% % (c) The University of Glasgow 2006 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998 % HsTypes: Abstract syntax: user-defined types \begin{code} 
{-# OPTIONS -fno-warn-tabs #-}
-- The above warning supression flag is a temporary kludge.
-- While working on this module you are encouraged to remove it and
-- detab the module (please do the detabbing in a separate patch). See
--     http://hackage.haskell.org/trac/ghc/wiki/Commentary/CodingStyle#TabsvsSpaces
-- for details

{-# LANGUAGE DeriveDataTypeable #-}

module HsTypes (
	HsType(..), LHsType, HsKind, LHsKind,
	HsTyVarBndr(..), LHsTyVarBndr,
	HsTupleSort(..), HsExplicitFlag(..),
	HsContext, LHsContext,
	HsQuasiQuote(..),
        HsTyWrapper(..),

	LBangType, BangType, HsBang(..), 
        getBangType, getBangStrictness, 

	ConDeclField(..), pprConDeclFields,
	
	mkExplicitHsForAllTy, mkImplicitHsForAllTy, hsExplicitTvs,
	hsTyVarName, hsTyVarNames, replaceTyVarName, replaceLTyVarName,
	hsTyVarKind, hsLTyVarKind, hsTyVarNameKind,
	hsLTyVarName, hsLTyVarNames, hsLTyVarLocName, hsLTyVarLocNames,
	splitHsInstDeclTy_maybe, splitLHsInstDeclTy_maybe,
        splitHsForAllTy, splitLHsForAllTy,
        splitHsClassTy_maybe, splitLHsClassTy_maybe,
        splitHsFunType,
	splitHsAppTys, mkHsAppTys, mkHsOpTy,

	-- Printing
	pprParendHsType, pprHsForAll, pprHsContext, ppr_hs_context,
    ) where

import {-# SOURCE #-} HsExpr ( HsSplice, pprSplice )

import HsLit

import NameSet( FreeVars )
import Type
import HsDoc
import BasicTypes
import SrcLoc
import StaticFlags
import Outputable
import FastString

import Data.Data
\end{code} %************************************************************************ %* * Quasi quotes; used in types and elsewhere %* * %************************************************************************ \begin{code} 
data HsQuasiQuote id = HsQuasiQuote 
		       	   id		-- The quasi-quoter
		       	   SrcSpan	-- The span of the enclosed string
		       	   FastString	-- The enclosed string
  deriving (Data, Typeable)

instance OutputableBndr id => Outputable (HsQuasiQuote id) where
    ppr = ppr_qq

ppr_qq :: OutputableBndr id => HsQuasiQuote id -> SDoc
ppr_qq (HsQuasiQuote quoter _ quote) =
    char '[' <> ppr quoter <> ptext (sLit "|") <>
    ppr quote <> ptext (sLit "|]")
\end{code} %************************************************************************ %* * \subsection{Bang annotations} %* * %************************************************************************ \begin{code} 
type LBangType name = Located (BangType name)
type BangType name  = HsType name	-- Bangs are in the HsType data type

getBangType :: LHsType a -> LHsType a
getBangType (L _ (HsBangTy _ ty)) = ty
getBangType ty                    = ty

getBangStrictness :: LHsType a -> HsBang
getBangStrictness (L _ (HsBangTy s _)) = s
getBangStrictness _                    = HsNoBang
\end{code} %************************************************************************ %* * \subsection{Data types} %* * %************************************************************************ This is the syntax for types as seen in type signatures. \begin{code} 
type LHsContext name = Located (HsContext name)

type HsContext name = [LHsType name]

type LHsType name = Located (HsType name)
type HsKind name = HsType name
type LHsKind name = Located (HsKind name)

data HsType name
  = HsForAllTy	HsExplicitFlag   	-- Renamer leaves this flag unchanged, to record the way
					-- the user wrote it originally, so that the printer can
					-- print it as the user wrote it
		[LHsTyVarBndr name]	-- With ImplicitForAll, this is the empty list
					-- until the renamer fills in the variables
		(LHsContext name)
		(LHsType name)

