th-abstraction-0.3.2.0: src/Language/Haskell/TH/Datatype.hs
{-# Language CPP, DeriveDataTypeable #-}
#if MIN_VERSION_base(4,4,0)
#define HAS_GENERICS
{-# Language DeriveGeneric #-}
#endif
{-|
Module : Language.Haskell.TH.Datatype
Description : Backwards-compatible interface to reified information about datatypes.
Copyright : Eric Mertens 2017
License : ISC
Maintainer : emertens@gmail.com
This module provides a flattened view of information about data types
and newtypes that can be supported uniformly across multiple versions
of the template-haskell package.
Sample output for @'reifyDatatype' ''Maybe@
@
'DatatypeInfo'
{ 'datatypeContext' = []
, 'datatypeName' = GHC.Base.Maybe
, 'datatypeVars' = [ 'KindedTV' a_3530822107858468866 'StarT' ]
, 'datatypeInstTypes' = [ 'SigT' ('VarT' a_3530822107858468866) 'StarT' ]
, 'datatypeVariant' = 'Datatype'
, 'datatypeCons' =
[ 'ConstructorInfo'
{ 'constructorName' = GHC.Base.Nothing
, 'constructorVars' = []
, 'constructorContext' = []
, 'constructorFields' = []
, 'constructorStrictness' = []
, 'constructorVariant' = 'NormalConstructor'
}
, 'ConstructorInfo'
{ 'constructorName' = GHC.Base.Just
, 'constructorVars' = []
, 'constructorContext' = []
, 'constructorFields' = [ 'VarT' a_3530822107858468866 ]
, 'constructorStrictness' = [ 'FieldStrictness'
'UnspecifiedUnpackedness'
'Lazy'
]
, 'constructorVariant' = 'NormalConstructor'
}
]
}
@
Datatypes declared with GADT syntax are normalized to constructors with existentially
quantified type variables and equality constraints.
-}
module Language.Haskell.TH.Datatype
(
-- * Types
DatatypeInfo(..)
, ConstructorInfo(..)
, DatatypeVariant(..)
, ConstructorVariant(..)
, FieldStrictness(..)
, Unpackedness(..)
, Strictness(..)
-- * Normalization functions
, reifyDatatype
, reifyConstructor
, reifyRecord
, normalizeInfo
, normalizeDec
, normalizeCon
-- * 'DatatypeInfo' lookup functions
, lookupByConstructorName
, lookupByRecordName
-- * Type variable manipulation
, TypeSubstitution(..)
, quantifyType
, freeVariablesWellScoped
, freshenFreeVariables
-- * 'Pred' functions
, equalPred
, classPred
, asEqualPred
, asClassPred
-- * Backward compatible data definitions
, dataDCompat
, newtypeDCompat
, tySynInstDCompat
, pragLineDCompat
, arrowKCompat
-- * Strictness annotations
, isStrictAnnot
, notStrictAnnot
, unpackedAnnot
-- * Type simplification
, resolveTypeSynonyms
, resolveKindSynonyms
, resolvePredSynonyms
, resolveInfixT
-- * Fixities
, reifyFixityCompat
, showFixity
, showFixityDirection
-- * Convenience functions
, unifyTypes
, tvName
, tvKind
, datatypeType
) where
import Data.Data (Typeable, Data)
import Data.Foldable (foldMap, foldl')
import Data.List (nub, find, union, (\\))
import Data.Map (Map)
import qualified Data.Map as Map
import Data.Maybe
import qualified Data.Set as Set
import Data.Set (Set)
import qualified Data.Traversable as T
import Control.Monad
import Language.Haskell.TH
#if MIN_VERSION_template_haskell(2,11,0)
hiding (Extension(..))
#endif
import Language.Haskell.TH.Datatype.Internal
import Language.Haskell.TH.Lib (arrowK, starK) -- needed for th-2.4
#ifdef HAS_GENERICS
import GHC.Generics (Generic)
#endif
#if !MIN_VERSION_base(4,8,0)
import Control.Applicative (Applicative(..), (<$>))
import Data.Monoid (Monoid(..))
#endif
-- | Normalized information about newtypes and data types.
--
-- 'DatatypeInfo' contains two fields, 'datatypeVars' and 'datatypeInstTypes',
-- which encode information about the argument types. The simplest explanation
-- is that 'datatypeVars' contains all the type /variables/ bound by the data
-- type constructor, while 'datatypeInstTypes' contains the type /arguments/
-- to the data type constructor. To be more precise:
--
-- * For ADTs declared with @data@ and @newtype@, it will likely be the case
-- that 'datatypeVars' and 'datatypeInstTypes' coincide. For instance, given
-- @newtype Id a = MkId a@, in the 'DatatypeInfo' for @Id@ we would
-- have @'datatypeVars' = ['KindedTV' a 'StarT']@ and
-- @'datatypeInstVars' = ['SigT' ('VarT' a) 'StarT']@.
--
-- ADTs that leverage @PolyKinds@ may have more 'datatypeVars' than
-- 'datatypeInstTypes'. For instance, given @data Proxy (a :: k) = MkProxy@,
-- in the 'DatatypeInfo' for @Proxy@ we would have
-- @'datatypeVars' = ['KindedTV' k 'StarT', 'KindedTV' a ('VarT' k)]@ (since
-- there are two variables, @k@ and @a@), whereas
-- @'datatypeInstTypes' = ['SigT' ('VarT' a) ('VarT' k)]@, since there is
-- only one explicit type argument to @Proxy@.
--
-- * For @data instance@s and @newtype instance@s of data families,
-- 'datatypeVars' and 'datatypeInstTypes' can be quite different. Here is
-- an example to illustrate the difference:
--
-- @
-- data family F a b
-- data instance F (Maybe c) (f x) = MkF c (f x)
-- @
--
-- Then in the 'DatatypeInfo' for @F@'s data instance, we would have:
--
-- @
-- 'datatypeVars' = [ 'KindedTV' c 'StarT'
-- , 'KindedTV' f 'StarT'
-- , 'KindedTV' x 'StarT' ]
-- 'datatypeInstTypes' = [ 'AppT' ('ConT' ''Maybe) ('VarT' c)
-- , 'AppT' ('VarT' f) ('VarT' x) ]
-- @
data DatatypeInfo = DatatypeInfo
{ datatypeContext :: Cxt -- ^ Data type context (deprecated)
, datatypeName :: Name -- ^ Type constructor
, datatypeVars :: [TyVarBndr] -- ^ Type parameters
, datatypeInstTypes :: [Type] -- ^ Argument types
, datatypeVariant :: DatatypeVariant -- ^ Extra information
, datatypeCons :: [ConstructorInfo] -- ^ Normalize constructor information
}
deriving (Show, Eq, Typeable, Data
#ifdef HAS_GENERICS
,Generic
#endif
)
-- | Possible variants of data type declarations.
data DatatypeVariant
= Datatype -- ^ Type declared with @data@
| Newtype -- ^ Type declared with @newtype@
| DataInstance -- ^ Type declared with @data instance@
| NewtypeInstance -- ^ Type declared with @newtype instance@
deriving (Show, Read, Eq, Ord, Typeable, Data
#ifdef HAS_GENERICS
,Generic
#endif
)
-- | Normalized information about constructors associated with newtypes and
-- data types.
data ConstructorInfo = ConstructorInfo
{ constructorName :: Name -- ^ Constructor name
, constructorVars :: [TyVarBndr] -- ^ Constructor type parameters
, constructorContext :: Cxt -- ^ Constructor constraints
, constructorFields :: [Type] -- ^ Constructor fields
, constructorStrictness :: [FieldStrictness] -- ^ Constructor fields' strictness
-- (Invariant: has the same length
-- as constructorFields)
, constructorVariant :: ConstructorVariant -- ^ Extra information
}
deriving (Show, Eq, Typeable, Data
#ifdef HAS_GENERICS
,Generic
#endif
)
-- | Possible variants of data constructors.
data ConstructorVariant
= NormalConstructor -- ^ Constructor without field names
| InfixConstructor -- ^ Constructor without field names that is
-- declared infix
| RecordConstructor [Name] -- ^ Constructor with field names
deriving (Show, Eq, Ord, Typeable, Data
#ifdef HAS_GENERICS
,Generic
#endif
)
-- | Normalized information about a constructor field's @UNPACK@ and
-- strictness annotations.
--
-- Note that the interface for reifying strictness in Template Haskell changed
-- considerably in GHC 8.0. The presentation in this library mirrors that which
-- can be found in GHC 8.0 or later, whereas previously, unpackedness and
-- strictness were represented with a single data type:
--
-- @
-- data Strict
-- = IsStrict
-- | NotStrict
-- | Unpacked -- On GHC 7.4 or later
-- @
--
-- For backwards compatibility, we retrofit these constructors onto the
-- following three values, respectively:
--
-- @
-- 'isStrictAnnot' = 'FieldStrictness' 'UnspecifiedUnpackedness' 'Strict'
-- 'notStrictAnnot' = 'FieldStrictness' 'UnspecifiedUnpackedness' 'UnspecifiedStrictness'
-- 'unpackedAnnot' = 'FieldStrictness' 'Unpack' 'Strict'
-- @
data FieldStrictness = FieldStrictness
{ fieldUnpackedness :: Unpackedness
, fieldStrictness :: Strictness
}
deriving (Show, Eq, Ord, Typeable, Data
#ifdef HAS_GENERICS
,Generic
#endif
)
-- | Information about a constructor field's unpackedness annotation.
data Unpackedness
= UnspecifiedUnpackedness -- ^ No annotation whatsoever
| NoUnpack -- ^ Annotated with @{\-\# NOUNPACK \#-\}@
| Unpack -- ^ Annotated with @{\-\# UNPACK \#-\}@
deriving (Show, Eq, Ord, Typeable, Data
#ifdef HAS_GENERICS
,Generic
#endif
)
-- | Information about a constructor field's strictness annotation.
data Strictness
= UnspecifiedStrictness -- ^ No annotation whatsoever
| Lazy -- ^ Annotated with @~@
| Strict -- ^ Annotated with @!@
deriving (Show, Eq, Ord, Typeable, Data
#ifdef HAS_GENERICS
,Generic
#endif
)
isStrictAnnot, notStrictAnnot, unpackedAnnot :: FieldStrictness
isStrictAnnot = FieldStrictness UnspecifiedUnpackedness Strict
notStrictAnnot = FieldStrictness UnspecifiedUnpackedness UnspecifiedStrictness
unpackedAnnot = FieldStrictness Unpack Strict
-- | Construct a Type using the datatype's type constructor and type
-- parameters. Kind signatures are removed.
datatypeType :: DatatypeInfo -> Type
datatypeType di
= foldl AppT (ConT (datatypeName di))
$ map stripSigT
$ datatypeInstTypes di
-- | Compute a normalized view of the metadata about a data type or newtype
-- given a constructor.
