{-# LANGUAGE BangPatterns #-} {-# LANGUAGE CPP #-} {-# LANGUAGE FlexibleInstances #-} {-# LANGUAGE NamedFieldPuns #-} {-# LANGUAGE NoImplicitPrelude #-} {-# LANGUAGE UndecidableInstances #-} #if __GLASGOW_HASKELL__ >= 800 -- a) THQ works on cross-compilers and unregisterised GHCs -- b) may make compilation faster as no dynamic loading is ever needed (not sure about this) -- c) removes one hindrance to have code inferred as SafeHaskell safe {-# LANGUAGE TemplateHaskellQuotes #-} #else {-# LANGUAGE TemplateHaskell #-} #endif #include "incoherent-compat.h" #include "overlapping-compat.h" {-| Module: Data.Aeson.TH Copyright: (c) 2011-2016 Bryan O'Sullivan (c) 2011 MailRank, Inc. License: BSD3 Stability: experimental Portability: portable Functions to mechanically derive 'ToJSON' and 'FromJSON' instances. Note that you need to enable the @TemplateHaskell@ language extension in order to use this module. An example shows how instances are generated for arbitrary data types. First we define a data type: @ data D a = Nullary | Unary Int | Product String Char a | Record { testOne :: Double , testTwo :: Bool , testThree :: D a } deriving Eq @ Next we derive the necessary instances. Note that we make use of the feature to change record field names. In this case we drop the first 4 characters of every field name. We also modify constructor names by lower-casing them: @ $('deriveJSON' 'defaultOptions'{'fieldLabelModifier' = 'drop' 4, 'constructorTagModifier' = map toLower} ''D) @ Now we can use the newly created instances. @ d :: D 'Int' d = Record { testOne = 3.14159 , testTwo = 'True' , testThree = Product \"test\" \'A\' 123 } @ >>> fromJSON (toJSON d) == Success d > True This also works for data family instances, but instead of passing in the data family name (with double quotes), we pass in a data family instance constructor (with a single quote): @ data family DF a data instance DF Int = DF1 Int | DF2 Int Int deriving Eq $('deriveJSON' 'defaultOptions' 'DF1) -- Alternatively, one could pass 'DF2 instead @ Please note that you can derive instances for tuples using the following syntax: @ -- FromJSON and ToJSON instances for 4-tuples. $('deriveJSON' 'defaultOptions' ''(,,,)) @ -} module Data.Aeson.TH ( -- * Encoding configuration Options(..) , SumEncoding(..) , defaultOptions , defaultTaggedObject -- * FromJSON and ToJSON derivation , deriveJSON , deriveJSON1 , deriveJSON2 , deriveToJSON , deriveToJSON1 , deriveToJSON2 , deriveFromJSON , deriveFromJSON1 , deriveFromJSON2 , mkToJSON , mkLiftToJSON , mkLiftToJSON2 , mkToEncoding , mkLiftToEncoding , mkLiftToEncoding2 , mkParseJSON , mkLiftParseJSON , mkLiftParseJSON2 ) where import Prelude.Compat import Control.Applicative ((<|>)) import Data.Aeson (Object, (.:), FromJSON(..), FromJSON1(..), FromJSON2(..), ToJSON(..), ToJSON1(..), ToJSON2(..)) import Data.Aeson.Types (Options(..), Parser, SumEncoding(..), Value(..), defaultOptions, defaultTaggedObject) import Data.Aeson.Types.Internal ((), JSONPathElement(Key)) import Data.Aeson.Types.FromJSON (parseOptionalFieldWith) import Data.Aeson.Types.ToJSON (fromPairs, pair) import Control.Monad (liftM2, unless, when) import Data.Foldable (foldr') #if MIN_VERSION_template_haskell(2,8,0) && !MIN_VERSION_template_haskell(2,10,0) import Data.List (nub) #endif import Data.List (foldl', genericLength, intercalate, partition, union) import Data.List.NonEmpty ((<|), NonEmpty((:|))) import Data.Map (Map) import Data.Maybe (catMaybes, fromMaybe, mapMaybe) import qualified Data.Monoid as Monoid import Data.Set (Set) #if MIN_VERSION_template_haskell(2,8,0) import Language.Haskell.TH hiding (Arity) #else import Language.Haskell.TH #endif import Language.Haskell.TH.Datatype #if MIN_VERSION_template_haskell(2,7,0) && !(MIN_VERSION_template_haskell(2,8,0)) import Language.Haskell.TH.Lib (starK) #endif #if MIN_VERSION_template_haskell(2,8,0) && !(MIN_VERSION_template_haskell(2,10,0)) import Language.Haskell.TH.Syntax (mkNameG_tc) #endif import Text.Printf (printf) import qualified Data.Aeson.Encoding.Internal as E import qualified Data.Foldable as F (all) import qualified Data.HashMap.Strict as H (lookup, toList) import qualified Data.List.NonEmpty as NE (length, reverse) import qualified Data.Map as M (fromList, keys, lookup , singleton, size) import qualified Data.Semigroup as Semigroup (Option(..)) import qualified Data.Set as Set (empty, insert, member) import qualified Data.Text as T (Text, pack, unpack) import qualified Data.Vector as V (unsafeIndex, null, length, create, empty) import qualified Data.Vector.Mutable as VM (unsafeNew, unsafeWrite) -------------------------------------------------------------------------------- -- Convenience -------------------------------------------------------------------------------- -- | Generates both 'ToJSON' and 'FromJSON' instance declarations for the given -- data type or data family instance constructor. -- -- This is a convienience function which is equivalent to calling both -- 'deriveToJSON' and 'deriveFromJSON'. deriveJSON :: Options -- ^ Encoding options. -> Name -- ^ Name of the type for which to generate 'ToJSON' and 'FromJSON' -- instances. -> Q [Dec] deriveJSON = deriveJSONBoth deriveToJSON deriveFromJSON -- | Generates both 'ToJSON1' and 'FromJSON1' instance declarations for the given -- data type or data family instance constructor. -- -- This is a convienience function which is equivalent to calling both -- 'deriveToJSON1' and 'deriveFromJSON1'. deriveJSON1 :: Options -- ^ Encoding options. -> Name -- ^ Name of the type for which to generate 'ToJSON1' and 'FromJSON1' -- instances. -> Q [Dec] deriveJSON1 = deriveJSONBoth deriveToJSON1 deriveFromJSON1 -- | Generates both 'ToJSON2' and 'FromJSON2' instance declarations for the given -- data type or data family instance constructor. -- -- This is a convienience function which is equivalent to calling both -- 'deriveToJSON2' and 'deriveFromJSON2'. deriveJSON2 :: Options -- ^ Encoding options. -> Name -- ^ Name of the type for which to generate 'ToJSON2' and 'FromJSON2' -- instances. -> Q [Dec] deriveJSON2 = deriveJSONBoth deriveToJSON2 deriveFromJSON2 -------------------------------------------------------------------------------- -- ToJSON -------------------------------------------------------------------------------- {- TODO: Don't constrain phantom type variables. data Foo a = Foo Int instance (ToJSON a) ⇒ ToJSON Foo where ... The above (ToJSON a) constraint