{-# LANGUAGE BangPatterns #-} {-# LANGUAGE CPP #-} {-# LANGUAGE MagicHash #-} {-# LANGUAGE TemplateHaskell #-} {-| Module: TextShow.TH.Internal Copyright: (C) 2014-2015 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 ) where import Control.Monad (liftM, unless, when) #if MIN_VERSION_template_haskell(2,11,0) import Control.Monad ((<=<)) #endif import Data.Foldable.Compat import Data.List.Compat import qualified Data.List.NonEmpty as NE (drop, length, reverse, splitAt) import Data.List.NonEmpty (NonEmpty(..), (<|)) import qualified Data.Map as Map (fromList, findWithDefault, 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 Data.Text.Lazy.Builder (Builder, fromString, singleton, 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(..)) #if __GLASGOW_HASKELL__ >= 800 import GHC.Lexeme (startsConSym) #endif import GHC.Prim (Char#, Double#, Float#, Int#, Word#) import GHC.Show (appPrec, appPrec1) 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, showbSpace) import TextShow.Utils (isInfixTypeCon, 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 ... @ If you are using @template-haskell-2.7.0.0@ or later (i.e., GHC 7.4 or later), '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 = 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 = 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 = 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 = [| toStrict . $(makeShowtl name) |] -- | Generates a lambda expression which behaves like 'showtl' (without requiring a -- 'TextShow' instance). -- -- /Since: 2/ makeShowtl :: Name -> Q Exp makeShowtl name = [| toLazyText . $(makeShowb name) |] -- | Generates a lambda expression which behaves like 'showtPrec' (without requiring a -- 'TextShow' instance). -- -- /Since: 2/ makeShowtPrec :: Name -> Q Exp makeShowtPrec name = [| \p -> toStrict . $(makeShowtlPrec name) p |] -- | Generates a lambda expression which behaves like 'showtlPrec' (without -- requiring a 'TextShow' instance). -- -- /Since: 2/ makeShowtlPrec :: Name -> Q Exp makeShowtlPrec name = [| \p -> toLazyText . $(makeShowbPrec name) p |] -- | 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` [| zero |] where -- To prevent the generated TH code from having a type ascription zero :: Int zero = 0 -- | Generates a lambda expression which behaves like 'showbPrec' (without requiring a -- 'TextShow' instance). -- -- /Since: 2/ makeShowbPrec :: Name -> Q Exp makeShowbPrec = makeShowbPrecClass TextShow -- | Generates a lambda expression which behaves like 'liftShowbPrec' (without -- requiring a 'TextShow1' instance). -- -- /Since: 3/ makeLiftShowbPrec :: Name -> Q Exp makeLiftShowbPrec = makeShowbPrecClass TextShow1 -- | 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 -- | 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 . $(makeShowtl name) |] ------------------------------------------------------------------------------- -- Code generation ------------------------------------------------------------------------------- -- | Derive a TextShow(1)(2) instance declaration (depending on the TextShowClass -- argument's value). deriveTextShowClass :: TextShowClass -> Name -> Q [Dec] deriveTextShowClass tsClass name = withType name fromCons where fromCons :: Name -> Cxt -> [TyVarBndr] -> [Con] -> Maybe [Type] -> Q [Dec] fromCons name' ctxt tvbs cons mbTys = (:[]) <$> do (instanceCxt, instanceType) <- buildTypeInstance tsClass name' ctxt tvbs mbTys instanceD (return instanceCxt) (return instanceType) (showbPrecDecs tsClass 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 -> [Con] -> [Q Dec] showbPrecDecs tsClass cons = [ funD (showbPrecName tsClass) [ clause [] (normalB $ makeTextShowForCons tsClass cons) [] ] ] -- | Generates a lambda expression which behaves like showbPrec (for TextShow), -- liftShowbPrec (for TextShow1), or liftShowbPrec2 (for TextShow2). makeShowbPrecClass :: TextShowClass -> Name -> Q Exp makeShowbPrecClass