHsType Name, LTyClDecl Name)] + -- Derived predicate paired with its data type declaration + all_tydata = extractTyDataPreds tycl_decls ++ + [ pd -- Traverse assoc data families + | L _ (InstDecl _ _ _ ats) <- inst_decls + , pd <- extractTyDataPreds ats ] - ------------------------------------------------------------------ - -- data/newtype T a = ... deriving( C t1 t2 ) - -- leads to a call to mk_eqn_help with - -- tycon = T, deriv_tvs = ftv(t1,t2), clas = C, tys = [t1,t2] - - mk_eqn_help gla_exts DataType tycon deriv_tvs clas tys - | Just err <- checkSideConditions gla_exts tycon deriv_tvs clas tys - = bale_out (derivingThingErr clas tys tycon (tyConTyVars tycon) err) - | otherwise - = do { eqn <- mkDataTypeEqn tycon clas - ; returnM (Just eqn, Nothing) } - - mk_eqn_help gla_exts NewType tycon deriv_tvs clas tys - | can_derive_via_isomorphism && (gla_exts || std_class_via_iso clas) - = -- Go ahead and use the isomorphism - traceTc (text "newtype deriving:" <+> ppr tycon <+> ppr rep_tys) `thenM_` - new_dfun_name clas tycon `thenM` \ dfun_name -> - returnM (Nothing, Just (InstInfo { iSpec = mk_inst_spec dfun_name, - iBinds = NewTypeDerived tycon rep_tys })) - | std_class gla_exts clas - = mk_eqn_help gla_exts DataType tycon deriv_tvs clas tys -- Go via bale-out route - - | otherwise -- Non-standard instance - = bale_out (if gla_exts then - cant_derive_err -- Too hard - else - non_std_err) -- Just complain about being a non-std instance - where - -- Here is the plan for newtype derivings. We see - -- newtype T a1...an = T (t ak...an) deriving (.., C s1 .. sm, ...) - -- where t is a type, - -- ak...an is a suffix of a1..an - -- ak...an do not occur free in t, - -- (C s1 ... sm) is a *partial applications* of class C - -- with the last parameter missing - -- - -- We generate the instances - -- instance C s1 .. sm (t ak...ap) => C s1 .. sm (T a1...ap) - -- where T a1...ap is the partial application of the LHS of the correct kind - -- and p >= k - -- - -- Running example: newtype T s a = MkT (ST s a) deriving( Monad ) - -- instance Monad (ST s) => Monad (T s) where - -- fail = coerce ... (fail @ ST s) - -- (Actually we don't need the coerce, because non-rec newtypes are transparent - - clas_tyvars = classTyVars clas - kind = tyVarKind (last clas_tyvars) - -- Kind of the thing we want to instance - -- e.g. argument kind of Monad, *->* - - (arg_kinds, _) = splitKindFunTys kind - n_args_to_drop = length arg_kinds - -- Want to drop 1 arg from (T s a) and (ST s a) - -- to get instance Monad (ST s) => Monad (T s) - - -- Note [newtype representation] - -- Need newTyConRhs *not* newTyConRep to get the representation - -- type, because the latter looks through all intermediate newtypes - -- For example - -- newtype B = MkB Int - -- newtype A = MkA B deriving( Num ) - -- We want the Num instance of B, *not* the Num instance of Int, - -- when making the Num instance of A! - (tc_tvs, rep_ty) = newTyConRhs tycon - (rep_fn, rep_ty_args) = tcSplitAppTys rep_ty - - n_tyvars_to_keep = tyConArity tycon - n_args_to_drop - tyvars_to_drop = drop n_tyvars_to_keep tc_tvs - tyvars_to_keep = take n_tyvars_to_keep tc_tvs + deriv_locs = map (getLoc . snd) all_tydata + ++ map getLoc deriv_decls - n_args_to_keep = length rep_ty_args - n_args_to_drop - args_to_drop = drop n_args_to_keep rep_ty_args - args_to_keep = take n_args_to_keep rep_ty_args - - rep_fn' = mkAppTys rep_fn args_to_keep - rep_tys = tys ++ [rep_fn'] - rep_pred = mkClassPred clas rep_tys - -- rep_pred is the representation dictionary, from where - -- we are gong to get all the methods for the newtype dictionary - -- here we are figuring out what superclass dictionaries to use - -- see Note [Newtype deriving superclasses] above - - inst_tys = (tys ++ [mkTyConApp tycon (mkTyVarTys tyvars_to_keep)]) + add_deriv_err loc = setSrcSpan loc $ + addErr (hang (ptext (sLit "Deriving not permitted in hs-boot file")) + 2 (ptext (sLit "Use an instance declaration instead"))) +------------------------------------------------------------------ +deriveStandalone :: LDerivDecl Name -> TcM EarlyDerivSpec +-- Standalone deriving declarations +-- e.g. deriving instance Show a => Show (T a) +-- Rather like tcLocalInstDecl +deriveStandalone (L loc (DerivDecl deriv_ty)) + = setSrcSpan loc $ + addErrCtxt (standaloneCtxt deriv_ty) $ + do { traceTc (text "standalone deriving decl for" <+> ppr deriv_ty) + ; (tvs, theta, tau) <- tcHsInstHead deriv_ty + ; traceTc (text "standalone deriving;" + <+> text "tvs:" <+> ppr tvs + <+> text "theta:" <+> ppr theta + <+> text "tau:" <+> ppr tau) + ; (cls, inst_tys) <- checkValidInstHead tau + ; checkValidInstance tvs theta cls inst_tys + -- C.f. TcInstDcls.tcLocalInstDecl1 + + ; let cls_tys = take (length inst_tys - 1) inst_tys + inst_ty = last inst_tys + ; traceTc (text "standalone deriving;" + <+> text "class:" <+> ppr cls + <+> text "class types:" <+> ppr cls_tys + <+> text "type:" <+> ppr inst_ty) + ; mkEqnHelp StandAloneDerivOrigin tvs cls cls_tys inst_ty + (Just theta) } - sc_theta = substTheta (zipOpenTvSubst clas_tyvars inst_tys) - (classSCTheta clas) +------------------------------------------------------------------ +deriveTyData :: (LHsType Name, LTyClDecl Name) -> TcM EarlyDerivSpec +deriveTyData (L loc deriv_pred, L _ decl@(TyData { tcdLName = L _ tycon_name, + tcdTyVars = tv_names, + tcdTyPats = ty_pats })) + = setSrcSpan loc $ -- Use the location of the 'deriving' item + tcAddDeclCtxt decl $ + do { (tvs, tc, tc_args) <- get_lhs ty_pats + ; tcExtendTyVarEnv tvs $ -- Deriving preds may (now) mention + -- the type variables for the type constructor + + do { (deriv_tvs, cls, cls_tys) <- tcHsDeriv deriv_pred + -- The "deriv_pred" is a LHsType to take account of the fact that for + -- newtype deriving we allow deriving (forall a. C [a]). + + -- Given data T a b c = ... deriving( C d ), + -- we want to drop type variables from T so that (C d (T a)) is well-kinded + ; let cls_tyvars = classTyVars cls + kind = tyVarKind (last cls_tyvars) + (arg_kinds, _) = splitKindFunTys kind + n_args_to_drop = length arg_kinds + n_args_to_keep = tyConArity tc - n_args_to_drop + inst_ty = mkTyConApp tc (take n_args_to_keep tc_args) + inst_ty_kind = typeKind inst_ty + + -- Check that the result really is well-kinded + ; checkTc (n_args_to_keep >= 0 && (inst_ty_kind `eqKind` kind)) + (derivingKindErr tc cls cls_tys kind) + + -- Type families can't be partially applied + -- e.g. newtype instance T Int a = ... deriving( Monad ) + ; checkTc (not (isOpenTyCon tc) || n_args_to_drop == 0) + (typeFamilyPapErr tc cls cls_tys inst_ty) + + ; mkEqnHelp DerivOrigin (tvs++deriv_tvs) cls cls_tys inst_ty Nothing } } + where + -- Tiresomely we must figure out the "lhs", which is awkward for type families + -- E.g. data T a b = .. deriving( Eq ) + -- Here, the lhs is (T a b) + -- data instance TF Int b = ... deriving( Eq ) + -- Here, the lhs is (TF Int b) + -- But if we just look up the tycon_name, we get is the *family* + -- tycon, but not pattern types -- they are in the *rep* tycon. + get_lhs Nothing = do { tc <- tcLookupTyCon tycon_name + ; let tvs = tyConTyVars tc + ; return (tvs, tc, mkTyVarTys tvs) } + get_lhs (Just pats) = do { let hs_app = nlHsTyConApp tycon_name pats + ; (tvs, tc_app) <- tcHsQuantifiedType tv_names hs_app + ; let (tc, tc_args) = tcSplitTyConApp tc_app + ; return (tvs, tc, tc_args) } + +deriveTyData _other + = panic "derivTyData" -- Caller ensures that only TyData can happen - -- If there are no tyvars, there's no need - -- to abstract over the dictionaries we need - dict_tvs = deriv_tvs ++ tc_tvs - dict_args -- | null dict_tvs = [] - | otherwise = rep_pred : sc_theta +------------------------------------------------------------------ +mkEqnHelp :: InstOrigin -> [TyVar] -> Class -> [Type] -> Type + -> Maybe ThetaType -- Just => context supplied (standalone deriving) + -- Nothing => context inferred (deriving on data decl) + -> TcRn EarlyDerivSpec +-- Make the EarlyDerivSpec for an instance +-- forall tvs. theta => cls (tys ++ [ty]) +-- where the 'theta' is optional (that's the Maybe part) +-- Assumes that this declaration is well-kinded + +mkEqnHelp orig tvs cls cls_tys tc_app mtheta + | Just (tycon, tc_args) <- tcSplitTyConApp_maybe tc_app + , isAlgTyCon tycon -- Check for functions, primitive types etc + = do { (rep_tc, rep_tc_args) <- tcLookupFamInstExact tycon tc_args + -- Be careful to test rep_tc here: in the case of families, + -- we want to check the instance tycon, not the family tycon + + -- For standalone deriving (mtheta /= Nothing), + -- check that all the data constructors are in scope. + -- No need for this when deriving Typeable, becuase we don't need + -- the constructors for that. + ; rdr_env <- getGlobalRdrEnv + ; let hidden_data_cons = isAbstractTyCon rep_tc || any not_in_scope (tyConDataCons rep_tc) + not_in_scope dc = null (lookupGRE_Name rdr_env (dataConName dc)) + ; checkTc (isNothing mtheta || + not hidden_data_cons || + className cls `elem` typeableClassNames) + (derivingHiddenErr tycon) + + ; mayDeriveDataTypeable <- doptM Opt_DeriveDataTypeable + ; newtype_deriving <- doptM Opt_GeneralizedNewtypeDeriving + + ; if isDataTyCon rep_tc then + mkDataTypeEqn orig mayDeriveDataTypeable tvs cls cls_tys + tycon tc_args rep_tc rep_tc_args mtheta + else + mkNewTypeEqn orig mayDeriveDataTypeable newtype_deriving + tvs cls cls_tys + tycon tc_args rep_tc rep_tc_args mtheta } + | otherwise + = failWithTc (derivingThingErr cls cls_tys tc_app + (ptext (sLit "The last argument of the instance must be a data or newtype application"))) +\end{code} - -- Finally! Here's where we build the dictionary Id - mk_inst_spec dfun_name - = mkLocalInstance dfun overlap_flag - where - dfun = mkDictFunId dfun_name dict_tvs dict_args clas inst_tys +Note [Looking up family instances for deriving] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +tcLookupFamInstExact is an auxiliary lookup wrapper which requires +that looked-up family instances exist. If called with a vanilla +tycon, the old type application is simply returned. + +If we have + data instance F () = ... deriving Eq + data instance F () = ... deriving Eq +then tcLookupFamInstExact will be confused by the two matches; +but that can't happen because tcInstDecls1 doesn't call tcDeriving +if there are any overlaps. + +There are two other things that might go wrong with the lookup. +First, we might see a standalone deriving clause + deriving Eq (F ()) +when there is no data instance F () in scope. + +Note that it's OK to have + data instance F [a] = ... + deriving Eq (F [(a,b)]) +where the match is not exact; the same holds for ordinary data types +with standalone deriving declrations. - ------------------------------------------------------------------- - -- Figuring out whether we can only do this newtype-deriving thing +\begin{code} +tcLookupFamInstExact :: TyCon -> [Type] -> TcM (TyCon, [Type]) +tcLookupFamInstExact tycon tys + | not (isOpenTyCon tycon) + = return (tycon, tys) + | otherwise + = do { maybeFamInst <- tcLookupFamInst tycon tys + ; case maybeFamInst of + Nothing -> famInstNotFound tycon tys + Just famInst -> return famInst + } + +famInstNotFound :: TyCon -> [Type] -> TcM a +famInstNotFound tycon tys + = failWithTc (ptext (sLit "No family instance for") + <+> quotes (pprTypeApp tycon tys)) +\end{code} - right_arity = length tys + 1 == classArity clas - -- Never derive Read,Show,Typeable,Data this way - non_iso_classes = [readClassKey, showClassKey, typeableClassKey, dataClassKey] - can_derive_via_isomorphism - = not (getUnique clas `elem` non_iso_classes) - && right_arity -- Well kinded; - -- eg not: newtype T ... deriving( ST ) - -- because ST needs *2* type params - && n_tyvars_to_keep >= 0 -- Type constructor has right kind: - -- eg not: newtype T = T Int deriving( Monad ) - && n_args_to_keep >= 0 -- Rep type has right kind: - -- eg not: newtype T a = T Int deriving( Monad ) - && eta_ok -- Eta reduction works - && not (isRecursiveTyCon tycon) -- Does not work for recursive tycons: - -- newtype A = MkA [A] - -- Don't want - -- instance Eq [A] => Eq A !! - -- Here's a recursive newtype that's actually OK - -- newtype S1 = S1 [T1 ()] - -- newtype T1 a = T1 (StateT S1 IO a ) deriving( Monad ) - -- It's currently rejected. Oh well. - -- In fact we generate an instance decl that has method of form - -- meth @ instTy = meth @ repTy - -- (no coerce's). We'd need a coerce if we wanted to handle - -- recursive newtypes too +%************************************************************************ +%* * + Deriving data types +%* * +%************************************************************************ - -- Check that eta reduction is OK - -- (a) the dropped-off args are identical - -- (b) the remaining type args mention - -- only the remaining type variables - eta_ok = (args_to_drop `tcEqTypes` mkTyVarTys tyvars_to_drop) - && (tyVarsOfType rep_fn' `subVarSet` mkVarSet tyvars_to_keep) - - cant_derive_err = derivingThingErr clas tys tycon tyvars_to_keep - (vcat [ptext SLIT("even with cunning newtype deriving:"), - if isRecursiveTyCon tycon then - ptext SLIT("the newtype is recursive") - else empty, - if not right_arity then - quotes (ppr (mkClassPred clas tys)) <+> ptext SLIT("does not have arity 1") - else empty, - if not (n_tyvars_to_keep >= 0) then - ptext SLIT("the type constructor has wrong kind") - else if not (n_args_to_keep >= 0) then - ptext SLIT("the representation type has wrong kind") - else if not eta_ok then - ptext SLIT("the eta-reduction property does not hold") - else empty - ]) - - non_std_err = derivingThingErr clas tys tycon tyvars_to_keep - (vcat [non_std_why clas, - ptext SLIT("Try -fglasgow-exts for GHC's newtype-deriving extension")]) - - bale_out err = addErrTc err `thenM_` returnM (Nothing, Nothing) - -std_class gla_exts clas - = key `elem` derivableClassKeys - || (gla_exts && (key == typeableClassKey || key == dataClassKey)) +\begin{code} +mkDataTypeEqn :: InstOrigin -> Bool -> [Var] -> Class -> [Type] + -> TyCon -> [Type] -> TyCon -> [Type] -> Maybe ThetaType + -> TcRn EarlyDerivSpec -- Return 'Nothing' if error + +mkDataTypeEqn orig mayDeriveDataTypeable tvs cls cls_tys + tycon tc_args rep_tc rep_tc_args mtheta + = case checkSideConditions mayDeriveDataTypeable cls cls_tys rep_tc of + -- NB: pass the *representation* tycon to checkSideConditions + CanDerive -> mk_data_eqn orig tvs cls tycon tc_args rep_tc rep_tc_args mtheta + NonDerivableClass -> bale_out (nonStdErr cls) + DerivableClassError msg -> bale_out msg where - key = classKey clas - -std_class_via_iso clas -- These standard classes can be derived for a newtype - -- using the isomorphism trick *even if no -fglasgow-exts* - = classKey clas `elem` [eqClassKey, ordClassKey, ixClassKey, boundedClassKey] - -- Not Read/Show because they respect the type - -- Not Enum, becuase newtypes are never in Enum + bale_out msg = failWithTc (derivingThingErr cls cls_tys (mkTyConApp tycon tc_args) msg) +mk_data_eqn, mk_typeable_eqn + :: InstOrigin -> [TyVar] -> Class + -> TyCon -> [TcType] -> TyCon -> [TcType] -> Maybe ThetaType + -> TcM EarlyDerivSpec +mk_data_eqn orig tvs cls tycon tc_args rep_tc rep_tc_args mtheta + | getName cls `elem` typeableClassNames + = mk_typeable_eqn orig tvs cls tycon tc_args rep_tc rep_tc_args mtheta -new_dfun_name clas tycon -- Just a simple wrapper - = newDFunName clas [mkTyConApp tycon []] (getSrcLoc tycon) - -- The type passed to newDFunName is only used to generate - -- a suitable string; hence the empty type arg list - ------------------------------------------------------------------- -mkDataTypeEqn :: TyCon -> Class -> TcM DerivEqn -mkDataTypeEqn tycon clas - | clas `hasKey` typeableClassKey - = -- The Typeable class is special in several ways + | otherwise + = do { dfun_name <- new_dfun_name cls tycon + ; loc <- getSrcSpanM + ; let ordinary_constraints + = [ mkClassPred cls [arg_ty] + | data_con <- tyConDataCons rep_tc, + arg_ty <- ASSERT( isVanillaDataCon data_con ) + dataConInstOrigArgTys data_con rep_tc_args, + not (isUnLiftedType arg_ty) ] + -- No constraints for unlifted types + -- Where they are legal we generate specilised function calls + + -- See Note [Superclasses of derived instance] + sc_constraints = substTheta (zipOpenTvSubst (classTyVars cls) inst_tys) + (classSCTheta cls) + inst_tys = [mkTyConApp tycon tc_args] + + stupid_subst = zipTopTvSubst (tyConTyVars rep_tc) rep_tc_args + stupid_constraints = substTheta stupid_subst (tyConStupidTheta rep_tc) + all_constraints = stupid_constraints ++ sc_constraints ++ ordinary_constraints + + spec = DS { ds_loc = loc, ds_orig = orig + , ds_name = dfun_name, ds_tvs = tvs + , ds_cls = cls, ds_tys = inst_tys, ds_tc = rep_tc + , ds_theta = mtheta `orElse` all_constraints + , ds_newtype = False } + + ; return (if isJust mtheta then Right spec -- Specified context + else Left spec) } -- Infer context + +mk_typeable_eqn orig tvs cls tycon tc_args rep_tc _rep_tc_args mtheta + -- The Typeable class is special in several ways -- data T a b = ... deriving( Typeable ) -- gives -- instance Typeable2 T where ... @@ -564,59 +647,71 @@ mkDataTypeEqn tycon clas -- 2. There are no type variables either -- 3. The actual class we want to generate isn't necessarily -- Typeable; it depends on the arity of the type - do { real_clas <- tcLookupClass (typeableClassNames !! tyConArity tycon) - ; dfun_name <- new_dfun_name real_clas tycon - ; return (dfun_name, real_clas, tycon, [], []) } - - | otherwise - = do { dfun_name <- new_dfun_name clas tycon - ; return (dfun_name, clas, tycon, tyvars, constraints) } - where - tyvars = tyConTyVars tycon - constraints = extra_constraints ++ ordinary_constraints - extra_constraints = tyConStupidTheta tycon - -- "extra_constraints": see note [Data decl contexts] above - - ordinary_constraints - = [ mkClassPred clas [arg_ty] - | data_con <- tyConDataCons tycon, - arg_ty <- dataConInstOrigArgTys data_con (map mkTyVarTy (tyConTyVars tycon)), - not (isUnLiftedType arg_ty) -- No constraints for unlifted types? - ] - + | isNothing mtheta -- deriving on a data type decl + = do { checkTc (cls `hasKey` typeableClassKey) + (ptext (sLit "Use deriving( Typeable ) on a data type declaration")) + ; real_cls <- tcLookupClass (typeableClassNames !! tyConArity tycon) + ; mk_typeable_eqn orig tvs real_cls tycon [] rep_tc [] (Just []) } + + | otherwise -- standaone deriving + = do { checkTc (null tc_args) + (ptext (sLit "Derived typeable instance must be of form (Typeable") + <> int (tyConArity tycon) <+> ppr tycon <> rparen) + ; dfun_name <- new_dfun_name cls tycon + ; loc <- getSrcSpanM + ; return (Right $ + DS { ds_loc = loc, ds_orig = orig, ds_name = dfun_name, ds_tvs = [] + , ds_cls = cls, ds_tys = [mkTyConApp tycon []], ds_tc = rep_tc + , ds_theta = mtheta `orElse` [], ds_newtype = False }) } ------------------------------------------------------------------ -- Check side conditions that dis-allow derivability for particular classes -- This is *apart* from the newtype-deriving mechanism - -checkSideConditions :: Bool -> TyCon -> [TyVar] -> Class -> [TcType] -> Maybe SDoc -checkSideConditions gla_exts tycon deriv_tvs clas tys - | notNull deriv_tvs || notNull tys - = Just ty_args_why -- e.g. deriving( Foo s ) +-- +-- Here we get the representation tycon in case of family instances as it has +-- the data constructors - but we need to be careful to fall back to the +-- family tycon (with indexes) in error messages. + +data DerivStatus = CanDerive + | NonDerivableClass + | DerivableClassError SDoc + +checkSideConditions :: Bool -> Class -> [TcType] -> TyCon -> DerivStatus +checkSideConditions mayDeriveDataTypeable cls cls_tys rep_tc + | notNull cls_tys + = DerivableClassError ty_args_why -- e.g. deriving( Foo s ) | otherwise - = case [cond | (key,cond) <- sideConditions, key == getUnique clas] of - [] -> Just (non_std_why clas) - [cond] -> cond (gla_exts, tycon) - other -> pprPanic "checkSideConditions" (ppr clas) + = case sideConditions cls of + Nothing -> NonDerivableClass + Just cond -> case (cond (mayDeriveDataTypeable, rep_tc)) of + Nothing -> CanDerive + Just err -> DerivableClassError err where - ty_args_why = quotes (ppr (mkClassPred clas tys)) <+> ptext SLIT("is not a class") - -non_std_why clas = quotes (ppr clas) <+> ptext SLIT("is not a derivable class") - -sideConditions :: [(Unique, Condition)] -sideConditions - = [ (eqClassKey, cond_std), - (ordClassKey, cond_std), - (readClassKey, cond_std), - (showClassKey, cond_std), - (enumClassKey, cond_std `andCond` cond_isEnumeration), - (ixClassKey, cond_std `andCond` (cond_isEnumeration `orCond` cond_isProduct)), - (boundedClassKey, cond_std `andCond` (cond_isEnumeration `orCond` cond_isProduct)), - (typeableClassKey, cond_glaExts `andCond` cond_typeableOK), - (dataClassKey, cond_glaExts `andCond` cond_std) - ] + ty_args_why = quotes (ppr (mkClassPred cls cls_tys)) <+> ptext (sLit "is not a class") + +nonStdErr :: Class -> SDoc +nonStdErr cls = quotes (ppr cls) <+> ptext (sLit "is not a derivable class") + +sideConditions :: Class -> Maybe Condition +sideConditions cls + | cls_key == eqClassKey = Just cond_std + | cls_key == ordClassKey = Just cond_std + | cls_key == showClassKey = Just cond_std + | cls_key == readClassKey = Just (cond_std `andCond` cond_noUnliftedArgs) + | cls_key == enumClassKey = Just (cond_std `andCond` cond_isEnumeration) + | cls_key == ixClassKey = Just (cond_std `andCond` cond_enumOrProduct) + | cls_key == boundedClassKey = Just (cond_std `andCond` cond_enumOrProduct) + | cls_key == dataClassKey = Just (cond_mayDeriveDataTypeable `andCond` cond_std `andCond` cond_noUnliftedArgs) + | getName cls `elem` typeableClassNames = Just (cond_mayDeriveDataTypeable `andCond` cond_typeableOK) + | otherwise = Nothing + where + cls_key = getUnique cls -type Condition = (Bool, TyCon) -> Maybe SDoc -- Nothing => OK +type Condition = (Bool, TyCon) -> Maybe SDoc + -- Bool is whether or not we are allowed to derive Data and Typeable + -- TyCon is the *representation* tycon if the + -- data type is an indexed one + -- Nothing => OK orCond :: Condition -> Condition -> Condition orCond c1 c2 tc @@ -624,56 +719,291 @@ orCond c1 c2 tc Nothing -> Nothing -- c1 succeeds Just x -> case c2 tc of -- c1 fails Nothing -> Nothing - Just y -> Just (x $$ ptext SLIT(" and") $$ y) + Just y -> Just (x $$ ptext (sLit " and") $$ y) -- Both fail +andCond :: Condition -> Condition -> Condition andCond c1 c2 tc = case c1 tc of Nothing -> c2 tc -- c1 succeeds Just x -> Just x -- c1 fails cond_std :: Condition -cond_std (gla_exts, tycon) +cond_std (_, rep_tc) | any (not . isVanillaDataCon) data_cons = Just existential_why | null data_cons = Just no_cons_why | otherwise = Nothing where - data_cons = tyConDataCons tycon - no_cons_why = quotes (ppr tycon) <+> ptext SLIT("has no data constructors") - existential_why = quotes (ppr tycon) <+> ptext SLIT("has non-Haskell-98 constructor(s)") + data_cons = tyConDataCons rep_tc + no_cons_why = quotes (pprSourceTyCon rep_tc) <+> + ptext (sLit "has no data constructors") + existential_why = quotes (pprSourceTyCon rep_tc) <+> + ptext (sLit "has non-Haskell-98 constructor(s)") +cond_enumOrProduct :: Condition +cond_enumOrProduct = cond_isEnumeration `orCond` + (cond_isProduct `andCond` cond_noUnliftedArgs) + +cond_noUnliftedArgs :: Condition +-- For some classes (eg Eq, Ord) we allow unlifted arg types +-- by generating specilaised code. For others (eg Data) we don't. +cond_noUnliftedArgs (_, tc) + | null bad_cons = Nothing + | otherwise = Just why + where + bad_cons = [ con | con <- tyConDataCons tc + , any isUnLiftedType (dataConOrigArgTys con) ] + why = ptext (sLit "Constructor") <+> quotes (ppr (head bad_cons)) + <+> ptext (sLit "has arguments of unlifted type") + cond_isEnumeration :: Condition -cond_isEnumeration (gla_exts, tycon) - | isEnumerationTyCon tycon = Nothing - | otherwise = Just why +cond_isEnumeration (_, rep_tc) + | isEnumerationTyCon rep_tc = Nothing + | otherwise = Just why where - why = quotes (ppr tycon) <+> ptext SLIT("has non-nullary constructors") + why = quotes (pprSourceTyCon rep_tc) <+> + ptext (sLit "has non-nullary constructors") cond_isProduct :: Condition -cond_isProduct (gla_exts, tycon) - | isProductTyCon tycon = Nothing - | otherwise = Just why +cond_isProduct (_, rep_tc) + | isProductTyCon rep_tc = Nothing + | otherwise = Just why where - why = quotes (ppr tycon) <+> ptext SLIT("has more than one constructor") + why = quotes (pprSourceTyCon rep_tc) <+> + ptext (sLit "has more than one constructor") cond_typeableOK :: Condition -- OK for Typeable class -- Currently: (a) args all of kind * -- (b) 7 or fewer args -cond_typeableOK (gla_exts, tycon) - | tyConArity tycon > 7 = Just too_many - | not (all (isSubArgTypeKind . tyVarKind) (tyConTyVars tycon)) = Just bad_kind - | otherwise = Nothing +cond_typeableOK (_, rep_tc) + | tyConArity rep_tc > 7 = Just too_many + | not (all (isSubArgTypeKind . tyVarKind) (tyConTyVars rep_tc)) + = Just bad_kind + | isFamInstTyCon rep_tc = Just fam_inst -- no Typable for family insts + | otherwise = Nothing where - too_many = quotes (ppr tycon) <+> ptext SLIT("has too many arguments") - bad_kind = quotes (ppr tycon) <+> ptext SLIT("has arguments of kind other than `*'") + too_many = quotes (pprSourceTyCon rep_tc) <+> + ptext (sLit "has too many arguments") + bad_kind = quotes (pprSourceTyCon rep_tc) <+> + ptext (sLit "has arguments of kind other than `*'") + fam_inst = quotes (pprSourceTyCon rep_tc) <+> + ptext (sLit "is a type family") + +cond_mayDeriveDataTypeable :: Condition +cond_mayDeriveDataTypeable (mayDeriveDataTypeable, _) + | mayDeriveDataTypeable = Nothing + | otherwise = Just why + where + why = ptext (sLit "You need -XDeriveDataTypeable to derive an instance for this class") + +std_class_via_iso :: Class -> Bool +std_class_via_iso clas -- These standard classes can be derived for a newtype + -- using the isomorphism trick *even if no -fglasgow-exts* + = classKey clas `elem` [eqClassKey, ordClassKey, ixClassKey, boundedClassKey] + -- Not Read/Show because they respect the type + -- Not Enum, because newtypes are never in Enum + + +new_dfun_name :: Class -> TyCon -> TcM Name +new_dfun_name clas tycon -- Just a simple wrapper + = do { loc <- getSrcSpanM -- The location of the instance decl, not of the tycon + ; newDFunName clas [mkTyConApp tycon []] loc } + -- The type passed to newDFunName is only used to generate + -- a suitable string; hence the empty type arg list +\end{code} + +Note [Superclasses of derived instance] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +In general, a derived instance decl needs the superclasses of the derived +class too. So if we have + data T a = ...deriving( Ord ) +then the initial context for Ord (T a) should include Eq (T a). Often this is +redundant; we'll also generate an Ord constraint for each constructor argument, +and that will probably generate enough constraints to make the Eq (T a) constraint +be satisfied too. But not always; consider: + + data S a = S + instance Eq (S a) + instance Ord (S a) + + data T a = MkT (S a) deriving( Ord ) + instance Num a => Eq (T a) + +The derived instance for (Ord (T a)) must have a (Num a) constraint! +Similarly consider: + data T a = MkT deriving( Data, Typeable ) +Here there *is* no argument field, but we must nevertheless generate +a context for the Data instances: + instance Typable a => Data (T a) where ... -cond_glaExts :: Condition -cond_glaExts (gla_exts, tycon) | gla_exts = Nothing - | otherwise = Just why + +%************************************************************************ +%* * + Deriving newtypes +%* * +%************************************************************************ + +\begin{code} +mkNewTypeEqn :: InstOrigin -> Bool -> Bool -> [Var] -> Class + -> [Type] -> TyCon -> [Type] -> TyCon -> [Type] + -> Maybe ThetaType + -> TcRn EarlyDerivSpec +mkNewTypeEqn orig mayDeriveDataTypeable newtype_deriving tvs + cls cls_tys tycon tc_args rep_tycon rep_tc_args mtheta + | can_derive_via_isomorphism && (newtype_deriving || std_class_via_iso cls) + = do { traceTc (text "newtype deriving:" <+> ppr tycon <+> ppr rep_tys) + ; dfun_name <- new_dfun_name cls tycon + ; loc <- getSrcSpanM + ; let spec = DS { ds_loc = loc, ds_orig = orig + , ds_name = dfun_name, ds_tvs = varSetElems dfun_tvs + , ds_cls = cls, ds_tys = inst_tys, ds_tc = rep_tycon + , ds_theta = mtheta `orElse` all_preds + , ds_newtype = True } + ; return (if isJust mtheta then Right spec + else Left spec) } + + | otherwise + = case check_conditions of + CanDerive -> mk_data_eqn orig tvs cls tycon tc_args rep_tycon rep_tc_args mtheta + -- Use the standard H98 method + DerivableClassError msg -> bale_out msg -- Error with standard class + NonDerivableClass -- Must use newtype deriving + | newtype_deriving -> bale_out cant_derive_err -- Too hard, even with newtype deriving + | otherwise -> bale_out non_std_err -- Try newtype deriving! where - why = ptext SLIT("You need -fglasgow-exts to derive an instance for this class") + check_conditions = checkSideConditions mayDeriveDataTypeable cls cls_tys rep_tycon + bale_out msg = failWithTc (derivingThingErr cls cls_tys inst_ty msg) + + non_std_err = nonStdErr cls $$ + ptext (sLit "Try -XGeneralizedNewtypeDeriving for GHC's newtype-deriving extension") + + -- Here is the plan for newtype derivings. We see + -- newtype T a1...an = MkT (t ak+1...an) deriving (.., C s1 .. sm, ...) + -- where t is a type, + -- ak+1...an is a suffix of a1..an, and are all tyars + -- ak+1...an do not occur free in t, nor in the s1..sm + -- (C s1 ... sm) is a *partial applications* of class C + -- with the last parameter missing + -- (T a1 .. ak) matches the kind of C's last argument + -- (and hence so does t) + -- The latter kind-check has been done by deriveTyData already, + -- and tc_args are already trimmed + -- + -- We generate the instance + -- instance forall ({a1..ak} u fvs(s1..sm)). + -- C s1 .. sm t => C s1 .. sm (T a1...ak) + -- where T a1...ap is the partial application of + -- the LHS of the correct kind and p >= k + -- + -- NB: the variables below are: + -- tc_tvs = [a1, ..., an] + -- tyvars_to_keep = [a1, ..., ak] + -- rep_ty = t ak .. an + -- deriv_tvs = fvs(s1..sm) \ tc_tvs + -- tys = [s1, ..., sm] + -- rep_fn' = t + -- + -- Running example: newtype T s a = MkT (ST s a) deriving( Monad ) + -- We generate the instance + -- instance Monad (ST s) => Monad (T s) where + + nt_eta_arity = length (fst (newTyConEtadRhs rep_tycon)) + -- For newtype T a b = MkT (S a a b), the TyCon machinery already + -- eta-reduces the represenation type, so we know that + -- T a ~ S a a + -- That's convenient here, because we may have to apply + -- it to fewer than its original complement of arguments + + -- Note [Newtype representation] + -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + -- Need newTyConRhs (*not* a recursive representation finder) + -- to get the representation type. For example + -- newtype B = MkB Int + -- newtype A = MkA B deriving( Num ) + -- We want the Num instance of B, *not* the Num instance of Int, + -- when making the Num instance of A! + rep_inst_ty = newTyConInstRhs rep_tycon rep_tc_args + rep_tys = cls_tys ++ [rep_inst_ty] + rep_pred = mkClassPred cls rep_tys + -- rep_pred is the representation dictionary, from where + -- we are gong to get all the methods for the newtype + -- dictionary + + + -- Next we figure out what superclass dictionaries to use + -- See Note [Newtype deriving superclasses] above + + cls_tyvars = classTyVars cls + dfun_tvs = tyVarsOfTypes tc_args + inst_ty = mkTyConApp tycon tc_args + inst_tys = cls_tys ++ [inst_ty] + sc_theta = substTheta (zipOpenTvSubst cls_tyvars inst_tys) + (classSCTheta cls) + + -- If there are no tyvars, there's no need + -- to abstract over the dictionaries we need + -- Example: newtype T = MkT Int deriving( C ) + -- We get the derived instance + -- instance C T + -- rather than + -- instance C Int => C T + all_preds = rep_pred : sc_theta -- NB: rep_pred comes first + + ------------------------------------------------------------------- + -- Figuring out whether we can only do this newtype-deriving thing + + right_arity = length cls_tys + 1 == classArity cls + + -- Never derive Read,Show,Typeable,Data this way + non_iso_class cls = className cls `elem` ([readClassName, showClassName, dataClassName] ++ + typeableClassNames) + can_derive_via_isomorphism + = not (non_iso_class cls) + && right_arity -- Well kinded; + -- eg not: newtype T ... deriving( ST ) + -- because ST needs *2* type params + && eta_ok -- Eta reduction works + && not (isRecursiveTyCon tycon) -- Does not work for recursive tycons: + -- newtype A = MkA [A] + -- Don't want + -- instance Eq [A] => Eq A !! + -- Here's a recursive newtype that's actually OK + -- newtype S1 = S1 [T1 ()] + -- newtype T1 a = T1 (StateT S1 IO a ) deriving( Monad ) + -- It's currently rejected. Oh well. + -- In fact we generate an instance decl that has method of form + -- meth @ instTy = meth @ repTy + -- (no coerce's). We'd need a coerce if we wanted to handle + -- recursive newtypes too + + -- Check that eta reduction is OK + eta_ok = (nt_eta_arity <= length rep_tc_args) + -- (a) the newtype can be eta-reduced to match the number + -- of type argument actually supplied + -- newtype T a b = MkT (S [a] b) deriving( Monad ) + -- Here the 'b' must be the same in the rep type (S [a] b) + -- And the [a] must not mention 'b'. That's all handled + -- by nt_eta_rity. + + && (tyVarsOfTypes cls_tys `subVarSet` dfun_tvs) + -- (c) the type class args do not mention any of the dropped type + -- variables + -- newtype T a b = ... deriving( Monad b ) + + cant_derive_err = vcat [ptext (sLit "even with cunning newtype deriving:"), + if isRecursiveTyCon tycon then + ptext (sLit "the newtype may be recursive") + else empty, + if not right_arity then + quotes (ppr (mkClassPred cls cls_tys)) <+> ptext (sLit "does not have arity 1") + else empty, + if not eta_ok then + ptext (sLit "cannot eta-reduce the representation type enough") + else empty + ] \end{code} + %************************************************************************ %* * \subsection[TcDeriv-fixpoint]{Finding the fixed point of \tr{deriving} equations} @@ -695,66 +1025,85 @@ ordered by sorting on type varible, tv, (major key) and then class, k, \end{itemize} \begin{code} -solveDerivEqns :: OverlapFlag - -> [DerivEqn] - -> TcM [Instance]-- Solns in same order as eqns. - -- This bunch is Absolutely minimal... +inferInstanceContexts :: OverlapFlag -> [DerivSpec] -> TcM [DerivSpec] -solveDerivEqns overlap_flag orig_eqns - = iterateDeriv 1 initial_solutions +inferInstanceContexts _ [] = return [] + +inferInstanceContexts oflag infer_specs + = do { traceTc (text "inferInstanceContexts" <+> vcat (map pprDerivSpec infer_specs)) + ; iterate_deriv 1 initial_solutions } where + ------------------------------------------------------------------ -- The initial solutions for the equations claim that each -- instance has an empty context; this solution is certainly -- in canonical form. - initial_solutions :: [DerivSoln] - initial_solutions = [ [] | _ <- orig_eqns ] + initial_solutions :: [ThetaType] + initial_solutions = [ [] | _ <- infer_specs ] ------------------------------------------------------------------ - -- iterateDeriv calculates the next batch of solutions, + -- iterate_deriv calculates the next batch of solutions, -- compares it with the current one; finishes if they are the -- same, otherwise recurses with the new solutions. -- It fails if any iteration fails - iterateDeriv :: Int -> [DerivSoln] -> TcM [Instance] - iterateDeriv n current_solns + iterate_deriv :: Int -> [ThetaType] -> TcM [DerivSpec] + iterate_deriv n current_solns | n > 20 -- Looks as if we are in an infinite loop - -- This can happen if we have -fallow-undecidable-instances + -- This