parser/RdrHsSyn.hs

    --
    --  (c) The University of Glasgow 2002-2006
    --

    -- Functions over HsSyn specialised to RdrName.

    {-# LANGUAGE CPP #-}
    {-# LANGUAGE FlexibleContexts #-}

    module RdrHsSyn (
            mkHsOpApp,
            mkHsIntegral, mkHsFractional, mkHsIsString,
            mkHsDo, mkSpliceDecl,
            mkRoleAnnotDecl,
            mkClassDecl,
            mkTyData, mkDataFamInst,
            mkTySynonym, mkTyFamInstEqn,
            mkTyFamInst,
            mkFamDecl, mkLHsSigType,
            splitCon, mkInlinePragma,
            mkPatSynMatchGroup,
            mkRecConstrOrUpdate, -- HsExp -> [HsFieldUpdate] -> P HsExp
            mkTyClD, mkInstD,
            mkRdrRecordCon, mkRdrRecordUpd,
            setRdrNameSpace,

            cvBindGroup,
            cvBindsAndSigs,
            cvTopDecls,
            placeHolderPunRhs,

            -- Stuff to do with Foreign declarations
            mkImport,
            parseCImport,
            mkExport,
            mkExtName,           -- RdrName -> CLabelString
            mkGadtDecl,          -- [Located RdrName] -> LHsType RdrName -> ConDecl RdrName
            mkConDeclH98,
            mkATDefault,

            -- Bunch of functions in the parser monad for
            -- checking and constructing values
            checkPrecP,           -- Int -> P Int
            checkContext,         -- HsType -> P HsContext
            checkPattern,         -- HsExp -> P HsPat
            bang_RDR,
            checkPatterns,        -- SrcLoc -> [HsExp] -> P [HsPat]
            checkMonadComp,       -- P (HsStmtContext RdrName)
            checkCommand,         -- LHsExpr RdrName -> P (LHsCmd RdrName)
            checkValDef,          -- (SrcLoc, HsExp, HsRhs, [HsDecl]) -> P HsDecl
            checkValSigLhs,
            checkDoAndIfThenElse,
            checkRecordSyntax,
            parseErrorSDoc,
            splitTilde, splitTildeApps,

            -- Help with processing exports
            ImpExpSubSpec(..),
            mkModuleImpExp,
            mkTypeImpExp,
            mkImpExpSubSpec,
            checkImportSpec

        ) where

    import HsSyn            -- Lots of it
    import Class            ( FunDep )
    import TyCon            ( TyCon, isTupleTyCon, tyConSingleDataCon_maybe )
    import DataCon          ( DataCon, dataConTyCon )
    import ConLike          ( ConLike(..) )
    import CoAxiom          ( Role, fsFromRole )
    import RdrName
    import Name
    import BasicTypes
    import TcEvidence       ( idHsWrapper )
    import Lexer
    import Type             ( TyThing(..) )
    import TysWiredIn       ( cTupleTyConName, tupleTyCon, tupleDataCon,
                              nilDataConName, nilDataConKey,
                              listTyConName, listTyConKey,
                              starKindTyConName, unicodeStarKindTyConName )
    import ForeignCall
    import PrelNames        ( forall_tv_RDR, eqTyCon_RDR, allNameStrings )
    import DynFlags
    import SrcLoc
    import Unique           ( hasKey )
    import OrdList          ( OrdList, fromOL )
    import Bag              ( emptyBag, consBag )
    import Outputable
    import FastString
    import Maybes
    import Util
    import ApiAnnotation
    import Data.List
    import qualified GHC.LanguageExtensions as LangExt
    import MonadUtils

    #if __GLASGOW_HASKELL__ < 709
    import Control.Applicative ((<$>))
    #endif
    import Control.Monad

    import Text.ParserCombinators.ReadP as ReadP
    import Data.Char

    import Data.Data       ( dataTypeOf, fromConstr, dataTypeConstrs )

    #include "HsVersions.h"

    {- **********************************************************************

      Construction functions for Rdr stuff

      ********************************************************************* -}

    -- | mkClassDecl builds a RdrClassDecl, filling in the names for tycon and
    -- datacon by deriving them from the name of the class.  We fill in the names
    -- for the tycon and datacon corresponding to the class, by deriving them
    -- from the name of the class itself.  This saves recording the names in the
    -- interface file (which would be equally good).

    -- Similarly for mkConDecl, mkClassOpSig and default-method names.

    --         *** See "THE NAMING STORY" in HsDecls ****

    mkTyClD :: LTyClDecl n -> LHsDecl n
    mkTyClD (L loc d) = L loc (TyClD d)

    mkInstD :: LInstDecl n -> LHsDecl n
    mkInstD (L loc d) = L loc (InstD d)

    mkClassDecl :: SrcSpan
                -> Located (Maybe (LHsContext RdrName), LHsType RdrName)
                -> Located (a,[Located (FunDep (Located RdrName))])
                -> OrdList (LHsDecl RdrName)
                -> P (LTyClDecl RdrName)

    mkClassDecl loc (L _ (mcxt, tycl_hdr)) fds where_cls
      = do { (binds, sigs, ats, at_insts, _, docs) <- cvBindsAndSigs where_cls
           ; let cxt = fromMaybe (noLoc []) mcxt
           ; (cls, tparams,ann) <- checkTyClHdr True tycl_hdr
           ; mapM_ (\a -> a loc) ann -- Add any API Annotations to the top SrcSpan
           ; tyvars <- checkTyVarsP (text "class") whereDots cls tparams
           ; at_defs <- mapM (eitherToP . mkATDefault) at_insts
           ; return (L loc (ClassDecl { tcdCtxt = cxt, tcdLName = cls, tcdTyVars = tyvars
                                      , tcdFDs = snd (unLoc fds)
                                      , tcdSigs = mkClassOpSigs sigs
                                      , tcdMeths = binds
                                      , tcdATs = ats, tcdATDefs = at_defs, tcdDocs  = docs
                                      , tcdFVs = placeHolderNames })) }

    mkATDefault :: LTyFamInstDecl RdrName
                -> Either (SrcSpan, SDoc) (LTyFamDefltEqn RdrName)
    -- Take a type-family instance declaration and turn it into
    -- a type-family default equation for a class declaration
    -- We parse things as the former and use this function to convert to the latter
    --
    -- We use the Either monad because this also called
    -- from Convert.hs
    mkATDefault (L loc (TyFamInstDecl { tfid_eqn = L _ e }))
          | TyFamEqn { tfe_tycon = tc, tfe_pats = pats, tfe_rhs = rhs } <- e
          = do { tvs <- checkTyVars (text "default") equalsDots tc (hsib_body pats)
               ; return (L loc (TyFamEqn { tfe_tycon = tc
                                         , tfe_pats = tvs
                                         , tfe_rhs = rhs })) }

    mkTyData :: SrcSpan
             -> NewOrData
             -> Maybe (Located CType)
             -> Located (Maybe (LHsContext RdrName), LHsType RdrName)
             -> Maybe (LHsKind RdrName)
             -> [LConDecl RdrName]
             -> HsDeriving RdrName
             -> P (LTyClDecl RdrName)
    mkTyData loc new_or_data cType (L _ (mcxt, tycl_hdr)) ksig data_cons maybe_deriv
      = do { (tc, tparams,ann) <- checkTyClHdr False tycl_hdr
           ; mapM_ (\a -> a loc) ann -- Add any API Annotations to the top SrcSpan
           ; tyvars <- checkTyVarsP (ppr new_or_data) equalsDots tc tparams
           ; defn <- mkDataDefn new_or_data cType mcxt ksig data_cons maybe_deriv
           ; return (L loc (DataDecl { tcdLName = tc, tcdTyVars = tyvars,
                                       tcdDataDefn = defn,
                                       tcdDataCusk = PlaceHolder,
                                       tcdFVs = placeHolderNames })) }

    mkDataDefn :: NewOrData
               -> Maybe (Located CType)
               -> Maybe (LHsContext RdrName)
               -> Maybe (LHsKind RdrName)
               -> [LConDecl RdrName]
               -> HsDeriving RdrName
               -> P (HsDataDefn RdrName)
    mkDataDefn new_or_data cType mcxt ksig data_cons maybe_deriv
      = do { checkDatatypeContext mcxt
           ; let cxt = fromMaybe (noLoc []) mcxt
           ; return (HsDataDefn { dd_ND = new_or_data, dd_cType = cType
                                , dd_ctxt = cxt
                                , dd_cons = data_cons
                                , dd_kindSig = ksig
                                , dd_derivs = maybe_deriv }) }