  | HsTyVar		name		-- Type variable, type constructor, or data constructor
                                        -- see Note [Promotions (HsTyVar)]

  | HsAppTy		(LHsType name)
			(LHsType name)

  | HsFunTy		(LHsType name)   -- function type
			(LHsType name)

  | HsListTy		(LHsType name)	-- Element type

  | HsPArrTy		(LHsType name)	-- Elem. type of parallel array: [:t:]

  | HsTupleTy		HsTupleSort
			[LHsType name]	-- Element types (length gives arity)

  | HsOpTy		(LHsType name) (LHsTyOp name) (LHsType name)

  | HsParTy		(LHsType name)   -- See Note [Parens in HsSyn] in HsExpr
	-- Parenthesis preserved for the precedence re-arrangement in RnTypes
	-- It's important that a * (b + c) doesn't get rearranged to (a*b) + c!

  | HsIParamTy		(IPName name)    -- (?x :: ty)
                        (LHsType name)   -- Implicit parameters as they occur in contexts

  | HsEqTy              (LHsType name)   -- ty1 ~ ty2
                        (LHsType name)   -- Always allowed even without TypeOperators, and has special kinding rule

  | HsKindSig		(LHsType name)	-- (ty :: kind)
			(LHsKind name)  -- A type with a kind signature

  | HsQuasiQuoteTy	(HsQuasiQuote name)

  | HsSpliceTy		(HsSplice name) 
                        FreeVars  	-- Variables free in the splice (filled in by renamer)
			PostTcKind

  | HsDocTy             (LHsType name) LHsDocString -- A documented type

  | HsBangTy	HsBang (LHsType name)	-- Bang-style type annotations 
  | HsRecTy [ConDeclField name]	        -- Only in data type declarations

  | HsCoreTy Type	-- An escape hatch for tunnelling a *closed* 
    	       		-- Core Type through HsSyn.  

  | HsExplicitListTy     -- A promoted explicit list
        PostTcKind       -- See Note [Promoted lists and tuples]
        [LHsType name]   
                         
  | HsExplicitTupleTy    -- A promoted explicit tuple
        [PostTcKind]     -- See Note [Promoted lists and tuples]
        [LHsType name]   

  | HsWrapTy HsTyWrapper (HsType name)  -- only in typechecker output
  deriving (Data, Typeable)

data HsTyWrapper
  = WpKiApps [Kind]  -- kind instantiation: [] k1 k2 .. kn
  deriving (Data, Typeable)

type LHsTyOp name = HsTyOp (Located name)
type HsTyOp name = (HsTyWrapper, name)

