{- (c) The University of Glasgow 2011 The deriving code for the Generic class (equivalent to the code in TcGenDeriv, for other classes) -} {-# LANGUAGE CPP, ScopedTypeVariables, TupleSections #-} {-# LANGUAGE FlexibleContexts #-} module TcGenGenerics (canDoGenerics, canDoGenerics1, GenericKind(..), gen_Generic_binds, get_gen1_constrained_tys) where import HsSyn import Type import TcType import TcGenDeriv import DataCon import TyCon import FamInstEnv ( FamInst, FamFlavor(..), mkSingleCoAxiom ) import FamInst import Module ( Module, moduleName, moduleNameFS , moduleUnitId, unitIdFS ) import IfaceEnv ( newGlobalBinder ) import Name hiding ( varName ) import RdrName import BasicTypes import TysPrim import TysWiredIn import PrelNames import TcEnv import TcRnMonad import HscTypes import ErrUtils( Validity(..), andValid ) import SrcLoc import Bag import VarEnv import VarSet (elemVarSet) import Outputable import FastString import Util import Control.Monad (mplus) import Data.List (zip4, partition) import Data.Maybe (isJust) #include "HsVersions.h" {- ************************************************************************ * * \subsection{Bindings for the new generic deriving mechanism} * * ************************************************************************ For the generic representation we need to generate: \begin{itemize} \item A Generic instance \item A Rep type instance \item Many auxiliary datatypes and instances for them (for the meta-information) \end{itemize} -} gen_Generic_binds :: GenericKind -> TyCon -> Type -> Module -> TcM (LHsBinds RdrName, FamInst) gen_Generic_binds gk tc inst_ty mod = do repTyInsts <- tc_mkRepFamInsts gk tc inst_ty mod return (mkBindsRep gk tc, repTyInsts) {- ************************************************************************ * * \subsection{Generating representation types} * * ************************************************************************ -} get_gen1_constrained_tys :: TyVar -> Type -> [Type] -- called by TcDeriv.inferConstraints; generates a list of types, each of which -- must be a Functor in order for the Generic1 instance to work. get_gen1_constrained_tys argVar = argTyFold argVar $ ArgTyAlg { ata_rec0 = const [] , ata_par1 = [], ata_rec1 = const [] , ata_comp = (:) } {- Note [Requirements for deriving Generic and Rep] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ In the following, T, Tfun, and Targ are "meta-variables" ranging over type expressions. (Generic T) and (Rep T) are derivable for some type expression T if the following constraints are satisfied. (a) D is a type constructor *value*. In other words, D is either a type constructor or it is equivalent to the head of a data family instance (up to alpha-renaming). (b) D cannot have a "stupid context". (c) The right-hand side of D cannot include existential types, universally quantified types, or "exotic" unlifted types. An exotic unlifted type is one which is not listed in the definition of allowedUnliftedTy (i.e., one for which we have no representation type). See Note [Generics and unlifted types] (d) T :: *. (Generic1 T) and (Rep1 T) are derivable for some type expression T if the following constraints are satisfied. (a),(b),(c) As above. (d) T must expect arguments, and its last parameter must have kind *. We use `a' to denote the parameter of D that corresponds to the last parameter of T. (e) For any type-level application (Tfun Targ) in the right-hand side of D where the head of Tfun is not a tuple constructor: (b1) `a' must not occur in Tfun. (b2) If `a' occurs in Targ, then Tfun :: * -> *. -} canDoGenerics :: TyCon -> Validity -- canDoGenerics determines if Generic/Rep can be derived. -- -- Check (a) from Note [Requirements for deriving Generic and Rep] is taken -- care of because canDoGenerics is applied to rep tycons. -- -- It returns Nothing if deriving is possible. It returns (Just reason) if not. canDoGenerics tc = mergeErrors ( -- Check (b) from Note [Requirements for deriving Generic and Rep]. (if (not (null (tyConStupidTheta tc))) then (NotValid (tc_name <+> text "must not have a datatype context")) else IsValid) -- See comment below : (map bad_con (tyConDataCons tc))) where -- The tc can be a representation tycon. When we want to display it to the -- user (in an error message) we