% % (c) The University of Glasgow 2006 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998 % This module converts Template Haskell syntax into HsSyn \begin{code}

    module Convert( convertToHsExpr, convertToPat, convertToHsDecls,
                    convertToHsType, convertToHsPred,
                    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 Coercion
    import TysWiredIn
    import BasicTypes as Hs
    import ForeignCall
    import Unique
    import MonadUtils
    import ErrUtils
    import Bag
    import Util
    import FastString
    import Outputable

    import Control.Monad( unless )

    import Language.Haskell.TH as TH hiding (sigP)
    import Language.Haskell.TH.Syntax as TH

    import GHC.Exts

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

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

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

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

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

    convertToHsPred :: SrcSpan -> TH.Pred -> Either Message (LHsPred RdrName)
    convertToHsPred loc t
      = initCvt loc $ wrapMsg "type" t $ cvtPred t

    -------------------------------------------------------------------
    newtype CvtM a = CvtM { unCvtM :: SrcSpan -> Either Message 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 Monad CvtM where
      return x       = CvtM $ \_   -> Right x
      (CvtM m) >>= k = CvtM $ \loc -> case m loc of
    				    Left err -> Left err
    				    Right v  -> unCvtM (k v) loc

    initCvt :: SrcSpan -> CvtM a -> Either Message a
    initCvt loc (CvtM m) = m loc

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

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

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

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

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

    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
    	; returnL $ Hs.ValD $ mkFunBind nm' cls' }

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

    cvtDec (PragmaD prag)
      = do { prag' <- cvtPragmaD prag
           ; returnL $ Hs.SigD prag' }

    cvtDec (TySynD tc tvs rhs)
      = do	{ (_, tc', tvs') <- cvt_tycl_hdr [] tc tvs
    	; rhs' <- cvtType rhs
    	; returnL $ TyClD (TySynonym tc' tvs' Nothing 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
    	; returnL $ TyClD (TyData { tcdND = DataType, tcdLName = tc', tcdCtxt = ctxt'
                                      , tcdTyVars = tvs', tcdTyPats = Nothing, tcdKindSig = Nothing
                                      , tcdCons = cons', tcdDerivs = derivs' }) }

    cvtDec (NewtypeD ctxt tc tvs constr derivs)
      = do	{ (ctxt', tc', tvs') <- cvt_tycl_hdr ctxt tc tvs
    	; con' <- cvtConstr constr
    	; derivs' <- cvtDerivs derivs
    	; returnL $ TyClD (TyData { tcdND = NewType, tcdLName = tc', tcdCtxt = ctxt'
    	  	    	  	  , tcdTyVars = tvs', tcdTyPats = Nothing, tcdKindSig = Nothing
                                      , tcdCons = [con'], tcdDerivs = derivs'}) }

    cvtDec (ClassD ctxt cl tvs fds decs)
      = do	{ (cxt', tc', tvs') <- cvt_tycl_hdr ctxt cl tvs
    	; fds'  <- mapM cvt_fundep fds
            ; (binds', sigs', ats') <- cvt_ci_decs (ptext (sLit "a class declaration")) decs
    	; returnL $
                TyClD $ ClassDecl { tcdCtxt = cxt', tcdLName = tc', tcdTyVars = tvs'
    	    	              , tcdFDs = fds', tcdSigs = sigs', tcdMeths = binds'
    			      , tcdATs = ats', tcdDocs = [] }
                                            -- no docs in TH ^^
    	}

    cvtDec (InstanceD ctxt ty decs)
      = do 	{ (binds', sigs', ats') <- cvt_ci_decs (ptext (sLit "an instance declaration")) decs
    	; ctxt' <- cvtContext ctxt
    	; L loc pred' <- cvtPredTy ty
    	; let inst_ty' = L loc $ mkImplicitHsForAllTy ctxt' $ L loc $ HsPredTy pred'
    	; returnL $ InstD (InstDecl inst_ty' binds' sigs' ats') }

