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{-# 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 ()
import Prelude.Compat hiding (exp)
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 ((<?>), Pair, JSONPathElement(Key))
import Data.Aeson.Types.FromJSON (parseOptionalFieldWith)
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 (find, foldl', genericLength , intercalate , intersperse, partition, union)
import Data.List.NonEmpty ((<|), NonEmpty((:|)))
import Data.Map (Map)
import Data.Maybe (catMaybes, fromMaybe, mapMaybe)
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.Syntax (VarStrictType)
#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 as A
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 (drop, length, reverse, splitAt)
import qualified Data.Map as M (fromList, findWithDefault, keys, lookup , singleton, size)
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, fromList)
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 jc)
, (ToEncoding, \jc _ -> consToEncoding 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 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 _ -> consToEncoding jc)
-- | Helper function used by both 'deriveToJSON' and 'mkToJSON'. Generates
-- code to generate a 'Value' of a number of constructors. All constructors
-- must be from the same type.
consToValue :: JSONClass
-- ^ The ToJSON variant being derived.
-> Options
-- ^ Encoding options.
-> [Con]
-- ^ Constructors for which to generate JSON generating code.
-> Q Exp
consToValue _ _ [] = error $ "Data.Aeson.TH.consToValue: "
++ "Not a single constructor given!"
consToValue jc opts cons = do
value <- newName "value"
tjs <- newNameList "_tj" $ arityInt jc
tjls <- newNameList "_tjl" $ arityInt jc
let zippedTJs = zip tjs tjls
interleavedTJs = interleave tjs tjls
lamE (map varP $ interleavedTJs ++ [value]) $
caseE (varE value) (matches zippedTJs)
where
matches tjs = case cons of
-- A single constructor is directly encoded. The constructor itself may be
-- forgotten.
[con] | not (tagSingleConstructors opts) -> [argsToValue jc tjs opts False con]
_ | allNullaryToStringTag opts && all isNullary cons ->
[ match (conP conName []) (normalB $ conStr opts conName) []
| con <- cons
, let conName = getConName con
]
| otherwise -> [argsToValue jc tjs opts True con | con <- cons]
conStr :: Options -> Name -> Q Exp
conStr opts = appE [|String|] . conTxt opts
conTxt :: Options -> Name -> Q Exp
conTxt opts = appE [|T.pack|] . conStringE opts
conStringE :: Options -> Name -> Q Exp
conStringE opts = stringE . constructorTagModifier opts . nameBase
-- | Helper function used by both 'deriveToJSON' and 'mkToEncoding'. Generates
-- code to write out a value for a number of constructors. All constructors
-- must be from the same type.
consToEncoding :: JSONClass
-- ^ The ToJSON variant being derived.
-> Options
-- ^ Encoding options.
-> [Con]
-- ^ Constructors for which to generate JSON generating code.
-> Q Exp
consToEncoding _ _ [] = error $ "Data.Aeson.TH.consToEncoding: "
++ "Not a single constructor given!"
consToEncoding jc opts cons = do
value <- newName "value"
tes <- newNameList "_te" $ arityInt jc
tels <- newNameList "_tel" $ arityInt jc
let zippedTEs = zip tes tels
interleavedTEs = interleave tes tels
lamE (map varP $ interleavedTEs ++ [value]) $
caseE (varE value) (matches zippedTEs)
where
matches tes = case cons of
-- A single constructor is directly encoded. The constructor itself may be
-- forgotten.
[con] | not (tagSingleConstructors opts) -> [argsToEncoding jc tes opts False con]
-- Encode just the name of the constructor of a sum type iff all the
-- constructors are nullary.
_ | allNullaryToStringTag opts && all isNullary cons ->
[ match (conP conName [])
(normalB $ encStr opts conName) []
| con <- cons
, let conName = getConName con
]
| otherwise -> [argsToEncoding jc tes opts True con | con <- cons]
encStr :: Options -> Name -> Q Exp
encStr opts = appE [|E.text|] . conTxt opts
-- | If constructor is nullary.