--
-- This function will accept any constructor (value or type) for a type
-- declared with newtype or data. Value constructors must be used to
-- lookup datatype information about /data instances/ and /newtype instances/,
-- as giving the type constructor of a data family is often not enough to
-- determine a particular data family instance.
--
-- In addition, this function will also accept a record selector for a
-- data type with a constructor which uses that record.
--
-- GADT constructors are normalized into datatypes with explicit equality
-- constraints. Note that no effort is made to distinguish between equalities of
-- the same (homogeneous) kind and equalities between different (heterogeneous)
-- kinds. For instance, the following GADT's constructors:
--
-- @
-- data T (a :: k -> *) where
-- MkT1 :: T Proxy
-- MkT2 :: T Maybe
-- @
--
-- will be normalized to the following equality constraints:
--
-- @
-- AppT (AppT EqualityT (VarT a)) (ConT Proxy) -- MkT1
-- AppT (AppT EqualityT (VarT a)) (ConT Maybe) -- MkT2
-- @
--
-- But only the first equality constraint is well kinded, since in the second
-- constraint, the kinds of @(a :: k -> *)@ and @(Maybe :: * -> *)@ are different.
-- Trying to categorize which constraints need homogeneous or heterogeneous
-- equality is tricky, so we leave that task to users of this library.
--
-- This function will apply various bug-fixes to the output of the underlying
-- @template-haskell@ library in order to provide a view of datatypes in
-- as uniform a way as possible.
reifyDatatype ::
Name {- ^ data type or constructor name -} ->
Q DatatypeInfo
reifyDatatype n = normalizeInfo' "reifyDatatype" isReified =<< reify n
-- | Compute a normalized view of the metadata about a constructor given its
-- 'Name'. This is useful for scenarios when you don't care about the info for
-- the enclosing data type.
reifyConstructor ::
Name {- ^ constructor name -} ->
Q ConstructorInfo
reifyConstructor conName = do
dataInfo <- reifyDatatype conName
return $ lookupByConstructorName conName dataInfo
-- | Compute a normalized view of the metadata about a constructor given the
-- 'Name' of one of its record selectors. This is useful for scenarios when you
-- don't care about the info for the enclosing data type.
reifyRecord ::
Name {- ^ record name -} ->
Q ConstructorInfo
reifyRecord recordName = do
dataInfo <- reifyDatatype recordName
return $ lookupByRecordName recordName dataInfo
-- | Given a 'DatatypeInfo', find the 'ConstructorInfo' corresponding to the
-- 'Name' of one of its constructors.
lookupByConstructorName ::
Name {- ^ constructor name -} ->
DatatypeInfo {- ^ info for the datatype which has that constructor -} ->
ConstructorInfo
lookupByConstructorName conName dataInfo =
case find ((== conName) . constructorName) (datatypeCons dataInfo) of
Just conInfo -> conInfo
Nothing -> error $ "Datatype " ++ nameBase (datatypeName dataInfo)
++ " does not have a constructor named " ++ nameBase conName
-- | Given a 'DatatypeInfo', find the 'ConstructorInfo' corresponding to the
-- 'Name' of one of its constructors.
lookupByRecordName ::
Name {- ^ record name -} ->
DatatypeInfo {- ^ info for the datatype which has that constructor -} ->
ConstructorInfo
lookupByRecordName recordName dataInfo =
case find (conHasRecord recordName) (datatypeCons dataInfo) of
Just conInfo -> conInfo
Nothing -> error $ "Datatype " ++ nameBase (datatypeName dataInfo)
++ " does not have any constructors with a "
++ "record selector named " ++ nameBase recordName
-- | Normalize 'Info' for a newtype or datatype into a 'DatatypeInfo'.
-- Fail in 'Q' otherwise.
normalizeInfo :: Info -> Q DatatypeInfo
normalizeInfo = normalizeInfo' "normalizeInfo" isn'tReified
normalizeInfo' :: String -> IsReifiedDec -> Info -> Q DatatypeInfo
normalizeInfo' entry reifiedDec i =
case i of
PrimTyConI{} -> bad "Primitive type not supported"
ClassI{} -> bad "Class not supported"
#if MIN_VERSION_template_haskell(2,11,0)
FamilyI DataFamilyD{} _ ->
#elif MIN_VERSION_template_haskell(2,7,0)
FamilyI (FamilyD DataFam _ _ _) _ ->
#else
TyConI (FamilyD DataFam _ _ _) ->
#endif
bad "Use a value constructor to reify a data family instance"
#if MIN_VERSION_template_haskell(2,7,0)
FamilyI _ _ -> bad "Type families not supported"
#endif
TyConI dec -> normalizeDecFor reifiedDec dec
#if MIN_VERSION_template_haskell(2,11,0)
DataConI name _ parent -> reifyParent name parent
-- NB: We do not pass the IsReifiedDec information here
-- because there's no point. We have no choice but to
-- call reify here, since we need to determine the
-- parent data type/family.
#else
DataConI name _ parent _ -> reifyParent name parent
#endif
#if MIN_VERSION_template_haskell(2,11,0)
VarI recName recTy _ -> reifyRecordType recName recTy
-- NB: Similarly, we do not pass the IsReifiedDec
-- information here.
#else
VarI recName recTy _ _ -> reifyRecordType recName recTy
#endif
_ -> bad "Expected a type constructor"
where
bad msg = fail (entry ++ ": " ++ msg)
reifyParent :: Name -> Name -> Q DatatypeInfo
reifyParent con = reifyParentWith "reifyParent" p
where
p :: DatatypeInfo -> Bool
p info = con `elem` map constructorName (datatypeCons info)
reifyRecordType :: Name -> Type -> Q DatatypeInfo
reifyRecordType recName recTy =
let (_, _, argTys :|- _) = uncurryType recTy
in case argTys of
dataTy:_ -> decomposeDataType dataTy
_ -> notRecSelFailure
where
decomposeDataType :: Type -> Q DatatypeInfo
decomposeDataType ty =
do case decomposeType ty of
ConT parent :| _ -> reifyParentWith "reifyRecordType" p parent
_ -> notRecSelFailure
notRecSelFailure :: Q a
notRecSelFailure = fail $
"reifyRecordType: Not a record selector type: " ++
nameBase recName ++ " :: " ++ show recTy
p :: DatatypeInfo -> Bool
p info = any (conHasRecord recName) (datatypeCons info)
reifyParentWith ::
String {- ^ prefix for error messages -} ->
(DatatypeInfo -> Bool) {- ^ predicate for finding the right
data family instance -} ->
Name {- ^ parent data type name -} ->
Q DatatypeInfo
reifyParentWith prefix p n =
do info <- reify n
case info of
#if !(MIN_VERSION_template_haskell(2,11,0))
-- This unusual combination of Info and Dec is only possible to reify on
-- GHC 7.0 and 7.2, when you try to reify a data family. Because there's
-- no way to reify the data family *instances* on these versions of GHC,
-- we have no choice but to fail.
TyConI FamilyD{} -> dataFamiliesOnOldGHCsError
#endif
TyConI dec -> normalizeDecFor isReified dec
#if MIN_VERSION_template_haskell(2,7,0)
FamilyI dec instances ->
do let instances1 = map (repairDataFam dec) instances
instances2 <- mapM (normalizeDecFor isReified) instances1
case find p instances2 of
Just inst -> return inst
Nothing -> panic "lost the instance"
#endif
_ -> panic "unexpected parent"
where
dataFamiliesOnOldGHCsError :: Q a
dataFamiliesOnOldGHCsError = fail $
prefix ++ ": Data family instances can only be reified with GHC 7.4 or later"
panic :: String -> Q a
panic message = fail $ "PANIC: " ++ prefix ++ " " ++ message
#if MIN_VERSION_template_haskell(2,8,0) && (!MIN_VERSION_template_haskell(2,10,0))
-- 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
-- A version of repairVarKindsWith that does much more extra work to
-- (1) eta-expand missing type patterns, and (2) ensure that the kind
-- signatures for these new type patterns match accordingly.
repairVarKindsWith' :: [TyVarBndr] -> [Type] -> [Type]
repairVarKindsWith' dvars ts =
let kindVars = freeVariables . map kindPart
kindPart (KindedTV _ k) = [k]
kindPart (PlainTV _ ) = []
nparams = length dvars
kparams = kindVars dvars
(tsKinds,tsNoKinds) = splitAt (length kparams) ts
tsKinds' = map sanitizeStars tsKinds
extraTys = drop (length tsNoKinds) (bndrParams dvars)
ts' = tsNoKinds ++ extraTys -- eta-expand
in applySubstitution (Map.fromList (zip kparams tsKinds')) $
repairVarKindsWith dvars ts'
-- Sadly, Template Haskell's treatment of data family instances leaves much
-- to be desired. Here are some problems that we have to work around:
--
-- 1. On all versions of GHC, TH leaves off the kind signatures on the
-- type patterns of data family instances where a kind signature isn't
-- specified explicitly. Here, we can use the parent data family's
-- type variable binders to reconstruct the kind signatures if they
-- are missing.
-- 2. On GHC 7.6 and 7.8, TH will eta-reduce data instances. We can find
-- the missing type variables on the data constructor.
--
-- We opt to avoid propagating these new type variables through to the
-- constructor now, but we will return to this task in normalizeCon.
repairDataFam ::
Dec {- ^ family declaration -} ->
Dec {- ^ instance declaration -} ->
Dec {- ^ instance declaration -}
repairDataFam
(FamilyD _ _ dvars _)
(NewtypeInstD cx n ts con deriv) =
NewtypeInstD cx n (repairVarKindsWith' dvars ts) con deriv
repairDataFam
(FamilyD _ _ dvars _)
(DataInstD cx n ts cons deriv) =
DataInstD cx n (repairVarKindsWith' dvars ts) cons deriv
#else
repairDataFam famD instD
# if MIN_VERSION_template_haskell(2,15,0)
| DataFamilyD _ dvars _ <- famD
, NewtypeInstD cx mbInstVars nts k c deriv <- instD
, con :| ts <- decomposeType nts
= NewtypeInstD cx mbInstVars
(foldl' AppT con (repairVarKindsWith dvars ts))
k c deriv
| DataFamilyD _ dvars _ <- famD
, DataInstD cx mbInstVars nts k c deriv <- instD
, con :| ts <- decomposeType nts
= DataInstD cx mbInstVars
(foldl' AppT con (repairVarKindsWith dvars ts))
k c deriv
# elif MIN_VERSION_template_haskell(2,11,0)
| DataFamilyD _ dvars _ <- famD
, NewtypeInstD cx n ts k c deriv <- instD
= NewtypeInstD cx n (repairVarKindsWith dvars ts) k c deriv
| DataFamilyD _ dvars _ <- famD
, DataInstD cx n ts k c deriv <- instD
= DataInstD cx n (repairVarKindsWith dvars ts) k c deriv
# else
| FamilyD _ _ dvars _ <- famD
, NewtypeInstD cx n ts c deriv <- instD
= NewtypeInstD cx n (repairVarKindsWith dvars ts) c deriv
| FamilyD _ _ dvars _ <- famD
, DataInstD cx n ts c deriv <- instD
= DataInstD cx n (repairVarKindsWith dvars ts) c deriv
# endif
#endif
repairDataFam _ instD = instD
repairVarKindsWith :: [TyVarBndr] -> [Type] -> [Type]
repairVarKindsWith = zipWith stealKindForType
-- If a VarT is missing an explicit kind signature, steal it from a TyVarBndr.
stealKindForType :: TyVarBndr -> Type -> Type
stealKindForType tvb t@VarT{} = SigT t (tvKind tvb)
stealKindForType _ t = t
-- | Normalize 'Dec' for a newtype or datatype into a 'DatatypeInfo'.