    mkTySynonym :: SrcSpan
                -> LHsType RdrName  -- LHS
                -> LHsType RdrName  -- RHS
                -> P (LTyClDecl RdrName)
    mkTySynonym loc lhs rhs
      = do { (tc, tparams,ann) <- checkTyClHdr False lhs
           ; mapM_ (\a -> a loc) ann -- Add any API Annotations to the top SrcSpan
           ; tyvars <- checkTyVarsP (text "type") equalsDots tc tparams
           ; return (L loc (SynDecl { tcdLName = tc, tcdTyVars = tyvars
                                    , tcdRhs = rhs, tcdFVs = placeHolderNames })) }

    mkTyFamInstEqn :: LHsType RdrName
                   -> LHsType RdrName
                   -> P (TyFamInstEqn RdrName,[AddAnn])
    mkTyFamInstEqn lhs rhs
      = do { (tc, tparams, ann) <- checkTyClHdr False lhs
           ; return (TyFamEqn { tfe_tycon = tc
                              , tfe_pats  = mkHsImplicitBndrs tparams
                              , tfe_rhs   = rhs },
                     ann) }

    mkDataFamInst :: SrcSpan
                  -> NewOrData
                  -> Maybe (Located CType)
                  -> Located (Maybe (LHsContext RdrName), LHsType RdrName)
                  -> Maybe (LHsKind RdrName)
                  -> [LConDecl RdrName]
                  -> HsDeriving RdrName
                  -> P (LInstDecl RdrName)
    mkDataFamInst loc new_or_data cType (L _ (mcxt, tycl_hdr)) ksig data_cons maybe_deriv
      = do { (tc, tparams,ann) <- checkTyClHdr False tycl_hdr
           ; mapM_ (\a -> a loc) ann -- Add any API Annotations to the top SrcSpan
           ; defn <- mkDataDefn new_or_data cType mcxt ksig data_cons maybe_deriv
           ; return (L loc (DataFamInstD (
                      DataFamInstDecl { dfid_tycon = tc
                                      , dfid_pats = mkHsImplicitBndrs tparams
                                      , dfid_defn = defn, dfid_fvs = placeHolderNames }))) }

    mkTyFamInst :: SrcSpan
                -> LTyFamInstEqn RdrName
                -> P (LInstDecl RdrName)
    mkTyFamInst loc eqn
      = return (L loc (TyFamInstD (TyFamInstDecl { tfid_eqn  = eqn
                                                 , tfid_fvs  = placeHolderNames })))

    mkFamDecl :: SrcSpan
              -> FamilyInfo RdrName
              -> LHsType RdrName                   -- LHS
              -> Located (FamilyResultSig RdrName) -- Optional result signature
              -> Maybe (LInjectivityAnn RdrName)   -- Injectivity annotation
              -> P (LTyClDecl RdrName)
    mkFamDecl loc info lhs ksig injAnn
      = do { (tc, tparams, ann) <- checkTyClHdr False lhs
           ; mapM_ (\a -> a loc) ann -- Add any API Annotations to the top SrcSpan
           ; tyvars <- checkTyVarsP (ppr info) equals_or_where tc tparams
           ; return (L loc (FamDecl (FamilyDecl{ fdInfo      = info, fdLName = tc
                                               , fdTyVars    = tyvars
                                               , fdResultSig = ksig
                                               , fdInjectivityAnn = injAnn }))) }
      where
        equals_or_where = case info of
                            DataFamily          -> empty
                            OpenTypeFamily      -> empty
                            ClosedTypeFamily {} -> whereDots

    mkSpliceDecl :: LHsExpr RdrName -> HsDecl RdrName
    -- If the user wrote
    --      [pads| ... ]   then return a QuasiQuoteD
    --      $(e)           then return a SpliceD
    -- but if she wrote, say,
    --      f x            then behave as if she'd written $(f x)
    --                     ie a SpliceD
    --
    -- Typed splices are not allowed at the top level, thus we do not represent them
    -- as spliced declaration.  See #10945
    mkSpliceDecl lexpr@(L loc expr)
      | HsSpliceE splice@(HsUntypedSplice {}) <- expr
      = SpliceD (SpliceDecl (L loc splice) ExplicitSplice)

      | HsSpliceE splice@(HsQuasiQuote {}) <- expr
      = SpliceD (SpliceDecl (L loc splice) ExplicitSplice)

      | otherwise
      = SpliceD (SpliceDecl (L loc (mkUntypedSplice lexpr)) ImplicitSplice)

    mkRoleAnnotDecl :: SrcSpan
                    -> Located RdrName                   -- type being annotated
                    -> [Located (Maybe FastString)]      -- roles
                    -> P (LRoleAnnotDecl RdrName)
    mkRoleAnnotDecl loc tycon roles
      = do { roles' <- mapM parse_role roles
           ; return $ L loc $ RoleAnnotDecl tycon roles' }
      where
        role_data_type = dataTypeOf (undefined :: Role)
        all_roles = map fromConstr $ dataTypeConstrs role_data_type
        possible_roles = [(fsFromRole role, role) | role <- all_roles]

        parse_role (L loc_role Nothing) = return $ L loc_role Nothing
        parse_role (L loc_role (Just role))
          = case lookup role possible_roles of
              Just found_role -> return $ L loc_role $ Just found_role
              Nothing         ->
                let nearby = fuzzyLookup (unpackFS role) (mapFst unpackFS possible_roles) in
                parseErrorSDoc loc_role
                  (text "Illegal role name" <+> quotes (ppr role) $$
                   suggestions nearby)

        suggestions []   = empty
        suggestions [r]  = text "Perhaps you meant" <+> quotes (ppr r)
          -- will this last case ever happen??
        suggestions list = hang (text "Perhaps you meant one of these:")
                           2 (pprWithCommas (quotes . ppr) list)

    {- **********************************************************************

      #cvBinds-etc# Converting to @HsBinds@, etc.

      ********************************************************************* -}

    -- | Function definitions are restructured here. Each is assumed to be recursive
    -- initially, and non recursive definitions are discovered by the dependency
    -- analyser.

    --  | Groups together bindings for a single function
    cvTopDecls :: OrdList (LHsDecl RdrName) -> [LHsDecl RdrName]
    cvTopDecls decls = go (fromOL decls)
      where
        go :: [LHsDecl RdrName] -> [LHsDecl RdrName]
        go []                   = []
        go (L l (ValD b) : ds)  = L l' (ValD b') : go ds'
                                where (L l' b', ds') = getMonoBind (L l b) ds
        go (d : ds)             = d : go ds

    -- Declaration list may only contain value bindings and signatures.
    cvBindGroup :: OrdList (LHsDecl RdrName) -> P (HsValBinds RdrName)
    cvBindGroup binding
      = do { (mbs, sigs, fam_ds, tfam_insts, dfam_insts, _) <- cvBindsAndSigs binding
           ; ASSERT( null fam_ds && null tfam_insts && null dfam_insts)
             return $ ValBindsIn mbs sigs }

    cvBindsAndSigs :: OrdList (LHsDecl RdrName)
      -> P (LHsBinds RdrName, [LSig RdrName], [LFamilyDecl RdrName]
              , [LTyFamInstDecl RdrName], [LDataFamInstDecl RdrName], [LDocDecl])
    -- Input decls contain just value bindings and signatures
    -- and in case of class or instance declarations also
    -- associated type declarations. They might also contain Haddock comments.
    cvBindsAndSigs fb = go (fromOL fb)
      where
        go []              = return (emptyBag, [], [], [], [], [])
        go (L l (ValD b) : ds)
          = do { (bs, ss, ts, tfis, dfis, docs) <- go ds'
               ; return (b' `consBag` bs, ss, ts, tfis, dfis, docs) }
          where
            (b', ds') = getMonoBind (L l b) ds
        go (L l decl : ds)
          = do { (bs, ss, ts, tfis, dfis, docs) <- go ds
               ; case decl of
                   SigD s
                     -> return (bs, L l s : ss, ts, tfis, dfis, docs)
                   TyClD (FamDecl t)
                     -> return (bs, ss, L l t : ts, tfis, dfis, docs)
                   InstD (TyFamInstD { tfid_inst = tfi })
                     -> return (bs, ss, ts, L l tfi : tfis, dfis, docs)
                   InstD (DataFamInstD { dfid_inst = dfi })
                     -> return (bs, ss, ts, tfis, L l dfi : dfis, docs)
                   DocD d
                     -> return (bs, ss, ts, tfis, dfis, L l d : docs)
                   SpliceD d
                     -> parseErrorSDoc l $
                        hang (text "Declaration splices are allowed only" <+>
                              text "at the top level:")
                           2 (ppr d)
                   _ -> pprPanic "cvBindsAndSigs" (ppr decl) }

