    {-# LANGUAGE ConstraintKinds #-}
    {-# LANGUAGE DeriveDataTypeable #-}
    {-# LANGUAGE FlexibleContexts #-}
    {-# LANGUAGE FlexibleInstances #-}
    {-# LANGUAGE ScopedTypeVariables #-}
    {-# LANGUAGE StandaloneDeriving #-}
    {-# LANGUAGE TypeFamilies #-}
    {-# LANGUAGE DataKinds #-}
    {-# LANGUAGE UndecidableInstances #-} -- Wrinkle in Note [Trees That Grow]
    {-# LANGUAGE LambdaCase #-}
                                          -- in module Language.Haskell.Syntax.Extension
    {-
    (c) The University of Glasgow 2006
    (c) The GRASP/AQUA Project, Glasgow University, 1992-1998

    GHC.Hs.Type: Abstract syntax: user-defined types
    -}

    -- See Note [Language.Haskell.Syntax.* Hierarchy] for why not GHC.Hs.*
    module Language.Haskell.Syntax.Type (
            HsScaled(..),
            hsMult, hsScaledThing,
            HsArrow(..), XUnrestrictedArrow, XLinearArrow, XExplicitMult, XXArrow,

            HsType(..), LHsType, HsKind, LHsKind,
            HsBndrVis(..), XBndrRequired, XBndrInvisible, XXBndrVis,
            isHsBndrInvisible,
            HsForAllTelescope(..), HsTyVarBndr(..), LHsTyVarBndr,
            LHsQTyVars(..),
            HsOuterTyVarBndrs(..), HsOuterFamEqnTyVarBndrs, HsOuterSigTyVarBndrs,
            HsWildCardBndrs(..),
            HsPatSigType(..),
            HsSigType(..), LHsSigType, LHsSigWcType, LHsWcType,
            HsTyPat(..), LHsTyPat,
            HsTupleSort(..),
            HsContext, LHsContext,
            HsTyLit(..),
            HsIPName(..), hsIPNameFS,
            HsArg(..), XValArg, XTypeArg, XArgPar, XXArg,

            LHsTypeArg,

            LBangType, BangType,
            HsSrcBang(..),
            PromotionFlag(..), isPromoted,

            ConDeclField(..), LConDeclField,

            HsConDetails(..), noTypeArgs, conDetailsArity,

            FieldOcc(..), LFieldOcc,
            AmbiguousFieldOcc(..), LAmbiguousFieldOcc,

            mapHsOuterImplicit,
            hsQTvExplicit,
            isHsKindedTyVar,
            hsPatSigType,
        ) where

    import {-# SOURCE #-} Language.Haskell.Syntax.Expr ( HsUntypedSplice )

    import Language.Haskell.Syntax.Extension

    import GHC.Types.Name.Reader ( RdrName )
    import GHC.Core.DataCon( HsSrcBang(..) )
    import GHC.Core.Type (Specificity)
    import GHC.Types.Basic (Arity)

    import GHC.Hs.Doc (LHsDoc)
    import GHC.Data.FastString (FastString)

    import Data.Data hiding ( Fixity, Prefix, Infix )
    import Data.Void
    import Data.Maybe
    import Data.Eq
    import Data.Bool
    import Data.Char
    import Prelude (Integer, length)

    {-
    ************************************************************************
    *                                                                      *
    \subsection{Promotion flag}
    *                                                                      *
    ************************************************************************
    -}