isNullary :: Con -> Bool
isNullary (NormalC _ []) = True
isNullary _ = False
sumToValue :: Options -> Bool -> Bool -> Name -> Q Exp -> Q Exp
sumToValue opts multiCons nullary conName exp
| multiCons =
case sumEncoding opts of
TwoElemArray ->
[|Array|] `appE` ([|V.fromList|] `appE` listE [conStr opts conName, exp])
TaggedObject{tagFieldName, contentsFieldName} ->
let tag = infixApp [|T.pack tagFieldName|] [|(.=)|] (conStr opts conName)
contents = infixApp [|T.pack contentsFieldName|] [|(.=)|] exp
in
[|A.object|] `appE` listE (if nullary then [tag] else [tag, contents])
ObjectWithSingleField ->
[|A.object|] `appE` listE
[ infixApp (conTxt opts conName) [|(.=)|] exp
]
UntaggedValue | nullary -> conStr opts conName
UntaggedValue -> exp
| otherwise = exp
-- | Generates code to generate the JSON encoding of a single constructor.
argsToValue :: JSONClass -> [(Name, Name)] -> Options -> Bool -> Con -> Q Match
-- Polyadic constructors with special case for unary constructors.
argsToValue jc tjs opts multiCons (NormalC conName ts) = do
(argTys, tvMap) <- reifyConTys jc tjs conName
let len = length ts
args <- newNameList "arg" len
js <- case [ dispatchToJSON jc conName tvMap argTy
`appE` varE arg
| (arg, argTy) <- zip args argTys
] of
-- Single argument is directly converted.
[e] -> return e
-- Multiple arguments are converted to a JSON array.
es -> do
mv <- newName "mv"
let newMV = bindS (varP mv)
([|VM.unsafeNew|] `appE`
litE (integerL $ fromIntegral len))
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
return $ [|Array|] `appE`
(varE 'V.create `appE`
doE (newMV:stmts++[ret]))
match (conP conName $ map varP args)
(normalB $ sumToValue opts multiCons (null ts) conName js)
[]
-- Records.
argsToValue jc tjs opts multiCons (RecC conName ts) = case (unwrapUnaryRecords opts, not multiCons, ts) of
(True,True,[(_,st,ty)]) -> argsToValue jc tjs opts multiCons (NormalC conName [(st,ty)])
_ -> do
(argTys, tvMap) <- reifyConTys jc tjs conName
args <- newNameList "arg" $ length ts
let exp = [|A.object|] `appE` pairs
pairs | omitNothingFields opts = infixApp maybeFields
[|(++)|]
restFields
| otherwise = listE $ map toPair argCons
argCons = zip3 args argTys ts
maybeFields = [|catMaybes|] `appE` listE (map maybeToPair maybes)
restFields = listE $ map toPair rest
(maybes, rest) = partition isMaybe argCons
maybeToPair (arg, argTy, (field, _, _)) =
infixApp ([|keyValuePairWith|]
`appE` dispatchToJSON jc conName tvMap argTy
`appE` toFieldName field)
[|(<$>)|]
(varE arg)
toPair (arg, argTy, (field, _, _)) =
[|keyValuePairWith|]
`appE` dispatchToJSON jc conName tvMap argTy
`appE` toFieldName field
`appE` varE arg
toFieldName field = [|T.pack|] `appE` fieldLabelExp opts field
match (conP conName $ map varP args)
( normalB
$ if multiCons
then case sumEncoding opts of
TwoElemArray -> [|toJSON|] `appE` tupE [conStr opts conName, exp]
TaggedObject{tagFieldName} ->
[|A.object|] `appE`
-- TODO: Maybe throw an error in case
-- tagFieldName overwrites a field in pairs.
infixApp (infixApp [|T.pack tagFieldName|]
[|(.=)|]
(conStr opts conName))
[|(:)|]
pairs
ObjectWithSingleField ->
[|A.object|] `appE` listE
[ infixApp (conTxt opts conName) [|(.=)|] exp ]
UntaggedValue -> exp
else exp
) []
-- Infix constructors.
argsToValue jc tjs opts multiCons (InfixC _ conName _) = do
([alTy, arTy], tvMap) <- reifyConTys jc tjs conName
al <- newName "argL"
ar <- newName "argR"
match (infixP (varP al) conName (varP ar))
( normalB
$ sumToValue opts multiCons False conName
$ [|toJSON|] `appE` listE [ dispatchToJSON jc conName tvMap aTy
`appE` varE a
| (a, aTy) <- [(al,alTy), (ar,arTy)]
]
)
[]
-- Existentially quantified constructors.