tsClass name = withType name fromCons where fromCons :: Name -> Cxt -> [TyVarBndr] -> [Con] -> Maybe [Type] -> Q Exp fromCons name' ctxt tvbs cons mbTys = -- 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 name' ctxt tvbs mbTys `seq` makeTextShowForCons tsClass cons -- | Generates a lambda expression for showbPrec/liftShowbPrec/etc. for the -- given constructors. All constructors must be from the same type. makeTextShowForCons :: TextShowClass -> [Con] -> Q Exp makeTextShowForCons _ [] = error "Must have at least one data constructor" makeTextShowForCons tsClass 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 matches <- concatMapM (makeTextShowForCon p tsClass spls) cons lamE (map varP $ spsAndSls ++ [p, value]) . appsE $ [ varE $ showbPrecConstName tsClass , caseE (varE value) (map return matches) ] ++ map varE spsAndSls ++ [varE p, varE value] -- | Generates a lambda expression for howbPrec/liftShowbPrec/etc. for a -- single constructor. makeTextShowForCon :: Name -> TextShowClass -> [(Name, Name)] -> Con -> Q [Match] makeTextShowForCon _ _ _ (NormalC conName []) = do m <- match (conP conName []) (normalB [| fromString $(stringE (parenInfixConName conName "")) |]) [] return [m] makeTextShowForCon p tsClass spls (NormalC conName [_]) = do ([argTy], tvMap) <- reifyConTys tsClass spls conName arg <- newName "arg" let showArg = makeTextShowForArg appPrec1 tsClass conName tvMap argTy arg namedArg = [| fromString $(stringE (parenInfixConName conName " ")) <> $(showArg) |] m <- match (conP conName [varP arg]) (normalB [| showbParen ($(varE p) > $(lift appPrec)) $(namedArg) |]) [] return [m] makeTextShowForCon p tsClass spls (NormalC conName _) = do (argTys, tvMap) <- reifyConTys tsClass spls conName args <- newNameList "arg" $ length argTys m <- if isNonUnitTuple conName then do let showArgs = zipWith (makeTextShowForArg 0 tsClass conName tvMap) argTys args parenCommaArgs = [| singleton '(' |] : intersperse [| singleton ',' |] showArgs mappendArgs = foldr (`infixApp` [| (<>) |]) [| singleton ')' |] parenCommaArgs match (conP conName $ map varP args) (normalB mappendArgs) [] else do let showArgs = zipWith (makeTextShowForArg appPrec1 tsClass conName tvMap) argTys args mappendArgs = foldr1 (\v q -> [| $(v) <> showbSpace <> $(q) |]) showArgs namedArgs = [| fromString $(stringE (parenInfixConName conName " ")) <> $(mappendArgs) |] match (conP conName $ map varP args) (normalB [| showbParen ($(varE p) > $(lift appPrec)) $(namedArgs) |]) [] return [m] makeTextShowForCon p tsClass spls (RecC conName []) = makeTextShowForCon p tsClass spls $ NormalC conName [] makeTextShowForCon _p tsClass spls (RecC conName ts) = do (argTys, tvMap) <- reifyConTys tsClass spls conName args <- newNameList "arg" $ length argTys let showArgs = concatMap (\((argName, _, _), argTy, arg) -> [ [| fromString $(stringE (nameBase argName ++ " = ")) |] , makeTextShowForArg 0 tsClass conName tvMap argTy arg , [| fromString ", " |] ] ) (zip3 ts argTys args) braceCommaArgs = [| singleton '{' |] : take (length showArgs - 1) showArgs mappendArgs = foldr (`infixApp` [| (<>) |]) [| singleton '}' |] braceCommaArgs namedArgs = [| fromString $(stringE (parenInfixConName conName " ")) <> $(mappendArgs) |] m <- match (conP conName $ map varP args) (normalB #if __GLASGOW_HASKELL__ >= 711 namedArgs #else [| showbParen ($(varE _p) > $(lift appPrec)) $(namedArgs) |] #endif ) [] return [m] makeTextShowForCon p tsClass spls (InfixC _ conName _) = do ([alTy, arTy], tvMap) <- reifyConTys tsClass spls conName al <- newName "argL" ar <- newName "argR" info <- reify conName #if __GLASGOW_HASKELL__ >= 711 conPrec <- case info of DataConI{} -> do fi <- fromMaybe defaultFixity <$> reifyFixity conName case fi of Fixity prec _ -> return prec #else let conPrec = case info of DataConI _ _ _ (Fixity prec _) -> prec #endif _ -> error $ "TextShow.TH.makeTextShowForCon: Unsupported type: " ++ show