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

    cvtDec (FamilyD flav tc tvs kind)
      = do { (_, tc', tvs') <- cvt_tycl_hdr [] tc tvs
           ; let kind' = fmap cvtKind kind
           ; returnL $ TyClD (TyFamily (cvtFamFlavour flav) tc' tvs' kind') }
      where
        cvtFamFlavour TypeFam = TypeFamily
        cvtFamFlavour DataFam = DataFamily

    cvtDec (DataInstD ctxt tc tys constrs derivs)
      = do { (ctxt', tc', tvs', typats') <- cvt_tyinst_hdr ctxt tc tys
           ; cons' <- mapM cvtConstr constrs
           ; derivs' <- cvtDerivs derivs
           ; returnL $ TyClD (TyData { tcdND = DataType, tcdLName = tc', tcdCtxt = ctxt'
                                      , tcdTyVars = tvs', tcdTyPats = typats', tcdKindSig = Nothing
                                      , tcdCons = cons', tcdDerivs = derivs' }) }

    cvtDec (NewtypeInstD ctxt tc tys constr derivs)
      = do { (ctxt', tc', tvs', typats') <- cvt_tyinst_hdr ctxt tc tys
           ; con' <- cvtConstr constr
           ; derivs' <- cvtDerivs derivs
           ; returnL $ TyClD (TyData { tcdND = NewType, tcdLName = tc', tcdCtxt = ctxt'
                                      , tcdTyVars = tvs', tcdTyPats = typats', tcdKindSig = Nothing
                                      , tcdCons = [con'], tcdDerivs = derivs' })
           }

    cvtDec (TySynInstD tc tys rhs)
      = do	{ (_, tc', tvs', tys') <- cvt_tyinst_hdr [] tc tys
    	; rhs' <- cvtType rhs
    	; returnL $ TyClD (TySynonym tc' tvs' tys' rhs') }

    ----------------
    cvt_ci_decs :: Message -> [TH.Dec]
                -> CvtM (LHsBinds RdrName,
                         [LSig RdrName],
                         [LTyClDecl RdrName])
    -- Convert the declarations inside a class or instance decl
    -- ie signatures, bindings, and associated types
    cvt_ci_decs doc decs
      = do  { decs' <- mapM cvtDec decs
            ; let (ats', bind_sig_decs') = partitionWith is_tycl decs'
    	; let (sigs', prob_binds') = partitionWith is_sig bind_sig_decs'
    	; let (binds', bads) = partitionWith is_bind prob_binds'
    	; unless (null bads) (failWith (mkBadDecMsg doc bads))
            ; return (listToBag binds', sigs', ats') }

    ----------------
    cvt_tycl_hdr :: TH.Cxt -> TH.Name -> [TH.TyVarBndr]
                 -> CvtM ( LHsContext RdrName
                         , Located RdrName
                         , [LHsTyVarBndr 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
                           , [LHsTyVarBndr RdrName]
                           , Maybe [LHsType RdrName])
    cvt_tyinst_hdr cxt tc tys
      = do { cxt' <- cvtContext cxt
           ; tc'  <- tconNameL tc
           ; tvs  <- concatMapM collect tys
           ; tvs' <- cvtTvs tvs
           ; tys' <- mapM cvtType tys
           ; return (cxt', tc', tvs', Just tys')
           }
      where
        collect (ForallT _ _ _)
          = failWith $ text "Forall type not allowed as type parameter"
        collect (VarT tv)    = return [PlainTV tv]
        collect (ConT _)     = return []
        collect (TupleT _)   = return []
        collect ArrowT       = return []
        collect ListT        = return []
        collect (AppT t1 t2)
          = do { tvs1 <- collect t1
               ; tvs2 <- collect t2
               ; return $ tvs1 ++ tvs2
               }
        collect (SigT (VarT tv) ki) = return [KindedTV tv ki]
        collect (SigT ty _)         = collect ty

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

    is_tycl :: LHsDecl RdrName -> Either (LTyClDecl RdrName) (LHsDecl RdrName)
    is_tycl (L loc (Hs.TyClD tcd)) = Left (L loc tcd)
    is_tycl 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 :: Message -> [LHsDecl RdrName] -> Message
    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 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 = tvs' ++ con_qvars con'
                             , con_cxt = L loc (ctxt' ++ (unLoc $ con_cxt con')) } }

    cvt_arg :: (TH.Strict, TH.Type) -> CvtM (LHsType RdrName)
    cvt_arg (IsStrict, ty)  = do { ty' <- cvtType ty; returnL $ HsBangTy HsStrict ty' }
    cvt_arg (NotStrict, ty) = cvtType ty

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

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

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

    noExistentials :: [LHsTyVarBndr RdrName]
    noExistentials = []

