hsSyn/HsTypes.hs

    {-
    (c) The University of Glasgow 2006
    (c) The GRASP/AQUA Project, Glasgow University, 1992-1998

    HsTypes: Abstract syntax: user-defined types
    -}

    {-# LANGUAGE DeriveDataTypeable #-}
    {-# LANGUAGE FlexibleContexts #-}
    {-# LANGUAGE FlexibleInstances #-}
    {-# LANGUAGE StandaloneDeriving #-}
    {-# LANGUAGE TypeSynonymInstances #-}
    {-# LANGUAGE UndecidableInstances #-} -- Note [Pass sensitive types]
                                          -- in module PlaceHolder
    {-# LANGUAGE ConstraintKinds #-}
    {-# LANGUAGE CPP #-}

    module HsTypes (
            HsType(..), LHsType, HsKind, LHsKind,
            HsTyVarBndr(..), LHsTyVarBndr,
            LHsQTyVars(..),
            HsImplicitBndrs(..),
            HsWildCardBndrs(..),
            LHsSigType, LHsSigWcType, LHsWcType,
            HsTupleSort(..),
            Promoted(..),
            HsContext, LHsContext,
            HsTyLit(..),
            HsIPName(..), hsIPNameFS,
            HsAppType(..),LHsAppType,

            LBangType, BangType,
            HsSrcBang(..), HsImplBang(..),
            SrcStrictness(..), SrcUnpackedness(..),
            getBangType, getBangStrictness,

            ConDeclField(..), LConDeclField, pprConDeclFields, updateGadtResult,

            HsConDetails(..),

            FieldOcc(..), LFieldOcc, mkFieldOcc,
            AmbiguousFieldOcc(..), mkAmbiguousFieldOcc,
            rdrNameAmbiguousFieldOcc, selectorAmbiguousFieldOcc,
            unambiguousFieldOcc, ambiguousFieldOcc,

            HsWildCardInfo(..), mkAnonWildCardTy,
            wildCardName, sameWildCard,

            mkHsImplicitBndrs, mkHsWildCardBndrs, hsImplicitBody,
            mkEmptyImplicitBndrs, mkEmptyWildCardBndrs,
            mkHsQTvs, hsQTvExplicit, emptyLHsQTvs, isEmptyLHsQTvs,
            isHsKindedTyVar, hsTvbAllKinded,
            hsScopedTvs, hsWcScopedTvs, dropWildCards,
            hsTyVarName, hsAllLTyVarNames, hsLTyVarLocNames,
            hsLTyVarName, hsLTyVarLocName, hsExplicitLTyVarNames,
            splitLHsInstDeclTy, getLHsInstDeclHead, getLHsInstDeclClass_maybe,
            splitLHsPatSynTy,
            splitLHsForAllTy, splitLHsQualTy, splitLHsSigmaTy,
            splitHsFunType, splitHsAppsTy,
            splitHsAppTys, getAppsTyHead_maybe, hsTyGetAppHead_maybe,
            mkHsOpTy, mkHsAppTy, mkHsAppTys,
            ignoreParens, hsSigType, hsSigWcType,
            hsLTyVarBndrToType, hsLTyVarBndrsToTypes,

            -- Printing
            pprParendHsType, pprHsForAll, pprHsForAllTvs, pprHsForAllExtra,
            pprHsContext, pprHsContextNoArrow, pprHsContextMaybe
        ) where

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

    import PlaceHolder ( PostTc,PostRn,DataId,PlaceHolder(..),
                         OutputableBndrId )

    import Id ( Id )
    import Name( Name )
    import RdrName ( RdrName )
    import NameSet ( NameSet, emptyNameSet )
    import DataCon( HsSrcBang(..), HsImplBang(..),
                    SrcStrictness(..), SrcUnpackedness(..) )
    import TysPrim( funTyConName )
    import Type
    import HsDoc
    import BasicTypes
    import SrcLoc
    import Outputable
    import FastString
    import Maybes( isJust )

    import Data.Data hiding ( Fixity, Prefix, Infix )
    import Data.Maybe ( fromMaybe )
    import Control.Monad ( unless )

    {-
    ************************************************************************
    *                                                                      *
    \subsection{Bang annotations}
    *                                                                      *
    ************************************************************************
    -}

    -- | Located Bang Type
    type LBangType name = Located (BangType name)

    -- | Bang Type
    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 -> HsSrcBang
    getBangStrictness (L _ (HsBangTy s _)) = s
    getBangStrictness _ = (HsSrcBang NoSourceText NoSrcUnpack NoSrcStrict)

    {-
    ************************************************************************
    *                                                                      *
    \subsection{Data types}
    *                                                                      *
    ************************************************************************

    This is the syntax for types as seen in type signatures.

    Note [HsBSig binder lists]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~
    Consider a binder (or pattern) decorated with a type or kind,
       \ (x :: a -> a). blah
       forall (a :: k -> *) (b :: k). blah
    Then we use a LHsBndrSig on the binder, so that the
    renamer can decorate it with the variables bound
    by the pattern ('a' in the first example, 'k' in the second),
    assuming that neither of them is in scope already
    See also Note [Kind and type-variable binders] in RnTypes

    Note [HsType binders]
    ~~~~~~~~~~~~~~~~~~~~~
    The system for recording type and kind-variable binders in HsTypes
    is a bit complicated.  Here's how it works.

    * In a HsType,
         HsForAllTy   represents an /explicit, user-written/ 'forall'
                       e.g.   forall a b. ...
         HsQualTy     represents an /explicit, user-written/ context
                       e.g.   (Eq a, Show a) => ...
                      The context can be empty if that's what the user wrote
      These constructors represent what the user wrote, no more
      and no less.

    * HsTyVarBndr describes a quantified type variable written by the
      user.  For example
         f :: forall a (b :: *).  blah
      here 'a' and '(b::*)' are each a HsTyVarBndr.  A HsForAllTy has
      a list of LHsTyVarBndrs.

    * HsImplicitBndrs is a wrapper that gives the implicitly-quantified
      kind and type variables of the wrapped thing.  It is filled in by
      the renamer. For example, if the user writes
         f :: a -> a
      the HsImplicitBinders binds the 'a' (not a HsForAllTy!).
      NB: this implicit quantification is purely lexical: we bind any
          type or kind variables that are not in scope. The type checker
          may subsequently quantify over further kind variables.

    * HsWildCardBndrs is a wrapper that binds the wildcard variables
      of the wrapped thing.  It is filled in by the renamer
         f :: _a -> _
      The enclosing HsWildCardBndrs binds the wildcards _a and _.

    * The explicit presence of these wrappers specifies, in the HsSyn,
      exactly where implicit quantification is allowed, and where
      wildcards are allowed.