-- Fail in 'Q' otherwise.
--
-- Beware: 'normalizeDec' can have surprising behavior when it comes to fixity.
-- For instance, if you have this quasiquoted data declaration:
--
-- @
-- [d| infix 5 :^^:
-- data Foo where
-- (:^^:) :: Int -> Int -> Foo |]
-- @
--
-- Then if you pass the 'Dec' for @Foo@ to 'normalizeDec' without splicing it
-- in a previous Template Haskell splice, then @(:^^:)@ will be labeled a 'NormalConstructor'
-- instead of an 'InfixConstructor'. This is because Template Haskell has no way to
-- reify the fixity declaration for @(:^^:)@, so it must assume there isn't one. To
-- work around this behavior, use 'reifyDatatype' instead.
normalizeDec :: Dec -> Q DatatypeInfo
normalizeDec = normalizeDecFor isn'tReified
normalizeDecFor :: IsReifiedDec -> Dec -> Q DatatypeInfo
normalizeDecFor isReified dec =
case dec of
#if MIN_VERSION_template_haskell(2,12,0)
NewtypeD context name tyvars mbKind con _derives ->
normalizeDataD context name tyvars mbKind [con] Newtype
DataD context name tyvars mbKind cons _derives ->
normalizeDataD context name tyvars mbKind cons Datatype
# if MIN_VERSION_template_haskell(2,15,0)
NewtypeInstD context mbTyvars nameInstTys mbKind con _derives ->
normalizeDataInstDPostTH2'15 "newtype" context mbTyvars nameInstTys
mbKind [con] NewtypeInstance
DataInstD context mbTyvars nameInstTys mbKind cons _derives ->
normalizeDataInstDPostTH2'15 "data" context mbTyvars nameInstTys
mbKind cons DataInstance
# else
NewtypeInstD context name instTys mbKind con _derives ->
normalizeDataInstDPreTH2'15 context name instTys mbKind [con] NewtypeInstance
DataInstD context name instTys mbKind cons _derives ->
normalizeDataInstDPreTH2'15 context name instTys mbKind cons DataInstance
# endif
#elif MIN_VERSION_template_haskell(2,11,0)
NewtypeD context name tyvars mbKind con _derives ->
normalizeDataD context name tyvars mbKind [con] Newtype
DataD context name tyvars mbKind cons _derives ->
normalizeDataD context name tyvars mbKind cons Datatype
NewtypeInstD context name instTys mbKind con _derives ->
normalizeDataInstDPreTH2'15 context name instTys mbKind [con] NewtypeInstance
DataInstD context name instTys mbKind cons _derives ->
normalizeDataInstDPreTH2'15 context name instTys mbKind cons DataInstance
#else
NewtypeD context name tyvars con _derives ->
normalizeDataD context name tyvars Nothing [con] Newtype
DataD context name tyvars cons _derives ->
normalizeDataD context name tyvars Nothing cons Datatype
NewtypeInstD context name instTys con _derives ->
normalizeDataInstDPreTH2'15 context name instTys Nothing [con] NewtypeInstance
DataInstD context name instTys cons _derives ->
normalizeDataInstDPreTH2'15 context name instTys Nothing cons DataInstance
#endif
_ -> fail "normalizeDecFor: DataD or NewtypeD required"
where
-- We only need to repair reified declarations for data family instances.
repair13618' :: DatatypeInfo -> Q DatatypeInfo
repair13618' di@DatatypeInfo{datatypeVariant = variant}
| isReified && isFamInstVariant variant
= repair13618 di
| otherwise
= return di
-- Given a data type's instance types and kind, compute its free variables.
datatypeFreeVars :: [Type] -> Maybe Kind -> [TyVarBndr]
datatypeFreeVars instTys mbKind =
freeVariablesWellScoped $ instTys ++
#if MIN_VERSION_template_haskell(2,8,0)
maybeToList mbKind
#else
[] -- No kind variables
#endif
normalizeDataD :: Cxt -> Name -> [TyVarBndr] -> Maybe Kind
-> [Con] -> DatatypeVariant -> Q DatatypeInfo
normalizeDataD context name tyvars mbKind cons variant =
let params = bndrParams tyvars in
normalize' context name (datatypeFreeVars params mbKind)
params mbKind cons variant
normalizeDataInstDPostTH2'15
:: String -> Cxt -> Maybe [TyVarBndr] -> Type -> Maybe Kind
-> [Con] -> DatatypeVariant -> Q DatatypeInfo
normalizeDataInstDPostTH2'15 what context mbTyvars nameInstTys
mbKind cons variant =
case decomposeType nameInstTys of
ConT name :| instTys ->
normalize' context name
(fromMaybe (datatypeFreeVars instTys mbKind) mbTyvars)
instTys mbKind cons variant
_ -> fail $ "Unexpected " ++ what ++ " instance head: " ++ pprint nameInstTys
normalizeDataInstDPreTH2'15
:: Cxt -> Name -> [Type] -> Maybe Kind
-> [Con] -> DatatypeVariant -> Q DatatypeInfo
normalizeDataInstDPreTH2'15 context name instTys mbKind cons variant =
normalize' context name (datatypeFreeVars instTys mbKind)
instTys mbKind cons variant
-- The main worker of this function.
normalize' :: Cxt -> Name -> [TyVarBndr] -> [Type] -> Maybe Kind
-> [Con] -> DatatypeVariant -> Q DatatypeInfo
normalize' context name tvbs instTys mbKind cons variant = do
extra_tvbs <- mkExtraKindBinders $ fromMaybe starK mbKind
let tvbs' = tvbs ++ extra_tvbs
instTys' = instTys ++ bndrParams extra_tvbs
dec <- normalizeDec' isReified context name tvbs' instTys' cons variant
repair13618' $ giveDIVarsStarKinds dec
-- | Create new kind variable binder names corresponding to the return kind of
-- a data type. This is useful when you have a data type like:
--
-- @
-- data Foo :: forall k. k -> Type -> Type where ...
-- @
--
-- But you want to be able to refer to the type @Foo a b@.
-- 'mkExtraKindBinders' will take the kind @forall k. k -> Type -> Type@,
-- discover that is has two visible argument kinds, and return as a result
-- two new kind variable binders @[a :: k, b :: Type]@, where @a@ and @b@
-- are fresh type variable names.
--
-- This expands kind synonyms if necessary.
mkExtraKindBinders :: Kind -> Q [TyVarBndr]
mkExtraKindBinders kind = do
kind' <- resolveKindSynonyms kind
let (_, _, args :|- _) = uncurryKind kind'
names <- replicateM (length args) (newName "x")
return $ zipWith KindedTV names args
-- | Is a declaration for a @data instance@ or @newtype instance@?
isFamInstVariant :: DatatypeVariant -> Bool
isFamInstVariant dv =
case dv of
Datatype -> False
Newtype -> False
DataInstance -> True
NewtypeInstance -> True
bndrParams :: [TyVarBndr] -> [Type]
bndrParams = map $ \bndr ->
case bndr of
KindedTV t k -> SigT (VarT t) k
PlainTV t -> VarT t
-- | Extract the kind from a 'TyVarBndr'. Assumes 'PlainTV' has kind @*@.
tvKind :: TyVarBndr -> Kind
tvKind (PlainTV _) = starK
tvKind (KindedTV _ k) = k
-- | Remove the outermost 'SigT'.
stripSigT :: Type -> Type
stripSigT (SigT t _) = t
stripSigT t = t
normalizeDec' ::
IsReifiedDec {- ^ Is this a reified 'Dec'? -} ->
Cxt {- ^ Datatype context -} ->
Name {- ^ Type constructor -} ->
[TyVarBndr] {- ^ Type parameters -} ->
[Type] {- ^ Argument types -} ->
[Con] {- ^ Constructors -} ->
DatatypeVariant {- ^ Extra information -} ->
Q DatatypeInfo
normalizeDec' reifiedDec context name params instTys cons variant =
do cons' <- concat <$> mapM (normalizeConFor reifiedDec name params instTys variant) cons
return DatatypeInfo
{ datatypeContext = context
, datatypeName = name
, datatypeVars = params
, datatypeInstTypes = instTys
, datatypeCons = cons'
, datatypeVariant = variant
}
-- | Normalize a 'Con' into a 'ConstructorInfo'. This requires knowledge of
-- the type and parameters of the constructor, as well as whether the constructor
-- is for a data family instance, as extracted from the outer
-- 'Dec'.
normalizeCon ::
Name {- ^ Type constructor -} ->
[TyVarBndr] {- ^ Type parameters -} ->
[Type] {- ^ Argument types -} ->
DatatypeVariant {- ^ Extra information -} ->
Con {- ^ Constructor -} ->
Q [ConstructorInfo]
normalizeCon = normalizeConFor isn'tReified
normalizeConFor ::
IsReifiedDec {- ^ Is this a reified 'Dec'? -} ->
Name {- ^ Type constructor -} ->
[TyVarBndr] {- ^ Type parameters -} ->
[Type] {- ^ Argument types -} ->
DatatypeVariant {- ^ Extra information -} ->
Con {- ^ Constructor -} ->
Q [ConstructorInfo]
normalizeConFor reifiedDec typename params instTys variant =
fmap (map giveCIVarsStarKinds) . dispatch
where
-- A GADT constructor is declared infix when:
--
-- 1. Its name uses operator syntax (e.g., (:*:))
-- 2. It has exactly two fields
-- 3. It has a programmer-supplied fixity declaration
checkGadtFixity :: [Type] -> Name -> Q ConstructorVariant
checkGadtFixity ts n = do
#if MIN_VERSION_template_haskell(2,11,0)
-- Don't call reifyFixityCompat here! We need to be able to distinguish
-- between a default fixity and an explicit @infixl 9@.
mbFi <- return Nothing `recover` reifyFixity n
let userSuppliedFixity = isJust mbFi
#else
-- On old GHCs, there is a bug where infix GADT constructors will
-- mistakenly be marked as (ForallC (NormalC ...)) instead of
-- (ForallC (InfixC ...)). This is especially annoying since on these
-- versions of GHC, Template Haskell doesn't grant the ability to query
-- whether a constructor was given a user-supplied fixity declaration.
