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{-# LANGUAGE RankNTypes, ScopedTypeVariables #-}
module Language.Haskell.TH.Quasi(
QuasiQuoter(..),
dataToQa, dataToExpQ, dataToPatQ
) where
import Data.Generics
import Language.Haskell.TH.Lib
import Language.Haskell.TH.Syntax
data QuasiQuoter = QuasiQuoter { quoteExp :: String -> Q Exp,
quotePat :: String -> Q Pat }
dataToQa :: forall a k q. Data a
=> (Name -> k)
-> (Lit -> Q q)
-> (k -> [Q q] -> Q q)
-> (forall a . Data a => a -> Maybe (Q q))
-> a
-> Q q
dataToQa mkCon mkLit appCon antiQ t =
case antiQ t of
Nothing ->
case constrRep constr of
AlgConstr _ ->
appCon con conArgs
IntConstr n ->
mkLit $ integerL n
FloatConstr n ->
mkLit $ rationalL (toRational n)
StringConstr (c:_) ->
mkLit $ charL c
where
constr :: Constr
constr = toConstr t
constrName :: Constr -> String
constrName k =
case showConstr k of
"(:)" -> ":"
name -> name
con :: k
con = mkCon (mkName (constrName constr))
conArgs :: [Q q]
conArgs = gmapQ (dataToQa mkCon mkLit appCon antiQ) t
Just y -> y
-- | 'dataToExpQ' converts a value to a 'Q Exp' representation of the same
-- value. It takes a function to handle type-specific cases.
dataToExpQ :: Data a
=> (forall a . Data a => a -> Maybe (Q Exp))
-> a
-> Q Exp
dataToExpQ = dataToQa conE litE (foldl appE)
-- | 'dataToPatQ' converts a value to a 'Q Pat' representation of the same
-- value. It takes a function to handle type-specific cases.
dataToPatQ :: Data a
=> (forall a . Data a => a -> Maybe (Q Pat))
-> a
-> Q Pat
dataToPatQ = dataToQa id litP conP
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