    * LHsQTyVars is used in data/class declarations, where the user gives
      explicit *type* variable bindings, but we need to implicitly bind
      *kind* variables.  For example
          class C (a :: k -> *) where ...
      The 'k' is implicitly bound in the hsq_tvs field of LHsQTyVars

    Note [The wildcard story for types]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Types can have wildcards in them, to support partial type signatures,
    like       f :: Int -> (_ , _a) -> _a

    A wildcard in a type can be

      * An anonymous wildcard,
            written '_'
        In HsType this is represented by HsWildCardTy.
        After the renamer, this contains a Name which uniquely
        identifies this particular occurrence.

      * A named wildcard,
            written '_a', '_foo', etc
        In HsType this is represented by (HsTyVar "_a")
        i.e. a perfectly ordinary type variable that happens
             to start with an underscore

    Note carefully:

    * When NamedWildCards is off, type variables that start with an
      underscore really /are/ ordinary type variables.  And indeed, even
      when NamedWildCards is on you can bind _a explicitly as an ordinary
      type variable:
            data T _a _b = MkT _b _a
      Or even:
            f :: forall _a. _a -> _b
      Here _a is an ordinary forall'd binder, but (With NamedWildCards)
      _b is a named wildcard.  (See the comments in Trac #10982)

    * All wildcards, whether named or anonymous, are bound by the
      HsWildCardBndrs construct, which wraps types that are allowed
      to have wildcards.

    * After type checking is done, we report what types the wildcards
      got unified with.

    -}

    -- | Located Haskell Context
    type LHsContext name = Located (HsContext name)
          -- ^ 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnUnit'

          -- For details on above see note [Api annotations] in ApiAnnotation

    -- | Haskell Context
    type HsContext name = [LHsType name]

    -- | Located Haskell Type
    type LHsType name = Located (HsType name)
          -- ^ May have 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnComma' when
          --   in a list

          -- For details on above see note [Api annotations] in ApiAnnotation

    -- | Haskell Kind
    type HsKind name = HsType name

    -- | Located Haskell Kind
    type LHsKind name = Located (HsKind name)
          -- ^ 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnDcolon'

          -- For details on above see note [Api annotations] in ApiAnnotation

    --------------------------------------------------
    --             LHsQTyVars
    --  The explicitly-quantified binders in a data/type declaration

    -- | Located Haskell Type Variable Binder
    type LHsTyVarBndr name = Located (HsTyVarBndr name)
                             -- See Note [HsType binders]

    -- | Located Haskell Quantified Type Variables
    data LHsQTyVars name   -- See Note [HsType binders]
      = HsQTvs { hsq_implicit :: PostRn name [Name]      -- implicit (dependent) variables
               , hsq_explicit :: [LHsTyVarBndr name]     -- explicit variables
                 -- See Note [HsForAllTy tyvar binders]
               , hsq_dependent :: PostRn name NameSet
                   -- which explicit vars are dependent
                   -- See Note [Dependent LHsQTyVars] in TcHsType
        }

    deriving instance (DataId name) => Data (LHsQTyVars name)

    mkHsQTvs :: [LHsTyVarBndr RdrName] -> LHsQTyVars RdrName
    mkHsQTvs tvs = HsQTvs { hsq_implicit = PlaceHolder, hsq_explicit = tvs
                          , hsq_dependent = PlaceHolder }

    hsQTvExplicit :: LHsQTyVars name -> [LHsTyVarBndr name]
    hsQTvExplicit = hsq_explicit

    emptyLHsQTvs :: LHsQTyVars Name
    emptyLHsQTvs = HsQTvs [] [] emptyNameSet

    isEmptyLHsQTvs :: LHsQTyVars Name -> Bool
    isEmptyLHsQTvs (HsQTvs [] [] _) = True
    isEmptyLHsQTvs _                = False

    ------------------------------------------------
    --            HsImplicitBndrs
    -- Used to quantify the binders of a type in cases
    -- when a HsForAll isn't appropriate:
    --    * Patterns in a type/data family instance (HsTyPats)
    --    * Type of a rule binder (RuleBndr)
    --    * Pattern type signatures (SigPatIn)
    -- In the last of these, wildcards can happen, so we must accommodate them

    -- | Haskell Implicit Binders
    data HsImplicitBndrs name thing   -- See Note [HsType binders]
      = HsIB { hsib_vars :: PostRn name [Name] -- Implicitly-bound kind & type vars
             , hsib_body :: thing              -- Main payload (type or list of types)
             , hsib_closed :: PostRn name Bool -- Taking the hsib_vars into account,
                                               -- is the payload closed? Used in
                                               -- TcHsType.decideKindGeneralisationPlan
        }

    -- | Haskell Wildcard Binders
    data HsWildCardBndrs name thing
        -- See Note [HsType binders]
        -- See Note [The wildcard story for types]
      = HsWC { hswc_wcs :: PostRn name [Name]
                    -- Wild cards, both named and anonymous
                    -- after the renamer

             , hswc_body :: thing
                    -- Main payload (type or list of types)
                    -- If there is an extra-constraints wildcard,
                    -- it's still there in the hsc_body.
        }

    deriving instance (Data name, Data thing, Data (PostRn name [Name]), Data (PostRn name Bool))
      => Data (HsImplicitBndrs name thing)

    deriving instance (Data name, Data thing, Data (PostRn name [Name]))
      => Data (HsWildCardBndrs name thing)

    -- | Located Haskell Signature Type
    type LHsSigType   name = HsImplicitBndrs name (LHsType name)    -- Implicit only

    -- | Located Haskell Wildcard Type
    type LHsWcType    name = HsWildCardBndrs name (LHsType name)    -- Wildcard only

    -- | Located Haskell Signature Wildcard Type
    type LHsSigWcType name = HsWildCardBndrs name (LHsSigType name) -- Both

    -- See Note [Representing type signatures]

    hsImplicitBody :: HsImplicitBndrs name thing -> thing
    hsImplicitBody (HsIB { hsib_body = body }) = body

    hsSigType :: LHsSigType name -> LHsType name
    hsSigType = hsImplicitBody

    hsSigWcType :: LHsSigWcType name -> LHsType name
    hsSigWcType sig_ty = hsib_body (hswc_body sig_ty)

    dropWildCards :: LHsSigWcType name -> LHsSigType name
    -- Drop the wildcard part of a LHsSigWcType
    dropWildCards sig_ty = hswc_body sig_ty

    {- Note [Representing type signatures]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    HsSigType is used to represent an explicit user type signature
    such as   f :: a -> a
         or   g (x :: a -> a) = x

    A HsSigType is just a HsImplicitBndrs wrapping a LHsType.
     * The HsImplicitBndrs binds the /implicitly/ quantified tyvars
     * The LHsType binds the /explicitly/ quantified tyvars

    E.g. For a signature like
       f :: forall (a::k). blah
    we get
       HsIB { hsib_vars = [k]
            , hsib_body = HsForAllTy { hst_bndrs = [(a::*)]
                                     , hst_body = blah }
    The implicit kind variable 'k' is bound by the HsIB;
    the explicitly forall'd tyvar 'a' is bound by the HsForAllTy
    -}

    mkHsImplicitBndrs :: thing -> HsImplicitBndrs RdrName thing
    mkHsImplicitBndrs x = HsIB { hsib_body   = x
                               , hsib_vars   = PlaceHolder
                               , hsib_closed = PlaceHolder }

    mkHsWildCardBndrs :: thing -> HsWildCardBndrs RdrName thing
    mkHsWildCardBndrs x = HsWC { hswc_body = x
                               , hswc_wcs  = PlaceHolder }

