th-desugar-1.14: Language/Haskell/TH/Desugar/Reify.hs
{- Language/Haskell/TH/Desugar/Reify.hs
(c) Richard Eisenberg 2014
rae@cs.brynmawr.edu
Allows for reification from a list of declarations, without looking a name
up in the environment.
-}
{-# LANGUAGE CPP, GeneralizedNewtypeDeriving, ScopedTypeVariables #-}
module Language.Haskell.TH.Desugar.Reify (
-- * Reification
reifyWithLocals_maybe, reifyWithLocals, reifyWithWarning, reifyInDecs,
-- ** Fixity reification
qReifyFixity, reifyFixity, reifyFixityWithLocals, reifyFixityInDecs,
-- ** Type reification
qReifyType, reifyType,
reifyTypeWithLocals_maybe, reifyTypeWithLocals, reifyTypeInDecs,
-- * Datatype lookup
getDataD, dataConNameToCon, dataConNameToDataName,
-- * Value and type lookup
lookupValueNameWithLocals, lookupTypeNameWithLocals,
mkDataNameWithLocals, mkTypeNameWithLocals,
reifyNameSpace,
-- * Monad support
DsMonad(..), DsM, withLocalDeclarations
) where
import Control.Applicative
import qualified Control.Monad.Fail as Fail
import Control.Monad.Reader
import Control.Monad.State
import Control.Monad.Writer
import Control.Monad.RWS
import Control.Monad.Trans.Instances ()
import qualified Data.Foldable as F
import Data.Function (on)
import qualified Data.List as List
import qualified Data.Map as Map
import Data.Map (Map)
import Data.Maybe
import qualified Data.Set as Set
import Data.Set (Set)
import Language.Haskell.TH.Datatype
import Language.Haskell.TH.Datatype.TyVarBndr
import Language.Haskell.TH.Instances ()
import Language.Haskell.TH.Syntax hiding ( lift )
import Language.Haskell.TH.Desugar.Util
-- | Like @reify@ from Template Haskell, but looks also in any not-yet-typechecked
-- declarations. To establish this list of not-yet-typechecked declarations,
-- use 'withLocalDeclarations'. Returns 'Nothing' if reification fails.
-- Note that no inferred type information is available from local declarations;
-- bottoms may be used if necessary.
reifyWithLocals_maybe :: DsMonad q => Name -> q (Maybe Info)
reifyWithLocals_maybe name = qRecover
(return . reifyInDecs name =<< localDeclarations)
(Just `fmap` qReify name)
-- | Like 'reifyWithLocals_maybe', but throws an exception upon failure,
-- warning the user about separating splices.
reifyWithLocals :: DsMonad q => Name -> q Info
reifyWithLocals name = do
m_info <- reifyWithLocals_maybe name
case m_info of
Nothing -> reifyFail name
Just i -> return i
-- | Reify a declaration, warning the user about splices if the reify fails.
-- The warning says that reification can fail if you try to reify a type in
-- the same splice as it is declared.
reifyWithWarning :: (Quasi q, Fail.MonadFail q) => Name -> q Info
reifyWithWarning name = qRecover (reifyFail name) (qReify name)
-- | Print out a warning about separating splices and fail.
reifyFail :: Fail.MonadFail m => Name -> m a
reifyFail name =
Fail.fail $ "Looking up " ++ (show name) ++ " in the list of available " ++
"declarations failed.\nThis lookup fails if the declaration " ++
"referenced was made in the same Template\nHaskell splice as the use " ++
"of the declaration. If this is the case, put\nthe reference to " ++
"the declaration in a new splice."
---------------------------------
-- Utilities
---------------------------------
-- | Extract the @TyVarBndr@s and constructors given the @Name@ of a type
getDataD :: DsMonad q
=> String -- ^ Print this out on failure
-> Name -- ^ Name of the datatype (@data@ or @newtype@) of interest
-> q ([TyVarBndrUnit], [Con])
getDataD err name = do
info <- reifyWithLocals name
dec <- case info of
TyConI dec -> return dec
_ -> badDeclaration
case dec of
DataD _cxt _name tvbs mk cons _derivings -> go tvbs mk cons
NewtypeD _cxt _name tvbs mk con _derivings -> go tvbs mk [con]
_ -> badDeclaration
where
go tvbs mk cons = do
let k = fromMaybe (ConT typeKindName) mk
extra_tvbs <- mkExtraKindBinders k
let all_tvbs = tvbs ++ extra_tvbs
return (all_tvbs, cons)
badDeclaration =
fail $ "The name (" ++ (show name) ++ ") refers to something " ++
"other than a datatype. " ++ err
-- | 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 :: forall q. Quasi q => Kind -> q [TyVarBndrUnit]
mkExtraKindBinders k = do
k' <- runQ $ resolveTypeSynonyms k
let (fun_args, _) = unravelType k'
vis_fun_args = filterVisFunArgs fun_args
mapM mk_tvb vis_fun_args
where
mk_tvb :: VisFunArg -> q TyVarBndrUnit
mk_tvb (VisFADep tvb) = return tvb
mk_tvb (VisFAAnon ki) = kindedTV <$> qNewName "a" <*> return ki
-- | From the name of a data constructor, retrive the datatype definition it
-- is a part of.
dataConNameToDataName :: DsMonad q => Name -> q Name
dataConNameToDataName con_name = do
info <- reifyWithLocals con_name
case info of
DataConI _name _type parent_name -> return parent_name
_ -> fail $ "The name " ++ show con_name ++ " does not appear to be " ++
"a data constructor."
