aeson-1.2.2.0: Data/Aeson/TH.hs
{-# 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 (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.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 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 (length, reverse)
import qualified Data.Map as M (fromList, 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.
-> [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 jc opts vars 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 vars - arityInt jc) vars
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 jc tvMap opts False con]
_ | allNullaryToStringTag opts && all isNullary cons ->
[ match (conP conName []) (normalB $ conStr opts conName) []
| con <- cons
, let conName = constructorName con
]
| otherwise -> [argsToValue jc tvMap 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.
-> [Type]
-- ^ The types from the data type/data family instance declaration
-> [ConstructorInfo]
-- ^ Constructors for which to generate JSON generating code.
-> Q Exp
consToEncoding _ _ _ [] = error $ "Data.Aeson.TH.consToEncoding: "
++ "Not a single constructor given!"
consToEncoding jc opts vars cons = do
value <- newName "value"
tes <- newNameList "_te" $ arityInt jc
tels <- newNameList "_tel" $ arityInt jc
let zippedTEs = zip tes tels
interleavedTEs = interleave tes tels
lastTyVars = map varTToName $ drop (length vars - arityInt jc) vars
tvMap = M.fromList $ zip lastTyVars zippedTEs
lamE (map varP $ interleavedTEs ++ [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) -> [argsToEncoding jc tvMap 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 = constructorName con
]
| otherwise -> [argsToEncoding jc tvMap opts True con | con <- cons]
encStr :: Options -> Name -> Q Exp
encStr opts = appE [|E.text|] . conTxt opts
-- | If constructor is nullary.
isNullary :: ConstructorInfo -> Bool
isNullary ConstructorInfo { constructorVariant = NormalConstructor
, constructorFields = tys } = null tys
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 -> TyVarMap -> Options -> Bool -> ConstructorInfo -> Q Match
-- Polyadic constructors with special case for unary constructors.
argsToValue jc tvMap opts multiCons
ConstructorInfo { constructorName = conName
, constructorVariant = NormalConstructor
, constructorFields = argTys } = do
argTys' <- mapM resolveTypeSynonyms argTys
let len = length argTys'
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 argTys') conName js)
[]
-- Records.
argsToValue jc tvMap opts multiCons
info@ConstructorInfo { constructorName = conName
, constructorVariant = RecordConstructor fields
, constructorFields = argTys } =
case (unwrapUnaryRecords opts, not multiCons, argTys) of
(True,True,[_]) -> argsToValue jc tvMap opts multiCons
(info{constructorVariant = NormalConstructor})
_ -> do
argTys' <- mapM resolveTypeSynonyms argTys
args <- newNameList "arg" $ length argTys'
let exp = [|A.object|] `appE` pairs
pairs | omitNothingFields opts = infixApp maybeFields
[|(++)|]
restFields
| otherwise = listE $ map toPair argCons
argCons = zip3 args argTys' fields
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 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
$ sumToValue opts multiCons False conName
$ [|toJSON|] `appE` listE [ dispatchToJSON 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
(<^>) :: 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 -> TyVarMap -> Options -> Bool -> ConstructorInfo -> Q Match
-- Polyadic constructors with special case for unary constructors.
argsToEncoding jc tvMap opts multiCons
ConstructorInfo { constructorName = conName
, constructorVariant = NormalConstructor
, constructorFields = argTys } = do
argTys' <- mapM resolveTypeSynonyms argTys
args <- newNameList "arg" $ length argTys'
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 argTys') conName js)
[]
-- Records.
argsToEncoding jc tvMap opts multiCons
info@ConstructorInfo { constructorName = conName
, constructorVariant = RecordConstructor fields
, constructorFields = argTys } =
case (unwrapUnaryRecords opts, not multiCons, argTys) of
(True,True,[_]) -> argsToEncoding jc tvMap opts multiCons
(info{constructorVariant = NormalConstructor})
_ -> do
argTys' <- mapM resolveTypeSynonyms argTys
args <- newNameList "arg" $ length argTys'
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' fields
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 tvMap opts multiCons
ConstructorInfo { constructorName = conName
, constructorVariant = InfixConstructor
, constructorFields = argTys } = do
al <- newName "argL"
ar <- newName "argR"
[alTy,arTy] <- mapM resolveTypeSynonyms argTys
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)]
])
)
[]
--------------------------------------------------------------------------------
-- 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 vars 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 vars - arityInt jc) vars
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)
[|(==)|]
([|T.pack|] `appE`
conStringE 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) [|(==)|] ([|T.pack|] `appE` conStringE 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` fieldLabelExp 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` <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 -> [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
, datatypeVars = vars
, datatypeVariant = variant
, datatypeCons = cons
} -> do
(instanceCxt, instanceType)
<- buildTypeInstance parentName jc ctxt vars variant
(:[]) <$> instanceD (return instanceCxt)
(return instanceType)
(methodDecs parentName vars cons)
where
methodDecs :: Name -> [Type] -> [ConstructorInfo] -> [Q Dec]
methodDecs parentName vars cons = flip map consFuns $ \(jf, jfMaker) ->
funD (jsonFunValName jf (arity jc))
[ clause []
(normalB $ jfMaker jc parentName opts vars 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
, datatypeVars = vars
, 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 vars variant
consFun jc parentName opts vars 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
--------------------------------------------------------------------------------
-- 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
-- | 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
-------------------------------------------------------------------------------
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 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