{-# LANGUAGE BangPatterns #-} {-# LANGUAGE CPP #-} {-# LANGUAGE MagicHash #-} {-# LANGUAGE TemplateHaskell #-} {-| Module: TextShow.TH.Internal Copyright: (C) 2014-2017 Ryan Scott License: BSD-style (see the file LICENSE) Maintainer: Ryan Scott Stability: Provisional Portability: GHC Functions to mechanically derive 'TextShow', 'TextShow1', or 'TextShow2' instances, or to splice their functions directly into Haskell source code. You need to enable the @TemplateHaskell@ language extension in order to use this module. This implementation is loosely based off of the @Data.Aeson.TH@ module from the @aeson@ library. -} module TextShow.TH.Internal ( -- * 'deriveTextShow' -- $deriveTextShow deriveTextShow -- * 'deriveTextShow1' -- $deriveTextShow1 , deriveTextShow1 -- * 'deriveTextShow2' -- $deriveTextShow2 , deriveTextShow2 -- * @make-@ functions -- $make , makeShowt , makeShowtl , makeShowtPrec , makeShowtlPrec , makeShowtList , makeShowtlList , makeShowb , makeShowbPrec , makeShowbList , makePrintT , makePrintTL , makeHPrintT , makeHPrintTL , makeLiftShowbPrec , makeShowbPrec1 , makeLiftShowbPrec2 , makeShowbPrec2 -- * 'Options' , Options(..) , defaultOptions , GenTextMethods(..) , deriveTextShowOptions , deriveTextShow1Options , deriveTextShow2Options ) where import Control.Monad (unless, when) import Data.Foldable.Compat import Data.List.Compat import qualified Data.List.NonEmpty as NE (reverse) import Data.List.NonEmpty (NonEmpty(..), (<|)) import qualified Data.Map as Map (fromList, keys, lookup, singleton) import Data.Map (Map) import Data.Maybe import Data.Monoid.Compat ((<>)) import qualified Data.Set as Set import Data.Set (Set) import qualified Data.Text as TS import qualified Data.Text.IO as TS (putStrLn, hPutStrLn) import Data.Text.Lazy (toStrict) import qualified Data.Text.Lazy.Builder as TB import Data.Text.Lazy.Builder (Builder, toLazyText) import qualified Data.Text.Lazy as TL import qualified Data.Text.Lazy.IO as TL (putStrLn, hPutStrLn) import GHC.Exts (Char(..), Double(..), Float(..), Int(..), Word(..)) import GHC.Prim (Char#, Double#, Float#, Int#, Word#) import GHC.Show (appPrec, appPrec1) import Language.Haskell.TH.Datatype import Language.Haskell.TH.Lib import Language.Haskell.TH.Ppr hiding (appPrec) import Language.Haskell.TH.Syntax import Prelude () import Prelude.Compat import TextShow.Classes (TextShow(..), TextShow1(..), TextShow2(..), showbListWith, showbParen, showbCommaSpace, showbSpace, showtParen, showtCommaSpace, showtSpace, showtlParen, showtlCommaSpace, showtlSpace) import TextShow.Options (Options(..), GenTextMethods(..), defaultOptions) import TextShow.Utils (isInfixDataCon, isSymVar, isTupleString) ------------------------------------------------------------------------------- -- User-facing API ------------------------------------------------------------------------------- {- $deriveTextShow 'deriveTextShow' automatically generates a 'TextShow' instance declaration for a data type, newtype, or data family instance. This emulates what would (hypothetically) happen if you could attach a @deriving 'TextShow'@ clause to the end of a data declaration. Here are some examples of how to derive 'TextShow' for simple data types: @ {-# LANGUAGE TemplateHaskell #-} import TextShow.TH data Letter = A | B | C $('deriveTextShow' ''Letter) -- instance TextShow Letter where ... newtype Box a = Box a $('deriveTextShow' ''Box) -- instance TextShow a => TextShow (Box a) where ... @ 'deriveTextShow' can also be used to derive 'TextShow' instances for data family instances (which requires the @-XTypeFamilies@ extension). To do so, pass the name of a data or newtype instance constructor (NOT a data family name!) to 'deriveTextShow'. Note that the generated code may require the @-XFlexibleInstances@ extension. Some examples: @ {-# LANGUAGE FlexibleInstances, TemplateHaskell, TypeFamilies #-} import TextShow.TH (deriveTextShow) class AssocClass a where data AssocData a instance AssocClass Int where data AssocData Int = AssocDataInt1 Int | AssocDataInt2 Int Int $('deriveTextShow' 'AssocDataInt1) -- instance TextShow (AssocData Int) where ... -- Alternatively, one could use $(deriveTextShow 'AssocDataInt2) data family DataFam a b newtype instance DataFam () b = DataFamB b $('deriveTextShow' 'DataFamB) -- instance TextShow b => TextShow (DataFam () b) @ Note that at the moment, there are some limitations: * The 'Name' argument to 'deriveTextShow' must not be a type synonym. * 'deriveTextShow' makes the assumption that all type variables of kind @*@ require a 'TextShow' constraint when creating the type context. For example, if you have @data Phantom a = Phantom@, then @('deriveTextShow' ''Phantom)@ will generate @instance 'TextShow' a => 'TextShow' (Phantom a) where ...@, even though @'TextShow' a@ is not required. If you want a proper 'TextShow' instance for @Phantom@, you will need to use 'makeShowbPrec' (see the documentation of the @make@ functions for more information). * 'deriveTextShow' lacks the ability to properly detect data types with higher-kinded type parameters (e.g., @data HK f a = HK (f a)@) or with kinds other than @*@ (e.g., @data List a (empty :: Bool)@). If you wish to derive 'TextShow' instances for these data types, you will need to use 'makeShowbPrec'. * Some data constructors have arguments whose 'TextShow' instance depends on a typeclass besides 'TextShow'. For example, consider @newtype MyFixed a = MyFixed (Fixed a)@. @'Fixed' a@ is a 'TextShow' instance only if @a@ is an instance of both @HasResolution@ and 'TextShow'. Unfortunately, 'deriveTextShow' cannot infer that 'a' must be an instance of 'HasResolution', so it cannot create a 'TextShow' instance for @MyFixed@. However, you can use 'makeShowbPrec' to get around this. -} -- | Generates a 'TextShow' instance declaration for the given data type or data -- family instance. -- -- /Since: 2/ deriveTextShow :: Name -> Q [Dec] deriveTextShow = deriveTextShowOptions defaultOptions -- | Like 'deriveTextShow', but takes an 'Options' argument. -- -- /Since: 3.4/ deriveTextShowOptions :: Options -> Name -> Q [Dec] deriveTextShowOptions = deriveTextShowClass TextShow {- $deriveTextShow1 'deriveTextShow1' automatically generates a 'Show1' instance declaration for a data type, newtype, or data family instance that has at least one type variable. This emulates what would (hypothetically) happen if you could attach a @deriving 'TextShow1'@ clause to the end of a data declaration. Examples: @ {-# LANGUAGE TemplateHaskell #-} import TextShow.TH data Stream a = Stream a (Stream a) $('deriveTextShow1' ''Stream) -- instance TextShow1 TextStream where ... newtype WrappedFunctor f a = WrapFunctor (f a) $('deriveTextShow1' ''WrappedFunctor) -- instance TextShow1 f => TextShow1 (WrappedFunctor f) where ... @ The same restrictions that apply to 'deriveTextShow' also apply to 'deriveTextShow1', with some caveats: * With 'deriveTextShow1', the last type variable must be of kind @*@. For other ones, type variables of kind @*@ are assumed to require a 'TextShow' context, and type variables of kind @* -> *@ are assumed to require a 'TextShow1' context. For more complicated scenarios, use 'makeLiftShowbPrec'. * If using @-XDatatypeContexts@, a datatype constraint cannot mention the last type variable. For example, @data Ord a => Illegal a = Illegal a@ cannot have a derived 'TextShow1' instance. * If the last type variable is used within a data field of a constructor, it must only be used in the last argument of the data type constructor. For example, @data Legal a = Legal (Either Int a)@ can have a derived 'TextShow1' instance, but @data Illegal a = Illegal (Either a a)@ cannot. * Data family instances must be able to eta-reduce the last type variable. In other words, if you have a instance of the form: @ data family Family a1 ... an t data instance Family e1 ... e2 v = ... @ Then the following conditions must hold: 1. @v@ must be a type variable. 2. @v@ must not be mentioned in any of @e1@, ..., @e2@. -} -- | Generates a 'TextShow1' instance declaration for the given data type or data -- family instance. -- -- /Since: 2/ deriveTextShow1 :: Name -> Q [Dec] deriveTextShow1 = deriveTextShow1Options defaultOptions -- | Like 'deriveTextShow1', but takes an 'Options' argument. -- -- /Since: 3.4/ deriveTextShow1Options :: Options -> Name -> Q [Dec] deriveTextShow1Options = deriveTextShowClass TextShow1 {- $deriveTextShow2 'deriveTextShow2' automatically generates a 'TextShow2' instance declaration for a data type, newtype, or data family instance that has at least two type variables. This emulates what would (hypothetically) happen if you could attach a @deriving 'TextShow2'@ clause to the end of a data declaration. Examples: @ {-# LANGUAGE TemplateHaskell #-} import TextShow.TH data OneOrNone a b = OneL a | OneR b | None $('deriveTextShow2' ''OneOrNone) -- instance TextShow2 OneOrNone where ... newtype WrappedBifunctor f a b = WrapBifunctor (f a b) $('deriveTextShow2' ''WrappedBifunctor) -- instance TextShow2 f => TextShow2 (WrappedBifunctor f) where ... @ The same restrictions that apply to 'deriveTextShow' and 'deriveTextShow1' also apply to 'deriveTextShow2', with some caveats: * With 'deriveTextShow2', the last type variables must both be of kind @*@. For other ones, type variables of kind @*@ are assumed to require a 'TextShow' constraint, type variables of kind @* -> *@ are assumed to require a 'TextShow1' constraint, and type variables of kind @* -> * -> *@ are assumed to require a 'TextShow2' constraint. For more complicated scenarios, use 'makeLiftShowbPrec2'. * If using @-XDatatypeContexts@, a datatype constraint cannot mention either of the last two type variables. For example, @data Ord a => Illegal a b = Illegal a b@ cannot have a derived 'TextShow2' instance. * If either of the last two type variables is used within a data field of a constructor, it must only be used in the last two arguments of the data type constructor. For example, @data Legal a b = Legal (Int, Int, a, b)@ can have a derived 'TextShow2' instance, but @data Illegal a b = Illegal (a, b, a, b)@ cannot. * Data family instances must be able to eta-reduce the last two type variables. In other words, if you have a instance of the form: @ data family Family a1 ... an t1 t2 data instance Family e1 ... e2 v1 v2 = ... @ Then the following conditions must hold: 1. @v1@ and @v2@ must be distinct type variables. 2. Neither @v1@ not @v2@ must be mentioned in any of @e1@, ..., @e2@. -} -- | Generates a 'TextShow2' instance declaration for the given data type or data -- family instance. -- -- /Since: 2/ deriveTextShow2 :: Name -> Q [Dec] deriveTextShow2 = deriveTextShow2Options defaultOptions -- | Like 'deriveTextShow2', but takes an 'Options' argument. -- -- /Since: 3.4/ deriveTextShow2Options :: Options -> Name -> Q [Dec] deriveTextShow2Options = deriveTextShowClass TextShow2 {- $make There may be scenarios in which you want to show an arbitrary data type or data family instance without having to make the type an instance of 'TextShow'. For these cases, this modules provides several functions (all prefixed with @make@-) that splice the appropriate lambda expression into your source code. Example: This is particularly useful for creating instances for sophisticated data types. For example, 'deriveTextShow' cannot infer the correct type context for @newtype HigherKinded f a = HigherKinded (f a)@, since @f@ is of kind @* -> *@. However, it is still possible to derive a 'TextShow' instance for @HigherKinded@ without too much trouble using 'makeShowbPrec': @ {-# LANGUAGE FlexibleContexts, TemplateHaskell #-} import TextShow import TextShow.TH instance TextShow (f a) => TextShow (HigherKinded f a) where showbPrec = $(makeShowbPrec ''HigherKinded) @ -} -- | Generates a lambda expression which behaves like 'showt' (without requiring a -- 'TextShow' instance). -- -- /Since: 2/ makeShowt :: Name -> Q Exp makeShowt name = makeShowtPrec name `appE` integerE 0 -- | Generates a lambda expression which behaves like 'showtl' (without requiring a -- 'TextShow' instance). -- -- /Since: 2/ makeShowtl :: Name -> Q Exp makeShowtl name = makeShowtlPrec name `appE` integerE 0 -- | Generates a lambda expression which behaves like 'showtPrec' (without requiring a -- 'TextShow' instance). -- -- /Since: 2/ makeShowtPrec :: Name -> Q Exp makeShowtPrec = makeShowbPrecClass TextShow ShowtPrec defaultOptions -- | Generates a lambda expression which behaves like 'showtlPrec' (without -- requiring a 'TextShow' instance). -- -- /Since: 2/ makeShowtlPrec :: Name -> Q Exp makeShowtlPrec = makeShowbPrecClass TextShow ShowtlPrec defaultOptions -- | Generates a lambda expression which behaves like 