hsSyn/Convert.hs

    {-
    (c) The University of Glasgow 2006
    (c) The GRASP/AQUA Project, Glasgow University, 1992-1998

    This module converts Template Haskell syntax into HsSyn
    -}

    {-# LANGUAGE ScopedTypeVariables #-}

    module Convert( convertToHsExpr, convertToPat, convertToHsDecls,
                    convertToHsType,
                    thRdrNameGuesses ) where

    import HsSyn as Hs
    import qualified Class
    import RdrName
    import qualified Name
    import Module
    import RdrHsSyn
    import qualified OccName
    import OccName
    import SrcLoc
    import Type
    import qualified Coercion ( Role(..) )
    import TysWiredIn
    import TysPrim (eqPrimTyCon)
    import BasicTypes as Hs
    import ForeignCall
    import Unique
    import ErrUtils
    import Bag
    import Lexeme
    import Util
    import FastString
    import Outputable
    import MonadUtils ( foldrM )

    import qualified Data.ByteString as BS
    import Control.Monad( unless, liftM, ap, (<=<) )

    import Data.Maybe( catMaybes, fromMaybe, isNothing )
    import Language.Haskell.TH as TH hiding (sigP)
    import Language.Haskell.TH.Syntax as TH

    -------------------------------------------------------------------
    --              The external interface

    convertToHsDecls :: SrcSpan -> [TH.Dec] -> Either MsgDoc [LHsDecl RdrName]
    convertToHsDecls loc ds = initCvt loc (fmap catMaybes (mapM cvt_dec ds))
      where
        cvt_dec d = wrapMsg "declaration" d (cvtDec d)

    convertToHsExpr :: SrcSpan -> TH.Exp -> Either MsgDoc (LHsExpr RdrName)
    convertToHsExpr loc e
      = initCvt loc $ wrapMsg "expression" e $ cvtl e

    convertToPat :: SrcSpan -> TH.Pat -> Either MsgDoc (LPat RdrName)
    convertToPat loc p
      = initCvt loc $ wrapMsg "pattern" p $ cvtPat p

    convertToHsType :: SrcSpan -> TH.Type -> Either MsgDoc (LHsType RdrName)
    convertToHsType loc t
      = initCvt loc $ wrapMsg "type" t $ cvtType t

    -------------------------------------------------------------------
    newtype CvtM a = CvtM { unCvtM :: SrcSpan -> Either MsgDoc (SrcSpan, a) }
            -- Push down the source location;
            -- Can fail, with a single error message

    -- NB: If the conversion succeeds with (Right x), there should
    --     be no exception values hiding in x
    -- Reason: so a (head []) in TH code doesn't subsequently
    --         make GHC crash when it tries to walk the generated tree

    -- Use the loc everywhere, for lack of anything better
    -- In particular, we want it on binding locations, so that variables bound in
    -- the spliced-in declarations get a location that at least relates to the splice point

    instance Functor CvtM where
        fmap = liftM

    instance Applicative CvtM where
        pure x = CvtM $ \loc -> Right (loc,x)
        (<*>) = ap

    instance Monad CvtM where
      (CvtM m) >>= k = CvtM $ \loc -> case m loc of
                                      Left err -> Left err
                                      Right (loc',v) -> unCvtM (k v) loc'

    initCvt :: SrcSpan -> CvtM a -> Either MsgDoc a
    initCvt loc (CvtM m) = fmap snd (m loc)

    force :: a -> CvtM ()
    force a = a `seq` return ()

    failWith :: MsgDoc -> CvtM a
    failWith m = CvtM (\_ -> Left m)

    getL :: CvtM SrcSpan
    getL = CvtM (\loc -> Right (loc,loc))

    setL :: SrcSpan -> CvtM ()
    setL loc = CvtM (\_ -> Right (loc, ()))

    returnL :: a -> CvtM (Located a)
    returnL x = CvtM (\loc -> Right (loc, L loc x))

    returnJustL :: a -> CvtM (Maybe (Located a))
    returnJustL = fmap Just . returnL

    wrapParL :: (Located a -> a) -> a -> CvtM a
    wrapParL add_par x = CvtM (\loc -> Right (loc, add_par (L loc x)))

    wrapMsg :: (Show a, TH.Ppr a) => String -> a -> CvtM b -> CvtM b
    -- E.g  wrapMsg "declaration" dec thing
    wrapMsg what item (CvtM m)
      = CvtM (\loc -> case m loc of
                         Left err -> Left (err $$ getPprStyle msg)
                         Right v  -> Right v)
      where
            -- Show the item in pretty syntax normally,
            -- but with all its constructors if you say -dppr-debug
        msg sty = hang (text "When splicing a TH" <+> text what <> colon)
                     2 (if debugStyle sty
                        then text (show item)
                        else text (pprint item))

    wrapL :: CvtM a -> CvtM (Located a)
    wrapL (CvtM m) = CvtM (\loc -> case m loc of
                                   Left err -> Left err
                                   Right (loc',v) -> Right (loc',L loc v))

    -------------------------------------------------------------------
    cvtDecs :: [TH.Dec] -> CvtM [LHsDecl RdrName]
    cvtDecs = fmap catMaybes . mapM cvtDec

    cvtDec :: TH.Dec -> CvtM (Maybe (LHsDecl RdrName))
    cvtDec (TH.ValD pat body ds)
      | TH.VarP s <- pat
      = do  { s' <- vNameL s
            ; cl' <- cvtClause (mkPrefixFunRhs s') (Clause [] body ds)
            ; returnJustL $ Hs.ValD $ mkFunBind s' [cl'] }

      | otherwise
      = do  { pat' <- cvtPat pat
            ; body' <- cvtGuard body
            ; ds' <- cvtLocalDecs (text "a where clause") ds
            ; returnJustL $ Hs.ValD $
              PatBind { pat_lhs = pat', pat_rhs = GRHSs body' (noLoc ds')
                      , pat_rhs_ty = placeHolderType, bind_fvs = placeHolderNames
                      , pat_ticks = ([],[]) } }

    cvtDec (TH.FunD nm cls)
      | null cls
      = failWith (text "Function binding for"
                     <+> quotes (text (TH.pprint nm))
                     <+> text "has no equations")
      | otherwise
      = do  { nm' <- vNameL nm
            ; cls' <- mapM (cvtClause (mkPrefixFunRhs nm')) cls
            ; returnJustL $ Hs.ValD $ mkFunBind nm' cls' }

    cvtDec (TH.SigD nm typ)
      = do  { nm' <- vNameL nm
            ; ty' <- cvtType typ
            ; returnJustL $ Hs.SigD (TypeSig [nm'] (mkLHsSigWcType ty')) }

    cvtDec (TH.InfixD fx nm)
      -- Fixity signatures are allowed for variables, constructors, and types
      -- the renamer automatically looks for types during renaming, even when
      -- the RdrName says it's a variable or a constructor. So, just assume
      -- it's a variable or constructor and proceed.
      = do { nm' <- vcNameL nm
           ; returnJustL (Hs.SigD (FixSig (FixitySig [nm'] (cvtFixity fx)))) }

    cvtDec (PragmaD prag)
      = cvtPragmaD prag

    cvtDec (TySynD tc tvs rhs)
      = do  { (_, tc', tvs') <- cvt_tycl_hdr [] tc tvs
            ; rhs' <- cvtType rhs
            ; returnJustL $ TyClD $
              SynDecl { tcdLName = tc', tcdTyVars = tvs'
                      , tcdFixity = Prefix
                      , tcdFVs = placeHolderNames
                      , tcdRhs = rhs' } }

    cvtDec (DataD ctxt tc tvs ksig constrs derivs)
      = do  { let isGadtCon (GadtC    _ _ _) = True
                  isGadtCon (RecGadtC _ _ _) = True
                  isGadtCon (ForallC  _ _ c) = isGadtCon c
                  isGadtCon _                = False
                  isGadtDecl  = all isGadtCon constrs
                  isH98Decl   = all (not . isGadtCon) constrs
            ; unless (isGadtDecl || isH98Decl)
                     (failWith (text "Cannot mix GADT constructors with Haskell 98"
                            <+> text "constructors"))
            ; unless (isNothing ksig || isGadtDecl)
                     (failWith (text "Kind signatures are only allowed on GADTs"))
            ; (ctxt', tc', tvs') <- cvt_tycl_hdr ctxt tc tvs
            ; ksig' <- cvtKind `traverse` ksig
            ; cons' <- mapM cvtConstr constrs
            ; derivs' <- cvtDerivs derivs
            ; let defn = HsDataDefn { dd_ND = DataType, dd_cType = Nothing
                                    , dd_ctxt = ctxt'
                                    , dd_kindSig = ksig'
                                    , dd_cons = cons', dd_derivs = derivs' }
            ; returnJustL $ TyClD (DataDecl { tcdLName = tc', tcdTyVars = tvs'
                                            , tcdFixity = Prefix
                                            , tcdDataDefn = defn
                                            , tcdDataCusk = PlaceHolder
                                            , tcdFVs = placeHolderNames }) }

    cvtDec (NewtypeD ctxt tc tvs ksig constr derivs)
      = do  { (ctxt', tc', tvs') <- cvt_tycl_hdr ctxt tc tvs
            ; ksig' <- cvtKind `traverse` ksig
            ; con' <- cvtConstr constr
            ; derivs' <- cvtDerivs derivs
            ; let defn = HsDataDefn { dd_ND = NewType, dd_cType = Nothing
                                    , dd_ctxt = ctxt'
                                    , dd_kindSig = ksig'
                                    , dd_cons = [con']
                                    , dd_derivs = derivs' }
            ; returnJustL $ TyClD (DataDecl { tcdLName = tc', tcdTyVars = tvs'
                                        , tcdFixity = Prefix
                                        , tcdDataDefn = defn
                                        , tcdDataCusk = PlaceHolder
                                        , tcdFVs = placeHolderNames }) }

