X-Git-Url: http://git.megacz.com/?p=ghc-hetmet.git;a=blobdiff_plain;f=compiler%2Ftypecheck%2FTcDeriv.lhs;h=b994a278298bce08f124cf378c463459bc613af5;hp=2563b0979dcf9b116e297244868e27d88f3f658d;hb=92267aa26adb1ab5a6d8004a80fdf6aa06ea4e44;hpb=5e0ea427646a5474dd7c659b0713c6a62d8c99c7 diff --git a/compiler/typecheck/TcDeriv.lhs b/compiler/typecheck/TcDeriv.lhs index 2563b09..b994a27 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 +11,125 @@ 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 Coercion +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 + +import Control.Monad \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 :: CtOrigin + , ds_name :: Name + , ds_tvs :: [TyVar] + , ds_theta :: ThetaType + , ds_cls :: Class + , ds_tys :: [Type] + , ds_tc :: TyCon + , ds_tc_args :: [Type] + , 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 type families, the tycon in + -- in ds_tys is the *family* tycon + -- in ds_tc, ds_tc_args is the *representation* tycon + -- For non-family tycons, both are the same + + -- ds_newtype = True <=> Newtype deriving + -- False <=> Vanilla deriving +\end{code} + +Example: + + newtype instance T [a] = MkT (Tree a) deriving( C s ) +==> + axiom T [a] = :RTList a + axiom :RTList a = Tree a + + DS { ds_tvs = [a,s], ds_cls = C, ds_tys = [s, T [a]] + , ds_tc = :RTList, ds_tc_args = [a] + , ds_newtype = True } + +\begin{code} +type DerivContext = Maybe ThetaType + -- Nothing <=> Vanilla deriving; infer the context of the instance decl + -- Just theta <=> Standalone deriving: context supplied by programmer + +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 +208,9 @@ 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 +237,8 @@ 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 @@ -196,8 +251,37 @@ 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 +Note [Unused constructors and deriving clauses] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +See Trac #3221. Consider + data T = T1 | T2 deriving( Show ) +Are T1 and T2 unused? Well, no: the deriving clause expands to mention +both of them. So we gather defs/uses from deriving just like anything else. + %************************************************************************ %* * \subsection[TcDeriv-driver]{Top-level function for \tr{derivings}} @@ -205,357 +289,397 @@ And then translate it to: %************************************************************************ \begin{code} -tcDeriving :: [LTyClDecl Name] -- All type constructors - -> TcM ([InstInfo], -- The generated "instance decls" - HsValBinds Name) -- Extra generated top-level bindings - -tcDeriving tycl_decls - = recoverM (returnM ([], emptyValBindsOut)) $ +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 + DefUses) + +tcDeriving tycl_decls inst_decls deriv_decls + = recoverM (return ([], emptyValBindsOut, emptyDUs)) $ 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 "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 True overlap_flag) given_specs + + ; final_specs <- extendLocalInstEnv (map (iSpec . fst) insts1) $ + inferInstanceContexts overlap_flag infer_specs + ; insts2 <- mapM (genInst False overlap_flag) final_specs + + -- Generate the generic to/from functions from each type declaration + ; gen_binds <- mkGenericBinds is_boot tycl_decls + ; (inst_info, rn_binds, rn_dus) <- 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, rn_dus) } 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 +renameDeriv :: Bool -> LHsBinds RdrName + -> [(InstInfo RdrName, DerivAuxBinds)] + -> TcM ([InstInfo Name], HsValBinds Name, DefUses) +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, fvs) <- mapAndUnzipM rn_inst_info inst_infos + ; return (rn_inst_infos, emptyValBindsOut, usesOnly (plusFVs fvs)) } - -- Generate the InstInfo for each dfun, - -- plus any auxiliary bindings it needs - ; (inst_infos, aux_binds_s) <- mapAndUnzipM genInst inst_specs - - -- 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, aux_sigs) = unzip $ map (genAuxBind loc) $ + rm_dups [] $ concat deriv_aux_binds + aux_val_binds = ValBindsIn (listToBag aux_binds) aux_sigs + ; rn_aux_lhs <- rnTopBindsLHS emptyFsEnv aux_val_binds + ; bindLocalNames (collectHsValBinders rn_aux_lhs) $ + do { (rn_aux, dus_aux) <- rnTopBindsRHS rn_aux_lhs + ; (rn_inst_infos, fvs_insts) <- mapAndUnzipM rn_inst_info inst_infos + ; return (rn_inst_infos, rn_aux `plusHsValBinds` rn_gen, + dus_gen `plusDU` dus_aux `plusDU` usesOnly (plusFVs fvs_insts)) } } - -- 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 RdrName -> TcM (InstInfo Name, FreeVars) + rn_inst_info info@(InstInfo { iBinds = NewTypeDerived coi tc }) + = return ( info { iBinds = NewTypeDerived coi tc } + , mkFVs (map dataConName (tyConDataCons tc))) + -- See Note [Newtype deriving and unused constructors] + + rn_inst_info (InstInfo { iSpec = inst, iBinds = VanillaInst binds sigs standalone_deriv }) + = -- 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 + ; let binds' = VanillaInst rn_binds [] standalone_deriv + ; return (InstInfo { iSpec = inst, iBinds = binds' }, fvs) } + 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 - ; return (unionManyBags [ mkTyConGenericBinds tc | - tc <- tcs, tyConHasGenerics tc ]) } - -- And then only in the ones whose 'has-generics' flag is on +mkGenericBinds :: Bool -> [LTyClDecl Name] -> TcM (LHsBinds RdrName) +mkGenericBinds is_boot tycl_decls + | is_boot + = return emptyBag + | otherwise + = do { tcs <- mapM tcLookupTyCon [ tcdName d + | L _ d <- tycl_decls, isDataDecl d ] + ; return (unionManyBags [ mkTyConGenericBinds tc + | tc <- tcs, tyConHasGenerics tc ]) } + -- 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} +Note [Newtype deriving and unused constructors] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +Consider this (see Trac #1954): + + module Bug(P) where + newtype P a = MkP (IO a) deriving Monad + +If you compile with -fwarn-unused-binds you do not expect the warning +"Defined but not used: data consructor MkP". Yet the newtype deriving +code does not explicitly mention MkP, but it should behave as if you +had written + instance Monad P where + return x = MkP (return x) + ...etc... + +So we want to signal a user of the data constructor 'MkP'. That's +what we do in rn_inst_info, and it's the only reason we have the TyCon +stored in NewTypeDerived. + %************************************************************************ %* * -\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} +@makeDerivSpecs@ fishes around to find the info about needed derived instances. -[See Appendix~E in the Haskell~1.2 report.] This code here deals w/ -all those. +\begin{code} +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 + extractTyDataPreds decls + = [(p, d) | d@(L _ (TyData {tcdDerivs = Just preds})) <- decls, p <- preds] -Note [Newtype deriving superclasses] -~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + all_tydata :: [(LHsType Name, LTyClDecl Name)] + -- Derived predicate paired with its data type declaration + all_tydata = extractTyDataPreds (instDeclATs inst_decls ++ tycl_decls) -The 'tys' here come from the partial application -in the deriving clause. The last arg is the new -instance type. + deriv_locs = map (getLoc . snd) all_tydata + ++ map getLoc deriv_decls -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 + 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 "Standalone deriving decl for" (ppr deriv_ty) + ; (tvs, theta, tau) <- tcHsInstHead deriv_ty + ; traceTc "Standalone deriving;" $ vcat + [ text "tvs:" <+> ppr tvs + , text "theta:" <+> ppr theta + , text "tau:" <+> ppr tau ] + ; (cls, inst_tys) <- checkValidInstance deriv_ty tvs theta tau + -- C.f. TcInstDcls.tcLocalInstDecl1 + + ; let cls_tys = take (length inst_tys - 1) inst_tys + inst_ty = last inst_tys + ; traceTc "Standalone deriving:" $ vcat + [ 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) } -\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) +------------------------------------------------------------------ +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 + args_to_drop = drop n_args_to_keep