'showtList' (without requiring a -- 'TextShow' instance). -- -- /Since: 2/ makeShowtList :: Name -> Q Exp makeShowtList name = [| toStrict . $(makeShowtlList name) |] -- | Generates a lambda expression which behaves like 'showtlList' (without -- requiring a 'TextShow' instance). -- -- /Since: 2/ makeShowtlList :: Name -> Q Exp makeShowtlList name = [| toLazyText . $(makeShowbList name) |] -- | Generates a lambda expression which behaves like 'showb' (without requiring a -- 'TextShow' instance). -- -- /Since: 2/ makeShowb :: Name -> Q Exp makeShowb name = makeShowbPrec name `appE` integerE 0 -- | Generates a lambda expression which behaves like 'showbPrec' (without requiring a -- 'TextShow' instance). -- -- /Since: 2/ makeShowbPrec :: Name -> Q Exp makeShowbPrec = makeShowbPrecClass TextShow ShowbPrec defaultOptions -- | Generates a lambda expression which behaves like 'liftShowbPrec' (without -- requiring a 'TextShow1' instance). -- -- /Since: 3/ makeLiftShowbPrec :: Name -> Q Exp makeLiftShowbPrec = makeShowbPrecClass TextShow1 ShowbPrec defaultOptions -- | Generates a lambda expression which behaves like 'showbPrec1' (without -- requiring a 'TextShow1' instance). -- -- /Since: 2/ makeShowbPrec1 :: Name -> Q Exp makeShowbPrec1 name = [| $(makeLiftShowbPrec name) showbPrec showbList |] -- | Generates a lambda expression which behaves like 'liftShowbPrec2' (without -- requiring a 'TextShow2' instance). -- -- /Since: 3/ makeLiftShowbPrec2 :: Name -> Q Exp makeLiftShowbPrec2 = makeShowbPrecClass TextShow2 ShowbPrec defaultOptions -- | Generates a lambda expression which behaves like 'showbPrec2' (without -- requiring a 'TextShow2' instance). -- -- /Since: 2/ makeShowbPrec2 :: Name -> Q Exp makeShowbPrec2 name = [| $(makeLiftShowbPrec2 name) showbPrec showbList showbPrec showbList |] -- | Generates a lambda expression which behaves like 'showbList' (without requiring a -- 'TextShow' instance). -- -- /Since: 2/ makeShowbList :: Name -> Q Exp makeShowbList name = [| showbListWith $(makeShowb name) |] -- | Generates a lambda expression which behaves like 'printT' (without requiring a -- 'TextShow' instance). -- -- /Since: 2/ makePrintT :: Name -> Q Exp makePrintT name = [| TS.putStrLn . $(makeShowt name) |] -- | Generates a lambda expression which behaves like 'printTL' (without requiring a -- 'TextShow' instance). -- -- /Since: 2/ makePrintTL :: Name -> Q Exp makePrintTL name = [| TL.putStrLn . $(makeShowtl name) |] -- | Generates a lambda expression which behaves like 'hPrintT' (without requiring a -- 'TextShow' instance). -- -- /Since: 2/ makeHPrintT :: Name -> Q Exp makeHPrintT name = [| \h -> TS.hPutStrLn h . $(makeShowt name) |] -- | Generates a lambda expression which behaves like 'hPrintTL' (without -- requiring a 'TextShow' instance). -- -- /Since: 2/ makeHPrintTL :: Name -> Q Exp makeHPrintTL name = [| \h -> TL.hPutStrLn h . $(makeShowtl name) |] ------------------------------------------------------------------------------- -- Code generation ------------------------------------------------------------------------------- -- | Derive a TextShow(1)(2) instance declaration (depending on the TextShowClass -- argument's value). deriveTextShowClass :: TextShowClass -> Options -> Name -> Q [Dec] deriveTextShowClass tsClass opts name = do info <- reifyDatatype name case info of DatatypeInfo { datatypeContext = ctxt , datatypeName = parentName , datatypeVars = vars , datatypeVariant = variant , datatypeCons = cons } -> do (instanceCxt, instanceType) <- buildTypeInstance tsClass parentName ctxt vars variant (:[]) <$> instanceD (return instanceCxt) (return instanceType) (showbPrecDecs tsClass opts vars cons) -- | Generates a declaration defining the primary function corresponding to a -- particular class (showbPrec for TextShow, liftShowbPrec for TextShow1, and -- liftShowbPrec2 for TextShow2). showbPrecDecs :: TextShowClass -> Options -> [Type] -> [ConstructorInfo] -> [Q Dec] showbPrecDecs tsClass opts vars cons = [genMethod ShowbPrec (showbPrecName tsClass)] ++ if tsClass == TextShow && shouldGenTextMethods then [genMethod ShowtPrec 'showtPrec, genMethod ShowtlPrec 'showtlPrec] else [] where shouldGenTextMethods :: Bool shouldGenTextMethods = case genTextMethods opts of AlwaysTextMethods -> True SometimesTextMethods -> all isNullaryCon cons NeverTextMethods -> False genMethod :: TextShowFun -> Name -> Q Dec genMethod method methodName = funD methodName [ clause [] (normalB $ makeTextShowForCons tsClass method opts vars cons) [] ] -- | Generates a lambda expression which behaves like showbPrec (for TextShow), -- liftShowbPrec (for TextShow1), or liftShowbPrec2 (for TextShow2). makeShowbPrecClass :: TextShowClass -> TextShowFun -> Options -> Name -> Q Exp makeShowbPrecClass tsClass tsFun opts name = do info <- reifyDatatype name case info of DatatypeInfo { datatypeContext = ctxt , datatypeName = parentName , datatypeVars = vars , datatypeVariant = variant , datatypeCons = cons } -> -- We force buildTypeInstance here since it performs some checks for whether -- or not the provided datatype can actually have showbPrec/liftShowbPrec/etc. -- implemented for it, and produces errors if it can't. buildTypeInstance tsClass parentName ctxt vars variant >> makeTextShowForCons tsClass tsFun opts vars cons -- | Generates a lambda expression for showbPrec/liftShowbPrec/etc. for the -- given constructors. All constructors must be from the same type. makeTextShowForCons :: TextShowClass -> TextShowFun -> Options -> [Type] -> [ConstructorInfo] -> Q Exp makeTextShowForCons tsClass tsFun opts vars cons = do p <- newName "p" value <- newName "value" sps <- newNameList "sp" $ fromEnum tsClass sls <- newNameList "sl" $ fromEnum tsClass let spls = zip sps sls spsAndSls = interleave sps sls lastTyVars = map varTToName $ drop (length vars - fromEnum tsClass) vars splMap = Map.fromList $ zip lastTyVars spls makeFun | null cons && emptyCaseBehavior opts && ghc7'8OrLater = caseE (varE value) [] | null cons = appE (varE 'seq) (varE value) `appE` appE (varE 'error) (stringE $ "Void " ++ nameBase (showPrecName tsClass tsFun)) | otherwise = caseE (varE value) (map (makeTextShowForCon p tsClass tsFun splMap) cons) lamE (map varP $ spsAndSls ++ [p, value]) . appsE $ [ varE $ showPrecConstName tsClass tsFun , makeFun ] ++ map varE spsAndSls ++ [varE p, varE value] where ghc7'8OrLater :: Bool #if __GLASGOW_HASKELL__ >= 708 ghc7'8OrLater = True #else ghc7'8OrLater = False #endif -- | Generates a lambda expression for howbPrec/liftShowbPrec/etc. for a -- single constructor. makeTextShowForCon :: Name -> TextShowClass -> TextShowFun -> TyVarMap -> ConstructorInfo -> Q Match makeTextShowForCon _ _ tsFun _ (ConstructorInfo { constructorName = conName, constructorFields = [] }) = match (conP conName []) (normalB $ varE (fromStringName tsFun) `appE` stringE (parenInfixConName conName "")) [] makeTextShowForCon p tsClass tsFun tvMap (ConstructorInfo { constructorName = conName , constructorVariant = NormalConstructor , constructorFields = [argTy] }) = do argTy' <- resolveTypeSynonyms argTy arg <- newName "arg" let showArg = makeTextShowForArg appPrec1 tsClass tsFun conName tvMap argTy' arg namedArg = infixApp (varE (fromStringName tsFun) `appE` stringE (parenInfixConName conName " ")) [| (<>) |] showArg match (conP conName [varP arg]) (normalB $ varE (showParenName tsFun) `appE` infixApp (varE p) [| (>) |] (integerE appPrec) `appE` namedArg) [] makeTextShowForCon p tsClass tsFun tvMap (ConstructorInfo { constructorName = conName , constructorVariant = NormalConstructor , constructorFields = argTys }) = do argTys' <- mapM resolveTypeSynonyms argTys args <- newNameList "arg" $ length argTys' if isNonUnitTuple conName then do let showArgs = zipWith (makeTextShowForArg 0 tsClass tsFun conName tvMap) argTys' args parenCommaArgs = (varE (singletonName tsFun) `appE` charE '(') : intersperse (varE (singletonName tsFun) `appE` charE ',') showArgs mappendArgs = foldr' (`infixApp` [| (<>) |]) (varE (singletonName tsFun) `appE` charE ')') parenCommaArgs match (conP conName $ map varP args) (normalB mappendArgs) [] else do let showArgs = zipWith (makeTextShowForArg appPrec1 tsClass tsFun conName tvMap) argTys' args mappendArgs = foldr1 (\v q -> infixApp v [| (<>) |] (infixApp (varE $ showSpaceName tsFun) [| (<>) |] q)) showArgs namedArgs = infixApp (varE (fromStringName tsFun) `appE` stringE (parenInfixConName conName " ")) [| (<>) |] mappendArgs match (conP conName $ map varP args) (normalB $ varE (showParenName tsFun) `appE` infixApp (varE p) [| (>) |] (integerE appPrec) `appE` namedArgs) [] makeTextShowForCon p tsClass tsFun tvMap (ConstructorInfo { constructorName = conName , constructorVariant = RecordConstructor argNames , constructorFields = argTys }) = do argTys' <- mapM resolveTypeSynonyms argTys args <- newNameList "arg" $ length argTys' let showArgs = concatMap (\(argName, argTy, arg) -> let argNameBase = nameBase argName infixRec = showParen (isSymVar argNameBase) (showString argNameBase) "" in [ varE (fromStringName tsFun) `appE` stringE (infixRec ++ " = ") , makeTextShowForArg 0 tsClass tsFun conName tvMap argTy arg , varE (showCommaSpaceName tsFun) ] ) (zip3 argNames argTys' args) braceCommaArgs = (varE (singletonName tsFun) `appE` charE '{') : take (length showArgs - 1) showArgs mappendArgs = foldr' (`infixApp` [| (<>) |]) (varE (singletonName tsFun) `appE` charE '}') braceCommaArgs namedArgs = infixApp (varE (fromStringName tsFun) `appE` stringE (parenInfixConName conName " ")) [| (<>) |] mappendArgs match (conP conName $ map varP args) (normalB $ varE (showParenName tsFun) `appE` infixApp (varE p) [| (>) |] (integerE appPrec) `appE` namedArgs) [] makeTextShowForCon p tsClass tsFun tvMap (ConstructorInfo { constructorName = conName , constructorVariant = InfixConstructor , constructorFields = argTys }) = do [alTy, arTy] <- mapM resolveTypeSynonyms argTys al <- newName "argL" ar <- newName "argR" fi <- fromMaybe defaultFixity <$> reifyFixityCompat conName let conPrec = case fi of Fixity prec _ -> prec opName = nameBase conName infixOpE = appE (varE $ fromStringName tsFun) . stringE $ if isInfixDataCon opName then " " ++ opName ++ " " else " `" ++ opName ++ "` " match (infixP (varP al) conName (varP ar)) (normalB $ (varE (showParenName tsFun) `appE` infixApp (varE p) [| (>) |] (integerE conPrec)) `appE` (infixApp (makeTextShowForArg (conPrec + 1) tsClass tsFun conName tvMap alTy al) [| (<>) |] (infixApp infixOpE [| (<>) |] (makeTextShowForArg (conPrec + 1) tsClass tsFun conName tvMap arTy ar))) ) [] -- | Generates a lambda expression for howbPrec/liftShowbPrec/etc. for an -- argument of a constructor. makeTextShowForArg :: Int -> TextShowClass -> TextShowFun -> Name -> TyVarMap -> Type -> Name -> Q Exp makeTextShowForArg p _ tsFun _ _ (ConT tyName) tyExpName = showE where tyVarE, showPrecE :: Q Exp tyVarE = varE tyExpName showPrecE = varE (showPrecName TextShow tsFun) showE :: Q Exp showE | tyName == ''Char# = showPrimE 'C# oneHashE | tyName == ''Double# = showPrimE 'D# twoHashE | tyName == ''Float# = showPrimE 'F# oneHashE | tyName == ''Int# = showPrimE 'I# oneHashE | tyName == ''Word# = showPrimE 'W# twoHashE | otherwise = showPrecE `appE` integerE p `appE` tyVarE -- Starting with GHC 7.10, data types containing unlifted types with derived Show -- instances show hashed literals with actual hash signs, and negative hashed -- literals are not surrounded with parentheses. showPrimE :: Name -> Q Exp -> Q Exp showPrimE con _hashE #if __GLASGOW_HASKELL__ >= 711 = infixApp (showPrecE `appE` integerE 0 `appE` (conE con `appE` tyVarE)) [| (<>) |] _hashE #else = showPrecE `appE` integerE p `appE` (conE con `appE` tyVarE) #endif oneHashE, twoHashE :: Q Exp oneHashE = varE (singletonName tsFun) `appE` charE '#' twoHashE = varE (fromStringName tsFun) `appE` stringE "##" makeTextShowForArg p tsClass tsFun conName tvMap ty tyExpName = [| $(makeTextShowForType tsClass tsFun conName tvMap False ty) p $(varE tyExpName) |] -- | Generates a lambda expression for howbPrec/liftShowbPrec/etc. for a -- specific type. The generated expression depends on the number of type variables. -- -- 1. If the type is of kind * (T), apply showbPrec. -- 2. If the type is of kind * -> * (T a), apply liftShowbPrec $(makeTextShowForType a) -- 3. If the type is of kind * -> * -> * (T a b), apply -- liftShowbPrec2 $(makeTextShowForType a) $(makeTextShowForType b) makeTextShowForType :: TextShowClass -> TextShowFun -> Name -> TyVarMap -> Bool -- ^ True if we are using the function of type ([a] -> Builder), -- False if we are using the function of type (Int -> a -> Builder). -> Type -> Q Exp makeTextShowForType _ tsFun _ tvMap sl (VarT tyName) = varE $ case Map.lookup