    -----------------------------------------------------------------------------
    -- Group function bindings into equation groups

    getMonoBind :: LHsBind RdrName -> [LHsDecl RdrName]
      -> (LHsBind RdrName, [LHsDecl RdrName])
    -- Suppose      (b',ds') = getMonoBind b ds
    --      ds is a list of parsed bindings
    --      b is a MonoBinds that has just been read off the front

    -- Then b' is the result of grouping more equations from ds that
    -- belong with b into a single MonoBinds, and ds' is the depleted
    -- list of parsed bindings.
    --
    -- All Haddock comments between equations inside the group are
    -- discarded.
    --
    -- No AndMonoBinds or EmptyMonoBinds here; just single equations

    getMonoBind (L loc1 (FunBind { fun_id = fun_id1@(L _ f1),
                                   fun_matches
                                     = MG { mg_alts = L _ mtchs1 } })) binds
      | has_args mtchs1
      = go mtchs1 loc1 binds []
      where
        go mtchs loc
           (L loc2 (ValD (FunBind { fun_id = L _ f2,
                                    fun_matches
                                      = MG { mg_alts = L _ mtchs2 } })) : binds) _
            | f1 == f2 = go (mtchs2 ++ mtchs)
                            (combineSrcSpans loc loc2) binds []
        go mtchs loc (doc_decl@(L loc2 (DocD _)) : binds) doc_decls
            = let doc_decls' = doc_decl : doc_decls
              in go mtchs (combineSrcSpans loc loc2) binds doc_decls'
        go mtchs loc binds doc_decls
            = ( L loc (makeFunBind fun_id1 (reverse mtchs))
              , (reverse doc_decls) ++ binds)
            -- Reverse the final matches, to get it back in the right order
            -- Do the same thing with the trailing doc comments

    getMonoBind bind binds = (bind, binds)

    has_args :: [LMatch RdrName (LHsExpr RdrName)] -> Bool
    has_args []                           = panic "RdrHsSyn:has_args"
    has_args ((L _ (Match _ args _ _)) : _) = not (null args)
            -- Don't group together FunBinds if they have
            -- no arguments.  This is necessary now that variable bindings
            -- with no arguments are now treated as FunBinds rather
            -- than pattern bindings (tests/rename/should_fail/rnfail002).

    {- **********************************************************************

      #PrefixToHS-utils# Utilities for conversion

      ********************************************************************* -}

    -----------------------------------------------------------------------------
    -- splitCon

    -- When parsing data declarations, we sometimes inadvertently parse
    -- a constructor application as a type (eg. in data T a b = C a b `D` E a b)
    -- This function splits up the type application, adds any pending
    -- arguments, and converts the type constructor back into a data constructor.

    splitCon :: LHsType RdrName
          -> P (Located RdrName, HsConDeclDetails RdrName)
    -- This gets given a "type" that should look like
    --      C Int Bool
    -- or   C { x::Int, y::Bool }
    -- and returns the pieces
    splitCon ty
     = split ty []
     where
       -- This is used somewhere where HsAppsTy is not used
       split (L _ (HsAppTy t u)) ts       = split t (u : ts)
       split (L l (HsTyVar (L _ tc)))  ts = do data_con <- tyConToDataCon l tc
                                               return (data_con, mk_rest ts)
       split (L l (HsTupleTy HsBoxedOrConstraintTuple ts)) []
          = return (L l (getRdrName (tupleDataCon Boxed (length ts))), PrefixCon ts)
       split (L l _) _ = parseErrorSDoc l (text "Cannot parse data constructor in a data/newtype declaration:" <+> ppr ty)

       mk_rest [L l (HsRecTy flds)] = RecCon (L l flds)
       mk_rest ts                   = PrefixCon ts

    recordPatSynErr :: SrcSpan -> LPat RdrName -> P a
    recordPatSynErr loc pat =
        parseErrorSDoc loc $
        text "record syntax not supported for pattern synonym declarations:" $$
        ppr pat

    mkPatSynMatchGroup :: Located RdrName
                       -> Located (OrdList (LHsDecl RdrName))
                       -> P (MatchGroup RdrName (LHsExpr RdrName))
    mkPatSynMatchGroup (L loc patsyn_name) (L _ decls) =
        do { matches <- mapM fromDecl (fromOL decls)
           ; when (null matches) (wrongNumberErr loc)
           ; return $ mkMatchGroup FromSource matches }
      where
        fromDecl (L loc decl@(ValD (PatBind pat@(L _ (ConPatIn ln@(L _ name) details)) rhs _ _ _))) =
            do { unless (name == patsyn_name) $
                   wrongNameBindingErr loc decl
               ; match <- case details of
                   PrefixCon pats -> return $ Match (FunBindMatch ln False) pats Nothing rhs
                   InfixCon pat1 pat2 ->
                             return $ Match (FunBindMatch ln True) [pat1, pat2] Nothing rhs
                   RecCon{} -> recordPatSynErr loc pat
               ; return $ L loc match }
        fromDecl (L loc decl) = extraDeclErr loc decl

        extraDeclErr loc decl =
            parseErrorSDoc loc $
            text "pattern synonym 'where' clause must contain a single binding:" $$
            ppr decl

        wrongNameBindingErr loc decl =
            parseErrorSDoc loc $
            text "pattern synonym 'where' clause must bind the pattern synonym's name" <+>
            quotes (ppr patsyn_name) $$ ppr decl

        wrongNumberErr loc =
          parseErrorSDoc loc $
          text "pattern synonym 'where' clause cannot be empty" $$
          text "In the pattern synonym declaration for: " <+> ppr (patsyn_name)

    mkConDeclH98 :: Located RdrName -> Maybe [LHsTyVarBndr RdrName]
                    -> LHsContext RdrName -> HsConDeclDetails RdrName
                    -> ConDecl RdrName

    mkConDeclH98 name mb_forall cxt details
      = ConDeclH98 { con_name     = name
                   , con_qvars    = fmap mkHsQTvs mb_forall
                   , con_cxt      = Just cxt
                                 -- AZ:TODO: when can cxt be Nothing?
                                 --          remembering that () is a valid context.
                   , con_details  = details
                   , con_doc      = Nothing }

    mkGadtDecl :: [Located RdrName]
               -> LHsSigType RdrName     -- Always a HsForAllTy
               -> ConDecl RdrName
    mkGadtDecl names ty = ConDeclGADT { con_names = names
                                      , con_type  = ty
                                      , con_doc   = Nothing }

    tyConToDataCon :: SrcSpan -> RdrName -> P (Located RdrName)
    tyConToDataCon loc tc
      | isTcOcc (rdrNameOcc tc)
      = return (L loc (setRdrNameSpace tc srcDataName))
      | otherwise
      = parseErrorSDoc loc (msg $$ extra)
      where
        msg = text "Not a data constructor:" <+> quotes (ppr tc)
        extra | tc == forall_tv_RDR
              = text "Perhaps you intended to use ExistentialQuantification"
              | otherwise = empty

    setRdrNameSpace :: RdrName -> NameSpace -> RdrName
    -- ^ This rather gruesome function is used mainly by the parser.
    -- When parsing:
    --
    -- > data T a = T | T1 Int
    --
    -- we parse the data constructors as /types/ because of parser ambiguities,
    -- so then we need to change the /type constr/ to a /data constr/
    --
    -- The exact-name case /can/ occur when parsing:
    --
    -- > data [] a = [] | a : [a]
    --
    -- For the exact-name case we return an original name.
    setRdrNameSpace (Unqual occ) ns = Unqual (setOccNameSpace ns occ)
    setRdrNameSpace (Qual m occ) ns = Qual m (setOccNameSpace ns occ)
    setRdrNameSpace (Orig m occ) ns = Orig m (setOccNameSpace ns occ)
    setRdrNameSpace (Exact n)    ns
      | Just thing <- wiredInNameTyThing_maybe n
      = setWiredInNameSpace thing ns
        -- Preserve Exact Names for wired-in things,
        -- notably tuples and lists