info let opName = nameBase conName infixOpE = if isInfixTypeCon opName then [| fromString $(stringE $ " " ++ opName ++ " " ) |] else [| fromString $(stringE $ " `" ++ opName ++ "` ") |] m <- match (infixP (varP al) conName (varP ar)) (normalB $ appE [| showbParen ($(varE p) > conPrec) |] [| $(makeTextShowForArg (conPrec + 1) tsClass conName tvMap alTy al) <> $(infixOpE) <> $(makeTextShowForArg (conPrec + 1) tsClass conName tvMap arTy ar) |] ) [] return [m] makeTextShowForCon p tsClass spls (ForallC _ _ con) = makeTextShowForCon p tsClass spls con #if MIN_VERSION_template_haskell(2,11,0) makeTextShowForCon p tsClass spls (GadtC conNames ts _) = let con :: Name -> Q Con con conName = do mbFi <- reifyFixity conName return $ if startsConSym (head $ nameBase conName) && length ts == 2 && isJust mbFi then let [t1, t2] = ts in InfixC t1 conName t2 else NormalC conName ts in concatMapM (makeTextShowForCon p tsClass spls <=< con) conNames makeTextShowForCon p tsClass spls (RecGadtC conNames ts _) = concatMapM (makeTextShowForCon p tsClass spls . flip RecC ts) conNames #endif -- | Generates a lambda expression for howbPrec/liftShowbPrec/etc. for an -- argument of a constructor. makeTextShowForArg :: Int -> TextShowClass -> Name -> TyVarMap -> Type -> Name -> Q Exp makeTextShowForArg p _ _ _ (ConT tyName) tyExpName = #if __GLASGOW_HASKELL__ >= 711 -- 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. showE where tyVarE :: Q Exp tyVarE = varE tyExpName showE :: Q Exp showE | tyName == ''Char# = [| showbPrec 0 (C# $(tyVarE)) <> singleton '#' |] | tyName == ''Double# = [| showbPrec 0 (D# $(tyVarE)) <> fromString "##" |] | tyName == ''Float# = [| showbPrec 0 (F# $(tyVarE)) <> singleton '#' |] | tyName == ''Int# = [| showbPrec 0 (I# $(tyVarE)) <> singleton '#' |] | tyName == ''Word# = [| showbPrec 0 (W# $(tyVarE)) <> fromString "##" |] | otherwise = [| showbPrec p $(tyVarE) |] #else [| showbPrec p $(expr) |] where tyVarE :: Q Exp tyVarE = varE tyExpName expr :: Q Exp expr | tyName == ''Char# = [| C# $(tyVarE) |] | tyName == ''Double# = [| D# $(tyVarE) |] | tyName == ''Float# = [| F# $(tyVarE) |] | tyName == ''Int# = [| I# $(tyVarE) |] | tyName == ''Word# = [| W# $(tyVarE) |] | otherwise = tyVarE #endif makeTextShowForArg p tsClass conName tvMap ty tyExpName = [| $(makeTextShowForType tsClass 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 -> 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 _ _ tvMap sl (VarT tyName) = case Map.lookup tyName tvMap of Just (spExp, slExp) -> varE (if sl then slExp else spExp) Nothing -> if sl then [| showbList |] else [| showbPrec |] makeTextShowForType tsClass conName tvMap sl (SigT ty _) = makeTextShowForType tsClass conName tvMap sl ty makeTextShowForType tsClass conName tvMap sl (ForallT _ _ ty) = makeTextShowForType tsClass conName tvMap sl ty makeTextShowForType tsClass 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 appsE $ [ varE . showbPrecOrListName sl $ toEnum numLastArgs] ++ zipWith (makeTextShowForType tsClass conName tvMap) (cycle [False,True]) (interleave rhsArgs rhsArgs) ------------------------------------------------------------------------------- -- Template Haskell reifying and AST manipulation ------------------------------------------------------------------------------- -- | Extracts a plain type constructor's information. -- | Boilerplate for top level splices. -- -- The given Name must meet one of two criteria: -- -- 1. It must be the name of a type constructor of a plain data type or newtype. -- 2. It must be the name of a data family instance or newtype instance constructor. -- -- Any other value will result in an exception. withType :: Name -> (Name -> Cxt -> [TyVarBndr] -> [Con] -> Maybe [Type] -> Q a) -> Q a withType name f = do info <- reify name case info of TyConI dec -> case dec of DataD ctxt _ tvbs #if MIN_VERSION_template_haskell(2,11,0) _ #endif cons _ -> f name ctxt tvbs