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

    cvtForD :: Foreign -> CvtM (ForeignDecl RdrName)
    cvtForD (ImportF callconv safety from nm ty)
      | Just impspec <- parseCImport (cvt_conv callconv) safety'
                                     (mkFastString (TH.nameBase nm)) from
      = do { nm' <- vNameL nm
           ; ty' <- cvtType ty
           ; return (ForeignImport nm' ty' impspec)
           }
      | otherwise
      = failWith $ text (show from) <+> ptext (sLit "is not a valid ccall impent")
      where
        safety' = case safety of
                         Unsafe     -> PlayRisky
                         Safe       -> PlaySafe False
                         Threadsafe -> PlaySafe True

    cvtForD (ExportF callconv as nm ty)
      = do	{ nm' <- vNameL nm
    	; ty' <- cvtType ty
    	; let e = CExport (CExportStatic (mkFastString as) (cvt_conv callconv))
     	; return $ ForeignExport nm' ty' e }

    cvt_conv :: TH.Callconv -> CCallConv
    cvt_conv TH.CCall   = CCallConv
    cvt_conv TH.StdCall = StdCallConv

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

    cvtPragmaD :: Pragma -> CvtM (Sig RdrName)
    cvtPragmaD (InlineP nm ispec)
      = do { nm'    <- vNameL nm
           ; return $ InlineSig nm' (cvtInlineSpec (Just ispec)) }

    cvtPragmaD (SpecialiseP nm ty opt_ispec)
      = do { nm' <- vNameL nm
           ; ty' <- cvtType ty
           ; return $ SpecSig nm' ty' (cvtInlineSpec opt_ispec) }

    cvtInlineSpec :: Maybe TH.InlineSpec -> Hs.InlinePragma
    cvtInlineSpec Nothing
      = defaultInlinePragma
    cvtInlineSpec (Just (TH.InlineSpec inline conlike opt_activation))
      = InlinePragma { inl_act = opt_activation', inl_rule = matchinfo
                     , inl_inline = inl_spec, inl_sat = Nothing }
      where
        matchinfo       = cvtRuleMatchInfo conlike
        opt_activation' = cvtActivation opt_activation

        cvtRuleMatchInfo False = FunLike
        cvtRuleMatchInfo True  = ConLike

        inl_spec | inline    = Inline
                 | otherwise = NoInline
     	     -- Currently we have no way to say Inlinable

        cvtActivation Nothing | inline      = AlwaysActive
                              | otherwise   = NeverActive
        cvtActivation (Just (False, phase)) = ActiveBefore phase
        cvtActivation (Just (True , phase)) = ActiveAfter  phase

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

    cvtLocalDecs :: Message -> [TH.Dec] -> CvtM (HsLocalBinds RdrName)
    cvtLocalDecs doc ds
      | null ds
      = return EmptyLocalBinds
      | otherwise
      = do { ds' <- mapM cvtDec 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)
    cvtClause (Clause ps body wheres)
      = do	{ ps' <- cvtPats ps
    	; g'  <- cvtGuard body
    	; ds' <- cvtLocalDecs (ptext (sLit "a where clause")) wheres
    	; returnL $ Hs.Match 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 [mkSimpleMatch ps' e']) }
        cvt (TupE [e])     = cvt e	-- Singleton tuples treated like nothing (just parens)
        cvt (TupE es)      = do { es' <- mapM cvtl es; return $ ExplicitTuple (map Present es') Boxed }
        cvt (CondE x y z)  = do { x' <- cvtl x; y' <- cvtl y; z' <- cvtl z;
    			    ; return $ HsIf (Just noSyntaxExpr) x' y' z' }
        cvt (LetE ds e)    = do { ds' <- cvtLocalDecs (ptext (sLit "a let expression")) ds
                                ; e' <- cvtl e; return $ HsLet ds' e' }
        cvt (CaseE e ms)
           | null ms       = failWith (ptext (sLit "Case expression with no alternatives"))
           | otherwise     = do { e' <- cvtl e; ms' <- mapM cvtMatch ms
    			    ; return $ HsCase e' (mkMatchGroup ms') }
        cvt (DoE ss)       = cvtHsDo DoExpr ss
        cvt (CompE ss)     = cvtHsDo ListComp ss
        cvt (ArithSeqE dd) = do { dd' <- cvtDD dd; return $ ArithSeq noPostTcExpr 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 void xs' }
        cvt (InfixE (Just x) s (Just y)) = do { x' <- cvtl x; s' <- cvtl s; y' <- cvtl y
    					  ; e' <- returnL $ OpApp x' s' undefined y'
    					  ; return $ HsPar e' }
        cvt (InfixE Nothing  s (Just y)) = do { s' <- cvtl s; y' <- cvtl y
    					  ; sec <- returnL $ SectionR s' y'
    					  ; return $ HsPar sec }
        cvt (InfixE (Just x) s Nothing ) = do { x' <- cvtl x; s' <- cvtl s
    					  ; sec <- returnL $ SectionL x' s'
    					  ; return $ HsPar sec }
        cvt (InfixE Nothing  s Nothing ) = cvt s	-- Can I indicate this is an infix thing?