      | isExternalName n
      = Orig (nameModule n) occ

      | otherwise   -- This can happen when quoting and then
                    -- splicing a fixity declaration for a type
      = Exact (mkSystemNameAt (nameUnique n) occ (nameSrcSpan n))
      where
        occ = setOccNameSpace ns (nameOccName n)

    setWiredInNameSpace :: TyThing -> NameSpace -> RdrName
    setWiredInNameSpace (ATyCon tc) ns
      | isDataConNameSpace ns
      = ty_con_data_con tc
      | isTcClsNameSpace ns
      = Exact (getName tc)      -- No-op

    setWiredInNameSpace (AConLike (RealDataCon dc)) ns
      | isTcClsNameSpace ns
      = data_con_ty_con dc
      | isDataConNameSpace ns
      = Exact (getName dc)      -- No-op

    setWiredInNameSpace thing ns
      = pprPanic "setWiredinNameSpace" (pprNameSpace ns <+> ppr thing)

    ty_con_data_con :: TyCon -> RdrName
    ty_con_data_con tc
      | isTupleTyCon tc
      , Just dc <- tyConSingleDataCon_maybe tc
      = Exact (getName dc)

      | tc `hasKey` listTyConKey
      = Exact nilDataConName

      | otherwise  -- See Note [setRdrNameSpace for wired-in names]
      = Unqual (setOccNameSpace srcDataName (getOccName tc))

    data_con_ty_con :: DataCon -> RdrName
    data_con_ty_con dc
      | let tc = dataConTyCon dc
      , isTupleTyCon tc
      = Exact (getName tc)

      | dc `hasKey` nilDataConKey
      = Exact listTyConName

      | otherwise  -- See Note [setRdrNameSpace for wired-in names]
      = Unqual (setOccNameSpace tcClsName (getOccName dc))

    {- Note [setRdrNameSpace for wired-in names]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    In GHC.Types, which declares (:), we have
      infixr 5 :
    The ambiguity about which ":" is meant is resolved by parsing it as a
    data constructor, but then using dataTcOccs to try the type constructor too;
    and that in turn calls setRdrNameSpace to change the name-space of ":" to
    tcClsName.  There isn't a corresponding ":" type constructor, but it's painful
    to make setRdrNameSpace partial, so we just make an Unqual name instead. It
    really doesn't matter!
    -}

    -- | Note [Sorting out the result type]
    -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    -- In a GADT declaration which is not a record, we put the whole constr type
    -- into the res_ty for a ConDeclGADT for now; the renamer will unravel it once
    -- it has sorted out operator fixities. Consider for example
    --      C :: a :*: b -> a :*: b -> a :+: b
    -- Initially this type will parse as
    --       a :*: (b -> (a :*: (b -> (a :+: b))))
    --
    -- so it's hard to split up the arguments until we've done the precedence
    -- resolution (in the renamer). On the other hand, for a record
    --         { x,y :: Int } -> a :*: b
    -- there is no doubt.  AND we need to sort records out so that
    -- we can bring x,y into scope.  So:
    --    * For PrefixCon we keep all the args in the res_ty
    --    * For RecCon we do not

    checkTyVarsP :: SDoc -> SDoc -> Located RdrName -> [LHsType RdrName] -> P (LHsQTyVars RdrName)
    -- Same as checkTyVars, but in the P monad
    checkTyVarsP pp_what equals_or_where tc tparms
      = eitherToP $ checkTyVars pp_what equals_or_where tc tparms

    eitherToP :: Either (SrcSpan, SDoc) a -> P a
    -- Adapts the Either monad to the P monad
    eitherToP (Left (loc, doc)) = parseErrorSDoc loc doc
    eitherToP (Right thing)     = return thing

    checkTyVars :: SDoc -> SDoc -> Located RdrName -> [LHsType RdrName]
                -> Either (SrcSpan, SDoc) (LHsQTyVars RdrName)
    -- Check whether the given list of type parameters are all type variables
    -- (possibly with a kind signature)
    -- We use the Either monad because it's also called (via mkATDefault) from
    -- Convert.hs
    checkTyVars pp_what equals_or_where tc tparms
      = do { tvs <- mapM chk tparms
           ; return (mkHsQTvs tvs) }
      where

        chk (L _ (HsParTy ty)) = chk ty
        chk (L _ (HsAppsTy [L _ (HsAppPrefix ty)])) = chk ty

            -- Check that the name space is correct!
        chk (L l (HsKindSig
                  (L _ (HsAppsTy [L _ (HsAppPrefix (L lv (HsTyVar (L _ tv))))])) k))
            | isRdrTyVar tv    = return (L l (KindedTyVar (L lv tv) k))
        chk (L l (HsTyVar (L ltv tv)))
            | isRdrTyVar tv    = return (L l (UserTyVar (L ltv tv)))
        chk t@(L loc _)
            = Left (loc,
                    vcat [ text "Unexpected type" <+> quotes (ppr t)
                         , text "In the" <+> pp_what <+> ptext (sLit "declaration for") <+> quotes (ppr tc)
                         , vcat[ (text "A" <+> pp_what <+> ptext (sLit "declaration should have form"))
                         , nest 2 (pp_what <+> ppr tc
                                           <+> hsep (map text (takeList tparms allNameStrings))
                                           <+> equals_or_where) ] ])

    whereDots, equalsDots :: SDoc
    -- Second argument to checkTyVars
    whereDots  = text "where ..."
    equalsDots = text "= ..."

    checkDatatypeContext :: Maybe (LHsContext RdrName) -> P ()
    checkDatatypeContext Nothing = return ()
    checkDatatypeContext (Just (L loc c))
        = do allowed <- extension datatypeContextsEnabled
             unless allowed $
                 parseErrorSDoc loc
                     (text "Illegal datatype context (use DatatypeContexts):" <+>
                      pprHsContext c)

    checkRecordSyntax :: Outputable a => Located a -> P (Located a)
    checkRecordSyntax lr@(L loc r)
        = do allowed <- extension traditionalRecordSyntaxEnabled
             if allowed
                 then return lr
                 else parseErrorSDoc loc
                          (text "Illegal record syntax (use TraditionalRecordSyntax):" <+>
                           ppr r)

    checkTyClHdr :: Bool               -- True  <=> class header
                                       -- False <=> type header
                 -> LHsType RdrName
                 -> P (Located RdrName,          -- the head symbol (type or class name)
                       [LHsType RdrName],        -- parameters of head symbol
                       [AddAnn]) -- API Annotation for HsParTy when stripping parens
    -- Well-formedness check and decomposition of type and class heads.
    -- Decomposes   T ty1 .. tyn   into    (T, [ty1, ..., tyn])
    --              Int :*: Bool   into    (:*:, [Int, Bool])
    -- returning the pieces
    checkTyClHdr is_cls ty
      = goL ty [] []
      where
        goL (L l ty) acc ann = go l ty acc ann

        go l (HsTyVar (L _ tc)) acc ann
          | isRdrTc tc               = return (L l tc, acc, ann)
        go _ (HsOpTy t1 ltc@(L _ tc) t2) acc ann
          | isRdrTc tc               = return (ltc, t1:t2:acc, ann)
        go l (HsParTy ty)    acc ann = goL ty acc (ann ++ mkParensApiAnn l)
        go _ (HsAppTy t1 t2) acc ann = goL t1 (t2:acc) ann
        go _ (HsAppsTy ts)   acc ann
          | Just (head, args) <- getAppsTyHead_maybe ts = goL head (args ++ acc) ann

        go _ (HsAppsTy [L _ (HsAppInfix (L loc star))]) [] ann
          | occNameFS (rdrNameOcc star) == fsLit "*"
          = return (L loc (nameRdrName starKindTyConName), [], ann)
          | occNameFS (rdrNameOcc star) == fsLit "★"
          = return (L loc (nameRdrName unicodeStarKindTyConName), [], ann)

        go l (HsTupleTy HsBoxedOrConstraintTuple ts) [] ann
          = return (L l (nameRdrName tup_name), ts, ann)
          where
            arity = length ts
            tup_name | is_cls    = cTupleTyConName arity
                     | otherwise = getName (tupleTyCon Boxed arity)
                     -- See Note [Unit tuples] in HsTypes  (TODO: is this still relevant?)
        go l _  _  _
          = parseErrorSDoc l (text "Malformed head of type or class declaration:"
                              <+> ppr ty)

    checkContext :: LHsType RdrName -> P ([AddAnn],LHsContext RdrName)
    checkContext (L l orig_t)
      = check [] (L l orig_t)
     where
      check anns (L lp (HsTupleTy _ ts))   -- (Eq a, Ord b) shows up as a tuple type
        = return (anns ++ mkParensApiAnn lp,L l ts)                -- Ditto ()

        -- don't let HsAppsTy get in the way
      check anns (L _ (HsAppsTy [L _ (HsAppPrefix ty)]))
        = check anns ty

      check anns (L lp1 (HsParTy ty))-- to be sure HsParTy doesn't get into the way
           = check anns' ty
             where anns' = if l == lp1 then anns
                                       else (anns ++ mkParensApiAnn lp1)

      check _anns _
        = return ([],L l [L l orig_t]) -- no need for anns, returning original

    -- -------------------------------------------------------------------------
    -- Checking Patterns.