mkHsOpTy :: LHsType name -> Located name -> LHsType name -> HsType name
mkHsOpTy ty1 op ty2 = HsOpTy ty1 (WpKiApps [], op) ty2
\end{code} Note [Promotions (HsTyVar)] ~~~~~~~~~~~~~~~~~~~~~~~~~~~ HsTyVar: A name in a type or kind. Here are the allowed namespaces for the name. In a type: Var: not allowed Data: promoted data constructor Tv: type variable TcCls before renamer: type constructor, class constructor, or promoted data constructor TcCls after renamer: type constructor or class constructor In a kind: Var, Data: not allowed Tv: kind variable TcCls: kind constructor or promoted type constructor Note [Promoted lists and tuples] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Notice the difference between HsListTy HsExplicitListTy HsTupleTy HsExplicitListTupleTy E.g. f :: [Int] HsListTy g3 :: T '[] All these use g2 :: T '[True] HsExplicitListTy g1 :: T '[True,False] g1a :: T [True,False] (can omit ' where unambiguous) kind of T :: [Bool] -> * This kind uses HsListTy! E.g. h :: (Int,Bool) HsTupleTy; f is a pair k :: S '(True,False) HsExplicitTypleTy; S is indexed by a type-level pair of booleans kind of S :: (Bool,Bool) -> * This kind uses HsExplicitTupleTy Note [Distinguishing tuple kinds] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Apart from promotion, tuples can have one of three different kinds: x :: (Int, Bool) -- Regular boxed tuples f :: Int# -> (# Int#, Int# #) -- Unboxed tuples g :: (Eq a, Ord a) => a -- Constraint tuples For convenience, internally we use a single constructor for all of these, namely HsTupleTy, but keep track of the tuple kind (in the first argument to HsTupleTy, a HsTupleSort). We can tell if a tuple is unboxed while parsing, because of the #. However, with -XConstraintKinds we can only distinguish between constraint and boxed tuples during type checking, in general. Hence the four constructors of HsTupleSort: HsUnboxedTuple -> Produced by the parser HsBoxedTuple -> Certainly a boxed tuple HsConstraintTuple -> Certainly a constraint tuple HsBoxedOrConstraintTuple -> Could be a boxed or a constraint tuple. Produced by the parser only, disappears after type checking \begin{code} 
data HsTupleSort = HsUnboxedTuple
                 | HsBoxedTuple
                 | HsConstraintTuple
                 | HsBoxedOrConstraintTuple
                 deriving (Data, Typeable)

data HsExplicitFlag = Explicit | Implicit deriving (Data, Typeable)

data ConDeclField name	-- Record fields have Haddoc docs on them
  = ConDeclField { cd_fld_name :: Located name,
		   cd_fld_type :: LBangType name, 
		   cd_fld_doc  :: Maybe LHsDocString }
  deriving (Data, Typeable)

-----------------------
-- Combine adjacent for-alls. 
-- The following awkward situation can happen otherwise:
--	f :: forall a. ((Num a) => Int)
-- might generate HsForAll (Just [a]) [] (HsForAll Nothing [Num a] t)
-- Then a isn't discovered as ambiguous, and we abstract the AbsBinds wrt []
-- but the export list abstracts f wrt [a].  Disaster.
--
-- A valid type must have one for-all at the top of the type, or of the fn arg types

mkImplicitHsForAllTy ::                        LHsContext name -> LHsType name -> HsType name
mkExplicitHsForAllTy :: [LHsTyVarBndr name] -> LHsContext name -> LHsType name -> HsType name
mkImplicitHsForAllTy     ctxt ty = mkHsForAllTy Implicit [] ctxt ty
mkExplicitHsForAllTy tvs ctxt ty = mkHsForAllTy Explicit tvs ctxt ty

mkHsForAllTy :: HsExplicitFlag -> [LHsTyVarBndr name] -> LHsContext name -> LHsType name -> HsType name
-- Smart constructor for HsForAllTy
mkHsForAllTy exp tvs (L _ []) ty = mk_forall_ty exp tvs ty
mkHsForAllTy exp tvs ctxt ty = HsForAllTy exp tvs ctxt ty

-- mk_forall_ty makes a pure for-all type (no context)
mk_forall_ty :: HsExplicitFlag -> [LHsTyVarBndr name] -> LHsType name -> HsType name
mk_forall_ty exp  tvs  (L _ (HsParTy ty))		    = mk_forall_ty exp tvs ty
mk_forall_ty exp1 tvs1 (L _ (HsForAllTy exp2 tvs2 ctxt ty)) = mkHsForAllTy (exp1 `plus` exp2) (tvs1 ++ tvs2) ctxt ty
mk_forall_ty exp  tvs  ty			            = HsForAllTy exp tvs (noLoc []) ty
	-- Even if tvs is empty, we still make a HsForAll!
	-- In the Implicit case, this signals the place to do implicit quantification
	-- In the Explicit case, it prevents implicit quantification	
	--	(see the sigtype production in Parser.y.pp)
	-- 	so that (forall. ty) isn't implicitly quantified

plus :: HsExplicitFlag -> HsExplicitFlag -> HsExplicitFlag
Implicit `plus` Implicit = Implicit
_        `plus` _        = Explicit

hsExplicitTvs :: LHsType name -> [name]
-- The explicitly-given forall'd type variables of a HsType
hsExplicitTvs (L _ (HsForAllTy Explicit tvs _ _)) = hsLTyVarNames tvs
hsExplicitTvs _                                   = []

