{-# Language CPP, DeriveDataTypeable #-} #if MIN_VERSION_base(4,4,0) #define HAS_GENERICS {-# Language DeriveGeneric #-} #endif {-| Module : Language.Haskell.TH.Datatype Description : Backwards-compatible interface to reified information about datatypes. Copyright : Eric Mertens 2017 License : ISC Maintainer : emertens@gmail.com This module provides a flattened view of information about data types and newtypes that can be supported uniformly across multiple versions of the template-haskell package. Sample output for @'reifyDatatype' ''Maybe@ @ 'DatatypeInfo' { 'datatypeContext' = [] , 'datatypeName' = GHC.Base.Maybe , 'datatypeVars' = [ 'SigT' ('VarT' a_3530822107858468866) 'StarT' ] , 'datatypeVariant' = 'Datatype' , 'datatypeCons' = [ 'ConstructorInfo' { 'constructorName' = GHC.Base.Nothing , 'constructorVars' = [] , 'constructorContext' = [] , 'constructorFields' = [] , 'constructorStrictness' = [] , 'constructorVariant' = 'NormalConstructor' } , 'ConstructorInfo' { 'constructorName' = GHC.Base.Just , 'constructorVars' = [] , 'constructorContext' = [] , 'constructorFields' = [ 'VarT' a_3530822107858468866 ] , 'constructorStrictness' = [ 'FieldStrictness' 'UnspecifiedUnpackedness' 'Lazy' ] , 'constructorVariant' = 'NormalConstructor' } ] } @ Datatypes declared with GADT syntax are normalized to constructors with existentially quantified type variables and equality constraints. -} module Language.Haskell.TH.Datatype ( -- * Types DatatypeInfo(..) , ConstructorInfo(..) , DatatypeVariant(..) , ConstructorVariant(..) , FieldStrictness(..) , Unpackedness(..) , Strictness(..) -- * Normalization functions , reifyDatatype , reifyConstructor , reifyRecord , normalizeInfo , normalizeDec , normalizeCon -- * 'DatatypeInfo' lookup functions , lookupByConstructorName , lookupByRecordName -- * Type variable manipulation , TypeSubstitution(..) , quantifyType , freeVariablesWellScoped , freshenFreeVariables -- * 'Pred' functions , equalPred , classPred , asEqualPred , asClassPred -- * Backward compatible data definitions , dataDCompat , newtypeDCompat , tySynInstDCompat , pragLineDCompat , arrowKCompat -- * Strictness annotations , isStrictAnnot , notStrictAnnot , unpackedAnnot -- * Type simplification , resolveTypeSynonyms , resolveKindSynonyms , resolvePredSynonyms , resolveInfixT -- * Fixities , reifyFixityCompat , showFixity , showFixityDirection -- * Convenience functions , unifyTypes , tvName , tvKind , datatypeType ) where import Data.Data (Typeable, Data) import Data.Foldable (foldMap, foldl') import Data.Graph import Data.List (nub, find, union, (\\)) import Data.Map (Map) import qualified Data.Map as Map import Data.Maybe import qualified Data.Traversable as T import Control.Monad import Language.Haskell.TH #if MIN_VERSION_template_haskell(2,11,0) hiding (Extension(..)) #endif import Language.Haskell.TH.Datatype.Internal import Language.Haskell.TH.Lib (arrowK, starK) -- needed for th-2.4 #ifdef HAS_GENERICS import GHC.Generics (Generic) #endif #if !MIN_VERSION_base(4,8,0) import Control.Applicative (Applicative(..), (<$>)) import Data.Monoid (Monoid(..)) #endif -- | Normalized information about newtypes and data types. -- -- 'datatypeVars' types will have an outermost 'SigT' to indicate the -- parameter's kind. These types will be simple variables for /ADT/s -- declared with @data@ and @newtype@, but can be more complex for -- types declared with @data instance@ and @newtype instance@. data DatatypeInfo = DatatypeInfo { datatypeContext :: Cxt -- ^ Data type context (deprecated) , datatypeName :: Name -- ^ Type constructor , datatypeVars :: [Type] -- ^ Type parameters , datatypeVariant :: DatatypeVariant -- ^ Extra information , datatypeCons :: [ConstructorInfo] -- ^ Normalize constructor information } deriving (Show, Eq, Typeable, Data #ifdef HAS_GENERICS ,Generic #endif ) -- | Possible variants of data type declarations. data DatatypeVariant = Datatype -- ^ Type declared with @data@ | Newtype -- ^ Type declared with @newtype@ | DataInstance -- ^ Type declared with @data instance@ | NewtypeInstance -- ^ Type declared with @newtype instance@ deriving (Show, Read, Eq, Ord, Typeable, Data #ifdef HAS_GENERICS ,Generic #endif ) -- | Normalized information about constructors associated with newtypes and -- data types. data ConstructorInfo = ConstructorInfo { constructorName :: Name -- ^ Constructor name , constructorVars :: [TyVarBndr] -- ^ Constructor type parameters , constructorContext :: Cxt -- ^ Constructor constraints , constructorFields :: [Type] -- ^ Constructor fields , constructorStrictness :: [FieldStrictness] -- ^ Constructor fields' strictness -- (Invariant: has the same length -- as constructorFields) , constructorVariant :: ConstructorVariant -- ^ Extra information } deriving (Show, Eq, Typeable, Data #ifdef HAS_GENERICS ,Generic #endif ) -- | Possible variants of data constructors. data ConstructorVariant = NormalConstructor -- ^ Constructor without field names | InfixConstructor -- ^ Constructor without field names that is -- declared infix | RecordConstructor [Name] -- ^ Constructor with field names deriving (Show, Eq, Ord, Typeable, Data #ifdef HAS_GENERICS ,Generic #endif ) -- | Normalized information about a constructor field's @UNPACK@ and -- strictness annotations. -- -- Note that the interface for reifying strictness in Template Haskell changed -- considerably in GHC 8.0. The presentation in this library mirrors that which -- can be found in GHC 8.0 or later, whereas previously, unpackedness and -- strictness were represented with a single data type: -- -- @ -- data Strict -- = IsStrict -- | NotStrict -- | Unpacked -- On GHC 7.4 or later -- @ -- -- For backwards compatibility, we retrofit these constructors onto the -- following three values, respectively: -- -- @ -- 'isStrictAnnot' = 'FieldStrictness' 'UnspecifiedUnpackedness' 'Strict' -- 'notStrictAnnot' = 'FieldStrictness' 'UnspecifiedUnpackedness' 'UnspecifiedStrictness' -- 'unpackedAnnot' = 'FieldStrictness' 'Unpack' 'Strict' -- @ data FieldStrictness = FieldStrictness { fieldUnpackedness :: Unpackedness , fieldStrictness :: Strictness } deriving (Show, Eq, Ord, Typeable, Data #ifdef HAS_GENERICS ,Generic #endif ) -- | Information about a constructor field's unpackedness annotation. data Unpackedness = UnspecifiedUnpackedness -- ^ No annotation whatsoever | NoUnpack -- ^ Annotated with @{\-\# NOUNPACK \#-\}@ | Unpack -- ^ Annotated with @{\-\# UNPACK \#-\}@ deriving (Show, Eq, Ord, Typeable, Data #ifdef HAS_GENERICS ,Generic #endif ) -- | Information about a constructor field's strictness annotation. data Strictness = UnspecifiedStrictness -- ^ No annotation whatsoever | Lazy -- ^ Annotated with @~@ | Strict -- ^ Annotated with @!