    -- We parse patterns as expressions and check for valid patterns below,
    -- converting the expression into a pattern at the same time.

    checkPattern :: SDoc -> LHsExpr RdrName -> P (LPat RdrName)
    checkPattern msg e = checkLPat msg e

    checkPatterns :: SDoc -> [LHsExpr RdrName] -> P [LPat RdrName]
    checkPatterns msg es = mapM (checkPattern msg) es

    checkLPat :: SDoc -> LHsExpr RdrName -> P (LPat RdrName)
    checkLPat msg e@(L l _) = checkPat msg l e []

    checkPat :: SDoc -> SrcSpan -> LHsExpr RdrName -> [LPat RdrName]
             -> P (LPat RdrName)
    checkPat _ loc (L l (HsVar (L _ c))) args
      | isRdrDataCon c = return (L loc (ConPatIn (L l c) (PrefixCon args)))
    checkPat msg loc e args     -- OK to let this happen even if bang-patterns
                            -- are not enabled, because there is no valid
                            -- non-bang-pattern parse of (C ! e)
      | Just (e', args') <- splitBang e
      = do  { args'' <- checkPatterns msg args'
            ; checkPat msg loc e' (args'' ++ args) }
    checkPat msg loc (L _ (HsApp f e)) args
      = do p <- checkLPat msg e
           checkPat msg loc f (p : args)
    checkPat msg loc (L _ e) []
      = do p <- checkAPat msg loc e
           return (L loc p)
    checkPat msg loc e _
      = patFail msg loc (unLoc e)

    checkAPat :: SDoc -> SrcSpan -> HsExpr RdrName -> P (Pat RdrName)
    checkAPat msg loc e0 = do
     pState <- getPState
     let dynflags = dflags pState
     case e0 of
       EWildPat -> return (WildPat placeHolderType)
       HsVar x  -> return (VarPat x)
       HsLit l  -> return (LitPat l)

       -- Overloaded numeric patterns (e.g. f 0 x = x)
       -- Negation is recorded separately, so that the literal is zero or +ve
       -- NB. Negative *primitive* literals are already handled by the lexer
       HsOverLit pos_lit          -> return (mkNPat (L loc pos_lit) Nothing)
       NegApp (L l (HsOverLit pos_lit)) _
                            -> return (mkNPat (L l pos_lit) (Just noSyntaxExpr))

       SectionR (L lb (HsVar (L _ bang))) e    -- (! x)
            | bang == bang_RDR
            -> do { bang_on <- extension bangPatEnabled
                  ; if bang_on then do { e' <- checkLPat msg e
                                       ; addAnnotation loc AnnBang lb
                                       ; return  (BangPat e') }
                    else parseErrorSDoc loc (text "Illegal bang-pattern (use BangPatterns):" $$ ppr e0) }

       ELazyPat e         -> checkLPat msg e >>= (return . LazyPat)
       EAsPat n e         -> checkLPat msg e >>= (return . AsPat n)
       -- view pattern is well-formed if the pattern is
       EViewPat expr patE  -> checkLPat msg patE >>=
                                (return . (\p -> ViewPat expr p placeHolderType))
       ExprWithTySig e t   -> do e <- checkLPat msg e
                                 return (SigPatIn e t)

       -- n+k patterns
       OpApp (L nloc (HsVar (L _ n))) (L _ (HsVar (L _ plus))) _
             (L lloc (HsOverLit lit@(OverLit {ol_val = HsIntegral {}})))
                          | xopt LangExt.NPlusKPatterns dynflags && (plus == plus_RDR)
                          -> return (mkNPlusKPat (L nloc n) (L lloc lit))

       OpApp l op _fix r  -> do l <- checkLPat msg l
                                r <- checkLPat msg r
                                case op of
                                   L cl (HsVar (L _ c)) | isDataOcc (rdrNameOcc c)
                                          -> return (ConPatIn (L cl c) (InfixCon l r))
                                   _ -> patFail msg loc e0

       HsPar e            -> checkLPat msg e >>= (return . ParPat)
       ExplicitList _ _ es  -> do ps <- mapM (checkLPat msg) es
                                  return (ListPat ps placeHolderType Nothing)
       ExplicitPArr _ es  -> do ps <- mapM (checkLPat msg) es
                                return (PArrPat ps placeHolderType)

       ExplicitTuple es b
         | all tupArgPresent es  -> do ps <- mapM (checkLPat msg)
                                                  [e | L _ (Present e) <- es]
                                       return (TuplePat ps b [])
         | otherwise -> parseErrorSDoc loc (text "Illegal tuple section in pattern:" $$ ppr e0)

       RecordCon { rcon_con_name = c, rcon_flds = HsRecFields fs dd }
                            -> do fs <- mapM (checkPatField msg) fs
                                  return (ConPatIn c (RecCon (HsRecFields fs dd)))
       HsSpliceE s | not (isTypedSplice s)
                   -> return (SplicePat s)
       _           -> patFail msg loc e0

    placeHolderPunRhs :: LHsExpr RdrName
    -- The RHS of a punned record field will be filled in by the renamer
    -- It's better not to make it an error, in case we want to print it when debugging
    placeHolderPunRhs = noLoc (HsVar (noLoc pun_RDR))

    plus_RDR, bang_RDR, pun_RDR :: RdrName
    plus_RDR = mkUnqual varName (fsLit "+") -- Hack
    bang_RDR = mkUnqual varName (fsLit "!") -- Hack
    pun_RDR  = mkUnqual varName (fsLit "pun-right-hand-side")

    checkPatField :: SDoc -> LHsRecField RdrName (LHsExpr RdrName)
                  -> P (LHsRecField RdrName (LPat RdrName))
    checkPatField msg (L l fld) = do p <- checkLPat msg (hsRecFieldArg fld)
                                     return (L l (fld { hsRecFieldArg = p }))

    patFail :: SDoc -> SrcSpan -> HsExpr RdrName -> P a
    patFail msg loc e = parseErrorSDoc loc err
        where err = text "Parse error in pattern:" <+> ppr e
                 $$ msg

    ---------------------------------------------------------------------------
    -- Check Equation Syntax

    checkValDef :: SDoc
                -> LHsExpr RdrName
                -> Maybe (LHsType RdrName)
                -> Located (a,GRHSs RdrName (LHsExpr RdrName))
                -> P ([AddAnn],HsBind RdrName)

    checkValDef msg lhs (Just sig) grhss
            -- x :: ty = rhs  parses as a *pattern* binding
      = checkPatBind msg (L (combineLocs lhs sig)
                            (ExprWithTySig lhs (mkLHsSigWcType sig))) grhss

    checkValDef msg lhs opt_sig g@(L l (_,grhss))
      = do  { mb_fun <- isFunLhs lhs
            ; case mb_fun of
                Just (fun, is_infix, pats, ann) ->
                  checkFunBind msg ann (getLoc lhs)
                               fun is_infix pats opt_sig (L l grhss)
                Nothing -> checkPatBind msg lhs g }

    checkFunBind :: SDoc
                 -> [AddAnn]
                 -> SrcSpan
                 -> Located RdrName
                 -> Bool
                 -> [LHsExpr RdrName]
                 -> Maybe (LHsType RdrName)
                 -> Located (GRHSs RdrName (LHsExpr RdrName))
                 -> P ([AddAnn],HsBind RdrName)
    checkFunBind msg ann lhs_loc fun is_infix pats opt_sig (L rhs_span grhss)
      = do  ps <- checkPatterns msg pats
            let match_span = combineSrcSpans lhs_loc rhs_span
            -- Add back the annotations stripped from any HsPar values in the lhs
            -- mapM_ (\a -> a match_span) ann
            return (ann, makeFunBind fun
                      [L match_span (Match { m_fixity = FunBindMatch fun is_infix
                                           , m_pats = ps
                                           , m_type = opt_sig
                                           , m_grhss = grhss })])
            -- The span of the match covers the entire equation.
            -- That isn't quite right, but it'll do for now.