-- Rather, you can only check the fixity that GHC ultimately decides on
-- for a constructor, regardless of whether it was a default fixity or
-- it was user-supplied.
--
-- We can approximate whether a fixity was user-supplied by checking if
-- it is not equal to defaultFixity (infixl 9). Unfortunately,
-- there is no way to distinguish between a user-supplied fixity of
-- infixl 9 and the fixity that GHC defaults to, so we cannot properly
-- handle that case.
mbFi <- reifyFixityCompat n
let userSuppliedFixity = isJust mbFi && mbFi /= Just defaultFixity
#endif
return $ if isInfixDataCon (nameBase n)
&& length ts == 2
&& userSuppliedFixity
then InfixConstructor
else NormalConstructor
-- Checks if a String names a valid Haskell infix data
-- constructor (i.e., does it begin with a colon?).
isInfixDataCon :: String -> Bool
isInfixDataCon (':':_) = True
isInfixDataCon _ = False
dispatch :: Con -> Q [ConstructorInfo]
dispatch =
let defaultCase :: Con -> Q [ConstructorInfo]
defaultCase = go [] [] False
where
go :: [TyVarBndr]
-> Cxt
-> Bool -- Is this a GADT? (see the documentation for
-- for checkGadtFixity)
-> Con
-> Q [ConstructorInfo]
go tyvars context gadt c =
case c of
NormalC n xs -> do
let (bangs, ts) = unzip xs
stricts = map normalizeStrictness bangs
fi <- if gadt
then checkGadtFixity ts n
else return NormalConstructor
return [ConstructorInfo n tyvars context ts stricts fi]
InfixC l n r ->
let (bangs, ts) = unzip [l,r]
stricts = map normalizeStrictness bangs in
return [ConstructorInfo n tyvars context ts stricts
InfixConstructor]
RecC n xs ->
let fns = takeFieldNames xs
stricts = takeFieldStrictness xs in
return [ConstructorInfo n tyvars context
(takeFieldTypes xs) stricts (RecordConstructor fns)]
ForallC tyvars' context' c' ->
go (tyvars'++tyvars) (context'++context) True c'
#if MIN_VERSION_template_haskell(2,11,0)
GadtC ns xs innerType ->
let (bangs, ts) = unzip xs
stricts = map normalizeStrictness bangs in
gadtCase ns innerType ts stricts (checkGadtFixity ts)
RecGadtC ns xs innerType ->
let fns = takeFieldNames xs
stricts = takeFieldStrictness xs in
gadtCase ns innerType (takeFieldTypes xs) stricts
(const $ return $ RecordConstructor fns)
where
gadtCase = normalizeGadtC typename params instTys tyvars context
#endif
#if MIN_VERSION_template_haskell(2,8,0) && (!MIN_VERSION_template_haskell(2,10,0))
dataFamCompatCase :: Con -> Q [ConstructorInfo]
dataFamCompatCase = go []
where
go tyvars c =
case c of
NormalC n xs ->
let stricts = map (normalizeStrictness . fst) xs in
dataFamCase' n stricts NormalConstructor
InfixC l n r ->
let stricts = map (normalizeStrictness . fst) [l,r] in
dataFamCase' n stricts InfixConstructor
RecC n xs ->
let stricts = takeFieldStrictness xs in
dataFamCase' n stricts
(RecordConstructor (takeFieldNames xs))
ForallC tyvars' context' c' ->
go (tyvars'++tyvars) c'
dataFamCase' :: Name -> [FieldStrictness]
-> ConstructorVariant
-> Q [ConstructorInfo]
dataFamCase' n stricts variant = do
mbInfo <- reifyMaybe n
case mbInfo of
Just (DataConI _ ty _ _) -> do
let (tyvars, context, argTys :|- returnTy) = uncurryType ty
returnTy' <- resolveTypeSynonyms returnTy
-- Notice that we've ignored the TyVarBndrs, Cxt and argument
-- Types from the Con argument above, as they might be scoped
-- over eta-reduced variables. Instead of trying to figure out
-- what the eta-reduced variables should be substituted with
-- post facto, we opt for the simpler approach of using the
-- context and argument types from the reified constructor
-- Info, which will at least be correctly scoped. This will
-- make the task of substituting those types with the variables
-- we put in place of the eta-reduced variables
-- (in normalizeDec) much easier.
normalizeGadtC typename params instTys tyvars context [n]
returnTy' argTys stricts (const $ return variant)
_ -> fail $ unlines
[ "normalizeCon: Cannot reify constructor " ++ nameBase n
, "You are likely calling normalizeDec on GHC 7.6 or 7.8 on a data family"
, "whose type variables have been eta-reduced due to GHC Trac #9692."
, "Unfortunately, without being able to reify the constructor's type,"
, "there is no way to recover the eta-reduced type variables in general."
, "A recommended workaround is to use reifyDatatype instead."
]
-- A very ad hoc way of determining if we need to perform some extra passes
-- to repair an eta-reduction bug for data family instances that only occurs
-- with GHC 7.6 and 7.8. We want to avoid doing these passes if at all possible,
-- since they require reifying extra information, and reifying during
-- normalization can be problematic for locally declared Template Haskell
-- splices (see ##22).
mightHaveBeenEtaReduced :: [Type] -> Bool
mightHaveBeenEtaReduced ts =
case unsnoc ts of
Nothing -> False
Just (initTs :|- lastT) ->
case varTName lastT of
Nothing -> False
Just n -> not (n `elem` freeVariables initTs)
-- If the list is empty returns 'Nothing', otherwise returns the
-- 'init' and the 'last'.
unsnoc :: [a] -> Maybe (NonEmptySnoc a)
unsnoc [] = Nothing
unsnoc (x:xs) = case unsnoc xs of
Just (a :|- b) -> Just ((x:a) :|- b)
Nothing -> Just ([] :|- x)
-- If a Type is a VarT, find Just its Name. Otherwise, return Nothing.
varTName :: Type -> Maybe Name
varTName (SigT t _) = varTName t
varTName (VarT n) = Just n
varTName _ = Nothing
in case variant of
-- On GHC 7.6 and 7.8, there's quite a bit of post-processing that
-- needs to be performed to work around an old bug that eta-reduces the
-- type patterns of data families (but only for reified data family instances).
DataInstance
| reifiedDec, mightHaveBeenEtaReduced instTys
-> dataFamCompatCase
NewtypeInstance
| reifiedDec, mightHaveBeenEtaReduced instTys
-> dataFamCompatCase
_ -> defaultCase
#else
in defaultCase
#endif
#if MIN_VERSION_template_haskell(2,11,0)
normalizeStrictness :: Bang -> FieldStrictness
normalizeStrictness (Bang upk str) =
FieldStrictness (normalizeSourceUnpackedness upk)
(normalizeSourceStrictness str)
where
normalizeSourceUnpackedness :: SourceUnpackedness -> Unpackedness
normalizeSourceUnpackedness NoSourceUnpackedness = UnspecifiedUnpackedness
normalizeSourceUnpackedness SourceNoUnpack = NoUnpack
normalizeSourceUnpackedness SourceUnpack = Unpack
normalizeSourceStrictness :: SourceStrictness -> Strictness
normalizeSourceStrictness NoSourceStrictness = UnspecifiedStrictness
normalizeSourceStrictness SourceLazy = Lazy
normalizeSourceStrictness SourceStrict = Strict
#else
normalizeStrictness :: Strict -> FieldStrictness
normalizeStrictness IsStrict = isStrictAnnot
normalizeStrictness NotStrict = notStrictAnnot
# if MIN_VERSION_template_haskell(2,7,0)
normalizeStrictness Unpacked = unpackedAnnot
# endif
#endif
normalizeGadtC ::
Name {- ^ Type constructor -} ->
[TyVarBndr] {- ^ Type parameters -} ->
[Type] {- ^ Argument types -} ->
[TyVarBndr] {- ^ Constructor parameters -} ->
Cxt {- ^ Constructor context -} ->
[Name] {- ^ Constructor names -} ->
Type {- ^ Declared type of constructor -} ->
[Type] {- ^ Constructor field types -} ->
[FieldStrictness] {- ^ Constructor field strictness -} ->
(Name -> Q ConstructorVariant)
{- ^ Determine a constructor variant
from its 'Name' -} ->
Q [ConstructorInfo]
normalizeGadtC typename params instTys tyvars context names innerType
fields stricts getVariant =
do -- It's possible that the constructor has implicitly quantified type
-- variables, such as in the following example (from #58):
--
-- [d| data Foo where
-- MkFoo :: a -> Foo |]
--
-- normalizeGadtC assumes that all type variables have binders, however,
-- so we use freeVariablesWellScoped to obtain the implicit type
-- variables' binders before proceeding.
let implicitTyvars = freeVariablesWellScoped
[curryType tyvars context fields innerType]
allTyvars = implicitTyvars ++ tyvars
-- Due to GHC Trac #13885, it's possible that the type variables bound by
-- a GADT constructor will shadow those that are bound by the data type.
-- This function assumes this isn't the case in certain parts (e.g., when
-- mergeArguments is invoked), so we do an alpha-renaming of the
-- constructor-bound variables before proceeding. See #36 for an example
-- of what can go wrong if this isn't done.
let conBoundNames =
concatMap (\tvb -> tvName tvb:freeVariables (tvKind tvb)) allTyvars
conSubst <- T.sequence $ Map.fromList [ (n, newName (nameBase n))
| n <- conBoundNames ]
let conSubst' = fmap VarT conSubst
renamedTyvars =
map (\tvb -> case tvb of
PlainTV n -> PlainTV (conSubst Map.! n)
KindedTV n k -> KindedTV (conSubst Map.! n)
(applySubstitution conSubst' k)) allTyvars
renamedContext = applySubstitution conSubst' context
renamedInnerType = applySubstitution conSubst' innerType
renamedFields = applySubstitution conSubst' fields
innerType' <- resolveTypeSynonyms renamedInnerType
case decomposeType innerType' of
ConT innerTyCon :| ts | typename == innerTyCon ->
let (substName, context1) =
closeOverKinds (kindsOfFVsOfTvbs renamedTyvars)
(kindsOfFVsOfTvbs params)
(mergeArguments instTys ts)
subst = VarT <$> substName
exTyvars = [ tv | tv <- renamedTyvars, Map.notMember (tvName tv) subst ]
exTyvars' = substTyVarBndrs subst exTyvars
context2 = applySubstitution subst (context1 ++ renamedContext)
fields' = applySubstitution subst renamedFields
in sequence [ ConstructorInfo name exTyvars' context2
fields' stricts <$> variantQ
| name <- names
, let variantQ = getVariant name
]
_ -> fail "normalizeGadtC: Expected type constructor application"
{-
Extend a type variable renaming subtitution and a list of equality
predicates by looking into kind information as much as possible.