cons Nothing NewtypeD ctxt _ tvbs #if MIN_VERSION_template_haskell(2,11,0) _ #endif con _ -> f name ctxt tvbs [con] Nothing _ -> error $ ns ++ "Unsupported type: " ++ show dec #if MIN_VERSION_template_haskell(2,7,0) # if MIN_VERSION_template_haskell(2,11,0) DataConI _ _ parentName -> do # else DataConI _ _ parentName _ -> do # endif parentInfo <- reify parentName case parentInfo of # if MIN_VERSION_template_haskell(2,11,0) FamilyI (DataFamilyD _ tvbs _) decs -> # else FamilyI (FamilyD DataFam _ tvbs _) decs -> # endif let instDec = flip find decs $ \dec -> case dec of DataInstD _ _ _ # if MIN_VERSION_template_haskell(2,11,0) _ # endif cons _ -> any ((name ==) . constructorName) cons NewtypeInstD _ _ _ # if MIN_VERSION_template_haskell(2,11,0) _ # endif con _ -> name == constructorName con _ -> error $ ns ++ "Must be a data or newtype instance." in case instDec of Just (DataInstD ctxt _ instTys # if MIN_VERSION_template_haskell(2,11,0) _ # endif cons _) -> f parentName ctxt tvbs cons $ Just instTys Just (NewtypeInstD ctxt _ instTys # if MIN_VERSION_template_haskell(2,11,0) _ # endif con _) -> f parentName ctxt tvbs [con] $ Just instTys _ -> error $ ns ++ "Could not find data or newtype instance constructor." _ -> error $ ns ++ "Data constructor " ++ show name ++ " is not from a data family instance constructor." # if MIN_VERSION_template_haskell(2,11,0) FamilyI DataFamilyD{} _ -> # else FamilyI (FamilyD DataFam _ _ _) _ -> # endif error $ ns ++ "Cannot use a data family name. Use a data family instance constructor instead." _ -> error $ ns ++ "The name must be of a plain data type constructor, " ++ "or a data family instance constructor." #else DataConI{} -> dataConIError _ -> error $ ns ++ "The name must be of a plain type constructor." #endif where ns :: String ns = "TextShow.TH.withType: " -- | Deduces the instance context and head for an instance. buildTypeInstance :: TextShowClass -- ^ TextShow, TextShow1, or TextShow2 -> Name -- ^ The type constructor or data family name -> Cxt -- ^ The datatype context -> [TyVarBndr] -- ^ The type variables from the data type/data family declaration -> Maybe [Type] -- ^ 'Just' the types used to instantiate a data family instance, -- or 'Nothing' if it's a plain data type -> Q (Cxt, Type) -- Plain data type/newtype case buildTypeInstance tsClass tyConName dataCxt tvbs Nothing = let varTys :: [Type] varTys = map tvbToType tvbs in buildTypeInstanceFromTys tsClass tyConName dataCxt varTys False -- Data family instance case -- -- The CPP is present to work around a couple of annoying old GHC bugs. -- See Note [Polykinded data families in Template Haskell] buildTypeInstance tsClass parentName dataCxt tvbs (Just instTysAndKinds) = do #if !(MIN_VERSION_template_haskell(2,8,0)) || MIN_VERSION_template_haskell(2,10,0) let instTys :: [Type] instTys = zipWith stealKindForType tvbs instTysAndKinds #else let kindVarNames :: [Name] kindVarNames = nub $ concatMap (tyVarNamesOfType . tvbKind) tvbs numKindVars :: Int numKindVars = length kindVarNames givenKinds, givenKinds' :: [Kind] givenTys :: [Type] (givenKinds, givenTys) = splitAt numKindVars instTysAndKinds givenKinds' = map sanitizeStars givenKinds -- 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 -- It's quite awkward to import * from GHC.Prim, so we'll just -- hack our way around it. starKindName :: Name starKindName = mkNameG_tc "ghc-prim" "GHC.Prim" "*" -- If we run this code with GHC 7.8, we might have to generate extra type -- variables to compensate for any type variables that Template Haskell -- eta-reduced away. -- See Note [Polykinded data families in Template Haskell] xTypeNames <- newNameList "tExtra" (length tvbs - length givenTys) let xTys :: [Type] xTys = map VarT xTypeNames -- ^ Because these type variables were eta-reduced away, we can only -- determine their kind by using stealKindForType. Therefore, we mark -- them as VarT to ensure they