@ deriving (Show, Eq, Ord, Typeable, Data #ifdef HAS_GENERICS ,Generic #endif ) isStrictAnnot, notStrictAnnot, unpackedAnnot :: FieldStrictness isStrictAnnot = FieldStrictness UnspecifiedUnpackedness Strict notStrictAnnot = FieldStrictness UnspecifiedUnpackedness UnspecifiedStrictness unpackedAnnot = FieldStrictness Unpack Strict -- | Construct a Type using the datatype's type constructor and type -- parameters. Kind signatures are removed. datatypeType :: DatatypeInfo -> Type datatypeType di = foldl AppT (ConT (datatypeName di)) $ map stripSigT $ datatypeVars di -- | Compute a normalized view of the metadata about a data type or newtype -- given a constructor. -- -- This function will accept any constructor (value or type) for a type -- declared with newtype or data. Value constructors must be used to -- lookup datatype information about /data instances/ and /newtype instances/, -- as giving the type constructor of a data family is often not enough to -- determine a particular data family instance. -- -- In addition, this function will also accept a record selector for a -- data type with a constructor which uses that record. -- -- GADT constructors are normalized into datatypes with explicit equality -- constraints. Note that no effort is made to distinguish between equalities of -- the same (homogeneous) kind and equalities between different (heterogeneous) -- kinds. For instance, the following GADT's constructors: -- -- @ -- data T (a :: k -> *) where -- MkT1 :: T Proxy -- MkT2 :: T Maybe -- @ -- -- will be normalized to the following equality constraints: -- -- @ -- AppT (AppT EqualityT (VarT a)) (ConT Proxy) -- MkT1 -- AppT (AppT EqualityT (VarT a)) (ConT Maybe) -- MkT2 -- @ -- -- But only the first equality constraint is well kinded, since in the second -- constraint, the kinds of @(a :: k -> *)@ and @(Maybe :: * -> *)@ are different. -- Trying to categorize which constraints need homogeneous or heterogeneous -- equality is tricky, so we leave that task to users of this library. -- -- This function will apply various bug-fixes to the output of the underlying -- @template-haskell@ library in order to provide a view of datatypes in -- as uniform a way as possible. reifyDatatype :: Name {- ^ data type or constructor name -} -> Q DatatypeInfo reifyDatatype n = normalizeInfo' "reifyDatatype" isReified =<< reify n -- | Compute a normalized view of the metadata about a constructor given its -- 'Name'. This is useful for scenarios when you don't care about the info for -- the enclosing data type. reifyConstructor :: Name {- ^ constructor name -} -> Q ConstructorInfo reifyConstructor conName = do dataInfo <- reifyDatatype conName return $ lookupByConstructorName conName dataInfo -- | Compute a normalized view of the metadata about a constructor given the -- 'Name' of one of its record selectors. This is useful for scenarios when you -- don't care about the info for the enclosing data type. reifyRecord :: Name {- ^ record name -} -> Q ConstructorInfo reifyRecord recordName = do dataInfo <- reifyDatatype recordName return $ lookupByRecordName recordName dataInfo -- | Given a 'DatatypeInfo', find the 'ConstructorInfo' corresponding to the -- 'Name' of one of its constructors. lookupByConstructorName :: Name {- ^ constructor name -} -> DatatypeInfo {- ^ info for the datatype which has that constructor -} -> ConstructorInfo lookupByConstructorName conName dataInfo = case find ((== conName) . constructorName) (datatypeCons dataInfo) of Just conInfo -> conInfo Nothing -> error $ "Datatype " ++ nameBase (datatypeName dataInfo) ++ " does not have a constructor named " ++ nameBase conName -- | Given a 'DatatypeInfo', find the 'ConstructorInfo' corresponding to the -- 'Name' of one of its constructors. lookupByRecordName :: Name {- ^ record name -} -> DatatypeInfo {- ^ info for the datatype which has that constructor -} -> ConstructorInfo lookupByRecordName recordName dataInfo = case find (conHasRecord recordName) (datatypeCons dataInfo) of Just conInfo -> conInfo Nothing -> error $ "Datatype " ++ nameBase (datatypeName dataInfo) ++ " does not have any constructors with a " ++ "record selector named " ++ nameBase recordName -- | Normalize 'Info' for a newtype or datatype into a 'DatatypeInfo'. -- Fail in 'Q' otherwise. normalizeInfo :: Info -> Q DatatypeInfo normalizeInfo = normalizeInfo' "normalizeInfo" isn'tReified normalizeInfo' :: String -> IsReifiedDec -> Info -> Q DatatypeInfo normalizeInfo' entry reifiedDec i = case i of PrimTyConI{} -> bad "Primitive type not supported" ClassI{} -> bad "Class not supported" #if MIN_VERSION_template_haskell(2,11,0) FamilyI DataFamilyD{} _ -> #elif MIN_VERSION_template_haskell(2,7,0) FamilyI (FamilyD DataFam _ _ _) _ -> #else TyConI (FamilyD DataFam _ _ _) -> #endif bad "Use a value constructor to reify a data family instance" #if MIN_VERSION_template_haskell(2,7,0) FamilyI _ _ -> bad "Type families not supported" #endif TyConI dec -> normalizeDecFor reifiedDec dec #if MIN_VERSION_template_haskell(2,11,0) DataConI name _ parent -> reifyParent name parent -- NB: We do not pass the IsReifiedDec information here -- because there's no point. We have no choice but to -- call reify here, since we need to determine the -- parent data type/family. #else DataConI name _ parent _ -> reifyParent name parent #endif #if MIN_VERSION_template_haskell(2,11,0) VarI recName recTy _ -> reifyRecordType recName recTy -- NB: Similarly, we do not pass the IsReifiedDec -- information here. #else VarI recName recTy _ _ -> reifyRecordType recName recTy #endif _ -> bad "Expected a type constructor" where bad msg = fail (entry ++ ": " ++ msg) reifyParent :: Name -> Name -> Q DatatypeInfo reifyParent con = reifyParentWith "reifyParent" p where p :: DatatypeInfo -> Bool p info = con `elem` map constructorName (datatypeCons info) reifyRecordType :: Name -> Type -> Q DatatypeInfo reifyRecordType recName recTy = let (_, argTys :|- _) = uncurryType recTy in case argTys of dataTy:_ -> decomposeDataType dataTy _ -> notRecSelFailure where decomposeDataType :: Type -> Q DatatypeInfo decomposeDataType ty = do case decomposeType ty of ConT parent :| _ -> reifyParentWith "reifyRecordType" p parent _ -> notRecSelFailure notRecSelFailure :: Q a notRecSelFailure = fail $ "reifyRecordType: Not a record selector type: " ++ nameBase recName ++ " :: " ++ show recTy p :: DatatypeInfo -> Bool p info = any (conHasRecord recName) (datatypeCons info) reifyParentWith :: String {- ^ prefix for error messages -} -> (DatatypeInfo -> Bool) {- ^ predicate for finding the right data family instance -} -> Name {- ^ parent data type name -} -> Q DatatypeInfo reifyParentWith prefix p n = do info <- reify n case info of #if !(MIN_VERSION_template_haskell(2,11,0)) -- This unusual combination of Info and Dec is only possible to reify on -- GHC 7.0 and 7.2, when you try to reify a data family. Because there's -- no way to reify the data family *instances* on these versions of GHC, -- we have no choice but to fail. TyConI FamilyD{} -> dataFamiliesOnOldGHCsError #endif TyConI dec -> normalizeDecFor isReified dec #if MIN_VERSION_template_haskell(2,7,0) FamilyI dec instances -> do let instances1 = map (repairDataFam dec) instances instances2 <- mapM (normalizeDecFor isReified) instances1 case find p instances2 of Just inst -> return inst Nothing -> panic "lost the instance" #endif _ -> panic "unexpected parent" where dataFamiliesOnOldGHCsError :: Q a dataFamiliesOnOldGHCsError = fail $ prefix ++ ": Data family instances can only be reified with GHC 7.4 or later" panic :: String -> Q a panic message = fail $ "PANIC: " ++ prefix ++ " " ++ message #if MIN_VERSION_template_haskell(2,8,0) && (!MIN_VERSION_template_haskell(2,10,0)) -- A GHC 7.6-specific bug requires us to replace all occurrences of -- (ConT GHC.Prim.*) with StarT, or else Template Haskell will reject it. -- Luckily, (ConT GHC.Prim.