-- | From the name of a data constructor, retrieve its definition as a @Con@
dataConNameToCon :: DsMonad q => Name -> q Con
dataConNameToCon con_name = do
-- we need to get the field ordering from the constructor. We must reify
-- the constructor to get the tycon, and then reify the tycon to get the `Con`s
type_name <- dataConNameToDataName con_name
(_, cons) <- getDataD "This seems to be an error in GHC." type_name
let m_con = List.find (any (con_name ==) . get_con_name) cons
case m_con of
Just con -> return con
Nothing -> impossible "Datatype does not contain one of its own constructors."
where
get_con_name (NormalC name _) = [name]
get_con_name (RecC name _) = [name]
get_con_name (InfixC _ name _) = [name]
get_con_name (ForallC _ _ con) = get_con_name con
get_con_name (GadtC names _ _) = names
get_con_name (RecGadtC names _ _) = names
--------------------------------------------------
-- DsMonad
--------------------------------------------------
-- | A 'DsMonad' stores some list of declarations that should be considered
-- in scope. 'DsM' is the prototypical inhabitant of 'DsMonad'.
class (Quasi m, Fail.MonadFail m) => DsMonad m where
-- | Produce a list of local declarations.
localDeclarations :: m [Dec]
instance DsMonad Q where
localDeclarations = return []
instance DsMonad IO where
localDeclarations = return []
-- | A convenient implementation of the 'DsMonad' class. Use by calling
-- 'withLocalDeclarations'.
newtype DsM q a = DsM (ReaderT [Dec] q a)
deriving ( Functor, Applicative, Monad, MonadTrans, Quasi, Fail.MonadFail
#if __GLASGOW_HASKELL__ >= 803
, MonadIO
#endif
)
instance (Quasi q, Fail.MonadFail q) => DsMonad (DsM q) where
localDeclarations = DsM ask
instance DsMonad m => DsMonad (ReaderT r m) where
localDeclarations = lift localDeclarations
instance DsMonad m => DsMonad (StateT s m) where
localDeclarations = lift localDeclarations
instance (DsMonad m, Monoid w) => DsMonad (WriterT w m) where
localDeclarations = lift localDeclarations
instance (DsMonad m, Monoid w) => DsMonad (RWST r w s m) where
localDeclarations = lift localDeclarations
-- | Add a list of declarations to be considered when reifying local
-- declarations.
withLocalDeclarations :: DsMonad q => [Dec] -> DsM q a -> q a
withLocalDeclarations new_decs (DsM x) = do
orig_decs <- localDeclarations
runReaderT x (orig_decs ++ new_decs)
---------------------------
-- Reifying local declarations
---------------------------
-- | Look through a list of declarations and possibly return a relevant 'Info'
reifyInDecs :: Name -> [Dec] -> Maybe Info
reifyInDecs n decs = snd `fmap` firstMatch (reifyInDec n decs) decs
-- | Look through a list of declarations and possibly return a fixity.
reifyFixityInDecs :: Name -> [Dec] -> Maybe Fixity
reifyFixityInDecs n = firstMatch match_fixity
where
match_fixity (InfixD fixity n') | n `nameMatches` n'
= Just fixity
match_fixity (ClassD _ _ _ _ sub_decs) = firstMatch match_fixity sub_decs
match_fixity _ = Nothing
-- | A reified thing along with the name of that thing.
type Named a = (Name, a)
reifyInDec :: Name -> [Dec] -> Dec -> Maybe (Named Info)
reifyInDec n decs (FunD n' _) | n `nameMatches` n' = Just (n', mkVarI n decs)
reifyInDec n decs (ValD pat _ _)
| Just n' <- List.find (nameMatches n) (F.toList (extractBoundNamesPat pat))
= Just (n', mkVarI n decs)
reifyInDec n _ dec@(DataD _ n' _ _ _ _) | n `nameMatches` n' = Just (n', TyConI dec)
reifyInDec n _ dec@(NewtypeD _ n' _ _ _ _) | n `nameMatches` n' = Just (n', TyConI dec)
reifyInDec n _ dec@(TySynD n' _ _) | n `nameMatches` n' = Just (n', TyConI dec)
reifyInDec n decs dec@(ClassD _ n' _ _ _) | n `nameMatches` n'
= Just (n', ClassI (quantifyClassDecMethods dec) (findInstances n decs))
reifyInDec n _ (ForeignD (ImportF _ _ _ n' ty)) | n `nameMatches` n'
= Just (n', mkVarITy n ty)
reifyInDec n _ (ForeignD (ExportF _ _ n' ty)) | n `nameMatches` n'
= Just (n', mkVarITy n ty)
reifyInDec n decs dec@(OpenTypeFamilyD (TypeFamilyHead n' _ _ _)) | n `nameMatches` n'
= Just (n', FamilyI dec (findInstances n decs))
reifyInDec n decs dec@(DataFamilyD n' _ _) | n `nameMatches` n'
= Just (n', FamilyI dec (findInstances n decs))
reifyInDec n _ dec@(ClosedTypeFamilyD (TypeFamilyHead n' _ _ _) _) | n `nameMatches` n'
= Just (n', FamilyI dec [])
#if __GLASGOW_HASKELL__ >= 801
reifyInDec n decs (PatSynD n' _ _ _) | n `nameMatches` n'
= Just (n', mkPatSynI n decs)
#endif
reifyInDec n decs (DataD _ ty_name tvbs _mk cons _)
| Just info <- maybeReifyCon n decs ty_name (map tvbToTANormalWithSig tvbs) cons
= Just info
reifyInDec n decs (NewtypeD _ ty_name tvbs _mk con _)
| Just info <- maybeReifyCon n decs ty_name (map tvbToTANormalWithSig tvbs) [con]
= Just info
reifyInDec n _decs (ClassD _ ty_name tvbs _ sub_decs)
| Just (n', ty) <- findType n sub_decs
= Just (n', ClassOpI n (quantifyClassMethodType ty_name tvbs True ty) ty_name)
reifyInDec n decs (ClassD _ _ _ _ sub_decs)
| Just info <- firstMatch (reifyInDec n decs) sub_decs
-- Important: don't pass (sub_decs ++ decs) to reifyInDec
-- above, or else type family defaults can be confused for
-- actual instances. See #134.