will be given an explicit kind annotation -- (and so the kind inference machinery has the right information). substNamesWithKinds :: [(Name, Kind)] -> Type -> Type substNamesWithKinds nks t = foldr' (uncurry substNameWithKind) t nks -- The types from the data family instance might not have explicit kind -- annotations, which the kind machinery needs to work correctly. To -- compensate, we use stealKindForType to explicitly annotate any -- types without kind annotations. instTys :: [Type] instTys = map (substNamesWithKinds (zip kindVarNames givenKinds')) -- ^ Note that due to a GHC 7.8-specific bug -- (see Note [Polykinded data families in Template Haskell]), -- there may be more kind variable names than there are kinds -- to substitute. But this is OK! If a kind is eta-reduced, it -- means that is was not instantiated to something more specific, -- so we need not substitute it. Using stealKindForType will -- grab the correct kind. $ zipWith stealKindForType tvbs (givenTys ++ xTys) #endif buildTypeInstanceFromTys tsClass parentName dataCxt instTys True -- 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] buildTypeInstanceFromTys :: 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 -> Bool -- ^ True if it's a data family, False otherwise -> Q (Cxt, Type) buildTypeInstanceFromTys tsClass tyConName dataCxt varTysOrig isDataFamily = 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 expandSyn 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 = concatMap tyVarNamesOfType droppedTysExpSubst -- If any of the dropped types were polykinded, ensure that there 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 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 [Polykinded data families in Template Haskell] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ In order to come up with the correct instance context and head for an instance, e.g., instance C a => C (Data a) where ... We need to know the exact types and kinds used to instantiate the instance. For plain old datatypes, this is simple: every type must be a type variable, and Template Haskell reliably tells us the type variables and their kinds. Doing the same for data families proves to be much harder for three reasons: 1. On any version of Template Haskell, it may not tell you what an instantiated type's kind is. For instance, in the following data family instance: data family Fam (f :: * -> *) (a :: *) data instance Fam f a Then if we use TH's reify function, it would tell us the TyVarBndrs of the data family declaration are: [KindedTV f (AppT (AppT ArrowT StarT) StarT),KindedTV a StarT] and the instantiated types of the data family instance are: [VarT f1,VarT a1] We can't just pass [VarT f1,VarT a1] to buildTypeInstanceFromTys, since we have no way of knowing their kinds. Luckily, the TyVarBndrs tell us what the kind is in case an instantiated type isn't a SigT, so we use the stealKindForType function to ensure all of the instantiated types are SigTs before passing them to buildTypeInstanceFromTys. 2. On GHC 7.6 and 7.8, a bug is present in which Template Haskell lists all of the specified kinds of a data family instance efore any of the instantiated types. Fortunately, this is easy to deal with: you simply count the number of distinct kind variables in the data family declaration, take that many elements from the front of the Types list of the data family instance, substitute the kind variables with their respective instantiated kinds (which you took earlier), and proceed as normal. 3. On GHC 7.8, an even uglier bug is present (GHC Trac #9692) in which Template Haskell might not even list all of the Types of a data family instance, since they are eta-reduced away! And yes, kinds can be eta-reduced too. The simplest workaround is to count how many instantiated types are missing from the list and generate extra type variables to use in their place. Luckily, we needn't worry much if its kind was eta-reduced away, since using stealKindForType will get it back. 