*) only seems to occur in this one spot. sanitizeStars :: Kind -> Kind sanitizeStars = go where go :: Kind -> Kind go (AppT t1 t2) = AppT (go t1) (go t2) go (SigT t k) = SigT (go t) (go k) go (ConT n) | n == starKindName = StarT go t = t -- A version of repairVarKindsWith that does much more extra work to -- (1) eta-expand missing type patterns, and (2) ensure that the kind -- signatures for these new type patterns match accordingly. repairVarKindsWith' :: [TyVarBndr] -> [Type] -> [Type] repairVarKindsWith' dvars ts = let kindVars = freeVariables . map kindPart kindPart (KindedTV _ k) = [k] kindPart (PlainTV _ ) = [] nparams = length dvars kparams = kindVars dvars (tsKinds,tsNoKinds) = splitAt (length kparams) ts tsKinds' = map sanitizeStars tsKinds extraTys = drop (length tsNoKinds) (bndrParams dvars) ts' = tsNoKinds ++ extraTys -- eta-expand in applySubstitution (Map.fromList (zip kparams tsKinds')) $ repairVarKindsWith dvars ts' -- Sadly, Template Haskell's treatment of data family instances leaves much -- to be desired. Here are some problems that we have to work around: -- -- 1. On all versions of GHC, TH leaves off the kind signatures on the -- type patterns of data family instances where a kind signature isn't -- specified explicitly. Here, we can use the parent data family's -- type variable binders to reconstruct the kind signatures if they -- are missing. -- 2. On GHC 7.6 and 7.8, TH will eta-reduce data instances. We can find -- the missing type variables on the data constructor. -- -- We opt to avoid propagating these new type variables through to the -- constructor now, but we will return to this task in normalizeCon. repairDataFam :: Dec {- ^ family declaration -} -> Dec {- ^ instance declaration -} -> Dec {- ^ instance declaration -} repairDataFam (FamilyD _ _ dvars _) (NewtypeInstD cx n ts con deriv) = NewtypeInstD cx n (repairVarKindsWith' dvars ts) con deriv repairDataFam (FamilyD _ _ dvars _) (DataInstD cx n ts cons deriv) = DataInstD cx n (repairVarKindsWith' dvars ts) cons deriv #else repairDataFam famD instD # if MIN_VERSION_template_haskell(2,11,0) | DataFamilyD _ dvars _ <- famD , NewtypeInstD cx n ts k c deriv <- instD = NewtypeInstD cx n (repairVarKindsWith dvars ts) k c deriv | DataFamilyD _ dvars _ <- famD , DataInstD cx n ts k c deriv <- instD = DataInstD cx n (repairVarKindsWith dvars ts) k c deriv # else | FamilyD _ _ dvars _ <- famD , NewtypeInstD cx n ts c deriv <- instD = NewtypeInstD cx n (repairVarKindsWith dvars ts) c deriv | FamilyD _ _ dvars _ <- famD , DataInstD cx n ts c deriv <- instD = DataInstD cx n (repairVarKindsWith dvars ts) c deriv # endif #endif repairDataFam _ instD = instD repairVarKindsWith :: [TyVarBndr] -> [Type] -> [Type] repairVarKindsWith = zipWith stealKindForType -- If a VarT is missing an explicit kind signature, steal it from a TyVarBndr. stealKindForType :: TyVarBndr -> Type -> Type stealKindForType tvb t@VarT{} = SigT t (tvKind tvb) stealKindForType _ t = t -- | Normalize 'Dec' for a newtype or datatype into a 'DatatypeInfo'. -- Fail in 'Q' otherwise. -- -- Beware: 'normalizeDec' can have surprising behavior when it comes to fixity. -- For instance, if you have this quasiquoted data declaration: -- -- @ -- [d| infix 5 :^^: -- data Foo where -- (:^^:) :: Int -> Int -> Foo |] -- @ -- -- Then if you pass the 'Dec' for @Foo@ to 'normalizeDec' without splicing it -- in a previous Template Haskell splice, then @(:^^:)@ will be labeled a 'NormalConstructor' -- instead of an 'InfixConstructor'. This is because Template Haskell has no way to -- reify the fixity declaration for @(:^^:)@, so it must assume there isn't one. To -- work around this behavior, use 'reifyDatatype' instead. normalizeDec :: Dec -> Q DatatypeInfo normalizeDec = normalizeDecFor isn'tReified normalizeDecFor :: IsReifiedDec -> Dec -> Q DatatypeInfo normalizeDecFor isReified dec = case dec of #if MIN_VERSION_template_haskell(2,12,0) NewtypeD context name tyvars _kind con _derives -> giveTypesStarKinds <$> normalizeDec' isReified context name (bndrParams tyvars) [con] Newtype DataD context name tyvars _kind cons _derives -> giveTypesStarKinds <$> normalizeDec' isReified context name (bndrParams tyvars) cons Datatype NewtypeInstD context name params _kind con _derives -> repair13618' . giveTypesStarKinds =<< normalizeDec' isReified context name params [con] NewtypeInstance DataInstD context name params _kind cons _derives -> repair13618' . giveTypesStarKinds =<< normalizeDec' isReified context name params cons DataInstance #elif MIN_VERSION_template_haskell(2,11,0) NewtypeD context name tyvars _kind con _derives -> giveTypesStarKinds <$> normalizeDec' isReified context name (bndrParams tyvars) [con] Newtype DataD context name tyvars _kind cons _derives -> giveTypesStarKinds <$> normalizeDec' isReified context name (bndrParams tyvars) cons Datatype NewtypeInstD context name params _kind con _derives -> repair13618' . giveTypesStarKinds =<< normalizeDec' isReified context name params [con] NewtypeInstance DataInstD context name params _kind cons _derives -> repair13618' . giveTypesStarKinds =<< normalizeDec' isReified context name params cons DataInstance #else NewtypeD context name tyvars con _derives -> giveTypesStarKinds <$> normalizeDec' isReified context name (bndrParams tyvars) [con] Newtype DataD context name tyvars cons _derives -> giveTypesStarKinds <$> normalizeDec' isReified context name (bndrParams tyvars) cons Datatype NewtypeInstD context name params con _derives -> repair13618' . giveTypesStarKinds =<< normalizeDec' isReified context name params [con] NewtypeInstance DataInstD context name params cons _derives -> repair13618' . giveTypesStarKinds =<< normalizeDec' isReified context name params cons DataInstance #endif _ -> fail "normalizeDecFor: DataD or NewtypeD required" where repair13618' | isReified = repair13618 | otherwise = return bndrParams :: [TyVarBndr] -> [Type] bndrParams = map $ \bndr -> case bndr of KindedTV t k -> SigT (VarT t) k PlainTV t -> VarT t -- | Extract the kind from a 'TyVarBndr'. Assumes 'PlainTV' has kind @*@. tvKind :: TyVarBndr -> Kind tvKind (PlainTV _) = starK tvKind (KindedTV _ k) = k -- | Remove the outermost 'SigT'. stripSigT :: Type -> Type stripSigT (SigT t _) = t stripSigT t = t normalizeDec' :: IsReifiedDec {- ^ Is this a reified 'Dec'? -} -> Cxt {- ^ Datatype context -} -> Name {- ^ Type constructor -} -> [Type] {- ^ Type parameters -} -> [Con] {- ^ Constructors -} -> DatatypeVariant {- ^ Extra information -} -> Q DatatypeInfo normalizeDec' reifiedDec context name params cons variant = do cons' <- concat <$> mapM (normalizeConFor reifiedDec name params variant) cons return DatatypeInfo { datatypeContext = context , datatypeName = name , datatypeVars = params , datatypeCons = cons' , datatypeVariant = variant } -- | Normalize a 'Con' into a 'ConstructorInfo'. This requires knowledge of -- the type and parameters of the constructor, as well as whether the constructor -- is for a data family instance, as extracted from the outer -- 'Dec'. normalizeCon :: Name {- ^ Type constructor -} -> [Type] {- ^ Type parameters -} -> DatatypeVariant {- ^ Extra information -} -> Con {- ^ Constructor -} -> Q [ConstructorInfo] normalizeCon = normalizeConFor isn'tReified normalizeConFor :: IsReifiedDec {- ^ Is this a reified 'Dec'? -} -> Name {- ^ Type constructor -} -> [Type] {- ^ Type parameters -} -> DatatypeVariant {- ^ Extra information -} -> Con {- ^ Constructor -} -> Q [ConstructorInfo] normalizeConFor reifiedDec typename params variant = fmap (map giveTyVarBndrsStarKinds) . dispatch where -- A GADT constructor is declared infix when: -- -- 1. Its name uses operator syntax (e.g., (:*:)) -- 2. It has exactly two fields -- 3. It has a programmer-supplied fixity declaration checkGadtFixity :: [Type] -> Name -> Q ConstructorVariant checkGadtFixity ts n = do #if MIN_VERSION_template_haskell(2,11,0) -- Don't call reifyFixityCompat here! We need to be able to distinguish -- between a default fixity and an explicit @infixl 9@. mbFi <- return Nothing `recover` reifyFixity n let userSuppliedFixity = isJust mbFi #else -- On old GHCs, there is a bug where infix GADT constructors will -- mistakenly be marked as (ForallC (NormalC ...)) instead of -- (ForallC (InfixC ...)). This is especially annoying since