is not necessary and perhaps undesirable. -} -- | Generates a 'ToJSON' instance declaration for the given data type or -- data family instance constructor. deriveToJSON :: Options -- ^ Encoding options. -> Name -- ^ Name of the type for which to generate a 'ToJSON' instance -- declaration. -> Q [Dec] deriveToJSON = deriveToJSONCommon toJSONClass -- | Generates a 'ToJSON1' instance declaration for the given data type or -- data family instance constructor. deriveToJSON1 :: Options -- ^ Encoding options. -> Name -- ^ Name of the type for which to generate a 'ToJSON1' instance -- declaration. -> Q [Dec] deriveToJSON1 = deriveToJSONCommon toJSON1Class -- | Generates a 'ToJSON2' instance declaration for the given data type or -- data family instance constructor. deriveToJSON2 :: Options -- ^ Encoding options. -> Name -- ^ Name of the type for which to generate a 'ToJSON2' instance -- declaration. -> Q [Dec] deriveToJSON2 = deriveToJSONCommon toJSON2Class deriveToJSONCommon :: JSONClass -- ^ The ToJSON variant being derived. -> Options -- ^ Encoding options. -> Name -- ^ Name of the type for which to generate an instance. -> Q [Dec] deriveToJSONCommon = deriveJSONClass [ (ToJSON, \jc _ -> consToValue Value jc) , (ToEncoding, \jc _ -> consToValue Encoding jc) ] -- | Generates a lambda expression which encodes the given data type or -- data family instance constructor as a 'Value'. mkToJSON :: Options -- ^ Encoding options. -> Name -- ^ Name of the type to encode. -> Q Exp mkToJSON = mkToJSONCommon toJSONClass -- | Generates a lambda expression which encodes the given data type or -- data family instance constructor as a 'Value' by using the given encoding -- function on occurrences of the last type parameter. mkLiftToJSON :: Options -- ^ Encoding options. -> Name -- ^ Name of the type to encode. -> Q Exp mkLiftToJSON = mkToJSONCommon toJSON1Class -- | Generates a lambda expression which encodes the given data type or -- data family instance constructor as a 'Value' by using the given encoding -- functions on occurrences of the last two type parameters. mkLiftToJSON2 :: Options -- ^ Encoding options. -> Name -- ^ Name of the type to encode. -> Q Exp mkLiftToJSON2 = mkToJSONCommon toJSON2Class mkToJSONCommon :: JSONClass -- ^ Which class's method is being derived. -> Options -- ^ Encoding options. -> Name -- ^ Name of the encoded type. -> Q Exp mkToJSONCommon = mkFunCommon (\jc _ -> consToValue Value jc) -- | Generates a lambda expression which encodes the given data type or -- data family instance constructor as a JSON string. mkToEncoding :: Options -- ^ Encoding options. -> Name -- ^ Name of the type to encode. -> Q Exp mkToEncoding = mkToEncodingCommon toJSONClass -- | Generates a lambda expression which encodes the given data type or -- data family instance constructor as a JSON string by using the given encoding -- function on occurrences of the last type parameter. mkLiftToEncoding :: Options -- ^ Encoding options. -> Name -- ^ Name of the type to encode. -> Q Exp mkLiftToEncoding = mkToEncodingCommon toJSON1Class -- | Generates a lambda expression which encodes the given data type or -- data family instance constructor as a JSON string by using the given encoding -- functions on occurrences of the last two type parameters. mkLiftToEncoding2 :: Options -- ^ Encoding options. -> Name -- ^ Name of the type to encode. -> Q Exp mkLiftToEncoding2 = mkToEncodingCommon toJSON2Class mkToEncodingCommon :: JSONClass -- ^ Which class's method is being derived. -> Options -- ^ Encoding options. -> Name -- ^ Name of the encoded type. -> Q Exp mkToEncodingCommon = mkFunCommon (\jc _ -> consToValue Encoding jc) -- | Helper function used by both 'deriveToJSON' and 'mkToJSON'. Generates -- code to generate a 'Value' or 'Encoding' of a number of constructors. All -- constructors must be from the same type. consToValue :: ToJSONFun -- ^ The method ('toJSON' or 'toEncoding') being derived. -> JSONClass -- ^ The ToJSON variant being derived. -> Options -- ^ Encoding options. -> [Type] -- ^ The types from the data type/data family instance declaration -> [ConstructorInfo] -- ^ Constructors for which to generate JSON generating code. -> Q Exp consToValue _ _ _ _ [] = error $ "Data.Aeson.TH.consToValue: " ++ "Not a single constructor given!" consToValue target jc opts instTys cons = do value <- newName "value" tjs <- newNameList "_tj" $ arityInt jc tjls <- newNameList "_tjl" $ arityInt jc let zippedTJs = zip tjs tjls interleavedTJs = interleave tjs tjls lastTyVars = map varTToName $ drop (length instTys - arityInt jc) instTys tvMap = M.fromList $ zip lastTyVars zippedTJs lamE (map varP $ interleavedTJs ++ [value]) $ caseE (varE value) (matches tvMap) where matches tvMap = case cons of -- A single constructor is directly encoded. The constructor itself may be -- forgotten. [con] | not (tagSingleConstructors opts) -> [argsToValue target jc tvMap opts False con] _ | allNullaryToStringTag opts && all isNullary cons -> [ match (conP conName []) (normalB $ conStr target opts conName) [] | con <- cons , let conName = constructorName con ] | otherwise -> [argsToValue target jc tvMap opts True con | con <- cons] -- | Name of the constructor as a quoted 'Value' or 'Encoding'. conStr :: ToJSONFun -> Options -> Name -> Q Exp conStr Value opts = appE [|String|] . conTxt opts conStr Encoding opts = appE [|E.text|] . conTxt opts -- | Name of the constructor as a quoted 'Text'. conTxt :: Options -> Name -> Q Exp conTxt opts = appE [|T.pack|] . stringE . conString opts -- | Name of the constructor. conString :: Options -> Name -> String conString opts = constructorTagModifier opts . nameBase -- | If constructor is nullary. isNullary :: ConstructorInfo -> Bool isNullary ConstructorInfo { constructorVariant = NormalConstructor , constructorFields = tys } = null tys isNullary _ = False -- | Wrap fields of a non-record constructor. See 'sumToValue'. opaqueSumToValue :: ToJSONFun -> Options -> Bool -> Bool -> Name -> ExpQ -> ExpQ opaqueSumToValue target opts multiCons nullary conName value = sumToValue target opts multiCons nullary conName value pairs where pairs contentsFieldName = pairE contentsFieldName value -- | Wrap fields of a record constructor. See 'sumToValue'. recordSumToValue :: ToJSONFun -> Options -> Bool -> Bool -> Name -> ExpQ -> ExpQ recordSumToValue target opts multiCons nullary conName pairs = sumToValue target opts multiCons nullary conName (fromPairsE