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 CPP #-}

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

    import HsSyn as Hs
    import HsTypes  ( mkHsForAllTy )
    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 qualified Data.ByteString as BS
    import Control.Monad( unless, liftM, ap )
    #if __GLASGOW_HASKELL__ < 709
    import Control.Applicative (Applicative(..))
    #endif

    import Data.Char ( chr )
    import Data.Word ( Word8 )
    import Data.Maybe( catMaybes )
    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 = return
        (<*>) = ap

    instance Monad CvtM where
      return x       = CvtM $ \loc -> Right (loc,x)
      (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 (ptext (sLit "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 (Clause [] body ds)
            ; returnJustL $ Hs.ValD $ mkFunBind s' [cl'] }

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

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

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

    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', tcdFVs = placeHolderNames
                      , tcdRhs = rhs' } }

    cvtDec (DataD ctxt tc tvs constrs derivs)
      = do  { (ctxt', tc', tvs') <- cvt_tycl_hdr ctxt tc tvs
            ; cons' <- mapM cvtConstr constrs
            ; derivs' <- cvtDerivs derivs
            ; let defn = HsDataDefn { dd_ND = DataType, dd_cType = Nothing
                                    , dd_ctxt = ctxt'
                                    , dd_kindSig = Nothing
                                    , dd_cons = cons', dd_derivs = derivs' }
            ; returnJustL $ TyClD (DataDecl { tcdLName = tc', tcdTyVars = tvs'
                                            , tcdDataDefn = defn
                                            , tcdFVs = placeHolderNames }) }

    cvtDec (NewtypeD ctxt tc tvs constr derivs)
      = do  { (ctxt', tc', tvs') <- cvt_tycl_hdr ctxt tc tvs
            ; con' <- cvtConstr constr
            ; derivs' <- cvtDerivs derivs
            ; let defn = HsDataDefn { dd_ND = NewType, dd_cType = Nothing
                                    , dd_ctxt = ctxt'
                                    , dd_kindSig = Nothing
                                    , dd_cons = [con']
                                    , dd_derivs = derivs' }
            ; returnJustL $ TyClD (DataDecl { tcdLName = tc', tcdTyVars = tvs'
                                        , tcdDataDefn = defn
                                        , 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 (ptext (sLit "a class declaration")) decs
            ; unless (null adts')
                (failWith $ (ptext (sLit "Default data instance declarations are not allowed:"))
                       $$ (Outputable.ppr adts'))
            ; at_defs <- mapM cvt_at_def ats'
            ; returnJustL $ TyClD $
              ClassDecl { tcdCtxt = cxt', tcdLName = tc', tcdTyVars = tvs'
                        , tcdFDs = fds', tcdSigs = 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 ctxt ty decs)
      = do  { let doc = ptext (sLit "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' = L loc $ mkHsForAllTy Implicit [] ctxt' $ L loc ty'
            ; returnJustL $ InstD $ ClsInstD $
              ClsInstDecl inst_ty' binds' sigs' ats' adts' Nothing }

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

    cvtDec (FamilyD flav tc tvs kind)
      = do { (_, tc', tvs') <- cvt_tycl_hdr [] tc tvs
           ; kind' <- cvtMaybeKind kind
           ; returnJustL $ TyClD $ FamDecl $
             FamilyDecl (cvtFamFlavour flav) tc' tvs' kind' }
      where
        cvtFamFlavour TypeFam = OpenTypeFamily
        cvtFamFlavour DataFam = DataFamily