can happen if we have -XUndecidableInstances -- (See TcSimplify.tcSimplifyDeriv.) = pprPanic "solveDerivEqns: probable loop" - (vcat (map pprDerivEqn orig_eqns) $$ ppr current_solns) + (vcat (map pprDerivSpec infer_specs) $$ ppr current_solns) | otherwise - = let - inst_specs = zipWithEqual "add_solns" mk_inst_spec - orig_eqns current_solns - in - checkNoErrs ( - -- Extend the inst info from the explicit instance decls + = do { -- Extend the inst info from the explicit instance decls -- with the current set of solutions, and simplify each RHS - extendLocalInstEnv inst_specs $ - mappM gen_soln orig_eqns - ) `thenM` \ new_solns -> - if (current_solns == new_solns) then - returnM inst_specs - else - iterateDeriv (n+1) new_solns + let inst_specs = zipWithEqual "add_solns" (mkInstance2 oflag) + current_solns infer_specs + ; new_solns <- checkNoErrs $ + extendLocalInstEnv inst_specs $ + mapM gen_soln infer_specs + + ; if (current_solns == new_solns) then + return [ spec { ds_theta = soln } + | (spec, soln) <- zip infer_specs current_solns ] + else + iterate_deriv (n+1) new_solns } ------------------------------------------------------------------ - gen_soln (_, clas, tc,tyvars,deriv_rhs) - = setSrcSpan (srcLocSpan (getSrcLoc tc)) $ - do { let inst_tys = [mkTyConApp tc (mkTyVarTys tyvars)] - ; theta <- addErrCtxt (derivInstCtxt1 clas inst_tys) $ - tcSimplifyDeriv tc tyvars deriv_rhs - ; addErrCtxt (derivInstCtxt2 theta clas inst_tys) $ - checkValidInstance tyvars theta clas inst_tys - ; return (sortLe (<=) theta) } -- Canonicalise before returning the soluction - where - + gen_soln :: DerivSpec -> TcM [PredType] + gen_soln (DS { ds_loc = loc, ds_orig = orig, ds_tvs = tyvars + , ds_cls = clas, ds_tys = inst_tys, ds_theta = deriv_rhs }) + = setSrcSpan loc $ + addErrCtxt (derivInstCtxt clas inst_tys) $ + do { theta <- tcSimplifyDeriv orig tyvars deriv_rhs + -- checkValidInstance tyvars theta clas inst_tys + -- Not necessary; see Note [Exotic derived instance contexts] + -- in TcSimplify + + -- Check for a bizarre corner case, when the derived instance decl should + -- have form instance C a b => D (T a) where ... + -- Note that 'b' isn't a parameter of T. This gives rise to all sorts + -- of problems; in particular, it's hard to compare solutions for + -- equality when finding the fixpoint. So I just rule it out for now. + ; let tv_set = mkVarSet tyvars + weird_preds = [pred | pred <- theta, not (tyVarsOfPred pred `subVarSet` tv_set)] + ; mapM_ (addErrTc . badDerivedPred) weird_preds + + -- Claim: the result instance declaration is guaranteed valid + -- Hence no need to call: + -- checkValidInstance tyvars theta clas inst_tys + ; return (sortLe (<=) theta) } -- Canonicalise before returning the solution + +------------------------------------------------------------------ +mkInstance1 :: OverlapFlag -> DerivSpec -> Instance +mkInstance1 overlap_flag spec = mkInstance2 overlap_flag (ds_theta spec) spec + +mkInstance2 :: OverlapFlag -> ThetaType -> DerivSpec -> Instance +mkInstance2 overlap_flag theta + (DS { ds_name = dfun_name + , ds_tvs = tyvars, ds_cls = clas, ds_tys = tys }) + = mkLocalInstance dfun overlap_flag + where + dfun = mkDictFunId dfun_name tyvars theta clas tys - ------------------------------------------------------------------ - mk_inst_spec (dfun_name, clas, tycon, tyvars, _) theta - = mkLocalInstance dfun overlap_flag - where - dfun = mkDictFunId dfun_name tyvars theta clas - [mkTyConApp tycon (mkTyVarTys tyvars)] extendLocalInstEnv :: [Instance] -> TcM a -> TcM a -- Add new locally-defined instances; don't bother to check @@ -766,6 +1115,7 @@ extendLocalInstEnv dfuns thing_inside ; setGblEnv env' thing_inside } \end{code} + %************************************************************************ %* * \subsection[TcDeriv-normal-binds]{Bindings for the various classes} @@ -829,56 +1179,56 @@ the renamer. What a great hack! \end{itemize} \begin{code} --- Generate the InstInfo for the required instance, +-- Generate the InstInfo for the required instance paired with the +-- *representation* tycon for that instance, -- plus any auxiliary bindings required -genInst :: Instance -> TcM (InstInfo, LHsBinds RdrName) -genInst spec - = do { fix_env <- getFixityEnv - ; let - (tyvars,_,clas,[ty]) = instanceHead spec - clas_nm = className clas - tycon = tcTyConAppTyCon ty - (meth_binds, aux_binds) = genDerivBinds clas fix_env tycon - - -- Bring the right type variables into - -- scope, and rename the method binds - -- It's a bit yukky that we return *renamed* InstInfo, but - -- *non-renamed* auxiliary bindings - ; (rn_meth_binds, _fvs) <- discardWarnings $ - bindLocalNames (map varName tyvars) $ - rnMethodBinds clas_nm (\n -> []) [] meth_binds +-- +-- Representation tycons differ from the tycon in the instance signature in +-- case of instances for indexed families. +-- +genInst :: OverlapFlag -> DerivSpec -> TcM (InstInfo RdrName, DerivAuxBinds) +genInst oflag spec + | ds_newtype spec + = return (InstInfo { iSpec = mkInstance1 oflag spec + , iBinds = NewTypeDerived }, []) + + | otherwise + = do { let loc = getSrcSpan (ds_name spec) + inst = mkInstance1 oflag spec + clas = ds_cls spec + rep_tycon = ds_tc spec + + -- In case of a family instance, we need to use the representation + -- tycon (after all, it has the data constructors) + ; fix_env <- getFixityEnv + ; let (meth_binds, aux_binds) = genDerivBinds loc fix_env clas rep_tycon -- Build the InstInfo - ; return (InstInfo { iSpec = spec, - iBinds = VanillaInst rn_meth_binds [] }, + ; return (InstInfo { iSpec = inst, + iBinds = VanillaInst meth_binds [] }, aux_binds) - } + } -genDerivBinds clas fix_env tycon +genDerivBinds :: SrcSpan -> FixityEnv -> Class -> TyCon -> (LHsBinds RdrName, DerivAuxBinds) +genDerivBinds loc fix_env clas tycon | className clas `elem` typeableClassNames - = (gen_Typeable_binds tycon, emptyLHsBinds) + = (gen_Typeable_binds loc tycon, []) | otherwise = case assocMaybe gen_list (getUnique clas) of - Just gen_fn -> gen_fn fix_env tycon + Just gen_fn -> gen_fn loc tycon Nothing -> pprPanic "genDerivBinds: bad derived class" (ppr clas) where - gen_list :: [(Unique, FixityEnv -> TyCon -> (LHsBinds RdrName, LHsBinds RdrName))] - gen_list = [(eqClassKey, no_aux_binds (ignore_fix_env gen_Eq_binds)) - ,(ordClassKey, no_aux_binds (ignore_fix_env gen_Ord_binds)) - ,(enumClassKey, no_aux_binds (ignore_fix_env gen_Enum_binds)) - ,(boundedClassKey, no_aux_binds (ignore_fix_env gen_Bounded_binds)) - ,(ixClassKey, no_aux_binds (ignore_fix_env gen_Ix_binds)) - ,(typeableClassKey,no_aux_binds (ignore_fix_env gen_Typeable_binds)) - ,(showClassKey, no_aux_binds gen_Show_binds) - ,(readClassKey, no_aux_binds gen_Read_binds) - ,(dataClassKey, gen_Data_binds) + gen_list :: [(Unique, SrcSpan -> TyCon -> (LHsBinds RdrName, DerivAuxBinds))] + gen_list = [(eqClassKey, gen_Eq_binds) + ,(ordClassKey, gen_Ord_binds) + ,(enumClassKey, gen_Enum_binds) + ,(boundedClassKey, gen_Bounded_binds) + ,(ixClassKey, gen_Ix_binds) + ,(showClassKey, gen_Show_binds fix_env) + ,(readClassKey, gen_Read_binds fix_env) + ,(dataClassKey, gen_Data_binds) ] - - -- no_aux_binds is used for generators that don't - -- need to produce any auxiliary bindings - no_aux_binds f fix_env tc = (f fix_env tc, emptyLHsBinds) - ignore_fix_env f fix_env tc = f tc \end{code} @@ -888,96 +1238,43 @@ genDerivBinds clas fix_env tycon %* * %************************************************************************ - -data Foo ... = ... - -con2tag_Foo :: Foo ... -> Int# -tag2con_Foo :: Int -> Foo ... -- easier if Int, not Int# -maxtag_Foo :: Int -- ditto (NB: not unlifted) - - -We have a @con2tag@ function for a tycon if: -\begin{itemize} -\item -We're deriving @Eq@ and the tycon has nullary data constructors. - -\item -Or: we're deriving @Ord@ (unless single-constructor), @Enum@, @Ix@ -(enum type only????) -\end{itemize} - -We have a @tag2con@ function for a tycon if: -\begin{itemize} -\item -We're deriving @Enum@, or @Ix@ (enum type only???) -\end{itemize} - -If we have a @tag2con@ function, we also generate a @maxtag@ constant. - -\begin{code} -genTaggeryBinds :: [InstInfo] -> TcM (LHsBinds RdrName) -genTaggeryBinds infos - = do { names_so_far <- foldlM do_con2tag [] tycons_of_interest - ; nm_alist_etc <- foldlM do_tag2con names_so_far tycons_of_interest - ; return (listToBag (map gen_tag_n_con_monobind nm_alist_etc)) } - where - all_CTs = [ (cls, tcTyConAppTyCon ty) - | info <- infos, - let (cls,ty) = simpleInstInfoClsTy info ] - all_tycons = map snd all_CTs - (tycons_of_interest, _) = removeDups compare all_tycons - - do_con2tag acc_Names tycon - | isDataTyCon tycon && - ((we_are_deriving eqClassKey tycon - && any isNullarySrcDataCon (tyConDataCons tycon)) - || (we_are_deriving ordClassKey tycon - && not (isProductTyCon tycon)) - || (we_are_deriving enumClassKey tycon) - || (we_are_deriving ixClassKey tycon)) - - = returnM ((con2tag_RDR tycon, tycon, GenCon2Tag) - : acc_Names) - | otherwise - = returnM acc_Names - - do_tag2con acc_Names tycon - | isDataTyCon tycon && - (we_are_deriving enumClassKey tycon || - we_are_deriving ixClassKey tycon - && isEnumerationTyCon tycon) - = returnM ( (tag2con_RDR tycon, tycon, GenTag2Con) - : (maxtag_RDR tycon, tycon, GenMaxTag) - : acc_Names) - | otherwise - = returnM acc_Names - - we_are_deriving clas_key tycon - = is_in_eqns clas_key tycon all_CTs - where - is_in_eqns clas_key tycon [] = False - is_in_eqns clas_key tycon ((c,t):cts) - = (clas_key == classKey c && tycon == t) - || is_in_eqns clas_key tycon cts -\end{code} - \begin{code} -derivingThingErr clas tys tycon tyvars why - = sep [hsep [ptext SLIT("Can't make a derived instance of"), quotes (ppr pred)], +derivingKindErr :: TyCon -> Class -> [Type] -> Kind -> Message +derivingKindErr tc cls cls_tys cls_kind + = hang (ptext (sLit "Cannot derive well-kinded instance of form") + <+> quotes (pprClassPred cls cls_tys <+> parens (ppr tc <+> ptext (sLit "...")))) + 2 (ptext (sLit "Class") <+> quotes (ppr cls) + <+> ptext (sLit "expects an argument of kind") <+> quotes (pprKind cls_kind)) + +typeFamilyPapErr :: TyCon -> Class -> [Type] -> Type -> Message +typeFamilyPapErr tc cls cls_tys inst_ty + = hang (ptext (sLit "Derived instance") <+> quotes (pprClassPred cls (cls_tys ++ [inst_ty]))) + 2 (ptext (sLit "requires illegal partial application of data type family") <+> ppr tc) + +derivingThingErr :: Class -> [Type] -> Type -> Message -> Message +derivingThingErr clas tys ty why + = sep [hsep [ptext (sLit "Can't make a derived instance of"), + quotes (ppr pred)], nest 2 (parens why)] where - pred = mkClassPred clas (tys ++ [mkTyConApp tycon (mkTyVarTys tyvars)]) - -derivCtxt :: TyCon -> SDoc -derivCtxt tycon - = ptext SLIT("When deriving instances for") <+> quotes (ppr tycon) - -derivInstCtxt1 clas inst_tys - = ptext SLIT("When deriving the instance for") <+> quotes (pprClassPred clas inst_tys) - -derivInstCtxt2 theta clas inst_tys - = vcat [ptext SLIT("In the derived instance declaration"), - nest 2 (ptext SLIT("instance") <+> sep [pprThetaArrow theta, - pprClassPred clas inst_tys])] + pred = mkClassPred clas (tys ++ [ty]) + +derivingHiddenErr :: TyCon -> SDoc +derivingHiddenErr tc + = hang (ptext (sLit "The data constructors of") <+> quotes (ppr tc) <+> ptext (sLit "are not all in scope")) + 2 (ptext (sLit "so you cannot derive an instance for it")) + +standaloneCtxt :: LHsType Name -> SDoc +standaloneCtxt ty = hang (ptext (sLit "In the stand-alone deriving instance for")) + 2 (quotes (ppr ty)) + +derivInstCtxt :: Class -> [Type] -> Message +derivInstCtxt clas inst_tys + = ptext (sLit "When deriving the instance for") <+> parens (pprClassPred clas inst_tys) + +badDerivedPred :: PredType -> Message +badDerivedPred pred + = vcat [ptext (sLit "Can't derive instances where the instance context mentions"), + ptext (sLit "type variables that are not data type parameters"), + nest 2 (ptext (sLit "Offending constraint:") <+> ppr pred)] \end{code} -