pairs) (const pairs) -- | Wrap fields of a constructor. sumToValue :: ToJSONFun -- ^ The method being derived. -> Options -- ^ Deriving options. -> Bool -- ^ Does this type have multiple constructors. -> Bool -- ^ Is this constructor nullary. -> Name -- ^ Constructor name. -> ExpQ -- ^ Fields of the constructor as a 'Value' or 'Encoding'. -> (String -> ExpQ) -- ^ Representation of an 'Object' fragment used for the 'TaggedObject' -- variant; of type @[(Text,Value)]@ or @[Encoding]@, depending on the method -- being derived. -- -- - For non-records, produces a pair @"contentsFieldName":value@, -- given a @contentsFieldName@ as an argument. See 'opaqueSumToValue'. -- - For records, produces the list of pairs corresponding to fields of the -- encoded value (ignores the argument). See 'recordSumToValue'. -> ExpQ sumToValue target opts multiCons nullary conName value pairs | multiCons = case sumEncoding opts of TwoElemArray -> array target [conStr target opts conName, value] TaggedObject{tagFieldName, contentsFieldName} -> -- TODO: Maybe throw an error in case -- tagFieldName overwrites a field in pairs. let tag = pairE tagFieldName (conStr target opts conName) content = pairs contentsFieldName in fromPairsE $ if nullary then tag else infixApp tag [|(Monoid.<>)|] content ObjectWithSingleField -> objectE [(conString opts conName, value)] UntaggedValue | nullary -> conStr target opts conName UntaggedValue -> value | otherwise = value -- | Generates code to generate the JSON encoding of a single constructor. argsToValue :: ToJSONFun -> JSONClass -> TyVarMap -> Options -> Bool -> ConstructorInfo -> Q Match -- Polyadic constructors with special case for unary constructors. argsToValue target jc tvMap opts multiCons ConstructorInfo { constructorName = conName , constructorVariant = NormalConstructor , constructorFields = argTys } = do argTys' <- mapM resolveTypeSynonyms argTys let len = length argTys' args <- newNameList "arg" len let js = case [ dispatchToJSON target jc conName tvMap argTy `appE` varE arg | (arg, argTy) <- zip args argTys' ] of -- Single argument is directly converted. [e] -> e -- Zero and multiple arguments are converted to a JSON array. es -> array target es match (conP conName $ map varP args) (normalB $ opaqueSumToValue target opts multiCons (null argTys') conName js) [] -- Records. argsToValue target jc tvMap opts multiCons info@ConstructorInfo { constructorName = conName , constructorVariant = RecordConstructor fields , constructorFields = argTys } = case (unwrapUnaryRecords opts, not multiCons, argTys) of (True,True,[_]) -> argsToValue target jc tvMap opts multiCons (info{constructorVariant = NormalConstructor}) _ -> do argTys' <- mapM resolveTypeSynonyms argTys args <- newNameList "arg" $ length argTys' let pairs | omitNothingFields opts = infixApp maybeFields [|(Monoid.<>)|] restFields | otherwise = mconcatE (map pureToPair argCons) argCons = zip3 (map varE args) argTys' fields maybeFields = mconcatE (map maybeToPair maybes) restFields = mconcatE (map pureToPair rest) (maybes0, rest0) = partition isMaybe argCons (options, rest) = partition isOption rest0 maybes = maybes0 ++ map optionToMaybe options maybeToPair = toPairLifted True pureToPair = toPairLifted False toPairLifted lifted (arg, argTy, field) = let toValue = dispatchToJSON target jc conName tvMap argTy fieldName = fieldLabel opts field e arg' = pairE fieldName (toValue `appE` arg') in if lifted then do x <- newName "x" [|maybe mempty|] `appE` lam1E (varP x) (e (varE x)) `appE` arg else e arg match (conP conName $ map varP args) (normalB $ recordSumToValue target opts multiCons (null argTys) conName pairs) [] -- Infix constructors. argsToValue target jc tvMap opts multiCons ConstructorInfo { constructorName = conName , constructorVariant = InfixConstructor , constructorFields = argTys } = do [alTy, arTy] <- mapM resolveTypeSynonyms argTys al <- newName "argL" ar <- newName "argR" match (infixP (varP al) conName (varP ar)) ( normalB $ opaqueSumToValue target opts multiCons False conName $ array target [ dispatchToJSON target jc conName tvMap aTy `appE` varE a | (a, aTy) <- [(al,alTy), (ar,arTy)] ] ) [] isMaybe :: (a, Type, b) -> Bool isMaybe (_, AppT (ConT t) _, _) = t == ''Maybe isMaybe _ = False isOption :: (a, Type, b) -> Bool isOption (_, AppT (ConT t) _, _) = t == ''Semigroup.Option isOption _ = False optionToMaybe :: (ExpQ, b, c) -> (ExpQ, b, c) optionToMaybe (a, b, c) = ([|Semigroup.getOption|] `appE` a, b, c) (<^>) :: ExpQ -> ExpQ -> ExpQ (<^>) a b = infixApp a [|(E.><)|] b infixr 6 <^> (<%>) :: ExpQ -> ExpQ -> ExpQ (<%>) a b = a <^> [|E.comma|] <^> b infixr 4 <%> -- | Wrap a list of quoted 'Value's in a quoted 'Array' (of type 'Value'). array :: ToJSONFun -> [ExpQ] -> ExpQ array Encoding [] = [|E.emptyArray_|] array Value [] = [|Array V.empty|] array Encoding es = [|E.wrapArray|] `appE` foldr1 (<%>) es array Value es = do mv <- newName "mv" let newMV = bindS (varP mv) ([|VM.unsafeNew|] `appE` litE (integerL $ fromIntegral (length es))) stmts = [ noBindS $ [|VM.unsafeWrite|] `appE` varE mv `appE` litE (integerL ix) `appE` e | (ix, e) <- zip [(0::Integer)..] es ] ret = noBindS $ [|return|] `appE` varE mv [|Array|] `appE` (varE 'V.create `appE` doE (newMV:stmts++[ret])) -- | Wrap an associative list of keys and quoted values in a quoted 'Object'. objectE :: [(String, ExpQ)] -> ExpQ objectE = fromPairsE . mconcatE . fmap (uncurry pairE) -- | 'mconcat' a list of fixed length. -- -- > mconcatE [ [|x|], [|y|], [|z|] ] = [| x <> (y <> z) |] mconcatE :: [ExpQ] -> ExpQ mconcatE [] = [|Monoid.mempty|] mconcatE [x] = x mconcatE (x : xs) = infixApp x [|(Monoid.