    makeFunBind :: Located RdrName -> [LMatch RdrName (LHsExpr RdrName)]
                -> HsBind RdrName
    -- Like HsUtils.mkFunBind, but we need to be able to set the fixity too
    makeFunBind fn ms
      = FunBind { fun_id = fn,
                  fun_matches = mkMatchGroup FromSource ms,
                  fun_co_fn = idHsWrapper,
                  bind_fvs = placeHolderNames,
                  fun_tick = [] }

    checkPatBind :: SDoc
                 -> LHsExpr RdrName
                 -> Located (a,GRHSs RdrName (LHsExpr RdrName))
                 -> P ([AddAnn],HsBind RdrName)
    checkPatBind msg lhs (L _ (_,grhss))
      = do  { lhs <- checkPattern msg lhs
            ; return ([],PatBind lhs grhss placeHolderType placeHolderNames
                        ([],[])) }

    checkValSigLhs :: LHsExpr RdrName -> P (Located RdrName)
    checkValSigLhs (L _ (HsVar lrdr@(L _ v)))
      | isUnqual v
      , not (isDataOcc (rdrNameOcc v))
      = return lrdr

    checkValSigLhs lhs@(L l _)
      = parseErrorSDoc l ((text "Invalid type signature:" <+>
                           ppr lhs <+> text ":: ...")
                          $$ text hint)
      where
        hint | foreign_RDR `looks_like` lhs
             = "Perhaps you meant to use ForeignFunctionInterface?"
             | default_RDR `looks_like` lhs
             = "Perhaps you meant to use DefaultSignatures?"
             | pattern_RDR `looks_like` lhs
             = "Perhaps you meant to use PatternSynonyms?"
             | otherwise
             = "Should be of form <variable> :: <type>"

        -- A common error is to forget the ForeignFunctionInterface flag
        -- so check for that, and suggest.  cf Trac #3805
        -- Sadly 'foreign import' still barfs 'parse error' because 'import' is a keyword
        looks_like s (L _ (HsVar (L _ v))) = v == s
        looks_like s (L _ (HsApp lhs _))   = looks_like s lhs
        looks_like _ _                     = False

        foreign_RDR = mkUnqual varName (fsLit "foreign")
        default_RDR = mkUnqual varName (fsLit "default")
        pattern_RDR = mkUnqual varName (fsLit "pattern")

    checkDoAndIfThenElse :: LHsExpr RdrName
                         -> Bool
                         -> LHsExpr RdrName
                         -> Bool
                         -> LHsExpr RdrName
                         -> P ()
    checkDoAndIfThenElse guardExpr semiThen thenExpr semiElse elseExpr
     | semiThen || semiElse
        = do pState <- getPState
             unless (xopt LangExt.DoAndIfThenElse (dflags pState)) $ do
                 parseErrorSDoc (combineLocs guardExpr elseExpr)
                                (text "Unexpected semi-colons in conditional:"
                              $$ nest 4 expr
                              $$ text "Perhaps you meant to use DoAndIfThenElse?")
     | otherwise            = return ()
        where pprOptSemi True  = semi
              pprOptSemi False = empty
              expr = text "if"   <+> ppr guardExpr <> pprOptSemi semiThen <+>
                     text "then" <+> ppr thenExpr  <> pprOptSemi semiElse <+>
                     text "else" <+> ppr elseExpr

            -- The parser left-associates, so there should
            -- not be any OpApps inside the e's
    splitBang :: LHsExpr RdrName -> Maybe (LHsExpr RdrName, [LHsExpr RdrName])
    -- Splits (f ! g a b) into (f, [(! g), a, b])
    splitBang (L _ (OpApp l_arg bang@(L _ (HsVar (L _ op))) _ r_arg))
      | op == bang_RDR = Just (l_arg, L l' (SectionR bang arg1) : argns)
      where
        l' = combineLocs bang arg1
        (arg1,argns) = split_bang r_arg []
        split_bang (L _ (HsApp f e)) es = split_bang f (e:es)
        split_bang e                 es = (e,es)
    splitBang _ = Nothing

    isFunLhs :: LHsExpr RdrName
             -> P (Maybe (Located RdrName, Bool, [LHsExpr RdrName],[AddAnn]))
    -- A variable binding is parsed as a FunBind.
    -- Just (fun, is_infix, arg_pats) if e is a function LHS
    --
    -- The whole LHS is parsed as a single expression.
    -- Any infix operators on the LHS will parse left-associatively
    -- E.g.         f !x y !z
    --      will parse (rather strangely) as
    --              (f ! x y) ! z
    --      It's up to isFunLhs to sort out the mess
    --
    -- a .!. !b

    isFunLhs e = go e [] []
     where
       go (L loc (HsVar (L _ f))) es ann
            | not (isRdrDataCon f)       = return (Just (L loc f, False, es, ann))
       go (L _ (HsApp f e)) es       ann = go f (e:es) ann
       go (L l (HsPar e))   es@(_:_) ann = go e es (ann ++ mkParensApiAnn l)

            -- For infix function defns, there should be only one infix *function*
            -- (though there may be infix *datacons* involved too).  So we don't
            -- need fixity info to figure out which function is being defined.
            --      a `K1` b `op` c `K2` d
            -- must parse as
            --      (a `K1` b) `op` (c `K2` d)
            -- The renamer checks later that the precedences would yield such a parse.
            --
            -- There is a complication to deal with bang patterns.
            --
            -- ToDo: what about this?
            --              x + 1 `op` y = ...

       go e@(L loc (OpApp l (L loc' (HsVar (L _ op))) fix r)) es ann
            | Just (e',es') <- splitBang e
            = do { bang_on <- extension bangPatEnabled
                 ; if bang_on then go e' (es' ++ es) ann
                   else return (Just (L loc' op, True, (l:r:es), ann)) }
                    -- No bangs; behave just like the next case
            | not (isRdrDataCon op)         -- We have found the function!
            = return (Just (L loc' op, True, (l:r:es), ann))
            | otherwise                     -- Infix data con; keep going
            = do { mb_l <- go l es ann
                 ; case mb_l of
                     Just (op', True, j : k : es', ann')
                       -> return (Just (op', True, j : op_app : es', ann'))
                       where
                         op_app = L loc (OpApp k (L loc' (HsVar (L loc' op))) fix r)
                     _ -> return Nothing }
       go _ _ _ = return Nothing

    -- | Transform btype_no_ops with strict_mark's into HsEqTy's
    -- (((~a) ~b) c) ~d ==> ((~a) ~ (b c)) ~ d
    splitTilde :: LHsType RdrName -> P (LHsType RdrName)
    splitTilde t = go t
      where go (L loc (HsAppTy t1 t2))
              | L lo (HsBangTy (HsSrcBang Nothing NoSrcUnpack SrcLazy) t2') <- t2
              = do
                  moveAnnotations lo loc
                  t1' <- go t1
                  return (L loc (HsEqTy t1' t2'))
              | otherwise
              = do
                  t1' <- go t1
                  case t1' of
                    (L lo (HsEqTy tl tr)) -> do
                      let lr = combineLocs tr t2
                      moveAnnotations lo loc
                      return (L loc (HsEqTy tl (L lr (HsAppTy tr t2))))
                    t -> do
                      return (L loc (HsAppTy t t2))

            go t = return t

    -- | Transform tyapps with strict_marks into uses of twiddle
    -- [~a, ~b, c, ~d] ==> (~a) ~ b c ~ d
    splitTildeApps :: [LHsAppType RdrName] -> P [LHsAppType RdrName]
    splitTildeApps []         = return []
    splitTildeApps (t : rest) = do
      rest' <- concatMapM go rest
      return (t : rest')
      where go (L l (HsAppPrefix
                (L loc (HsBangTy
                        (HsSrcBang Nothing NoSrcUnpack SrcLazy)
                        ty))))
              = addAnnotation l AnnTilde tilde_loc >>
                return
                  [L tilde_loc (HsAppInfix (L tilde_loc eqTyCon_RDR)),
                   L l (HsAppPrefix ty)]
                   -- NOTE: no annotation is attached to an HsAppPrefix, so the
                   --       surrounding SrcSpan is not critical
              where
                tilde_loc = srcSpanFirstCharacter loc

            go t = return [t]

    ---------------------------------------------------------------------------
    -- Check for monad comprehensions
    --
    -- If the flag MonadComprehensions is set, return a `MonadComp' context,
    -- otherwise use the usual `ListComp' context

    checkMonadComp :: P (HsStmtContext Name)
    checkMonadComp = do
        pState <- getPState
        return $ if xopt LangExt.MonadComprehensions (dflags pState)
                    then MonadComp
                    else ListComp

    -- -------------------------------------------------------------------------
    -- Checking arrow syntax.