    cvtDec (ClassD ctxt cl tvs fds decs)
      = do  { (cxt', tc', tvs') <- cvt_tycl_hdr ctxt cl tvs
            ; fds'  <- mapM cvt_fundep fds
            ; (binds', sigs', fams', ats', adts') <- cvt_ci_decs (text "a class declaration") decs
            ; unless (null adts')
                (failWith $ (text "Default data instance declarations"
                         <+> text "are not allowed:")
                       $$ (Outputable.ppr adts'))
            ; at_defs <- mapM cvt_at_def ats'
            ; returnJustL $ TyClD $
              ClassDecl { tcdCtxt = cxt', tcdLName = tc', tcdTyVars = tvs'
                        , tcdFixity = Prefix
                        , tcdFDs = fds', tcdSigs = Hs.mkClassOpSigs sigs'
                        , tcdMeths = binds'
                        , tcdATs = fams', tcdATDefs = at_defs, tcdDocs = []
                        , tcdFVs = placeHolderNames }
                                  -- no docs in TH ^^
            }
      where
        cvt_at_def :: LTyFamInstDecl RdrName -> CvtM (LTyFamDefltEqn RdrName)
        -- Very similar to what happens in RdrHsSyn.mkClassDecl
        cvt_at_def decl = case RdrHsSyn.mkATDefault decl of
                            Right def     -> return def
                            Left (_, msg) -> failWith msg

    cvtDec (InstanceD o ctxt ty decs)
      = do  { let doc = text "an instance declaration"
            ; (binds', sigs', fams', ats', adts') <- cvt_ci_decs doc decs
            ; unless (null fams') (failWith (mkBadDecMsg doc fams'))
            ; ctxt' <- cvtContext ctxt
            ; L loc ty' <- cvtType ty
            ; let inst_ty' = mkHsQualTy ctxt loc ctxt' $ L loc ty'
            ; returnJustL $ InstD $ ClsInstD $
              ClsInstDecl { cid_poly_ty = mkLHsSigType inst_ty'
                          , cid_binds = binds'
                          , cid_sigs = Hs.mkClassOpSigs sigs'
                          , cid_tyfam_insts = ats', cid_datafam_insts = adts'
                          , cid_overlap_mode = fmap (L loc . overlap) o } }
      where
      overlap pragma =
        case pragma of
          TH.Overlaps      -> Hs.Overlaps     (SourceText "OVERLAPS")
          TH.Overlappable  -> Hs.Overlappable (SourceText "OVERLAPPABLE")
          TH.Overlapping   -> Hs.Overlapping  (SourceText "OVERLAPPING")
          TH.Incoherent    -> Hs.Incoherent   (SourceText "INCOHERENT")

    cvtDec (ForeignD ford)
      = do { ford' <- cvtForD ford
           ; returnJustL $ ForD ford' }

    cvtDec (DataFamilyD tc tvs kind)
      = do { (_, tc', tvs') <- cvt_tycl_hdr [] tc tvs
           ; result <- cvtMaybeKindToFamilyResultSig kind
           ; returnJustL $ TyClD $ FamDecl $
             FamilyDecl DataFamily tc' tvs' Prefix result Nothing }

    cvtDec (DataInstD ctxt tc tys ksig constrs derivs)
      = do { (ctxt', tc', typats') <- cvt_tyinst_hdr ctxt tc tys
           ; ksig' <- cvtKind `traverse` ksig
           ; cons' <- mapM cvtConstr constrs
           ; derivs' <- cvtDerivs derivs
           ; let defn = HsDataDefn { dd_ND = DataType, dd_cType = Nothing
                                   , dd_ctxt = ctxt'
                                   , dd_kindSig = ksig'
                                   , dd_cons = cons', dd_derivs = derivs' }

           ; returnJustL $ InstD $ DataFamInstD
               { dfid_inst = DataFamInstDecl { dfid_tycon = tc', dfid_pats = typats'
                                             , dfid_defn = defn
                                             , dfid_fixity = Prefix
                                             , dfid_fvs = placeHolderNames } }}

    cvtDec (NewtypeInstD ctxt tc tys ksig constr derivs)
      = do { (ctxt', tc', typats') <- cvt_tyinst_hdr ctxt tc tys
           ; ksig' <- cvtKind `traverse` ksig
           ; con' <- cvtConstr constr
           ; derivs' <- cvtDerivs derivs
           ; let defn = HsDataDefn { dd_ND = NewType, dd_cType = Nothing
                                   , dd_ctxt = ctxt'
                                   , dd_kindSig = ksig'
                                   , dd_cons = [con'], dd_derivs = derivs' }
           ; returnJustL $ InstD $ DataFamInstD
               { dfid_inst = DataFamInstDecl { dfid_tycon = tc', dfid_pats = typats'
                                             , dfid_defn = defn
                                             , dfid_fixity = Prefix
                                             , dfid_fvs = placeHolderNames } }}

    cvtDec (TySynInstD tc eqn)
      = do  { tc' <- tconNameL tc
            ; eqn' <- cvtTySynEqn tc' eqn
            ; returnJustL $ InstD $ TyFamInstD
                { tfid_inst = TyFamInstDecl { tfid_eqn = eqn'
                                            , tfid_fvs = placeHolderNames } } }

    cvtDec (OpenTypeFamilyD head)
      = do { (tc', tyvars', result', injectivity') <- cvt_tyfam_head head
           ; returnJustL $ TyClD $ FamDecl $
             FamilyDecl OpenTypeFamily tc' tyvars' Prefix result' injectivity' }

    cvtDec (ClosedTypeFamilyD head eqns)
      = do { (tc', tyvars', result', injectivity') <- cvt_tyfam_head head
           ; eqns' <- mapM (cvtTySynEqn tc') eqns
           ; returnJustL $ TyClD $ FamDecl $
             FamilyDecl (ClosedTypeFamily (Just eqns')) tc' tyvars' Prefix result'
                                          injectivity' }

    cvtDec (TH.RoleAnnotD tc roles)
      = do { tc' <- tconNameL tc
           ; let roles' = map (noLoc . cvtRole) roles
           ; returnJustL $ Hs.RoleAnnotD (RoleAnnotDecl tc' roles') }

    cvtDec (TH.StandaloneDerivD ds cxt ty)
      = do { cxt' <- cvtContext cxt
           ; L loc ty'  <- cvtType ty
           ; let inst_ty' = mkHsQualTy cxt loc cxt' $ L loc ty'
           ; returnJustL $ DerivD $
             DerivDecl { deriv_strategy = fmap (L loc . cvtDerivStrategy) ds
                       , deriv_type = mkLHsSigType inst_ty'
                       , deriv_overlap_mode = Nothing } }

    cvtDec (TH.DefaultSigD nm typ)
      = do { nm' <- vNameL nm
           ; ty' <- cvtType typ
           ; returnJustL $ Hs.SigD $ ClassOpSig True [nm'] (mkLHsSigType ty') }

    cvtDec (TH.PatSynD nm args dir pat)
      = do { nm'   <- cNameL nm
           ; args' <- cvtArgs args
           ; dir'  <- cvtDir nm' dir
           ; pat'  <- cvtPat pat
           ; returnJustL $ Hs.ValD $ PatSynBind $
               PSB nm' placeHolderType args' pat' dir' }
      where
        cvtArgs (TH.PrefixPatSyn args) = Hs.PrefixPatSyn <$> mapM vNameL args
        cvtArgs (TH.InfixPatSyn a1 a2) = Hs.InfixPatSyn <$> vNameL a1 <*> vNameL a2
        cvtArgs (TH.RecordPatSyn sels)
          = do { sels' <- mapM vNameL sels
               ; vars' <- mapM (vNameL . mkNameS . nameBase) sels
               ; return $ Hs.RecordPatSyn $ zipWith RecordPatSynField sels' vars' }

        cvtDir _ Unidir          = return Unidirectional
        cvtDir _ ImplBidir       = return ImplicitBidirectional
        cvtDir n (ExplBidir cls) =
          do { ms <- mapM (cvtClause (mkPrefixFunRhs n)) cls
             ; return $ ExplicitBidirectional $ mkMatchGroup FromSource ms }

    cvtDec (TH.PatSynSigD nm ty)
      = do { nm' <- cNameL nm
           ; ty' <- cvtPatSynSigTy ty
           ; returnJustL $ Hs.SigD $ PatSynSig [nm'] (mkLHsSigType ty') }

    ----------------
    cvtTySynEqn :: Located RdrName -> TySynEqn -> CvtM (LTyFamInstEqn RdrName)
    cvtTySynEqn tc (TySynEqn lhs rhs)
      = do  { lhs' <- mapM (wrap_apps <=< cvtType) lhs
            ; rhs' <- cvtType rhs
            ; returnL $ TyFamEqn { tfe_tycon = tc
                                 , tfe_pats = mkHsImplicitBndrs lhs'
                                 , tfe_fixity = Prefix
                                 , tfe_rhs = rhs' } }

    ----------------
    cvt_ci_decs :: MsgDoc -> [TH.Dec]
                -> CvtM (LHsBinds RdrName,
                         [LSig RdrName],
                         [LFamilyDecl RdrName],
                         [LTyFamInstDecl RdrName],
                         [LDataFamInstDecl RdrName])
    -- Convert the declarations inside a class or instance decl
    -- ie signatures, bindings, and associated types
    cvt_ci_decs doc decs
      = do  { decs' <- cvtDecs decs
            ; let (ats', bind_sig_decs') = partitionWith is_tyfam_inst decs'
            ; let (adts', no_ats')       = partitionWith is_datafam_inst bind_sig_decs'
            ; let (sigs', prob_binds')   = partitionWith is_sig no_ats'
            ; let (binds', prob_fams')   = partitionWith is_bind prob_binds'
            ; let (fams', bads)          = partitionWith is_fam_decl prob_fams'
            ; unless (null bads) (failWith (mkBadDecMsg doc bads))
              --We use FromSource as the origin of the bind
              -- because the TH declaration is user-written
            ; return (listToBag binds', sigs', fams', ats', adts') }

    ----------------
    cvt_tycl_hdr :: TH.Cxt -> TH.Name -> [TH.TyVarBndr]
                 -> CvtM ( LHsContext RdrName
                         , Located RdrName
                         , LHsQTyVars RdrName)
    cvt_tycl_hdr cxt tc tvs
      = do { cxt' <- cvtContext cxt
           ; tc'  <- tconNameL tc
           ; tvs' <- cvtTvs tvs
           ; return (cxt', tc', tvs')
           }

    cvt_tyinst_hdr :: TH.Cxt -> TH.Name -> [TH.Type]
                   -> CvtM ( LHsContext RdrName
                           , Located RdrName
                           , HsImplicitBndrs RdrName [LHsType RdrName])
    cvt_tyinst_hdr cxt tc tys
      = do { cxt' <- cvtContext cxt
           ; tc'  <- tconNameL tc
           ; tys' <- mapM (wrap_apps <=< cvtType) tys
           ; return (cxt', tc', mkHsImplicitBndrs tys') }