on these -- versions of GHC, Template Haskell doesn't grant the ability to query -- whether a constructor was given a user-supplied fixity declaration. -- Rather, you can only check the fixity that GHC ultimately decides on -- for a constructor, regardless of whether it was a default fixity or -- it was user-supplied. -- -- We can approximate whether a fixity was user-supplied by checking if -- it is not equal to defaultFixity (infixl 9). Unfortunately, -- there is no way to distinguish between a user-supplied fixity of -- infixl 9 and the fixity that GHC defaults to, so we cannot properly -- handle that case. mbFi <- reifyFixityCompat n let userSuppliedFixity = isJust mbFi && mbFi /= Just defaultFixity #endif return $ if isInfixDataCon (nameBase n) && length ts == 2 && userSuppliedFixity then InfixConstructor else NormalConstructor -- Checks if a String names a valid Haskell infix data -- constructor (i.e., does it begin with a colon?). isInfixDataCon :: String -> Bool isInfixDataCon (':':_) = True isInfixDataCon _ = False dispatch :: Con -> Q [ConstructorInfo] dispatch = let defaultCase :: Con -> Q [ConstructorInfo] defaultCase = go [] [] False where go :: [TyVarBndr] -> Cxt -> Bool -- Is this a GADT? (see the documentation for -- for checkGadtFixity) -> Con -> Q [ConstructorInfo] go tyvars context gadt c = case c of NormalC n xs -> do let (bangs, ts) = unzip xs stricts = map normalizeStrictness bangs fi <- if gadt then checkGadtFixity ts n else return NormalConstructor return [ConstructorInfo n tyvars context ts stricts fi] InfixC l n r -> let (bangs, ts) = unzip [l,r] stricts = map normalizeStrictness bangs in return [ConstructorInfo n tyvars context ts stricts InfixConstructor] RecC n xs -> let fns = takeFieldNames xs stricts = takeFieldStrictness xs in return [ConstructorInfo n tyvars context (takeFieldTypes xs) stricts (RecordConstructor fns)] ForallC tyvars' context' c' -> go (tyvars'++tyvars) (context'++context) True c' #if MIN_VERSION_template_haskell(2,11,0) GadtC ns xs innerType -> let (bangs, ts) = unzip xs stricts = map normalizeStrictness bangs in gadtCase ns innerType ts stricts (checkGadtFixity ts) RecGadtC ns xs innerType -> let fns = takeFieldNames xs stricts = takeFieldStrictness xs in gadtCase ns innerType (takeFieldTypes xs) stricts (const $ return $ RecordConstructor fns) where gadtCase = normalizeGadtC typename params tyvars context #endif #if MIN_VERSION_template_haskell(2,8,0) && (!MIN_VERSION_template_haskell(2,10,0)) dataFamCompatCase :: Con -> Q [ConstructorInfo] dataFamCompatCase = go [] where go tyvars c = case c of NormalC n xs -> let stricts = map (normalizeStrictness . fst) xs in dataFamCase' n tyvars stricts NormalConstructor InfixC l n r -> let stricts = map (normalizeStrictness . fst) [l,r] in dataFamCase' n tyvars stricts InfixConstructor RecC n xs -> let stricts = takeFieldStrictness xs in dataFamCase' n tyvars stricts (RecordConstructor (takeFieldNames xs)) ForallC tyvars' context' c' -> go (tyvars'++tyvars) c' dataFamCase' :: Name -> [TyVarBndr] -> [FieldStrictness] -> ConstructorVariant -> Q [ConstructorInfo] dataFamCase' n tyvars stricts variant = do mbInfo <- reifyMaybe n case mbInfo of Just (DataConI _ ty _ _) -> do let (context, argTys :|- returnTy) = uncurryType ty returnTy' <- resolveTypeSynonyms returnTy -- Notice that we've ignored the Cxt and argument Types from the -- Con argument above, as they might be scoped over eta-reduced -- variables. Instead of trying to figure out what the -- eta-reduced variables should be substituted with post facto, -- we opt for the simpler approach of using the context and -- argument types from the reified constructor Info, which will -- at least be correctly scoped. This will make the task of -- substituting those types with the variables we put in -- place of the eta-reduced variables (in normalizeDec) -- much easier. normalizeGadtC typename params tyvars context [n] returnTy' argTys stricts (const $ return variant) _ -> fail $ unlines [ "normalizeCon: Cannot reify constructor " ++ nameBase n , "You are likely calling normalizeDec on GHC 7.6 or 7.8 on a data family" , "whose type variables have been eta-reduced due to GHC Trac #9692." , "Unfortunately, without being able to reify the constructor's type," , "there is no way to recover the eta-reduced type variables in general." , "A recommended workaround is to use reifyDatatype instead." ] -- A very ad hoc way of determining if we need to perform some extra passes -- to repair an eta-reduction bug for data family instances that only occurs -- with GHC 7.6 and 7.8. We want to avoid doing these passes if at all possible, -- since they require reifying extra information, and reifying during -- normalization can be problematic for locally declared Template Haskell -- splices (see ##22). mightHaveBeenEtaReduced :: [Type] -> Bool mightHaveBeenEtaReduced ts = case unsnoc ts of Nothing -> False Just (initTs :|- lastT) -> case varTName lastT of Nothing -> False Just n -> not (n `elem` freeVariables initTs) -- If the list is empty returns 'Nothing', otherwise returns the -- 'init' and the 'last'. unsnoc :: [a] -> Maybe (NonEmptySnoc a) unsnoc [] = Nothing unsnoc (x:xs) = case unsnoc xs of Just (a :|- b) -> Just ((x:a) :|- b) Nothing -> Just ([] :|- x) -- If a Type is a VarT, find Just its Name. Otherwise, return Nothing. varTName :: Type -> Maybe Name varTName (SigT t _) = varTName t varTName (VarT n) = Just n varTName _ = Nothing in case variant of -- On GHC 7.6 and 7.8, there's quite a bit of post-processing that -- needs to be performed to work around an old bug that eta-reduces the -- type patterns of data families (but only for reified data family instances). DataInstance | reifiedDec, mightHaveBeenEtaReduced params -> dataFamCompatCase NewtypeInstance | reifiedDec, mightHaveBeenEtaReduced params -> dataFamCompatCase _ -> defaultCase #else in defaultCase #endif #if MIN_VERSION_template_haskell(2,11,0) normalizeStrictness :: Bang -> FieldStrictness normalizeStrictness (Bang upk str) = FieldStrictness (normalizeSourceUnpackedness upk) (normalizeSourceStrictness str) where normalizeSourceUnpackedness :: SourceUnpackedness -> Unpackedness normalizeSourceUnpackedness NoSourceUnpackedness = UnspecifiedUnpackedness normalizeSourceUnpackedness SourceNoUnpack = NoUnpack normalizeSourceUnpackedness SourceUnpack = Unpack normalizeSourceStrictness :: SourceStrictness -> Strictness normalizeSourceStrictness NoSourceStrictness = UnspecifiedStrictness normalizeSourceStrictness SourceLazy = Lazy normalizeSourceStrictness SourceStrict = Strict #else normalizeStrictness :: Strict -> FieldStrictness normalizeStrictness IsStrict = isStrictAnnot normalizeStrictness NotStrict = notStrictAnnot # if MIN_VERSION_template_haskell(2,7,0) normalizeStrictness Unpacked = unpackedAnnot # endif #endif normalizeGadtC :: Name {- ^ Type constructor -} -> [Type] {- ^ Type parameters -} -> [TyVarBndr] {- ^ Constructor parameters -} -> Cxt {- ^ Constructor context -} -> [Name] {- ^ Constructor names -} -> Type {- ^ Declared type of constructor -} -> [Type] {- ^ Constructor field types -} -> [FieldStrictness] {- ^ Constructor field strictness -} -> (Name -> Q ConstructorVariant) {- ^ Determine a constructor variant from its 'Name' -} -> Q [ConstructorInfo] normalizeGadtC typename params tyvars context names innerType fields stricts getVariant = do -- Due to GHC Trac #13885, it's possible that the type variables bound by -- a GADT constructor will shadow those that are bound by the data type. -- This function assumes this isn't the case in certain parts (e.g., when -- mergeArguments is invoked), so we do