    -- We parse arrow syntax as expressions and check for valid syntax below,
    -- converting the expression into a pattern at the same time.

    checkCommand :: LHsExpr RdrName -> P (LHsCmd RdrName)
    checkCommand lc = locMap checkCmd lc

    locMap :: (SrcSpan -> a -> P b) -> Located a -> P (Located b)
    locMap f (L l a) = f l a >>= (\b -> return $ L l b)

    checkCmd :: SrcSpan -> HsExpr RdrName -> P (HsCmd RdrName)
    checkCmd _ (HsArrApp e1 e2 ptt haat b) =
        return $ HsCmdArrApp e1 e2 ptt haat b
    checkCmd _ (HsArrForm e mf args) =
        return $ HsCmdArrForm e mf args
    checkCmd _ (HsApp e1 e2) =
        checkCommand e1 >>= (\c -> return $ HsCmdApp c e2)
    checkCmd _ (HsLam mg) =
        checkCmdMatchGroup mg >>= (\mg' -> return $ HsCmdLam mg')
    checkCmd _ (HsPar e) =
        checkCommand e >>= (\c -> return $ HsCmdPar c)
    checkCmd _ (HsCase e mg) =
        checkCmdMatchGroup mg >>= (\mg' -> return $ HsCmdCase e mg')
    checkCmd _ (HsIf cf ep et ee) = do
        pt <- checkCommand et
        pe <- checkCommand ee
        return $ HsCmdIf cf ep pt pe
    checkCmd _ (HsLet lb e) =
        checkCommand e >>= (\c -> return $ HsCmdLet lb c)
    checkCmd _ (HsDo DoExpr (L l stmts) ty) =
        mapM checkCmdLStmt stmts >>= (\ss -> return $ HsCmdDo (L l ss) ty)

    checkCmd _ (OpApp eLeft op _fixity eRight) = do
        -- OpApp becomes a HsCmdArrForm with a (Just fixity) in it
        c1 <- checkCommand eLeft
        c2 <- checkCommand eRight
        let arg1 = L (getLoc c1) $ HsCmdTop c1 placeHolderType placeHolderType []
            arg2 = L (getLoc c2) $ HsCmdTop c2 placeHolderType placeHolderType []
        return $ HsCmdArrForm op Nothing [arg1, arg2]

    checkCmd l e = cmdFail l e

    checkCmdLStmt :: ExprLStmt RdrName -> P (CmdLStmt RdrName)
    checkCmdLStmt = locMap checkCmdStmt

    checkCmdStmt :: SrcSpan -> ExprStmt RdrName -> P (CmdStmt RdrName)
    checkCmdStmt _ (LastStmt e s r) =
        checkCommand e >>= (\c -> return $ LastStmt c s r)
    checkCmdStmt _ (BindStmt pat e b f t) =
        checkCommand e >>= (\c -> return $ BindStmt pat c b f t)
    checkCmdStmt _ (BodyStmt e t g ty) =
        checkCommand e >>= (\c -> return $ BodyStmt c t g ty)
    checkCmdStmt _ (LetStmt bnds) = return $ LetStmt bnds
    checkCmdStmt _ stmt@(RecStmt { recS_stmts = stmts }) = do
        ss <- mapM checkCmdLStmt stmts
        return $ stmt { recS_stmts = ss }
    checkCmdStmt l stmt = cmdStmtFail l stmt

    checkCmdMatchGroup :: MatchGroup RdrName (LHsExpr RdrName) -> P (MatchGroup RdrName (LHsCmd RdrName))
    checkCmdMatchGroup mg@(MG { mg_alts = L l ms }) = do
        ms' <- mapM (locMap $ const convert) ms
        return $ mg { mg_alts = L l ms' }
        where convert (Match mf pat mty grhss) = do
                grhss' <- checkCmdGRHSs grhss
                return $ Match mf pat mty grhss'

    checkCmdGRHSs :: GRHSs RdrName (LHsExpr RdrName) -> P (GRHSs RdrName (LHsCmd RdrName))
    checkCmdGRHSs (GRHSs grhss binds) = do
        grhss' <- mapM checkCmdGRHS grhss
        return $ GRHSs grhss' binds

    checkCmdGRHS :: LGRHS RdrName (LHsExpr RdrName) -> P (LGRHS RdrName (LHsCmd RdrName))
    checkCmdGRHS = locMap $ const convert
      where
        convert (GRHS stmts e) = do
            c <- checkCommand e
    --        cmdStmts <- mapM checkCmdLStmt stmts
            return $ GRHS {- cmdStmts -} stmts c

    cmdFail :: SrcSpan -> HsExpr RdrName -> P a
    cmdFail loc e = parseErrorSDoc loc (text "Parse error in command:" <+> ppr e)
    cmdStmtFail :: SrcSpan -> Stmt RdrName (LHsExpr RdrName) -> P a
    cmdStmtFail loc e = parseErrorSDoc loc
                        (text "Parse error in command statement:" <+> ppr e)

    ---------------------------------------------------------------------------
    -- Miscellaneous utilities

    checkPrecP :: Located (SourceText,Int) -> P (Located (SourceText,Int))
    checkPrecP (L l (src,i))
     | 0 <= i && i <= maxPrecedence = return (L l (src,i))
     | otherwise
        = parseErrorSDoc l (text ("Precedence out of range: " ++ show i))

    mkRecConstrOrUpdate
            :: LHsExpr RdrName
            -> SrcSpan
            -> ([LHsRecField RdrName (LHsExpr RdrName)], Bool)
            -> P (HsExpr RdrName)

    mkRecConstrOrUpdate (L l (HsVar (L _ c))) _ (fs,dd)
      | isRdrDataCon c
      = return (mkRdrRecordCon (L l c) (mk_rec_fields fs dd))
    mkRecConstrOrUpdate exp@(L l _) _ (fs,dd)
      | dd        = parseErrorSDoc l (text "You cannot use `..' in a record update")
      | otherwise = return (mkRdrRecordUpd exp (map (fmap mk_rec_upd_field) fs))

    mkRdrRecordUpd :: LHsExpr RdrName -> [LHsRecUpdField RdrName] -> HsExpr RdrName
    mkRdrRecordUpd exp flds
      = RecordUpd { rupd_expr = exp
                  , rupd_flds = flds
                  , rupd_cons    = PlaceHolder, rupd_in_tys  = PlaceHolder
                  , rupd_out_tys = PlaceHolder, rupd_wrap    = PlaceHolder }

    mkRdrRecordCon :: Located RdrName -> HsRecordBinds RdrName -> HsExpr RdrName
    mkRdrRecordCon con flds
      = RecordCon { rcon_con_name = con, rcon_flds = flds
                  , rcon_con_expr = noPostTcExpr, rcon_con_like = PlaceHolder }

    mk_rec_fields :: [LHsRecField id arg] -> Bool -> HsRecFields id arg
    mk_rec_fields fs False = HsRecFields { rec_flds = fs, rec_dotdot = Nothing }
    mk_rec_fields fs True  = HsRecFields { rec_flds = fs, rec_dotdot = Just (length fs) }

    mk_rec_upd_field :: HsRecField RdrName (LHsExpr RdrName) -> HsRecUpdField RdrName
    mk_rec_upd_field (HsRecField (L loc (FieldOcc rdr _)) arg pun)
      = HsRecField (L loc (Unambiguous rdr PlaceHolder)) arg pun

    mkInlinePragma :: String -> (InlineSpec, RuleMatchInfo) -> Maybe Activation
                   -> InlinePragma
    -- The (Maybe Activation) is because the user can omit
    -- the activation spec (and usually does)
    mkInlinePragma src (inl, match_info) mb_act
      = InlinePragma { inl_src = src -- Note [Pragma source text] in BasicTypes
                     , inl_inline = inl
                     , inl_sat    = Nothing
                     , inl_act    = act
                     , inl_rule   = match_info }
      where
        act = case mb_act of
                Just act -> act
                Nothing  -> -- No phase specified
                            case inl of
                              NoInline -> NeverActive
                              _other   -> AlwaysActive