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

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

    cvtDec (NewtypeInstD ctxt tc tys constr derivs)
      = do { (ctxt', tc', typats') <- cvt_tyinst_hdr ctxt tc tys
           ; con' <- cvtConstr constr
           ; derivs' <- cvtDerivs derivs
           ; let defn = HsDataDefn { dd_ND = NewType, dd_cType = Nothing
                                   , dd_ctxt = ctxt'
                                   , dd_kindSig = Nothing
                                   , dd_cons = [con'], dd_derivs = derivs' }
           ; returnJustL $ InstD $ DataFamInstD
               { dfid_inst = DataFamInstDecl { dfid_tycon = tc', dfid_pats = typats'
                                             , dfid_defn = defn
                                             , 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 (ClosedTypeFamilyD tc tyvars mkind eqns)
      | not $ null eqns
      = do { (_, tc', tvs') <- cvt_tycl_hdr [] tc tyvars
           ; mkind' <- cvtMaybeKind mkind
           ; eqns' <- mapM (cvtTySynEqn tc') eqns
           ; returnJustL $ TyClD $ FamDecl $
             FamilyDecl (ClosedTypeFamily eqns') tc' tvs' mkind' }
      | otherwise
      = failWith (ptext (sLit "Illegal empty closed type family"))

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

    cvtDec (TH.StandaloneDerivD cxt ty)
      = do { cxt' <- cvtContext cxt
           ; L loc ty'  <- cvtType ty
           ; let inst_ty' = L loc $ mkHsForAllTy Implicit [] cxt' $ L loc ty'
           ; returnJustL $ DerivD $
             DerivDecl { deriv_type = inst_ty', deriv_overlap_mode = Nothing } }

    cvtDec (TH.DefaultSigD nm typ)
      = do { nm' <- vNameL nm
           ; ty' <- cvtType typ
           ; returnJustL $ Hs.SigD $ GenericSig [nm'] ty' }
    ----------------
    cvtTySynEqn :: Located RdrName -> TySynEqn -> CvtM (LTyFamInstEqn RdrName)
    cvtTySynEqn tc (TySynEqn lhs rhs)
      = do  { lhs' <- mapM cvtType lhs
            ; rhs' <- cvtType rhs
            ; returnL $ TyFamEqn { tfe_tycon = tc
                                 , tfe_pats = mkHsWithBndrs lhs'
                                 , 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
                         , LHsTyVarBndrs 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
                           , HsWithBndrs RdrName [LHsType RdrName])
    cvt_tyinst_hdr cxt tc tys
      = do { cxt' <- cvtContext cxt
           ; tc'  <- tconNameL tc
           ; tys' <- mapM cvtType tys
           ; return (cxt', tc', mkHsWithBndrs tys') }

    -------------------------------------------------------------------
    --              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 [ ptext (sLit "Illegal declaration(s) in") <+> doc <> colon
            , nest 2 (vcat (map Outputable.ppr bads)) ]

    ---------------------------------------------------
    --      Data types
    -- Can't handle GADTs yet
    ---------------------------------------------------

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

    cvtConstr (NormalC c strtys)
      = do  { c'   <- cNameL c
            ; cxt' <- returnL []
            ; tys' <- mapM cvt_arg strtys
            ; returnL $ mkSimpleConDecl c' noExistentials cxt' (PrefixCon tys') }

    cvtConstr (RecC c varstrtys)
      = do  { c'    <- cNameL c
            ; cxt'  <- returnL []
            ; args' <- mapM cvt_id_arg varstrtys
            ; returnL $ mkSimpleConDecl c' noExistentials cxt'
                                       (RecCon (noLoc args')) }

    cvtConstr (InfixC st1 c st2)
      = do  { c' <- cNameL c
            ; cxt' <- returnL []
            ; st1' <- cvt_arg st1
            ; st2' <- cvt_arg st2
            ; returnL $ mkSimpleConDecl c' noExistentials cxt' (InfixCon st1' st2') }

    cvtConstr (ForallC tvs ctxt con)
      = do  { tvs'  <- cvtTvs tvs
            ; L loc ctxt' <- cvtContext ctxt
            ; L _ con' <- cvtConstr con
            ; returnL $ con' { con_qvars = mkHsQTvs (hsQTvBndrs tvs' ++ hsQTvBndrs (con_qvars con'))
                             , con_cxt = L loc (ctxt' ++ (unLoc $ con_cxt con')) } }