an alpha-renaming of the -- constructor-bound variables before proceeding. See #36 for an example -- of what can go wrong if this isn't done. let conBoundNames = concatMap (\tvb -> tvName tvb:freeVariables (tvKind tvb)) tyvars conSubst <- T.sequence $ Map.fromList [ (n, newName (nameBase n)) | n <- conBoundNames ] let conSubst' = fmap VarT conSubst renamedTyvars = map (\tvb -> case tvb of PlainTV n -> PlainTV (conSubst Map.! n) KindedTV n k -> KindedTV (conSubst Map.! n) (applySubstitution conSubst' k)) tyvars renamedContext = applySubstitution conSubst' context renamedInnerType = applySubstitution conSubst' innerType renamedFields = applySubstitution conSubst' fields innerType' <- resolveTypeSynonyms renamedInnerType case decomposeType innerType' of ConT innerTyCon :| ts | typename == innerTyCon -> let (substName, context1) = closeOverKinds (kindsOfFVsOfTvbs renamedTyvars) (kindsOfFVsOfTypes params) (mergeArguments params ts) subst = VarT <$> substName exTyvars = [ tv | tv <- renamedTyvars, Map.notMember (tvName tv) subst ] exTyvars' = substTyVarBndrs subst exTyvars context2 = applySubstitution subst (context1 ++ renamedContext) fields' = applySubstitution subst renamedFields in sequence [ ConstructorInfo name exTyvars' context2 fields' stricts <$> variantQ | name <- names , let variantQ = getVariant name ] _ -> fail "normalizeGadtC: Expected type constructor application" {- Extend a type variable renaming subtitution and a list of equality predicates by looking into kind information as much as possible. Why is this necessary? Consider the following example: data (a1 :: k1) :~: (b1 :: k1) where Refl :: forall k2 (a2 :: k2). a2 :~: a2 After an initial call to mergeArguments, we will have the following substitution and context: * Substitution: [a2 :-> a1] * Context: (a2 ~ b1) We shouldn't stop there, however! We determine the existentially quantified type variables of a constructor by filtering out those constructor-bound variables which do not appear in the substitution that mergeArguments returns. In this example, Refl's bound variables are k2 and a2. a2 appears in the returned substitution, but k2 does not, which means that we would mistakenly conclude that k2 is existential! Although we don't have the full power of kind inference to guide us here, we can at least do the next best thing. Generally, the datatype-bound type variables and the constructor type variable binders contain all of the kind information we need, so we proceed as follows: 1. Construct a map from each constructor-bound variable to its kind. (Do the same for each datatype-bound variable). These maps are the first and second arguments to closeOverKinds, respectively. 2. Call mergeArguments once on the GADT return type and datatype-bound types, and pass that in as the third argument to closeOverKinds. 3. For each name-name pair in the supplied substitution, check if the first and second names map to kinds in the first and second kind maps in closeOverKinds, respectively. If so, associate the first kind with the second kind. 4. For each kind association discovered in part (3), call mergeArguments on the lists of kinds. This will yield a kind substitution and kind equality context. 5. If the kind substitution is non-empty, then go back to step (3) and repeat the process on the new kind substitution and context. Otherwise, if the kind substitution is empty, then we have reached a fixed- point (i.e., we have closed over the kinds), so proceed. 6. Union up all of the substitutions and contexts, and return those. This algorithm is not perfect, as it will only catch everything if all of the kinds are explicitly mentioned somewhere (and not left quantified implicitly). Thankfully, reifying data types via Template Haskell tends to yield a healthy amount of kind signatures, so this works quite well in practice. -} closeOverKinds :: Map Name Kind -> Map Name Kind -> (Map Name Name, Cxt) -> (Map Name Name, Cxt) closeOverKinds domainFVKinds rangeFVKinds = go where go :: (Map Name Name, Cxt) -> (Map Name Name, Cxt) go (subst, context) = let substList = Map.toList subst (kindsInner, kindsOuter) = unzip $ mapMaybe (\(d, r) -> do d' <- Map.lookup d domainFVKinds r' <- Map.lookup r rangeFVKinds return (d', r')) substList (kindSubst, kindContext) = mergeArgumentKinds kindsOuter kindsInner (restSubst, restContext) = if Map.null kindSubst -- Fixed-point calculation then (Map.empty, []) else go (kindSubst, kindContext) finalSubst = Map.unions [subst, kindSubst, restSubst] finalContext = nub $ concat [context, kindContext, restContext] -- Use `nub` here in an effort to minimize the number of -- redundant equality constraints in the returned context. in (finalSubst, finalContext) -- Look into a list of types and map each free variable name to its kind. kindsOfFVsOfTypes :: [Type] -> Map Name Kind kindsOfFVsOfTypes = foldMap go where go :: Type -> Map Name Kind go (ForallT {}) = error "`forall` type used in data family pattern" go (AppT t1 t2) = go t1 `Map.union` go t2 go (SigT t k) = let kSigs = #if MIN_VERSION_template_haskell(2,8,0) go k #else Map.empty #endif in case t of VarT n -> Map.insert n k kSigs _ -> go t `Map.union` kSigs go _ = Map.empty -- Look into a list of type variable binder and map each free variable name -- to its kind (also map the names that KindedTVs bind to their respective -- kinds). This function considers the kind of a PlainTV to be *. kindsOfFVsOfTvbs :: [TyVarBndr] -> Map Name Kind kindsOfFVsOfTvbs = foldMap go where go :: TyVarBndr -> Map Name Kind go (PlainTV n) = Map.singleton n starK go (KindedTV n k) = let kSigs = #if MIN_VERSION_template_haskell(2,8,0) kindsOfFVsOfTypes [k] #else Map.empty #endif in Map.insert n k kSigs mergeArguments :: [Type] {- ^ outer parameters -} -> [Type] {- ^ inner parameters (specializations ) -} -> (Map Name Name, Cxt) mergeArguments ns ts = foldr aux (Map.empty, []) (zip ns ts) where aux (f `AppT` x, g `AppT` y) sc = aux (x,y) (aux (f,g) sc) aux (VarT n,p) (subst, context) = case p of VarT m | m == n -> (subst, context) -- If the two variables are the same, don't bother extending -- the substitution. (This is purely an optimization.) | Just n' <- Map.lookup m subst , n == n' -> (subst, context) -- If a variable is already in a substitution and it maps -- to the variable that we are trying to unify with, then -- leave the context alone. (Not doing so caused #46.) | Map.notMember m subst -> (Map.insert m n subst, context) _ -> (subst, equalPred (VarT n) p : context) aux (SigT x _, y) sc = aux (x,y) sc -- learn about kinds?? -- This matches *after* VarT so that we can compute a substitution -- that includes the kind signature. aux (x, SigT y _) sc = aux (x,y) sc aux _ sc = sc -- | A specialization of 'mergeArguments' to 'Kind'. -- Needed only for backwards compatibility with older versions of -- @template-haskell@. mergeArgumentKinds :: [Kind] -> [Kind] -> (Map Name Name, Cxt) #if MIN_VERSION_template_haskell(2,8,0) mergeArgumentKinds = mergeArguments #else mergeArgumentKinds _ _ = (Map.empty, []) #endif -- | Expand all of the type synonyms in a type. -- -- Note that this function will drop parentheses as a side effect. resolveTypeSynonyms :: Type -> Q Type resolveTypeSynonyms t = let f :| xs = decomposeType t notTypeSynCase :: Type -> Q Type notTypeSynCase ty = foldl AppT ty <$> mapM resolveTypeSynonyms xs expandCon :: Name -- The Name to check whether it is a type synonym or not -> Type -- The argument type to fall back on if the supplied -- Name isn't a type synonym -> Q Type expandCon n ty = do mbInfo <- reifyMaybe n case mbInfo of Just (TyConI (TySynD _ synvars def)) -> resolveTypeSynonyms $ expandSynonymRHS synvars xs def _ -> notTypeSynCase ty in case f of ForallT tvbs ctxt body -> ForallT `fmap` mapM resolve_tvb_syns tvbs `ap` mapM resolvePredSynonyms ctxt `ap` resolveTypeSynonyms body SigT ty ki -> do ty' <- resolveTypeSynonyms ty ki' <- resolveKindSynonyms ki notTypeSynCase $ SigT ty' ki' ConT n -> expandCon n (ConT n) #if MIN_VERSION_template_haskell(2,11,0) InfixT t1 n t2 -> do t1' <- resolveTypeSynonyms t1 t2' <- resolveTypeSynonyms t2 expandCon n (InfixT t1' n t2') UInfixT t1 n t2 -> do t1' <- resolveTypeSynonyms t1 t2' <- resolveTypeSynonyms t2 expandCon n (UInfixT t1' n t2') #endif _ -> notTypeSynCase f -- | Expand all of the type synonyms in a 'Kind'. resolveKindSynonyms :: Kind -> Q Kind #if MIN_VERSION_template_haskell(2,8,0) resolveKindSynonyms = resolveTypeSynonyms #else resolveKindSynonyms = return -- One simply couldn't put type synonyms into -- kinds on old versions of GHC. #endif -- | Expand all of the type synonyms in a the kind of a 'TyVarBndr'. resolve_tvb_syns :: TyVarBndr -> Q TyVarBndr resolve_tvb_syns tvb@PlainTV{} = return tvb resolve_tvb_syns (KindedTV n k) = KindedTV n <$> resolveKindSynonyms k expandSynonymRHS :: [TyVarBndr] {- ^ Substitute these variables... -} -> [Type] {- ^ ...with these types... -} -> Type {- ^ ...inside of this type. -} -> Type expandSynonymRHS synvars ts def = let argNames = map tvName synvars (args,rest) = splitAt (length argNames) ts subst = Map.fromList (zip argNames args) in foldl AppT (applySubstitution subst def) rest -- | Expand all of the type synonyms in a 'Pred'. resolvePredSynonyms :: Pred -> Q Pred #if MIN_VERSION_template_haskell(2,10,0) resolvePredSynonyms = resolveTypeSynonyms #else resolvePredSynonyms (ClassP n ts) = do mbInfo <- reifyMaybe n case mbInfo of Just (TyConI (TySynD _ synvars def)) -> resolvePredSynonyms $ typeToPred $ expandSynonymRHS synvars ts def _ -> ClassP n <$> mapM resolveTypeSynonyms ts resolvePredSynonyms (EqualP t1 t2) = do t1' <- resolveTypeSynonyms t1 t2' <- resolveTypeSynonyms t2 return (EqualP t1' t2') typeToPred :: Type -> Pred typeToPred t = let f :| xs = decomposeType t in case f of ConT n | n == eqTypeName # if __GLASGOW_HASKELL__ == 704 -- There's an unfortunate bug in GHC 7.4 where the (~) type is reified -- with an explicit kind argument. To work around this, we ignore it. , [_,t1,t2] <- xs # else , [t1,t2] <- xs # endif -> EqualP t1 t2 | otherwise -> ClassP n xs _ -> error $ "typeToPred: Can't handle type " ++ show t #endif -- | Decompose a type into a list of it's outermost applications. This process -- forgets about infix application and explicit parentheses. -- -- This operation should be used after all 'UInfixT' cases have been resolved -- by 'resolveFixities' if the argument is being user generated. -- -- > t ~= foldl1 AppT (decomposeType t) decomposeType :: Type -> NonEmpty Type decomposeType = go [] where go args (AppT f x) = go (x:args) f #if MIN_VERSION_template_haskell(2,11,0) go args (ParensT t) = go args t #endif go args t = t :| args -- 'NonEmpty' didn't move into base until recently. Reimplementing it locally -- saves dependencies for supporting older GHCs data NonEmpty a = a :| [a] data NonEmptySnoc a = [a] :|- a -- Decompose a function type into its context, argument types, -- and return types. For instance, this -- -- (Show a, b ~ Int) => (a -> b) -> Char -> Int -- -- becomes -- -- ([Show a, b ~ Int], [a -> b, Char] :|- Int) uncurryType :: Type -> (Cxt, NonEmptySnoc Type) uncurryType = go [] [] where go ctxt args (AppT (AppT ArrowT t1) t2) = go ctxt (t1:args) t2 go ctxt args (ForallT _ ctxt' t) = go (ctxt++ctxt') args t go ctxt args t = (ctxt, reverse args :|- t) -- | Resolve any infix type application in a type using the fixities that -- are currently available. Starting in `template-haskell-2.11` types could -- contain unresolved infix applications. resolveInfixT :: Type -> Q Type #if MIN_VERSION_template_haskell(2,11,0) resolveInfixT (ForallT vs cx t) = forallT vs (mapM resolveInfixT cx) (resolveInfixT t) resolveInfixT (f `AppT` x) = resolveInfixT f `appT` resolveInfixT x resolveInfixT (ParensT t) = resolveInfixT t resolveInfixT (InfixT l o r) = conT o `appT` resolveInfixT l `appT` resolveInfixT r resolveInfixT (SigT t k) = SigT <$> resolveInfixT t <*> resolveInfixT k resolveInfixT t@UInfixT{} = resolveInfixT =<< resolveInfixT1 (gatherUInfixT t) resolveInfixT t = return t gatherUInfixT :: Type -> InfixList gatherUInfixT (UInfixT l o r) = ilAppend (gatherUInfixT l) o (gatherUInfixT r) gatherUInfixT t = ILNil t -- This can fail due to incompatible fixities resolveInfixT1 :: InfixList -> TypeQ resolveInfixT1 = go [] where go :: [(Type,Name,Fixity)] -> InfixList -> TypeQ go ts (ILNil u) = return (foldl (\acc (l,o,_) -> ConT o `AppT` l `AppT` acc) u ts) go ts (ILCons l o r) = do ofx <- fromMaybe defaultFixity <$> reifyFixityCompat o let push = go ((l,o,ofx):ts) r case ts of (l1,o1,o1fx):ts' -> case compareFixity o1fx ofx of Just True -> go ((ConT o1 `AppT` l1 `AppT` l, o, ofx):ts') r Just False -> push Nothing -> fail (precedenceError o1 o1fx o ofx) _ -> push compareFixity :: Fixity -> Fixity -> Maybe Bool compareFixity (Fixity n1 InfixL) (Fixity n2 InfixL) = Just (n1 >= n2) compareFixity (Fixity n1 InfixR) (Fixity n2 InfixR) = Just (n1 > n2) compareFixity (Fixity n1 _ ) (Fixity n2 _ ) = case compare n1 n2 of GT -> Just True LT -> Just False EQ -> Nothing precedenceError :: Name -> Fixity -> Name -> Fixity -> String precedenceError o1 ofx1 o2 ofx2 = "Precedence parsing error: cannot mix ‘" ++ nameBase o1 ++ "’ [" ++ showFixity ofx1 ++ "] and ‘" ++ nameBase o2 ++ "’ [" ++ showFixity ofx2 ++ "] in the same infix type expression" data InfixList = ILCons Type Name InfixList | ILNil Type ilAppend :: InfixList -> Name -> InfixList -> InfixList ilAppend (ILNil l) o r = ILCons l o r ilAppend (ILCons l1 o1 r1) o r = ILCons l1 o1 (ilAppend r1 o r) #else -- older template-haskell packages don't have UInfixT resolveInfixT = return #endif -- | Render a 'Fixity' as it would appear in Haskell source. -- -- Example: @infixl 5@ showFixity :: Fixity -> String showFixity (Fixity n d) = showFixityDirection d ++ " " ++ show n -- | Render a 'FixityDirection' like it would appear in Haskell source. -- -- Examples: @infixl@ @infixr@ @infix@ showFixityDirection :: FixityDirection -> String showFixityDirection InfixL = "infixl" showFixityDirection InfixR = "infixr" showFixityDirection InfixN = "infix" -- | Extract the type variable name from a 'TyVarBndr' ignoring the -- kind signature if one exists. tvName :: TyVarBndr -> Name tvName (PlainTV name ) = name tvName (KindedTV name _) = name takeFieldNames :: [(Name,a,b)] -> [Name] takeFieldNames xs = [a | (a,_,_) <- xs] #if MIN_VERSION_template_haskell(2,11,0) takeFieldStrictness :: [(a,Bang,b)] -> [FieldStrictness] #else takeFieldStrictness :: [(a,Strict,b)] -> [FieldStrictness] #endif takeFieldStrictness xs = [normalizeStrictness a | (_,a,_) <- xs] takeFieldTypes :: [(a,b,Type)] -> [Type] takeFieldTypes xs = [a | (_,_,a) <- xs] conHasRecord :: Name -> ConstructorInfo -> Bool conHasRecord recName info = case constructorVariant info of NormalConstructor -> False InfixConstructor -> False RecordConstructor fields -> recName `elem` fields ------------------------------------------------------------------------ -- | Add universal quantifier for all free variables in the type. This is -- useful when constructing a type signature for a declaration. -- This code is careful to ensure that the order of the variables quantified -- is determined by their order of appearance in the type signature. (In -- contrast with being dependent upon the Ord instance