---------------------
type LHsTyVarBndr name = Located (HsTyVarBndr name)

data HsTyVarBndr name
  = UserTyVar		-- No explicit kinding
         name 		-- See Note [Printing KindedTyVars]
         PostTcKind

  | KindedTyVar
         name
         (LHsKind name)	-- The user-supplied kind signature
         PostTcKind
      --  *** NOTA BENE *** A "monotype" in a pragma can have
      -- for-alls in it, (mostly to do with dictionaries).  These
      -- must be explicitly Kinded.
  deriving (Data, Typeable)

hsTyVarName :: HsTyVarBndr name -> name
hsTyVarName (UserTyVar n _)   = n
hsTyVarName (KindedTyVar n _ _) = n

hsTyVarKind :: HsTyVarBndr name -> Kind
hsTyVarKind (UserTyVar _ k)   = k
hsTyVarKind (KindedTyVar _ _ k) = k

hsLTyVarKind :: LHsTyVarBndr name -> Kind
hsLTyVarKind  = hsTyVarKind . unLoc

hsTyVarNameKind :: HsTyVarBndr name -> (name, Kind)
hsTyVarNameKind (UserTyVar n k)   = (n,k)
hsTyVarNameKind (KindedTyVar n _ k) = (n,k)

hsLTyVarName :: LHsTyVarBndr name -> name
hsLTyVarName = hsTyVarName . unLoc

hsTyVarNames :: [HsTyVarBndr name] -> [name]
hsTyVarNames tvs = map hsTyVarName tvs

hsLTyVarNames :: [LHsTyVarBndr name] -> [name]
hsLTyVarNames = map hsLTyVarName

hsLTyVarLocName :: LHsTyVarBndr name -> Located name
hsLTyVarLocName = fmap hsTyVarName

hsLTyVarLocNames :: [LHsTyVarBndr name] -> [Located name]
hsLTyVarLocNames = map hsLTyVarLocName

replaceTyVarName :: (Monad m) => HsTyVarBndr name1 -> name2  -- new type name
                    -> (LHsKind name1 -> m (LHsKind name2))  -- kind renaming
                    -> m (HsTyVarBndr name2)
replaceTyVarName (UserTyVar _ k) n' _ = return $ UserTyVar n' k
replaceTyVarName (KindedTyVar _ k tck) n' rn = do
  k' <- rn k
  return $ KindedTyVar n' k' tck

replaceLTyVarName :: (Monad m) => LHsTyVarBndr name1 -> name2
                  -> (LHsKind name1 -> m (LHsKind name2))
                  -> m (LHsTyVarBndr name2)
replaceLTyVarName (L loc n1) n2 rn = replaceTyVarName n1 n2 rn >>= return . L loc
\end{code} \begin{code} 
splitHsAppTys :: LHsType n -> [LHsType n] -> (LHsType n, [LHsType n])
splitHsAppTys (L _ (HsAppTy f a)) as = splitHsAppTys f (a:as)
splitHsAppTys f          	  as = (f,as)

mkHsAppTys :: OutputableBndr n => LHsType n -> [LHsType n] -> HsType n
mkHsAppTys fun_ty [] = pprPanic "mkHsAppTys" (ppr fun_ty)
mkHsAppTys fun_ty (arg_ty:arg_tys)
  = foldl mk_app (HsAppTy fun_ty arg_ty) arg_tys
  where
    mk_app fun arg = HsAppTy (noLoc fun) arg	
       -- Add noLocs for inner nodes of the application; 
       -- they are never used 