    cvt_arg :: (TH.Strict, TH.Type) -> CvtM (LHsType RdrName)
    cvt_arg (NotStrict, ty) = cvtType ty
    cvt_arg (IsStrict,  ty)
      = do { ty' <- cvtType ty
           ; returnL $ HsBangTy (HsSrcBang Nothing Nothing     True) ty' }
    cvt_arg (Unpacked,  ty)
      = do { ty' <- cvtType ty
           ; returnL $ HsBangTy (HsSrcBang Nothing (Just True) True) ty' }

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

    cvtDerivs :: [TH.Name] -> CvtM (Maybe (Located [LHsType RdrName]))
    cvtDerivs [] = return Nothing
    cvtDerivs cs = do { cs' <- mapM cvt_one cs
                      ; return (Just (noLoc cs')) }
            where
              cvt_one c = do { c' <- tconName c
                             ; returnL $ HsTyVar c' }

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

    noExistentials :: [LHsTyVarBndr RdrName]
    noExistentials = []

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

    cvtForD :: Foreign -> CvtM (ForeignDecl RdrName)
    cvtForD (ImportF callconv safety from nm ty)
      | callconv == TH.Prim || callconv == TH.JavaScript
      = mk_imp (CImport (noLoc (cvt_conv callconv)) (noLoc safety') Nothing
                        (CFunction (StaticTarget (mkFastString from) Nothing True))
                        (noLoc from))
      | Just impspec <- parseCImport (noLoc (cvt_conv callconv)) (noLoc safety')
                                     (mkFastString (TH.nameBase nm))
                                     from (noLoc from)
      = mk_imp impspec
      | otherwise
      = failWith $ text (show from) <+> ptext (sLit "is not a valid ccall impent")
      where
        mk_imp impspec
          = do { nm' <- vNameL nm
               ; ty' <- cvtType ty
               ; return (ForeignImport nm' ty' noForeignImportCoercionYet 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 (mkFastString as)
                                                    (cvt_conv callconv)))
                                                    (noLoc as)
            ; return $ ForeignExport nm' ty' noForeignExportCoercionYet 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 ip   = InlinePragma { inl_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 (inline', dflt) = case inline of
                   Just inline1 -> (cvtInline inline1, dfltActivation inline1)
                   Nothing      -> (EmptyInlineSpec,   AlwaysActive)
           ; let ip = InlinePragma { inl_src    = "{-# INLINE"
                                   , inl_inline = inline'
                                   , inl_rule   = Hs.FunLike
                                   , inl_act    = cvtPhases phases dflt
                                   , inl_sat    = Nothing }
           ; returnJustL $ Hs.SigD $ SpecSig nm' [ty'] ip }

    cvtPragmaD (SpecialiseInstP ty)
      = do { ty' <- cvtType ty
           ; returnJustL $ Hs.SigD $ SpecInstSig "{-# SPECIALISE" 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 "{-# RULES" [noLoc $ HsRule (noLoc 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 "{-# ANN" target' exp'
           }

    cvtPragmaD (LineP line file)
      = do { setL (srcLocSpan (mkSrcLoc (fsLit file) line 1))
           ; return Nothing
           }

    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 i
    cvtPhases (BeforePhase i) _    = ActiveBefore 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' $ mkHsWithBndrs 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 :: TH.Clause -> CvtM (Hs.LMatch RdrName (LHsExpr RdrName))
    cvtClause (Clause ps body wheres)
      = do  { ps' <- cvtPats ps
            ; g'  <- cvtGuard body
            ; ds' <- cvtLocalDecs (ptext (sLit "a where clause")) wheres
            ; returnL $ Hs.Match Nothing ps' Nothing (GRHSs g' ds') }