argsToValue jc tjs opts multiCons (ForallC _ _ con) =
argsToValue jc tjs opts multiCons con
#if MIN_VERSION_template_haskell(2,11,0)
-- GADTs.
argsToValue jc tjs opts multiCons (GadtC conNames ts _) =
argsToValue jc tjs opts multiCons $ NormalC (head conNames) ts
argsToValue jc tjs opts multiCons (RecGadtC conNames ts _) =
argsToValue jc tjs opts multiCons $ RecC (head conNames) ts
#endif
isMaybe :: (a, b, (c, d, Type)) -> Bool
isMaybe (_, _, (_, _, AppT (ConT t) _)) = t == ''Maybe
isMaybe _ = False
(<^>) :: ExpQ -> ExpQ -> ExpQ
(<^>) a b = infixApp a [|(E.><)|] b
infixr 6 <^>
(<:>) :: ExpQ -> ExpQ -> ExpQ
(<:>) a b = a <^> [|E.colon|] <^> b
infixr 5 <:>
(<%>) :: ExpQ -> ExpQ -> ExpQ
(<%>) a b = a <^> [|E.comma|] <^> b
infixr 4 <%>
array :: ExpQ -> ExpQ
array exp = [|E.wrapArray|] `appE` exp
object :: ExpQ -> ExpQ
object exp = [|E.wrapObject|] `appE` exp
sumToEncoding :: Options -> Bool -> Bool -> Name -> Q Exp -> Q Exp
sumToEncoding opts multiCons nullary conName exp
| multiCons =
let fexp = exp in
case sumEncoding opts of
TwoElemArray ->
array (encStr opts conName <%> fexp)
TaggedObject{tagFieldName, contentsFieldName} ->
let tag = [|E.text (T.pack tagFieldName)|] <:> encStr opts conName
contents = [|E.text (T.pack contentsFieldName)|] <:> fexp
in
object $
if nullary then tag else tag <%> contents
ObjectWithSingleField ->
object (encStr opts conName <:> fexp)
UntaggedValue | nullary -> encStr opts conName
UntaggedValue -> exp
| otherwise = exp
-- | Generates code to generate the JSON encoding of a single constructor.
argsToEncoding :: JSONClass -> [(Name, Name)] -> Options -> Bool -> Con -> Q Match
-- Polyadic constructors with special case for unary constructors.
argsToEncoding jc tes opts multiCons (NormalC conName ts) = do
(argTys, tvMap) <- reifyConTys jc tes conName
let len = length ts
args <- newNameList "arg" len
js <- case zip args argTys of
-- Nullary constructors are converted to an empty array.
[] -> return [| E.emptyArray_ |]
-- Single argument is directly converted.
[(e,eTy)] -> return (dispatchToEncoding jc conName tvMap eTy
`appE` varE e)
-- Multiple arguments are converted to a JSON array.
es ->
return (array (foldr1 (<%>) [ dispatchToEncoding jc conName tvMap xTy
`appE` varE x
| (x,xTy) <- es
]))
match (conP conName $ map varP args)
(normalB $ sumToEncoding opts multiCons (null ts) conName js)
[]
-- Records.
argsToEncoding jc tes opts multiCons (RecC conName ts) = case (unwrapUnaryRecords opts, not multiCons, ts) of
(True,True,[(_,st,ty)]) -> argsToEncoding jc tes opts multiCons (NormalC conName [(st,ty)])
_ -> do
args <- newNameList "arg" $ length ts
(argTys, tvMap) <- reifyConTys jc tes conName
let exp = object objBody
objBody = [|E.econcat|] `appE`
([|intersperse E.comma|] `appE` pairs)
pairs | omitNothingFields opts = infixApp maybeFields
[|(++)|]
restFields
| otherwise = listE (map toPair argCons)
argCons = zip3 args argTys ts
maybeFields = [|catMaybes|] `appE` listE (map maybeToPair maybes)
restFields = listE (map toPair rest)
(maybes, rest) = partition isMaybe argCons
maybeToPair (arg, argTy, (field, _, _)) =
infixApp
(infixApp
(infixE
(Just $ toFieldName field <^> [|E.colon|])
[|(E.><)|]
Nothing)
[|(.)|]
(dispatchToEncoding jc conName tvMap argTy))
[|(<$>)|]
(varE arg)
toPair (arg, argTy, (field, _, _)) =
toFieldName field
<:> dispatchToEncoding jc conName tvMap argTy
`appE` varE arg
toFieldName field = [|E.text|] `appE`
([|T.pack|] `appE` fieldLabelExp opts field)
match (conP conName $ map varP args)
( normalB
$ if multiCons
then case sumEncoding opts of
TwoElemArray -> array $
encStr opts conName <%> exp
TaggedObject{tagFieldName} -> object $
([|E.text (T.pack tagFieldName)|] <:>
encStr opts conName) <%>
objBody
ObjectWithSingleField -> object $
encStr opts conName <:> exp
UntaggedValue -> exp
else exp
) []
-- Infix constructors.