tc_args + inst_ty = mkTyConApp tc (take n_args_to_keep tc_args) + inst_ty_kind = typeKind inst_ty + dropped_tvs = mkVarSet (mapCatMaybes getTyVar_maybe args_to_drop) + univ_tvs = (mkVarSet tvs `extendVarSetList` deriv_tvs) + `minusVarSet` dropped_tvs + + -- 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) + + ; checkTc (sizeVarSet dropped_tvs == n_args_to_drop && -- (a) + tyVarsOfTypes (inst_ty:cls_tys) `subVarSet` univ_tvs) -- (b) + (derivingEtaErr cls cls_tys inst_ty) + -- Check that + -- (a) The data type can be eta-reduced; eg reject: + -- data instance T a a = ... deriving( Monad ) + -- (b) The type class args do not mention any of the dropped type + -- variables + -- newtype T a s = ... deriving( ST s ) + + -- Type families can't be partially applied + -- e.g. newtype instance T Int a = MkT [a] deriving( Monad ) + -- Note [Deriving, type families, and partial applications] + ; checkTc (not (isFamilyTyCon tc) || n_args_to_drop == 0) + (typeFamilyPapErr tc cls cls_tys inst_ty) + + ; mkEqnHelp DerivOrigin (varSetElems univ_tvs) cls cls_tys inst_ty Nothing } } 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 ] - - ------------------------------------------------------------------ - 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 - - ------------------------------------------------------------------ - -- 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 + -- 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 +\end{code} - 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 +Note [Deriving, type families, and partial applications] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +When there are no type families, it's quite easy: - 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 + newtype S a = MkS [a] + -- :CoS :: S ~ [] -- Eta-reduced - 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 + instance Eq [a] => Eq (S a) -- by coercion sym (Eq (:CoS a)) : Eq [a] ~ Eq (S a) + instance Monad [] => Monad S -- by coercion sym (Monad :CoS) : Monad [] ~ Monad S - inst_tys = (tys ++ [mkTyConApp tycon (mkTyVarTys tyvars_to_keep)]) +When type familes are involved it's trickier: + data family T a b + newtype instance T Int a = MkT [a] deriving( Eq, Monad ) + -- :RT is the representation type for (T Int a) + -- :CoF:R1T a :: T Int a ~ :RT a -- Not eta reduced + -- :Co:R1T :: :RT ~ [] -- Eta-reduced - sc_theta = substTheta (zipOpenTvSubst clas_tyvars inst_tys) - (classSCTheta clas) + instance Eq [a] => Eq (T Int a) -- easy by coercion + instance Monad [] => Monad (T Int) -- only if we can eta reduce??? - -- 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 +The "???" bit is that we don't build the :CoF thing in eta-reduced form +Henc the current typeFamilyPapErr, even though the instance makes sense. +After all, we can write it out + instance Monad [] => Monad (T Int) -- only if we can eta reduce??? + return x = MkT [x] + ... etc ... - -- 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 +\begin{code} +mkEqnHelp :: CtOrigin -> [TyVar] -> Class -> [Type] -> Type + -> DerivContext -- 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) <- tcLookupDataFamInst 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) - ------------------------------------------------------------------- - -- Figuring out whether we can only do this newtype-deriving thing + ; dflags <- getDOpts + ; if isDataTyCon rep_tc then + mkDataTypeEqn orig dflags tvs cls cls_tys + tycon tc_args rep_tc rep_tc_args mtheta + else + mkNewTypeEqn orig dflags tvs cls cls_tys + tycon tc_args rep_tc rep_tc_args mtheta } + | otherwise + = failWithTc (derivingThingErr False cls cls_tys tc_app + (ptext (sLit "The last argument of the instance must be a data or newtype application"))) +\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 :: CtOrigin + -> DynFlags + -> [Var] -- Universally quantified type variables in the instance + -> Class -- Class for which we need to derive an instance + -> [Type] -- Other parameters to the class except the last + -> TyCon -- Type constructor for which