    -- Add empty binders.  This is a bit suspicious; what if
    -- the wrapped thing had free type variables?
    mkEmptyImplicitBndrs :: thing -> HsImplicitBndrs Name thing
    mkEmptyImplicitBndrs x = HsIB { hsib_body   = x
                                  , hsib_vars   = []
                                  , hsib_closed = False }

    mkEmptyWildCardBndrs :: thing -> HsWildCardBndrs Name thing
    mkEmptyWildCardBndrs x = HsWC { hswc_body = x
                                  , hswc_wcs  = [] }

    --------------------------------------------------
    -- | These names are used early on to store the names of implicit
    -- parameters.  They completely disappear after type-checking.
    newtype HsIPName = HsIPName FastString
      deriving( Eq, Data )

    hsIPNameFS :: HsIPName -> FastString
    hsIPNameFS (HsIPName n) = n

    instance Outputable HsIPName where
        ppr (HsIPName n) = char '?' <> ftext n -- Ordinary implicit parameters

    instance OutputableBndr HsIPName where
        pprBndr _ n   = ppr n         -- Simple for now
        pprInfixOcc  n = ppr n
        pprPrefixOcc n = ppr n

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

    -- | Haskell Type Variable Binder
    data HsTyVarBndr name
      = UserTyVar        -- no explicit kinding
             (Located name)
            -- See Note [Located RdrNames] in HsExpr
      | KindedTyVar
             (Located name)
             (LHsKind name)  -- The user-supplied kind signature
            -- ^
            --  - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnOpen',
            --          'ApiAnnotation.AnnDcolon', 'ApiAnnotation.AnnClose'

            -- For details on above see note [Api annotations] in ApiAnnotation
    deriving instance (DataId name) => Data (HsTyVarBndr name)

    -- | Does this 'HsTyVarBndr' come with an explicit kind annotation?
    isHsKindedTyVar :: HsTyVarBndr name -> Bool
    isHsKindedTyVar (UserTyVar {})   = False
    isHsKindedTyVar (KindedTyVar {}) = True

    -- | Do all type variables in this 'LHsQTyVars' come with kind annotations?
    hsTvbAllKinded :: LHsQTyVars name -> Bool
    hsTvbAllKinded = all (isHsKindedTyVar . unLoc) . hsQTvExplicit

    -- | Haskell Type
    data HsType name
      = HsForAllTy   -- See Note [HsType binders]
          { hst_bndrs :: [LHsTyVarBndr name]   -- Explicit, user-supplied 'forall a b c'
          , hst_body  :: LHsType name          -- body type
          }
          -- ^ - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnForall',
          --         'ApiAnnotation.AnnDot','ApiAnnotation.AnnDarrow'
          -- For details on above see note [Api annotations] in ApiAnnotation

      | HsQualTy   -- See Note [HsType binders]
          { hst_ctxt :: LHsContext name       -- Context C => blah
          , hst_body :: LHsType name }

      | HsTyVar             Promoted -- whether explicitly promoted, for the pretty
                                     -- printer
                            (Located name)
                      -- Type variable, type constructor, or data constructor
                      -- see Note [Promotions (HsTyVar)]
                      -- See Note [Located RdrNames] in HsExpr
          -- ^ - 'ApiAnnotation.AnnKeywordId' : None

          -- For details on above see note [Api annotations] in ApiAnnotation

      | HsAppsTy            [LHsAppType name] -- Used only before renaming,
                                              -- Note [HsAppsTy]
          -- ^ - 'ApiAnnotation.AnnKeywordId' : None

      | HsAppTy             (LHsType name)
                            (LHsType name)
          -- ^ - 'ApiAnnotation.AnnKeywordId' : None

          -- For details on above see note [Api annotations] in ApiAnnotation

      | HsFunTy             (LHsType name)   -- function type
                            (LHsType name)
          -- ^ - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnRarrow',

          -- For details on above see note [Api annotations] in ApiAnnotation

      | HsListTy            (LHsType name)  -- Element type
          -- ^ - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnOpen' @'['@,
          --         'ApiAnnotation.AnnClose' @']'@

          -- For details on above see note [Api annotations] in ApiAnnotation

      | HsPArrTy            (LHsType name)  -- Elem. type of parallel array: [:t:]
          -- ^ - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnOpen' @'[:'@,
          --         'ApiAnnotation.AnnClose' @':]'@

          -- For details on above see note [Api annotations] in ApiAnnotation

      | HsTupleTy           HsTupleSort
                            [LHsType name]  -- Element types (length gives arity)
        -- ^ - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnOpen' @'(' or '(#'@,
        --         'ApiAnnotation.AnnClose' @')' or '#)'@

        -- For details on above see note [Api annotations] in ApiAnnotation

      | HsSumTy             [LHsType name]  -- Element types (length gives arity)
        -- ^ - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnOpen' @'(#'@,
        --         'ApiAnnotation.AnnClose' '#)'@

        -- For details on above see note [Api annotations] in ApiAnnotation

      | HsOpTy              (LHsType name) (Located name) (LHsType name)
          -- ^ - 'ApiAnnotation.AnnKeywordId' : None

          -- For details on above see note [Api annotations] in ApiAnnotation

      | 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!
          -- ^ - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnOpen' @'('@,
          --         'ApiAnnotation.AnnClose' @')'@

          -- For details on above see note [Api annotations] in ApiAnnotation

      | HsIParamTy          (Located HsIPName) -- (?x :: ty)
                            (LHsType name)   -- Implicit parameters as they occur in contexts
          -- ^
          -- > (?x :: ty)
          --
          -- - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnDcolon'

          -- For details on above see note [Api annotations] in ApiAnnotation

      | HsEqTy              (LHsType name)   -- ty1 ~ ty2
                            (LHsType name)   -- Always allowed even without TypeOperators, and has special kinding rule
          -- ^
          -- > ty1 ~ ty2
          --
          -- - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnTilde'

          -- For details on above see note [Api annotations] in ApiAnnotation

      | HsKindSig           (LHsType name)  -- (ty :: kind)
                            (LHsKind name)  -- A type with a kind signature
          -- ^
          -- > (ty :: kind)
          --
          -- - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnOpen' @'('@,
          --         'ApiAnnotation.AnnDcolon','ApiAnnotation.AnnClose' @')'@

          -- For details on above see note [Api annotations] in ApiAnnotation

      | HsSpliceTy          (HsSplice name)   -- Includes quasi-quotes
                            (PostTc name Kind)
          -- ^ - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnOpen' @'$('@,
          --         'ApiAnnotation.AnnClose' @')'@