Why is this necessary? Consider the following example:
data (a1 :: k1) :~: (b1 :: k1) where
Refl :: forall k2 (a2 :: k2). a2 :~: a2
After an initial call to mergeArguments, we will have the following
substitution and context:
* Substitution: [a2 :-> a1]
* Context: (a2 ~ b1)
We shouldn't stop there, however! We determine the existentially quantified
type variables of a constructor by filtering out those constructor-bound
variables which do not appear in the substitution that mergeArguments
returns. In this example, Refl's bound variables are k2 and a2. a2 appears
in the returned substitution, but k2 does not, which means that we would
mistakenly conclude that k2 is existential!
Although we don't have the full power of kind inference to guide us here, we
can at least do the next best thing. Generally, the datatype-bound type
variables and the constructor type variable binders contain all of the kind
information we need, so we proceed as follows:
1. Construct a map from each constructor-bound variable to its kind. (Do the
same for each datatype-bound variable). These maps are the first and second
arguments to closeOverKinds, respectively.
2. Call mergeArguments once on the GADT return type and datatype-bound types,
and pass that in as the third argument to closeOverKinds.
3. For each name-name pair in the supplied substitution, check if the first and
second names map to kinds in the first and second kind maps in
closeOverKinds, respectively. If so, associate the first kind with the
second kind.
4. For each kind association discovered in part (3), call mergeArguments
on the lists of kinds. This will yield a kind substitution and kind
equality context.
5. If the kind substitution is non-empty, then go back to step (3) and repeat
the process on the new kind substitution and context.
Otherwise, if the kind substitution is empty, then we have reached a fixed-
point (i.e., we have closed over the kinds), so proceed.
6. Union up all of the substitutions and contexts, and return those.
This algorithm is not perfect, as it will only catch everything if all of
the kinds are explicitly mentioned somewhere (and not left quantified
implicitly). Thankfully, reifying data types via Template Haskell tends to
yield a healthy amount of kind signatures, so this works quite well in
practice.
-}
closeOverKinds :: Map Name Kind
-> Map Name Kind
-> (Map Name Name, Cxt)
-> (Map Name Name, Cxt)
closeOverKinds domainFVKinds rangeFVKinds = go
where
go :: (Map Name Name, Cxt) -> (Map Name Name, Cxt)
go (subst, context) =
let substList = Map.toList subst
(kindsInner, kindsOuter) =
unzip $
mapMaybe (\(d, r) -> do d' <- Map.lookup d domainFVKinds
r' <- Map.lookup r rangeFVKinds
return (d', r'))
substList
(kindSubst, kindContext) = mergeArgumentKinds kindsOuter kindsInner
(restSubst, restContext)
= if Map.null kindSubst -- Fixed-point calculation
then (Map.empty, [])
else go (kindSubst, kindContext)
finalSubst = Map.unions [subst, kindSubst, restSubst]
finalContext = nub $ concat [context, kindContext, restContext]
-- Use `nub` here in an effort to minimize the number of
-- redundant equality constraints in the returned context.
in (finalSubst, finalContext)
-- Look into a list of types and map each free variable name to its kind.
kindsOfFVsOfTypes :: [Type] -> Map Name Kind
kindsOfFVsOfTypes = foldMap go
where
go :: Type -> Map Name Kind
go (AppT t1 t2) = go t1 `Map.union` go t2
go (SigT t k) =
let kSigs =
#if MIN_VERSION_template_haskell(2,8,0)
go k
#else
Map.empty
#endif
in case t of
VarT n -> Map.insert n k kSigs
_ -> go t `Map.union` kSigs
go (ForallT {}) = forallError
#if MIN_VERSION_template_haskell(2,16,0)
go (ForallVisT {}) = forallError
#endif
go _ = Map.empty
forallError :: a
forallError = error "`forall` type used in data family pattern"
-- Look into a list of type variable binder and map each free variable name
-- to its kind (also map the names that KindedTVs bind to their respective
-- kinds). This function considers the kind of a PlainTV to be *.
kindsOfFVsOfTvbs :: [TyVarBndr] -> Map Name Kind
kindsOfFVsOfTvbs = foldMap go
where
go :: TyVarBndr -> Map Name Kind
go (PlainTV n) = Map.singleton n starK
go (KindedTV n k) =
let kSigs =
#if MIN_VERSION_template_haskell(2,8,0)
kindsOfFVsOfTypes [k]
#else
Map.empty
#endif
in Map.insert n k kSigs
mergeArguments ::
[Type] {- ^ outer parameters -} ->
[Type] {- ^ inner parameters (specializations ) -} ->
(Map Name Name, Cxt)
mergeArguments ns ts = foldr aux (Map.empty, []) (zip ns ts)
where
aux (f `AppT` x, g `AppT` y) sc =
aux (x,y) (aux (f,g) sc)
aux (VarT n,p) (subst, context) =
case p of
VarT m | m == n -> (subst, context)
-- If the two variables are the same, don't bother extending
-- the substitution. (This is purely an optimization.)
| Just n' <- Map.lookup m subst
, n == n' -> (subst, context)
-- If a variable is already in a substitution and it maps
-- to the variable that we are trying to unify with, then
-- leave the context alone. (Not doing so caused #46.)
| Map.notMember m subst -> (Map.insert m n subst, context)
_ -> (subst, equalPred (VarT n) p : context)
aux (SigT x _, y) sc = aux (x,y) sc -- learn about kinds??
-- This matches *after* VarT so that we can compute a substitution
-- that includes the kind signature.
aux (x, SigT y _) sc = aux (x,y) sc
aux _ sc = sc
-- | A specialization of 'mergeArguments' to 'Kind'.
-- Needed only for backwards compatibility with older versions of
-- @template-haskell@.
mergeArgumentKinds ::
[Kind] ->
[Kind] ->
(Map Name Name, Cxt)
#if MIN_VERSION_template_haskell(2,8,0)
mergeArgumentKinds = mergeArguments
#else
mergeArgumentKinds _ _ = (Map.empty, [])
#endif
-- | Expand all of the type synonyms in a type.
--
-- Note that this function will drop parentheses as a side effect.
resolveTypeSynonyms :: Type -> Q Type
resolveTypeSynonyms t =
let (f, xs) = decomposeTypeArgs t
notTypeSynCase :: Type -> Q Type
notTypeSynCase ty = foldl appTypeArg ty <$> mapM resolveTypeArgSynonyms xs
expandCon :: Name -- The Name to check whether it is a type synonym or not
-> Type -- The argument type to fall back on if the supplied
-- Name isn't a type synonym
-> Q Type
expandCon n ty = do
mbInfo <- reifyMaybe n
case mbInfo of
Just (TyConI (TySynD _ synvars def))
-> resolveTypeSynonyms $ expandSynonymRHS synvars (filterTANormals xs) def
_ -> notTypeSynCase ty
in case f of
ForallT tvbs ctxt body ->
ForallT `fmap` mapM resolve_tvb_syns tvbs
`ap` mapM resolvePredSynonyms ctxt
`ap` resolveTypeSynonyms body
SigT ty ki -> do
ty' <- resolveTypeSynonyms ty
ki' <- resolveKindSynonyms ki
notTypeSynCase $ SigT ty' ki'
ConT n -> expandCon n (ConT n)
#if MIN_VERSION_template_haskell(2,11,0)
InfixT t1 n t2 -> do
t1' <- resolveTypeSynonyms t1
t2' <- resolveTypeSynonyms t2
expandCon n (InfixT t1' n t2')
UInfixT t1 n t2 -> do
t1' <- resolveTypeSynonyms t1
t2' <- resolveTypeSynonyms t2
expandCon n (UInfixT t1' n t2')
#endif
#if MIN_VERSION_template_haskell(2,15,0)
ImplicitParamT n t -> do
ImplicitParamT n <$> resolveTypeSynonyms t
#endif
#if MIN_VERSION_template_haskell(2,16,0)
ForallVisT tvbs body ->
ForallVisT `fmap` mapM resolve_tvb_syns tvbs
`ap` resolveTypeSynonyms body
#endif
_ -> notTypeSynCase f
-- | Expand all of the type synonyms in a 'TypeArg'.
resolveTypeArgSynonyms :: TypeArg -> Q TypeArg
resolveTypeArgSynonyms (TANormal t) = TANormal <$> resolveTypeSynonyms t
resolveTypeArgSynonyms (TyArg k) = TyArg <$> resolveKindSynonyms k
-- | Expand all of the type synonyms in a 'Kind'.
resolveKindSynonyms :: Kind -> Q Kind
#if MIN_VERSION_template_haskell(2,8,0)
resolveKindSynonyms = resolveTypeSynonyms
#else
resolveKindSynonyms = return -- One simply couldn't put type synonyms into
-- kinds on old versions of GHC.
#endif
-- | Expand all of the type synonyms in a the kind of a 'TyVarBndr'.
resolve_tvb_syns :: TyVarBndr -> Q TyVarBndr
resolve_tvb_syns tvb@PlainTV{} = return tvb
resolve_tvb_syns (KindedTV n k) = KindedTV n <$> resolveKindSynonyms k
expandSynonymRHS ::
[TyVarBndr] {- ^ Substitute these variables... -} ->
[Type] {- ^ ...with these types... -} ->
Type {- ^ ...inside of this type. -} ->
Type
expandSynonymRHS synvars ts def =
let argNames = map tvName synvars
(args,rest) = splitAt (length argNames) ts
subst = Map.fromList (zip argNames args)
in foldl AppT (applySubstitution subst def) rest
-- | Expand all of the type synonyms in a 'Pred'.
resolvePredSynonyms :: Pred -> Q Pred
#if MIN_VERSION_template_haskell(2,10,0)
resolvePredSynonyms = resolveTypeSynonyms
#else
resolvePredSynonyms (ClassP n ts) = do
mbInfo <- reifyMaybe n
case mbInfo of
Just (TyConI (TySynD _ synvars def))
-> resolvePredSynonyms $ typeToPred $ expandSynonymRHS synvars ts def
_ -> ClassP n <$> mapM resolveTypeSynonyms ts
resolvePredSynonyms (EqualP t1 t2) = do
t1' <- resolveTypeSynonyms t1
t2' <- resolveTypeSynonyms t2
return (EqualP t1' t2')
typeToPred :: Type -> Pred
typeToPred t =
let f :| xs = decomposeType t in
case f of
ConT n
| n == eqTypeName
# if __GLASGOW_HASKELL__ == 704
-- There's an unfortunate bug in GHC 7.4 where the (~) type is reified
-- with an explicit kind argument. To work around this, we ignore it.
