    -----------------------------------------------------------------------------
    --
    -- Pretty-printing TyThings
    --
    -- (c) The GHC Team 2005
    --
    -----------------------------------------------------------------------------

    module PprTyThing (
    	PrintExplicitForalls,
    	pprTyThing,
    	pprTyThingInContext, pprTyThingParent_maybe,
    	pprTyThingLoc,
    	pprTyThingInContextLoc,
    	pprTyThingHdr,
      	pprTypeForUser
      ) where

    import qualified GHC

    import GHC ( TyThing(..) )
    import DataCon
    import Id
    import IdInfo
    import TyCon
    import TcType
    import Var
    import Name
    import Outputable
    import FastString

    -- -----------------------------------------------------------------------------
    -- Pretty-printing entities that we get from the GHC API

    -- This should be a good source of sample code for using the GHC API to
    -- inspect source code entities.

    type PrintExplicitForalls = Bool

    type ShowMe = Name -> Bool
    -- The ShowMe function says which sub-components to print
    --   True  <=> print
    --   False <=> elide to "..."

    ----------------------------
    -- | Pretty-prints a 'TyThing' with its defining location.
    pprTyThingLoc :: PrintExplicitForalls -> TyThing -> SDoc
    pprTyThingLoc pefas tyThing
      = showWithLoc loc (pprTyThing pefas tyThing)
      where loc = pprNameLoc (GHC.getName tyThing)

    -- | Pretty-prints a 'TyThing'.
    pprTyThing :: PrintExplicitForalls -> TyThing -> SDoc
    pprTyThing pefas thing = ppr_ty_thing pefas (const True) thing

    ppr_ty_thing :: PrintExplicitForalls -> ShowMe -> TyThing -> SDoc
    ppr_ty_thing pefas _ 	 (AnId id)          = pprId         pefas id
    ppr_ty_thing pefas _ 	 (ADataCon dataCon) = pprDataConSig pefas dataCon
    ppr_ty_thing pefas show_me (ATyCon tyCon)   = pprTyCon      pefas show_me tyCon
    ppr_ty_thing pefas show_me (AClass cls)     = pprClass      pefas show_me cls

    -- | Pretty-prints a 'TyThing' in context: that is, if the entity
    -- is a data constructor, record selector, or class method, then
    -- the entity's parent declaration is pretty-printed with irrelevant
    -- parts omitted.
    pprTyThingInContext :: PrintExplicitForalls -> TyThing -> SDoc
    pprTyThingInContext pefas thing
      | Just parent <- pprTyThingParent_maybe thing
      = ppr_ty_thing pefas (== GHC.getName thing) parent
      | otherwise
      = pprTyThing pefas thing

    -- | Like 'pprTyThingInContext', but adds the defining location.
    pprTyThingInContextLoc :: PrintExplicitForalls -> TyThing -> SDoc
    pprTyThingInContextLoc pefas tyThing
      = showWithLoc (pprNameLoc (GHC.getName tyThing))
                    (pprTyThingInContext pefas tyThing)

    pprTyThingParent_maybe :: TyThing -> Maybe TyThing
    -- (pprTyThingParent_maybe x) returns (Just p)
    -- when pprTyThingInContext sould print a declaration for p
    -- (albeit with some "..." in it) when asked to show x
    pprTyThingParent_maybe (ADataCon dc) = Just (ATyCon (dataConTyCon dc))
    pprTyThingParent_maybe (AnId id)     = case idDetails id of
          				      	 RecSelId { sel_tycon = tc } -> Just (ATyCon tc)
          				      	 ClassOpId cls               -> Just (AClass cls)
                                          	 _other                      -> Nothing
    pprTyThingParent_maybe _other = Nothing