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

    cvtl :: TH.Exp -> CvtM (LHsExpr RdrName)
    cvtl e = wrapL (cvt e)
      where
        cvt (VarE s)        = do { s' <- vName s; return $ HsVar s' }
        cvt (ConE s)        = do { s' <- cName s; return $ HsVar s' }
        cvt (LitE l)
          | overloadedLit l = do { l' <- cvtOverLit l; return $ HsOverLit l' }
          | otherwise       = do { l' <- cvtLit l;     return $ HsLit l' }

        cvt (AppE x y)     = do { x' <- cvtl x; y' <- cvtl y; return $ HsApp x' y' }
        cvt (LamE ps e)    = do { ps' <- cvtPats ps; e' <- cvtl e
                                ; return $ HsLam (mkMatchGroup FromSource [mkSimpleMatch ps' e']) }
        cvt (LamCaseE ms)  = do { ms' <- mapM cvtMatch ms
                                ; return $ HsLamCase placeHolderType
                                                     (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 (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 (ptext (sLit "Multi-way if-expression with no alternatives"))
          | otherwise      = do { alts' <- mapM cvtpair alts
                                ; return $ HsMultiIf placeHolderType alts' }
        cvt (LetE ds e)    = do { ds' <- cvtLocalDecs (ptext (sLit "a let expression")) ds
                                ; e' <- cvtl e; return $ HsLet ds' e' }
        cvt (CaseE e ms)   = do { e' <- cvtl e; ms' <- mapM cvtMatch 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' t' PlaceHolder }
        cvt (RecConE c flds) = do { c' <- cNameL c
                                  ; flds' <- mapM cvtFld flds
                                  ; return $ RecordCon c' noPostTcExpr (HsRecFields flds' Nothing)}
        cvt (RecUpdE e flds) = do { e' <- cvtl e
                                  ; flds' <- mapM cvtFld flds
                                  ; return $ RecordUpd e' (HsRecFields flds' Nothing) [] [] [] }
        cvt (StaticE e)      = fmap HsStatic $ cvtl e

    {- 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 :: (TH.Name, TH.Exp) -> CvtM (LHsRecField RdrName (LHsExpr RdrName))
    cvtFld (v,e)
      = do  { v' <- vNameL v; e' <- cvtl e
            ; return (noLoc $ HsRecField { hsRecFieldId = 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@ and @UInfixP@ 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@ and @mkConOppPatRn@ in
    RnTypes), which expects that the input will be completely left-biased.
    So we left-bias the trees  of @UInfixP@ and @UInfixE@ that we come across.

    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@ and @cvtOpAppP@ are responsible for this
    left-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 (ptext (sLit "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 (stmts'' ++ [last'']) placeHolderType }
      where
        bad_last stmt = vcat [ ptext (sLit "Illegal last statement of") <+> pprAStmtContext do_or_lc <> colon
                             , nest 2 $ Outputable.ppr stmt
                             , ptext (sLit "(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 (ptext (sLit "a let binding")) ds
                                ; returnL $ LetStmt ds' }
    cvtStmt (TH.ParS dss)  = do { dss' <- mapM cvt_one dss; returnL $ ParStmt dss' noSyntaxExpr noSyntaxExpr }
                           where
                             cvt_one ds = do { ds' <- cvtStmts ds; return (ParStmtBlock ds' undefined noSyntaxExpr) }

    cvtMatch :: TH.Match -> CvtM (Hs.LMatch RdrName (LHsExpr RdrName))
    cvtMatch (TH.Match p body decs)
      = do  { p' <- cvtPat p
            ; g' <- cvtGuard body
            ; decs' <- cvtLocalDecs (ptext (sLit "a where clause")) decs
            ; returnL $ Hs.Match Nothing [p'] Nothing (GRHSs g' 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 (show i) 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 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 (show i) i }
    cvtLit (WordPrimL w)   = do { force w; return $ HsWordPrim (show w) 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 (show c) c }
    cvtLit (StringL s)     = do { let { s' = mkFastString s }
                                ; force s'
                                ; return $ HsString s s' }
    cvtLit (StringPrimL s) = do { let { s' = BS.pack s }
                                ; force s'
                                ; return $ HsStringPrim (w8ToString s) s' }
    cvtLit _ = panic "Convert.cvtLit: Unexpected literal"
            -- cvtLit should not be called on IntegerL, RationalL
            -- That precondition is established right here in
            -- Convert.lhs, hence panic

    w8ToString :: [Word8] -> String
    w8ToString ws = map (\w -> chr (fromIntegral w)) ws