, [_,t1,t2] <- xs
# else
, [t1,t2] <- xs
# endif
-> EqualP t1 t2
| otherwise
-> ClassP n xs
_ -> error $ "typeToPred: Can't handle type " ++ show t
#endif
-- | Decompose a type into a list of it's outermost applications. This process
-- forgets about infix application, explicit parentheses, and visible kind
-- applications.
--
-- This operation should be used after all 'UInfixT' cases have been resolved
-- by 'resolveFixities' if the argument is being user generated.
--
-- > t ~= foldl1 AppT (decomposeType t)
decomposeType :: Type -> NonEmpty Type
decomposeType t =
case decomposeTypeArgs t of
(f, x) -> f :| filterTANormals x
-- | A variant of 'decomposeType' that preserves information about visible kind
-- applications by returning a 'NonEmpty' list of 'TypeArg's.
decomposeTypeArgs :: Type -> (Type, [TypeArg])
decomposeTypeArgs = go []
where
go :: [TypeArg] -> Type -> (Type, [TypeArg])
go args (AppT f x) = go (TANormal x:args) f
#if MIN_VERSION_template_haskell(2,11,0)
go args (ParensT t) = go args t
#endif
#if MIN_VERSION_template_haskell(2,15,0)
go args (AppKindT f x) = go (TyArg x:args) f
#endif
go args t = (t, args)
-- | An argument to a type, either a normal type ('TANormal') or a visible
-- kind application ('TyArg').
data TypeArg
= TANormal Type
| TyArg Kind
-- | Apply a 'Type' to a 'TypeArg'.
appTypeArg :: Type -> TypeArg -> Type
appTypeArg f (TANormal x) = f `AppT` x
appTypeArg f (TyArg _k) =
#if MIN_VERSION_template_haskell(2,15,0)
f `AppKindT` _k
#else
f -- VKA isn't supported, so conservatively drop the argument
#endif
-- | Filter out all of the normal type arguments from a list of 'TypeArg's.
filterTANormals :: [TypeArg] -> [Type]
filterTANormals = mapMaybe f
where
f :: TypeArg -> Maybe Type
f (TANormal t) = Just t
f (TyArg {}) = Nothing
-- 'NonEmpty' didn't move into base until recently. Reimplementing it locally
-- saves dependencies for supporting older GHCs
data NonEmpty a = a :| [a]
data NonEmptySnoc a = [a] :|- a
-- Decompose a function type into its context, argument types,
-- and return type. For instance, this
--
-- forall a b. (Show a, b ~ Int) => (a -> b) -> Char -> Int
--
-- becomes
--
-- ([a, b], [Show a, b ~ Int], [a -> b, Char] :|- Int)
uncurryType :: Type -> ([TyVarBndr], Cxt, NonEmptySnoc Type)
uncurryType = go [] [] []
where
go tvbs ctxt args (AppT (AppT ArrowT t1) t2) = go tvbs ctxt (t1:args) t2
go tvbs ctxt args (ForallT tvbs' ctxt' t) = go (tvbs++tvbs') (ctxt++ctxt') args t
go tvbs ctxt args t = (tvbs, ctxt, reverse args :|- t)
-- | Decompose a function kind into its context, argument kinds,
-- and return kind. For instance, this
--
-- forall a b. Maybe a -> Maybe b -> Type
--
-- becomes
--
-- ([a, b], [], [Maybe a, Maybe b] :|- Type)
uncurryKind :: Kind -> ([TyVarBndr], Cxt, NonEmptySnoc Kind)
#if MIN_VERSION_template_haskell(2,8,0)
uncurryKind = uncurryType
#else
uncurryKind = go []
where
go args (ArrowK k1 k2) = go (k1:args) k2
go args StarK = ([], [], reverse args :|- StarK)
#endif
-- Reconstruct a function type from its type variable binders, context,
-- argument types and return type.
curryType :: [TyVarBndr] -> Cxt -> [Type] -> Type -> Type
curryType tvbs ctxt args res =
ForallT tvbs ctxt $ foldr (\arg t -> ArrowT `AppT` arg `AppT` t) res args
-- | Resolve any infix type application in a type using the fixities that
-- are currently available. Starting in `template-haskell-2.11` types could
-- contain unresolved infix applications.
resolveInfixT :: Type -> Q Type
#if MIN_VERSION_template_haskell(2,11,0)
resolveInfixT (ForallT vs cx t) = ForallT <$> traverse (traverseTvbKind resolveInfixT) vs
<*> mapM resolveInfixT cx
<*> resolveInfixT t
resolveInfixT (f `AppT` x) = resolveInfixT f `appT` resolveInfixT x
resolveInfixT (ParensT t) = resolveInfixT t
resolveInfixT (InfixT l o r) = conT o `appT` resolveInfixT l `appT` resolveInfixT r
resolveInfixT (SigT t k) = SigT <$> resolveInfixT t <*> resolveInfixT k
resolveInfixT t@UInfixT{} = resolveInfixT =<< resolveInfixT1 (gatherUInfixT t)
# if MIN_VERSION_template_haskell(2,15,0)
resolveInfixT (f `AppKindT` x) = appKindT (resolveInfixT f) (resolveInfixT x)
resolveInfixT (ImplicitParamT n t)
= implicitParamT n $ resolveInfixT t
# endif
# if MIN_VERSION_template_haskell(2,16,0)
resolveInfixT (ForallVisT vs t) = ForallVisT <$> traverse (traverseTvbKind resolveInfixT) vs
<*> resolveInfixT t
# endif
resolveInfixT t = return t
gatherUInfixT :: Type -> InfixList
gatherUInfixT (UInfixT l o r) = ilAppend (gatherUInfixT l) o (gatherUInfixT r)
gatherUInfixT t = ILNil t
-- This can fail due to incompatible fixities
resolveInfixT1 :: InfixList -> TypeQ
resolveInfixT1 = go []
where
go :: [(Type,Name,Fixity)] -> InfixList -> TypeQ
go ts (ILNil u) = return (foldl (\acc (l,o,_) -> ConT o `AppT` l `AppT` acc) u ts)
go ts (ILCons l o r) =
do ofx <- fromMaybe defaultFixity <$> reifyFixityCompat o
let push = go ((l,o,ofx):ts) r
case ts of
(l1,o1,o1fx):ts' ->
case compareFixity o1fx ofx of
Just True -> go ((ConT o1 `AppT` l1 `AppT` l, o, ofx):ts') r
Just False -> push
Nothing -> fail (precedenceError o1 o1fx o ofx)
_ -> push
compareFixity :: Fixity -> Fixity -> Maybe Bool
compareFixity (Fixity n1 InfixL) (Fixity n2 InfixL) = Just (n1 >= n2)
compareFixity (Fixity n1 InfixR) (Fixity n2 InfixR) = Just (n1 > n2)
compareFixity (Fixity n1 _ ) (Fixity n2 _ ) =
case compare n1 n2 of
GT -> Just True
LT -> Just False
EQ -> Nothing
precedenceError :: Name -> Fixity -> Name -> Fixity -> String
precedenceError o1 ofx1 o2 ofx2 =
"Precedence parsing error: cannot mix ‘" ++
nameBase o1 ++ "’ [" ++ showFixity ofx1 ++ "] and ‘" ++
nameBase o2 ++ "’ [" ++ showFixity ofx2 ++
"] in the same infix type expression"
data InfixList = ILCons Type Name InfixList | ILNil Type
ilAppend :: InfixList -> Name -> InfixList -> InfixList
ilAppend (ILNil l) o r = ILCons l o r
ilAppend (ILCons l1 o1 r1) o r = ILCons l1 o1 (ilAppend r1 o r)
#else
-- older template-haskell packages don't have UInfixT
resolveInfixT = return
#endif
-- | Render a 'Fixity' as it would appear in Haskell source.
--
-- Example: @infixl 5@
showFixity :: Fixity -> String
showFixity (Fixity n d) = showFixityDirection d ++ " " ++ show n
-- | Render a 'FixityDirection' like it would appear in Haskell source.
--
-- Examples: @infixl@ @infixr@ @infix@
showFixityDirection :: FixityDirection -> String
showFixityDirection InfixL = "infixl"
showFixityDirection InfixR = "infixr"
showFixityDirection InfixN = "infix"
-- | Extract the type variable name from a 'TyVarBndr' ignoring the
-- kind signature if one exists.
tvName :: TyVarBndr -> Name
tvName (PlainTV name ) = name
tvName (KindedTV name _) = name
takeFieldNames :: [(Name,a,b)] -> [Name]
takeFieldNames xs = [a | (a,_,_) <- xs]
#if MIN_VERSION_template_haskell(2,11,0)
takeFieldStrictness :: [(a,Bang,b)] -> [FieldStrictness]
#else
takeFieldStrictness :: [(a,Strict,b)] -> [FieldStrictness]
#endif
takeFieldStrictness xs = [normalizeStrictness a | (_,a,_) <- xs]
takeFieldTypes :: [(a,b,Type)] -> [Type]
takeFieldTypes xs = [a | (_,_,a) <- xs]
conHasRecord :: Name -> ConstructorInfo -> Bool
conHasRecord recName info =
case constructorVariant info of
NormalConstructor -> False
InfixConstructor -> False
RecordConstructor fields -> recName `elem` fields
------------------------------------------------------------------------
-- | Add universal quantifier for all free variables in the type. This is
-- useful when constructing a type signature for a declaration.
-- This code is careful to ensure that the order of the variables quantified
-- is determined by their order of appearance in the type signature. (In
-- contrast with being dependent upon the Ord instance for 'Name')
quantifyType :: Type -> Type
quantifyType t
| null tvbs
= t
| ForallT tvbs' ctxt' t' <- t -- Collapse two consecutive foralls (#63)
= ForallT (tvbs ++ tvbs') ctxt' t'
| otherwise
= ForallT tvbs [] t
where
tvbs = freeVariablesWellScoped [t]
-- | Take a list of 'Type's, find their free variables, and sort them
-- according to dependency order.
--
-- As an example of how this function works, consider the following type:
--
-- @
-- Proxy (a :: k)
-- @
--
-- Calling 'freeVariables' on this type would yield @[a, k]@, since that is
-- the order in which those variables appear in a left-to-right fashion. But
-- this order does not preserve the fact that @k@ is the kind of @a@. Moreover,
-- if you tried writing the type @forall a k. Proxy (a :: k)@, GHC would reject
-- this, since GHC would demand that @k@ come before @a@.