    -- | Pretty-prints the 'TyThing' header. For functions and data constructors
    -- the function is equivalent to 'pprTyThing' but for type constructors
    -- and classes it prints only the header part of the declaration.
    pprTyThingHdr :: PrintExplicitForalls -> TyThing -> SDoc
    pprTyThingHdr pefas (AnId id)          = pprId         pefas id
    pprTyThingHdr pefas (ADataCon dataCon) = pprDataConSig pefas dataCon
    pprTyThingHdr pefas (ATyCon tyCon)     = pprTyConHdr   pefas tyCon
    pprTyThingHdr pefas (AClass cls)       = pprClassHdr   pefas cls

    pprTyConHdr :: PrintExplicitForalls -> TyCon -> SDoc
    pprTyConHdr _ tyCon
      | Just (_fam_tc, tys) <- tyConFamInst_maybe tyCon
      = ptext keyword <+> ptext (sLit "instance") <+> pprTypeApp tyCon tys
      | otherwise
      = ptext keyword <+> opt_family <+> opt_stupid <+> ppr_bndr tyCon <+> hsep (map ppr vars)
      where
        vars | GHC.isPrimTyCon tyCon ||
    	   GHC.isFunTyCon tyCon = take (GHC.tyConArity tyCon) GHC.alphaTyVars
    	 | otherwise = GHC.tyConTyVars tyCon

        keyword | GHC.isSynTyCon tyCon = sLit "type"
                | GHC.isNewTyCon tyCon = sLit "newtype"
                | otherwise            = sLit "data"

        opt_family
          | GHC.isFamilyTyCon tyCon = ptext (sLit "family")
          | otherwise             = empty

        opt_stupid 	-- The "stupid theta" part of the declaration
    	| isAlgTyCon tyCon = GHC.pprThetaArrow (tyConStupidTheta tyCon)
    	| otherwise	   = empty	-- Returns 'empty' if null theta

    pprDataConSig :: PrintExplicitForalls -> GHC.DataCon -> SDoc
    pprDataConSig pefas dataCon
      = ppr_bndr dataCon <+> dcolon <+> pprTypeForUser pefas (GHC.dataConType dataCon)

    pprClassHdr :: PrintExplicitForalls -> GHC.Class -> SDoc
    pprClassHdr _ cls
      = ptext (sLit "class") <+>
        GHC.pprThetaArrow (GHC.classSCTheta cls) <+>
        ppr_bndr cls <+>
        hsep (map ppr tyVars) <+>
        GHC.pprFundeps funDeps
      where
         (tyVars, funDeps) = GHC.classTvsFds cls

    pprId :: PrintExplicitForalls -> Var -> SDoc
    pprId pefas ident
      = hang (ppr_bndr ident <+> dcolon)
    	 2 (pprTypeForUser pefas (GHC.idType ident))

    pprTypeForUser :: PrintExplicitForalls -> GHC.Type -> SDoc
    -- We do two things here.
    -- a) We tidy the type, regardless
    -- b) If PrintExplicitForAlls is True, we discard the foralls
    -- 	but we do so `deeply'
    -- Prime example: a class op might have type
    --	forall a. C a => forall b. Ord b => stuff
    -- Then we want to display
    --	(C a, Ord b) => stuff
    pprTypeForUser print_foralls ty
      | print_foralls = ppr tidy_ty
      | otherwise     = ppr (mkPhiTy ctxt ty')
      where
        tidy_ty     = tidyTopType ty
        (_, ctxt, ty') = tcSplitSigmaTy tidy_ty

    pprTyCon :: PrintExplicitForalls -> ShowMe -> TyCon -> SDoc
    pprTyCon pefas show_me tyCon
      | GHC.isSynTyCon tyCon
      = if GHC.isFamilyTyCon tyCon
        then pprTyConHdr pefas tyCon <+> dcolon <+>
    	 pprTypeForUser pefas (GHC.synTyConResKind tyCon)
        else
          let rhs_type = GHC.synTyConType tyCon
          in hang (pprTyConHdr pefas tyCon <+> equals) 2 (pprTypeForUser pefas rhs_type)
      | otherwise
      = pprAlgTyCon pefas show_me tyCon

    pprAlgTyCon :: PrintExplicitForalls -> ShowMe -> TyCon -> SDoc
    pprAlgTyCon pefas show_me tyCon
      | gadt      = pprTyConHdr pefas tyCon <+> ptext (sLit "where") $$
    		   nest 2 (vcat (ppr_trim show_con datacons))
      | otherwise = hang (pprTyConHdr pefas tyCon)
        		   2 (add_bars (ppr_trim show_con datacons))
      where
        datacons = GHC.tyConDataCons tyCon
        gadt = any (not . GHC.isVanillaDataCon) datacons

        ok_con dc = show_me (dataConName dc) || any show_me (dataConFieldLabels dc)
        show_con dc
          | ok_con dc = Just (pprDataConDecl pefas show_me gadt dc)
          | otherwise = Nothing