tyName tvMap of Just (spExp, slExp) -> if sl then slExp else spExp Nothing -> if sl then showListName TextShow tsFun else showPrecName TextShow tsFun makeTextShowForType tsClass tsFun conName tvMap sl (SigT ty _) = makeTextShowForType tsClass tsFun conName tvMap sl ty makeTextShowForType tsClass tsFun conName tvMap sl (ForallT _ _ ty) = makeTextShowForType tsClass tsFun conName tvMap sl ty makeTextShowForType tsClass tsFun conName tvMap sl ty = do let tyCon :: Type tyArgs :: [Type] tyCon :| tyArgs = unapplyTy ty numLastArgs :: Int numLastArgs = min (fromEnum tsClass) (length tyArgs) lhsArgs, rhsArgs :: [Type] (lhsArgs, rhsArgs) = splitAt (length tyArgs - numLastArgs) tyArgs tyVarNames :: [Name] tyVarNames = Map.keys tvMap itf <- isTyFamily tyCon if any (`mentionsName` tyVarNames) lhsArgs || itf && any (`mentionsName` tyVarNames) tyArgs then outOfPlaceTyVarError tsClass conName else if any (`mentionsName` tyVarNames) rhsArgs then appsE $ [ varE $ showPrecOrListName sl (toEnum numLastArgs) tsFun] ++ zipWith (makeTextShowForType tsClass tsFun conName tvMap) (cycle [False,True]) (interleave rhsArgs rhsArgs) else varE $ if sl then showListName TextShow tsFun else showPrecName TextShow tsFun ------------------------------------------------------------------------------- -- Template Haskell reifying and AST manipulation ------------------------------------------------------------------------------- -- For the given Types, generate an instance context and head. Coming up with -- the instance type isn't as simple as dropping the last types, as you need to -- be wary of kinds being instantiated with *. -- See Note [Type inference in derived instances] buildTypeInstance :: TextShowClass -- ^ TextShow, TextShow1, or TextShow2 -> Name -- ^ The type constructor or data family name -> Cxt -- ^ The datatype context -> [Type] -- ^ The types to instantiate the instance with -> DatatypeVariant -- ^ Are we dealing with a data family instance or not -> Q (Cxt, Type) buildTypeInstance tsClass tyConName dataCxt varTysOrig variant = do -- Make sure to expand through type/kind synonyms! Otherwise, the -- eta-reduction check might get tripped up over type variables in a -- synonym that are actually dropped. -- (See GHC Trac #11416 for a scenario where this actually happened.) varTysExp <- mapM resolveTypeSynonyms varTysOrig let remainingLength :: Int remainingLength = length varTysOrig - fromEnum tsClass droppedTysExp :: [Type] droppedTysExp = drop remainingLength varTysExp droppedStarKindStati :: [StarKindStatus] droppedStarKindStati = map canRealizeKindStar droppedTysExp -- Check there are enough types to drop and that all of them are either of -- kind * or kind k (for some kind variable k). If not, throw an error. when (remainingLength < 0 || any (== NotKindStar) droppedStarKindStati) $ derivingKindError tsClass tyConName let droppedKindVarNames :: [Name] droppedKindVarNames = catKindVarNames droppedStarKindStati -- Substitute kind * for any dropped kind variables varTysExpSubst :: [Type] varTysExpSubst = map (substNamesWithKindStar droppedKindVarNames) varTysExp remainingTysExpSubst, droppedTysExpSubst :: [Type] (remainingTysExpSubst, droppedTysExpSubst) = splitAt remainingLength varTysExpSubst -- All of the type variables mentioned in the dropped types -- (post-synonym expansion) droppedTyVarNames :: [Name] droppedTyVarNames = freeVariables droppedTysExpSubst -- If any of the dropped types were polykinded, ensure that they are of kind * -- after substituting * for the dropped kind variables. If not, throw an error. unless (all hasKindStar droppedTysExpSubst) $ derivingKindError tsClass tyConName let preds :: [Maybe Pred] kvNames :: [[Name]] kvNames' :: [Name] -- Derive instance constraints (and any kind variables which are specialized -- to * in those constraints) (preds, kvNames) = unzip $ map (deriveConstraint tsClass) remainingTysExpSubst kvNames' = concat kvNames -- Substitute the kind variables specialized in the constraints with * remainingTysExpSubst' :: [Type] remainingTysExpSubst' = map (substNamesWithKindStar kvNames') remainingTysExpSubst -- We now substitute all of the specialized-to-* kind variable names with -- *, but in the original types, not the synonym-expanded types. The reason -- we do this is a superficial one: we want the derived instance to resemble -- the datatype written in source code as closely as possible. For example, -- for the following data family instance: -- -- data family Fam a -- newtype instance Fam String = Fam String -- -- We'd want to generate the instance: -- -- instance C (Fam String) -- -- Not: -- -- instance C (Fam [Char]) remainingTysOrigSubst :: [Type] remainingTysOrigSubst = map (substNamesWithKindStar (union droppedKindVarNames kvNames')) $ take remainingLength varTysOrig isDataFamily :: Bool isDataFamily = case variant of Datatype -> False Newtype -> False DataInstance -> True NewtypeInstance -> True remainingTysOrigSubst' :: [Type] -- See Note [Kind signatures in derived instances] for an explanation -- of the isDataFamily check. remainingTysOrigSubst' = if isDataFamily then remainingTysOrigSubst else map unSigT remainingTysOrigSubst instanceCxt :: Cxt instanceCxt = catMaybes preds instanceType :: Type instanceType = AppT (ConT $ textShowClassName tsClass) $ applyTyCon tyConName remainingTysOrigSubst' -- If the datatype context mentions any of the dropped type variables, -- we can't derive an instance, so throw an error. when (any (`predMentionsName` droppedTyVarNames) dataCxt) $ datatypeContextError tyConName instanceType -- Also ensure the dropped types can be safely eta-reduced. Otherwise, -- throw an error. unless (canEtaReduce remainingTysExpSubst' droppedTysExpSubst) $ etaReductionError instanceType return (instanceCxt, instanceType) -- | Attempt to derive a constraint on a Type. If successful, return -- Just the constraint and any kind variable names constrained to *. -- Otherwise, return Nothing and the empty list. -- -- See Note [Type inference in derived instances] for the heuristics used to -- come up with constraints. deriveConstraint :: TextShowClass -> Type -> (Maybe Pred, [Name]) deriveConstraint tsClass t | not (isTyVar t) = (Nothing, []) | hasKindStar t = (Just (applyClass ''TextShow tName), []) | otherwise = case hasKindVarChain 1 t of Just ns | tsClass >= TextShow1 -> (Just (applyClass ''TextShow1 