splitHsInstDeclTy_maybe :: HsType name 
                        -> Maybe ([LHsTyVarBndr name], HsContext name, name, [LHsType name])
splitHsInstDeclTy_maybe ty
  = fmap (\(tvs, cxt, L _ n, tys) -> (tvs, cxt, n, tys)) $ splitLHsInstDeclTy_maybe (noLoc ty)

splitLHsInstDeclTy_maybe
    :: LHsType name 
    -> Maybe ([LHsTyVarBndr name], HsContext name, Located name, [LHsType name])
	-- Split up an instance decl type, returning the pieces
splitLHsInstDeclTy_maybe inst_ty = do
    let (tvs, cxt, ty) = splitLHsForAllTy inst_ty
    (cls, tys) <- splitLHsClassTy_maybe ty
    return (tvs, cxt, cls, tys)

splitHsForAllTy :: HsType name -> ([LHsTyVarBndr name], HsContext name, HsType name)
splitHsForAllTy ty = case splitLHsForAllTy (noLoc ty) of (tvs, cxt, L _ ty) -> (tvs, cxt, ty)

splitLHsForAllTy
    :: LHsType name 
    -> ([LHsTyVarBndr name], HsContext name, LHsType name)
splitLHsForAllTy poly_ty
  = case unLoc poly_ty of
        HsParTy ty              -> splitLHsForAllTy ty
        HsForAllTy _ tvs cxt ty -> (tvs, unLoc cxt, ty)
        _                       -> ([], [], poly_ty)
        -- The type vars should have been computed by now, even if they were implicit

splitHsClassTy_maybe :: HsType name -> Maybe (name, [LHsType name])
splitHsClassTy_maybe ty = fmap (\(L _ n, tys) -> (n, tys)) $ splitLHsClassTy_maybe (noLoc ty)

splitLHsClassTy_maybe :: LHsType name -> Maybe (Located name, [LHsType name])
--- Watch out.. in ...deriving( Show )... we use this on 
--- the list of partially applied predicates in the deriving,
--- so there can be zero args.

-- In TcDeriv we also use this to figure out what data type is being
-- mentioned in a deriving (Generic (Foo bar baz)) declaration (i.e. "Foo").
splitLHsClassTy_maybe ty
  = checkl ty []
  where
    checkl (L l ty) args = case ty of
        HsTyVar t          -> Just (L l t, args)
        HsAppTy l r        -> checkl l (r:args)
        HsOpTy l (_, tc) r -> checkl (fmap HsTyVar tc) (l:r:args)
        HsParTy t          -> checkl t args
        HsKindSig ty _     -> checkl ty args
        _                  -> Nothing

-- Splits HsType into the (init, last) parts
-- Breaks up any parens in the result type: 
--	splitHsFunType (a -> (b -> c)) = ([a,b], c)
splitHsFunType :: LHsType name -> ([LHsType name], LHsType name)
splitHsFunType (L _ (HsFunTy x y)) = (x:args, res)
  where
  (args, res) = splitHsFunType y
splitHsFunType (L _ (HsParTy ty))  = splitHsFunType ty
splitHsFunType other 	   	   = ([], other)
\end{code} %************************************************************************ %* * \subsection{Pretty printing} %* * %************************************************************************ \begin{code} 
instance (OutputableBndr name) => Outputable (HsType name) where
    ppr ty = pprHsType ty

instance (OutputableBndr name) => Outputable (HsTyVarBndr name) where
    ppr (UserTyVar name _)      = ppr name
    ppr (KindedTyVar name kind _) = parens $ hsep [ppr name, dcolon, ppr kind]

pprHsForAll :: OutputableBndr name => HsExplicitFlag -> [LHsTyVarBndr name] ->  LHsContext name -> SDoc
pprHsForAll exp tvs cxt 
  | show_forall = forall_part <+> pprHsContext (unLoc cxt)
  | otherwise   = pprHsContext (unLoc cxt)
  where
    show_forall =  opt_PprStyle_Debug
		|| (not (null tvs) && is_explicit)
    is_explicit = case exp of {Explicit -> True; Implicit -> False}
    forall_part = ptext (sLit "forall") <+> interppSP tvs <> dot