= Just info
reifyInDec n decs (InstanceD _ _ _ sub_decs)
| Just info <- firstMatch reify_in_instance sub_decs
= Just info
where
reify_in_instance dec@(DataInstD {}) = reifyInDec n (sub_decs ++ decs) dec
reify_in_instance dec@(NewtypeInstD {}) = reifyInDec n (sub_decs ++ decs) dec
reify_in_instance _ = Nothing
#if __GLASGOW_HASKELL__ >= 807
reifyInDec n decs (DataInstD _ _ lhs _ cons _)
| (ConT ty_name, tys) <- unfoldType lhs
, Just info <- maybeReifyCon n decs ty_name tys cons
= Just info
reifyInDec n decs (NewtypeInstD _ _ lhs _ con _)
| (ConT ty_name, tys) <- unfoldType lhs
, Just info <- maybeReifyCon n decs ty_name tys [con]
= Just info
#else
reifyInDec n decs (DataInstD _ ty_name tys _ cons _)
| Just info <- maybeReifyCon n decs ty_name (map TANormal tys) cons
= Just info
reifyInDec n decs (NewtypeInstD _ ty_name tys _ con _)
| Just info <- maybeReifyCon n decs ty_name (map TANormal tys) [con]
= Just info
#endif
reifyInDec _ _ _ = Nothing
maybeReifyCon :: Name -> [Dec] -> Name -> [TypeArg] -> [Con] -> Maybe (Named Info)
maybeReifyCon n _decs ty_name ty_args cons
| Just (n', con) <- findCon n cons
-- See Note [Use unSigType in maybeReifyCon]
, let full_con_ty = unSigType $ con_to_type h98_tvbs h98_res_ty con
= Just (n', DataConI n full_con_ty ty_name)
| Just (n', rec_sel_info) <- findRecSelector n cons
, let (tvbs, sel_ty, con_res_ty) = extract_rec_sel_info rec_sel_info
-- See Note [Use unSigType in maybeReifyCon]
full_sel_ty = unSigType $ maybeForallT tvbs [] $ mkArrows [con_res_ty] sel_ty
-- we don't try to ferret out naughty record selectors.
= Just (n', VarI n full_sel_ty Nothing)
where
extract_rec_sel_info :: RecSelInfo -> ([TyVarBndrUnit], Type, Type)
-- Returns ( Selector type variable binders
-- , Record field type
-- , constructor result type )
extract_rec_sel_info rec_sel_info =
case rec_sel_info of
RecSelH98 sel_ty -> (h98_tvbs, sel_ty, h98_res_ty)
RecSelGADT sel_ty con_res_ty ->
( freeVariablesWellScoped [con_res_ty, sel_ty]
, sel_ty, con_res_ty)
h98_tvbs = freeVariablesWellScoped $ map probablyWrongUnTypeArg ty_args
h98_res_ty = applyType (ConT ty_name) ty_args
maybeReifyCon _ _ _ _ _ = Nothing
{-
Note [Use unSigType in maybeReifyCon]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Make sure to call unSigType on the type of a reified data constructor or
record selector. Otherwise, if you have this:
data D (a :: k) = MkD { unD :: Proxy a }
Then the type of unD will be reified as:
unD :: forall k (a :: k). D (a :: k) -> Proxy a
This is contrast to GHC's own reification, which will produce `D a`
(without the explicit kind signature) as the type of the first argument.
-}
-- Reverse-engineer the type of a data constructor.
con_to_type :: [TyVarBndrUnit] -- The type variables bound by a data type head.
-- Only used for Haskell98-style constructors.
-> Type -- The constructor result type.
-- Only used for Haskell98-style constructors.
-> Con -> Type
con_to_type h98_tvbs h98_result_ty con =
case go con of
(is_gadt, ty) | is_gadt -> ty
| otherwise -> maybeForallT h98_tvbs [] ty
where
-- Note that we deliberately ignore linear types and use (->) everywhere.
-- See [Gracefully handling linear types] in L.H.TH.Desugar.Core.