    ----------------
    cvt_tyfam_head :: TypeFamilyHead
                   -> CvtM ( Located RdrName
                           , LHsQTyVars RdrName
                           , Hs.LFamilyResultSig RdrName
                           , Maybe (Hs.LInjectivityAnn RdrName))

    cvt_tyfam_head (TypeFamilyHead tc tyvars result injectivity)
      = do {(_, tc', tyvars') <- cvt_tycl_hdr [] tc tyvars
           ; result' <- cvtFamilyResultSig result
           ; injectivity' <- traverse cvtInjectivityAnnotation injectivity
           ; return (tc', tyvars', result', injectivity') }

    -------------------------------------------------------------------
    --              Partitioning declarations
    -------------------------------------------------------------------

    is_fam_decl :: LHsDecl RdrName -> Either (LFamilyDecl RdrName) (LHsDecl RdrName)
    is_fam_decl (L loc (TyClD (FamDecl { tcdFam = d }))) = Left (L loc d)
    is_fam_decl decl = Right decl

    is_tyfam_inst :: LHsDecl RdrName -> Either (LTyFamInstDecl RdrName) (LHsDecl RdrName)
    is_tyfam_inst (L loc (Hs.InstD (TyFamInstD { tfid_inst = d }))) = Left (L loc d)
    is_tyfam_inst decl                                              = Right decl

    is_datafam_inst :: LHsDecl RdrName -> Either (LDataFamInstDecl RdrName) (LHsDecl RdrName)
    is_datafam_inst (L loc (Hs.InstD (DataFamInstD { dfid_inst = d }))) = Left (L loc d)
    is_datafam_inst decl                                                = Right decl

    is_sig :: LHsDecl RdrName -> Either (LSig RdrName) (LHsDecl RdrName)
    is_sig (L loc (Hs.SigD sig)) = Left (L loc sig)
    is_sig decl                  = Right decl

    is_bind :: LHsDecl RdrName -> Either (LHsBind RdrName) (LHsDecl RdrName)
    is_bind (L loc (Hs.ValD bind)) = Left (L loc bind)
    is_bind decl                   = Right decl

    mkBadDecMsg :: Outputable a => MsgDoc -> [a] -> MsgDoc
    mkBadDecMsg doc bads
      = sep [ text "Illegal declaration(s) in" <+> doc <> colon
            , nest 2 (vcat (map Outputable.ppr bads)) ]

    ---------------------------------------------------
    --      Data types
    ---------------------------------------------------

    cvtConstr :: TH.Con -> CvtM (LConDecl RdrName)

    cvtConstr (NormalC c strtys)
      = do  { c'   <- cNameL c
            ; cxt' <- returnL []
            ; tys' <- mapM cvt_arg strtys
            ; returnL $ mkConDeclH98 c' Nothing cxt' (PrefixCon tys') }

    cvtConstr (RecC c varstrtys)
      = do  { c'    <- cNameL c
            ; cxt'  <- returnL []
            ; args' <- mapM cvt_id_arg varstrtys
            ; returnL $ mkConDeclH98 c' Nothing cxt'
                                       (RecCon (noLoc args')) }

    cvtConstr (InfixC st1 c st2)
      = do  { c'   <- cNameL c
            ; cxt' <- returnL []
            ; st1' <- cvt_arg st1
            ; st2' <- cvt_arg st2
            ; returnL $ mkConDeclH98 c' Nothing cxt' (InfixCon st1' st2') }

    cvtConstr (ForallC tvs ctxt con)
      = do  { tvs'        <- cvtTvs tvs
            ; L loc ctxt' <- cvtContext ctxt
            ; L _ con'    <- cvtConstr con
            ; returnL $ case con' of
                    ConDeclGADT { con_type = conT } ->
                      let hs_ty  = mkHsForAllTy tvs noSrcSpan tvs' rho_ty
                          rho_ty = mkHsQualTy ctxt noSrcSpan (L loc ctxt')
                                                             (hsib_body conT)
                      in con' { con_type = mkHsImplicitBndrs hs_ty }
                    ConDeclH98  {} ->
                      let qvars = case (tvs, con_qvars con') of
                            ([], Nothing) -> Nothing
                            (_ , m_qvs  ) -> Just $
                              mkHsQTvs (hsQTvExplicit tvs' ++
                                        maybe [] hsQTvExplicit m_qvs)
                      in con' { con_qvars = qvars
                              , con_cxt = Just $
                                L loc (ctxt' ++
                                       unLoc (fromMaybe (noLoc [])
                                              (con_cxt con'))) } }

    cvtConstr (GadtC c strtys ty)
      = do  { c'      <- mapM cNameL c
            ; args    <- mapM cvt_arg strtys
            ; L _ ty' <- cvtType ty
            ; c_ty    <- mk_arr_apps args ty'
            ; returnL $ mkGadtDecl c' (mkLHsSigType c_ty)}

    cvtConstr (RecGadtC c varstrtys ty)
      = do  { c'       <- mapM cNameL c
            ; ty'      <- cvtType ty
            ; rec_flds <- mapM cvt_id_arg varstrtys
            ; let rec_ty = noLoc (HsFunTy (noLoc $ HsRecTy rec_flds) ty')
            ; returnL $ mkGadtDecl c' (mkLHsSigType rec_ty) }

    cvtSrcUnpackedness :: TH.SourceUnpackedness -> SrcUnpackedness
    cvtSrcUnpackedness NoSourceUnpackedness = NoSrcUnpack
    cvtSrcUnpackedness SourceNoUnpack       = SrcNoUnpack
    cvtSrcUnpackedness SourceUnpack         = SrcUnpack

    cvtSrcStrictness :: TH.SourceStrictness -> SrcStrictness
    cvtSrcStrictness NoSourceStrictness = NoSrcStrict
    cvtSrcStrictness SourceLazy         = SrcLazy
    cvtSrcStrictness SourceStrict       = SrcStrict

    cvt_arg :: (TH.Bang, TH.Type) -> CvtM (LHsType RdrName)
    cvt_arg (Bang su ss, ty)
      = do { ty'' <- cvtType ty
           ; ty' <- wrap_apps ty''
           ; let su' = cvtSrcUnpackedness su
           ; let ss' = cvtSrcStrictness ss
           ; returnL $ HsBangTy (HsSrcBang NoSourceText su' ss') ty' }

    cvt_id_arg :: (TH.Name, TH.Bang, TH.Type) -> CvtM (LConDeclField RdrName)
    cvt_id_arg (i, str, ty)
      = do  { L li i' <- vNameL i
            ; ty' <- cvt_arg (str,ty)
            ; return $ noLoc (ConDeclField
                              { cd_fld_names
                                  = [L li $ FieldOcc (L li i') PlaceHolder]
                              , cd_fld_type =  ty'
                              , cd_fld_doc = Nothing}) }

    cvtDerivs :: [TH.DerivClause] -> CvtM (HsDeriving RdrName)
    cvtDerivs cs = do { cs' <- mapM cvtDerivClause cs
                      ; returnL cs' }

    cvt_fundep :: FunDep -> CvtM (Located (Class.FunDep (Located RdrName)))
    cvt_fundep (FunDep xs ys) = do { xs' <- mapM tNameL xs
                                   ; ys' <- mapM tNameL ys
                                   ; returnL (xs', ys') }

    ------------------------------------------
    --      Foreign declarations
    ------------------------------------------

    cvtForD :: Foreign -> CvtM (ForeignDecl RdrName)
    cvtForD (ImportF callconv safety from nm ty)
      -- the prim and javascript calling conventions do not support headers
      -- and are inserted verbatim, analogous to mkImport in RdrHsSyn
      | callconv == TH.Prim || callconv == TH.JavaScript
      = mk_imp (CImport (noLoc (cvt_conv callconv)) (noLoc safety') Nothing
                        (CFunction (StaticTarget (SourceText from)
                                                 (mkFastString from) Nothing
                                                 True))
                        (noLoc $ quotedSourceText from))
      | Just impspec <- parseCImport (noLoc (cvt_conv callconv)) (noLoc safety')
                                     (mkFastString (TH.nameBase nm))
                                     from (noLoc $ quotedSourceText from)
      = mk_imp impspec
      | otherwise
      = failWith $ text (show from) <+> text "is not a valid ccall impent"
      where
        mk_imp impspec
          = do { nm' <- vNameL nm
               ; ty' <- cvtType ty
               ; return (ForeignImport { fd_name = nm'
                                       , fd_sig_ty = mkLHsSigType ty'
                                       , fd_co = noForeignImportCoercionYet
                                       , fd_fi = impspec })
               }
        safety' = case safety of
                         Unsafe     -> PlayRisky
                         Safe       -> PlaySafe
                         Interruptible -> PlayInterruptible

    cvtForD (ExportF callconv as nm ty)
      = do  { nm' <- vNameL nm
            ; ty' <- cvtType ty
            ; let e = CExport (noLoc (CExportStatic (SourceText as)
                                                    (mkFastString as)
                                                    (cvt_conv callconv)))
                                                    (noLoc (SourceText as))
            ; return $ ForeignExport { fd_name = nm'
                                     , fd_sig_ty = mkLHsSigType ty'
                                     , fd_co = noForeignExportCoercionYet
                                     , fd_fe = e } }

    cvt_conv :: TH.Callconv -> CCallConv
    cvt_conv TH.CCall      = CCallConv
    cvt_conv TH.StdCall    = StdCallConv
    cvt_conv TH.CApi       = CApiConv
    cvt_conv TH.Prim       = PrimCallConv
    cvt_conv TH.JavaScript = JavaScriptCallConv