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 #if !(MIN_VERSION_template_haskell(2,7,0)) -- | Template Haskell didn't list all of a data family's instances upon reification -- until template-haskell-2.7.0.0, which is necessary for a derived TextShow(1)(2) -- instance to work. dataConIError :: a dataConIError = error . showString "Cannot use a data constructor." . showString "\n\t(Note: if you are trying to derive TextShow for a" . showString "\n\ttype family, use GHC >= 7.4 instead.)" $ "" #endif ------------------------------------------------------------------------------- -- Expanding type synonyms ------------------------------------------------------------------------------- -- | Expands all type synonyms in a type. Written by Dan Rosén in the -- @genifunctors@ package (licensed under BSD3). expandSyn :: Type -> Q Type expandSyn (ForallT tvs ctx t) = fmap (ForallT tvs ctx) $ expandSyn t expandSyn t@AppT{} = expandSynApp t [] expandSyn t@ConT{} = expandSynApp t [] expandSyn (SigT t k) = do t' <- expandSyn t k' <- expandSynKind k return (SigT t' k') expandSyn t = return t expandSynKind :: Kind -> Q Kind #if MIN_VERSION_template_haskell(2,8,0) expandSynKind = expandSyn #else expandSynKind = return -- There are no kind synonyms to deal with #endif expandSynApp :: Type -> [Type] -> Q Type expandSynApp (AppT t1 t2) ts = do t2' <- expandSyn t2 expandSynApp t1 (t2':ts) expandSynApp (ConT n) ts | nameBase n == "[]" = return $ foldl' AppT ListT ts expandSynApp t@(ConT n) ts = do info <- reify n case info of TyConI (TySynD _ tvs rhs) -> let (ts', ts'') = splitAt (length tvs) ts subs = mkSubst tvs ts' rhs' = substType subs rhs in expandSynApp rhs' ts'' _ -> return $ foldl' AppT t ts expandSynApp t ts = do t' <- expandSyn t return $ foldl' AppT t' ts type TypeSubst = Map Name Type type KindSubst = Map Name Kind mkSubst :: [TyVarBndr] -> [Type] -> TypeSubst mkSubst vs ts = let vs' = map un vs un (PlainTV v) = v un (KindedTV v _) = v in Map.fromList $ zip vs' ts substType :: TypeSubst -> Type -> Type substType subs (ForallT v c t) = ForallT v c $ substType subs t substType subs t@(VarT n) = Map.findWithDefault t n subs substType subs (AppT t1 t2) = AppT (substType subs t1) (substType subs t2) substType subs (SigT t k) = SigT (substType subs t) #if MIN_VERSION_template_haskell(2,8,0) (substType subs k) #else k #endif substType _ t = t substKind :: KindSubst -> Type -> Type #if MIN_VERSION_template_haskell(2,8,0) substKind = substType #else substKind _ = id -- There are no kind variables! #endif substNameWithKind :: Name -> Kind -> Type -> Type substNameWithKind n k = substKind (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) showbPrecConstName :: TextShowClass -> Name showbPrecConstName TextShow = 'showbPrecConst showbPrecConstName TextShow1 = 'liftShowbPrecConst showbPrecConstName TextShow2 = 'liftShowbPrec2Const textShowClassName :: TextShowClass -> Name textShowClassName TextShow = ''TextShow textShowClassName TextShow1 = ''TextShow1 textShowClassName TextShow2 = ''TextShow2 showbPrecName :: TextShowClass -> Name showbPrecName TextShow = 'showbPrec showbPrecName TextShow1 = 'liftShowbPrec showbPrecName TextShow2 = 'liftShowbPrec2 showbListName :: TextShowClass -> Name showbListName TextShow = 'showbList showbListName TextShow1 = 'liftShowbList showbListName TextShow2 = 'liftShowbList2 showbPrecOrListName :: Bool -- ^ showbListName if True, showbPrecName if False -> TextShowClass -> Name showbPrecOrListName False = showbPrecName showbPrecOrListName True = showbListName -- | 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 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 ------------------------------------------------------------------------------- -- | 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] -- | Gets all of the type/kind variable