go :: Con -> (Bool, Type) -- The Bool is True when dealing with a GADT
go (NormalC _ stys) = (False, mkArrows (map snd stys) h98_result_ty)
go (RecC _ vstys) = (False, mkArrows (map thdOf3 vstys) h98_result_ty)
go (InfixC t1 _ t2) = (False, mkArrows (map snd [t1, t2]) h98_result_ty)
go (ForallC bndrs cxt c) = liftSnd (ForallT bndrs cxt) (go c)
go (GadtC _ stys rty) = (True, mkArrows (map snd stys) rty)
go (RecGadtC _ vstys rty) = (True, mkArrows (map thdOf3 vstys) rty)
mkVarI :: Name -> [Dec] -> Info
mkVarI n decs = mkVarITy n (maybe (no_type n) snd $ findType n decs)
mkVarITy :: Name -> Type -> Info
mkVarITy n ty = VarI n ty Nothing
findType :: Name -> [Dec] -> Maybe (Named Type)
findType n = firstMatch match_type
where
match_type (SigD n' ty) | n `nameMatches` n' = Just (n', ty)
match_type _ = Nothing
#if __GLASGOW_HASKELL__ >= 801
mkPatSynI :: Name -> [Dec] -> Info
mkPatSynI n decs = PatSynI n (fromMaybe (no_type n) $ findPatSynType n decs)
findPatSynType :: Name -> [Dec] -> Maybe PatSynType
findPatSynType n = firstMatch match_pat_syn_type
where
match_pat_syn_type (PatSynSigD n' psty) | n `nameMatches` n' = Just psty
match_pat_syn_type _ = Nothing
#endif
no_type :: Name -> Type
no_type n = error $ "No type information found in local declaration for "
++ show n
findInstances :: Name -> [Dec] -> [Dec]
findInstances n = map stripInstanceDec . concatMap match_instance
where
match_instance d@(InstanceD _ _ ty _) | ConT n' <- ty_head ty
, n `nameMatches` n' = [d]
#if __GLASGOW_HASKELL__ >= 807
match_instance (DataInstD ctxt _ lhs mk cons derivs)
| ConT n' <- ty_head lhs
, n `nameMatches` n' = [d]
where
mtvbs = rejig_data_inst_tvbs ctxt lhs mk
d = DataInstD ctxt mtvbs lhs mk cons derivs
match_instance (NewtypeInstD ctxt _ lhs mk con derivs)
| ConT n' <- ty_head lhs
, n `nameMatches` n' = [d]
where
mtvbs = rejig_data_inst_tvbs ctxt lhs mk
d = NewtypeInstD ctxt mtvbs lhs mk con derivs
#else
match_instance d@(DataInstD _ n' _ _ _ _) | n `nameMatches` n' = [d]
match_instance d@(NewtypeInstD _ n' _ _ _ _) | n `nameMatches` n' = [d]
#endif
#if __GLASGOW_HASKELL__ >= 807
match_instance (TySynInstD (TySynEqn _ lhs rhs))
| ConT n' <- ty_head lhs
, n `nameMatches` n' = [d]
where
mtvbs = rejig_tvbs [lhs, rhs]
d = TySynInstD (TySynEqn mtvbs lhs rhs)
#else
match_instance d@(TySynInstD n' _) | n `nameMatches` n' = [d]
#endif
match_instance (InstanceD _ _ _ decs)
= concatMap match_instance decs
match_instance _ = []
#if __GLASGOW_HASKELL__ >= 807
-- See Note [Rejigging reified type family equations variable binders]
-- for why this is necessary.
rejig_tvbs :: [Type] -> Maybe [TyVarBndrUnit]
rejig_tvbs ts =
let tvbs = freeVariablesWellScoped ts
in if null tvbs
then Nothing
else Just tvbs
rejig_data_inst_tvbs :: Cxt -> Type -> Maybe Kind -> Maybe [TyVarBndrUnit]
rejig_data_inst_tvbs cxt lhs mk =
rejig_tvbs $ cxt ++ [lhs] ++ maybeToList mk
#endif
ty_head = fst . unfoldType
{-
Note [Rejigging reified type family equations variable binders]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
When reifying a type family instance (on GHC 8.8 or later), which quantified
type variables do you use? This might seem like a strange question to ask since
these instances already come equipped with a field of type `Maybe [TyVarBndr]`,
but it's not always the case that you want to use exactly that field. Here is
an example to better explain it:
class C a where
type T b a
instance C (Maybe a) where
type forall b. T b (Maybe a) = a
If the above instance were quoted, it would give you `Just [PlainTV b]`. But if
you were to reify ''T (and therefore retrieve the instance for T), you wouldn't
want to use that as your list of type variable binders! This is because
reifiying any type family always presents the information as though the type
family were top-level. Therefore, reifying T (in GHC, at least) would yield:
type family T b a
type instance forall b a. T b (Maybe a) = a
Note that we quantify over `b` *and* `a` here, not just `b`. To emulate this
GHC quirk, whenever we reify any type family instance, we just ignore the field
of type `Maybe [TyVarBndr]` and quantify over the instance afresh. It's a bit
tedious, but it gets the job done. (This is accomplished by the rejig_tvbs
function.)
-}
-- Consider the following class declaration:
--
-- [d| class C a where
-- method :: a -> b -> a |]
--
-- When reifying C locally, quantifyClassDecMethods serves two purposes:
--
-- 1. It quantifies the class method's local type variables. To illustrate this
-- point, this is how GHC would reify C:
--
-- class C a where
-- method :: forall b. a -> b -> a
--
-- Notice the presence of the explicit `forall b.`. quantifyClassDecMethods
-- performs this explicit quantification if necessary (as in the case in the
-- local C declaration, where `b` is implicitly quantified.)
-- 2. It emulates a quirk in the way old versions of GHC would reify class
-- declarations (Trac #15551). On versions of GHC older than 8.8, it would
-- reify C like so:
--
-- class C a where
-- method :: forall a. C a => forall b. a -> b -> a
--
-- Notice how GHC has added the (totally extraneous) `forall a. C a =>`
-- part! This is weird, but our primary goal in this module is to mimic
-- GHC's reification, so we play the part by adding the `forall`/class
-- context to each class method in quantifyClassDecMethods.
--
-- Since Trac #15551 was fixed in GHC 8.8, this function doesn't perform
-- this step on 8.7 or later.
quantifyClassDecMethods :: Dec -> Dec
quantifyClassDecMethods (ClassD cxt cls_name cls_tvbs fds sub_decs)
= ClassD cxt cls_name cls_tvbs fds sub_decs'
where
sub_decs' = mapMaybe go sub_decs
go (SigD n ty) =
Just $ SigD n
$ quantifyClassMethodType cls_name cls_tvbs prepend_cls ty
go d@(TySynInstD {}) = Just d
go d@(OpenTypeFamilyD {}) = Just d
go d@(DataFamilyD {}) = Just d
go _ = Nothing
-- See (2) in the comments for quantifyClassDecMethods.
prepend_cls :: Bool
#if __GLASGOW_HASKELL__ >= 807
prepend_cls = False
#else
prepend_cls = True
#endif
quantifyClassDecMethods dec = dec
-- Add explicit quantification to a class method's type if necessary. In this
-- example:
--
-- [d| class C a where
-- method :: a -> b -> a |]
--
-- If one invokes `quantifyClassMethodType C [a] prepend (a -> b -> a)`, then
-- the output will be:
--
-- 1. `forall a. C a => forall b. a -> b -> a` (if `prepend` is True)
-- 2. `forall b. a -> b -> a` (if `prepend` is False)
--
-- Whether you want `prepend` to be True or False depends on the situation.