    -- | Is a TyCon a promoted data constructor or just a normal type constructor?
    data PromotionFlag
      = NotPromoted
      | IsPromoted
      deriving ( PromotionFlag -> PromotionFlag -> Bool
    (PromotionFlag -> PromotionFlag -> Bool)
    -> (PromotionFlag -> PromotionFlag -> Bool) -> Eq PromotionFlag
    forall a. (a -> a -> Bool) -> (a -> a -> Bool) -> Eq a
    $c== :: PromotionFlag -> PromotionFlag -> Bool
    == :: PromotionFlag -> PromotionFlag -> Bool
    $c/= :: PromotionFlag -> PromotionFlag -> Bool
    /= :: PromotionFlag -> PromotionFlag -> Bool
    Eq, Typeable PromotionFlag
    Typeable PromotionFlag =>
    (forall (c :: * -> *).
     (forall d b. Data d => c (d -> b) -> d -> c b)
     -> (forall g. g -> c g) -> PromotionFlag -> c PromotionFlag)
    -> (forall (c :: * -> *).
        (forall b r. Data b => c (b -> r) -> c r)
        -> (forall r. r -> c r) -> Constr -> c PromotionFlag)
    -> (PromotionFlag -> Constr)
    -> (PromotionFlag -> DataType)
    -> (forall (t :: * -> *) (c :: * -> *).
        Typeable t =>
        (forall d. Data d => c (t d)) -> Maybe (c PromotionFlag))
    -> (forall (t :: * -> * -> *) (c :: * -> *).
        Typeable t =>
        (forall d e. (Data d, Data e) => c (t d e))
        -> Maybe (c PromotionFlag))
    -> ((forall b. Data b => b -> b) -> PromotionFlag -> PromotionFlag)
    -> (forall r r'.
        (r -> r' -> r)
        -> r -> (forall d. Data d => d -> r') -> PromotionFlag -> r)
    -> (forall r r'.
        (r' -> r -> r)
        -> r -> (forall d. Data d => d -> r') -> PromotionFlag -> r)
    -> (forall u. (forall d. Data d => d -> u) -> PromotionFlag -> [u])
    -> (forall u.
        Int -> (forall d. Data d => d -> u) -> PromotionFlag -> u)
    -> (forall (m :: * -> *).
        Monad m =>
        (forall d. Data d => d -> m d) -> PromotionFlag -> m PromotionFlag)
    -> (forall (m :: * -> *).
        MonadPlus m =>
        (forall d. Data d => d -> m d) -> PromotionFlag -> m PromotionFlag)
    -> (forall (m :: * -> *).
        MonadPlus m =>
        (forall d. Data d => d -> m d) -> PromotionFlag -> m PromotionFlag)
    -> Data PromotionFlag
    PromotionFlag -> Constr
    PromotionFlag -> DataType
    (forall b. Data b => b -> b) -> PromotionFlag -> PromotionFlag
    forall a.
    Typeable a =>
    (forall (c :: * -> *).
     (forall d b. Data d => c (d -> b) -> d -> c b)
     -> (forall g. g -> c g) -> a -> c a)
    -> (forall (c :: * -> *).
        (forall b r. Data b => c (b -> r) -> c r)
        -> (forall r. r -> c r) -> Constr -> c a)
    -> (a -> Constr)
    -> (a -> DataType)
    -> (forall (t :: * -> *) (c :: * -> *).
        Typeable t =>
        (forall d. Data d => c (t d)) -> Maybe (c a))
    -> (forall (t :: * -> * -> *) (c :: * -> *).
        Typeable t =>
        (forall d e. (Data d, Data e) => c (t d e)) -> Maybe (c a))
    -> ((forall b. Data b => b -> b) -> a -> a)
    -> (forall r r'.
        (r -> r' -> r) -> r -> (forall d. Data d => d -> r') -> a -> r)
    -> (forall r r'.
        (r' -> r -> r) -> r -> (forall d. Data d => d -> r') -> a -> r)
    -> (forall u. (forall d. Data d => d -> u) -> a -> [u])
    -> (forall u. Int -> (forall d. Data d => d -> u) -> a -> u)
    -> (forall (m :: * -> *).
        Monad m =>
        (forall d. Data d => d -> m d) -> a -> m a)
    -> (forall (m :: * -> *).
        MonadPlus m =>
        (forall d. Data d => d -> m d) -> a -> m a)
    -> (forall (m :: * -> *).
        MonadPlus m =>
        (forall d. Data d => d -> m d) -> a -> m a)
    -> Data a
    forall u. Int -> (forall d. Data d => d -> u) -> PromotionFlag -> u
    forall u. (forall d. Data d => d -> u) -> PromotionFlag -> [u]
    forall r r'.
    (r -> r' -> r)
    -> r -> (forall d. Data d => d -> r') -> PromotionFlag -> r
    forall r r'.
    (r' -> r -> r)