        cvt (SigE e t)	 = do { e' <- cvtl e; t' <- cvtType t
    			      ; return $ ExprWithTySig e' t' }
        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) [] [] [] }

    cvtFld :: (TH.Name, TH.Exp) -> CvtM (HsRecField RdrName (LHsExpr RdrName))
    cvtFld (v,e)
      = do	{ v' <- vNameL v; e' <- cvtl e
    	; return (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' }

    -------------------------------------
    -- 	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
    	; body <- case last stmts' of
    		    L _ (ExprStmt body _ _) -> return body
                        stmt' -> failWith (bad_last stmt')
    	; return $ HsDo do_or_lc (init stmts') body void }
      where
        bad_last stmt = vcat [ ptext (sLit "Illegal last statement of") <+> pprStmtContext do_or_lc <> colon
                             , nest 2 $ Outputable.ppr stmt
    			 , ptext (sLit "(It should be an expression.)") ]

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

    cvtStmt :: TH.Stmt -> CvtM (Hs.LStmt RdrName)
    cvtStmt (NoBindS e)    = do { e' <- cvtl e; returnL $ mkExprStmt 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' }
    		       where
    			 cvt_one ds = do { ds' <- cvtStmts ds; return (ds', undefined) }

    cvtMatch :: TH.Match -> CvtM (Hs.LMatch 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 [p'] Nothing (GRHSs g' decs') }

    cvtGuard :: TH.Body -> CvtM [LGRHS 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)
    cvtpair (NormalG ge,rhs) = do { ge' <- cvtl ge; rhs' <- cvtl rhs
    			      ; g' <- returnL $ mkExprStmt 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 i placeHolderType}
    cvtOverLit (RationalL r)
      = do { force r; return $ mkHsFractional r placeHolderType}
    cvtOverLit (StringL s)
      = do { let { s' = mkFastString s }
           ; force s'
           ; return $ mkHsIsString 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 i }
    cvtLit (WordPrimL w)   = do { force w; return $ HsWordPrim w }
    cvtLit (FloatPrimL f)  = do { force f; return $ HsFloatPrim f }
    cvtLit (DoublePrimL f) = do { force f; return $ HsDoublePrim f }
    cvtLit (CharL c)       = do { force c; return $ HsChar c }
    cvtLit (StringL s)     = do { let { s' = mkFastString s }
           		       	    ; force s'
           		       	    ; return $ HsString s' }
    cvtLit (StringPrimL s) = do { let { s' = mkFastString s }
           			    ; force s'
           			    ; return $ HsStringPrim 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

    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 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])       = cvtp p
    cvtp (TupP ps)        = do { ps' <- cvtPats ps; return $ TuplePat ps' Boxed void }
    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
    			   ; return $ ConPatIn s' (InfixCon p1' p2') }
    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 void
    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' void }
    cvtp (SigP p t)       = do { p' <- cvtPat p; t' <- cvtType t; return $ SigPatIn p' t' }
    cvtp (ViewP e p)      = do { e' <- cvtl e; p' <- cvtPat p; return $ ViewPat e' p' void }

    cvtPatFld :: (TH.Name, TH.Pat) -> CvtM (HsRecField RdrName (LPat RdrName))
    cvtPatFld (s,p)
      = do	{ s' <- vNameL s; p' <- cvtPat p
    	; return (HsRecField { hsRecFieldId = s', hsRecFieldArg = p', hsRecPun = False}) }

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

    cvtTvs :: [TH.TyVarBndr] -> CvtM [LHsTyVarBndr RdrName]
    cvtTvs tvs = mapM cvt_tv tvs

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

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

    cvtPred :: TH.Pred -> CvtM (LHsPred RdrName)
    cvtPred (TH.ClassP cla tys)
      = do { cla' <- if isVarName cla then tName cla else tconName cla
           ; tys' <- mapM cvtType tys
           ; returnL $ HsClassP cla' tys'
           }
    cvtPred (TH.EqualP ty1 ty2)
      = do { ty1' <- cvtType ty1
           ; ty2' <- cvtType ty2
           ; returnL $ HsEqualP ty1' ty2'
           }

    cvtPredTy :: TH.Type -> CvtM (LHsPred RdrName)
    cvtPredTy ty
      = do	{ (head, tys') <- split_ty_app ty
    	; case head of
    	    ConT tc -> do { tc' <- tconName tc; returnL $ HsClassP tc' tys' }
    	    VarT tv -> do { tv' <- tName tv;    returnL $ HsClassP tv' tys' }
    	    _       -> failWith (ptext (sLit "Malformed predicate") <+>
                           text (TH.pprint ty)) }

    cvtType :: TH.Type -> CvtM (LHsType RdrName)
    cvtType 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 Boxed tys')
                 | n == 1
                 -> failWith (ptext (sLit "Illegal 1-tuple type constructor"))
                 | otherwise
                 -> mk_apps (HsTyVar (getRdrName (tupleTyCon Boxed 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 tvs' cxt' ty'
                       }

