{-# LANGUAGE RankNTypes, ScopedTypeVariables #-}
module Language.Haskell.TH.Quote(
	QuasiQuoter(..),
        dataToQa, dataToExpQ, dataToPatQ,
        quoteFile
    ) where

import Data.Data
import Language.Haskell.TH.Lib
import Language.Haskell.TH.Syntax

data QuasiQuoter = QuasiQuoter { quoteExp  :: String -> Q Exp,
                                 quotePat  :: String -> Q Pat,
                                 quoteType :: String -> Q Type,
                                 quoteDec  :: String -> Q [Dec] }

dataToQa  ::  forall a k q. Data a
          =>  (Name -> k)
          ->  (Lit -> Q q)
          ->  (k -> [Q q] -> Q q)
          ->  (forall b . Data b => b -> 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)
            CharConstr 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 b . Data b => b -> 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 b . Data b => b -> Maybe (Q Pat))
            ->  a
            ->  Q Pat
dataToPatQ = dataToQa id litP conP

-- | 'quoteFile' takes a 'QuasiQuoter' and lifts it into one that read
-- the data out of a file.  For example, suppose 'asmq' is an 
-- assembly-language quoter, so that you can write [asmq| ld r1, r2 |]
-- as an expression. Then if you define @asmq_f = quoteFile asmq@, then
-- the quote [asmq_f| foo.s |] will take input from file "foo.s" instead
-- of the inline text
quoteFile :: QuasiQuoter -> QuasiQuoter
quoteFile (QuasiQuoter { quoteExp = qe, quotePat = qp, quoteType = qt, quoteDec = qd }) 
  = QuasiQuoter { quoteExp = get qe, quotePat = get qp, quoteType = get qt, quoteDec = get qd }
  where
   get :: (String -> Q a) -> String -> Q a
   get old_quoter file_name = do { file_cts <- runIO (readFile file_name) 
                                 ; old_quoter file_cts }