should print its parent tc_name = ppr $ case tyConFamInst_maybe tc of Just (ptc, _) -> ptc _ -> tc -- Check (c) from Note [Requirements for deriving Generic and Rep]. -- -- If any of the constructors has an exotic unlifted type as argument, -- then we can't build the embedding-projection pair, because -- it relies on instantiating *polymorphic* sum and product types -- at the argument types of the constructors bad_con dc = if (any bad_arg_type (dataConOrigArgTys dc)) then (NotValid (ppr dc <+> text "must not have exotic unlifted or polymorphic arguments")) else (if (not (isVanillaDataCon dc)) then (NotValid (ppr dc <+> text "must be a vanilla data constructor")) else IsValid) -- Nor can we do the job if it's an existential data constructor, -- Nor if the args are polymorphic types (I don't think) bad_arg_type ty = (isUnliftedType ty && not (allowedUnliftedTy ty)) || not (isTauTy ty) -- Returns True the Type argument is an unlifted type which has a -- corresponding generic representation type. For example, -- (allowedUnliftedTy Int#) would return True since there is the UInt -- representation type. allowedUnliftedTy :: Type -> Bool allowedUnliftedTy = isJust . unboxedRepRDRs mergeErrors :: [Validity] -> Validity mergeErrors [] = IsValid mergeErrors (NotValid s:t) = case mergeErrors t of IsValid -> NotValid s NotValid s' -> NotValid (s <> text ", and" $$ s') mergeErrors (IsValid : t) = mergeErrors t -- A datatype used only inside of canDoGenerics1. It's the result of analysing -- a type term. data Check_for_CanDoGenerics1 = CCDG1 { _ccdg1_hasParam :: Bool -- does the parameter of interest occurs in -- this type? , _ccdg1_errors :: Validity -- errors generated by this type } {- Note [degenerate use of FFoldType] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ We use foldDataConArgs here only for its ability to treat tuples specially. foldDataConArgs also tracks covariance (though it assumes all higher-order type parameters are covariant) and has hooks for special handling of functions and polytypes, but we do *not* use those. The key issue is that Generic1 deriving currently offers no sophisticated support for functions. For example, we cannot handle data F a = F ((a -> Int) -> Int) even though a is occurring covariantly. In fact, our rule is harsh: a is simply not allowed to occur within the first argument of (->). We treat (->) the same as any other non-tuple tycon. Unfortunately, this means we have to track "the parameter occurs in this type" explicitly, even though foldDataConArgs is also doing this internally. -} -- canDoGenerics1 determines if a Generic1/Rep1 can be derived. -- -- Checks (a) through (c) from Note [Requirements for deriving Generic and Rep] -- are taken care of by the call to canDoGenerics. -- -- It returns Nothing if deriving is possible. It returns (Just reason) if not. canDoGenerics1 :: TyCon -> Validity canDoGenerics1 rep_tc = canDoGenerics rep_tc `andValid` additionalChecks where additionalChecks -- check (d) from Note [Requirements for deriving Generic and Rep] | null (tyConTyVars rep_tc) = NotValid $ text "Data type" <+> quotes (ppr rep_tc) <+> text "must have some type parameters" | otherwise = mergeErrors $ concatMap check_con data_cons data_cons = tyConDataCons rep_tc check_con con = case check_vanilla con of j@(NotValid {}) -> [j] IsValid -> _ccdg1_errors `map` foldDataConArgs (ft_check con) con bad :: DataCon -> SDoc -> SDoc bad con msg = text "Constructor" <+> quotes (ppr con) <+> msg check_vanilla :: DataCon -> Validity check_vanilla con | isVanillaDataCon con = IsValid | otherwise = NotValid (bad con existential) bmzero = CCDG1 False IsValid bmbad con s = CCDG1 True $ NotValid $ bad con s bmplus (CCDG1 b1 m1) (CCDG1 b2 m2) = CCDG1 (b1 || b2) (m1 `andValid` m2) -- check (e) from Note [Requirements for deriving Generic and Rep] -- See also Note [degenerate use of FFoldType] ft_check :: DataCon -> FFoldType Check_for_CanDoGenerics1 ft_check con = FT { ft_triv = bmzero , ft_var = caseVar, ft_co_var = caseVar -- (component_0,component_1,...,component_n) , ft_tup = \_ components -> if any _ccdg1_hasParam (init components) then bmbad con wrong_arg else foldr bmplus bmzero components -- (dom -> rng), where the head of ty is not a tuple tycon , ft_fun = \dom rng -> -- cf #8516 if _ccdg1_hasParam dom then bmbad con wrong_arg else bmplus dom rng -- (ty arg), where head of ty is neither (->) nor a tuple constructor and -- the parameter of interest does not occur in ty , ft_ty_app = \_ arg -> arg , ft_bad_app = bmbad con wrong_arg , ft_forall = \_ body -> body -- polytypes are handled elsewhere } where caseVar = CCDG1 True IsValid existential = text "must not have existential arguments" wrong_arg = text "applies a type to an argument involving the last parameter" $$ text "but the applied type is not of kind * -> *" {- ************************************************************************ * * \subsection{Generating the RHS of a generic default method} * * ************************************************************************ -} type US = Int -- Local unique supply, just a plain Int type Alt = (LPat RdrName, LHsExpr RdrName) -- GenericKind serves to mark if a datatype derives Generic (Gen0) or -- Generic1 (Gen1). data GenericKind = Gen0 | Gen1 -- as above, but with a payload of the TyCon's name for "the" parameter data GenericKind_ = Gen0_ | Gen1_ TyVar -- as above, but using a single datacon's name for "the" parameter data GenericKind_DC = Gen0_DC | Gen1_DC TyVar forgetArgVar :: GenericKind_DC -> GenericKind forgetArgVar Gen0_DC = Gen0 forgetArgVar Gen1_DC{} = Gen1 -- When working only within a single datacon, "the" parameter's name should -- match that datacon's name for it. gk2gkDC :: GenericKind_ -> DataCon -> GenericKind_DC gk2gkDC Gen0_ _ = Gen0_DC gk2gkDC Gen1_{} d = Gen1_DC $ last $ dataConUnivTyVars d -- Bindings for the Generic instance mkBindsRep :: GenericKind -> TyCon -> LHsBinds RdrName mkBindsRep gk tycon = unitBag (mkRdrFunBind (L loc from01_RDR) [from_eqn]) `unionBags` unitBag (mkRdrFunBind (L loc to01_RDR) [to_eqn]) where -- The topmost M1 (the datatype metadata) has the exact same type -- across all cases of a from/to definition, and can be factored out -- to save some allocations during typechecking. -- See Note [Generics compilation speed tricks] from_eqn = mkSimpleHsAlt x_Pat $ mkM1_E $ nlHsCase x_Expr from_matches to_eqn = mkSimpleHsAlt (mkM1_P x_Pat) $ nlHsCase x_Expr to_matches from_matches = [mkSimpleHsAlt pat rhs | (pat,rhs) <- from_alts] to_matches = [mkSimpleHsAlt pat rhs | (pat,rhs) <- to_alts ] loc = srcLocSpan (getSrcLoc tycon) datacons = tyConDataCons tycon (from01_RDR, to01_RDR) = case gk of Gen0 -> (from_RDR, to_RDR) Gen1 -> (from1_RDR, to1_RDR) -- Recurse over the sum first from_alts, to_alts :: [Alt] (from_alts, to_alts) = mkSum gk_ (1 :: US) tycon datacons where gk_ = case gk of Gen0 -> Gen0_ Gen1 -> ASSERT(length tyvars >= 1) Gen1_ (last tyvars) where tyvars = tyConTyVars tycon -------------------------------------------------------------------------------- -- The type synonym instance and synonym -- type instance Rep (D a b) = Rep_D a b -- type Rep_D a b = ...representation type for D ... -------------------------------------------------------------------------------- tc_mkRepFamInsts :: GenericKind -- Gen0 or Gen1 -> TyCon -- The type to generate representation for -> Type -- The above TyCon applied to its type -- arguments in the generated instance -> Module -- Used as the location of the new RepTy -> TcM (FamInst) -- Generated representation0 coercion tc_mkRepFamInsts gk tycon inst_ty mod = -- Consider the example input tycon `D`, where data D a b = D_ a -- Also consider `R:DInt`, where { data family D x y :: * -> * -- ; data instance D Int a b = D_ a } do { -- `rep` = GHC.Generics.Rep or GHC.Generics.Rep1 (type family) fam_tc <- case gk of Gen0 -> tcLookupTyCon repTyConName Gen1 -> tcLookupTyCon rep1TyConName ; fam_envs <- tcGetFamInstEnvs ; let mbFamInst = tyConFamInst_maybe tycon -- If we're examining a data family instance, we grab the parent -- TyCon (ptc) and use it to determine the type arguments -- (inst_args) for the data family *instance*'s type variables. ptc = maybe tycon fst mbFamInst (_, inst_args, _) = tcLookupDataFamInst fam_envs ptc $ snd $ tcSplitTyConApp inst_ty ; let -- `tyvars` = [a,b] (tyvars, gk_) = case gk of Gen0 -> (all_tyvars, Gen0_) Gen1 -> ASSERT(not $ null all_tyvars) (init all_tyvars, Gen1_ $ last all_tyvars) where all_tyvars = tyConTyVars tycon -- `repTy` = D1 ... (C1 ... (S1 ... (Rec0 a))) :: * -> * ; repTy <- tc_mkRepTy gk_ tycon -- `rep_name` is a name we generate for the synonym ; rep_name <- let mkGen = case gk of Gen0 -> mkGenR; Gen1 -> mkGen1R in newGlobalBinder mod (mkGen (nameOccName (tyConName tycon))) (nameSrcSpan (tyConName tycon)) -- We make sure to substitute the tyvars with their user-supplied -- type arguments before generating the Rep/Rep1 instance, since some -- of the tyvars might have been instantiated when deriving. -- See Note [Generating a correctly typed Rep instance]. ; let env = zipTyEnv tyvars inst_args in_scope = mkInScopeSet (tyCoVarsOfType inst_ty) subst = mkTvSubst in_scope env repTy' = substTy subst repTy tcv' = tyCoVarsOfTypeList inst_ty (tv', cv') = partition isTyVar tcv' tvs' = toposortTyVars tv' cvs' = toposortTyVars cv' axiom = mkSingleCoAxiom Nominal rep_name tvs' cvs' fam_tc [inst_ty] repTy' ; newFamInst SynFamilyInst axiom } -------------------------------------------------------------------------------- -- Type representation -------------------------------------------------------------------------------- -- | See documentation of 'argTyFold'; that function uses the fields of this -- type to interpret the structure of a type when that type is considered as an -- argument to a constructor that is being represented with 'Rep1'. data ArgTyAlg a = ArgTyAlg { ata_rec0 :: (Type -> a) , ata_par1 :: a, ata_rec1 :: (Type -> a) , ata_comp :: (Type -> a -> a) } -- | @argTyFold@ implements a generalised and safer variant of the @arg@ -- function from Figure 3 in <http://dreixel.net/research/pdf/gdmh.pdf>. @arg@ -- is conceptually equivalent to: -- -- > arg t = case t of -- > _ | isTyVar t -> if (t == argVar) then Par1 else Par0 t -- > App f [t'] | -- > representable1 f && -- > t' == argVar -> Rec1 f -- > App f [t'] | -- > representable1 f && -- > t' has tyvars -> f :.: (arg t') -- > _ -> Rec0 t -- -- where @argVar@ is the last type variable in the data type declaration we are -- finding the representation for. -- -- @argTyFold@ is more general than @arg@ because it uses 'ArgTyAlg' to -- abstract out the concrete invocations of @Par0@, @Rec0@, @Par1@, @Rec1@, and -- @:.:@. -- -- @argTyFold@ is safer than @arg@ because @arg@ would lead to a GHC panic for -- some data types. The problematic case is when @t@ is an application of a -- non-representable type @f@ to @argVar@: @App f [argVar]@ is caught by the -- @_@ pattern, and ends up represented as @Rec0 t@. This type occurs /free/ in -- the RHS of the eventual @Rep1@ instance, which is therefore ill-formed. Some -- representable1 checks have been relaxed, and others were moved to -- @canDoGenerics1@. argTyFold :: forall a. TyVar -> ArgTyAlg a -> Type -> a argTyFold argVar (ArgTyAlg {ata_rec0 = mkRec0, ata_par1 = mkPar1, ata_rec1 = mkRec1, ata_comp = mkComp}) = -- mkRec0 is the default; use it if there is no interesting structure -- (e.g. occurrences of parameters or recursive occurrences) \t -> maybe (mkRec0 t) id $ go t where go :: Type -> -- type to fold through Maybe a -- the result (e.g. representation type), unless it's trivial go t = isParam `mplus` isApp where isParam = do -- handles parameters t' <- getTyVar_maybe t Just $ if t' == argVar then mkPar1 -- moreover, it is "the" parameter else mkRec0 t -- NB mkRec0 instead of the conventional mkPar0 isApp = do -- handles applications (phi, beta) <- tcSplitAppTy_maybe t let interesting = argVar `elemVarSet` exactTyCoVarsOfType beta -- Does it have no interesting structure to represent? if not interesting then Nothing else -- Is the argument the parameter? Special case for mkRec1. if Just argVar == getTyVar_maybe beta then Just $ mkRec1 phi else mkComp phi `fmap` go beta -- It must be a composition. tc_mkRepTy :: -- Gen0_ or Gen1_, for Rep or Rep1 GenericKind_ -- The type to generate representation for -> TyCon -- Generated representation0 type -> TcM Type tc_mkRepTy gk_ tycon = do d1 <- tcLookupTyCon d1TyConName c1 <- tcLookupTyCon c1TyConName s1 <- tcLookupTyCon s1TyConName rec0 <- tcLookupTyCon rec0TyConName rec1 <- tcLookupTyCon rec1TyConName par1 <- tcLookupTyCon par1TyConName u1 <- tcLookupTyCon u1TyConName v1 <- tcLookupTyCon v1TyConName plus <- tcLookupTyCon sumTyConName times <- tcLookupTyCon prodTyConName comp <- tcLookupTyCon compTyConName uAddr <- tcLookupTyCon uAddrTyConName