pprHsContext :: (OutputableBndr name) => HsContext name -> SDoc
pprHsContext []	        = empty
pprHsContext [L _ pred] = ppr pred <+> darrow
pprHsContext cxt        = ppr_hs_context cxt <+> darrow

ppr_hs_context :: (OutputableBndr name) => HsContext name -> SDoc
ppr_hs_context []  = empty
ppr_hs_context cxt = parens (interpp'SP cxt)

pprConDeclFields :: OutputableBndr name => [ConDeclField name] -> SDoc
pprConDeclFields fields = braces (sep (punctuate comma (map ppr_fld fields)))
  where
    ppr_fld (ConDeclField { cd_fld_name = n, cd_fld_type = ty, 
			    cd_fld_doc = doc })
  	= ppr n <+> dcolon <+> ppr ty <+> ppr_mbDoc doc
\end{code} Note [Printing KindedTyVars] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Trac #3830 reminded me that we should really only print the kind signature on a KindedTyVar if the kind signature was put there by the programmer. During kind inference GHC now adds a PostTcKind to UserTyVars, rather than converting to KindedTyVars as before. (As it happens, the message in #3830 comes out a different way now, and the problem doesn't show up; but having the flag on a KindedTyVar seems like the Right Thing anyway.) \begin{code} 
pREC_TOP, pREC_FUN, pREC_OP, pREC_CON :: Int
pREC_TOP = 0  -- type   in ParseIface.y
pREC_FUN = 1  -- btype  in ParseIface.y
              -- Used for LH arg of (->)
pREC_OP  = 2  -- Used for arg of any infix operator
              -- (we don't keep their fixities around)
pREC_CON = 3  -- Used for arg of type applicn:
              -- always parenthesise unless atomic

maybeParen :: Int 	-- Precedence of context
	   -> Int	-- Precedence of top-level operator
	   -> SDoc -> SDoc	-- Wrap in parens if (ctxt >= op)
maybeParen ctxt_prec op_prec p | ctxt_prec >= op_prec = parens p
			       | otherwise	      = p
	
-- printing works more-or-less as for Types

pprHsType, pprParendHsType :: (OutputableBndr name) => HsType name -> SDoc

pprHsType ty       = getPprStyle $ \sty -> ppr_mono_ty pREC_TOP (prepare sty ty)
pprParendHsType ty = ppr_mono_ty pREC_CON ty

-- Before printing a type
-- (a) Remove outermost HsParTy parens
-- (b) Drop top-level for-all type variables in user style
--     since they are implicit in Haskell
prepare :: PprStyle -> HsType name -> HsType name
prepare sty (HsParTy ty)	  = prepare sty (unLoc ty)
prepare _   ty                    = ty

ppr_mono_lty :: (OutputableBndr name) => Int -> LHsType name -> SDoc
ppr_mono_lty ctxt_prec ty = ppr_mono_ty ctxt_prec (unLoc ty)

ppr_mono_ty :: (OutputableBndr name) => Int -> HsType name -> SDoc
ppr_mono_ty ctxt_prec (HsForAllTy exp tvs ctxt ty)
  = maybeParen ctxt_prec pREC_FUN $
    sep [pprHsForAll exp tvs ctxt, ppr_mono_lty pREC_TOP ty]