tName), ns) _ -> case hasKindVarChain 2 t of Just ns | tsClass == TextShow2 -> (Just (applyClass ''TextShow2 tName), ns) _ -> (Nothing, []) where tName :: Name tName = varTToName t {- Note [Kind signatures in derived instances] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ It is possible to put explicit kind signatures into the derived instances, e.g., instance C a => C (Data (f :: * -> *)) where ... But it is preferable to avoid this if possible. If we come up with an incorrect kind signature (which is entirely possible, since our type inferencer is pretty unsophisticated - see Note [Type inference in derived instances]), then GHC will flat-out reject the instance, which is quite unfortunate. Plain old datatypes have the advantage that you can avoid using any kind signatures at all in their instances. This is because a datatype declaration uses all type variables, so the types that we use in a derived instance uniquely determine their kinds. As long as we plug in the right types, the kind inferencer can do the rest of the work. For this reason, we use unSigT to remove all kind signatures before splicing in the instance context and head. Data family instances are trickier, since a data family can have two instances that are distinguished by kind alone, e.g., data family Fam (a :: k) data instance Fam (a :: * -> *) data instance Fam (a :: *) If we dropped the kind signatures for C (Fam a), then GHC will have no way of knowing which instance we are talking about. To avoid this scenario, we always include explicit kind signatures in data family instances. There is a chance that the inferred kind signatures will be incorrect, but if so, we can always fall back on the make- functions. Note [Type inference in derived instances] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Type inference is can be tricky to get right, and we want to avoid recreating the entirety of GHC's type inferencer in Template Haskell. For this reason, we will probably never come up with derived instance contexts that are as accurate as GHC's. But that doesn't mean we can't do anything! There are a couple of simple things we can do to make instance contexts that work for 80% of use cases: 1. If one of the last type parameters is polykinded, then its kind will be specialized to * in the derived instance. We note what kind variable the type parameter had and substitute it with * in the other types as well. For example, imagine you had data Data (a :: k) (b :: k) Then you'd want to derived instance to be: instance C (Data (a :: *)) Not: instance C (Data (a :: k)) 2. We naïvely come up with instance constraints using the following criteria: (i) If there's a type parameter n of kind *, generate a TextShow n constraint. (ii) If there's a type parameter n of kind k1 -> k2 (where k1/k2 are * or kind variables), then generate a TextShow1 n constraint, and if k1/k2 are kind variables, then substitute k1/k2 with * elsewhere in the types. We must consider the case where they are kind variables because you might have a scenario like this: newtype Compose (f :: k2 -> *) (g :: k1 -> k2) (a :: k1) = Compose (f (g a)) Which would have a derived TextShow1 instance of: instance (TextShow1 f, TextShow1 g) => TextShow1 (Compose f g) where ... (iii) If there's a type parameter n of kind k1 -> k2 -> k3 (where k1/k2/k3 are * or kind variables), then generate a TextShow2 constraint and perform kind substitution as in the other cases. -} ------------------------------------------------------------------------------- -- Error messages ------------------------------------------------------------------------------- -- | Either the given data type doesn't have enough type variables, or one of -- the type variables to be eta-reduced cannot realize kind *. derivingKindError :: TextShowClass -> Name -> a derivingKindError tsClass tyConName = error . showString "Cannot derive well-kinded instance of form ‘" . showString className . showChar ' ' . showParen True ( showString (nameBase tyConName) . showString " ..." ) . showString "‘\n\tClass " . showString className . showString " expects an argument of kind " . showString (pprint . createKindChain $ fromEnum tsClass) $ "" where className :: String className = nameBase $ textShowClassName tsClass -- | One of the last type variables cannot be eta-reduced (see the canEtaReduce -- function for the criteria it would have to meet). etaReductionError :: Type -> a etaReductionError instanceType = error $ "Cannot eta-reduce to an instance of form \n\tinstance (...) => " ++ pprint instanceType -- | The data type has a DatatypeContext which mentions one of the eta-reduced -- type variables. datatypeContextError :: Name -> Type -> a datatypeContextError dataName instanceType = error . showString "Can't make a derived instance of ‘" . showString (pprint instanceType) . showString "‘:\n\tData type ‘" . showString (nameBase dataName) . showString "‘ must not have a class context involving the last type argument(s)" $ "" -- | The data type mentions one of the n eta-reduced type variables in a place other -- than the last nth positions of a data type in a constructor's field. outOfPlaceTyVarError :: TextShowClass -> Name -> a outOfPlaceTyVarError tsClass conName = error . showString "Constructor ‘" . showString (nameBase conName) . showString "‘ must only use its last " . shows n . showString " type variable(s) within the last " . shows n . showString " argument(s) of a data type" $ "" where n :: Int n = fromEnum tsClass ------------------------------------------------------------------------------- -- Expanding type synonyms ------------------------------------------------------------------------------- applySubstitutionKind :: Map Name Kind -> Type -> Type #if MIN_VERSION_template_haskell(2,8,0) applySubstitutionKind = applySubstitution #else applySubstitutionKind _ t = t #endif substNameWithKind :: Name -> Kind -> Type -> Type substNameWithKind n k = applySubstitutionKind (Map.singleton n k) substNamesWithKindStar :: [Name] -> Type -> Type substNamesWithKindStar ns t = foldr' (flip substNameWithKind starK) t ns ------------------------------------------------------------------------------- -- Class-specific constants ------------------------------------------------------------------------------- -- | A representation of which TextShow variant is being derived. data