    -----------------------------------------------------------------------------
    -- utilities for foreign declarations

    -- construct a foreign import declaration
    --
    mkImport :: Located CCallConv
             -> Located Safety
             -> (Located StringLiteral, Located RdrName, LHsSigType RdrName)
             -> P (HsDecl RdrName)
    mkImport cconv safety (L loc (StringLiteral esrc entity), v, ty) =
        case cconv of
          L _ CCallConv          -> mkCImport
          L _ CApiConv           -> mkCImport
          L _ StdCallConv        -> mkCImport
          L _ PrimCallConv       -> mkOtherImport
          L _ JavaScriptCallConv -> mkOtherImport
      where
        -- Parse a C-like entity string of the following form:
        --   "[static] [chname] [&] [cid]" | "dynamic" | "wrapper"
        -- If 'cid' is missing, the function name 'v' is used instead as symbol
        -- name (cf section 8.5.1 in Haskell 2010 report).
        mkCImport = do
          let e = unpackFS entity
          case parseCImport cconv safety (mkExtName (unLoc v)) e (L loc esrc) of
            Nothing         -> parseErrorSDoc loc (text "Malformed entity string")
            Just importSpec -> returnSpec importSpec

        -- currently, all the other import conventions only support a symbol name in
        -- the entity string. If it is missing, we use the function name instead.
        mkOtherImport = returnSpec importSpec
          where
            entity'    = if nullFS entity
                            then mkExtName (unLoc v)
                            else entity
            funcTarget = CFunction (StaticTarget esrc entity' Nothing True)
            importSpec = CImport cconv safety Nothing funcTarget (L loc esrc)

        returnSpec spec = return $ ForD $ ForeignImport
              { fd_name   = v
              , fd_sig_ty = ty
              , fd_co     = noForeignImportCoercionYet
              , fd_fi     = spec
              }

    -- the string "foo" is ambiguous: either a header or a C identifier.  The
    -- C identifier case comes first in the alternatives below, so we pick
    -- that one.
    parseCImport :: Located CCallConv -> Located Safety -> FastString -> String
                 -> Located SourceText
                 -> Maybe ForeignImport
    parseCImport cconv safety nm str sourceText =
     listToMaybe $ map fst $ filter (null.snd) $
         readP_to_S parse str
     where
       parse = do
           skipSpaces
           r <- choice [
              string "dynamic" >> return (mk Nothing (CFunction DynamicTarget)),
              string "wrapper" >> return (mk Nothing CWrapper),
              do optional (token "static" >> skipSpaces)
                 ((mk Nothing <$> cimp nm) +++
                  (do h <- munch1 hdr_char
                      skipSpaces
                      mk (Just (Header h (mkFastString h))) <$> cimp nm))
             ]
           skipSpaces
           return r

       token str = do _ <- string str
                      toks <- look
                      case toks of
                          c : _
                           | id_char c -> pfail
                          _            -> return ()

       mk h n = CImport cconv safety h n sourceText

       hdr_char c = not (isSpace c) -- header files are filenames, which can contain
                                    -- pretty much any char (depending on the platform),
                                    -- so just accept any non-space character
       id_first_char c = isAlpha    c || c == '_'
       id_char       c = isAlphaNum c || c == '_'

       cimp nm = (ReadP.char '&' >> skipSpaces >> CLabel <$> cid)
                 +++ (do isFun <- case cconv of
                                  L _ CApiConv ->
                                      option True
                                             (do token "value"
                                                 skipSpaces
                                                 return False)
                                  _ -> return True
                         cid' <- cid
                         return (CFunction (StaticTarget (unpackFS cid') cid'
                                            Nothing isFun)))
              where
                cid = return nm +++
                      (do c  <- satisfy id_first_char
                          cs <-  many (satisfy id_char)
                          return (mkFastString (c:cs)))

    -- construct a foreign export declaration
    --
    mkExport :: Located CCallConv
             -> (Located StringLiteral, Located RdrName, LHsSigType RdrName)
             -> P (HsDecl RdrName)
    mkExport (L lc cconv) (L le (StringLiteral esrc entity), v, ty)
     = return $ ForD $
       ForeignExport { fd_name = v, fd_sig_ty = ty
                     , fd_co = noForeignExportCoercionYet
                     , fd_fe = CExport (L lc (CExportStatic esrc entity' cconv))
                                       (L le (unpackFS entity)) }
      where
        entity' | nullFS entity = mkExtName (unLoc v)
                | otherwise     = entity

    -- Supplying the ext_name in a foreign decl is optional; if it
    -- isn't there, the Haskell name is assumed. Note that no transformation
    -- of the Haskell name is then performed, so if you foreign export (++),
    -- it's external name will be "++". Too bad; it's important because we don't
    -- want z-encoding (e.g. names with z's in them shouldn't be doubled)
    --
    mkExtName :: RdrName -> CLabelString
    mkExtName rdrNm = mkFastString (occNameString (rdrNameOcc rdrNm))

    --------------------------------------------------------------------------------
    -- Help with module system imports/exports

    data ImpExpSubSpec = ImpExpAbs
                       | ImpExpAll
                       | ImpExpList [Located RdrName]
                       | ImpExpAllWith [Located (Maybe RdrName)]

    mkModuleImpExp :: Located RdrName -> ImpExpSubSpec -> P (IE RdrName)
    mkModuleImpExp n@(L l name) subs =
      case subs of
        ImpExpAbs
          | isVarNameSpace (rdrNameSpace name) -> return $ IEVar  n
          | otherwise                          -> IEThingAbs . L l <$> nameT
        ImpExpAll                              -> IEThingAll . L l <$> nameT
        ImpExpList xs                          ->
          (\newName -> IEThingWith (L l newName) NoIEWildcard xs []) <$> nameT
        ImpExpAllWith xs                       ->
          do allowed <- extension patternSynonymsEnabled
             if allowed
              then
                let withs = map unLoc xs
                    pos   = maybe NoIEWildcard IEWildcard
                              (findIndex isNothing withs)
                    ies   = [L l n | L l (Just n) <- xs]
                in (\newName -> IEThingWith (L l newName) pos ies []) <$> nameT
              else parseErrorSDoc l
                (text "Illegal export form (use PatternSynonyms to enable)")
      where
        nameT =
          if isVarNameSpace (rdrNameSpace name)
            then parseErrorSDoc l
                  (text "Expecting a type constructor but found a variable,"
                   <+> quotes (ppr name) <> text "."
                  $$ if isSymOcc $ rdrNameOcc name
                       then text "If" <+> quotes (ppr name) <+> text "is a type constructor"
                        <+> text "then enable ExplicitNamespaces and use the 'type' keyword."
                       else empty)
            else return $ name

    mkTypeImpExp :: Located RdrName   -- TcCls or Var name space
                 -> P (Located RdrName)
    mkTypeImpExp name =
      do allowed <- extension explicitNamespacesEnabled
         if allowed
           then return (fmap (`setRdrNameSpace` tcClsName) name)
           else parseErrorSDoc (getLoc name)
                  (text "Illegal keyword 'type' (use ExplicitNamespaces to enable)")

    checkImportSpec :: Located [LIE RdrName] -> P (Located [LIE RdrName])
    checkImportSpec ie@(L _ specs) =
        case [l | (L l (IEThingWith _ (IEWildcard _) _ _)) <- specs] of
          [] -> return ie
          (l:_) -> importSpecError l
      where
        importSpecError l =
          parseErrorSDoc l
            (text "Illegal import form, this syntax can only be used to bundle"
            $+$ text "pattern synonyms with types in module exports.")

    -- In the correct order
    mkImpExpSubSpec :: [Located (Maybe RdrName)] -> P ([AddAnn], ImpExpSubSpec)
    mkImpExpSubSpec [] = return ([], ImpExpList [])
    mkImpExpSubSpec [L l Nothing] =
      return ([\s -> addAnnotation s AnnDotdot l], ImpExpAll)
    mkImpExpSubSpec xs =
      if (any (isNothing . unLoc) xs)
        then return $ ([], ImpExpAllWith xs)
        else return $ ([], ImpExpList ([L l x | L l (Just x) <- xs]))

    -----------------------------------------------------------------------------
    -- Misc utils

    parseErrorSDoc :: SrcSpan -> SDoc -> P a
    parseErrorSDoc span s = failSpanMsgP span s