-- When reifying an entire type class, like C, one does not need to prepend a
-- class context to each of the bundled method types (see the comments for
-- quantifyClassDecMethods), so False is appropriate. When one is only reifying
-- a single class method, like `method`, then one needs the class context to
-- appear in the reified type, so `True` is appropriate.
quantifyClassMethodType
:: Name -- ^ The class name.
-> [TyVarBndrUnit] -- ^ The class's type variable binders.
-> Bool -- ^ If 'True', prepend a class predicate.
-> Type -- ^ The method type.
-> Type
quantifyClassMethodType cls_name cls_tvbs prepend meth_ty =
add_cls_cxt quantified_meth_ty
where
add_cls_cxt :: Type -> Type
add_cls_cxt
| prepend = ForallT (changeTVFlags SpecifiedSpec all_cls_tvbs) cls_cxt
| otherwise = id
cls_cxt :: Cxt
cls_cxt = [foldl AppT (ConT cls_name) (map tvbToType cls_tvbs)]
quantified_meth_ty :: Type
quantified_meth_ty
| null meth_tvbs
= meth_ty
| ForallT meth_tvbs' meth_ctxt meth_tau <- meth_ty
= ForallT (meth_tvbs ++ meth_tvbs') meth_ctxt meth_tau
| otherwise
= ForallT meth_tvbs [] meth_ty
meth_tvbs :: [TyVarBndrSpec]
meth_tvbs = changeTVFlags SpecifiedSpec $
List.deleteFirstsBy ((==) `on` tvName)
(freeVariablesWellScoped [meth_ty]) all_cls_tvbs
-- Explicitly quantify any kind variables bound by the class, if any.
all_cls_tvbs :: [TyVarBndrUnit]
all_cls_tvbs = freeVariablesWellScoped $ map tvbToTypeWithSig cls_tvbs
stripInstanceDec :: Dec -> Dec
stripInstanceDec (InstanceD over cxt ty _) = InstanceD over cxt ty []
stripInstanceDec dec = dec
mkArrows :: [Type] -> Type -> Type
mkArrows [] res_ty = res_ty
mkArrows (t:ts) res_ty = AppT (AppT ArrowT t) $ mkArrows ts res_ty
maybeForallT :: [TyVarBndrUnit] -> Cxt -> Type -> Type
maybeForallT tvbs cxt ty
| null tvbs && null cxt = ty
| ForallT tvbs2 cxt2 ty2 <- ty = ForallT (tvbs_spec ++ tvbs2) (cxt ++ cxt2) ty2
| otherwise = ForallT tvbs_spec cxt ty
where
tvbs_spec = changeTVFlags SpecifiedSpec tvbs
findCon :: Name -> [Con] -> Maybe (Named Con)
findCon n = firstMatch match_con
where
match_con :: Con -> Maybe (Named Con)
match_con con =
case con of
NormalC n' _ | n `nameMatches` n' -> Just (n', con)
RecC n' _ | n `nameMatches` n' -> Just (n', con)
InfixC _ n' _ | n `nameMatches` n' -> Just (n', con)
ForallC _ _ c -> case match_con c of
Just (n', _) -> Just (n', con)
Nothing -> Nothing
GadtC nms _ _ -> gadt_case con nms
RecGadtC nms _ _ -> gadt_case con nms
_ -> Nothing
gadt_case :: Con -> [Name] -> Maybe (Named Con)
gadt_case con nms = case List.find (n `nameMatches`) nms of
Just n' -> Just (n', con)
Nothing -> Nothing
data RecSelInfo
= RecSelH98 Type -- The record field's type
| RecSelGADT Type -- The record field's type
Type -- The GADT return type
findRecSelector :: Name -> [Con] -> Maybe (Named RecSelInfo)
findRecSelector n = firstMatch match_con
where
match_con :: Con -> Maybe (Named RecSelInfo)
match_con (RecC _ vstys) = fmap (liftSnd RecSelH98) $
firstMatch match_rec_sel vstys
match_con (RecGadtC _ vstys ret_ty) = fmap (liftSnd (`RecSelGADT` ret_ty)) $
firstMatch match_rec_sel vstys
match_con (ForallC _ _ c) = match_con c
match_con _ = Nothing
match_rec_sel (n', _, sel_ty)
| n `nameMatches` n' = Just (n', sel_ty)
match_rec_sel _ = Nothing
---------------------------------
-- Reifying fixities
---------------------------------
-- | Like 'reifyWithLocals_maybe', but for fixities. Note that a return value
-- of @Nothing@ might mean that the name is not in scope, or it might mean
-- that the name has no assigned fixity. (Use 'reifyWithLocals_maybe' if
-- you really need to tell the difference.)
reifyFixityWithLocals :: DsMonad q => Name -> q (Maybe Fixity)
reifyFixityWithLocals name = qRecover
(return . reifyFixityInDecs name =<< localDeclarations)
(qReifyFixity name)
--------------------------------------
-- Reifying types
--------------------------------------
--
-- This section allows GHC <8.9 to call reifyFixity
#if __GLASGOW_HASKELL__ < 809
qReifyType :: forall m. Quasi m => Name -> m Type
qReifyType name = do
info <- qReify name
case infoType info <|> info_kind info of
Just t -> return t
Nothing -> fail $ "Could not reify the full type of " ++ nameBase name
where
info_kind :: Info -> Maybe Kind
info_kind info = do
dec <- case info of
ClassI d _ -> Just d
TyConI d -> Just d
FamilyI d _ -> Just d
_ -> Nothing
match_cusk name dec
{- | @reifyType nm@ attempts to find the type or kind of @nm@. For example,
@reifyType 'not@ returns @Bool -> Bool@, and
@reifyType ''Bool@ returns @Type@.