          -- For details on above see note [Api annotations] in ApiAnnotation

      | HsDocTy             (LHsType name) LHsDocString -- A documented type
          -- ^ - 'ApiAnnotation.AnnKeywordId' : None

          -- For details on above see note [Api annotations] in ApiAnnotation

      | HsBangTy    HsSrcBang (LHsType name)   -- Bang-style type annotations
          -- ^ - 'ApiAnnotation.AnnKeywordId' :
          --         'ApiAnnotation.AnnOpen' @'{-\# UNPACK' or '{-\# NOUNPACK'@,
          --         'ApiAnnotation.AnnClose' @'#-}'@
          --         'ApiAnnotation.AnnBang' @\'!\'@

          -- For details on above see note [Api annotations] in ApiAnnotation

      | HsRecTy     [LConDeclField name]    -- Only in data type declarations
          -- ^ - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnOpen' @'{'@,
          --         'ApiAnnotation.AnnClose' @'}'@

          -- For details on above see note [Api annotations] in ApiAnnotation

      | HsCoreTy Type       -- An escape hatch for tunnelling a *closed*
                            -- Core Type through HsSyn.
          -- ^ - 'ApiAnnotation.AnnKeywordId' : None

          -- For details on above see note [Api annotations] in ApiAnnotation

      | HsExplicitListTy       -- A promoted explicit list
            Promoted           -- whether explcitly promoted, for pretty printer
            (PostTc name Kind) -- See Note [Promoted lists and tuples]
            [LHsType name]
          -- ^ - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnOpen' @"'["@,
          --         'ApiAnnotation.AnnClose' @']'@

          -- For details on above see note [Api annotations] in ApiAnnotation

      | HsExplicitTupleTy      -- A promoted explicit tuple
            [PostTc name Kind] -- See Note [Promoted lists and tuples]
            [LHsType name]
          -- ^ - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnOpen' @"'("@,
          --         'ApiAnnotation.AnnClose' @')'@

          -- For details on above see note [Api annotations] in ApiAnnotation

      | HsTyLit HsTyLit      -- A promoted numeric literal.
          -- ^ - 'ApiAnnotation.AnnKeywordId' : None

          -- For details on above see note [Api annotations] in ApiAnnotation

      | HsWildCardTy (HsWildCardInfo name)  -- A type wildcard
          -- See Note [The wildcard story for types]
          -- ^ - 'ApiAnnotation.AnnKeywordId' : None

          -- For details on above see note [Api annotations] in ApiAnnotation
    deriving instance (DataId name) => Data (HsType name)

    -- Note [Literal source text] in BasicTypes for SourceText fields in
    -- the following
    -- | Haskell Type Literal
    data HsTyLit
      = HsNumTy SourceText Integer
      | HsStrTy SourceText FastString
        deriving Data

    newtype HsWildCardInfo name      -- See Note [The wildcard story for types]
        = AnonWildCard (PostRn name (Located Name))
          -- A anonymous wild card ('_'). A fresh Name is generated for
          -- each individual anonymous wildcard during renaming
    deriving instance (DataId name) => Data (HsWildCardInfo name)

    -- | Located Haskell Application Type
    type LHsAppType name = Located (HsAppType name)
          -- ^ 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnSimpleQuote'

    -- | Haskell Application Type
    data HsAppType name
      = HsAppInfix (Located name)       -- either a symbol or an id in backticks
      | HsAppPrefix (LHsType name)      -- anything else, including things like (+)
    deriving instance (DataId name) => Data (HsAppType name)

    instance (OutputableBndrId name) => Outputable (HsAppType name) where
      ppr = ppr_app_ty TopPrec

    {-
    Note [HsForAllTy tyvar binders]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    After parsing:
      * Implicit => empty
        Explicit => the variables the user wrote

    After renaming
      * Implicit => the *type* variables free in the type
        Explicit => the variables the user wrote (renamed)

    Qualified currently behaves exactly as Implicit,
    but it is deprecated to use it for implicit quantification.
    In this case, GHC 7.10 gives a warning; see
    Note [Context quantification] in RnTypes, and Trac #4426.
    In GHC 8.0, Qualified will no longer bind variables
    and this will become an error.

    The kind variables bound in the hsq_implicit field come both
      a) from the kind signatures on the kind vars (eg k1)
      b) from the scope of the forall (eg k2)
    Example:   f :: forall (a::k1) b. T a (b::k2)

    Note [Unit tuples]
    ~~~~~~~~~~~~~~~~~~
    Consider the type
        type instance F Int = ()
    We want to parse that "()"
        as HsTupleTy HsBoxedOrConstraintTuple [],
    NOT as HsTyVar unitTyCon

    Why? Because F might have kind (* -> Constraint), so we when parsing we
    don't know if that tuple is going to be a constraint tuple or an ordinary
    unit tuple.  The HsTupleSort flag is specifically designed to deal with
    that, but it has to work for unit tuples too.

    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

      The 'Promoted' field in an HsTyVar captures whether the type was promoted in
      the source code by prefixing an apostrophe.

    Note [HsAppsTy]
    ~~~~~~~~~~~~~~~
    How to parse

      Foo * Int

    ? Is it `(*) Foo Int` or `Foo GHC.Types.* Int`? There's no way to know until renaming.
    So we just take type expressions like this and put each component in a list, so be
    sorted out in the renamer. The sorting out is done by RnTypes.mkHsOpTyRn. This means
    that the parser should never produce HsAppTy or HsOpTy.

    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
    -}

    -- | Haskell Tuple Sort
    data HsTupleSort = HsUnboxedTuple
                     | HsBoxedTuple
                     | HsConstraintTuple
                     | HsBoxedOrConstraintTuple
                     deriving Data

    -- | Promoted data types.
    data Promoted = Promoted
                  | NotPromoted
                  deriving (Data, Eq, Show)

    -- | Located Constructor Declaration Field
    type LConDeclField name = Located (ConDeclField name)
          -- ^ May have 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnComma' when
          --   in a list

          -- For details on above see note [Api annotations] in ApiAnnotation

    -- | Constructor Declaration Field
    data ConDeclField name  -- Record fields have Haddoc docs on them
      = ConDeclField { cd_fld_names :: [LFieldOcc name],
                                       -- ^ See Note [ConDeclField names]
                       cd_fld_type :: LBangType name,
                       cd_fld_doc  :: Maybe LHsDocString }
          -- ^ - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnDcolon'

          -- For details on above see note [Api annotations] in ApiAnnotation
    deriving instance (DataId name) => Data (ConDeclField name)

    instance (OutputableBndrId name) => Outputable (ConDeclField name) where
      ppr (ConDeclField fld_n fld_ty _) = ppr fld_n <+> dcolon <+> ppr fld_ty