uChar <- tcLookupTyCon uCharTyConName uDouble <- tcLookupTyCon uDoubleTyConName uFloat <- tcLookupTyCon uFloatTyConName uInt <- tcLookupTyCon uIntTyConName uWord <- tcLookupTyCon uWordTyConName let tcLookupPromDataCon = fmap promoteDataCon . tcLookupDataCon md <- tcLookupPromDataCon metaDataDataConName mc <- tcLookupPromDataCon metaConsDataConName ms <- tcLookupPromDataCon metaSelDataConName pPrefix <- tcLookupPromDataCon prefixIDataConName pInfix <- tcLookupPromDataCon infixIDataConName pLA <- tcLookupPromDataCon leftAssociativeDataConName pRA <- tcLookupPromDataCon rightAssociativeDataConName pNA <- tcLookupPromDataCon notAssociativeDataConName pSUpk <- tcLookupPromDataCon sourceUnpackDataConName pSNUpk <- tcLookupPromDataCon sourceNoUnpackDataConName pNSUpkness <- tcLookupPromDataCon noSourceUnpackednessDataConName pSLzy <- tcLookupPromDataCon sourceLazyDataConName pSStr <- tcLookupPromDataCon sourceStrictDataConName pNSStrness <- tcLookupPromDataCon noSourceStrictnessDataConName pDLzy <- tcLookupPromDataCon decidedLazyDataConName pDStr <- tcLookupPromDataCon decidedStrictDataConName pDUpk <- tcLookupPromDataCon decidedUnpackDataConName fix_env <- getFixityEnv let mkSum' a b = mkTyConApp plus [a,b] mkProd a b = mkTyConApp times [a,b] mkComp a b = mkTyConApp comp [a,b] mkRec0 a = mkBoxTy uAddr uChar uDouble uFloat uInt uWord rec0 a mkRec1 a = mkTyConApp rec1 [a] mkPar1 = mkTyConTy par1 mkD a = mkTyConApp d1 [ metaDataTy, sumP (tyConDataCons a) ] mkC a = mkTyConApp c1 [ metaConsTy a , prod (dataConInstOrigArgTys a . mkTyVarTys . tyConTyVars $ tycon) (dataConSrcBangs a) (dataConImplBangs a) (dataConFieldLabels a)] mkS mlbl su ss ib a = mkTyConApp s1 [metaSelTy mlbl su ss ib, a] -- Sums and products are done in the same way for both Rep and Rep1 sumP [] = mkTyConTy v1 sumP l = foldBal mkSum' . map mkC $ l -- The Bool is True if this constructor has labelled fields prod :: [Type] -> [HsSrcBang] -> [HsImplBang] -> [FieldLabel] -> Type prod [] _ _ _ = mkTyConTy u1 prod l sb ib fl = foldBal mkProd [ ASSERT(null fl || length fl > j) arg t sb' ib' (if null fl then Nothing else Just (fl !! j)) | (t,sb',ib',j) <- zip4 l sb ib [0..] ] arg :: Type -> HsSrcBang -> HsImplBang -> Maybe FieldLabel -> Type arg t (HsSrcBang _ su ss) ib fl = mkS fl su ss ib $ case gk_ of -- Here we previously used Par0 if t was a type variable, but we -- realized that we can't always guarantee that we are wrapping-up -- all type variables in Par0. So we decided to stop using Par0 -- altogether, and use Rec0 all the time. Gen0_ -> mkRec0 t Gen1_ argVar -> argPar argVar t where -- Builds argument representation for Rep1 (more complicated due to -- the presence of composition). argPar argVar = argTyFold argVar $ ArgTyAlg {ata_rec0 = mkRec0, ata_par1 = mkPar1, ata_rec1 = mkRec1, ata_comp = mkComp} tyConName_user = case tyConFamInst_maybe tycon of Just (ptycon, _) -> tyConName ptycon Nothing -> tyConName tycon dtName = mkStrLitTy . occNameFS . nameOccName $ tyConName_user mdName = mkStrLitTy . moduleNameFS . moduleName . nameModule . tyConName $ tycon pkgName = mkStrLitTy . unitIdFS . moduleUnitId . nameModule . tyConName $ tycon isNT = mkTyConTy $ if isNewTyCon tycon then promotedTrueDataCon else promotedFalseDataCon ctName = mkStrLitTy . occNameFS . nameOccName . dataConName ctFix c | dataConIsInfix c = case lookupFixity fix_env (dataConName c) of Fixity _ n InfixL -> buildFix n pLA Fixity _ n InfixR -> buildFix n pRA Fixity _ n InfixN -> buildFix n pNA | otherwise = mkTyConTy pPrefix buildFix n assoc = mkTyConApp pInfix [ mkTyConTy assoc , mkNumLitTy (fromIntegral n)] isRec c = mkTyConTy $ if length (dataConFieldLabels c) > 0 then promotedTrueDataCon else promotedFalseDataCon selName = mkStrLitTy . flLabel mbSel Nothing = mkTyConApp promotedNothingDataCon [typeSymbolKind] mbSel (Just s) = mkTyConApp promotedJustDataCon [typeSymbolKind, selName s] metaDataTy = mkTyConApp md [dtName, mdName, pkgName, isNT] metaConsTy c = mkTyConApp mc [ctName c, ctFix c, isRec c] metaSelTy mlbl su ss ib = mkTyConApp ms [mbSel mlbl, pSUpkness, pSStrness, pDStrness] where pSUpkness = mkTyConTy $ case su of SrcUnpack -> pSUpk SrcNoUnpack -> pSNUpk NoSrcUnpack -> pNSUpkness pSStrness = mkTyConTy $ case ss of SrcLazy -> pSLzy SrcStrict -> pSStr NoSrcStrict -> pNSStrness