    pprDataConDecl :: PrintExplicitForalls -> ShowMe -> Bool -> GHC.DataCon -> SDoc
    pprDataConDecl pefas show_me gadt_style dataCon
      | not gadt_style = ppr_fields tys_w_strs
      | otherwise      = ppr_bndr dataCon <+> dcolon <+>
    			sep [ pp_foralls, GHC.pprThetaArrow theta, pp_tau ]
    	-- Printing out the dataCon as a type signature, in GADT style
      where
        (forall_tvs, theta, tau) = tcSplitSigmaTy (GHC.dataConUserType dataCon)
        (arg_tys, res_ty)        = tcSplitFunTys tau
        labels     = GHC.dataConFieldLabels dataCon
        stricts    = GHC.dataConStrictMarks dataCon
        tys_w_strs = zip stricts arg_tys
        pp_foralls | pefas     = GHC.pprForAll forall_tvs
                   | otherwise = empty

        pp_tau = foldr add (ppr res_ty) tys_w_strs
        add str_ty pp_ty = pprParendBangTy str_ty <+> arrow <+> pp_ty

        pprParendBangTy (bang,ty) = ppr bang <> GHC.pprParendType ty

        pprBangTy bang ty = ppr bang <> ppr ty

        maybe_show_label (lbl,(strict,tp))
    	| show_me lbl = Just (ppr lbl <+> dcolon <+> pprBangTy strict tp)
    	| otherwise   = Nothing

        ppr_fields [ty1, ty2]
    	| GHC.dataConIsInfix dataCon && null labels
    	= sep [pprParendBangTy ty1, pprInfixName dataCon, pprParendBangTy ty2]
        ppr_fields fields
    	| null labels
    	= ppr_bndr dataCon <+> sep (map pprParendBangTy fields)
    	| otherwise
    	= ppr_bndr dataCon <+>
    		braces (sep (punctuate comma (ppr_trim maybe_show_label
    					(zip labels fields))))

    pprClass :: PrintExplicitForalls -> ShowMe -> GHC.Class -> SDoc
    pprClass pefas show_me cls
      | null methods
      = pprClassHdr pefas cls
      | otherwise
      = hang (pprClassHdr pefas cls <+> ptext (sLit "where"))
           2 (vcat (ppr_trim show_meth methods))
      where
        methods = GHC.classMethods cls
        show_meth id | show_me (idName id) = Just (pprClassMethod pefas id)
    	         | otherwise           = Nothing

    pprClassMethod :: PrintExplicitForalls -> Id -> SDoc
    pprClassMethod pefas id
      = hang (ppr_bndr id <+> dcolon) 2 (pprTypeForUser pefas op_ty)
      where
      -- Here's the magic incantation to strip off the dictionary
      -- from the class op type.  Stolen from IfaceSyn.tyThingToIfaceDecl.
      --
      -- It's important to tidy it *before* splitting it up, so that if
      -- we have	class C a b where
      --	          op :: forall a. a -> b
      -- then the inner forall on op gets renamed to a1, and we print
      -- (when dropping foralls)
      --		class C a b where
      --		  op :: a1 -> b

      tidy_sel_ty = tidyTopType (GHC.idType id)
      (_sel_tyvars, rho_ty) = GHC.splitForAllTys tidy_sel_ty
      op_ty = GHC.funResultTy rho_ty

    ppr_trim :: (a -> Maybe SDoc) -> [a] -> [SDoc]
    ppr_trim show xs
      = snd (foldr go (False, []) xs)
      where
        go x (eliding, so_far)
    	| Just doc <- show x = (False, doc : so_far)
    	| otherwise = if eliding then (True, so_far)
    		                 else (True, ptext (sLit "...") : so_far)

    add_bars :: [SDoc] -> SDoc
    add_bars []      = empty
    add_bars [c]     = equals <+> c
    add_bars (c:cs)  = sep ((equals <+> c) : map (char '|' <+>) cs)

    -- Wrap operators in ()
    ppr_bndr :: GHC.NamedThing a => a -> SDoc
    ppr_bndr a = GHC.pprParenSymName a

    showWithLoc :: SDoc -> SDoc -> SDoc
    showWithLoc loc doc
        = hang doc 2 (char '\t' <> comment <+> loc)
    		-- The tab tries to make them line up a bit
      where
        comment = ptext (sLit "--")