argsToEncoding jc tes opts multiCons (InfixC _ conName _) = do
al <- newName "argL"
ar <- newName "argR"
([alTy,arTy], tvMap) <- reifyConTys jc tes conName
match (infixP (varP al) conName (varP ar))
( normalB
$ sumToEncoding opts multiCons False conName
$ array (foldr1 (<%>) [ dispatchToEncoding jc conName tvMap aTy
`appE` varE a
| (a,aTy) <- [(al,alTy), (ar,arTy)]
])
)
[]
-- Existentially quantified constructors.
argsToEncoding jc tes opts multiCons (ForallC _ _ con) =
argsToEncoding jc tes opts multiCons con
#if MIN_VERSION_template_haskell(2,11,0)
-- GADTs.
argsToEncoding jc tes opts multiCons (GadtC conNames ts _) =
argsToEncoding jc tes opts multiCons $ NormalC (head conNames) ts
argsToEncoding jc tes opts multiCons (RecGadtC conNames ts _) =
argsToEncoding jc tes opts multiCons $ RecC (head conNames) ts
#endif
--------------------------------------------------------------------------------
-- 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
-> [Con]
-- ^ 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 cons = do
value <- newName "value"
pjs <- newNameList "_pj" $ arityInt jc
pjls <- newNameList "_pjl" $ arityInt jc
let zippedPJs = zip pjs pjls
interleavedPJs = interleave pjs pjls
lamE (map varP $ interleavedPJs ++ [value]) $ lamExpr value zippedPJs
where
lamExpr value pjs = case cons of
[con]
| not (tagSingleConstructors opts)
-> parseArgs jc pjs tName opts con (Right value)
_ | sumEncoding opts == UntaggedValue
-> parseUntaggedValue pjs cons value
| otherwise
-> caseE (varE value) $
if allNullaryToStringTag opts && all isNullary cons
then allNullaryMatches
else mixedMatches pjs
allNullaryMatches =
[ do txt <- newName "txt"
match (conP 'String [varP txt])
(guardedB $
[ liftM2 (,) (normalG $
infixApp (varE txt)
[|(==)|]
([|T.pack|] `appE`
conStringE opts conName)
)
([|pure|] `appE` conE conName)
| con <- cons
, let conName = getConName 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 pjs =
case sumEncoding opts of
TaggedObject {tagFieldName, contentsFieldName} ->
parseObject $ parseTaggedObject pjs tagFieldName contentsFieldName
UntaggedValue -> error "UntaggedValue: Should be handled already"
ObjectWithSingleField ->
parseObject $ parseObjectWithSingleField pjs
TwoElemArray ->
[ do arr <- newName "array"
match (conP 'Array [varP arr])
(guardedB
[ liftM2 (,) (normalG $ infixApp ([|V.length|] `appE` varE arr)
[|(==)|]
(litE $ integerL 2))
(parse2ElemArray pjs 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 pjs typFieldName valFieldName obj = do
conKey <- newName "conKey"
doE [ bindS (varP conKey)
(infixApp (varE obj)
[|(.:)|]
([|T.pack|] `appE` stringE typFieldName))
, noBindS $ parseContents pjs conKey (Left (valFieldName, obj)) 'conNotFoundFailTaggedObject
]
parseUntaggedValue pjs cons' conVal =
foldr1 (\e e' -> infixApp e [|(<|>)|] e')
(map (\x -> parseValue pjs x conVal) cons')
parseValue _pjs (NormalC conName []) conVal = do
str <- newName "str"
caseE (varE conVal)
[ match (conP 'String [varP str])
(guardedB
[ liftM2 (,) (normalG $ infixApp (varE str) [|(==)|] ([|T.pack|] `appE` conStringE opts conName)
)
([|pure|] `appE` conE conName)
]
)
[]
, matchFailed tName conName "String"
]
parseValue pjs con conVal =
parseArgs jc pjs tName opts con (Right conVal)
parse2ElemArray pjs 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 pjs
txt
(Right conVal)