pDStrness = mkTyConTy $ case ib of HsLazy -> pDLzy HsStrict -> pDStr HsUnpack{} -> pDUpk return (mkD tycon) -- Given the TyCons for each URec-related type synonym, check to see if the -- given type is an unlifted type that generics understands. If so, return -- its representation type. Otherwise, return Rec0. -- See Note [Generics and unlifted types] mkBoxTy :: TyCon -- UAddr -> TyCon -- UChar -> TyCon -- UDouble -> TyCon -- UFloat -> TyCon -- UInt -> TyCon -- UWord -> TyCon -- Rec0 -> Type -> Type mkBoxTy uAddr uChar uDouble uFloat uInt uWord rec0 ty | ty `eqType` addrPrimTy = mkTyConTy uAddr | ty `eqType` charPrimTy = mkTyConTy uChar | ty `eqType` doublePrimTy = mkTyConTy uDouble | ty `eqType` floatPrimTy = mkTyConTy uFloat | ty `eqType` intPrimTy = mkTyConTy uInt | ty `eqType` wordPrimTy = mkTyConTy uWord | otherwise = mkTyConApp rec0 [ty] -------------------------------------------------------------------------------- -- Dealing with sums -------------------------------------------------------------------------------- mkSum :: GenericKind_ -- Generic or Generic1? -> US -- Base for generating unique names -> TyCon -- The type constructor -> [DataCon] -- The data constructors -> ([Alt], -- Alternatives for the T->Trep "from" function [Alt]) -- Alternatives for the Trep->T "to" function -- Datatype without any constructors mkSum _ _ tycon [] = ([from_alt], [to_alt]) where from_alt = (nlWildPat, makeError errMsgFrom) to_alt = (nlWildPat, makeError errMsgTo) -- These M1s are meta-information for the datatype makeError s = nlHsApp (nlHsVar error_RDR) (nlHsLit (mkHsString s)) tyConStr = occNameString (nameOccName (tyConName tycon)) errMsgFrom = "No generic representation for empty datatype " ++ tyConStr errMsgTo = "No values for empty datatype " ++ tyConStr -- Datatype with at least one constructor mkSum gk_ us _ datacons = -- switch the payload of gk_ to be datacon-centric instead of tycon-centric unzip [ mk1Sum (gk2gkDC gk_ d) us i (length datacons) d | (d,i) <- zip datacons [1..] ] -- Build the sum for a particular constructor mk1Sum :: GenericKind_DC -- Generic or Generic1? -> US -- Base for generating unique names -> Int -- The index of this constructor -> Int -- Total number of constructors -> DataCon -- The data constructor -> (Alt, -- Alternative for the T->Trep "from" function Alt) -- Alternative for the Trep->T "to" function mk1Sum gk_ us i n datacon = (from_alt, to_alt) where gk = forgetArgVar gk_ -- Existentials already excluded argTys = dataConOrigArgTys datacon n_args = dataConSourceArity datacon datacon_varTys = zip (map mkGenericLocal [us .. us+n_args-1]) argTys datacon_vars = map fst datacon_varTys us' = us + n_args datacon_rdr = getRdrName datacon from_alt = (nlConVarPat datacon_rdr datacon_vars, from_alt_rhs) from_alt_rhs = genLR_E i n (mkProd_E gk_ us' datacon_varTys) to_alt = ( genLR_P i n (mkProd_P gk us' datacon_varTys) , to_alt_rhs ) -- These M1s are meta-information for the datatype to_alt_rhs = case gk_ of Gen0_DC -> nlHsVarApps datacon_rdr datacon_vars Gen1_DC argVar -> nlHsApps datacon_rdr $ map argTo datacon_varTys where argTo (var, ty) = converter ty `nlHsApp` nlHsVar var where converter = argTyFold argVar $ ArgTyAlg {ata_rec0 = nlHsVar . unboxRepRDR, ata_par1 = nlHsVar unPar1_RDR, ata_rec1 = const $ nlHsVar unRec1_RDR, ata_comp = \_ cnv -> (nlHsVar fmap_RDR `nlHsApp` cnv) `nlHsCompose` nlHsVar unComp1_RDR} -- Generates the L1/R1 sum pattern genLR_P :: Int -> Int -> LPat RdrName -> LPat RdrName genLR_P i n p | n == 0 = error "impossible" | n == 1 = p | i <= div n 2 = nlConPat l1DataCon_RDR [genLR_P i (div n 2) p] | otherwise = nlConPat r1DataCon_RDR [genLR_P (i-m) (n-m) p] where m = div n 2 -- Generates the L1/R1 sum expression genLR_E :: Int -> Int -> LHsExpr RdrName -> LHsExpr RdrName genLR_E i n e | n == 0 = error "impossible" | n == 1 = e | i <= div n 2 = nlHsVar l1DataCon_RDR `nlHsApp` genLR_E i (div n 2) e | otherwise = nlHsVar r1DataCon_RDR `nlHsApp` genLR_E (i-m) (n-m) e where m = div n 2 -------------------------------------------------------------------------------- -- Dealing with products -------------------------------------------------------------------------------- -- Build a product expression mkProd_E :: GenericKind_DC -- Generic or Generic1? -> US -- Base for unique