    -> r -> (forall d. Data d => d -> r') -> PromotionFlag -> r
    forall (m :: * -> *).
    Monad m =>
    (forall d. Data d => d -> m d) -> PromotionFlag -> m PromotionFlag
    forall (m :: * -> *).
    MonadPlus m =>
    (forall d. Data d => d -> m d) -> PromotionFlag -> m PromotionFlag
    forall (c :: * -> *).
    (forall b r. Data b => c (b -> r) -> c r)
    -> (forall r. r -> c r) -> Constr -> c PromotionFlag
    forall (c :: * -> *).
    (forall d b. Data d => c (d -> b) -> d -> c b)
    -> (forall g. g -> c g) -> PromotionFlag -> c PromotionFlag
    forall (t :: * -> *) (c :: * -> *).
    Typeable t =>
    (forall d. Data d => c (t d)) -> Maybe (c PromotionFlag)
    forall (t :: * -> * -> *) (c :: * -> *).
    Typeable t =>
    (forall d e. (Data d, Data e) => c (t d e))
    -> Maybe (c PromotionFlag)
    $cgfoldl :: forall (c :: * -> *).
    (forall d b. Data d => c (d -> b) -> d -> c b)
    -> (forall g. g -> c g) -> PromotionFlag -> c PromotionFlag
    gfoldl :: forall (c :: * -> *).
    (forall d b. Data d => c (d -> b) -> d -> c b)
    -> (forall g. g -> c g) -> PromotionFlag -> c PromotionFlag
    $cgunfold :: forall (c :: * -> *).
    (forall b r. Data b => c (b -> r) -> c r)
    -> (forall r. r -> c r) -> Constr -> c PromotionFlag
    gunfold :: forall (c :: * -> *).
    (forall b r. Data b => c (b -> r) -> c r)
    -> (forall r. r -> c r) -> Constr -> c PromotionFlag
    $ctoConstr :: PromotionFlag -> Constr
    toConstr :: PromotionFlag -> Constr
    $cdataTypeOf :: PromotionFlag -> DataType
    dataTypeOf :: PromotionFlag -> DataType
    $cdataCast1 :: forall (t :: * -> *) (c :: * -> *).
    Typeable t =>
    (forall d. Data d => c (t d)) -> Maybe (c PromotionFlag)
    dataCast1 :: forall (t :: * -> *) (c :: * -> *).
    Typeable t =>
    (forall d. Data d => c (t d)) -> Maybe (c PromotionFlag)
    $cdataCast2 :: forall (t :: * -> * -> *) (c :: * -> *).
    Typeable t =>
    (forall d e. (Data d, Data e) => c (t d e))
    -> Maybe (c PromotionFlag)
    dataCast2 :: forall (t :: * -> * -> *) (c :: * -> *).
    Typeable t =>
    (forall d e. (Data d, Data e) => c (t d e))
    -> Maybe (c PromotionFlag)
    $cgmapT :: (forall b. Data b => b -> b) -> PromotionFlag -> PromotionFlag
    gmapT :: (forall b. Data b => b -> b) -> PromotionFlag -> PromotionFlag
    $cgmapQl :: forall r r'.
    (r -> r' -> r)
    -> r -> (forall d. Data d => d -> r') -> PromotionFlag -> r
    gmapQl :: forall r r'.
    (r -> r' -> r)
    -> r -> (forall d. Data d => d -> r') -> PromotionFlag -> r
    $cgmapQr :: forall r r'.
    (r' -> r -> r)
    -> r -> (forall d. Data d => d -> r') -> PromotionFlag -> r
    gmapQr :: forall r r'.
    (r' -> r -> r)
    -> r -> (forall d. Data d => d -> r') -> PromotionFlag -> r
    $cgmapQ :: forall u. (forall d. Data d => d -> u) -> PromotionFlag -> [u]
    gmapQ :: forall u. (forall d. Data d => d -> u) -> PromotionFlag -> [u]
    $cgmapQi :: forall u. Int -> (forall d. Data d => d -> u) -> PromotionFlag -> u
    gmapQi :: forall u. Int -> (forall d. Data d => d -> u) -> PromotionFlag -> u
    $cgmapM :: forall (m :: * -> *).
    Monad m =>
    (forall d. Data d => d -> m d) -> PromotionFlag -> m PromotionFlag
    gmapM :: forall (m :: * -> *).
    Monad m =>
    (forall d. Data d => d -> m d) -> PromotionFlag -> m PromotionFlag
    $cgmapMp :: forall (m :: * -> *).
    MonadPlus m =>
    (forall d. Data d => d -> m d) -> PromotionFlag -> m PromotionFlag
    gmapMp :: forall (m :: * -> *).
    MonadPlus m =>
    (forall d. Data d => d -> m d) -> PromotionFlag -> m PromotionFlag
    $cgmapMo :: forall (m :: * -> *).
    MonadPlus m =>
    (forall d. Data d => d -> m d) -> PromotionFlag -> m PromotionFlag
    gmapMo :: forall (m :: * -> *).
    MonadPlus m =>
    (forall d. Data d => d -> m d) -> PromotionFlag -> m PromotionFlag
    Data )