<>)|] (mconcatE xs) fromPairsE :: ExpQ -> ExpQ fromPairsE = ([|fromPairs|] `appE`) -- | Create (an encoding of) a key-value pair. -- -- > pairE "k" [|v|] = [|pair "k" v|] pairE :: String -> ExpQ -> ExpQ pairE k v = [|pair k|] `appE` v -------------------------------------------------------------------------------- -- FromJSON -------------------------------------------------------------------------------- -- | Generates a 'FromJSON' instance declaration for the given data type or -- data family instance constructor. deriveFromJSON :: Options -- ^ Encoding options. -> Name -- ^ Name of the type for which to generate a 'FromJSON' instance -- declaration. -> Q [Dec] deriveFromJSON = deriveFromJSONCommon fromJSONClass -- | Generates a 'FromJSON1' instance declaration for the given data type or -- data family instance constructor. deriveFromJSON1 :: Options -- ^ Encoding options. -> Name -- ^ Name of the type for which to generate a 'FromJSON1' instance -- declaration. -> Q [Dec] deriveFromJSON1 = deriveFromJSONCommon fromJSON1Class -- | Generates a 'FromJSON2' instance declaration for the given data type or -- data family instance constructor. deriveFromJSON2 :: Options -- ^ Encoding options. -> Name -- ^ Name of the type for which to generate a 'FromJSON3' instance -- declaration. -> Q [Dec] deriveFromJSON2 = deriveFromJSONCommon fromJSON2Class deriveFromJSONCommon :: JSONClass -- ^ The FromJSON variant being derived. -> Options -- ^ Encoding options. -> Name -- ^ Name of the type for which to generate an instance. -- declaration. -> Q [Dec] deriveFromJSONCommon = deriveJSONClass [(ParseJSON, consFromJSON)] -- | Generates a lambda expression which parses the JSON encoding of the given -- data type or data family instance constructor. mkParseJSON :: Options -- ^ Encoding options. -> Name -- ^ Name of the encoded type. -> Q Exp mkParseJSON = mkParseJSONCommon fromJSONClass -- | Generates a lambda expression which parses the JSON encoding of the given -- data type or data family instance constructor by using the given parsing -- function on occurrences of the last type parameter. mkLiftParseJSON :: Options -- ^ Encoding options. -> Name -- ^ Name of the encoded type. -> Q Exp mkLiftParseJSON = mkParseJSONCommon fromJSON1Class -- | Generates a lambda expression which parses the JSON encoding of the given -- data type or data family instance constructor by using the given parsing -- functions on occurrences of the last two type parameters. mkLiftParseJSON2 :: Options -- ^ Encoding options. -> Name -- ^ Name of the encoded type. -> Q Exp mkLiftParseJSON2 = mkParseJSONCommon fromJSON2Class mkParseJSONCommon :: JSONClass -- ^ Which class's method is being derived. -> Options -- ^ Encoding options. -> Name -- ^ Name of the encoded type. -> Q Exp mkParseJSONCommon = mkFunCommon consFromJSON -- | Helper function used by both 'deriveFromJSON' and 'mkParseJSON'. Generates -- code to parse the JSON encoding of a number of constructors. All constructors -- must be from the same type. consFromJSON :: JSONClass -- ^ The FromJSON variant being derived. -> Name -- ^ Name of the type to which the constructors belong. -> Options -- ^ Encoding options -> [Type] -- ^ The types from the data type/data family instance declaration -> [ConstructorInfo] -- ^ Constructors for which to generate JSON parsing code. -> Q Exp consFromJSON _ _ _ _ [] = error $ "Data.Aeson.TH.consFromJSON: " ++ "Not a single constructor given!" consFromJSON jc tName opts instTys cons = do value <- newName "value" pjs <- newNameList "_pj" $ arityInt jc pjls <- newNameList "_pjl" $ arityInt jc let zippedPJs = zip pjs pjls interleavedPJs = interleave pjs pjls lastTyVars = map varTToName $ drop (length instTys - arityInt jc) instTys tvMap = M.fromList $ zip lastTyVars zippedPJs lamE (map varP $ interleavedPJs ++ [value]) $ lamExpr value tvMap where checkExi tvMap con = checkExistentialContext jc tvMap (constructorContext con) (constructorName con) lamExpr value tvMap = case cons of [con] | not (tagSingleConstructors opts) -> checkExi tvMap con $ parseArgs jc tvMap tName opts con (Right value) _ | sumEncoding opts == UntaggedValue -> parseUntaggedValue tvMap cons value | otherwise -> caseE (varE value) $ if allNullaryToStringTag opts && all isNullary cons then allNullaryMatches else mixedMatches tvMap allNullaryMatches = [ do txt <- newName "txt" match (conP 'String [varP txt]) (guardedB $ [ liftM2 (,) (normalG $ infixApp (varE txt) [|(==)|] (conTxt opts conName) ) ([|pure|] `appE` conE conName) | con <- cons , let conName = constructorName con ] ++ [ liftM2 (,) (normalG [|otherwise|]) ( [|noMatchFail|] `appE` litE (stringL $ show tName) `appE` ([|T.unpack|] `appE` varE txt) ) ] ) [] , do other <- newName "other" match (varP other) (normalB $ [|noStringFail|] `appE` litE (stringL $ show tName) `appE` ([|valueConName|] `appE` varE other) ) [] ] mixedMatches tvMap = case sumEncoding opts of TaggedObject {tagFieldName, contentsFieldName} -> parseObject $ parseTaggedObject tvMap tagFieldName contentsFieldName UntaggedValue -> error "UntaggedValue: Should be handled already" ObjectWithSingleField -> parseObject $ parseObjectWithSingleField tvMap TwoElemArray -> [ do arr <- newName "array" match (conP 'Array [varP arr]) (guardedB [ liftM2 (,) (normalG $ infixApp ([|V.length|] `appE` varE arr) [|(==)|] (litE $ integerL 2)) (parse2ElemArray tvMap arr) , liftM2 (,) (normalG [|otherwise|]) ([|not2ElemArray|] `appE` litE (stringL $ show tName) `appE` ([|V.length|] `appE` varE arr)) ] ) [] , do other <- newName "other" match (varP other) ( normalB $ [|noArrayFail|] `appE` litE (stringL $ show tName) `appE` ([|valueConName|] `appE` varE other) ) [] ] parseObject f = [ do obj <- newName "obj" match (conP 'Object [varP obj]) (normalB $ f obj) [] , do other <- newName "other" match (varP other) ( normalB $ [|noObjectFail|] `appE` litE (stringL $ show tName) `appE` ([|valueConName|] `appE` varE other) ) [] ] parseTaggedObject tvMap typFieldName valFieldName obj = do conKey <- newName "conKey" doE [ bindS (varP conKey) (infixApp (varE obj) [|(.:)|] ([|T.pack|] `appE` stringE typFieldName)) , noBindS $ parseContents tvMap conKey (Left (valFieldName, obj)) 'conNotFoundFailTaggedObject ] parseUntaggedValue tvMap cons' conVal = foldr1 (\e e' -> infixApp e [|(<|>)|] e') (map (\x -> parseValue tvMap x conVal) cons') parseValue _tvMap ConstructorInfo { constructorName = conName , constructorVariant = NormalConstructor , constructorFields = [] } conVal = do str <- newName "str" caseE (varE conVal) [ match (conP 'String [varP str]) (guardedB [ liftM2 (,) (normalG $ infixApp (varE str) [|(==)|] (conTxt opts conName) ) ([|pure|] `appE` conE conName) ] ) [] , matchFailed tName conName "String" ] parseValue tvMap con conVal = checkExi tvMap con $ parseArgs jc tvMap tName opts con (Right conVal) parse2ElemArray tvMap arr = do conKey <- newName "conKey" conVal <- newName "conVal" let letIx n ix = valD (varP n) (normalB ([|V.unsafeIndex|] `appE` varE arr `appE` litE (integerL ix))) [] letE [ letIx conKey 0 , letIx conVal 1 ] (caseE (varE conKey) [ do txt <- newName "txt" match (conP 'String [varP txt]) (normalB $ parseContents tvMap txt (Right conVal) 'conNotFoundFail2ElemArray ) [] , do other <- newName "other" match (varP other) ( normalB $ [|firstElemNoStringFail|] `appE` litE (stringL $ show tName) `appE` ([|valueConName|] `appE` varE other) ) [] ] ) parseObjectWithSingleField tvMap obj = do conKey <- newName "conKey" conVal <- newName "conVal" caseE ([e|H.toList|] `appE` varE obj) [ match (listP [tupP [varP conKey, varP conVal]]) (normalB $ parseContents tvMap conKey (Right conVal) 'conNotFoundFailObjectSingleField) [] , do other <- newName "other" match (varP other) (normalB $ [|wrongPairCountFail|] `appE` litE (stringL $ show tName) `appE` ([|show . length|] `appE` varE other) ) [] ] parseContents tvMap conKey contents errorFun = caseE (varE conKey) [ match wildP ( guardedB $ [ do g <- normalG $ infixApp (varE conKey) [|(==)|] ([|T.pack|] `appE` conNameExp opts con) e <- checkExi tvMap con $ parseArgs jc tvMap tName opts con contents return (g, e) | con <- cons ] ++ [ liftM2 (,) (normalG [e|otherwise|]) ( varE errorFun `appE` litE (stringL $ show tName) `appE` listE (map ( litE . stringL . constructorTagModifier opts . nameBase . constructorName ) cons ) `appE` ([|T.unpack|] `appE` varE conKey) ) ] ) [] ] parseNullaryMatches :: Name -> Name -> [Q Match] parseNullaryMatches tName conName = [ do arr <- newName "arr" match (conP 'Array [varP arr]) (guardedB [ liftM2 (,) (normalG $ [|V.null|] `appE` varE arr) ([|pure|] `appE` conE conName) , liftM2 (,) (normalG [|otherwise|]) (parseTypeMismatch tName conName (litE $ stringL "an empty Array") (infixApp (litE $ stringL "Array of length ") [|(++)|] ([|show . V.length|] `appE` varE arr) ) ) ] ) [] , matchFailed tName conName "Array" ] parseUnaryMatches :: JSONClass -> TyVarMap -> Type -> Name -> [Q Match] parseUnaryMatches jc tvMap argTy conName = [ do arg <- newName "arg" match (varP arg) ( normalB $ infixApp (conE conName) [|(<$>)|] (dispatchParseJSON jc conName tvMap argTy `appE` varE arg) ) [] ] parseRecord :: JSONClass -> TyVarMap -> [Type] -> Options -> Name -> Name -> [Name] -> Name -> ExpQ parseRecord jc tvMap argTys opts tName conName fields obj = foldl' (\a b -> infixApp a [|(<*>)|] b) (infixApp (conE conName) [|(<$>)|] x) xs where x:xs = [ [|lookupField|] `appE` dispatchParseJSON jc conName tvMap argTy `appE` litE (stringL $ show tName) `appE` litE (stringL $ constructorTagModifier opts $ nameBase conName) `appE` varE obj `appE` ( [|T.pack|] `appE` stringE (fieldLabel opts field) ) | (field, argTy) <- zip fields argTys ] getValField :: Name -> String -> [MatchQ] -> Q Exp getValField obj valFieldName matches = do val <- newName "val" doE [ bindS (varP val) $ infixApp (varE obj) [|(.:)|] ([|T.pack|] `appE` litE (stringL valFieldName)) , noBindS $ caseE (varE val) matches ] matchCases :: Either (String, Name) Name -> [MatchQ] -> Q Exp matchCases (Left (valFieldName, obj)) = getValField obj valFieldName matchCases (Right valName) = caseE (varE valName) -- | Generates code to parse the JSON encoding of a single constructor. parseArgs :: JSONClass -- ^ The FromJSON variant being derived. -> TyVarMap -- ^ Maps the last type variables to their decoding -- function arguments. -> Name -- ^ Name of the type to which the constructor belongs. -> Options -- ^ Encoding options. -> ConstructorInfo -- ^ Constructor for which to generate JSON parsing code. -> Either (String, Name) Name -- ^ Left (valFieldName, objName) or -- Right valName -> Q Exp -- Nullary constructors. parseArgs _ _ _ _ ConstructorInfo { constructorName = conName , constructorVariant = NormalConstructor , constructorFields = [] } (Left _) = [|pure|] `appE` conE conName parseArgs _ _ tName _ ConstructorInfo { constructorName = conName , constructorVariant = NormalConstructor , constructorFields = [] } (Right valName) = caseE (varE valName) $ parseNullaryMatches tName conName -- Unary constructors. parseArgs jc tvMap _ _ ConstructorInfo { constructorName = conName , constructorVariant = NormalConstructor , constructorFields = [argTy] } contents = do argTy' <- resolveTypeSynonyms argTy matchCases contents $ parseUnaryMatches jc tvMap argTy' conName -- Polyadic constructors. parseArgs jc tvMap tName _ ConstructorInfo { constructorName = conName , constructorVariant = NormalConstructor , constructorFields = argTys } contents = do argTys' <- mapM resolveTypeSynonyms argTys let len = genericLength argTys' matchCases contents $ parseProduct jc tvMap argTys' tName conName len -- Records. parseArgs jc tvMap tName opts ConstructorInfo { constructorName = conName , constructorVariant = RecordConstructor fields , constructorFields = argTys } (Left (_, obj)) = do argTys' <- mapM resolveTypeSynonyms argTys parseRecord jc tvMap argTys' opts tName conName fields obj parseArgs jc tvMap tName opts info@ConstructorInfo { constructorName = conName , constructorVariant = RecordConstructor fields , constructorFields = argTys } (Right valName) = case (unwrapUnaryRecords opts,argTys) of (True,[_])-> parseArgs jc tvMap tName opts (info{constructorVariant = NormalConstructor}) (Right valName) _ -> do obj <- newName "recObj" argTys' <- mapM resolveTypeSynonyms argTys caseE (varE valName) [ match (conP 'Object [varP obj]) (normalB $ parseRecord jc tvMap argTys' opts tName conName fields obj) [] , matchFailed tName conName "Object" ] -- Infix constructors. Apart from syntax these are the same as -- polyadic constructors. parseArgs jc tvMap tName _ ConstructorInfo { constructorName = conName , constructorVariant = InfixConstructor , constructorFields = argTys } contents = do argTys' <- mapM resolveTypeSynonyms argTys matchCases contents $ parseProduct jc tvMap argTys' tName conName 2 -- | Generates code to parse the JSON encoding of an n-ary -- constructor. parseProduct :: JSONClass -- ^ The FromJSON variant being derived. -> TyVarMap -- ^ Maps the last type variables to their decoding -- function arguments. -> [Type] -- ^ The argument types of the constructor. -> Name -- ^ Name of the type to which the constructor belongs. -> Name -- ^ 'Con'structor name. -> Integer -- ^ 'Con'structor arity. -> [Q Match] parseProduct jc tvMap argTys tName conName numArgs = [ do arr <- newName "arr" -- List of: "parseJSON (arr `V.unsafeIndex` )" let x:xs = [ dispatchParseJSON jc conName tvMap argTy `appE` infixApp (varE arr) [|V.unsafeIndex|] (litE $ integerL ix) | (argTy, ix) <- zip argTys [0 .. numArgs - 1] ] match (conP 'Array [varP arr]) (normalB $ condE ( infixApp ([|V.length|] `appE` varE arr) [|(==)|] (litE $ integerL numArgs) ) ( foldl' (\a b -> infixApp a [|(<*>)|] b) (infixApp (conE conName) [|(<$>)|] x) xs ) ( parseTypeMismatch tName conName (litE $ stringL $ "Array of length " ++ show numArgs) ( infixApp (litE $ stringL "Array of length ") [|(++)|] ([|show . V.length|] `appE` varE arr) ) ) ) [] , matchFailed tName conName "Array" ] -------------------------------------------------------------------------------- -- Parsing errors -------------------------------------------------------------------------------- matchFailed :: Name -> Name -> String -> MatchQ matchFailed tName conName expected = do other <- newName "other" match (varP other) ( normalB $ parseTypeMismatch tName conName (litE $ stringL expected) ([|valueConName|] `appE` varE other) ) [] parseTypeMismatch :: Name -> Name -> ExpQ -> ExpQ -> ExpQ parseTypeMismatch tName conName expected actual = foldl appE [|parseTypeMismatch'|] [ litE $ stringL $ nameBase conName , litE $ stringL $ show tName , expected , actual ] class LookupField a where lookupField :: (Value -> Parser a) -> String -> String -> Object -> T.Text -> Parser a instance OVERLAPPABLE_ LookupField a where lookupField = lookupFieldWith instance INCOHERENT_ LookupField (Maybe a) where lookupField pj _ _ = parseOptionalFieldWith pj instance INCOHERENT_ LookupField (Semigroup.Option a) where lookupField pj tName rec obj key = fmap Semigroup.Option (lookupField (fmap Semigroup.getOption . pj) tName rec obj key) lookupFieldWith :: (Value -> Parser a) -> String -> String -> Object -> T.Text -> Parser a lookupFieldWith pj tName rec obj key = case H.lookup key obj of Nothing -> unknownFieldFail tName rec (T.unpack key) Just v -> pj v Key key unknownFieldFail :: String -> String -> String -> Parser fail unknownFieldFail tName rec key = fail $ printf "When parsing the record %s of type %s the key %s was not present." rec tName key noArrayFail :: String -> String -> Parser fail noArrayFail t o = fail $ printf "When parsing %s expected Array but got %s." t o noObjectFail :: String -> String -> Parser fail noObjectFail t o = fail $ printf "When parsing %s expected Object but got %s." t o firstElemNoStringFail :: String -> String -> Parser fail firstElemNoStringFail t o = fail $ printf "When parsing %s expected an Array of 2 elements where the first element is a String but got %s at the first element." t o wrongPairCountFail :: String -> String -> Parser fail wrongPairCountFail t n = fail $ printf "When parsing %s expected an Object with a single tag/contents pair but got %s pairs." t n noStringFail :: String -> String -> Parser fail noStringFail t o = fail $ printf "When parsing %s expected String but got %s." t o noMatchFail :: String -> String -> Parser fail noMatchFail t o = fail $ printf "When parsing %s expected a String with the tag of a constructor but got %s." t o not2ElemArray :: String -> Int -> Parser fail not2ElemArray t i = fail $ printf "When parsing %s expected an Array of 2 elements but got %i elements" t i conNotFoundFail2ElemArray :: String -> [String] -> String -> Parser fail conNotFoundFail2ElemArray t cs o = fail $ printf "When parsing %s expected a 2-element Array with a tag and contents element where the tag is one of [%s], but got %s." t (intercalate ", " cs) o conNotFoundFailObjectSingleField :: String -> [String] -> String -> Parser fail conNotFoundFailObjectSingleField t cs o = fail $ printf "When parsing %s expected an Object with a single tag/contents pair where the tag is one of [%s], but got %s." t (intercalate ", " cs) o conNotFoundFailTaggedObject :: String -> [String] -> String -> Parser fail conNotFoundFailTaggedObject t cs o = fail $ printf "When parsing %s expected an Object with a tag field where the value is one of [%s], but got %s." t (intercalate ", " cs) o parseTypeMismatch' :: String -> String -> String -> String -> Parser fail parseTypeMismatch' conName tName expected actual = fail $ printf "When parsing the constructor %s of type %s expected %s but got %s." conName tName expected actual -------------------------------------------------------------------------------- -- Shared ToJSON and FromJSON code -------------------------------------------------------------------------------- -- | Functionality common to 'deriveJSON', 'deriveJSON1', and 'deriveJSON2'. deriveJSONBoth :: (Options -> Name -> Q [Dec]) -- ^ Function which derives a flavor of 'ToJSON'. -> (Options -> Name -> Q [Dec]) -- ^ Function which derives a flavor of 'FromJSON'. -> Options -- ^ Encoding options. -> Name -- ^ Name of the type for which to generate 'ToJSON' and 'FromJSON' -- instances. -> Q [Dec] deriveJSONBoth dtj dfj opts name = liftM2 (++) (dtj opts name) (dfj opts name) -- | Functionality common to @deriveToJSON(1)(2)@ and @deriveFromJSON(1)(2)@. deriveJSONClass :: [(JSONFun, JSONClass -> Name -> Options -> [Type] -> [ConstructorInfo] -> Q Exp)] -- ^ The class methods and the functions which derive them. -> JSONClass -- ^ The class for which to generate an instance. -> Options -- ^ Encoding options. -> Name -- ^ Name of the type for which to generate a class instance -- declaration. -> Q [Dec] deriveJSONClass consFuns jc opts name = do info <- reifyDatatype name case info of DatatypeInfo { datatypeContext = ctxt , datatypeName = parentName #if MIN_VERSION_th_abstraction(0,3,0) , datatypeInstTypes = instTys #else , datatypeVars = instTys #endif , datatypeVariant = variant , datatypeCons = cons } -> do (instanceCxt, instanceType) <- buildTypeInstance parentName jc ctxt instTys variant (:[]) <$> instanceD (return instanceCxt) (return instanceType) (methodDecs parentName instTys cons) where methodDecs :: Name -> [Type] -> [ConstructorInfo] -> [Q Dec] methodDecs parentName instTys cons = flip map consFuns $ \(jf, jfMaker) -> funD (jsonFunValName jf (arity jc)) [ clause [] (normalB $ jfMaker jc parentName opts instTys cons) [] ] mkFunCommon :: (JSONClass -> Name -> Options -> [Type] -> [ConstructorInfo] -> Q Exp) -- ^ The function which derives the expression. -> JSONClass -- ^ Which class's method is being derived. -> Options -- ^ Encoding options. -> Name -- ^ Name of the encoded type. -> Q Exp mkFunCommon consFun jc opts name = do info <- reifyDatatype name case info of DatatypeInfo { datatypeContext = ctxt , datatypeName = parentName #if MIN_VERSION_th_abstraction(0,3,0) , datatypeInstTypes = instTys #else , datatypeVars = instTys #endif , datatypeVariant = variant , datatypeCons = cons } -> do -- We force buildTypeInstance here since it performs some checks for whether -- or not the provided datatype's kind matches the derived method's -- typeclass, and produces errors if it can't. !