names -> [(RdrName, Type)] -- List of variables matched on the lhs and their types -> LHsExpr RdrName -- Resulting product expression mkProd_E _ _ [] = mkM1_E (nlHsVar u1DataCon_RDR) mkProd_E gk_ _ varTys = mkM1_E (foldBal prod appVars) -- These M1s are meta-information for the constructor where appVars = map (wrapArg_E gk_) varTys prod a b = prodDataCon_RDR `nlHsApps` [a,b] wrapArg_E :: GenericKind_DC -> (RdrName, Type) -> LHsExpr RdrName wrapArg_E Gen0_DC (var, ty) = mkM1_E $ boxRepRDR ty `nlHsVarApps` [var] -- This M1 is meta-information for the selector wrapArg_E (Gen1_DC argVar) (var, ty) = mkM1_E $ converter ty `nlHsApp` nlHsVar var -- This M1 is meta-information for the selector where converter = argTyFold argVar $ ArgTyAlg {ata_rec0 = nlHsVar . boxRepRDR, ata_par1 = nlHsVar par1DataCon_RDR, ata_rec1 = const $ nlHsVar rec1DataCon_RDR, ata_comp = \_ cnv -> nlHsVar comp1DataCon_RDR `nlHsCompose` (nlHsVar fmap_RDR `nlHsApp` cnv)} boxRepRDR :: Type -> RdrName boxRepRDR = maybe k1DataCon_RDR fst . unboxedRepRDRs unboxRepRDR :: Type -> RdrName unboxRepRDR = maybe unK1_RDR snd . unboxedRepRDRs -- Retrieve the RDRs associated with each URec data family instance -- constructor. See Note [Generics and unlifted types] unboxedRepRDRs :: Type -> Maybe (RdrName, RdrName) unboxedRepRDRs ty | ty `eqType` addrPrimTy = Just (uAddrDataCon_RDR, uAddrHash_RDR) | ty `eqType` charPrimTy = Just (uCharDataCon_RDR, uCharHash_RDR) | ty `eqType` doublePrimTy = Just (uDoubleDataCon_RDR, uDoubleHash_RDR) | ty `eqType` floatPrimTy = Just (uFloatDataCon_RDR, uFloatHash_RDR) | ty `eqType` intPrimTy = Just (uIntDataCon_RDR, uIntHash_RDR) | ty `eqType` wordPrimTy = Just (uWordDataCon_RDR, uWordHash_RDR) | otherwise = Nothing -- Build a product pattern mkProd_P :: GenericKind -- Gen0 or Gen1 -> US -- Base for unique names -> [(RdrName, Type)] -- List of variables to match, -- along with their types -> LPat RdrName -- Resulting product pattern mkProd_P _ _ [] = mkM1_P (nlNullaryConPat u1DataCon_RDR) mkProd_P gk _ varTys = mkM1_P (foldBal prod appVars) -- These M1s are meta-information for the constructor where appVars = unzipWith (wrapArg_P gk) varTys prod a b = prodDataCon_RDR `nlConPat` [a,b] wrapArg_P :: GenericKind -> RdrName -> Type -> LPat RdrName wrapArg_P Gen0 v ty = mkM1_P (boxRepRDR ty `nlConVarPat` [v]) -- This M1 is meta-information for the selector wrapArg_P Gen1 v _ = m1DataCon_RDR `nlConVarPat` [v] mkGenericLocal :: US -> RdrName mkGenericLocal u = mkVarUnqual (mkFastString ("g" ++ show u)) x_RDR :: RdrName x_RDR = mkVarUnqual (fsLit "x") x_Expr :: LHsExpr RdrName x_Expr = nlHsVar x_RDR x_Pat :: LPat RdrName x_Pat = nlVarPat x_RDR mkM1_E :: LHsExpr RdrName -> LHsExpr RdrName mkM1_E e = nlHsVar m1DataCon_RDR `nlHsApp` e mkM1_P :: LPat RdrName -> LPat RdrName mkM1_P p = m1DataCon_RDR `nlConPat` [p] nlHsCompose :: LHsExpr RdrName -> LHsExpr RdrName -> LHsExpr RdrName nlHsCompose x y = compose_RDR `nlHsApps` [x, y] -- | Variant of foldr1 for producing balanced lists foldBal :: (a -> a -> a) -> [a] -> a foldBal op = foldBal' op (error "foldBal: empty list") foldBal' :: (a -> a -> a) -> a -> [a] -> a foldBal' _ x [] = x foldBal' _ _ [y] = y foldBal' op x l = let (a,b) = splitAt (length l `div` 2) l in foldBal' op x a `op` foldBal' op x b {- Note [Generics and unlifted types] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Normally, all constants are marked with K1/Rec0. The exception to this rule is when a data constructor has an unlifted argument (e.g., Int#, Char#, etc.). In that case, we must use a data family instance of URec (from GHC.Generics) to mark it. As a result, before we can generate K1 or unK1, we must first check to see if the type is actually one of the unlifted types for which URec has a data family instance; if so, we generate that instead. See wiki:Commentary/Compiler/GenericDeriving#Handlingunliftedtypes for more details on why URec is implemented the way it is. Note [Generating a correctly typed Rep instance] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ tc_mkRepTy derives the RHS of the Rep(1) type family instance when deriving Generic(1). That is, it derives the ellipsis in the following: instance Generic Foo where type Rep Foo = ... However, tc_mkRepTy only has knowledge of the *TyCon* of the