    isPromoted :: PromotionFlag -> Bool
    isPromoted :: PromotionFlag -> Bool
    isPromoted PromotionFlag
    IsPromoted  = Bool
    True
    isPromoted PromotionFlag
    NotPromoted = Bool
    False

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

    -- | Located Bang Type
    type LBangType pass = XRec pass (BangType pass)

    -- | Bang Type
    --
    -- In the parser, strictness and packedness annotations bind more tightly
    -- than docstrings. This means that when consuming a 'BangType' (and looking
    -- for 'HsBangTy') we must be ready to peer behind a potential layer of
    -- 'HsDocTy'. See #15206 for motivation and 'getBangType' for an example.
    type BangType pass  = HsType pass       -- Bangs are in the HsType data type

    {-
    ************************************************************************
    *                                                                      *
    \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 GHC.Rename.HsType

    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' that
                      is nested within another HsType
                       e.g.   forall a b.   {...} or
                              forall a b -> {...}

                      Note that top-level 'forall's are represented with a
                      different AST form. See the description of HsOuterTyVarBndrs
                      below.
         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.

    * The ForAllTelescope field of HsForAllTy represents whether a forall is
      invisible (e.g., forall a b. {...}, with a dot) or visible
      (e.g., forall a b -> {...}, with an arrow).

    * 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.

    * HsOuterTyVarBndrs is used to represent the outermost quantified type
      variables in a type that obeys the forall-or-nothing rule. An
      HsOuterTyVarBndrs can be one of the following:

        HsOuterImplicit (implicit quantification, added by renamer)
              f :: a -> a     -- Desugars to f :: forall {a}. a -> a
        HsOuterExplicit (explicit user quantification):
              f :: forall a. a -> a

      See Note [forall-or-nothing rule].

    * An HsSigType is an LHsType with an accompanying HsOuterTyVarBndrs that
      represents the presence (or absence) of its outermost 'forall'.
      See Note [Representing type signatures].

    * 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 _.

    * HsSigPatType describes types that appear in pattern signatures and
      the signatures of term-level binders in RULES. Like
      HsWildCardBndrs/HsOuterTyVarBndrs, they track the names of wildcard
      variables and implicitly bound type variables. Unlike
      HsOuterTyVarBndrs, however, HsSigPatTypes do not obey the
      forall-or-nothing rule. See Note [Pattern signature binders and scoping].

    * 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.
        The renamer leaves it untouched, and it is later given a fresh
        meta tyvar in the typechecker.

      * 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 #10982)

    * Named wildcards are bound by the HsWildCardBndrs (for types that obey the
      forall-or-nothing rule) and HsPatSigType (for type signatures in patterns
      and term-level binders in RULES), which wrap types that are allowed to have
      wildcards. Unnamed wildcards, however are left unchanged until typechecking,
      where we give them fresh wild tyvars and determine whether or not to emit
      hole constraints on each wildcard (we don't if it's a visible type/kind
      argument or a type family pattern). See related notes
      Note [Wildcards in visible kind application] and
      Note [Wildcards in visible type application] in GHC.Tc.Gen.HsType.

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

    Note [Ordering of implicit variables]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Since the advent of -XTypeApplications, GHC makes promises about the ordering
    of implicit variable quantification. Specifically, we offer that implicitly
    quantified variables (such as those in const :: a -> b -> a, without a `forall`)
    will occur in left-to-right order of first occurrence. Here are a few examples:

      const :: a -> b -> a       -- forall a b. ...
      f :: Eq a => b -> a -> a   -- forall a b. ...  contexts are included

      type a <-< b = b -> a
      g :: a <-< b               -- forall a b. ...  type synonyms matter

      class Functor f where
        fmap :: (a -> b) -> f a -> f b   -- forall f a b. ...
        -- The f is quantified by the class, so only a and b are considered in fmap

    This simple story is complicated by the possibility of dependency: all variables
    must come after any variables mentioned in their kinds.

      typeRep :: Typeable a => TypeRep (a :: k)   -- forall k a. ...

    The k comes first because a depends on k, even though the k appears later than
    the a in the code. Thus, GHC does a *stable topological sort* on the variables.
    By "stable", we mean that any two variables who do not depend on each other
    preserve their existing left-to-right ordering.