    -- HsConDetails is used for patterns/expressions *and* for data type
    -- declarations
    -- | Haskell Constructor Details
    data HsConDetails arg rec
      = PrefixCon [arg]             -- C p1 p2 p3
      | RecCon    rec               -- C { x = p1, y = p2 }
      | InfixCon  arg arg           -- p1 `C` p2
      deriving Data

    instance (Outputable arg, Outputable rec)
             => Outputable (HsConDetails arg rec) where
      ppr (PrefixCon args) = text "PrefixCon" <+> ppr args
      ppr (RecCon rec)     = text "RecCon:" <+> ppr rec
      ppr (InfixCon l r)   = text "InfixCon:" <+> ppr [l, r]

    -- Takes details and result type of a GADT data constructor as created by the
    -- parser and rejigs them using information about fixities from the renamer.
    -- See Note [Sorting out the result type] in RdrHsSyn
    updateGadtResult
      :: (Monad m)
         => (SDoc -> m ())
         -> SDoc
         -> HsConDetails (LHsType Name) (Located [LConDeclField Name])
                         -- ^ Original details
         -> LHsType Name -- ^ Original result type
         -> m (HsConDetails (LHsType Name) (Located [LConDeclField Name]),
               LHsType Name)
    updateGadtResult failWith doc details ty
      = do { let (arg_tys, res_ty) = splitHsFunType ty
                 badConSig         = text "Malformed constructor signature"
           ; case details of
               InfixCon {}  -> pprPanic "updateGadtResult" (ppr ty)

               RecCon {}    -> do { unless (null arg_tys)
                                           (failWith (doc <+> badConSig))
                                  ; return (details, res_ty) }

               PrefixCon {} -> return (PrefixCon arg_tys, res_ty)}

    {-
    Note [ConDeclField names]
    ~~~~~~~~~~~~~~~~~~~~~~~~~

    A ConDeclField contains a list of field occurrences: these always
    include the field label as the user wrote it.  After the renamer, it
    will additionally contain the identity of the selector function in the
    second component.

    Due to DuplicateRecordFields, the OccName of the selector function
    may have been mangled, which is why we keep the original field label
    separately.  For example, when DuplicateRecordFields is enabled

        data T = MkT { x :: Int }

    gives

        ConDeclField { cd_fld_names = [L _ (FieldOcc "x" $sel:x:MkT)], ... }.
    -}

    -----------------------
    -- A valid type must have a for-all at the top of the type, or of the fn arg
    -- types

    ---------------------
    hsWcScopedTvs :: LHsSigWcType Name -> [Name]
    -- Get the lexically-scoped type variables of a HsSigType
    --  - the explicitly-given forall'd type variables
    --  - the implicitly-bound kind variables
    --  - the named wildcars; see Note [Scoping of named wildcards]
    -- because they scope in the same way
    hsWcScopedTvs sig_ty
      | HsWC { hswc_wcs = nwcs, hswc_body = sig_ty1 }  <- sig_ty
      , HsIB { hsib_vars = vars, hsib_body = sig_ty2 } <- sig_ty1
      = case sig_ty2 of
          L _ (HsForAllTy { hst_bndrs = tvs }) -> vars ++ nwcs ++
                                                  map hsLTyVarName tvs
                   -- include kind variables only if the type is headed by forall
                   -- (this is consistent with GHC 7 behaviour)
          _                                    -> nwcs

    hsScopedTvs :: LHsSigType Name -> [Name]
    -- Same as hsWcScopedTvs, but for a LHsSigType
    hsScopedTvs sig_ty
      | HsIB { hsib_vars = vars,  hsib_body = sig_ty2 } <- sig_ty
      , L _ (HsForAllTy { hst_bndrs = tvs }) <- sig_ty2
      = vars ++ map hsLTyVarName tvs
      | otherwise
      = []

    {- Note [Scoping of named wildcards]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Consider
      f :: _a -> _a
      f x = let g :: _a -> _a
                g = ...
            in ...

    Currently, for better or worse, the "_a" variables are all the same. So
    although there is no explicit forall, the "_a" scopes over the definition.
    I don't know if this is a good idea, but there it is.
    -}

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

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

    hsExplicitLTyVarNames :: LHsQTyVars name -> [name]
    -- Explicit variables only
    hsExplicitLTyVarNames qtvs = map hsLTyVarName (hsQTvExplicit qtvs)

    hsAllLTyVarNames :: LHsQTyVars Name -> [Name]
    -- All variables
    hsAllLTyVarNames (HsQTvs { hsq_implicit = kvs, hsq_explicit = tvs })
      = kvs ++ map hsLTyVarName tvs

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

    hsLTyVarLocNames :: LHsQTyVars name -> [Located name]
    hsLTyVarLocNames qtvs = map hsLTyVarLocName (hsQTvExplicit qtvs)

    -- | Convert a LHsTyVarBndr to an equivalent LHsType.
    hsLTyVarBndrToType :: LHsTyVarBndr name -> LHsType name
    hsLTyVarBndrToType = fmap cvt
      where cvt (UserTyVar n) = HsTyVar NotPromoted n
            cvt (KindedTyVar (L name_loc n) kind)
              = HsKindSig (L name_loc (HsTyVar NotPromoted (L name_loc n))) kind

    -- | Convert a LHsTyVarBndrs to a list of types.
    -- Works on *type* variable only, no kind vars.
    hsLTyVarBndrsToTypes :: LHsQTyVars name -> [LHsType name]
    hsLTyVarBndrsToTypes (HsQTvs { hsq_explicit = tvbs }) = map hsLTyVarBndrToType tvbs

    ---------------------
    wildCardName :: HsWildCardInfo Name -> Name
    wildCardName (AnonWildCard  (L _ n)) = n

    -- Two wild cards are the same when they have the same location
    sameWildCard :: Located (HsWildCardInfo name)
                 -> Located (HsWildCardInfo name) -> Bool
    sameWildCard (L l1 (AnonWildCard _))   (L l2 (AnonWildCard _))   = l1 == l2

    ignoreParens :: LHsType name -> LHsType name
    ignoreParens (L _ (HsParTy ty))                      = ignoreParens ty
    ignoreParens (L _ (HsAppsTy [L _ (HsAppPrefix ty)])) = ignoreParens ty
    ignoreParens ty                                      = ty

    {-
    ************************************************************************
    *                                                                      *
                    Building types
    *                                                                      *
    ************************************************************************
    -}

    mkAnonWildCardTy :: HsType RdrName
    mkAnonWildCardTy = HsWildCardTy (AnonWildCard PlaceHolder)

    mkHsOpTy :: LHsType name -> Located name -> LHsType name -> HsType name
    mkHsOpTy ty1 op ty2 = HsOpTy ty1 op ty2

    mkHsAppTy :: LHsType name -> LHsType name -> LHsType name
    mkHsAppTy t1 t2 = addCLoc t1 t2 (HsAppTy t1 t2)

    mkHsAppTys :: LHsType name -> [LHsType name] -> LHsType name
    mkHsAppTys = foldl mkHsAppTy

    {-
    ************************************************************************
    *                                                                      *
                    Decomposing HsTypes
    *                                                                      *
    ************************************************************************
    -}