type for which a Generic(1) instance is being derived, not the fully instantiated type. As a result, tc_mkRepTy builds the most generalized Rep(1) instance possible using the type variables it learns from the TyCon (i.e., it uses tyConTyVars). This can cause problems when the instance has instantiated type variables (see Trac #11732). As an example: data T a = MkT a deriving instance Generic (T Int) ==> instance Generic (T Int) where type Rep (T Int) = (... (Rec0 a)) -- wrong! -XStandaloneDeriving is one way for the type variables to become instantiated. Another way is when Generic1 is being derived for a datatype with a visible kind binder, e.g., data P k (a :: k) = MkP k deriving Generic1 ==> instance Generic1 (P *) where type Rep1 (P *) = (... (Rec0 k)) -- wrong! See Note [Unify kinds in deriving] in TcDeriv. In any such scenario, we must prevent a discrepancy between the LHS and RHS of a Rep(1) instance. To do so, we create a type variable substitution that maps the tyConTyVars of the TyCon to their counterparts in the fully instantiated type. (For example, using T above as example, you'd map a :-> Int.) We then apply the substitution to the RHS before generating the instance. Note [Handling kinds in a Rep instance] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Because Generic1 is poly-kinded, the representation types were generalized to be kind-polymorphic as well. As a result, tc_mkRepTy must explicitly apply the kind of the instance being derived to all the representation type constructors. For instance, if you have data Empty (a :: k) = Empty deriving Generic1 Then the generated code is now approximately (with -fprint-explicit-kinds syntax): instance Generic1 k (Empty k) where type Rep1 k (Empty k) = U1 k Most representation types have only one kind variable, making them easy to deal with. The only non-trivial case is (:.:), which is only used in Generic1 instances: newtype (:.:) (f :: k2 -> *) (g :: k1 -> k2) (p :: k1) = Comp1 { unComp1 :: f (g p) } Here, we do something a bit counter-intuitive: we make k1 be the kind of the instance being derived, and we always make k2 be *. Why *? It's because the code that GHC generates using (:.:) is always of the form x :.: Rec1 y for some types x and y. In other words, the second type to which (:.:) is applied always has kind k -> *, for some kind k, so k2 cannot possibly be anything other than * in a generated Generic1 instance. Note [Generics compilation speed tricks] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Deriving Generic(1) is known to have a large constant factor during compilation, which contributes to noticeable compilation slowdowns when deriving Generic(1) for large datatypes (see Trac #5642). To ease the pain, there is a trick one can play when generating definitions for to(1) and from(1). If you have a datatype like: data Letter = A | B | C | D then a naïve Generic instance for Letter would be: instance Generic Letter where type Rep Letter = D1 ('MetaData ...) ... to (M1 (L1 (L1 (M1 U1)))) = A to (M1 (L1 (R1 (M1 U1)))) = B to (M1 (R1 (L1 (M1 U1)))) = C to (M1 (R1 (R1 (M1 U1)))) = D from A = M1 (L1 (L1 (M1 U1))) from B = M1 (L1 (R1 (M1 U1))) from C = M1 (R1 (L1 (M1 U1))) from D = M1 (R1 (R1 (M1 U1))) Notice that in every LHS pattern-match of the 'to' definition, and in every RHS expression in the 'from' definition, the topmost constructor is M1. This corresponds to the datatype-specific metadata (the D1 in the Rep Letter instance). But this is wasteful from a typechecking perspective, since this definition requires GHC to typecheck an application of M1 in every single case, leading to an O(n) increase in the number of coercions the typechecker has to solve, which in turn increases allocations and degrades compilation speed. Luckily, since the topmost M1 has the exact same type across every case, we can factor it out reduce the typechecker's burden: instance Generic Letter where type Rep Letter = D1 ('MetaData ...) ... to (M1 x) = case x of L1 (L1 (M1 U1)) -> A L1 (R1 (M1 U1)) -> B R1 (L1 (M1 U1)) -> C R1 (R1 (M1 U1)) -> D from x = M1 (case x of A -> L1 (L1 (M1 U1)) B -> L1 (R1 (M1 U1)) C -> R1 (L1 (M1 U1)) D -> R1 (R1 (M1 U1))) A simple change, but one that pays off, since it goes turns an O(n) amount of coercions to an O(1) amount. -}