    ------------------------------------------
    --              Pragmas
    ------------------------------------------

    cvtPragmaD :: Pragma -> CvtM (Maybe (LHsDecl RdrName))
    cvtPragmaD (InlineP nm inline rm phases)
      = do { nm' <- vNameL nm
           ; let dflt = dfltActivation inline
           ; let src TH.NoInline  = "{-# NOINLINE"
                 src TH.Inline    = "{-# INLINE"
                 src TH.Inlinable = "{-# INLINABLE"
           ; let ip   = InlinePragma { inl_src    = SourceText $ src inline
                                     , inl_inline = cvtInline inline
                                     , inl_rule   = cvtRuleMatch rm
                                     , inl_act    = cvtPhases phases dflt
                                     , inl_sat    = Nothing }
           ; returnJustL $ Hs.SigD $ InlineSig nm' ip }

    cvtPragmaD (SpecialiseP nm ty inline phases)
      = do { nm' <- vNameL nm
           ; ty' <- cvtType ty
           ; let src TH.NoInline  = "{-# SPECIALISE NOINLINE"
                 src TH.Inline    = "{-# SPECIALISE INLINE"
                 src TH.Inlinable = "{-# SPECIALISE INLINE"
           ; let (inline', dflt,srcText) = case inline of
                   Just inline1 -> (cvtInline inline1, dfltActivation inline1,
                                    src inline1)
                   Nothing      -> (EmptyInlineSpec,   AlwaysActive,
                                    "{-# SPECIALISE")
           ; let ip = InlinePragma { inl_src    = SourceText srcText
                                   , inl_inline = inline'
                                   , inl_rule   = Hs.FunLike
                                   , inl_act    = cvtPhases phases dflt
                                   , inl_sat    = Nothing }
           ; returnJustL $ Hs.SigD $ SpecSig nm' [mkLHsSigType ty'] ip }

    cvtPragmaD (SpecialiseInstP ty)
      = do { ty' <- cvtType ty
           ; returnJustL $ Hs.SigD $
             SpecInstSig (SourceText "{-# SPECIALISE") (mkLHsSigType ty') }

    cvtPragmaD (RuleP nm bndrs lhs rhs phases)
      = do { let nm' = mkFastString nm
           ; let act = cvtPhases phases AlwaysActive
           ; bndrs' <- mapM cvtRuleBndr bndrs
           ; lhs'   <- cvtl lhs
           ; rhs'   <- cvtl rhs
           ; returnJustL $ Hs.RuleD
                $ HsRules (SourceText "{-# RULES")
                          [noLoc $ HsRule (noLoc (SourceText nm,nm')) act bndrs'
                                                      lhs' placeHolderNames
                                                      rhs' placeHolderNames]
           }

    cvtPragmaD (AnnP target exp)
      = do { exp' <- cvtl exp
           ; target' <- case target of
             ModuleAnnotation  -> return ModuleAnnProvenance
             TypeAnnotation n  -> do
               n' <- tconName n
               return (TypeAnnProvenance  (noLoc n'))
             ValueAnnotation n -> do
               n' <- vcName n
               return (ValueAnnProvenance (noLoc n'))
           ; returnJustL $ Hs.AnnD $ HsAnnotation (SourceText "{-# ANN") target'
                                                   exp'
           }

    cvtPragmaD (LineP line file)
      = do { setL (srcLocSpan (mkSrcLoc (fsLit file) line 1))
           ; return Nothing
           }
    cvtPragmaD (CompleteP cls mty)
      = do { cls' <- noLoc <$> mapM cNameL cls
           ; mty'  <- traverse tconNameL mty
           ; returnJustL $ Hs.SigD
                       $ CompleteMatchSig NoSourceText cls' mty' }

    dfltActivation :: TH.Inline -> Activation
    dfltActivation TH.NoInline = NeverActive
    dfltActivation _           = AlwaysActive

    cvtInline :: TH.Inline -> Hs.InlineSpec
    cvtInline TH.NoInline  = Hs.NoInline
    cvtInline TH.Inline    = Hs.Inline
    cvtInline TH.Inlinable = Hs.Inlinable

    cvtRuleMatch :: TH.RuleMatch -> RuleMatchInfo
    cvtRuleMatch TH.ConLike = Hs.ConLike
    cvtRuleMatch TH.FunLike = Hs.FunLike

    cvtPhases :: TH.Phases -> Activation -> Activation
    cvtPhases AllPhases       dflt = dflt
    cvtPhases (FromPhase i)   _    = ActiveAfter NoSourceText i
    cvtPhases (BeforePhase i) _    = ActiveBefore NoSourceText i

    cvtRuleBndr :: TH.RuleBndr -> CvtM (Hs.LRuleBndr RdrName)
    cvtRuleBndr (RuleVar n)
      = do { n' <- vNameL n
           ; return $ noLoc $ Hs.RuleBndr n' }
    cvtRuleBndr (TypedRuleVar n ty)
      = do { n'  <- vNameL n
           ; ty' <- cvtType ty
           ; return $ noLoc $ Hs.RuleBndrSig n' $ mkLHsSigWcType ty' }

    ---------------------------------------------------
    --              Declarations
    ---------------------------------------------------

    cvtLocalDecs :: MsgDoc -> [TH.Dec] -> CvtM (HsLocalBinds RdrName)
    cvtLocalDecs doc ds
      | null ds
      = return EmptyLocalBinds
      | otherwise
      = do { ds' <- cvtDecs ds
           ; let (binds, prob_sigs) = partitionWith is_bind ds'
           ; let (sigs, bads) = partitionWith is_sig prob_sigs
           ; unless (null bads) (failWith (mkBadDecMsg doc bads))
           ; return (HsValBinds (ValBindsIn (listToBag binds) sigs)) }

    cvtClause :: HsMatchContext RdrName
              -> TH.Clause -> CvtM (Hs.LMatch RdrName (LHsExpr RdrName))
    cvtClause ctxt (Clause ps body wheres)
      = do  { ps' <- cvtPats ps
            ; pps <- mapM wrap_conpat ps'
            ; g'  <- cvtGuard body
            ; ds' <- cvtLocalDecs (text "a where clause") wheres
            ; returnL $ Hs.Match ctxt pps Nothing
                                 (GRHSs g' (noLoc ds')) }

    -------------------------------------------------------------------
    --              Expressions
    -------------------------------------------------------------------

    cvtl :: TH.Exp -> CvtM (LHsExpr RdrName)
    cvtl e = wrapL (cvt e)
      where
        cvt (VarE s)        = do { s' <- vName s; return $ HsVar (noLoc s') }
        cvt (ConE s)        = do { s' <- cName s; return $ HsVar (noLoc s') }
        cvt (LitE l)
          | overloadedLit l = do { l' <- cvtOverLit l; return $ HsOverLit l' }
          | otherwise       = do { l' <- cvtLit l;     return $ HsLit l' }
        cvt (AppE x@(LamE _ _) y) = do { x' <- cvtl x; y' <- cvtl y
                                       ; return $ HsApp (mkLHsPar x') (mkLHsPar y')}
        cvt (AppE x y)            = do { x' <- cvtl x; y' <- cvtl y
                                       ; return $ HsApp (mkLHsPar x') (mkLHsPar y')}
        cvt (AppTypeE e t) = do { e' <- cvtl e
                                ; t' <- cvtType t
                                ; tp <- wrap_apps t'
                                ; return $ HsAppType e' $ mkHsWildCardBndrs tp }
        cvt (LamE ps e)    = do { ps' <- cvtPats ps; e' <- cvtl e
                                ; return $ HsLam (mkMatchGroup FromSource
                                                 [mkSimpleMatch LambdaExpr ps' e'])}
        cvt (LamCaseE ms)  = do { ms' <- mapM (cvtMatch LambdaExpr) ms
                                ; return $ HsLamCase (mkMatchGroup FromSource ms')
                                }
        cvt (TupE [e])     = do { e' <- cvtl e; return $ HsPar e' }
                                     -- Note [Dropping constructors]
                                     -- Singleton tuples treated like nothing (just parens)
        cvt (TupE es)      = do { es' <- mapM cvtl es
                                ; return $ ExplicitTuple (map (noLoc . Present) es')
                                                          Boxed }
        cvt (UnboxedTupE es)      = do { es' <- mapM cvtl es
                                       ; return $ ExplicitTuple
                                               (map (noLoc . Present) es') Unboxed }
        cvt (UnboxedSumE e alt arity) = do { e' <- cvtl e
                                           ; unboxedSumChecks alt arity
                                           ; return $ ExplicitSum
                                                 alt arity e' placeHolderType }
        cvt (CondE x y z)  = do { x' <- cvtl x; y' <- cvtl y; z' <- cvtl z;
                                ; return $ HsIf (Just noSyntaxExpr) x' y' z' }
        cvt (MultiIfE alts)
          | null alts      = failWith (text "Multi-way if-expression with no alternatives")
          | otherwise      = do { alts' <- mapM cvtpair alts
                                ; return $ HsMultiIf placeHolderType alts' }
        cvt (LetE ds e)    = do { ds' <- cvtLocalDecs (text "a let expression") ds
                                ; e' <- cvtl e; return $ HsLet (noLoc ds') e' }
        cvt (CaseE e ms)   = do { e' <- cvtl e; ms' <- mapM (cvtMatch CaseAlt) ms
                                ; return $ HsCase e' (mkMatchGroup FromSource ms') }
        cvt (DoE ss)       = cvtHsDo DoExpr ss
        cvt (CompE ss)     = cvtHsDo ListComp ss
        cvt (ArithSeqE dd) = do { dd' <- cvtDD dd; return $ ArithSeq noPostTcExpr Nothing dd' }
        cvt (ListE xs)
          | Just s <- allCharLs xs       = do { l' <- cvtLit (StringL s); return (HsLit l') }
                 -- Note [Converting strings]
          | otherwise       = do { xs' <- mapM cvtl xs
                                 ; return $ ExplicitList placeHolderType Nothing xs'
                                 }

        -- Infix expressions
        cvt (InfixE (Just x) s (Just y)) = do { x' <- cvtl x; s' <- cvtl s; y' <- cvtl y
                                              ; wrapParL HsPar $
                                                OpApp (mkLHsPar x') s' undefined (mkLHsPar y') }
                                                -- Parenthesise both arguments and result,
                                                -- to ensure this operator application does
                                                -- does not get re-associated
                                -- See Note [Operator association]
        cvt (InfixE Nothing  s (Just y)) = do { s' <- cvtl s; y' <- cvtl y
                                              ; wrapParL HsPar $ SectionR s' y' }
                                                -- See Note [Sections in HsSyn] in HsExpr
        cvt (InfixE (Just x) s Nothing ) = do { x' <- cvtl x; s' <- cvtl s
                                              ; wrapParL HsPar $ SectionL x' s' }

        cvt (InfixE Nothing  s Nothing ) = do { s' <- cvtl s; return $ HsPar s' }
                                           -- Can I indicate this is an infix thing?
                                           -- Note [Dropping constructors]

        cvt (UInfixE x s y)  = do { x' <- cvtl x
                                  ; let x'' = case x' of
                                                L _ (OpApp {}) -> x'
                                                _ -> mkLHsPar x'
                                  ; cvtOpApp x'' s y } --  Note [Converting UInfix]

        cvt (ParensE e)      = do { e' <- cvtl e; return $ HsPar e' }
        cvt (SigE e t)       = do { e' <- cvtl e; t' <- cvtType t
                                  ; return $ ExprWithTySig e' (mkLHsSigWcType t') }
        cvt (RecConE c flds) = do { c' <- cNameL c
                                  ; flds' <- mapM (cvtFld (mkFieldOcc . noLoc)) flds
                                  ; return $ mkRdrRecordCon c' (HsRecFields flds' Nothing) }
        cvt (RecUpdE e flds) = do { e' <- cvtl e
                                  ; flds'
                                      <- mapM (cvtFld (mkAmbiguousFieldOcc . noLoc))
                                               flds
                                  ; return $ mkRdrRecordUpd e' flds' }
        cvt (StaticE e)      = fmap (HsStatic placeHolderNames) $ cvtl e
        cvt (UnboundVarE s)  = do { s' <- vName s; return $ HsVar (noLoc s') }