_ <- buildTypeInstance parentName jc ctxt instTys variant consFun jc parentName opts instTys cons dispatchFunByType :: JSONClass -> JSONFun -> Name -> TyVarMap -> Bool -- True if we are using the function argument that works -- on lists (e.g., [a] -> Value). False is we are using -- the function argument that works on single values -- (e.g., a -> Value). -> Type -> Q Exp dispatchFunByType _ jf _ tvMap list (VarT tyName) = varE $ case M.lookup tyName tvMap of Just (tfjExp, tfjlExp) -> if list then tfjlExp else tfjExp Nothing -> jsonFunValOrListName list jf Arity0 dispatchFunByType jc jf conName tvMap list (SigT ty _) = dispatchFunByType jc jf conName tvMap list ty dispatchFunByType jc jf conName tvMap list (ForallT _ _ ty) = dispatchFunByType jc jf conName tvMap list ty dispatchFunByType jc jf conName tvMap list ty = do let tyCon :: Type tyArgs :: [Type] tyCon :| tyArgs = unapplyTy ty numLastArgs :: Int numLastArgs = min (arityInt jc) (length tyArgs) lhsArgs, rhsArgs :: [Type] (lhsArgs, rhsArgs) = splitAt (length tyArgs - numLastArgs) tyArgs tyVarNames :: [Name] tyVarNames = M.keys tvMap itf <- isTyFamily tyCon if any (`mentionsName` tyVarNames) lhsArgs || itf && any (`mentionsName` tyVarNames) tyArgs then outOfPlaceTyVarError jc conName else if any (`mentionsName` tyVarNames) rhsArgs then appsE $ varE (jsonFunValOrListName list jf $ toEnum numLastArgs) : zipWith (dispatchFunByType jc jf conName tvMap) (cycle [False,True]) (interleave rhsArgs rhsArgs) else varE $ jsonFunValOrListName list jf Arity0 dispatchToJSON :: ToJSONFun -> JSONClass -> Name -> TyVarMap -> Type -> Q Exp dispatchToJSON target jc n tvMap = dispatchFunByType jc (targetToJSONFun target) n tvMap False dispatchParseJSON :: JSONClass -> Name -> TyVarMap -> Type -> Q Exp dispatchParseJSON jc n tvMap = dispatchFunByType jc ParseJSON n tvMap False -------------------------------------------------------------------------------- -- Utility functions -------------------------------------------------------------------------------- -- For the given Types, generate an instance context and head. buildTypeInstance :: Name -- ^ The type constructor or data family name -> JSONClass -- ^ The typeclass to derive -> 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 tyConName jc 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 - arityInt jc 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 || elem NotKindStar droppedStarKindStati) $ derivingKindError jc 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 jc 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 jc) 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 (droppedKindVarNames `union` 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 $ jsonClassName jc) $ 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 :: JSONClass -> Type -> (Maybe Pred, [Name]) deriveConstraint jc t | not (isTyVar t) = (Nothing, []) | hasKindStar t = (Just (applyCon (jcConstraint Arity0) tName), []) | otherwise = case hasKindVarChain 1 t of Just ns | jcArity >= Arity1 -> (Just (applyCon (jcConstraint Arity1) tName), ns) _ -> case hasKindVarChain 2 t of Just ns | jcArity == Arity2 -> (Just (applyCon (jcConstraint Arity2) tName), ns) _ -> (Nothing, []) where tName :: Name tName = varTToName t jcArity :: Arity jcArity = arity jc jcConstraint :: Arity -> Name jcConstraint = jsonClassName . JSONClass (direction jc) {- 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 Template Haskell doesn't always have the best track record with reifying kind signatures), 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 mk- 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 ToJSON n/FromJSON n constraint. (ii) If there's a type parameter n of kind k1 -> k2 (where k1/k2 are * or kind variables), then generate a ToJSON1 n/FromJSON1 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 ToJSON1 instance of: instance (ToJSON1 f, ToJSON1 g) => ToJSON1 (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 ToJSON2 n/FromJSON2 n constraint and perform kind substitution as in the other cases. -} checkExistentialContext :: JSONClass -> TyVarMap -> Cxt -> Name -> Q a -> Q a checkExistentialContext jc tvMap ctxt conName q = if (any (`predMentionsName` M.keys tvMap) ctxt || M.size tvMap < arityInt jc) && not (allowExQuant jc) then existentialContextError conName else q {- Note [Matching functions with GADT type variables] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ When deriving ToJSON2, there is a tricky corner case to consider: data Both a b where BothCon :: x -> x -> Both x x Which encoding functions should be applied to which arguments of BothCon? We have a choice, since both the function of type (a -> Value) and of type (b -> Value) can be applied to either argument. In such a scenario, the second encoding function takes precedence over the first encoding function, so the derived ToJSON2 instance would be something like: instance ToJSON2 Both where liftToJSON2 tj1 tj2 p (BothCon x1 x2) = Array $ create $ do mv <- unsafeNew 2 unsafeWrite mv 0 (tj1 x1) unsafeWrite mv 1 (tj2 x2) return mv This is not an arbitrary choice, as this definition ensures that liftToJSON2 toJSON = liftToJSON for a derived ToJSON1 instance for Both. -} -- A mapping of type variable Names to their encoding/decoding function Names. -- For example, in a ToJSON2 declaration, a TyVarMap might look like -- -- { a ~> (tj1, tjl1) -- , b ~> (tj2, tjl2) } -- -- where a and b are the last two type variables of the datatype, tj1 and tjl1 are -- the function arguments of types (a -> Value) and ([a] -> Value), and tj2 and tjl2 -- are the function arguments of types (b -> Value) and ([b] -> Value). type TyVarMap = Map Name (Name, Name) -- | 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 len = mapM newName [prefix ++ show n | n <- [1..len]] -- | @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 (NE.length uk - 1 == kindArrows) && F.