--
-- 'freeVariablesWellScoped' orders the free variables of a type in a way that
-- preserves this dependency ordering. If one were to call
-- 'freeVariablesWellScoped' on the type above, it would return
-- @[k, (a :: k)]@. (This is why 'freeVariablesWellScoped' returns a list of
-- 'TyVarBndr's instead of 'Name's, since it must make it explicit that @k@
-- is the kind of @a@.)
--
-- 'freeVariablesWellScoped' guarantees the free variables returned will be
-- ordered such that:
--
-- 1. Whenever an explicit kind signature of the form @(A :: K)@ is
-- encountered, the free variables of @K@ will always appear to the left of
-- the free variables of @A@ in the returned result.
--
-- 2. The constraint in (1) notwithstanding, free variables will appear in
-- left-to-right order of their original appearance.
--
-- On older GHCs, this takes measures to avoid returning explicitly bound
-- kind variables, which was not possible before @TypeInType@.
freeVariablesWellScoped :: [Type] -> [TyVarBndr]
freeVariablesWellScoped tys =
let fvs :: [Name]
fvs = freeVariables tys
varKindSigs :: Map Name Kind
varKindSigs = foldMap go_ty tys
where
go_ty :: Type -> Map Name Kind
go_ty (ForallT tvbs ctxt t) =
foldr (\tvb -> Map.delete (tvName tvb))
(foldMap go_pred ctxt `mappend` go_ty t) tvbs
go_ty (AppT t1 t2) = go_ty t1 `mappend` go_ty t2
go_ty (SigT t k) =
let kSigs =
#if MIN_VERSION_template_haskell(2,8,0)
go_ty k
#else
mempty
#endif
in case t of
VarT n -> Map.insert n k kSigs
_ -> go_ty t `mappend` kSigs
#if MIN_VERSION_template_haskell(2,15,0)
go_ty (AppKindT t k) = go_ty t `mappend` go_ty k
go_ty (ImplicitParamT _ t) = go_ty t
#endif
#if MIN_VERSION_template_haskell(2,16,0)
go_ty (ForallVisT tvbs t) =
foldr (\tvb -> Map.delete (tvName tvb)) (go_ty t) tvbs
#endif
go_ty _ = mempty
go_pred :: Pred -> Map Name Kind
#if MIN_VERSION_template_haskell(2,10,0)
go_pred = go_ty
#else
go_pred (ClassP _ ts) = foldMap go_ty ts
go_pred (EqualP t1 t2) = go_ty t1 `mappend` go_ty t2
#endif
-- | Do a topological sort on a list of tyvars,
-- so that binders occur before occurrences
-- E.g. given [ a::k, k::*, b::k ]
-- it'll return a well-scoped list [ k::*, a::k, b::k ]
--
-- This is a deterministic sorting operation
-- (that is, doesn't depend on Uniques).
--
-- It is also meant to be stable: that is, variables should not
-- be reordered unnecessarily.
scopedSort :: [Name] -> [Name]
scopedSort = go [] []
go :: [Name] -- already sorted, in reverse order
-> [Set Name] -- each set contains all the variables which must be placed
-- before the tv corresponding to the set; they are accumulations
-- of the fvs in the sorted tvs' kinds
-- This list is in 1-to-1 correspondence with the sorted tyvars
-- INVARIANT:
-- all (\tl -> all (`isSubsetOf` head tl) (tail tl)) (tails fv_list)
-- That is, each set in the list is a superset of all later sets.
-> [Name] -- yet to be sorted
-> [Name]
go acc _fv_list [] = reverse acc
go acc fv_list (tv:tvs)
= go acc' fv_list' tvs
where
(acc', fv_list') = insert tv acc fv_list
insert :: Name -- var to insert
-> [Name] -- sorted list, in reverse order
-> [Set Name] -- list of fvs, as above
-> ([Name], [Set Name]) -- augmented lists
insert tv [] [] = ([tv], [kindFVSet tv])
insert tv (a:as) (fvs:fvss)
| tv `Set.member` fvs
, (as', fvss') <- insert tv as fvss
= (a:as', fvs `Set.union` fv_tv : fvss')
| otherwise
= (tv:a:as, fvs `Set.union` fv_tv : fvs : fvss)
where
fv_tv = kindFVSet tv
-- lists not in correspondence
insert _ _ _ = error "scopedSort"
kindFVSet n =
maybe Set.empty (Set.fromList . freeVariables) (Map.lookup n varKindSigs)
ascribeWithKind n =
maybe (PlainTV n) (KindedTV n) (Map.lookup n varKindSigs)
-- An annoying wrinkle: GHCs before 8.0 don't support explicitly
-- quantifying kinds, so something like @forall k (a :: k)@ would be
-- rejected. To work around this, we filter out any binders whose names
-- also appear in a kind on old GHCs.
isKindBinderOnOldGHCs
#if __GLASGOW_HASKELL__ >= 800
= const False
#else
= (`elem` kindVars)
where
kindVars = freeVariables $ Map.elems varKindSigs
#endif
in map ascribeWithKind $
filter (not . isKindBinderOnOldGHCs) $
scopedSort fvs
-- | Substitute all of the free variables in a type with fresh ones
freshenFreeVariables :: Type -> Q Type
freshenFreeVariables t =
do let xs = [ (n, VarT <$> newName (nameBase n)) | n <- freeVariables t]
subst <- T.sequence (Map.fromList xs)
return (applySubstitution subst t)
-- | Class for types that support type variable substitution.
class TypeSubstitution a where
-- | Apply a type variable substitution.
--
-- Note that 'applySubstitution' is /not/ capture-avoiding. To illustrate
-- this, observe that if you call this function with the following
-- substitution:
--
-- * @b :-> a@
--
-- On the following 'Type':
--
-- * @forall a. b@
--
-- Then it will return:
--
-- * @forall a. a@
--
-- However, because the same @a@ type variable was used in the range of the
-- substitution as was bound by the @forall@, the substituted @a@ is now
-- captured by the @forall@, resulting in a completely different function.
--
-- For @th-abstraction@'s purposes, this is acceptable, as it usually only
-- deals with globally unique type variable 'Name's. If you use
-- 'applySubstitution' in a context where the 'Name's aren't globally unique,
-- however, be aware of this potential problem.
applySubstitution :: Map Name Type -> a -> a
-- | Compute the free type variables
freeVariables :: a -> [Name]
instance TypeSubstitution a => TypeSubstitution [a] where
freeVariables = nub . concat . map freeVariables
applySubstitution = fmap . applySubstitution
instance TypeSubstitution Type where
applySubstitution subst = go
where
go (ForallT tvs context t) =
subst_tvbs tvs $ \subst' ->
ForallT (map (mapTvbKind (applySubstitution subst')) tvs)
(applySubstitution subst' context)
(applySubstitution subst' t)
go (AppT f x) = AppT (go f) (go x)
go (SigT t k) = SigT (go t) (applySubstitution subst k) -- k could be Kind
go (VarT v) = Map.findWithDefault (VarT v) v subst
#if MIN_VERSION_template_haskell(2,11,0)
go (InfixT l c r) = InfixT (go l) c (go r)
go (UInfixT l c r) = UInfixT (go l) c (go r)
go (ParensT t) = ParensT (go t)
#endif
#if MIN_VERSION_template_haskell(2,15,0)
go (AppKindT t k) = AppKindT (go t) (go k)
go (ImplicitParamT n t)
= ImplicitParamT n (go t)
#endif
#if MIN_VERSION_template_haskell(2,16,0)
go (ForallVisT tvs t) =
subst_tvbs tvs $ \subst' ->
ForallVisT (map (mapTvbKind (applySubstitution subst')) tvs)
(applySubstitution subst' t)
#endif
go t = t
subst_tvbs :: [TyVarBndr] -> (Map Name Type -> a) -> a
subst_tvbs tvs k = k $ foldl' (flip Map.delete) subst (map tvName tvs)
freeVariables t =
case t of
ForallT tvs context t' ->
fvs_under_forall tvs (freeVariables context `union` freeVariables t')
AppT f x -> freeVariables f `union` freeVariables x
SigT t' k -> freeVariables t' `union` freeVariables k
VarT v -> [v]
#if MIN_VERSION_template_haskell(2,11,0)
InfixT l _ r -> freeVariables l `union` freeVariables r
UInfixT l _ r -> freeVariables l `union` freeVariables r
ParensT t' -> freeVariables t'
#endif
#if MIN_VERSION_template_haskell(2,15,0)
AppKindT t k -> freeVariables t `union` freeVariables k
ImplicitParamT _ t
-> freeVariables t
#endif
#if MIN_VERSION_template_haskell(2,16,0)
ForallVisT tvs t'
-> fvs_under_forall tvs (freeVariables t')
#endif
_ -> []
where
fvs_under_forall :: [TyVarBndr] -> [Name] -> [Name]
fvs_under_forall tvs fvs =
(freeVariables (map tvKind tvs) `union` fvs)
\\ map tvName tvs
instance TypeSubstitution ConstructorInfo where
freeVariables ci =
(freeVariables (map tvKind (constructorVars ci))
`union` freeVariables (constructorContext ci)
`union` freeVariables (constructorFields ci))
\\ (tvName <$> constructorVars ci)
applySubstitution subst ci =
let subst' = foldl' (flip Map.delete) subst (map tvName (constructorVars ci)) in
ci { constructorVars = map (mapTvbKind (applySubstitution subst'))
(constructorVars ci)
, constructorContext = applySubstitution subst' (constructorContext ci)
, constructorFields = applySubstitution subst' (constructorFields ci)
}
mapTvbKind :: (Kind -> Kind) -> TyVarBndr -> TyVarBndr
mapTvbKind f tvb@PlainTV{} = tvb
mapTvbKind f (KindedTV n k) = KindedTV n (f k)
traverseTvbKind :: Applicative f => (Kind -> f Kind) -> TyVarBndr -> f TyVarBndr
traverseTvbKind f tvb@PlainTV{} = pure tvb
traverseTvbKind f (KindedTV n k) = KindedTV n <$> f k
-- 'Pred' became a type synonym for 'Type'
#if !MIN_VERSION_template_haskell(2,10,0)
instance TypeSubstitution Pred where
freeVariables (ClassP _ xs) = freeVariables xs
freeVariables (EqualP x y) = freeVariables x `union` freeVariables y
applySubstitution p (ClassP n xs) = ClassP n (applySubstitution p xs)
applySubstitution p (EqualP x y) = EqualP (applySubstitution p x)
(applySubstitution p y)
#endif
-- 'Kind' became a type synonym for 'Type'. Previously there were no kind variables
#if !MIN_VERSION_template_haskell(2,8,0)
instance TypeSubstitution Kind where
freeVariables _ = []
applySubstitution _ k = k
#endif
-- | Substitutes into the kinds of type variable binders.