    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 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 (ConP s ps)       = do { s' <- cNameL s; ps' <- cvtPats ps
                                ; return $ ConPatIn s' (PrefixCon ps') }
    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; 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' (mkHsWithBndrs 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  { s' <- vNameL s; p' <- cvtPat p
            ; return (noLoc $ HsRecField { hsRecFieldId = s', hsRecFieldArg = p'
                                         , hsRecPun = False}) }

    {- | @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 (LHsTyVarBndrs 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' <- tName nm
           ; returnL $ UserTyVar nm' }
    cvt_tv (TH.KindedTV nm ki)
      = do { nm' <- tName nm
           ; ki' <- cvtKind ki
           ; returnL $ KindedTyVar (noLoc 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

    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 (getRdrName (tupleTyCon BoxedTuple n))) tys'
               UnboxedTupleT n
                 | length tys' == n         -- Saturated
                 -> if n==1 then return (head tys') -- Singleton tuples treated
                                                    -- like nothing (ie just parens)
                            else returnL (HsTupleTy HsUnboxedTuple tys')
                 | otherwise
                 -> mk_apps (HsTyVar (getRdrName (tupleTyCon UnboxedTuple n))) tys'
               ArrowT
                 | [x',y'] <- tys' -> returnL (HsFunTy x' y')
                 | otherwise       -> mk_apps (HsTyVar (getRdrName funTyCon)) tys'
               ListT
                 | [x']    <- tys' -> returnL (HsListTy x')
                 | otherwise       -> mk_apps (HsTyVar (getRdrName listTyCon)) tys'
               VarT nm -> do { nm' <- tName nm;    mk_apps (HsTyVar nm') tys' }
               ConT nm -> do { nm' <- tconName nm; mk_apps (HsTyVar nm') tys' }

               ForallT tvs cxt ty
                 | null tys'
                 -> do { tvs' <- cvtTvs tvs
                       ; cxt' <- cvtContext cxt
                       ; ty'  <- cvtType ty
                       ; returnL $ mkExplicitHsForAllTy (hsQTvBndrs tvs') cxt' ty'
                       }

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

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

               PromotedT nm -> do { nm' <- cName nm; mk_apps (HsTyVar 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 placeHolderKind [])

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

               StarT
                 -> returnL (HsTyVar (getRdrName liftedTypeKindTyCon))

               ConstraintT
                 -> returnL (HsTyVar (getRdrName constraintKindTyCon))

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

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

    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
                                  ; mk_apps (HsAppTy head_ty' ty) tys }

    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 (NumTyLit i) = HsNumTy (show i) i
    cvtTyLit (StrTyLit s) = HsStrTy s        (fsLit s)

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

    cvtMaybeKind :: Maybe TH.Kind -> CvtM (Maybe (LHsKind RdrName))
    cvtMaybeKind Nothing = return Nothing
    cvtMaybeKind (Just ki) = do { ki' <- cvtKind ki
                                ; return (Just ki') }

    -----------------------------------------------------------
    cvtFixity :: TH.Fixity -> Hs.Fixity
    cvtFixity (TH.Fixity prec dir) = Hs.Fixity 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 }

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

    -- variable names
    vNameL, cNameL, vcNameL, 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
    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
      = ptext (sLit "Illegal") <+> pprNameSpace ctxt_ns
            <+> ptext (sLit "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 -> PackageKey
    mk_pkg pkg = stringToPackageKey (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.
    -}