the instance is requested + -- (last parameter to the type class) + -> [Type] -- Parameters to the type constructor + -> TyCon -- rep of the above (for type families) + -> [Type] -- rep of the above + -> DerivContext -- Context of the instance, for standalone deriving + -> TcRn EarlyDerivSpec -- Return 'Nothing' if error + +mkDataTypeEqn orig dflags tvs cls cls_tys + tycon tc_args rep_tc rep_tc_args mtheta + = case checkSideConditions dflags mtheta cls cls_tys rep_tc of + -- NB: pass the *representation* tycon to checkSideConditions + CanDerive -> go_for_it + 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 - + go_for_it = mk_data_eqn orig tvs cls tycon tc_args rep_tc rep_tc_args mtheta + bale_out msg = failWithTc (derivingThingErr False cls cls_tys (mkTyConApp tycon tc_args) msg) -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 +mk_data_eqn, mk_typeable_eqn + :: CtOrigin -> [TyVar] -> Class + -> TyCon -> [TcType] -> TyCon -> [TcType] -> DerivContext + -> 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 ------------------------------------------------------------------- -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 inst_tys = [mkTyConApp tycon tc_args] + inferred_constraints = inferConstraints tvs cls inst_tys rep_tc rep_tc_args + 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_tc_args = rep_tc_args + , ds_theta = mtheta `orElse` inferred_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 ... @@ -564,116 +688,522 @@ 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) } + | 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_tc_args = rep_tc_args + , ds_theta = mtheta `orElse` [], ds_newtype = False }) } + + +inferConstraints :: [TyVar] -> Class -> [TcType] -> TyCon -> [TcType] -> ThetaType +-- Generate a sufficiently large set of constraints that typechecking the +-- generated method definitions should succeed. This set will be simplified +-- before being used in the instance declaration +inferConstraints _ cls inst_tys rep_tc rep_tc_args + = ASSERT2( equalLength rep_tc_tvs all_rep_tc_args, ppr cls <+> ppr rep_tc ) + stupid_constraints ++ extra_constraints + ++ sc_constraints ++ con_arg_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? - ] - + -- Constraints arising from the arguments of each constructor + con_arg_constraints + = [ mkClassPred cls [arg_ty] + | data_con <- tyConDataCons rep_tc, + arg_ty <- ASSERT( isVanillaDataCon data_con ) + get_constrained_tys $ + dataConInstOrigArgTys data_con all_rep_tc_args, + not (isUnLiftedType arg_ty) ] + -- No constraints for unlifted types + -- Where they are legal we generate specilised function calls + + -- For functor-like classes, two things are different + -- (a) We recurse over argument types to generate constraints + -- See Functor examples in TcGenDeriv + -- (b) The rep_tc_args will be one short + is_functor_like = getUnique cls `elem` functorLikeClassKeys + + get_constrained_tys :: [Type] -> [Type] + get_constrained_tys tys + | is_functor_like = concatMap (deepSubtypesContaining last_tv) tys + | otherwise = tys + + rep_tc_tvs = tyConTyVars rep_tc + last_tv = last rep_tc_tvs + all_rep_tc_args | is_functor_like = rep_tc_args ++ [mkTyVarTy last_tv] + | otherwise = rep_tc_args + + -- Constraints arising from superclasses + -- See Note [Superclasses of derived instance] + sc_constraints = substTheta (zipOpenTvSubst (classTyVars cls) inst_tys) + (classSCTheta cls) + + -- Stupid constraints + stupid_constraints = substTheta subst (tyConStupidTheta rep_tc) + subst = zipTopTvSubst rep_tc_tvs all_rep_tc_args + + -- Extra Data constraints + -- The Data class (only) requires that for + -- instance (...) => Data (T t1 t2) + -- IF t1:*, t2:* + -- THEN (Data t1, Data t2) are among the (...) constraints + -- Reason: when the IF holds, we generate a method + -- dataCast2 f = gcast2 f + -- and we need the Data constraints to typecheck the method + extra_constraints + | cls `hasKey` dataClassKey + , all (isLiftedTypeKind . typeKind) rep_tc_args + = [mkClassPred cls [ty] | ty <- rep_tc_args] + | otherwise + = [] ------------------------------------------------------------------ -- 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 ) - | 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) +-- +-- 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 + | DerivableClassError SDoc -- Standard class, but can't do it + | NonDerivableClass -- Non-standard class + +checkSideConditions :: DynFlags -> DerivContext -> Class -> [TcType] -> TyCon -> DerivStatus +checkSideConditions dflags mtheta cls cls_tys rep_tc + | Just cond <- sideConditions mtheta cls + = case (cond (dflags, rep_tc)) of + Just err -> DerivableClassError err -- Class-specific error + Nothing | null cls_tys -> CanDerive -- All derivable classes are unary, so + -- cls_tys (the type args other than last) + -- should be null + | otherwise -> DerivableClassError ty_args_why -- e.g. deriving( Eq s ) + | otherwise = NonDerivableClass -- Not a standard class 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 :: DerivContext -> Class -> Maybe Condition +sideConditions mtheta 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 (checkFlag Opt_DeriveDataTypeable `andCond` + cond_std `andCond` cond_noUnliftedArgs) + | cls_key == functorClassKey = Just (checkFlag Opt_DeriveFunctor `andCond` + cond_functorOK True) -- NB: no cond_std! + | cls_key == foldableClassKey = Just (checkFlag Opt_DeriveFoldable `andCond` + cond_functorOK False) -- Functor/Fold/Trav works ok for rank-n types + | cls_key == traversableClassKey = Just (checkFlag Opt_DeriveTraversable `andCond` + cond_functorOK False) + | getName cls `elem` typeableClassNames = Just (checkFlag Opt_DeriveDataTypeable `andCond` cond_typeableOK) + | otherwise = Nothing + where + cls_key = getUnique cls + cond_std = cond_stdOK mtheta -type Condition = (Bool, TyCon) -> Maybe SDoc -- Nothing => OK +type Condition = (DynFlags, TyCon) -> Maybe SDoc + -- first Bool is whether or not we are allowed to derive Data and Typeable + -- second Bool is whether or not we are allowed to derive Functor + -- TyCon is the *representation* tycon if the + -- data type is an indexed one + -- Nothing => OK orCond :: Condition -> Condition -> Condition orCond c1 c2 tc = case c1 tc of - Nothing -> Nothing -- c1 succeeds - Just x -> case c2 tc of -- c1 fails + Nothing -> Nothing -- c1 succeeds + Just x -> case c2 tc of -- c1 fails Nothing -> Nothing - Just y -> Just (x $$ ptext SLIT(" and") $$ y) - -- Both fail + Just y -> Just (x $$ ptext (sLit " and") $$ y) + -- Both fail +andCond :: Condition -> Condition -> Condition andCond c1 c2 tc = case c1 tc of Nothing -> c2 tc -- c1 succeeds Just x -> Just x -- c1 fails -cond_std :: Condition -cond_std (gla_exts, tycon) - | any (not . isVanillaDataCon) data_cons = Just existential_why - | null data_cons = Just no_cons_why - | otherwise = Nothing +cond_stdOK :: DerivContext -> Condition +cond_stdOK (Just _) _ + = Nothing -- Don't check these conservative conditions for + -- standalone deriving; just generate the code + -- and let the typechecker handle the result +cond_stdOK Nothing (_, rep_tc) + | null data_cons = Just (no_cons_why rep_tc $$ suggestion) + | not (null con_whys) = Just (vcat con_whys $$ suggestion) + | 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)") + suggestion = ptext (sLit "Possible fix: use a standalone deriving declaration instead") + data_cons = tyConDataCons rep_tc + con_whys = mapCatMaybes check_con data_cons + + check_con :: DataCon -> Maybe SDoc + check_con con + | isVanillaDataCon con + , all isTauTy (dataConOrigArgTys con) = Nothing + | otherwise = Just (badCon con (ptext (sLit "does not have a Haskell-98 type"))) +no_cons_why :: TyCon -> SDoc +no_cons_why rep_tc = quotes (pprSourceTyCon rep_tc) <+> + ptext (sLit "has no data constructors") + +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 = badCon (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 = sep [ quotes (pprSourceTyCon rep_tc) <+> + ptext (sLit "is not an enumeration type") + , nest 2 $ ptext (sLit "(an enumeration consists of one or more