for 'Name') quantifyType :: Type -> Type quantifyType t | null tvbs = t | otherwise = ForallT tvbs [] t where tvbs = freeVariablesWellScoped [t] -- | Take a list of 'Type's, find their free variables, and sort them -- according to dependency order. -- -- As an example of how this function works, consider the following type: -- -- @ -- Proxy (a :: k) -- @ -- -- Calling 'freeVariables' on this type would yield @[a, k]@, since that is -- the order in which those variables appear in a left-to-right fashion. But -- this order does not preserve the fact that @k@ is the kind of @a@. Moreover, -- if you tried writing the type @forall a k. Proxy (a :: k)@, GHC would reject -- this, since GHC would demand that @k@ come before @a@. -- -- 'freeVariablesWellScoped' orders the free variables of a type in a way that -- preserves this dependency ordering. If one were to call -- 'freeVariablesWellScoped' on the type above, it would return -- @[k, (a :: k)]@. (This is why 'freeVariablesWellScoped' returns a list of -- 'TyVarBndr's instead of 'Name's, since it must make it explicit that @k@ -- is the kind of @a@.) -- -- On older GHCs, this takes measures to avoid returning explicitly bound -- kind variables, which was not possible before @TypeInType@. freeVariablesWellScoped :: [Type] -> [TyVarBndr] freeVariablesWellScoped tys = let fvs :: [Name] fvs = freeVariables tys varKindSigs :: Map Name Kind varKindSigs = foldMap go_ty tys where go_ty :: Type -> Map Name Kind go_ty (ForallT tvbs ctxt t) = foldr (\tvb -> Map.delete (tvName tvb)) (foldMap go_pred ctxt `mappend` go_ty t) tvbs go_ty (AppT t1 t2) = go_ty t1 `mappend` go_ty t2 go_ty (SigT t k) = let kSigs = #if MIN_VERSION_template_haskell(2,8,0) go_ty k #else mempty #endif in case t of VarT n -> Map.insert n k kSigs _ -> go_ty t `mappend` kSigs go_ty _ = mempty go_pred :: Pred -> Map Name Kind #if MIN_VERSION_template_haskell(2,10,0) go_pred = go_ty #else go_pred (ClassP _ ts) = foldMap go_ty ts go_pred (EqualP t1 t2) = go_ty t1 `mappend` go_ty t2 #endif (g, gLookup, _) = graphFromEdges [ (fv, fv, kindVars) | fv <- fvs , let kindVars = case Map.lookup fv varKindSigs of Nothing -> [] Just ks -> freeVariables ks ] tg = reverse $ topSort g lookupVertex x = case gLookup x of (n, _, _) -> n ascribeWithKind n | Just k <- Map.lookup n varKindSigs = KindedTV n k | otherwise = PlainTV n -- An annoying wrinkle: GHCs before 8.0 don't support explicitly -- quantifying kinds, so something like @forall k (a :: k)@ would be -- rejected. To work around this, we filter out any binders whose names -- also appear in a kind on old GHCs. isKindBinderOnOldGHCs #if __GLASGOW_HASKELL__ >= 800 = const False #else = (`elem` kindVars) where kindVars = freeVariables $ Map.elems varKindSigs #endif in map ascribeWithKind $ filter (not . isKindBinderOnOldGHCs) $ map lookupVertex tg -- | Substitute all of the free variables in a type with fresh ones freshenFreeVariables :: Type -> Q Type freshenFreeVariables t = do let xs = [ (n, VarT <$> newName (nameBase n)) | n <- freeVariables t] subst <- T.sequence (Map.fromList xs) return (applySubstitution subst t) -- | Class for types that support type variable substitution. class TypeSubstitution a where -- | Apply a type variable substitution. -- -- Note that 'applySubstitution' is /not/ capture-avoiding. To illustrate -- this, observe that if you call this function with the following -- substitution: -- -- * @b :-> a@ -- -- On the following 'Type': -- -- * @forall a. b@ -- -- Then it will return: -- -- * @forall a. a@ -- -- However, because the same @a@ type variable was used in the range of the -- substitution as was bound by the @forall@, the substituted @a@ is now -- captured by the @forall@, resulting in a completely different function. -- -- For @th-abstraction@'s purposes, this is acceptable, as it usually only -- deals with globally unique type variable 'Name's. If you use -- 'applySubstitution' in a context where the 'Name's aren't globally unique, -- however, be aware of this potential problem. applySubstitution :: Map Name Type -> a -> a -- | Compute the free type variables freeVariables :: a -> [Name] instance TypeSubstitution a => TypeSubstitution [a] where freeVariables = nub . concat . map freeVariables applySubstitution = fmap . applySubstitution instance TypeSubstitution Type where applySubstitution subst = go where go (ForallT tvs context t) = let subst' = foldl' (flip Map.delete) subst (map tvName tvs) mapTvbKind :: (Kind -> Kind) -> TyVarBndr -> TyVarBndr mapTvbKind f (PlainTV n) = PlainTV n mapTvbKind f (KindedTV n k) = KindedTV n (f k) in ForallT (map (mapTvbKind (applySubstitution subst')) tvs) (applySubstitution subst' context) (applySubstitution subst' t) go (AppT f x) = AppT (go f) (go x) go (SigT t k) = SigT (go t) (applySubstitution subst k) -- k could be Kind go (VarT v) = Map.findWithDefault (VarT v) v subst #if MIN_VERSION_template_haskell(2,11,0) go (InfixT l c r) = InfixT (go l) c (go r) go (UInfixT l c r) = UInfixT (go l) c (go r) go (ParensT t) = ParensT (go t) #endif go t = t freeVariables t = case t of ForallT tvs context t' -> (concatMap (freeVariables . tvKind) tvs `union` freeVariables context `union` freeVariables t') \\ map tvName tvs AppT f x -> freeVariables f `union` freeVariables x SigT t' k -> freeVariables t' `union` freeVariables k VarT v -> [v] #if MIN_VERSION_template_haskell(2,11,0) InfixT l _ r -> freeVariables l `union` freeVariables r UInfixT l _ r -> freeVariables l `union` freeVariables r ParensT t' -> freeVariables t' #endif _ -> [] instance TypeSubstitution ConstructorInfo where freeVariables ci = (freeVariables (constructorContext ci) `union` freeVariables (constructorFields ci)) \\ (tvName <$> constructorVars ci) applySubstitution subst ci = let subst' = foldl' (flip Map.delete) subst (map tvName (constructorVars ci)) in ci { constructorContext = applySubstitution subst' (constructorContext ci) , constructorFields = applySubstitution subst' (constructorFields ci) } -- 'Pred' became a type synonym for 'Type' #if !MIN_VERSION_template_haskell(2,10,0) instance TypeSubstitution Pred where freeVariables (ClassP _ xs) = freeVariables xs freeVariables (EqualP x y) = freeVariables x `union` freeVariables y applySubstitution p (ClassP n xs) = ClassP n (applySubstitution p xs) applySubstitution p (EqualP x y) = EqualP (applySubstitution p x) (applySubstitution p y) #endif -- 'Kind' became a type synonym for 'Type'. Previously there were no kind variables #if !MIN_VERSION_template_haskell(2,8,0) instance TypeSubstitution Kind where freeVariables _ = [] applySubstitution _ k = k #endif -- | Substitutes into the kinds of type variable binders. -- Not capture-avoiding. substTyVarBndrs :: Map Name Type -> [TyVarBndr] -> [TyVarBndr] substTyVarBndrs subst = map go where go tvb@(PlainTV {}) = tvb go (KindedTV n k) = KindedTV n (applySubstitution subst k) ------------------------------------------------------------------------ combineSubstitutions :: Map Name Type -> Map Name Type -> Map Name Type combineSubstitutions x y = Map.union (fmap (applySubstitution y) x) y -- | Compute the type variable substitution that unifies a list of types, -- or fail in 'Q'. -- -- All infix issue should be resolved before using 'unifyTypes' -- -- Alpha equivalent quantified types are not unified. unifyTypes :: [Type] -> Q (Map Name Type) unifyTypes [] = return Map.empty unifyTypes (t:ts) = do t':ts' <- mapM resolveTypeSynonyms (t:ts) let aux sub u = do sub' <- unify' (applySubstitution sub t') (applySubstitution sub u) return (combineSubstitutions sub sub') case foldM aux Map.empty ts' of Right m -> return m Left (x,y) -> fail $ showString "Unable to unify types " . showsPrec 11 x . showString " and " . showsPrec 11 y $ "" unify' :: Type -> Type -> Either (Type,Type) (Map Name Type) unify' (VarT n) (VarT m) | n == m = pure Map.empty unify' (VarT n) t | n `elem` freeVariables t = Left (VarT n, t) | otherwise = Right (Map.singleton n t) unify' t (VarT n) | n `elem` freeVariables t = Left (VarT n, t) | otherwise = Right (Map.singleton n t) unify' (AppT f1 x1) (AppT f2 x2) = do sub1 <- unify' f1 f2 sub2 <- unify' (applySubstitution sub1 x1) (applySubstitution sub1 x2) Right (combineSubstitutions sub1 sub2) -- Doesn't unify kind signatures unify' (SigT t _) u = unify' t u unify' t (SigT u _) = unify' t u -- only non-recursive cases should remain at this point unify' t u | t == u = Right Map.empty | otherwise = Left (t,u) -- | Construct an equality constraint. The implementation of 'Pred' varies -- across versions of Template Haskell. equalPred :: Type -> Type -> Pred equalPred x y = #if MIN_VERSION_template_haskell(2,10,0) AppT (AppT EqualityT x) y #else EqualP x y #endif -- | Construct a typeclass constraint. The implementation of 'Pred' varies -- across versions of Template Haskell. classPred :: Name {- ^ class -} -> [Type] {- ^ parameters -} -> Pred classPred = #if MIN_VERSION_template_haskell(2,10,0) foldl AppT . ConT #else ClassP #endif -- | Match a 'Pred' representing an equality constraint. Returns -- arguments to the equality constraint if successful. asEqualPred :: Pred -> Maybe (Type,Type) #if MIN_VERSION_template_haskell(2,10,0) asEqualPred (EqualityT `AppT` x `AppT` y) = Just (x,y) asEqualPred (ConT eq `AppT` x `AppT` y) | eq == eqTypeName = Just (x,y) #else asEqualPred (EqualP x y) = Just (x,y) #endif asEqualPred _ = Nothing -- | Match a 'Pred' representing a class constraint. -- Returns the classname and parameters if successful. asClassPred :: Pred -> Maybe (Name, [Type]) #if MIN_VERSION_template_haskell(2,10,0) asClassPred t = case decomposeType t of ConT f :| xs | f /= eqTypeName -> Just (f,xs) _ -> Nothing #else asClassPred (ClassP f xs) = Just (f,xs) asClassPred _ = Nothing #endif ------------------------------------------------------------------------ -- | If we are working with a 'Dec' obtained via 'reify' (as opposed to one -- created from, say, [d| ... |] quotes), then we need to apply more hacks than -- we otherwise would to sanitize the 'Dec'. See #28. type IsReifiedDec = Bool isReified, isn'tReified :: IsReifiedDec isReified = True isn'tReified = False -- On old versions of GHC, reify would not give you kind signatures for -- GADT type variables of kind *. To work around this, we insert the kinds -- manually on any types without a signature. giveTypesStarKinds :: DatatypeInfo -> DatatypeInfo giveTypesStarKinds info = info { datatypeVars = annotateVars (datatypeVars info) } where annotateVars :: [Type] -> [Type] annotateVars = map $ \t -> case t of VarT n -> SigT (VarT n) starK _ -> t giveTyVarBndrsStarKinds :: ConstructorInfo -> ConstructorInfo giveTyVarBndrsStarKinds info = info { constructorVars = annotateVars (constructorVars info) } where annotateVars :: [TyVarBndr] -> [TyVarBndr] annotateVars = map $ \tvb -> case tvb of PlainTV n -> KindedTV n starK _ -> tvb -- | Prior to GHC 8.2.1, reify was broken for data instances and newtype -- instances. This code attempts to detect the problem and repair it if -- possible. -- -- The particular problem is that the type variables used in the patterns -- while defining a data family instance do not completely match those -- used when defining the fields of the value constructors beyond the -- base names. This code attempts to recover the relationship between the -- type variables. -- -- It is possible, however, to generate these kinds of declarations by -- means other than reify. In these cases the name bases might not be -- unique and the declarations might be well formed. In such a case this -- code attempts to avoid altering the declaration. -- -- https://ghc.haskell.org/trac/ghc/ticket/13618 repair13618 :: DatatypeInfo -> Q DatatypeInfo repair13618 info = do s <- T.sequence (Map.fromList substList) return info { datatypeCons = applySubstitution s (datatypeCons info) } where used = freeVariables (datatypeCons info) bound = freeVariables (datatypeVars info) free = used \\ bound substList = [ (u, substEntry u vs) | u <- free , let vs = [v | v <- bound, nameBase v == nameBase u] ] substEntry _ [v] = varT v substEntry u [] = fail ("Impossible free variable: " ++ show u) substEntry u _ = fail ("Ambiguous free variable: " ++ show u) ------------------------------------------------------------------------ -- | Backward compatible version of 'dataD' dataDCompat :: CxtQ {- ^ context -} -> Name {- ^ type constructor -} -> [TyVarBndr] {- ^ type parameters -} -> [ConQ] {- ^ constructor definitions -} -> [Name] {- ^ derived class names -} -> DecQ #if MIN_VERSION_template_haskell(2,12,0) dataDCompat c n ts cs ds = dataD c n ts Nothing cs (if null ds then [] else [derivClause Nothing (map conT ds)]) #elif MIN_VERSION_template_haskell(2,11,0) dataDCompat c n ts cs ds = dataD c n ts Nothing cs (return (map ConT ds)) #else dataDCompat = dataD #endif -- | Backward compatible version of 'newtypeD' newtypeDCompat :: CxtQ {- ^ context -} -> Name {- ^ type constructor -} -> [TyVarBndr] {- ^ type parameters -} -> ConQ {- ^ constructor definition -} -> [Name] {- ^ derived class names -} -> DecQ #if MIN_VERSION_template_haskell(2,12,0) newtypeDCompat c n ts cs ds = newtypeD c n ts Nothing cs (if null ds then [] else [derivClause Nothing (map conT ds)]) #elif MIN_VERSION_template_haskell(2,11,0) newtypeDCompat c n ts cs ds = newtypeD c n ts Nothing cs (return (map ConT ds)) #else newtypeDCompat = newtypeD #endif -- | Backward compatible version of 'tySynInstD' tySynInstDCompat :: Name {- ^ type family name -} -> [TypeQ] {- ^ instance parameters -} -> TypeQ {- ^ instance result -} -> DecQ #if MIN_VERSION_template_haskell(2,9,0) tySynInstDCompat n ps r = TySynInstD n <$> (TySynEqn <$> sequence ps <*> r) #else tySynInstDCompat = tySynInstD #endif -- | Backward compatible version of 'pragLineD'. Returns -- 'Nothing' if line pragmas are not suported. pragLineDCompat :: Int {- ^ line number -} -> String {- ^ file name -} -> Maybe DecQ #if MIN_VERSION_template_haskell(2,10,0) pragLineDCompat ln fn = Just (pragLineD ln fn) #else pragLineDCompat _ _ = Nothing #endif arrowKCompat :: Kind -> Kind -> Kind #if MIN_VERSION_template_haskell(2,8,0) arrowKCompat x y = arrowK `appK` x `appK` y #else arrowKCompat = arrowK #endif ------------------------------------------------------------------------ -- | Backwards compatibility wrapper for 'Fixity' lookup. -- -- In @template-haskell-2.11.0.0@ and later, the answer will always -- be 'Just' of a fixity. -- -- Before @template-haskell-2.11.0.0@ it was only possible to determine -- fixity information for variables, class methods, and data constructors. -- In this case for type operators the answer could be 'Nothing', which -- indicates that the answer is unavailable. reifyFixityCompat :: Name -> Q (Maybe Fixity) #if MIN_VERSION_template_haskell(2,11,0) reifyFixityCompat n = recover (return Nothing) ((`mplus` Just defaultFixity) <$> reifyFixity n) #else reifyFixityCompat n = recover (return Nothing) $ do info <- reify n return $! case info of ClassOpI _ _ _ fixity -> Just fixity DataConI _ _ _ fixity -> Just fixity VarI _ _ _ fixity -> Just fixity _ -> Nothing #endif -- | Call 'reify' and return @'Just' info@ if successful or 'Nothing' if -- reification failed. reifyMaybe :: Name -> Q (Maybe Info) reifyMaybe n = return Nothing `recover` fmap Just (reify n)