    {- Note [Dropping constructors]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    When we drop constructors from the input (for instance, when we encounter @TupE [e]@)
    we must insert parentheses around the argument. Otherwise, @UInfix@ constructors in @e@
    could meet @UInfix@ constructors containing the @TupE [e]@. For example:

      UInfixE x * (TupE [UInfixE y + z])

    If we drop the singleton tuple but don't insert parentheses, the @UInfixE@s would meet
    and the above expression would be reassociated to

      OpApp (OpApp x * y) + z

    which we don't want.
    -}

    cvtFld :: (RdrName -> t) -> (TH.Name, TH.Exp) -> CvtM (LHsRecField' t (LHsExpr RdrName))
    cvtFld f (v,e)
      = do  { v' <- vNameL v; e' <- cvtl e
            ; return (noLoc $ HsRecField { hsRecFieldLbl = fmap f v'
                                         , hsRecFieldArg = e'
                                         , hsRecPun      = False}) }

    cvtDD :: Range -> CvtM (ArithSeqInfo RdrName)
    cvtDD (FromR x)           = do { x' <- cvtl x; return $ From x' }
    cvtDD (FromThenR x y)     = do { x' <- cvtl x; y' <- cvtl y; return $ FromThen x' y' }
    cvtDD (FromToR x y)       = do { x' <- cvtl x; y' <- cvtl y; return $ FromTo x' y' }
    cvtDD (FromThenToR x y z) = do { x' <- cvtl x; y' <- cvtl y; z' <- cvtl z; return $ FromThenTo x' y' z' }

    {- Note [Operator assocation]
    We must be quite careful about adding parens:
      * Infix (UInfix ...) op arg      Needs parens round the first arg
      * Infix (Infix ...) op arg       Needs parens round the first arg
      * UInfix (UInfix ...) op arg     No parens for first arg
      * UInfix (Infix ...) op arg      Needs parens round first arg

    Note [Converting UInfix]
    ~~~~~~~~~~~~~~~~~~~~~~~~
    When converting @UInfixE@, @UInfixP@, and @UInfixT@ values, we want to readjust
    the trees to reflect the fixities of the underlying operators:

      UInfixE x * (UInfixE y + z) ---> (x * y) + z

    This is done by the renamer (see @mkOppAppRn@, @mkConOppPatRn@, and
    @mkHsOpTyRn@ in RnTypes), which expects that the input will be completely
    right-biased for types and left-biased for everything else. So we left-bias the
    trees of @UInfixP@ and @UInfixE@ and use HsAppsTy for UInfixT.

    Sample input:

      UInfixE
       (UInfixE x op1 y)
       op2
       (UInfixE z op3 w)

    Sample output:

      OpApp
        (OpApp
          (OpApp x op1 y)
          op2
          z)
        op3
        w

    The functions @cvtOpApp@, @cvtOpAppP@, and @cvtOpAppT@ are responsible for this
    biasing.
    -}

    {- | @cvtOpApp x op y@ converts @op@ and @y@ and produces the operator application @x `op` y@.
    The produced tree of infix expressions will be left-biased, provided @x@ is.

    We can see that @cvtOpApp@ is correct as follows. The inductive hypothesis
    is that @cvtOpApp x op y@ is left-biased, provided @x@ is. It is clear that
    this holds for both branches (of @cvtOpApp@), provided we assume it holds for
    the recursive calls to @cvtOpApp@.

    When we call @cvtOpApp@ from @cvtl@, the first argument will always be left-biased
    since we have already run @cvtl@ on it.
    -}
    cvtOpApp :: LHsExpr RdrName -> TH.Exp -> TH.Exp -> CvtM (HsExpr RdrName)
    cvtOpApp x op1 (UInfixE y op2 z)
      = do { l <- wrapL $ cvtOpApp x op1 y
           ; cvtOpApp l op2 z }
    cvtOpApp x op y
      = do { op' <- cvtl op
           ; y' <- cvtl y
           ; return (OpApp x op' undefined y') }

    -------------------------------------
    --      Do notation and statements
    -------------------------------------

    cvtHsDo :: HsStmtContext Name.Name -> [TH.Stmt] -> CvtM (HsExpr RdrName)
    cvtHsDo do_or_lc stmts
      | null stmts = failWith (text "Empty stmt list in do-block")
      | otherwise
      = do  { stmts' <- cvtStmts stmts
            ; let Just (stmts'', last') = snocView stmts'

            ; last'' <- case last' of
                        L loc (BodyStmt body _ _ _) -> return (L loc (mkLastStmt body))
                        _ -> failWith (bad_last last')

            ; return $ HsDo do_or_lc (noLoc (stmts'' ++ [last''])) placeHolderType }
      where
        bad_last stmt = vcat [ text "Illegal last statement of" <+> pprAStmtContext do_or_lc <> colon
                             , nest 2 $ Outputable.ppr stmt
                             , text "(It should be an expression.)" ]

    cvtStmts :: [TH.Stmt] -> CvtM [Hs.LStmt RdrName (LHsExpr RdrName)]
    cvtStmts = mapM cvtStmt

    cvtStmt :: TH.Stmt -> CvtM (Hs.LStmt RdrName (LHsExpr RdrName))
    cvtStmt (NoBindS e)    = do { e' <- cvtl e; returnL $ mkBodyStmt e' }
    cvtStmt (TH.BindS p e) = do { p' <- cvtPat p; e' <- cvtl e; returnL $ mkBindStmt p' e' }
    cvtStmt (TH.LetS ds)   = do { ds' <- cvtLocalDecs (text "a let binding") ds
                                ; returnL $ LetStmt (noLoc ds') }
    cvtStmt (TH.ParS dss)  = do { dss' <- mapM cvt_one dss; returnL $ ParStmt dss' noExpr noSyntaxExpr placeHolderType }
                           where
                             cvt_one ds = do { ds' <- cvtStmts ds; return (ParStmtBlock ds' undefined noSyntaxExpr) }

    cvtMatch :: HsMatchContext RdrName
             -> TH.Match -> CvtM (Hs.LMatch RdrName (LHsExpr RdrName))
    cvtMatch ctxt (TH.Match p body decs)
      = do  { p' <- cvtPat p
            ; lp <- case ctxt of
                CaseAlt -> return p'
                _       -> wrap_conpat p'
            ; g' <- cvtGuard body
            ; decs' <- cvtLocalDecs (text "a where clause") decs
            ; returnL $ Hs.Match ctxt [lp] Nothing
                                 (GRHSs g' (noLoc decs')) }

    cvtGuard :: TH.Body -> CvtM [LGRHS RdrName (LHsExpr RdrName)]
    cvtGuard (GuardedB pairs) = mapM cvtpair pairs
    cvtGuard (NormalB e)      = do { e' <- cvtl e; g' <- returnL $ GRHS [] e'; return [g'] }

    cvtpair :: (TH.Guard, TH.Exp) -> CvtM (LGRHS RdrName (LHsExpr RdrName))
    cvtpair (NormalG ge,rhs) = do { ge' <- cvtl ge; rhs' <- cvtl rhs
                                  ; g' <- returnL $ mkBodyStmt ge'
                                  ; returnL $ GRHS [g'] rhs' }
    cvtpair (PatG gs,rhs)    = do { gs' <- cvtStmts gs; rhs' <- cvtl rhs
                                  ; returnL $ GRHS gs' rhs' }

    cvtOverLit :: Lit -> CvtM (HsOverLit RdrName)
    cvtOverLit (IntegerL i)
      = do { force i; return $ mkHsIntegral NoSourceText i placeHolderType}
    cvtOverLit (RationalL r)
      = do { force r; return $ mkHsFractional (cvtFractionalLit r) placeHolderType}
    cvtOverLit (StringL s)
      = do { let { s' = mkFastString s }
           ; force s'
           ; return $ mkHsIsString (quotedSourceText s) s' placeHolderType
           }
    cvtOverLit _ = panic "Convert.cvtOverLit: Unexpected overloaded literal"
    -- An Integer is like an (overloaded) '3' in a Haskell source program
    -- Similarly 3.5 for fractionals

    {- Note [Converting strings]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    If we get (ListE [CharL 'x', CharL 'y']) we'd like to convert to
    a string literal for "xy".  Of course, we might hope to get
    (LitE (StringL "xy")), but not always, and allCharLs fails quickly
    if it isn't a literal string
    -}

    allCharLs :: [TH.Exp] -> Maybe String
    -- Note [Converting strings]
    -- NB: only fire up this setup for a non-empty list, else
    --     there's a danger of returning "" for [] :: [Int]!
    allCharLs xs
      = case xs of
          LitE (CharL c) : ys -> go [c] ys
          _                   -> Nothing
      where
        go cs []                    = Just (reverse cs)
        go cs (LitE (CharL c) : ys) = go (c:cs) ys
        go _  _                     = Nothing

    cvtLit :: Lit -> CvtM HsLit
    cvtLit (IntPrimL i)    = do { force i; return $ HsIntPrim NoSourceText i }
    cvtLit (WordPrimL w)   = do { force w; return $ HsWordPrim NoSourceText w }
    cvtLit (FloatPrimL f)  = do { force f; return $ HsFloatPrim (cvtFractionalLit f) }
    cvtLit (DoublePrimL f) = do { force f; return $ HsDoublePrim (cvtFractionalLit f) }
    cvtLit (CharL c)       = do { force c; return $ HsChar NoSourceText c }
    cvtLit (CharPrimL c)   = do { force c; return $ HsCharPrim NoSourceText c }
    cvtLit (StringL s)     = do { let { s' = mkFastString s }
                                ; force s'
                                ; return $ HsString (quotedSourceText s) s' }
    cvtLit (StringPrimL s) = do { let { s' = BS.pack s }
                                ; force s'
                                ; return $ HsStringPrim NoSourceText s' }
    cvtLit _ = panic "Convert.cvtLit: Unexpected literal"
            -- cvtLit should not be called on IntegerL, RationalL
            -- That precondition is established right here in
            -- Convert.hs, hence panic