'conNotFoundFail2ElemArray
)
[]
, do other <- newName "other"
match (varP other)
( normalB
$ [|firstElemNoStringFail|]
`appE` litE (stringL $ show tName)
`appE` ([|valueConName|] `appE` varE other)
)
[]
]
)
parseObjectWithSingleField pjs obj = do
conKey <- newName "conKey"
conVal <- newName "conVal"
caseE ([e|H.toList|] `appE` varE obj)
[ match (listP [tupP [varP conKey, varP conVal]])
(normalB $ parseContents pjs 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 pjs conKey contents errorFun =
caseE (varE conKey)
[ match wildP
( guardedB $
[ do g <- normalG $ infixApp (varE conKey)
[|(==)|]
([|T.pack|] `appE`
conNameExp opts con)
e <- parseArgs jc pjs 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
. getConName
) 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)
[|(<$>)|]
(dispatchParseJSON jc conName tvMap argTy
`appE` varE arg)
)
[]
]
parseRecord :: JSONClass
-> TyVarMap
-> [Type]
-> Options
-> Name
-> Name
-> [VarStrictType]
-> Name
-> ExpQ
parseRecord jc tvMap argTys opts tName conName ts obj =
foldl' (\a b -> infixApp a [|(<*>)|] b)
(infixApp (conE conName) [|(<$>)|] 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` fieldLabelExp opts field
)
| ((field, _, _), argTy) <- zip ts 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.
-> [(Name, Name)] -- ^ The names of the encoding/decoding function arguments.
-> Name -- ^ Name of the type to which the constructor belongs.
-> Options -- ^ Encoding options.
-> Con -- ^ Constructor for which to generate JSON parsing code.
-> Either (String, Name) Name -- ^ Left (valFieldName, objName) or
-- Right valName
-> Q Exp
-- Nullary constructors.
parseArgs jc pjs _ _ (NormalC conName []) (Left _) = do
([], _) <- reifyConTys jc pjs conName
[|pure|] `appE` conE conName
parseArgs jc pjs tName _ (NormalC conName []) (Right valName) = do
([], _) <- reifyConTys jc pjs conName
caseE (varE valName) $ parseNullaryMatches tName conName
-- Unary constructors.
parseArgs jc pjs _ _ (NormalC conName [_]) contents = do
([argTy], tvMap) <- reifyConTys jc pjs conName
matchCases contents $ parseUnaryMatches jc tvMap argTy conName
-- Polyadic constructors.
parseArgs jc pjs tName _ (NormalC conName ts) contents = do
(argTys, tvMap) <- reifyConTys jc pjs conName
let len = genericLength ts
matchCases contents $ parseProduct jc tvMap argTys tName conName len
-- Records.
parseArgs jc pjs tName opts (RecC conName ts) (Left (_, obj)) = do
(argTys, tvMap) <- reifyConTys jc pjs conName
parseRecord jc tvMap argTys opts tName conName ts obj
parseArgs jc pjs tName opts (RecC conName ts) (Right valName) = case (unwrapUnaryRecords opts,ts) of
(True,[(_,st,ty)])-> parseArgs jc pjs tName opts (NormalC conName [(st,ty)]) (Right valName)
_ -> do
obj <- newName "recObj"
(argTys, tvMap) <- reifyConTys jc pjs conName
caseE (varE valName)
[ match (conP 'Object [varP obj]) (normalB $
parseRecord jc tvMap argTys opts tName conName ts obj) []
, matchFailed tName conName "Object"
]
-- Infix constructors. Apart from syntax these are the same as
-- polyadic constructors.
parseArgs jc pjs tName _ (InfixC _ conName _) contents = do
(argTys, tvMap) <- reifyConTys jc pjs conName
matchCases contents $ parseProduct jc tvMap argTys tName conName 2
-- Existentially quantified constructors. We ignore the quantifiers
-- and proceed with the contained constructor.