names mentioned somewhere in a Type. tyVarNamesOfType :: Type -> [Name] tyVarNamesOfType = go where go :: Type -> [Name] go (AppT t1 t2) = go t1 ++ go t2 go (SigT t _k) = go t #if MIN_VERSION_template_haskell(2,8,0) ++ go _k #endif go (VarT n) = [n] go _ = [] -- | Gets all of the type/kind variable names mentioned somewhere in a Kind. tyVarNamesOfKind :: Kind -> [Name] #if MIN_VERSION_template_haskell(2,8,0) tyVarNamesOfKind = tyVarNamesOfType #else tyVarNamesOfKind _ = [] -- There are no kind variables #endif -- | @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 tyVarNamesOfKind uk) else Nothing -- | If a Type is a SigT, returns its kind signature. Otherwise, return *. tyKind :: Type -> Kind tyKind (SigT _ k) = k tyKind _ = starK -- | If a VarT is missing an explicit kind signature, steal it from a TyVarBndr. stealKindForType :: TyVarBndr -> Type -> Type stealKindForType tvb t@VarT{} = SigT t (tvbKind tvb) stealKindForType _ t = t -- | Monadic version of concatMap concatMapM :: Monad m => (a -> m [b]) -> [a] -> m [b] concatMapM f xs = liftM concat (mapM f xs) -- | 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 (isInfixTypeCon conNameBase) $ showString conNameBase -- | Extracts the kind from a TyVarBndr. tvbKind :: TyVarBndr -> Kind tvbKind (PlainTV _) = starK tvbKind (KindedTV _ k) = k -- | Convert a TyVarBndr to a Type. tvbToType :: TyVarBndr -> Type tvbToType (PlainTV n) = VarT n tvbToType (KindedTV n k) = SigT (VarT n) k -- | 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 #elif MIN_VERSION_template_haskell(2,7,0) FamilyI (FamilyD TypeFam _ _ _) _ -> True #else TyConI (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 #if MIN_VERSION_template_haskell(2,8,0) go k !n = go (AppT (AppT ArrowT StarT) k) (n - 1) #else go k !n = go (ArrowK StarK k) (n - 1) #endif #if MIN_VERSION_template_haskell(2,7,0) -- | Extracts the name of a constructor. constructorName :: Con -> Name constructorName (NormalC name _ ) = name constructorName (RecC name _ ) = name constructorName (InfixC _ name _ ) = name constructorName (ForallC _ _ con) = constructorName con # if MIN_VERSION_template_haskell(2,11,0) constructorName (GadtC names _ _) = head names constructorName (RecGadtC names _ _) = head names # endif #endif interleave :: [a] -> [a] -> [a] interleave (a1:a1s) (a2:a2s) = a1:a2:interleave a1s a2s interleave _ _ = [] -- Determines the types of a constructor's arguments as well as the last type -- parameters (mapped to their show functions), expanding through any type synonyms. -- The type parameters are determined on a constructor-by-constructor basis since -- they may be refined to be particular types in a GADT. reifyConTys :: TextShowClass -> [(Name, Name)] -> Name -> Q ([Type], TyVarMap) reifyConTys tsClass spls conName = do info <- reify conName uncTy <- case info of DataConI _ ty _ #if !(MIN_VERSION_template_haskell(2,11,0)) _ #endif -> fmap uncurryTy (expandSyn ty) _ -> error "Must be a data constructor" let (argTys, [resTy]) = NE.splitAt (length uncTy - 1) uncTy unapResTy = unapplyTy resTy -- If one of the last type variables is refined to a particular type -- (i.e., not truly polymorphic), we mark it with Nothing and filter -- it out later, since we only apply show functions to arguments of -- a type that it (1) one of the last type variables, and (2) -- of a truly polymorphic type. mbTvNames = map varTToName_maybe $ NE.drop (NE.length unapResTy - fromEnum tsClass) unapResTy -- We use Map.fromList to ensure that if there are any duplicate type -- variables (as can happen in a GADT), the rightmost type variable gets -- associated with the show function. -- -- See Note [Matching functions with GADT type variables] tvMap = Map.fromList . catMaybes -- Drop refined types $ zipWith (\mbTvName sp -> fmap (\tvName -> (tvName, sp)) mbTvName) mbTvNames spls return (argTys, tvMap) {- 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. -}