    quotedSourceText :: String -> SourceText
    quotedSourceText s = SourceText $ "\"" ++ s ++ "\""

    cvtPats :: [TH.Pat] -> CvtM [Hs.LPat RdrName]
    cvtPats pats = mapM cvtPat pats

    cvtPat :: TH.Pat -> CvtM (Hs.LPat RdrName)
    cvtPat pat = wrapL (cvtp pat)

    cvtp :: TH.Pat -> CvtM (Hs.Pat RdrName)
    cvtp (TH.LitP l)
      | overloadedLit l    = do { l' <- cvtOverLit l
                                ; return (mkNPat (noLoc l') Nothing) }
                                      -- Not right for negative patterns;
                                      -- need to think about that!
      | otherwise          = do { l' <- cvtLit l; return $ Hs.LitPat l' }
    cvtp (TH.VarP s)       = do { s' <- vName s; return $ Hs.VarPat (noLoc s') }
    cvtp (TupP [p])        = do { p' <- cvtPat p; return $ ParPat p' } -- Note [Dropping constructors]
    cvtp (TupP ps)         = do { ps' <- cvtPats ps; return $ TuplePat ps' Boxed   [] }
    cvtp (UnboxedTupP ps)  = do { ps' <- cvtPats ps; return $ TuplePat ps' Unboxed [] }
    cvtp (UnboxedSumP p alt arity)
                           = do { p' <- cvtPat p
                                ; unboxedSumChecks alt arity
                                ; return $ SumPat p' alt arity placeHolderType }
    cvtp (ConP s ps)       = do { s' <- cNameL s; ps' <- cvtPats ps
                                ; pps <- mapM wrap_conpat ps'
                                ; return $ ConPatIn s' (PrefixCon pps) }
    cvtp (InfixP p1 s p2)  = do { s' <- cNameL s; p1' <- cvtPat p1; p2' <- cvtPat p2
                                ; wrapParL ParPat $
                                  ConPatIn s' (InfixCon (mkParPat p1') (mkParPat p2')) }
                                -- See Note [Operator association]
    cvtp (UInfixP p1 s p2) = do { p1' <- cvtPat p1; cvtOpAppP p1' s p2 } -- Note [Converting UInfix]
    cvtp (ParensP p)       = do { p' <- cvtPat p;
                                ; case p' of  -- may be wrapped ConPatIn
                                    (L _ (ParPat {})) -> return $ unLoc p'
                                    _                 -> return $ ParPat p' }
    cvtp (TildeP p)        = do { p' <- cvtPat p; return $ LazyPat p' }
    cvtp (BangP p)         = do { p' <- cvtPat p; return $ BangPat p' }
    cvtp (TH.AsP s p)      = do { s' <- vNameL s; p' <- cvtPat p; return $ AsPat s' p' }
    cvtp TH.WildP          = return $ WildPat placeHolderType
    cvtp (RecP c fs)       = do { c' <- cNameL c; fs' <- mapM cvtPatFld fs
                                ; return $ ConPatIn c'
                                         $ Hs.RecCon (HsRecFields fs' Nothing) }
    cvtp (ListP ps)        = do { ps' <- cvtPats ps
                                ; return $ ListPat ps' placeHolderType Nothing }
    cvtp (SigP p t)        = do { p' <- cvtPat p; t' <- cvtType t
                                ; return $ SigPatIn p' (mkLHsSigWcType t') }
    cvtp (ViewP e p)       = do { e' <- cvtl e; p' <- cvtPat p
                                ; return $ ViewPat e' p' placeHolderType }

    cvtPatFld :: (TH.Name, TH.Pat) -> CvtM (LHsRecField RdrName (LPat RdrName))
    cvtPatFld (s,p)
      = do  { L ls s' <- vNameL s; p' <- cvtPat p
            ; return (noLoc $ HsRecField { hsRecFieldLbl
                                             = L ls $ mkFieldOcc (L ls s')
                                         , hsRecFieldArg = p'
                                         , hsRecPun      = False}) }

    wrap_conpat :: Hs.LPat RdrName -> CvtM (Hs.LPat RdrName)
    wrap_conpat p@(L _ (ConPatIn _ (InfixCon{})))   = returnL $ ParPat p
    wrap_conpat p@(L _ (ConPatIn _ (PrefixCon []))) = return p
    wrap_conpat p@(L _ (ConPatIn _ (PrefixCon _)))  = returnL $ ParPat p
    wrap_conpat p                                   = return p

    {- | @cvtOpAppP x op y@ converts @op@ and @y@ and produces the operator application @x `op` y@.
    The produced tree of infix patterns will be left-biased, provided @x@ is.

    See the @cvtOpApp@ documentation for how this function works.
    -}
    cvtOpAppP :: Hs.LPat RdrName -> TH.Name -> TH.Pat -> CvtM (Hs.Pat RdrName)
    cvtOpAppP x op1 (UInfixP y op2 z)
      = do { l <- wrapL $ cvtOpAppP x op1 y
           ; cvtOpAppP l op2 z }
    cvtOpAppP x op y
      = do { op' <- cNameL op
           ; y' <- cvtPat y
           ; return (ConPatIn op' (InfixCon x y')) }

    -----------------------------------------------------------
    --      Types and type variables

    cvtTvs :: [TH.TyVarBndr] -> CvtM (LHsQTyVars RdrName)
    cvtTvs tvs = do { tvs' <- mapM cvt_tv tvs; return (mkHsQTvs tvs') }

    cvt_tv :: TH.TyVarBndr -> CvtM (LHsTyVarBndr RdrName)
    cvt_tv (TH.PlainTV nm)
      = do { nm' <- tNameL nm
           ; returnL $ UserTyVar nm' }
    cvt_tv (TH.KindedTV nm ki)
      = do { nm' <- tNameL nm
           ; ki' <- cvtKind ki
           ; returnL $ KindedTyVar nm' ki' }

    cvtRole :: TH.Role -> Maybe Coercion.Role
    cvtRole TH.NominalR          = Just Coercion.Nominal
    cvtRole TH.RepresentationalR = Just Coercion.Representational
    cvtRole TH.PhantomR          = Just Coercion.Phantom
    cvtRole TH.InferR            = Nothing

    cvtContext :: TH.Cxt -> CvtM (LHsContext RdrName)
    cvtContext tys = do { preds' <- mapM cvtPred tys; returnL preds' }

    cvtPred :: TH.Pred -> CvtM (LHsType RdrName)
    cvtPred = cvtType

    cvtDerivClause :: TH.DerivClause
                   -> CvtM (LHsDerivingClause RdrName)
    cvtDerivClause (TH.DerivClause ds ctxt)
      = do { ctxt'@(L loc _) <- fmap (map mkLHsSigType) <$> cvtContext ctxt
           ; let ds' = fmap (L loc . cvtDerivStrategy) ds
           ; returnL $ HsDerivingClause ds' ctxt' }

    cvtDerivStrategy :: TH.DerivStrategy -> Hs.DerivStrategy
    cvtDerivStrategy TH.StockStrategy    = Hs.StockStrategy
    cvtDerivStrategy TH.AnyclassStrategy = Hs.AnyclassStrategy
    cvtDerivStrategy TH.NewtypeStrategy  = Hs.NewtypeStrategy

    cvtType :: TH.Type -> CvtM (LHsType RdrName)
    cvtType = cvtTypeKind "type"

    cvtTypeKind :: String -> TH.Type -> CvtM (LHsType RdrName)
    cvtTypeKind ty_str ty
      = do { (head_ty, tys') <- split_ty_app ty
           ; case head_ty of
               TupleT n
                 | length tys' == n         -- Saturated
                 -> if n==1 then return (head tys') -- Singleton tuples treated
                                                    -- like nothing (ie just parens)
                            else returnL (HsTupleTy HsBoxedOrConstraintTuple tys')
                 | n == 1
                 -> failWith (ptext (sLit ("Illegal 1-tuple " ++ ty_str ++ " constructor")))
                 | otherwise
                 -> mk_apps (HsTyVar NotPromoted
                                   (noLoc (getRdrName (tupleTyCon Boxed n)))) tys'
               UnboxedTupleT n
                 | length tys' == n         -- Saturated
                 -> returnL (HsTupleTy HsUnboxedTuple tys')
                 | otherwise
                 -> mk_apps (HsTyVar NotPromoted
                                 (noLoc (getRdrName (tupleTyCon Unboxed n)))) tys'
               UnboxedSumT n
                 | n < 2
                -> failWith $
                       vcat [ text "Illegal sum arity:" <+> text (show n)
                            , nest 2 $
                                text "Sums must have an arity of at least 2" ]
                 | length tys' == n -- Saturated
                 -> returnL (HsSumTy tys')
                 | otherwise
                 -> mk_apps (HsTyVar NotPromoted (noLoc (getRdrName (sumTyCon n))))
                            tys'
               ArrowT
                 | [x',y'] <- tys' -> returnL (HsFunTy x' y')
                 | otherwise ->
                      mk_apps (HsTyVar NotPromoted (noLoc (getRdrName funTyCon)))
                              tys'
               ListT
                 | [x']    <- tys' -> returnL (HsListTy x')
                 | otherwise ->
                      mk_apps (HsTyVar NotPromoted (noLoc (getRdrName listTyCon)))
                               tys'
               VarT nm -> do { nm' <- tNameL nm
                             ; mk_apps (HsTyVar NotPromoted nm') tys' }
               ConT nm -> do { nm' <- tconName nm
                             ; mk_apps (HsTyVar NotPromoted (noLoc nm')) tys' }

               ForallT tvs cxt ty
                 | null tys'
                 -> do { tvs' <- cvtTvs tvs
                       ; cxt' <- cvtContext cxt
                       ; ty'  <- cvtType ty
                       ; loc <- getL
                       ; let hs_ty  = mkHsForAllTy tvs loc tvs' rho_ty
                             rho_ty = mkHsQualTy cxt loc cxt' ty'

                       ; return hs_ty }

               SigT ty ki
                 -> do { ty' <- cvtType ty
                       ; ki' <- cvtKind ki
                       ; mk_apps (HsKindSig ty' ki') tys'
                       }

               LitT lit
                 -> returnL (HsTyLit (cvtTyLit lit))

               WildCardT
                 -> mk_apps mkAnonWildCardTy tys'

               InfixT t1 s t2
                 -> do { s'  <- tconName s
                       ; t1' <- cvtType t1
                       ; t2' <- cvtType t2
                       ; mk_apps (HsTyVar NotPromoted (noLoc s')) [t1', t2']
                       }