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

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

    cvtKind :: TH.Kind -> Type.Kind
    cvtKind StarK          = liftedTypeKind
    cvtKind (ArrowK k1 k2) = mkArrowKind (cvtKind k1) (cvtKind k2)

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

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

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

    void :: Type.Type
    void = placeHolderType

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

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

    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

    -- 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 		        = force rdr_name >> return rdr_name
      where
        occ_str = TH.occString occ
        rdr_name = thRdrName ctxt_ns occ_str flavour

    okOcc :: OccName.NameSpace -> String -> Bool
    okOcc _  []      = False
    okOcc ns str@(c:_)
      | OccName.isVarNameSpace ns = startsVarId c || startsVarSym c
      | otherwise 	 	      = startsConId c || startsConSym c || 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 :: OccName.NameSpace -> String -> TH.NameFlavour -> RdrName
    -- This turns a Name into a RdrName
    -- 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
    --
    -- 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 _       occ (TH.NameG th_ns pkg mod) = thOrigRdrName occ th_ns pkg mod
    thRdrName ctxt_ns occ (TH.NameL uniq)      = nameRdrName $! (((Name.mkInternalName $! (mk_uniq uniq)) $! (mk_occ ctxt_ns occ)) noSrcSpan)
    thRdrName ctxt_ns occ (TH.NameQ mod)       = (mkRdrQual  $! (mk_mod mod)) $! (mk_occ ctxt_ns occ)
    thRdrName ctxt_ns occ (TH.NameU uniq)      = mkRdrUnqual $! (mk_uniq_occ ctxt_ns occ uniq)
    thRdrName ctxt_ns occ TH.NameS
      | Just name <- isBuiltInOcc ctxt_ns occ  = nameRdrName $! name
      | otherwise			           = mkRdrUnqual $! (mk_occ ctxt_ns 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 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

    isBuiltInOcc :: OccName.NameSpace -> String -> Maybe Name.Name
    -- Built in syntax isn't "in scope" so an Unqual RdrName won't do
    -- We must generate an Exact name, just as the parser does
    isBuiltInOcc ctxt_ns occ
      = case occ of
    	":" 		 -> Just (Name.getName consDataCon)
    	"[]"		 -> Just (Name.getName nilDataCon)
    	"()"		 -> Just (tup_name 0)
    	'(' : ',' : rest -> go_tuple 2 rest
    	_                -> Nothing
      where
        go_tuple n ")" 	    = Just (tup_name n)
        go_tuple n (',' : rest) = go_tuple (n+1) rest
        go_tuple _ _            = Nothing

        tup_name n
    	| OccName.isTcClsNameSpace ctxt_ns = Name.getName (tupleTyCon Boxed n)
    	| otherwise 		           = Name.getName (tupleCon Boxed n)

    mk_uniq_occ :: OccName.NameSpace -> String -> Int# -> OccName.OccName
    mk_uniq_occ ns occ uniq
      = OccName.mkOccName ns (occ ++ '[' : shows (mk_uniq uniq) "]")
            -- See Note [Unique OccNames from Template Haskell]

    -- The packing and unpacking is rather turgid :-(
    mk_occ :: OccName.NameSpace -> String -> OccName.OccName
    mk_occ ns occ = OccName.mkOccNameFS ns (mkFastString 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 -> PackageId
    mk_pkg pkg = stringToPackageId (TH.pkgString pkg)

    mk_uniq :: Int# -> Unique
    mk_uniq u = mkUniqueGrimily (I# u)

\end{code} Note [Unique OccNames from Template Haskell] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ The idea here is to make a name that a) the user could not possibly write (it has a "[" and letters or digits from the unique) b) cannot clash with another NameU Previously I generated an Exact RdrName with mkInternalName. This works fine for local binders, but does not work at all for top-level binders, which must have External Names, since they are rapidly baked into data constructors and the like. Baling out and generating an unqualified RdrName here is the simple solution See also Note [Suppressing uniques in OccNames] in OccName, which suppresses the unique when opt_SuppressUniques is on.