parseArgs jc pjs tName opts (ForallC _ _ con) contents =
parseArgs jc pjs tName opts con contents
#if MIN_VERSION_template_haskell(2,11,0)
-- GADTs. We ignore the refined return type and proceed as if it were a
-- NormalC or RecC.
parseArgs jc pjs tName opts (GadtC conNames ts _) contents =
parseArgs jc pjs tName opts (NormalC (head conNames) ts) contents
parseArgs jc pjs tName opts (RecGadtC conNames ts _) contents =
parseArgs jc pjs tName opts (RecC (head conNames) ts) contents
#endif
-- | 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` <IX>)"
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
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
keyValuePairWith :: (v -> Value) -> T.Text -> v -> Pair
keyValuePairWith tj name value = (name, tj value)
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 -> [Con] -> 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 =
withType name $ \name' ctxt tvbs cons mbTys ->
(:[]) <$> fromCons name' ctxt tvbs cons mbTys
where
fromCons :: Name -> Cxt -> [TyVarBndr] -> [Con] -> Maybe [Type] -> Q Dec
fromCons name' ctxt tvbs cons mbTys = do
(instanceCxt, instanceType)
<- buildTypeInstance name' jc ctxt tvbs mbTys
instanceD (return instanceCxt)
(return instanceType)
(methodDecs name' cons)
methodDecs :: Name -> [Con] -> [Q Dec]
methodDecs name' cons = flip map consFuns $ \(jf, jfMaker) ->
funD (jsonFunValName jf (arity jc))
[ clause []
(normalB $ jfMaker jc name' opts cons)
[]
]
mkFunCommon :: (JSONClass -> Name -> Options -> [Con] -> 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 = withType name fromCons
where
fromCons :: Name -> Cxt -> [TyVarBndr] -> [Con] -> Maybe [Type] -> Q Exp
fromCons name' ctxt tvbs cons mbTys = 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 name' jc ctxt tvbs mbTys
consFun jc name' opts 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, dispatchToEncoding, dispatchParseJSON
:: JSONClass -> Name -> TyVarMap -> Type -> Q Exp
dispatchToJSON jc n tvMap = dispatchFunByType jc ToJSON n tvMap False
dispatchToEncoding jc n tvMap = dispatchFunByType jc ToEncoding n tvMap False
dispatchParseJSON jc n tvMap = dispatchFunByType jc ParseJSON n tvMap False
--------------------------------------------------------------------------------
-- Utility functions
--------------------------------------------------------------------------------
-- | 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)
-- ^ Function that generates the actual code. Will be applied
-- to the datatype/data family 'Name', datatype context, type
-- variable binders and constructors extracted from the given
-- 'Name'. If the 'Name' is from a data family instance
-- constructor, it will also have its instantiated types;
-- otherwise, it will be 'Nothing'.
-> Q a
-- ^ Resulting value in the 'Q'uasi monad.
withType name f = do
info <- reify name
case info of
TyConI dec ->
case dec of
#if MIN_VERSION_template_haskell(2,11,0)
DataD ctxt _ tvbs _ cons _ -> f name ctxt tvbs cons Nothing
NewtypeD ctxt _ tvbs _ con _ -> f name ctxt tvbs [con] Nothing
#else
DataD ctxt _ tvbs cons _ -> f name ctxt tvbs cons Nothing
NewtypeD ctxt _ tvbs con _ -> f name ctxt tvbs [con] Nothing
#endif
other -> fail $ ns ++ "Unsupported type: " ++ show other
#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
#if MIN_VERSION_template_haskell(2,11,0)
DataInstD _ _ _ _ cons _ -> any ((name ==) . getConName) cons
NewtypeInstD _ _ _ _ con _ -> name == getConName con
#else
DataInstD _ _ _ cons _ -> any ((name ==) . getConName) cons
NewtypeInstD _ _ _ con _ -> name == getConName con
#endif
_ -> error $ ns ++ "Must be a data or newtype instance."
in case instDec of
#if MIN_VERSION_template_haskell(2,11,0)
Just (DataInstD ctxt _ instTys _ cons _) -> f parentName ctxt tvbs cons $ Just instTys
Just (NewtypeInstD ctxt _ instTys _ con _) -> f parentName ctxt tvbs [con] $ Just instTys
#else
Just (DataInstD ctxt _ instTys cons _) -> f parentName ctxt tvbs cons $ Just instTys
Just (NewtypeInstD ctxt _ instTys con _) -> f parentName ctxt tvbs [con] $ Just instTys
#endif
_ -> fail $ ns ++
"Could not find data or newtype instance constructor."