TextShowClass = TextShow | TextShow1 | TextShow2 deriving (Enum, Eq, Ord) -- | A representation of which TextShow method is being used to -- implement something. data TextShowFun = ShowbPrec | ShowtPrec | ShowtlPrec fromStringName :: TextShowFun -> Name fromStringName ShowbPrec = 'TB.fromString fromStringName ShowtPrec = 'TS.pack fromStringName ShowtlPrec = 'TL.pack singletonName :: TextShowFun -> Name singletonName ShowbPrec = 'TB.singleton singletonName ShowtPrec = 'TS.singleton singletonName ShowtlPrec = 'TL.singleton showParenName :: TextShowFun -> Name showParenName ShowbPrec = 'showbParen showParenName ShowtPrec = 'showtParen showParenName ShowtlPrec = 'showtlParen showCommaSpaceName :: TextShowFun -> Name showCommaSpaceName ShowbPrec = 'showbCommaSpace showCommaSpaceName ShowtPrec = 'showtCommaSpace showCommaSpaceName ShowtlPrec = 'showtlCommaSpace showSpaceName :: TextShowFun -> Name showSpaceName ShowbPrec = 'showbSpace showSpaceName ShowtPrec = 'showtSpace showSpaceName ShowtlPrec = 'showtlSpace showPrecConstName :: TextShowClass -> TextShowFun -> Name showPrecConstName tsClass ShowbPrec = showbPrecConstName tsClass showPrecConstName TextShow ShowtPrec = 'showtPrecConst showPrecConstName TextShow ShowtlPrec = 'showtlPrecConst showPrecConstName _ _ = error "showPrecConstName" showbPrecConstName :: TextShowClass -> Name showbPrecConstName TextShow = 'showbPrecConst showbPrecConstName TextShow1 = 'liftShowbPrecConst showbPrecConstName TextShow2 = 'liftShowbPrec2Const textShowClassName :: TextShowClass -> Name textShowClassName TextShow = ''TextShow textShowClassName TextShow1 = ''TextShow1 textShowClassName TextShow2 = ''TextShow2 showPrecName :: TextShowClass -> TextShowFun -> Name showPrecName tsClass ShowbPrec = showbPrecName tsClass showPrecName TextShow ShowtPrec = 'showtPrec showPrecName TextShow ShowtlPrec = 'showtlPrec showPrecName _ _ = error "showPrecName" showbPrecName :: TextShowClass -> Name showbPrecName TextShow = 'showbPrec showbPrecName TextShow1 = 'liftShowbPrec showbPrecName TextShow2 = 'liftShowbPrec2 showListName :: TextShowClass -> TextShowFun -> Name showListName tsClass ShowbPrec = showbListName tsClass showListName TextShow ShowtPrec = 'showtPrec showListName TextShow ShowtlPrec = 'showtlPrec showListName _ _ = error "showListName" showbListName :: TextShowClass -> Name showbListName TextShow = 'showbList showbListName TextShow1 = 'liftShowbList showbListName TextShow2 = 'liftShowbList2 showPrecOrListName :: Bool -- ^ showbListName if True, showbPrecName if False -> TextShowClass -> TextShowFun -> Name showPrecOrListName False = showPrecName showPrecOrListName True = showListName -- | A type-restricted version of 'const'. This is useful when generating the lambda -- expression in 'makeShowbPrec' for a data type with only nullary constructors (since -- the expression wouldn't depend on the precedence). For example, if you had @data -- Nullary = Nullary@ and attempted to run @$(makeShowbPrec ''Nullary) Nullary@, simply -- ignoring the precedence argument would cause the type signature of @$(makeShowbPrec -- ''Nullary)@ to be @a -> Nullary -> Builder@, not @Int -> Nullary -> Builder@. showbPrecConst :: Builder -> Int -> a -> Builder showbPrecConst b _ _ = b showtPrecConst :: TS.Text -> Int -> a -> TS.Text showtPrecConst t _ _ = t showtlPrecConst :: TL.Text -> Int -> a -> TL.Text showtlPrecConst tl _ _ = tl liftShowbPrecConst :: Builder -> (Int -> a -> Builder) -> ([a] -> Builder) -> Int -> f a -> Builder liftShowbPrecConst b _ _ _ _ = b liftShowbPrec2Const :: Builder -> (Int -> a -> Builder) -> ([a] -> Builder) -> (Int -> b -> Builder) -> ([b] -> Builder) -> Int -> f a b -> Builder liftShowbPrec2Const b _ _ _ _ _ _ = b ------------------------------------------------------------------------------- -- StarKindStatus ------------------------------------------------------------------------------- -- | Whether a type is not of kind *, is of kind *, or is a kind variable. data StarKindStatus = NotKindStar | KindStar | IsKindVar Name deriving Eq -- | Does a Type have kind * or k (for some kind variable k)? canRealizeKindStar :: Type -> StarKindStatus canRealizeKindStar t | hasKindStar t = KindStar | otherwise = case t of #if MIN_VERSION_template_haskell(2,8,0) SigT _ (VarT k) -> IsKindVar k #endif _ -> NotKindStar -- | Returns 'Just' the kind variable 'Name' of a 'StarKindStatus' if it exists. -- Otherwise, returns 'Nothing'. starKindStatusToName :: StarKindStatus -> Maybe Name starKindStatusToName (IsKindVar n) = Just n starKindStatusToName _ = Nothing -- | Concat together all of the StarKindStatuses that are IsKindVar and extract -- the kind variables' Names out. catKindVarNames :: [StarKindStatus] -> [Name] catKindVarNames = mapMaybe starKindStatusToName ------------------------------------------------------------------------------- -- Assorted utilities ------------------------------------------------------------------------------- integerE :: Int -> Q Exp integerE = litE . integerL . fromIntegral charE :: Char -> Q Exp charE = litE . charL -- | Returns True if a Type has kind *. hasKindStar :: Type -> Bool hasKindStar VarT{} = True #if MIN_VERSION_template_haskell(2,8,0) hasKindStar (SigT _ StarT) = True #else hasKindStar (SigT _ StarK) = True #endif hasKindStar _ = False -- Returns True is a kind is equal to *, or if it is a kind variable. isStarOrVar :: Kind -> Bool #if MIN_VERSION_template_haskell(2,8,0) isStarOrVar StarT = True isStarOrVar VarT{} = True #else isStarOrVar StarK = True #endif isStarOrVar _ = False -- Generate a list of fresh names with a common prefix, and numbered suffixes. newNameList :: String -> Int -> Q [Name] newNameList prefix n = mapM (newName . (prefix ++) . show) [1..n] -- | @hasKindVarChain n kind@ Checks if @kind@ is of the form -- k_0 -> k_1 -> ... -> k_(n-1), where k0, k1, ..., and k_(n-1) can be * or -- kind variables. hasKindVarChain :: Int -> Type -> Maybe [Name] hasKindVarChain kindArrows t = let uk = uncurryKind (tyKind t) in if (length uk - 1 == kindArrows) && all isStarOrVar uk then Just (concatMap freeVariables uk) else Nothing -- | If a Type is a SigT, returns its kind signature. Otherwise, return *. tyKind :: Type -> Kind tyKind (SigT _ k) = k tyKind _ = starK -- | A mapping of type variable Names to their show function Names. For example, in a -- TextShow2 declaration, a