    ---------------------------------
    -- splitHsFunType decomposes a type (t1 -> t2 ... -> tn)
    -- Breaks up any parens in the result type:
    --      splitHsFunType (a -> (b -> c)) = ([a,b], c)
    -- Also deals with (->) t1 t2; that is why it only works on LHsType Name
    --   (see Trac #9096)
    splitHsFunType :: LHsType Name -> ([LHsType Name], LHsType Name)
    splitHsFunType (L _ (HsParTy ty))
      = splitHsFunType ty

    splitHsFunType (L _ (HsFunTy x y))
      | (args, res) <- splitHsFunType y
      = (x:args, res)

    splitHsFunType orig_ty@(L _ (HsAppTy t1 t2))
      = go t1 [t2]
      where  -- Look for (->) t1 t2, possibly with parenthesisation
        go (L _ (HsTyVar _ (L _ fn))) tys | fn == funTyConName
                                     , [t1,t2] <- tys
                                     , (args, res) <- splitHsFunType t2
                                     = (t1:args, res)
        go (L _ (HsAppTy t1 t2)) tys = go t1 (t2:tys)
        go (L _ (HsParTy ty))    tys = go ty tys
        go _                     _   = ([], orig_ty)  -- Failure to match

    splitHsFunType other = ([], other)

    --------------------------------
    -- | Retrieves the head of an HsAppsTy, if this can be done unambiguously,
    -- without consulting fixities.
    getAppsTyHead_maybe :: [LHsAppType name]
                        -> Maybe (LHsType name, [LHsType name], LexicalFixity)
    getAppsTyHead_maybe tys = case splitHsAppsTy tys of
      ([app1:apps], []) ->  -- no symbols, some normal types
        Just (mkHsAppTys app1 apps, [], Prefix)
      ([app1l:appsl, app1r:appsr], [L loc op]) ->  -- one operator
        Just ( L loc (HsTyVar NotPromoted (L loc op))
             , [mkHsAppTys app1l appsl, mkHsAppTys app1r appsr], Infix)
      _ -> -- can't figure it out
        Nothing

    -- | Splits a [HsAppType name] (the payload of an HsAppsTy) into regions of prefix
    -- types (normal types) and infix operators.
    -- If @splitHsAppsTy tys = (non_syms, syms)@, then @tys@ starts with the first
    -- element of @non_syms@ followed by the first element of @syms@ followed by
    -- the next element of @non_syms@, etc. It is guaranteed that the non_syms list
    -- has one more element than the syms list.
    splitHsAppsTy :: [LHsAppType name] -> ([[LHsType name]], [Located name])
    splitHsAppsTy = go [] [] []
      where
        go acc acc_non acc_sym [] = (reverse (reverse acc : acc_non), reverse acc_sym)
        go acc acc_non acc_sym (L _ (HsAppPrefix ty) : rest)
          = go (ty : acc) acc_non acc_sym rest
        go acc acc_non acc_sym (L _ (HsAppInfix op) : rest)
          = go [] (reverse acc : acc_non) (op : acc_sym) rest

    -- Retrieve the name of the "head" of a nested type application
    -- somewhat like splitHsAppTys, but a little more thorough
    -- used to examine the result of a GADT-like datacon, so it doesn't handle
    -- *all* cases (like lists, tuples, (~), etc.)
    hsTyGetAppHead_maybe :: LHsType name -> Maybe (Located name, [LHsType name])
    hsTyGetAppHead_maybe = go []
      where
        go tys (L _ (HsTyVar _ ln))          = Just (ln, tys)
        go tys (L _ (HsAppsTy apps))
          | Just (head, args, _) <- getAppsTyHead_maybe apps
                                             = go (args ++ tys) head
        go tys (L _ (HsAppTy l r))           = go (r : tys) l
        go tys (L _ (HsOpTy l (L loc n) r))  = Just (L loc n, l : r : tys)
        go tys (L _ (HsParTy t))             = go tys t
        go tys (L _ (HsKindSig t _))         = go tys t
        go _   _                             = Nothing

    splitHsAppTys :: LHsType Name -> [LHsType Name] -> (LHsType Name, [LHsType Name])
      -- no need to worry about HsAppsTy here
    splitHsAppTys (L _ (HsAppTy f a)) as = splitHsAppTys f (a:as)
    splitHsAppTys (L _ (HsParTy f))   as = splitHsAppTys f as
    splitHsAppTys f                   as = (f,as)

    --------------------------------
    splitLHsPatSynTy :: LHsType name
                     -> ( [LHsTyVarBndr name]    -- universals
                        , LHsContext name        -- required constraints
                        , [LHsTyVarBndr name]    -- existentials
                        , LHsContext name        -- provided constraints
                        , LHsType name)          -- body type
    splitLHsPatSynTy ty = (univs, reqs, exis, provs, ty4)
      where
        (univs, ty1) = splitLHsForAllTy ty
        (reqs,  ty2) = splitLHsQualTy ty1
        (exis,  ty3) = splitLHsForAllTy ty2
        (provs, ty4) = splitLHsQualTy ty3

    splitLHsSigmaTy :: LHsType name -> ([LHsTyVarBndr name], LHsContext name, LHsType name)
    splitLHsSigmaTy ty
      | (tvs, ty1)  <- splitLHsForAllTy ty
      , (ctxt, ty2) <- splitLHsQualTy ty1
      = (tvs, ctxt, ty2)

    splitLHsForAllTy :: LHsType name -> ([LHsTyVarBndr name], LHsType name)
    splitLHsForAllTy (L _ (HsForAllTy { hst_bndrs = tvs, hst_body = body })) = (tvs, body)
    splitLHsForAllTy body                                                    = ([], body)

    splitLHsQualTy :: LHsType name -> (LHsContext name, LHsType name)
    splitLHsQualTy (L _ (HsQualTy { hst_ctxt = ctxt, hst_body = body })) = (ctxt,     body)
    splitLHsQualTy body                                                  = (noLoc [], body)

    splitLHsInstDeclTy :: LHsSigType Name
                       -> ([Name], LHsContext Name, LHsType Name)
    -- Split up an instance decl type, returning the pieces
    splitLHsInstDeclTy (HsIB { hsib_vars = itkvs
                             , hsib_body = inst_ty })
      | (tvs, cxt, body_ty) <- splitLHsSigmaTy inst_ty
      = (itkvs ++ map hsLTyVarName tvs, cxt, body_ty)
             -- Return implicitly bound type and kind vars
             -- For an instance decl, all of them are in scope

    getLHsInstDeclHead :: LHsSigType name -> LHsType name
    getLHsInstDeclHead inst_ty
      | (_tvs, _cxt, body_ty) <- splitLHsSigmaTy (hsSigType inst_ty)
      = body_ty

    getLHsInstDeclClass_maybe :: LHsSigType name -> Maybe (Located name)
    -- Works on (HsSigType RdrName)
    getLHsInstDeclClass_maybe inst_ty
      = do { let head_ty = getLHsInstDeclHead inst_ty
           ; (cls, _) <- hsTyGetAppHead_maybe head_ty
           ; return cls }