This works even if there's no explicit signature and the type or kind is inferred.
-}
reifyType :: Name -> Q Type
reifyType = qReifyType
#endif
-- | Like 'reifyTypeWithLocals_maybe', but throws an exception upon failure,
-- warning the user about separating splices.
reifyTypeWithLocals :: DsMonad q => Name -> q Type
reifyTypeWithLocals name = do
m_info <- reifyTypeWithLocals_maybe name
case m_info of
Nothing -> reifyFail name
Just i -> return i
-- | Like 'reifyWithLocals_maybe' but for types and kinds. Note that a return
-- value of @Nothing@ might mean that the name is not in scope, or it might
-- mean that the full type of the name cannot be determined. (Use
-- 'reifyWithLocals_maybe' if you really need to tell the difference.)
reifyTypeWithLocals_maybe :: DsMonad q => Name -> q (Maybe Type)
reifyTypeWithLocals_maybe name = do
#if __GLASGOW_HASKELL__ >= 809
cusks <- qIsExtEnabled CUSKs
#else
-- On earlier GHCs, the behavior of -XCUSKs was the norm.
let cusks = True
#endif
qRecover (return . reifyTypeInDecs cusks name =<< localDeclarations)
(Just `fmap` qReifyType name)
-- | Look through a list of declarations and return its full type, if
-- available.
reifyTypeInDecs :: Bool -> Name -> [Dec] -> Maybe Type
reifyTypeInDecs cusks name decs =
(reifyInDecs name decs >>= infoType) <|> findKind cusks name decs
-- Extract the type information (if any) contained in an Info.
infoType :: Info -> Maybe Type
infoType info =
case info of
ClassOpI _ t _ -> Just t
DataConI _ t _ -> Just t
VarI _ t _ -> Just t
TyVarI _ t -> Just t
#if __GLASGOW_HASKELL__ >= 802
PatSynI _ t -> Just t
#endif
_ -> Nothing
-- Like findType, but instead searching for kind signatures.
-- This mostly searches through `KiSigD`s, but if the -XCUSKs extension is
-- enabled, this also retrieves kinds for declarations with CUSKs.
findKind :: Bool -- Is -XCUSKs enabled?
-> Name -> [Dec] -> Maybe Kind
findKind cusks name decls =
firstMatch (match_kind_sig name decls) decls
<|> whenAlt cusks (firstMatch (match_cusk name) decls)
-- Look for a declaration's kind by searching for its standalone kind
-- signature, if available.
match_kind_sig :: Name -> [Dec] -> Dec -> Maybe Kind
match_kind_sig n decs (ClassD _ n' tvbs _ sub_decs)
-- If a class has a standalone kind signature, then we can determine the
-- full kind of its associated types in 99% of cases.
-- See Note [The limitations of standalone kind signatures] for what
-- happens in the other 1% of cases.
| Just ki <- firstMatch (find_kind_sig n') decs
, let (arg_kis, _res_ki) = unravelType ki
mb_vis_arg_kis = map vis_arg_kind_maybe $ filterVisFunArgs arg_kis
cls_tvb_kind_map =
Map.fromList [ (tvName tvb, tvb_kind)
| (tvb, mb_vis_arg_ki) <- zip tvbs mb_vis_arg_kis
, Just tvb_kind <- [mb_vis_arg_ki <|> tvb_kind_maybe tvb]
]
= firstMatch (find_assoc_type_kind n cls_tvb_kind_map) sub_decs
match_kind_sig n _ dec = find_kind_sig n dec
find_kind_sig :: Name -> Dec -> Maybe Kind
#if __GLASGOW_HASKELL__ >= 809
find_kind_sig n (KiSigD n' ki)
| n `nameMatches` n' = Just ki
#endif
find_kind_sig _ _ = Nothing
-- Compute a declaration's kind by retrieving its CUSK, if it has one.
-- This is only done when -XCUSKs is enabled, or on older GHCs where
-- CUSKs were the only means of specifying this information.
match_cusk :: Name -> Dec -> Maybe Kind
match_cusk n (DataD _ n' tvbs m_ki _ _)
| n `nameMatches` n'
= datatype_kind tvbs m_ki
match_cusk n (NewtypeD _ n' tvbs m_ki _ _)
| n `nameMatches` n'
= datatype_kind tvbs m_ki
match_cusk n (DataFamilyD n' tvbs m_ki)
| n `nameMatches` n'
= open_ty_fam_kind tvbs m_ki
match_cusk n (OpenTypeFamilyD (TypeFamilyHead n' tvbs res_sig _))
| n `nameMatches` n'
= open_ty_fam_kind tvbs (res_sig_to_kind res_sig)
match_cusk n (ClosedTypeFamilyD (TypeFamilyHead n' tvbs res_sig _) _)
| n `nameMatches` n'
= closed_ty_fam_kind tvbs (res_sig_to_kind res_sig)
match_cusk n (TySynD n' tvbs rhs)
| n `nameMatches` n'
= ty_syn_kind tvbs rhs
match_cusk n (ClassD _ n' tvbs _ sub_decs)
| n `nameMatches` n'
= class_kind tvbs
| -- An associated type family can only have a CUSK if its parent class
-- also has a CUSK.
all tvb_is_kinded tvbs
, let cls_tvb_kind_map = Map.fromList [ (tvName tvb, tvb_kind)
| tvb <- tvbs
, Just tvb_kind <- [tvb_kind_maybe tvb]
]
= firstMatch (find_assoc_type_kind n cls_tvb_kind_map) sub_decs
match_cusk _ _ = Nothing
-- Uncover the kind of an associated type family. There is an invariant
-- that this function should only ever be called when the kind of the
-- parent class is known (i.e., if it has a standalone kind signature or a
-- CUSK). Despite this, it is possible for this function to return Nothing.