nullary constructors)") ] + -- See Note [Enumeration types] in TyCon 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 "does not have precisely 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 (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") + + +functorLikeClassKeys :: [Unique] +functorLikeClassKeys = [functorClassKey, foldableClassKey, traversableClassKey] + +cond_functorOK :: Bool -> Condition +-- OK for Functor/Foldable/Traversable class +-- Currently: (a) at least one argument +-- (b) don't use argument contravariantly +-- (c) don't use argument in the wrong place, e.g. data T a = T (X a a) +-- (d) optionally: don't use function types +-- (e) no "stupid context" on data type +cond_functorOK allowFunctions (dflags, rep_tc) + | not (xopt Opt_DeriveFunctor dflags) + = Just (ptext (sLit "You need -XDeriveFunctor to derive an instance for this class")) + + | null tc_tvs + = Just (ptext (sLit "Data type") <+> quotes (ppr rep_tc) + <+> ptext (sLit "has no parameters")) + + | not (null bad_stupid_theta) + = Just (ptext (sLit "Data type") <+> quotes (ppr rep_tc) + <+> ptext (sLit "has a class context") <+> pprTheta bad_stupid_theta) + + | otherwise + = msum (map check_con data_cons) -- msum picks the first 'Just', if any + where + tc_tvs = tyConTyVars rep_tc + Just (_, last_tv) = snocView tc_tvs + bad_stupid_theta = filter is_bad (tyConStupidTheta rep_tc) + is_bad pred = last_tv `elemVarSet` tyVarsOfPred pred + + data_cons = tyConDataCons rep_tc + check_con con = msum (check_vanilla con : foldDataConArgs (ft_check con) con) + + check_vanilla :: DataCon -> Maybe SDoc + check_vanilla con | isVanillaDataCon con = Nothing + | otherwise = Just (badCon con existential) + + ft_check :: DataCon -> FFoldType (Maybe SDoc) + ft_check con = FT { ft_triv = Nothing, ft_var = Nothing + , ft_co_var = Just (badCon con covariant) + , ft_fun = \x y -> if allowFunctions then x `mplus` y + else Just (badCon con functions) + , ft_tup = \_ xs -> msum xs + , ft_ty_app = \_ x -> x + , ft_bad_app = Just (badCon con wrong_arg) + , ft_forall = \_ x -> x } + + existential = ptext (sLit "has existential arguments") + covariant = ptext (sLit "uses the type variable in a function argument") + functions = ptext (sLit "contains function types") + wrong_arg = ptext (sLit "uses the type variable in an argument other than the last") + +checkFlag :: ExtensionFlag -> Condition +checkFlag flag (dflags, _) + | xopt flag dflags = Nothing + | otherwise = Just why 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 `*'") + why = ptext (sLit "You need -X") <> text flag_str + <+> ptext (sLit "to derive an instance for this class") + flag_str = case [ s | (s, f, _) <- xFlags, f==flag ] of + [s] -> s + other -> pprPanic "checkFlag" (ppr other) + +std_class_via_iso :: Class -> Bool +-- These standard classes can be derived for a newtype +-- using the isomorphism trick *even if no -XGeneralizedNewtypeDeriving +-- because giving so gives the same results as generating the boilerplate +std_class_via_iso clas + = classKey clas `elem` [eqClassKey, ordClassKey, ixClassKey, boundedClassKey] + -- Not Read/Show because they respect the type + -- Not Enum, because newtypes are never in Enum + + +non_iso_class :: Class -> Bool +-- *Never* derive Read,Show,Typeable,Data by isomorphism, +-- even with -XGeneralizedNewtypeDeriving +non_iso_class cls + = classKey cls `elem` ([readClassKey, showClassKey, dataClassKey] ++ + typeableClassKeys) + +typeableClassKeys :: [Unique] +typeableClassKeys = map getUnique typeableClassNames + +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 + +badCon :: DataCon -> SDoc -> SDoc +badCon con msg = ptext (sLit "Constructor") <+> quotes (ppr con) <+> msg +\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 ... + + +%************************************************************************ +%* * + Deriving newtypes +%* * +%************************************************************************ + +\begin{code} +mkNewTypeEqn :: CtOrigin -> DynFlags -> [Var] -> Class + -> [Type] -> TyCon -> [Type] -> TyCon -> [Type] + -> DerivContext + -> TcRn EarlyDerivSpec +mkNewTypeEqn orig dflags tvs + cls cls_tys tycon tc_args rep_tycon rep_tc_args mtheta +-- Want: instance (...) => cls (cls_tys ++ [tycon tc_args]) where ... + | can_derive_via_isomorphism && (newtype_deriving || std_class_via_iso cls) + = do { traceTc "newtype deriving:" (ppr tycon <+> ppr rep_tys <+> ppr all_preds) + ; 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_tc_args = rep_tc_args + , ds_theta = mtheta `orElse` all_preds + , ds_newtype = True } + ; return (if isJust mtheta then Right spec + else Left spec) } -cond_glaExts :: Condition -cond_glaExts (gla_exts, tycon) | gla_exts = Nothing - | otherwise = Just why + | otherwise + = case checkSideConditions dflags mtheta cls cls_tys rep_tycon of + CanDerive -> go_for_it -- Use the standard H98 method + DerivableClassError msg -- Error with standard class + | can_derive_via_isomorphism -> bale_out (msg $$ suggest_nd) + | otherwise -> bale_out msg + NonDerivableClass -- Must use newtype deriving + | newtype_deriving -> bale_out cant_derive_err -- Too hard, even with newtype deriving + | can_derive_via_isomorphism -> bale_out (non_std $$ suggest_nd) -- Try newtype deriving! + | otherwise -> bale_out non_std where - why = ptext SLIT("You need -fglasgow-exts to derive an instance for this class") + newtype_deriving = xopt Opt_GeneralizedNewtypeDeriving dflags + go_for_it = mk_data_eqn orig tvs cls tycon tc_args rep_tycon rep_tc_args mtheta + bale_out msg = failWithTc (derivingThingErr newtype_deriving cls cls_tys inst_ty msg) + + non_std = nonStdErr cls + suggest_nd = 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 representation 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 inst_tys + 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 + + can_derive_via_isomorphism + = not (non_iso_class cls) + && arity_ok + && eta_ok + && ats_ok +-- && not (isRecursiveTyCon tycon) -- Note [Recursive newtypes] + + arity_ok = length cls_tys + 1 == classArity cls + -- Well kinded; eg not: newtype T ... deriving( ST ) + -- because ST needs *2* type params + + -- Check that eta reduction is OK + eta_ok = nt_eta_arity <= length rep_tc_args + -- 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. + + ats_ok = null (classATs cls) + -- No associated types for the class, because we don't + -- currently generate type 'instance' decls; and cannot do + -- so for 'data' instance decls + + cant_derive_err + = vcat [ ppUnless arity_ok arity_msg + , ppUnless eta_ok eta_msg + , ppUnless ats_ok ats_msg ] + arity_msg = quotes (ppr (mkClassPred cls cls_tys)) <+> ptext (sLit "does not have arity 1") + eta_msg = ptext (sLit "cannot eta-reduce the representation type enough") + ats_msg = ptext (sLit "the class has associated types") \end{code} +Note [Recursive newtypes] +~~~~~~~~~~~~~~~~~~~~~~~~~ +Newtype deriving works fine, even if the newtype is recursive. +e.g. newtype S1 = S1 [T1 ()] + newtype T1 a = T1 (StateT S1 IO a ) deriving( Monad ) +Remember, too, that type families are curretly (conservatively) given +a recursive flag, so this also allows newtype deriving to work +for type famillies. + +We used to exclude recursive types, because we had a rather simple +minded way of generating the instance decl: + newtype A = MkA [A] + instance Eq [A] => Eq A -- Makes typechecker loop! +But now we require a simple context, so it's ok. + + %************************************************************************ %* * \subsection[TcDeriv-fixpoint]{Finding the fixed point of \tr{deriving} equations} @@ -695,66 +1225,88 @@ 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] + +inferInstanceContexts _ [] = return [] -solveDerivEqns overlap_flag orig_eqns - = iterateDeriv 1 initial_solutions +inferInstanceContexts oflag infer_specs + = do { traceTc "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" (mkInstance 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 { -- 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. Moreover, simplifyDeriv + -- has an assert