    {-
    ************************************************************************
    *                                                                      *
                    FieldOcc
    *                                                                      *
    ************************************************************************
    -}

    -- | Located Field Occurrence
    type LFieldOcc name = Located (FieldOcc name)

    -- | Field Occurrence
    --
    -- Represents an *occurrence* of an unambiguous field.  We store
    -- both the 'RdrName' the user originally wrote, and after the
    -- renamer, the selector function.
    data FieldOcc name = FieldOcc { rdrNameFieldOcc  :: Located RdrName
                                     -- ^ See Note [Located RdrNames] in HsExpr
                                  , selectorFieldOcc :: PostRn name name
                                  }
    deriving instance Eq (PostRn name name) => Eq (FieldOcc name)
    deriving instance Ord (PostRn name name) => Ord (FieldOcc name)
    deriving instance (Data name, Data (PostRn name name)) => Data (FieldOcc name)

    instance Outputable (FieldOcc name) where
      ppr = ppr . rdrNameFieldOcc

    mkFieldOcc :: Located RdrName -> FieldOcc RdrName
    mkFieldOcc rdr = FieldOcc rdr PlaceHolder

    -- | Ambiguous Field Occurrence
    --
    -- Represents an *occurrence* of a field that is potentially
    -- ambiguous after the renamer, with the ambiguity resolved by the
    -- typechecker.  We always store the 'RdrName' that the user
    -- originally wrote, and store the selector function after the renamer
    -- (for unambiguous occurrences) or the typechecker (for ambiguous
    -- occurrences).
    --
    -- See Note [HsRecField and HsRecUpdField] in HsPat and
    -- Note [Disambiguating record fields] in TcExpr.
    -- See Note [Located RdrNames] in HsExpr
    data AmbiguousFieldOcc name
      = Unambiguous (Located RdrName) (PostRn name name)
      | Ambiguous   (Located RdrName) (PostTc name name)
    deriving instance ( Data name
                      , Data (PostRn name name)
                      , Data (PostTc name name))
                      => Data (AmbiguousFieldOcc name)

    instance Outputable (AmbiguousFieldOcc name) where
      ppr = ppr . rdrNameAmbiguousFieldOcc

    instance OutputableBndr (AmbiguousFieldOcc name) where
      pprInfixOcc  = pprInfixOcc . rdrNameAmbiguousFieldOcc
      pprPrefixOcc = pprPrefixOcc . rdrNameAmbiguousFieldOcc

    mkAmbiguousFieldOcc :: Located RdrName -> AmbiguousFieldOcc RdrName
    mkAmbiguousFieldOcc rdr = Unambiguous rdr PlaceHolder

    rdrNameAmbiguousFieldOcc :: AmbiguousFieldOcc name -> RdrName
    rdrNameAmbiguousFieldOcc (Unambiguous (L _ rdr) _) = rdr
    rdrNameAmbiguousFieldOcc (Ambiguous   (L _ rdr) _) = rdr

    selectorAmbiguousFieldOcc :: AmbiguousFieldOcc Id -> Id
    selectorAmbiguousFieldOcc (Unambiguous _ sel) = sel
    selectorAmbiguousFieldOcc (Ambiguous   _ sel) = sel

    unambiguousFieldOcc :: AmbiguousFieldOcc Id -> FieldOcc Id
    unambiguousFieldOcc (Unambiguous rdr sel) = FieldOcc rdr sel
    unambiguousFieldOcc (Ambiguous   rdr sel) = FieldOcc rdr sel

    ambiguousFieldOcc :: FieldOcc name -> AmbiguousFieldOcc name
    ambiguousFieldOcc (FieldOcc rdr sel) = Unambiguous rdr sel

    {-
    ************************************************************************
    *                                                                      *
    \subsection{Pretty printing}
    *                                                                      *
    ************************************************************************
    -}

    instance (OutputableBndrId name) => Outputable (HsType name) where
        ppr ty = pprHsType ty

    instance Outputable HsTyLit where
        ppr = ppr_tylit

    instance (OutputableBndrId name) => Outputable (LHsQTyVars name) where
        ppr (HsQTvs { hsq_explicit = tvs }) = interppSP tvs

    instance (OutputableBndrId name) => Outputable (HsTyVarBndr name) where
        ppr (UserTyVar n)     = ppr n
        ppr (KindedTyVar n k) = parens $ hsep [ppr n, dcolon, ppr k]

    instance (Outputable thing) => Outputable (HsImplicitBndrs name thing) where
        ppr (HsIB { hsib_body = ty }) = ppr ty

    instance (Outputable thing) => Outputable (HsWildCardBndrs name thing) where
        ppr (HsWC { hswc_body = ty }) = ppr ty

    instance Outputable (HsWildCardInfo name) where
        ppr (AnonWildCard _)  = char '_'

    pprHsForAll :: (OutputableBndrId name)
                => [LHsTyVarBndr name] -> LHsContext name -> SDoc
    pprHsForAll = pprHsForAllExtra Nothing

    -- | Version of 'pprHsForAll' that can also print an extra-constraints
    -- wildcard, e.g. @_ => a -> Bool@ or @(Show a, _) => a -> String@. This
    -- underscore will be printed when the 'Maybe SrcSpan' argument is a 'Just'
    -- containing the location of the extra-constraints wildcard. A special
    -- function for this is needed, as the extra-constraints wildcard is removed
    -- from the actual context and type, and stored in a separate field, thus just
    -- printing the type will not print the extra-constraints wildcard.
    pprHsForAllExtra :: (OutputableBndrId name)
                     => Maybe SrcSpan -> [LHsTyVarBndr name] -> LHsContext name
                     -> SDoc
    pprHsForAllExtra extra qtvs cxt
      = pprHsForAllTvs qtvs <+> pprHsContextExtra show_extra (unLoc cxt)
      where
        show_extra = isJust extra

    pprHsForAllTvs :: (OutputableBndrId name) => [LHsTyVarBndr name] -> SDoc
    pprHsForAllTvs qtvs = sdocWithPprDebug $ \debug ->
      ppWhen (debug || not (null qtvs)) $ forAllLit <+> interppSP qtvs <> dot

    pprHsContext :: (OutputableBndrId name) => HsContext name -> SDoc
    pprHsContext = maybe empty (<+> darrow) . pprHsContextMaybe

    pprHsContextNoArrow :: (OutputableBndrId name) => HsContext name -> SDoc
    pprHsContextNoArrow = fromMaybe empty . pprHsContextMaybe

    pprHsContextMaybe :: (OutputableBndrId name) => HsContext name -> Maybe SDoc
    pprHsContextMaybe []         = Nothing
    pprHsContextMaybe [L _ pred] = Just $ ppr_mono_ty FunPrec pred
    pprHsContextMaybe cxt        = Just $ parens (interpp'SP cxt)