-- See Note [The limitations of standalone kind signatures].
find_assoc_type_kind :: Name -> Map Name Kind -> Dec -> Maybe Kind
find_assoc_type_kind n cls_tvb_kind_map sub_dec =
case sub_dec of
DataFamilyD n' tf_tvbs m_ki
| n `nameMatches` n'
-> build_kind (map ascribe_tf_tvb_kind tf_tvbs) (default_res_ki m_ki)
OpenTypeFamilyD (TypeFamilyHead n' tf_tvbs res_sig _)
| n `nameMatches` n'
-> build_kind (map ascribe_tf_tvb_kind tf_tvbs)
(default_res_ki $ res_sig_to_kind res_sig)
_ -> Nothing
where
ascribe_tf_tvb_kind :: TyVarBndrUnit -> TyVarBndrUnit
ascribe_tf_tvb_kind tvb =
elimTV (\tvn -> kindedTV tvn $ fromMaybe StarT $ Map.lookup tvn cls_tvb_kind_map)
(\_ _ -> tvb)
tvb
-- Data types have CUSKs when:
--
-- 1. All of their type variables have explicit kinds.
-- 2. All kind variables in the result kind are explicitly quantified.
datatype_kind :: [TyVarBndrUnit] -> Maybe Kind -> Maybe Kind
datatype_kind tvbs m_ki =
whenAlt (all tvb_is_kinded tvbs && ki_fvs_are_bound) $
build_kind tvbs (default_res_ki m_ki)
where
ki_fvs_are_bound :: Bool
ki_fvs_are_bound =
let ki_fvs = Set.fromList $ foldMap freeVariables m_ki
tvb_vars = Set.fromList $ freeVariables $ map tvbToTypeWithSig tvbs
in ki_fvs `Set.isSubsetOf` tvb_vars
-- Classes have CUSKs when all of their type variables have explicit kinds.
class_kind :: [TyVarBndrUnit] -> Maybe Kind
class_kind tvbs = whenAlt (all tvb_is_kinded tvbs) $
build_kind tvbs ConstraintT
-- Open type families and data families always have CUSKs. Type variables
-- without explicit kinds default to Type, as does the return kind if it
-- is not specified.
open_ty_fam_kind :: [TyVarBndrUnit] -> Maybe Kind -> Maybe Kind
open_ty_fam_kind tvbs m_ki =
build_kind (map default_tvb tvbs) (default_res_ki m_ki)
-- Closed type families have CUSKs when:
--
-- 1. All of their type variables have explicit kinds.
-- 2. An explicit return kind is supplied.
closed_ty_fam_kind :: [TyVarBndrUnit] -> Maybe Kind -> Maybe Kind
closed_ty_fam_kind tvbs m_ki =
case m_ki of
Just ki -> whenAlt (all tvb_is_kinded tvbs) $
build_kind tvbs ki
Nothing -> Nothing
-- Type synonyms have CUSKs when:
--
-- 1. All of their type variables have explicit kinds.
-- 2. The right-hand-side type is annotated with an explicit kind.
ty_syn_kind :: [TyVarBndrUnit] -> Type -> Maybe Kind
ty_syn_kind tvbs rhs =
case rhs of
SigT _ ki -> whenAlt (all tvb_is_kinded tvbs) $
build_kind tvbs ki
_ -> Nothing
-- Attempt to construct the full kind of a type-level declaration from its
-- type variable binders and return kind. Do note that the result type of
-- this function is `Maybe Kind` because there are situations where even
-- this amount of information is not sufficient to determine the full kind.
-- See Note [The limitations of standalone kind signatures].
build_kind :: [TyVarBndrUnit] -> Kind -> Maybe Kind
build_kind arg_kinds res_kind =
fmap quantifyType $ fst $
foldr go (Just res_kind, Set.fromList (freeVariables res_kind)) arg_kinds
where
go :: TyVarBndrUnit -> (Maybe Kind, Set Name) -> (Maybe Kind, Set Name)
go tvb (res, res_fvs) =
elimTV (\n ->
( if n `Set.member` res_fvs
then forall_vis tvb res
else Nothing -- We have a type variable binder without an
-- explicit kind that is not used dependently, so
-- we cannot build a kind from it. This is the
-- only case where we return Nothing.
, res_fvs
))
(\n k ->
( if n `Set.member` res_fvs
then forall_vis tvb res
else fmap (ArrowT `AppT` k `AppT`) res
, Set.fromList (freeVariables k) `Set.union` res_fvs
))
tvb
forall_vis :: TyVarBndrUnit -> Maybe Kind -> Maybe Kind
#if __GLASGOW_HASKELL__ >= 809
forall_vis tvb m_ki = fmap (ForallVisT [tvb]) m_ki
-- One downside of this approach is that we generate kinds like this:
--
-- forall a -> forall b -> forall c -> (a, b, c)
--
-- Instead of this more compact kind:
--
-- forall a b c -> (a, b, c)
--
-- Thankfully, the difference is only cosmetic.
#else
forall_vis _ _ = Nothing
#endif
tvb_is_kinded :: TyVarBndr_ flag -> Bool
tvb_is_kinded = isJust . tvb_kind_maybe
tvb_kind_maybe :: TyVarBndr_ flag -> Maybe Kind
tvb_kind_maybe = elimTV (\_ -> Nothing) (\_ k -> Just k)
vis_arg_kind_maybe :: VisFunArg -> Maybe Kind
vis_arg_kind_maybe (VisFADep tvb) = tvb_kind_maybe tvb
vis_arg_kind_maybe (VisFAAnon k) = Just k
default_tvb :: TyVarBndrUnit -> TyVarBndrUnit
default_tvb tvb = elimTV (\n -> kindedTV n StarT) (\_ _ -> tvb) tvb
default_res_ki :: Maybe Kind -> Kind
default_res_ki = fromMaybe StarT
res_sig_to_kind :: FamilyResultSig -> Maybe Kind
res_sig_to_kind NoSig = Nothing
res_sig_to_kind (KindSig k) = Just k
res_sig_to_kind (TyVarSig tvb) = tvb_kind_maybe tvb
whenAlt :: Alternative f => Bool -> f a -> f a
whenAlt b fa = if b then fa else empty
{-
Note [The limitations of standalone kind signatures]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
A current limitation of StandaloneKindSignatures is that they cannot be applied
to associated type families. This can have some surprising consequences.