               UInfixT t1 s t2
                 -> do { t1' <- cvtType t1
                       ; t2' <- cvtType t2
                       ; s'  <- tconName s
                       ; return $ cvtOpAppT t1' s' t2'
                       } -- Note [Converting UInfix]

               ParensT t
                 -> do { t' <- cvtType t
                       ; returnL $ HsParTy t'
                       }

               PromotedT nm -> do { nm' <- cName nm
                                  ; mk_apps (HsTyVar NotPromoted (noLoc nm')) tys' }
                     -- Promoted data constructor; hence cName

               PromotedTupleT n
                 | n == 1
                 -> failWith (ptext (sLit ("Illegal promoted 1-tuple " ++ ty_str)))
                 | m == n   -- Saturated
                 -> do  { let kis = replicate m placeHolderKind
                        ; returnL (HsExplicitTupleTy kis tys')
                        }
                 where
                   m = length tys'

               PromotedNilT
                 -> returnL (HsExplicitListTy Promoted placeHolderKind [])

               PromotedConsT  -- See Note [Representing concrete syntax in types]
                              -- in Language.Haskell.TH.Syntax
                 | [ty1, L _ (HsExplicitListTy ip _ tys2)] <- tys'
                 -> returnL (HsExplicitListTy ip placeHolderKind (ty1:tys2))
                 | otherwise
                 -> mk_apps (HsTyVar NotPromoted (noLoc (getRdrName consDataCon)))
                            tys'

               StarT
                 -> returnL (HsTyVar NotPromoted (noLoc
                                                  (getRdrName liftedTypeKindTyCon)))

               ConstraintT
                 -> returnL (HsTyVar NotPromoted
                                  (noLoc (getRdrName constraintKindTyCon)))

               EqualityT
                 | [x',y'] <- tys' -> returnL (HsEqTy x' y')
                 | otherwise ->
                       mk_apps (HsTyVar NotPromoted
                                (noLoc (getRdrName eqPrimTyCon))) tys'

               _ -> failWith (ptext (sLit ("Malformed " ++ ty_str)) <+> text (show ty))
        }

    -- | Constructs an application of a type to arguments passed in a list.
    mk_apps :: HsType RdrName -> [LHsType RdrName] -> CvtM (LHsType RdrName)
    mk_apps head_ty []       = returnL head_ty
    mk_apps head_ty (ty:tys) =
      do { head_ty' <- returnL head_ty
         ; p_ty      <- add_parens ty
         ; mk_apps (HsAppTy head_ty' p_ty) tys }
      where
        add_parens t@(L _ HsAppTy{}) = returnL (HsParTy t)
        add_parens t                 = return t

    wrap_apps  :: LHsType RdrName -> CvtM (LHsType RdrName)
    wrap_apps t@(L _ HsAppTy {}) = returnL (HsParTy t)
    wrap_apps t                  = return t

    -- | Constructs an arrow type with a specified return type
    mk_arr_apps :: [LHsType RdrName] -> HsType RdrName -> CvtM (LHsType RdrName)
    mk_arr_apps tys return_ty = foldrM go return_ty tys >>= returnL
        where go :: LHsType RdrName -> HsType RdrName -> CvtM (HsType RdrName)
              go arg ret_ty = do { ret_ty_l <- returnL ret_ty
                                 ; return (HsFunTy arg ret_ty_l) }

    split_ty_app :: TH.Type -> CvtM (TH.Type, [LHsType RdrName])
    split_ty_app ty = go ty []
      where
        go (AppT f a) as' = do { a' <- cvtType a; go f (a':as') }
        go f as           = return (f,as)

    cvtTyLit :: TH.TyLit -> HsTyLit
    cvtTyLit (TH.NumTyLit i) = HsNumTy NoSourceText i
    cvtTyLit (TH.StrTyLit s) = HsStrTy NoSourceText (fsLit s)

    {- | @cvtOpAppT x op y@ takes converted arguments and flattens any HsAppsTy
       structure in them.
    -}
    cvtOpAppT :: LHsType RdrName -> RdrName -> LHsType RdrName -> LHsType RdrName
    cvtOpAppT t1@(L loc1 _) op t2@(L loc2 _)
      = L (combineSrcSpans loc1 loc2) $
        HsAppsTy (t1' ++ [noLoc $ HsAppInfix (noLoc op)] ++ t2')
      where
        t1' | L _ (HsAppsTy t1s) <- t1
            = t1s
            | otherwise
            = [noLoc $ HsAppPrefix t1]

        t2' | L _ (HsAppsTy t2s) <- t2
            = t2s
            | otherwise
            = [noLoc $ HsAppPrefix t2]

    cvtKind :: TH.Kind -> CvtM (LHsKind RdrName)
    cvtKind = cvtTypeKind "kind"

    -- | Convert Maybe Kind to a type family result signature. Used with data
    -- families where naming of the result is not possible (thus only kind or no
    -- signature is possible).
    cvtMaybeKindToFamilyResultSig :: Maybe TH.Kind
                                  -> CvtM (LFamilyResultSig RdrName)
    cvtMaybeKindToFamilyResultSig Nothing   = returnL Hs.NoSig
    cvtMaybeKindToFamilyResultSig (Just ki) = do { ki' <- cvtKind ki
                                                 ; returnL (Hs.KindSig ki') }

    -- | Convert type family result signature. Used with both open and closed type
    -- families.
    cvtFamilyResultSig :: TH.FamilyResultSig -> CvtM (Hs.LFamilyResultSig RdrName)
    cvtFamilyResultSig TH.NoSig           = returnL Hs.NoSig
    cvtFamilyResultSig (TH.KindSig ki)    = do { ki' <- cvtKind ki
                                               ; returnL (Hs.KindSig ki') }
    cvtFamilyResultSig (TH.TyVarSig bndr) = do { tv <- cvt_tv bndr
                                               ; returnL (Hs.TyVarSig tv) }

    -- | Convert injectivity annotation of a type family.
    cvtInjectivityAnnotation :: TH.InjectivityAnn
                             -> CvtM (Hs.LInjectivityAnn RdrName)
    cvtInjectivityAnnotation (TH.InjectivityAnn annLHS annRHS)
      = do { annLHS' <- tNameL annLHS
           ; annRHS' <- mapM tNameL annRHS
           ; returnL (Hs.InjectivityAnn annLHS' annRHS') }

    cvtPatSynSigTy :: TH.Type -> CvtM (LHsType RdrName)
    -- pattern synonym types are of peculiar shapes, which is why we treat
    -- them separately from regular types;
    -- see Note [Pattern synonym type signatures and Template Haskell]
    cvtPatSynSigTy (ForallT univs reqs (ForallT exis provs ty))
      | null exis, null provs = cvtType (ForallT univs reqs ty)
      | null univs, null reqs = do { l   <- getL
                                   ; ty' <- cvtType (ForallT exis provs ty)
                                   ; return $ L l (HsQualTy { hst_ctxt = L l []
                                                            , hst_body = ty' }) }
      | null reqs             = do { l      <- getL
                                   ; univs' <- hsQTvExplicit <$> cvtTvs univs
                                   ; ty'    <- cvtType (ForallT exis provs ty)
                                   ; let forTy = HsForAllTy { hst_bndrs = univs'
                                                            , hst_body = L l cxtTy }
                                         cxtTy = HsQualTy { hst_ctxt = L l []
                                                          , hst_body = ty' }
                                   ; return $ L l forTy }
      | otherwise             = cvtType (ForallT univs reqs (ForallT exis provs ty))
    cvtPatSynSigTy ty         = cvtType ty

    -----------------------------------------------------------
    cvtFixity :: TH.Fixity -> Hs.Fixity
    cvtFixity (TH.Fixity prec dir) = Hs.Fixity NoSourceText prec (cvt_dir dir)
       where
         cvt_dir TH.InfixL = Hs.InfixL
         cvt_dir TH.InfixR = Hs.InfixR
         cvt_dir TH.InfixN = Hs.InfixN

    -----------------------------------------------------------

    -----------------------------------------------------------
    -- some useful things

    overloadedLit :: Lit -> Bool
    -- True for literals that Haskell treats as overloaded
    overloadedLit (IntegerL  _) = True
    overloadedLit (RationalL _) = True
    overloadedLit _             = False

    cvtFractionalLit :: Rational -> FractionalLit
    cvtFractionalLit r = FL { fl_text = show (fromRational r :: Double), fl_value = r }

    -- Checks that are performed when converting unboxed sum expressions and
    -- patterns alike.
    unboxedSumChecks :: TH.SumAlt -> TH.SumArity -> CvtM ()
    unboxedSumChecks alt arity
        | alt > arity
        = failWith $ text "Sum alternative"    <+> text (show alt)
                 <+> text "exceeds its arity," <+> text (show arity)
        | alt <= 0
        = failWith $ vcat [ text "Illegal sum alternative:" <+> text (show alt)
                          , nest 2 $ text "Sum alternatives must start from 1" ]
        | arity < 2
        = failWith $ vcat [ text "Illegal sum arity:" <+> text (show arity)
                          , nest 2 $ text "Sums must have an arity of at least 2" ]
        | otherwise
        = return ()

    -- | If passed an empty list of 'TH.TyVarBndr's, this simply returns the
    -- third argument (an 'LHsType'). Otherwise, return an 'HsForAllTy'
    -- using the provided 'LHsQTyVars' and 'LHsType'.
    mkHsForAllTy :: [TH.TyVarBndr]
                 -- ^ The original Template Haskell type variable binders
                 -> SrcSpan
                 -- ^ The location of the returned 'LHsType' if it needs an
                 --   explicit forall
                 -> LHsQTyVars name
                 -- ^ The converted type variable binders
                 -> LHsType name
                 -- ^ The converted rho type
                 -> LHsType name
                 -- ^ The complete type, quantified with a forall if necessary
    mkHsForAllTy tvs loc tvs' rho_ty
      | null tvs  = rho_ty
      | otherwise = L loc $ HsForAllTy { hst_bndrs = hsQTvExplicit tvs'
                                       , hst_body = rho_ty }

    -- | If passed an empty 'TH.Cxt', this simply returns the third argument
    -- (an 'LHsType'). Otherwise, return an 'HsQualTy' using the provided
    -- 'LHsContext' and 'LHsType'.