ppr_mono_ty _    (HsBangTy b ty)     = ppr b <> ppr ty
ppr_mono_ty _    (HsQuasiQuoteTy qq) = ppr qq
ppr_mono_ty _    (HsRecTy flds)      = pprConDeclFields flds
ppr_mono_ty _    (HsTyVar name)      = ppr name
ppr_mono_ty prec (HsFunTy ty1 ty2)   = ppr_fun_ty prec ty1 ty2
ppr_mono_ty _    (HsTupleTy con tys) = tupleParens std_con (interpp'SP tys)
  where std_con = case con of
                    HsUnboxedTuple -> UnboxedTuple
                    _              -> BoxedTuple
ppr_mono_ty _    (HsKindSig ty kind) = parens (ppr_mono_lty pREC_TOP ty <+> dcolon <+> ppr kind)
ppr_mono_ty _    (HsListTy ty)	     = brackets (ppr_mono_lty pREC_TOP ty)
ppr_mono_ty _    (HsPArrTy ty)	     = pabrackets (ppr_mono_lty pREC_TOP ty)
ppr_mono_ty prec (HsIParamTy n ty)   = maybeParen prec pREC_FUN (ppr n <+> dcolon <+> ppr_mono_lty pREC_TOP ty)
ppr_mono_ty _    (HsSpliceTy s _ _)  = pprSplice s
ppr_mono_ty _    (HsCoreTy ty)       = ppr ty
ppr_mono_ty _    (HsExplicitListTy _ tys) = quote $ brackets (interpp'SP tys)
ppr_mono_ty _    (HsExplicitTupleTy _ tys) = quote $ parens (interpp'SP tys)

ppr_mono_ty ctxt_prec (HsWrapTy (WpKiApps _kis) ty)
  = ppr_mono_ty ctxt_prec ty
-- We are not printing kind applications. If we wanted to do so, we should do
-- something like this:
{-
  = go ctxt_prec kis ty
  where
    go ctxt_prec [] ty = ppr_mono_ty ctxt_prec ty
    go ctxt_prec (ki:kis) ty
      = maybeParen ctxt_prec pREC_CON $
        hsep [ go pREC_FUN kis ty
             , ptext (sLit "@") <> pprParendKind ki ]
-}

ppr_mono_ty ctxt_prec (HsEqTy ty1 ty2)
  = maybeParen ctxt_prec pREC_OP $
    ppr_mono_lty pREC_OP ty1 <+> char '~' <+> ppr_mono_lty pREC_OP ty2

ppr_mono_ty ctxt_prec (HsAppTy fun_ty arg_ty)
  = maybeParen ctxt_prec pREC_CON $
    hsep [ppr_mono_lty pREC_FUN fun_ty, ppr_mono_lty pREC_CON arg_ty]

ppr_mono_ty ctxt_prec (HsOpTy ty1 (wrapper, op) ty2)
  = maybeParen ctxt_prec pREC_OP $
    ppr_mono_lty pREC_OP ty1 <+> ppr_mono_ty pREC_CON (HsWrapTy wrapper (HsTyVar (unLoc op))) <+> ppr_mono_lty pREC_OP ty2

ppr_mono_ty _         (HsParTy ty)
  = parens (ppr_mono_lty pREC_TOP ty)
  -- Put the parens in where the user did
  -- But we still use the precedence stuff to add parens because
  --	toHsType doesn't put in any HsParTys, so we may still need them

ppr_mono_ty ctxt_prec (HsDocTy ty doc) 
  = maybeParen ctxt_prec pREC_OP $
    ppr_mono_lty pREC_OP ty <+> ppr (unLoc doc)
  -- we pretty print Haddock comments on types as if they were
  -- postfix operators

--------------------------
ppr_fun_ty :: (OutputableBndr name) => Int -> LHsType name -> LHsType name -> SDoc
ppr_fun_ty ctxt_prec ty1 ty2
  = let p1 = ppr_mono_lty pREC_FUN ty1
	p2 = ppr_mono_lty pREC_TOP ty2
    in
    maybeParen ctxt_prec pREC_FUN $
    sep [p1, ptext (sLit "->") <+> p2]

--------------------------
pabrackets :: SDoc -> SDoc
pabrackets p = ptext (sLit "[:") <> p <> ptext (sLit ":]")
\end{code}