TyVarMap might look like (a ~> sp1, b ~> sp2), where -- a and b are the last two type variables of the datatype, and sp1 and sp2 are the two -- functions which show their respective type variables. type TyVarMap = Map Name (Name, Name) -- | Checks if a 'Name' represents a tuple type constructor (other than '()') isNonUnitTuple :: Name -> Bool isNonUnitTuple = isTupleString . nameBase -- | Parenthesize an infix constructor name if it is being applied as a prefix -- function (e.g., data Amp a = (:&) a a) parenInfixConName :: Name -> ShowS parenInfixConName conName = let conNameBase = nameBase conName in showParen (isInfixDataCon conNameBase) $ showString conNameBase -- | Applies a typeclass constraint to a type. applyClass :: Name -> Name -> Pred #if MIN_VERSION_template_haskell(2,10,0) applyClass con t = AppT (ConT con) (VarT t) #else applyClass con t = ClassP con [VarT t] #endif -- | Checks to see if the last types in a data family instance can be safely eta- -- reduced (i.e., dropped), given the other types. This checks for three conditions: -- -- (1) All of the dropped types are type variables -- (2) All of the dropped types are distinct -- (3) None of the remaining types mention any of the dropped types canEtaReduce :: [Type] -> [Type] -> Bool canEtaReduce remaining dropped = all isTyVar dropped && allDistinct droppedNames -- Make sure not to pass something of type [Type], since Type -- didn't have an Ord instance until template-haskell-2.10.0.0 && not (any (`mentionsName` droppedNames) remaining) where droppedNames :: [Name] droppedNames = map varTToName dropped -- | Extract Just the Name from a type variable. If the argument Type is not a -- type variable, return Nothing. varTToName_maybe :: Type -> Maybe Name varTToName_maybe (VarT n) = Just n varTToName_maybe (SigT t _) = varTToName_maybe t varTToName_maybe _ = Nothing -- | Extract the Name from a type variable. If the argument Type is not a -- type variable, throw an error. varTToName :: Type -> Name varTToName = fromMaybe (error "Not a type variable!") . varTToName_maybe -- | Peel off a kind signature from a Type (if it has one). unSigT :: Type -> Type unSigT (SigT t _) = t unSigT t = t -- | Is the given type a variable? isTyVar :: Type -> Bool isTyVar (VarT _) = True isTyVar (SigT t _) = isTyVar t isTyVar _ = False -- | Is the given type a type family constructor (and not a data family constructor)? isTyFamily :: Type -> Q Bool isTyFamily (ConT n) = do info <- reify n return $ case info of #if MIN_VERSION_template_haskell(2,11,0) FamilyI OpenTypeFamilyD{} _ -> True #else FamilyI (FamilyD TypeFam _ _ _) _ -> True #endif #if MIN_VERSION_template_haskell(2,9,0) FamilyI ClosedTypeFamilyD{} _ -> True #endif _ -> False isTyFamily _ = return False -- | Are all of the items in a list (which have an ordering) distinct? -- -- This uses Set (as opposed to nub) for better asymptotic time complexity. allDistinct :: Ord a => [a] -> Bool allDistinct = allDistinct' Set.empty where allDistinct' :: Ord a => Set a -> [a] -> Bool allDistinct' uniqs (x:xs) | x `Set.member` uniqs = False | otherwise = allDistinct' (Set.insert x uniqs) xs allDistinct' _ _ = True -- | Does the given type mention any of the Names in the list? mentionsName :: Type -> [Name] -> Bool mentionsName = go where go :: Type -> [Name] -> Bool go (AppT t1 t2) names = go t1 names || go t2 names go (SigT t _k) names = go t names #if MIN_VERSION_template_haskell(2,8,0) || go _k names #endif go (VarT n) names = n `elem` names go _ _ = False -- | Does an instance predicate mention any of the Names in the list? predMentionsName :: Pred -> [Name] -> Bool #if MIN_VERSION_template_haskell(2,10,0) predMentionsName = mentionsName #else predMentionsName (ClassP n tys) names = n `elem` names || any (`mentionsName` names) tys predMentionsName (EqualP t1 t2) names = mentionsName t1 names || mentionsName t2 names #endif -- | Construct a type via curried application. applyTy :: Type -> [Type] -> Type applyTy = foldl' AppT -- | Fully applies a type constructor to its type variables. applyTyCon :: Name -> [Type] -> Type applyTyCon = applyTy . ConT -- | Split an applied type into its individual components. For example, this: -- -- @ -- Either Int Char -- @ -- -- would split to this: -- -- @ -- [Either, Int, Char] -- @ unapplyTy :: Type -> NonEmpty Type unapplyTy = NE.reverse . go where go :: Type -> NonEmpty Type go (AppT t1 t2) = t2 <| go t1 go (SigT t _) = go t go (ForallT _ _ t) = go t go t = t :| [] -- | Split a type signature by the arrows on its spine. For example, this: -- -- @ -- (Int -> String) -> Char -> () -- @ -- -- would split to this: -- -- @ -- [Int -> String, Char, ()] -- @ uncurryTy :: Type -> NonEmpty Type uncurryTy (AppT (AppT ArrowT t1) t2) = t1 <| uncurryTy t2 uncurryTy (SigT t _) = uncurryTy t uncurryTy (ForallT _ _ t) = uncurryTy t uncurryTy t = t :| [] -- | Like uncurryType, except on a kind level. uncurryKind :: Kind -> NonEmpty Kind #if MIN_VERSION_template_haskell(2,8,0) uncurryKind = uncurryTy #else uncurryKind (ArrowK k1 k2) = k1 <| uncurryKind k2 uncurryKind k = k :| [] #endif createKindChain :: Int -> Kind createKindChain = go starK where go :: Kind -> Int -> Kind go k !0 = k go k !n = go (arrowKCompat starK k) (n - 1) isNullaryCon :: ConstructorInfo -> Bool isNullaryCon (ConstructorInfo { constructorFields = [] }) = True isNullaryCon _ = False interleave :: [a] -> [a] -> [a] interleave (a1:a1s) (a2:a2s) = a1:a2:interleave a1s a2s interleave _ _ = [] {- Note [Matching functions with GADT type variables] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ When deriving TextShow2, there is a tricky corner case to consider: data Both a b where BothCon :: x -> x -> Both x x Which show functions should be applied to which arguments of BothCon? We have a choice, since both the function of type (Int -> a -> Builder) and of type (Int -> b -> Builder) can be applied to either argument. In such a scenario, the second show function takes precedence over the first show function, so the derived TextShow2 instance would be: instance TextShow Both where liftShowsPrec2 sp1 sp2 p (BothCon x1 x2) = showbParen (p > appPrec) $ "BothCon " <> sp2 appPrec1 x1 <> showbSpace <> sp2 appPrec1 x2 This is not an arbitrary choice, as this definition ensures that liftShowsPrec2 showsPrec = liftShowsPrec for a derived TextShow1 instance for Both. -}