    -- It's important that we don't build an HsQualTy if the context is empty,
    -- as the pretty-printer for HsType _always_ prints contexts, even if
    -- they're empty. See Trac #13183.
    mkHsQualTy :: TH.Cxt
               -- ^ The original Template Haskell context
               -> SrcSpan
               -- ^ The location of the returned 'LHsType' if it needs an
               --   explicit context
               -> LHsContext name
               -- ^ The converted context
               -> LHsType name
               -- ^ The converted tau type
               -> LHsType name
               -- ^ The complete type, qualified with a context if necessary
    mkHsQualTy ctxt loc ctxt' ty
      | null ctxt = ty
      | otherwise = L loc $ HsQualTy { hst_ctxt = ctxt', hst_body = ty }

    --------------------------------------------------------------------
    --      Turning Name back into RdrName
    --------------------------------------------------------------------

    -- variable names
    vNameL, cNameL, vcNameL, tNameL, tconNameL :: TH.Name -> CvtM (Located RdrName)
    vName,  cName,  vcName,  tName,  tconName  :: TH.Name -> CvtM RdrName

    -- Variable names
    vNameL n = wrapL (vName n)
    vName n = cvtName OccName.varName n

    -- Constructor function names; this is Haskell source, hence srcDataName
    cNameL n = wrapL (cName n)
    cName n = cvtName OccName.dataName n

    -- Variable *or* constructor names; check by looking at the first char
    vcNameL n = wrapL (vcName n)
    vcName n = if isVarName n then vName n else cName n

    -- Type variable names
    tNameL n = wrapL (tName n)
    tName n = cvtName OccName.tvName n

    -- Type Constructor names
    tconNameL n = wrapL (tconName n)
    tconName n = cvtName OccName.tcClsName n

    cvtName :: OccName.NameSpace -> TH.Name -> CvtM RdrName
    cvtName ctxt_ns (TH.Name occ flavour)
      | not (okOcc ctxt_ns occ_str) = failWith (badOcc ctxt_ns occ_str)
      | otherwise
      = do { loc <- getL
           ; let rdr_name = thRdrName loc ctxt_ns occ_str flavour
           ; force rdr_name
           ; return rdr_name }
      where
        occ_str = TH.occString occ

    okOcc :: OccName.NameSpace -> String -> Bool
    okOcc ns str
      | OccName.isVarNameSpace ns     = okVarOcc str
      | OccName.isDataConNameSpace ns = okConOcc str
      | otherwise                     = okTcOcc  str

    -- Determine the name space of a name in a type
    --
    isVarName :: TH.Name -> Bool
    isVarName (TH.Name occ _)
      = case TH.occString occ of
          ""    -> False
          (c:_) -> startsVarId c || startsVarSym c

    badOcc :: OccName.NameSpace -> String -> SDoc
    badOcc ctxt_ns occ
      = text "Illegal" <+> pprNameSpace ctxt_ns
            <+> text "name:" <+> quotes (text occ)

    thRdrName :: SrcSpan -> OccName.NameSpace -> String -> TH.NameFlavour -> RdrName
    -- This turns a TH Name into a RdrName; used for both binders and occurrences
    -- See Note [Binders in Template Haskell]
    -- The passed-in name space tells what the context is expecting;
    --      use it unless the TH name knows what name-space it comes
    --      from, in which case use the latter
    --
    -- We pass in a SrcSpan (gotten from the monad) because this function
    -- is used for *binders* and if we make an Exact Name we want it
    -- to have a binding site inside it.  (cf Trac #5434)
    --
    -- ToDo: we may generate silly RdrNames, by passing a name space
    --       that doesn't match the string, like VarName ":+",
    --       which will give confusing error messages later
    --
    -- The strict applications ensure that any buried exceptions get forced
    thRdrName loc ctxt_ns th_occ th_name
      = case th_name of
         TH.NameG th_ns pkg mod -> thOrigRdrName th_occ th_ns pkg mod
         TH.NameQ mod  -> (mkRdrQual  $! mk_mod mod) $! occ
         TH.NameL uniq -> nameRdrName $! (((Name.mkInternalName $! mk_uniq uniq) $! occ) loc)
         TH.NameU uniq -> nameRdrName $! (((Name.mkSystemNameAt $! mk_uniq uniq) $! occ) loc)
         TH.NameS | Just name <- isBuiltInOcc_maybe occ -> nameRdrName $! name
                  | otherwise                           -> mkRdrUnqual $! occ
                  -- We check for built-in syntax here, because the TH
                  -- user might have written a (NameS "(,,)"), for example
      where
        occ :: OccName.OccName
        occ = mk_occ ctxt_ns th_occ

    thOrigRdrName :: String -> TH.NameSpace -> PkgName -> ModName -> RdrName
    thOrigRdrName occ th_ns pkg mod = (mkOrig $! (mkModule (mk_pkg pkg) (mk_mod mod))) $! (mk_occ (mk_ghc_ns th_ns) occ)

    thRdrNameGuesses :: TH.Name -> [RdrName]
    thRdrNameGuesses (TH.Name occ flavour)
      -- This special case for NameG ensures that we don't generate duplicates in the output list
      | TH.NameG th_ns pkg mod <- flavour = [ thOrigRdrName occ_str th_ns pkg mod]
      | otherwise                         = [ thRdrName noSrcSpan gns occ_str flavour
                                            | gns <- guessed_nss]
      where
        -- guessed_ns are the name spaces guessed from looking at the TH name
        guessed_nss | isLexCon (mkFastString occ_str) = [OccName.tcName,  OccName.dataName]
                    | otherwise                       = [OccName.varName, OccName.tvName]
        occ_str = TH.occString occ

    -- The packing and unpacking is rather turgid :-(
    mk_occ :: OccName.NameSpace -> String -> OccName.OccName
    mk_occ ns occ = OccName.mkOccName ns occ

    mk_ghc_ns :: TH.NameSpace -> OccName.NameSpace
    mk_ghc_ns TH.DataName  = OccName.dataName
    mk_ghc_ns TH.TcClsName = OccName.tcClsName
    mk_ghc_ns TH.VarName   = OccName.varName

    mk_mod :: TH.ModName -> ModuleName
    mk_mod mod = mkModuleName (TH.modString mod)

    mk_pkg :: TH.PkgName -> UnitId
    mk_pkg pkg = stringToUnitId (TH.pkgString pkg)

    mk_uniq :: Int -> Unique
    mk_uniq u = mkUniqueGrimily u

    {-
    Note [Binders in Template Haskell]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Consider this TH term construction:
      do { x1 <- TH.newName "x"   -- newName :: String -> Q TH.Name
         ; x2 <- TH.newName "x"   -- Builds a NameU
         ; x3 <- TH.newName "x"

         ; let x = mkName "x"     -- mkName :: String -> TH.Name
                                  -- Builds a NameS

         ; return (LamE (..pattern [x1,x2]..) $
                   LamE (VarPat x3) $
                   ..tuple (x1,x2,x3,x)) }

    It represents the term   \[x1,x2]. \x3. (x1,x2,x3,x)

    a) We don't want to complain about "x" being bound twice in
       the pattern [x1,x2]
    b) We don't want x3 to shadow the x1,x2
    c) We *do* want 'x' (dynamically bound with mkName) to bind
       to the innermost binding of "x", namely x3.
    d) When pretty printing, we want to print a unique with x1,x2
       etc, else they'll all print as "x" which isn't very helpful

    When we convert all this to HsSyn, the TH.Names are converted with
    thRdrName.  To achieve (b) we want the binders to be Exact RdrNames.
    Achieving (a) is a bit awkward, because
       - We must check for duplicate and shadowed names on Names,
         not RdrNames, *after* renaming.
         See Note [Collect binders only after renaming] in HsUtils

       - But to achieve (a) we must distinguish between the Exact
         RdrNames arising from TH and the Unqual RdrNames that would
         come from a user writing \[x,x] -> blah

    So in Convert.thRdrName we translate
       TH Name                          RdrName
       --------------------------------------------------------
       NameU (arising from newName) --> Exact (Name{ System })
       NameS (arising from mkName)  --> Unqual

    Notice that the NameUs generate *System* Names.  Then, when
    figuring out shadowing and duplicates, we can filter out
    System Names.

    This use of System Names fits with other uses of System Names, eg for
    temporary variables "a". Since there are lots of things called "a" we
    usually want to print the name with the unique, and that is indeed
    the way System Names are printed.

    There's a small complication of course; see Note [Looking up Exact
    RdrNames] in RnEnv.
    -}

    {-
    Note [Pattern synonym type signatures and Template Haskell]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

    In general, the type signature of a pattern synonym

      pattern P x1 x2 .. xn = <some-pattern>

    is of the form

       forall univs. reqs => forall exis. provs => t1 -> t2 -> ... -> tn -> t

    with the following parts:

       1) the (possibly empty lists of) universally quantified type
          variables `univs` and required constraints `reqs` on them.
       2) the (possibly empty lists of) existentially quantified type
          variables `exis` and the provided constraints `provs` on them.
       3) the types `t1`, `t2`, .., `tn` of the pattern synonym's arguments x1,
          x2, .., xn, respectively
       4) the type `t` of <some-pattern>, mentioning only universals from `univs`.

    Due to the two forall quantifiers and constraint contexts (either of
    which might be empty), pattern synonym type signatures are treated
    specially in `deSugar/DsMeta.hs`, `hsSyn/Convert.hs`, and
    `typecheck/TcSplice.hs`:

       (a) When desugaring a pattern synonym from HsSyn to TH.Dec in
           `deSugar/DsMeta.hs`, we represent its *full* type signature in TH, i.e.:

               ForallT univs reqs (ForallT exis provs ty)
                  (where ty is the AST representation of t1 -> t2 -> ... -> tn -> t)

       (b) When converting pattern synonyms from TH.Dec to HsSyn in
           `hsSyn/Convert.hs`, we convert their TH type signatures back to an
           appropriate Haskell pattern synonym type of the form

             forall univs. reqs => forall exis. provs => t1 -> t2 -> ... -> tn -> t

           where initial empty `univs` type variables or an empty `reqs`
           constraint context are represented *explicitly* as `() =>`.

       (c) When reifying a pattern synonym in `typecheck/TcSplice.hs`, we always
           return its *full* type, i.e.:

               ForallT univs reqs (ForallT exis provs ty)
                  (where ty is the AST representation of t1 -> t2 -> ... -> tn -> t)

    The key point is to always represent a pattern synonym's *full* type
    in cases (a) and (c) to make it clear which of the two forall
    quantifiers and/or constraint contexts are specified, and which are
    not. See GHC's user's guide on pattern synonyms for more information
    about pattern synonym type signatures.

    -}