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 -- | Extract Just the Name from a type variable. If the argument Type is not a -- type variable, return Nothing. varTToNameMaybe :: Type -> Maybe Name varTToNameMaybe (VarT n) = Just n varTToNameMaybe (SigT t _) = varTToNameMaybe t varTToNameMaybe _ = 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!") . varTToNameMaybe interleave :: [a] -> [a] -> [a] interleave (a1:a1s) (a2:a2s) = a1:a2:interleave a1s a2s interleave _ _ = [] -- | Fully applies a type constructor to its type variables. applyTyCon :: Name -> [Type] -> Type applyTyCon = foldl' AppT . ConT -- | 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 -- | Peel off a kind signature from a Type (if it has one). unSigT :: Type -> Type unSigT (SigT t _) = t unSigT t = t -- | 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 -- | 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: -- -- @ -- forall a b. (a ~ b) => (a -> b) -> Char -> () -- @ -- -- would split to this: -- -- @ -- (a ~ b, [a -> b, Char, ()]) -- @ uncurryTy :: Type -> (Cxt, NonEmpty Type) uncurryTy (AppT (AppT ArrowT t1) t2) = let (ctxt, tys) = uncurryTy t2 in (ctxt, t1 <| tys) uncurryTy (SigT t _) = uncurryTy t uncurryTy (ForallT _ ctxt t) = let (ctxt', tys) = uncurryTy t in (ctxt ++ ctxt', tys) uncurryTy t = ([], t :| []) -- | Like uncurryType, except on a kind level. uncurryKind :: Kind -> NonEmpty Kind #if MIN_VERSION_template_haskell(2,8,0) uncurryKind = snd . 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 -- | Makes a string literal expression from a constructor's name. conNameExp :: Options -> ConstructorInfo -> Q Exp conNameExp opts = litE . stringL . constructorTagModifier opts . nameBase . constructorName -- | Extracts a record field label. fieldLabel :: Options -- ^ Encoding options -> Name -> String fieldLabel opts = fieldLabelModifier opts . nameBase -- | The name of the outermost 'Value' constructor. valueConName :: Value -> String valueConName (Object _) = "Object" valueConName (Array _) = "Array" valueConName (String _) = "String" valueConName (Number _) = "Number" valueConName (Bool _) = "Boolean" valueConName Null = "Null" applyCon :: Name -> Name -> Pred applyCon con t = #if MIN_VERSION_template_haskell(2,10,0) AppT (ConT con) (VarT t) #else 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 ------------------------------------------------------------------------------- -- 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 (M.singleton n k) substNamesWithKindStar :: [Name] -> Type -> Type substNamesWithKindStar ns t = foldr' (`substNameWithKind` starK) t ns ------------------------------------------------------------------------------- -- 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 :: JSONClass -> Name -> Q a derivingKindError jc tyConName = fail . 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 $ arityInt jc) $ "" where className :: String className = nameBase $ jsonClassName jc -- | One of the last type variables cannot be eta-reduced (see the canEtaReduce -- function for the criteria it would have to meet). etaReductionError :: Type -> Q a etaReductionError instanceType = fail $ "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 -> Q a datatypeContextError dataName instanceType = fail . 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 :: JSONClass -> Name -> a outOfPlaceTyVarError jc 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 = arityInt jc -- | The data type has an existential constraint which mentions one of the -- eta-reduced type variables. existentialContextError :: Name -> a existentialContextError conName = error . showString "Constructor ‘" . showString (nameBase conName) . showString "‘ must be truly polymorphic in the last argument(s) of the data type" $ "" ------------------------------------------------------------------------------- -- Class-specific constants ------------------------------------------------------------------------------- -- | A representation of the arity of the ToJSON/FromJSON typeclass being derived. data Arity = Arity0 | Arity1 | Arity2 deriving (Enum, Eq, Ord) -- | Whether ToJSON(1)(2) or FromJSON(1)(2) is being derived. data Direction = To | From -- | A representation of which typeclass method is being spliced in. data JSONFun = ToJSON | ToEncoding | ParseJSON -- | A refinement of JSONFun to [ToJSON, ToEncoding]. data ToJSONFun = Value | Encoding targetToJSONFun :: ToJSONFun -> JSONFun targetToJSONFun Value = ToJSON targetToJSONFun Encoding = ToEncoding -- | A representation of which typeclass is being derived. data JSONClass = JSONClass { direction :: Direction, arity :: Arity } toJSONClass, toJSON1Class, toJSON2Class, fromJSONClass, fromJSON1Class, fromJSON2Class :: JSONClass toJSONClass = JSONClass To Arity0 toJSON1Class = JSONClass To Arity1 toJSON2Class = JSONClass To Arity2 fromJSONClass = JSONClass From Arity0 fromJSON1Class = JSONClass From Arity1 fromJSON2Class = JSONClass From Arity2 jsonClassName :: JSONClass -> Name jsonClassName (JSONClass To Arity0) = ''ToJSON jsonClassName (JSONClass To Arity1) = ''ToJSON1 jsonClassName (JSONClass To Arity2) = ''ToJSON2 jsonClassName (JSONClass From Arity0) = ''FromJSON jsonClassName (JSONClass From Arity1) = ''FromJSON1 jsonClassName (JSONClass From Arity2) = ''FromJSON2 jsonFunValName :: JSONFun -> Arity -> Name jsonFunValName ToJSON Arity0 = 'toJSON jsonFunValName ToJSON Arity1 = 'liftToJSON jsonFunValName ToJSON Arity2 = 'liftToJSON2 jsonFunValName ToEncoding Arity0 = 'toEncoding jsonFunValName ToEncoding Arity1 = 'liftToEncoding jsonFunValName ToEncoding Arity2 = 'liftToEncoding2 jsonFunValName ParseJSON Arity0 = 'parseJSON jsonFunValName ParseJSON Arity1 = 'liftParseJSON jsonFunValName ParseJSON Arity2 = 'liftParseJSON2 jsonFunListName :: JSONFun -> Arity -> Name jsonFunListName ToJSON Arity0 = 'toJSONList jsonFunListName ToJSON Arity1 = 'liftToJSONList jsonFunListName ToJSON Arity2 = 'liftToJSONList2 jsonFunListName ToEncoding Arity0 = 'toEncodingList jsonFunListName ToEncoding Arity1 = 'liftToEncodingList jsonFunListName ToEncoding Arity2 = 'liftToEncodingList2 jsonFunListName ParseJSON Arity0 = 'parseJSONList jsonFunListName ParseJSON Arity1 = 'liftParseJSONList jsonFunListName ParseJSON Arity2 = 'liftParseJSONList2 jsonFunValOrListName :: Bool -- e.g., toJSONList if True, toJSON if False -> JSONFun -> Arity -> Name jsonFunValOrListName False = jsonFunValName jsonFunValOrListName True = jsonFunListName arityInt :: JSONClass -> Int arityInt = fromEnum . arity allowExQuant :: JSONClass -> Bool allowExQuant (JSONClass To _) = True allowExQuant _ = False ------------------------------------------------------------------------------- -- 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 = case t of _ | hasKindStar t -> KindStar #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