    -- For use in a HsQualTy, which always gets printed if it exists.
    pprHsContextAlways :: (OutputableBndrId name) => HsContext name -> SDoc
    pprHsContextAlways []  = parens empty <+> darrow
    pprHsContextAlways [L _ ty] = ppr_mono_ty FunPrec ty <+> darrow
    pprHsContextAlways cxt = parens (interpp'SP cxt) <+> darrow

    -- True <=> print an extra-constraints wildcard, e.g. @(Show a, _) =>@
    pprHsContextExtra :: (OutputableBndrId name) => Bool -> HsContext name -> SDoc
    pprHsContextExtra show_extra ctxt
      | not show_extra
      = pprHsContext ctxt
      | null ctxt
      = char '_' <+> darrow
      | otherwise
      = parens (sep (punctuate comma ctxt')) <+> darrow
      where
        ctxt' = map ppr ctxt ++ [char '_']

    pprConDeclFields :: (OutputableBndrId name) => [LConDeclField name] -> SDoc
    pprConDeclFields fields = braces (sep (punctuate comma (map ppr_fld fields)))
      where
        ppr_fld (L _ (ConDeclField { cd_fld_names = ns, cd_fld_type = ty,
                                     cd_fld_doc = doc }))
            = ppr_names ns <+> dcolon <+> ppr ty <+> ppr_mbDoc doc
        ppr_names [n] = ppr n
        ppr_names ns = sep (punctuate comma (map ppr ns))

    {-
    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.)
    -}

    -- Printing works more-or-less as for Types

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

    pprHsType ty       = ppr_mono_ty TopPrec ty
    pprParendHsType ty = ppr_mono_ty TyConPrec ty

    ppr_mono_lty :: (OutputableBndrId name) => TyPrec -> LHsType name -> SDoc
    ppr_mono_lty ctxt_prec ty = ppr_mono_ty ctxt_prec (unLoc ty)

    ppr_mono_ty :: (OutputableBndrId name) => TyPrec -> HsType name -> SDoc
    ppr_mono_ty ctxt_prec (HsForAllTy { hst_bndrs = tvs, hst_body = ty })
      = maybeParen ctxt_prec FunPrec $
        sep [pprHsForAllTvs tvs, ppr_mono_lty TopPrec ty]

    ppr_mono_ty _ctxt_prec (HsQualTy { hst_ctxt = L _ ctxt, hst_body = ty })
      = sep [pprHsContextAlways ctxt, ppr_mono_lty TopPrec ty]

    ppr_mono_ty _    (HsBangTy b ty)     = ppr b <> ppr_mono_lty TyConPrec ty
    ppr_mono_ty _    (HsRecTy flds)      = pprConDeclFields flds
    ppr_mono_ty _    (HsTyVar NotPromoted (L _ name))= pprPrefixOcc name
    ppr_mono_ty _    (HsTyVar Promoted (L _ name))
      = space <> quote (pprPrefixOcc name)
                             -- We need a space before the ' above, so the parser
                             -- does not attach it to the previous symbol
    ppr_mono_ty prec (HsFunTy ty1 ty2)   = ppr_fun_ty prec ty1 ty2
    ppr_mono_ty _    (HsTupleTy con tys) = tupleParens std_con (pprWithCommas ppr tys)
      where std_con = case con of
                        HsUnboxedTuple -> UnboxedTuple
                        _              -> BoxedTuple
    ppr_mono_ty _    (HsSumTy tys)       = tupleParens UnboxedTuple (pprWithBars ppr tys)
    ppr_mono_ty _    (HsKindSig ty kind) = parens (ppr_mono_lty TopPrec ty <+> dcolon <+> ppr kind)
    ppr_mono_ty _    (HsListTy ty)       = brackets (ppr_mono_lty TopPrec ty)
    ppr_mono_ty _    (HsPArrTy ty)       = paBrackets (ppr_mono_lty TopPrec ty)
    ppr_mono_ty prec (HsIParamTy n ty)   = maybeParen prec FunPrec (ppr n <+> dcolon <+> ppr_mono_lty TopPrec ty)
    ppr_mono_ty _    (HsSpliceTy s _)    = pprSplice s
    ppr_mono_ty _    (HsCoreTy ty)       = ppr ty
    ppr_mono_ty _    (HsExplicitListTy Promoted _ tys)
      = quote $ brackets (interpp'SP tys)
    ppr_mono_ty _    (HsExplicitListTy NotPromoted _ tys)
      = brackets (interpp'SP tys)
    ppr_mono_ty _    (HsExplicitTupleTy _ tys) = quote $ parens (interpp'SP tys)
    ppr_mono_ty _    (HsTyLit t)         = ppr_tylit t
    ppr_mono_ty _    (HsWildCardTy {})   = char '_'

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

    ppr_mono_ty _ctxt_prec (HsAppsTy tys)
      = hsep (map (ppr_app_ty TopPrec . unLoc) tys)

    ppr_mono_ty _ctxt_prec (HsAppTy fun_ty arg_ty)
      = hsep [ppr_mono_lty FunPrec fun_ty, ppr_mono_lty TyConPrec arg_ty]

    ppr_mono_ty ctxt_prec (HsOpTy ty1 (L _ op) ty2)
      = maybeParen ctxt_prec TyOpPrec $
        sep [ ppr_mono_lty TyOpPrec ty1
            , sep [pprInfixOcc op, ppr_mono_lty TyOpPrec ty2 ] ]

    ppr_mono_ty _         (HsParTy ty)
      = parens (ppr_mono_lty TopPrec 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 TyOpPrec $
        ppr_mono_lty TyOpPrec ty <+> ppr (unLoc doc)
      -- we pretty print Haddock comments on types as if they were
      -- postfix operators

    --------------------------
    ppr_fun_ty :: (OutputableBndrId name)
               => TyPrec -> LHsType name -> LHsType name -> SDoc
    ppr_fun_ty ctxt_prec ty1 ty2
      = let p1 = ppr_mono_lty FunPrec ty1
            p2 = ppr_mono_lty TopPrec ty2
        in
        maybeParen ctxt_prec FunPrec $
        sep [p1, text "->" <+> p2]

    --------------------------
    ppr_app_ty :: (OutputableBndrId name) => TyPrec -> HsAppType name -> SDoc
    ppr_app_ty _    (HsAppInfix (L _ n))                  = pprInfixOcc n
    ppr_app_ty _    (HsAppPrefix (L _ (HsTyVar NotPromoted (L _ n))))
      = pprPrefixOcc n
    ppr_app_ty _    (HsAppPrefix (L _ (HsTyVar Promoted  (L _ n))))
      = space <> quote (pprPrefixOcc n) -- We need a space before the ' above, so
                                        -- the parser does not attach it to the
                                        -- previous symbol
    ppr_app_ty ctxt (HsAppPrefix ty)                      = ppr_mono_lty ctxt ty

    --------------------------
    ppr_tylit :: HsTyLit -> SDoc
    ppr_tylit (HsNumTy _ i) = integer i
    ppr_tylit (HsStrTy _ s) = text (show s)