failure because it finds a TyVar when it expects + -- only TcTyVars. So I just rule it out for now. I'm not + -- even sure how it can arise. + + ; let tv_set = mkVarSet tyvars + weird_preds = [pred | pred <- deriv_rhs + , not (tyVarsOfPred pred `subVarSet` tv_set)] + ; mapM_ (addErrTc . badDerivedPred) weird_preds + + ; theta <- simplifyDeriv orig tyvars deriv_rhs + -- checkValidInstance tyvars theta clas inst_tys + -- Not necessary; see Note [Exotic derived instance contexts] + -- in TcSimplify + + ; traceTc "TcDeriv" (ppr deriv_rhs $$ ppr theta) + -- 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 + +------------------------------------------------------------------ +mkInstance :: OverlapFlag -> ThetaType -> DerivSpec -> Instance +mkInstance 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 +1318,7 @@ extendLocalInstEnv dfuns thing_inside ; setGblEnv env' thing_inside } \end{code} + %************************************************************************ %* * \subsection[TcDeriv-normal-binds]{Bindings for the various classes} @@ -829,56 +1382,77 @@ 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 - - -- Build the InstInfo - ; return (InstInfo { iSpec = spec, - iBinds = VanillaInst rn_meth_binds [] }, - aux_binds) - } - -genDerivBinds clas fix_env tycon +-- +-- Representation tycons differ from the tycon in the instance signature in +-- case of instances for indexed families. +-- +genInst :: Bool -- True <=> standalone deriving + -> OverlapFlag + -> DerivSpec -> TcM (InstInfo RdrName, DerivAuxBinds) +genInst standalone_deriv oflag spec + | ds_newtype spec + = return (InstInfo { iSpec = mkInstance oflag (ds_theta spec) spec + , iBinds = NewTypeDerived co rep_tycon }, []) + + | otherwise + = do { let loc = getSrcSpan (ds_name spec) + inst = mkInstance oflag (ds_theta spec) spec + clas = ds_cls 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 + binds = VanillaInst meth_binds [] standalone_deriv + ; return (InstInfo { iSpec = inst, iBinds = binds }, aux_binds) + } + where + rep_tycon = ds_tc spec + rep_tc_args = ds_tc_args spec + co1 = case tyConFamilyCoercion_maybe rep_tycon of + Just co_con -> ACo (mkTyConApp co_con rep_tc_args) + Nothing -> id_co + -- Not a family => rep_tycon = main tycon + co2 = case newTyConCo_maybe rep_tycon of + Just co_con -> ACo (mkTyConApp co_con rep_tc_args) + Nothing -> id_co -- The newtype is transparent; no need for a cast + co = co1 `mkTransCoI` co2 + id_co = IdCo (mkTyConApp rep_tycon rep_tc_args) + +-- Example: newtype instance N [a] = N1 (Tree a) +-- deriving instance Eq b => Eq (N [(b,b)]) +-- From the instance, we get an implicit newtype R1:N a = N1 (Tree a) +-- When dealing with the deriving clause +-- co1 : N [(b,b)] ~ R1:N (b,b) +-- co2 : R1:N (b,b) ~ Tree (b,b) +-- co : N [(b,b)] ~ Tree (b,b) + +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) + ,(functorClassKey, gen_Functor_binds) + ,(foldableClassKey, gen_Foldable_binds) + ,(traversableClassKey, gen_Traversable_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 +1462,52 @@ 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)) } +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)) + +derivingEtaErr :: Class -> [Type] -> Type -> Message +derivingEtaErr cls cls_tys inst_ty + = sep [ptext (sLit "Cannot eta-reduce to an instance of form"), + nest 2 (ptext (sLit "instance (...) =>") + <+> pprClassPred cls (cls_tys ++ [inst_ty]))] + +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 :: Bool -> Class -> [Type] -> Type -> Message -> Message +derivingThingErr newtype_deriving clas tys ty why + = sep [(hang (ptext (sLit "Can't make a derived instance of")) + 2 (quotes (ppr pred)) + $$ nest 2 extra) <> colon, + nest 2 why] 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 + extra | newtype_deriving = ptext (sLit "(even with cunning newtype deriving)") + | otherwise = empty + 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} - -\begin{code} -derivingThingErr clas tys tycon tyvars 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])] -\end{code} -