-- Not capture-avoiding.
substTyVarBndrs :: Map Name Type -> [TyVarBndr] -> [TyVarBndr]
substTyVarBndrs subst = map go
where
go tvb@(PlainTV {}) = tvb
go (KindedTV n k) = KindedTV n (applySubstitution subst k)
------------------------------------------------------------------------
combineSubstitutions :: Map Name Type -> Map Name Type -> Map Name Type
combineSubstitutions x y = Map.union (fmap (applySubstitution y) x) y
-- | Compute the type variable substitution that unifies a list of types,
-- or fail in 'Q'.
--
-- All infix issue should be resolved before using 'unifyTypes'
--
-- Alpha equivalent quantified types are not unified.
unifyTypes :: [Type] -> Q (Map Name Type)
unifyTypes [] = return Map.empty
unifyTypes (t:ts) =
do t':ts' <- mapM resolveTypeSynonyms (t:ts)
let aux sub u =
do sub' <- unify' (applySubstitution sub t')
(applySubstitution sub u)
return (combineSubstitutions sub sub')
case foldM aux Map.empty ts' of
Right m -> return m
Left (x,y) ->
fail $ showString "Unable to unify types "
. showsPrec 11 x
. showString " and "
. showsPrec 11 y
$ ""
unify' :: Type -> Type -> Either (Type,Type) (Map Name Type)
unify' (VarT n) (VarT m) | n == m = pure Map.empty
unify' (VarT n) t | n `elem` freeVariables t = Left (VarT n, t)
| otherwise = Right (Map.singleton n t)
unify' t (VarT n) | n `elem` freeVariables t = Left (VarT n, t)
| otherwise = Right (Map.singleton n t)
unify' (AppT f1 x1) (AppT f2 x2) =
do sub1 <- unify' f1 f2
sub2 <- unify' (applySubstitution sub1 x1) (applySubstitution sub1 x2)
Right (combineSubstitutions sub1 sub2)
-- Doesn't unify kind signatures
unify' (SigT t _) u = unify' t u
unify' t (SigT u _) = unify' t u
-- only non-recursive cases should remain at this point
unify' t u
| t == u = Right Map.empty
| otherwise = Left (t,u)
-- | Construct an equality constraint. The implementation of 'Pred' varies
-- across versions of Template Haskell.
equalPred :: Type -> Type -> Pred
equalPred x y =
#if MIN_VERSION_template_haskell(2,10,0)
AppT (AppT EqualityT x) y
#else
EqualP x y
#endif
-- | Construct a typeclass constraint. The implementation of 'Pred' varies
-- across versions of Template Haskell.
classPred :: Name {- ^ class -} -> [Type] {- ^ parameters -} -> Pred
classPred =
#if MIN_VERSION_template_haskell(2,10,0)
foldl AppT . ConT
#else
ClassP
#endif
-- | Match a 'Pred' representing an equality constraint. Returns
-- arguments to the equality constraint if successful.
asEqualPred :: Pred -> Maybe (Type,Type)
#if MIN_VERSION_template_haskell(2,10,0)
asEqualPred (EqualityT `AppT` x `AppT` y) = Just (x,y)
asEqualPred (ConT eq `AppT` x `AppT` y) | eq == eqTypeName = Just (x,y)
#else
asEqualPred (EqualP x y) = Just (x,y)
#endif
asEqualPred _ = Nothing
-- | Match a 'Pred' representing a class constraint.
-- Returns the classname and parameters if successful.
asClassPred :: Pred -> Maybe (Name, [Type])
#if MIN_VERSION_template_haskell(2,10,0)
asClassPred t =
case decomposeType t of
ConT f :| xs | f /= eqTypeName -> Just (f,xs)
_ -> Nothing
#else
asClassPred (ClassP f xs) = Just (f,xs)
asClassPred _ = Nothing
#endif
------------------------------------------------------------------------
-- | If we are working with a 'Dec' obtained via 'reify' (as opposed to one
-- created from, say, [d| ... |] quotes), then we need to apply more hacks than
-- we otherwise would to sanitize the 'Dec'. See #28.
type IsReifiedDec = Bool
isReified, isn'tReified :: IsReifiedDec
isReified = True
isn'tReified = False
-- On old versions of GHC, reify would not give you kind signatures for
-- GADT type variables of kind *. To work around this, we insert the kinds
-- manually on any types without a signature.
giveDIVarsStarKinds :: DatatypeInfo -> DatatypeInfo
giveDIVarsStarKinds info =
info { datatypeVars = map giveTyVarBndrStarKind (datatypeVars info)
, datatypeInstTypes = map giveTypeStarKind (datatypeInstTypes info) }
giveCIVarsStarKinds :: ConstructorInfo -> ConstructorInfo
giveCIVarsStarKinds info =
info { constructorVars = map giveTyVarBndrStarKind (constructorVars info) }
giveTyVarBndrStarKind :: TyVarBndr -> TyVarBndr
giveTyVarBndrStarKind (PlainTV n) = KindedTV n starK
giveTyVarBndrStarKind tvb@KindedTV{} = tvb
giveTypeStarKind :: Type -> Type
giveTypeStarKind t@(VarT n) = SigT t starK
giveTypeStarKind t = t
-- | Prior to GHC 8.2.1, reify was broken for data instances and newtype
-- instances. This code attempts to detect the problem and repair it if
-- possible.
--
-- The particular problem is that the type variables used in the patterns
-- while defining a data family instance do not completely match those
-- used when defining the fields of the value constructors beyond the
-- base names. This code attempts to recover the relationship between the
-- type variables.
--
-- It is possible, however, to generate these kinds of declarations by
-- means other than reify. In these cases the name bases might not be
-- unique and the declarations might be well formed. In such a case this
-- code attempts to avoid altering the declaration.
--
-- https://ghc.haskell.org/trac/ghc/ticket/13618
repair13618 :: DatatypeInfo -> Q DatatypeInfo
repair13618 info =
do s <- T.sequence (Map.fromList substList)
return info { datatypeCons = applySubstitution s (datatypeCons info) }
where
used = freeVariables (datatypeCons info)
bound = map tvName (datatypeVars info)
free = used \\ bound
substList =
[ (u, substEntry u vs)
| u <- free
, let vs = [v | v <- bound, nameBase v == nameBase u]
]
substEntry _ [v] = varT v
substEntry u [] = fail ("Impossible free variable: " ++ show u)
substEntry u _ = fail ("Ambiguous free variable: " ++ show u)
------------------------------------------------------------------------
-- | Backward compatible version of 'dataD'
dataDCompat ::
CxtQ {- ^ context -} ->
Name {- ^ type constructor -} ->
[TyVarBndr] {- ^ type parameters -} ->
[ConQ] {- ^ constructor definitions -} ->
[Name] {- ^ derived class names -} ->
DecQ
#if MIN_VERSION_template_haskell(2,12,0)
dataDCompat c n ts cs ds =
dataD c n ts Nothing cs
(if null ds then [] else [derivClause Nothing (map conT ds)])
#elif MIN_VERSION_template_haskell(2,11,0)
dataDCompat c n ts cs ds =
dataD c n ts Nothing cs
(return (map ConT ds))
#else
dataDCompat = dataD
#endif
-- | Backward compatible version of 'newtypeD'
newtypeDCompat ::
CxtQ {- ^ context -} ->
Name {- ^ type constructor -} ->
[TyVarBndr] {- ^ type parameters -} ->
ConQ {- ^ constructor definition -} ->
[Name] {- ^ derived class names -} ->
DecQ
#if MIN_VERSION_template_haskell(2,12,0)
newtypeDCompat c n ts cs ds =
newtypeD c n ts Nothing cs
(if null ds then [] else [derivClause Nothing (map conT ds)])
#elif MIN_VERSION_template_haskell(2,11,0)
newtypeDCompat c n ts cs ds =
newtypeD c n ts Nothing cs
(return (map ConT ds))
#else
newtypeDCompat = newtypeD
#endif
-- | Backward compatible version of 'tySynInstD'
tySynInstDCompat ::
Name {- ^ type family name -} ->
Maybe [Q TyVarBndr] {- ^ type variable binders -} ->
[TypeQ] {- ^ instance parameters -} ->
TypeQ {- ^ instance result -} ->
DecQ
#if MIN_VERSION_template_haskell(2,15,0)
tySynInstDCompat n mtvbs ps r = TySynInstD <$> (TySynEqn <$> mapM sequence mtvbs
<*> foldl' appT (conT n) ps
<*> r)
#elif MIN_VERSION_template_haskell(2,9,0)
tySynInstDCompat n _ ps r = TySynInstD n <$> (TySynEqn <$> sequence ps <*> r)
#else
tySynInstDCompat n _ = tySynInstD n
#endif
-- | Backward compatible version of 'pragLineD'. Returns
-- 'Nothing' if line pragmas are not suported.
pragLineDCompat ::
Int {- ^ line number -} ->
String {- ^ file name -} ->
Maybe DecQ
#if MIN_VERSION_template_haskell(2,10,0)
pragLineDCompat ln fn = Just (pragLineD ln fn)
#else
pragLineDCompat _ _ = Nothing
#endif
arrowKCompat :: Kind -> Kind -> Kind
#if MIN_VERSION_template_haskell(2,8,0)
arrowKCompat x y = arrowK `appK` x `appK` y
#else
arrowKCompat = arrowK
#endif
------------------------------------------------------------------------
-- | Backwards compatibility wrapper for 'Fixity' lookup.
--
-- In @template-haskell-2.11.0.0@ and later, the answer will always
-- be 'Just' of a fixity.
--
-- Before @template-haskell-2.11.0.0@ it was only possible to determine
-- fixity information for variables, class methods, and data constructors.
-- In this case for type operators the answer could be 'Nothing', which
-- indicates that the answer is unavailable.
reifyFixityCompat :: Name -> Q (Maybe Fixity)
#if MIN_VERSION_template_haskell(2,11,0)
reifyFixityCompat n = recover (return Nothing) ((`mplus` Just defaultFixity) <$> reifyFixity n)
#else
reifyFixityCompat n = recover (return Nothing) $
do info <- reify n
return $! case info of
ClassOpI _ _ _ fixity -> Just fixity
DataConI _ _ _ fixity -> Just fixity
VarI _ _ _ fixity -> Just fixity
_ -> Nothing
#endif
-- | Call 'reify' and return @'Just' info@ if successful or 'Nothing' if
-- reification failed.
reifyMaybe :: Name -> Q (Maybe Info)
reifyMaybe n = return Nothing `recover` fmap Just (reify n)