_ -> fail $ 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
fail $ ns ++
"Cannot use a data family name. Use a data family instance constructor instead."
_ -> fail $ ns ++ "I need the name of a plain data type constructor, "
++ "or a data family instance constructor."
where
ns :: String
ns = "Data.Aeson.TH.withType: "
-- | Infer the context and instance head needed for a FromJSON or ToJSON instance.
buildTypeInstance :: Name
-- ^ The type constructor or data family name
-> JSONClass
-- ^ The typeclass to derive
-> 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)
-- ^ The resulting 'Cxt' and 'Type' to use in a class instance
-- Plain data type/newtype case
buildTypeInstance tyConName jc dataCxt tvbs Nothing =
let varTys :: [Type]
varTys = map tvbToType tvbs
in buildTypeInstanceFromTys tyConName jc 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 dataFamName jc 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 dataFamName jc dataCxt instTys True
-- For the given Types, generate an instance context and head.
buildTypeInstanceFromTys :: 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
-> Bool
-- ^ True if it's a data family, False otherwise
-> Q (Cxt, Type)
buildTypeInstanceFromTys tyConName jc 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 - 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 = concatMap tyVarNamesOfType 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
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 [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 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.
-}
-- Determines the types of a constructor's arguments as well as the last type
-- parameters (mapped to their encoding/decoding 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 :: JSONClass
-> [(Name, Name)]
-> Name
-> Q ([Type], TyVarMap)
reifyConTys jc tpjs conName = do
info <- reify conName
(ctxt, 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 (NE.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 encoding/decoding functions to
-- arguments of a type that it (1) one of the last type variables,
-- and (2) of a truly polymorphic type.
jArity = arityInt jc
mbTvNames = map varTToNameMaybe $
NE.drop (NE.length unapResTy - jArity) unapResTy
-- We use M.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 = M.fromList
. catMaybes -- Drop refined types
$ zipWith (\mbTvName tpj ->
fmap (\tvName -> (tvName, tpj)) mbTvName)
mbTvNames tpjs
if (any (`predMentionsName` M.keys tvMap) ctxt
|| M.size tvMap < jArity)
&& not (allowExQuant jc)
then existentialContextError conName
else return (argTys, tvMap)
{-
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)
-- | 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
-- | Extracts the kind from a type variable binder.
tvbKind :: TyVarBndr -> Kind
#if MIN_VERSION_template_haskell(2,8,0)
tvbKind (PlainTV _ ) = StarT
#else
tvbKind (PlainTV _ ) = StarK
#endif
tvbKind (KindedTV _ k) = k
tvbToType :: TyVarBndr -> Type
tvbToType (PlainTV n) = VarT n
tvbToType (KindedTV n k) = SigT (VarT n) k
-- | 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]]
-- 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 (NE.length uk - 1 == kindArrows) && F.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
-- | 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
-- | Extracts the name from a constructor.
getConName :: Con -> Name
getConName (NormalC name _) = name
getConName (RecC name _) = name
getConName (InfixC _ name _) = name
getConName (ForallC _ _ con) = getConName con
#if MIN_VERSION_template_haskell(2,11,0)
getConName (GadtC names _ _) = head names
getConName (RecGadtC names _ _) = head names
#endif
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 -> Con -> Q Exp
conNameExp opts = litE
. stringL
. constructorTagModifier opts
. nameBase
. getConName
-- | Creates a string literal expression from a record field label.
fieldLabelExp :: Options -- ^ Encoding options
-> Name
-> Q Exp
fieldLabelExp opts = litE . stringL . 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
-------------------------------------------------------------------------------
-- | 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) = 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 M.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) = M.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 _ t = t -- There are no kind variables!
#endif
substNameWithKind :: Name -> Kind -> Type -> Type
substNameWithKind n k = substKind (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 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