module Language.Haskell.TH.Lift (deriveLift, deriveLiftMany, deriveLift', deriveLiftMany', Lift(..)) where
import GHC.Exts
import Language.Haskell.TH
import Language.Haskell.TH.Syntax
import Control.Monad ((<=<))
modName :: String
modName = "Language.Haskell.TH.Lift"
deriveLift :: Name -> Q [Dec]
deriveLift = deriveLift' <=< reify
deriveLiftMany :: [Name] -> Q [Dec]
deriveLiftMany = deriveLiftMany' <=< mapM reify
deriveLift' :: Info -> Q [Dec]
deriveLift' = fmap (:[]) . deriveLiftOne
deriveLiftMany' :: [Info] -> Q [Dec]
deriveLiftMany' = mapM deriveLiftOne
deriveLiftOne :: Info -> Q Dec
deriveLiftOne i =
case i of
TyConI (DataD dcx n vsk cons _) ->
liftInstance dcx n (map unTyVarBndr vsk) (map doCons cons)
TyConI (NewtypeD dcx n vsk con _) ->
liftInstance dcx n (map unTyVarBndr vsk) [doCons con]
_ -> error (modName ++ ".deriveLift: unhandled: " ++ pprint i)
where liftInstance dcx n vs cases =
instanceD (ctxt dcx vs) (conT ''Lift `appT` typ n vs) [funD 'lift cases]
unTyVarBndr (PlainTV v) = v
unTyVarBndr (KindedTV v _) = v
ctxt dcx = fmap (dcx ++) . cxt . map (\n -> classP ''Lift [varT n])
typ n = foldl appT (conT n) . map varT
doCons :: Con -> Q Clause
doCons (NormalC c sts) = do
let ns = zipWith (\_ i -> "x" ++ show i) sts [0..]
con = [| conE c |]
args = [ [| lift $(varE (mkName n)) |] | n <- ns ]
e = foldl (\e1 e2 -> [| appE $e1 $e2 |]) con args
clause [conP c (map (varP . mkName) ns)] (normalB e) []
doCons (RecC c sts) = doCons $ NormalC c [(s, t) | (_, s, t) <- sts]
doCons (InfixC sty1 c sty2) = do
let con = [| conE c |]
left = [| lift $(varE (mkName "x0")) |]
right = [| lift $(varE (mkName "x1")) |]
e = [| infixApp $left $con $right |]
clause [infixP (varP (mkName "x0")) c (varP (mkName "x1"))] (normalB e) []
doCons c = error (modName ++ ".doCons: Unhandled constructor: " ++ pprint c)
instance Lift Name where
lift (Name occName nameFlavour) = [| Name occName nameFlavour |]
instance Lift OccName where
lift n = [| mkOccName $(lift $ occString n) |]
instance Lift PkgName where
lift n = [| mkPkgName $(lift $ pkgString n) |]
instance Lift ModName where
lift n = [| mkModName $(lift $ modString n) |]
instance Lift NameFlavour where
lift NameS = [| NameS |]
lift (NameQ modName) = [| NameQ modName |]
lift (NameU i) = [| case $( lift (I# i) ) of
I# i' -> NameU i' |]
lift (NameL i) = [| case $( lift (I# i) ) of
I# i' -> NameL i' |]
lift (NameG nameSpace pkgName modName)
= [| NameG nameSpace pkgName modName |]
instance Lift NameSpace where
lift VarName = [| VarName |]
lift DataName = [| DataName |]
lift TcClsName = [| TcClsName |]
instance Lift () where
lift _ = [| () |]
instance Lift Rational where
lift x = return (LitE (RationalL x))