Consider the following code, taken from
https://gitlab.haskell.org/ghc/ghc/issues/17072#note_221324:
type C :: forall a -> a -> Constraint
class C a b where
type T a :: Type
The parent class C has a standalone kind signature, so GHC treats its
associated types as if they had CUSKs. Can th-desugar figure out the kind
that GHC gives to T?
Unfortunately, the answer is "not easily". This is because `type T a` says
nothing about the kind of `a`, so th-desugar's only other option is to inspect
the kind signature for C. Even this is for naught, as the `forall a -> ...`
part doesn't state the kind of `a` either! The only way to know that the kind
of `a` should be Type is to infer that from the rest of the kind
(`a -> Constraint`), but this gets perilously close to requiring full kind
inference, which is rather unwieldy in Template Haskell.
In cases like T, we simply give up and return Nothing when trying to reify
its kind. It's not ideal, but them's the breaks when you try to extract kinds
from syntax. There is a rather simple workaround available: just write
`type C :: forall (a :: Type) -> a -> Constraint` instead.
-}
--------------------------------------
-- Looking up name value and type names
--------------------------------------
-- | Like 'lookupValueName' from Template Haskell, but looks also in 'Names' of
-- not-yet-typechecked declarations. To establish this list of not-yet-typechecked
-- declarations, use 'withLocalDeclarations'. Returns 'Nothing' if no value
-- with the same name can be found.
lookupValueNameWithLocals :: DsMonad q => String -> q (Maybe Name)
lookupValueNameWithLocals = lookupNameWithLocals False
-- | Like 'lookupTypeName' from Template Haskell, but looks also in 'Names' of
-- not-yet-typechecked declarations. To establish this list of not-yet-typechecked
-- declarations, use 'withLocalDeclarations'. Returns 'Nothing' if no type
-- with the same name can be found.
lookupTypeNameWithLocals :: DsMonad q => String -> q (Maybe Name)
lookupTypeNameWithLocals = lookupNameWithLocals True
lookupNameWithLocals :: DsMonad q => Bool -> String -> q (Maybe Name)
lookupNameWithLocals ns s = do
mb_name <- qLookupName ns s
case mb_name of
j_name@(Just{}) -> return j_name
Nothing -> consult_locals
where
built_name = mkName s
consult_locals = do
decs <- localDeclarations
let mb_infos = map (reifyInDec built_name decs) decs
infos = catMaybes mb_infos
return $ firstMatch (if ns then find_type_name
else find_value_name) infos
-- These functions work over Named Infos so we can avoid performing
-- tiresome pattern-matching to retrieve the name associated with each Info.
find_type_name, find_value_name :: Named Info -> Maybe Name
find_type_name (n, info) =
case infoNameSpace info of
TcClsName -> Just n
VarName -> Nothing
DataName -> Nothing
find_value_name (n, info) =
case infoNameSpace info of
VarName -> Just n
DataName -> Just n
TcClsName -> Nothing
-- | Like TH's @lookupValueName@, but if this name is not bound, then we assume
-- it is declared in the current module.
--
-- Unlike 'mkDataName', this also consults the local declarations in scope when
-- determining if the name is currently bound.
mkDataNameWithLocals :: DsMonad q => String -> q Name
mkDataNameWithLocals = mkNameWith lookupValueNameWithLocals mkNameG_d
-- | Like TH's @lookupTypeName@, but if this name is not bound, then we assume
-- it is declared in the current module.
--
-- Unlike 'mkTypeName', this also consults the local declarations in scope when
-- determining if the name is currently bound.
mkTypeNameWithLocals :: DsMonad q => String -> q Name
mkTypeNameWithLocals = mkNameWith lookupTypeNameWithLocals mkNameG_tc
-- | Determines a `Name`'s 'NameSpace'. If the 'NameSpace' is attached to
-- the 'Name' itself (i.e., it is unambiguous), then that 'NameSpace' is
-- immediately returned. Otherwise, reification is used to lookup up the
-- 'NameSpace' (consulting local declarations if necessary).
--
-- Note that if a 'Name' lives in two different 'NameSpaces' (which can
-- genuinely happen--for instance, @'mkName' \"==\"@, where @==@ is both
-- a function and a type family), then this function will simply return
-- whichever 'NameSpace' is discovered first via reification. If you wish
-- to find a 'Name' in a particular 'NameSpace', use the
-- 'lookupValueNameWithLocals' or 'lookupTypeNameWithLocals' functions.
reifyNameSpace :: DsMonad q => Name -> q (Maybe NameSpace)
reifyNameSpace n@(Name _ nf) =
case nf of
-- NameGs are simple, as they have a NameSpace attached.
NameG ns _ _ -> pure $ Just ns
-- For other names, we must use reification to determine what NameSpace
-- it lives in (if any).
_ -> do mb_info <- reifyWithLocals_maybe n
pure $ fmap infoNameSpace mb_info
-- | Determine a name's 'NameSpace' from its 'Info'.
infoNameSpace :: Info -> NameSpace
infoNameSpace info =
case info of
ClassI{} -> TcClsName
TyConI{} -> TcClsName
FamilyI{} -> TcClsName
PrimTyConI{} -> TcClsName
TyVarI{} -> TcClsName
ClassOpI{} -> VarName
VarI{} -> VarName
DataConI{} -> DataName
#if __GLASGOW_HASKELL__ >= 801
PatSynI{} -> DataName
#endif