    Implicitly bound variables are collected by the extract- family of functions
    (extractHsTysRdrTyVars, extractHsTyVarBndrsKVs, etc.) in GHC.Rename.HsType.
    These functions thus promise to keep left-to-right ordering.
    Look for pointers to this note to see the places where the action happens.

    Note that we also maintain this ordering in kind signatures. Even though
    there's no visible kind application (yet), having implicit variables be
    quantified in left-to-right order in kind signatures is nice since:

    * It's consistent with the treatment for type signatures.
    * It can affect how types are displayed with -fprint-explicit-kinds (see
      #15568 for an example), which is a situation where knowing the order in
      which implicit variables are quantified can be useful.
    * In the event that visible kind application is implemented, the order in
      which we would expect implicit variables to be ordered in kinds will have
      already been established.
    -}

    -- | Located Haskell Context
    type LHsContext pass = XRec pass (HsContext pass)
          -- ^ 'GHC.Parser.Annotation.AnnKeywordId' : 'GHC.Parser.Annotation.AnnUnit'
          -- For details on above see Note [exact print annotations] in GHC.Parser.Annotation

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

    -- | Located Haskell Type
    type LHsType pass = XRec pass (HsType pass)
          -- ^ May have 'GHC.Parser.Annotation.AnnKeywordId' : 'GHC.Parser.Annotation.AnnComma' when
          --   in a list

          -- For details on above see Note [exact print annotations] in GHC.Parser.Annotation

    -- | Haskell Kind
    type HsKind pass = HsType pass

    -- | Located Haskell Kind
    type LHsKind pass = XRec pass (HsKind pass)
          -- ^ 'GHC.Parser.Annotation.AnnKeywordId' : 'GHC.Parser.Annotation.AnnDcolon'

          -- For details on above see Note [exact print annotations] in GHC.Parser.Annotation

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

    -- | The type variable binders in an 'HsForAllTy'.
    -- See also @Note [Variable Specificity and Forall Visibility]@ in
    -- "GHC.Tc.Gen.HsType".
    data HsForAllTelescope pass
      = HsForAllVis -- ^ A visible @forall@ (e.g., @forall a -> {...}@).
                    --   These do not have any notion of specificity, so we use
                    --   '()' as a placeholder value.
        { forall pass. HsForAllTelescope pass -> XHsForAllVis pass
    hsf_xvis      :: XHsForAllVis pass
        , forall pass. HsForAllTelescope pass -> [LHsTyVarBndr () pass]
    hsf_vis_bndrs :: [LHsTyVarBndr () pass]
        }
      | HsForAllInvis -- ^ An invisible @forall@ (e.g., @forall a {b} c. {...}@),
                      --   where each binder has a 'Specificity'.
        { forall pass. HsForAllTelescope pass -> XHsForAllInvis pass
    hsf_xinvis       :: XHsForAllInvis pass
        , forall pass.
    HsForAllTelescope pass -> [LHsTyVarBndr Specificity pass]
    hsf_invis_bndrs  :: [LHsTyVarBndr Specificity pass]
        }
      | XHsForAllTelescope !(XXHsForAllTelescope pass)

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

    -- | Located Haskell Quantified Type Variables
    data LHsQTyVars pass   -- See Note [HsType binders]
      = HsQTvs { forall pass. LHsQTyVars pass -> XHsQTvs pass
    hsq_ext :: XHsQTvs pass

               , forall pass.
    LHsQTyVars pass -> [LHsTyVarBndr (HsBndrVis pass) pass]
    hsq_explicit :: [LHsTyVarBndr (HsBndrVis pass) pass]
                    -- Explicit variables, written by the user
        }
      | XLHsQTyVars !(XXLHsQTyVars pass)

    hsQTvExplicit :: LHsQTyVars pass -> [LHsTyVarBndr (HsBndrVis pass) pass]
    hsQTvExplicit :: forall pass.
    LHsQTyVars pass -> [LHsTyVarBndr (HsBndrVis pass) pass]
    hsQTvExplicit = LHsQTyVars pass -> [LHsTyVarBndr (HsBndrVis pass) pass]
    forall pass.
    LHsQTyVars pass -> [LHsTyVarBndr (HsBndrVis pass) pass]
    hsq_explicit

    ------------------------------------------------
    --            HsOuterTyVarBndrs
    -- Used to quantify the outermost type variable binders of a type that obeys
    -- the forall-or-nothing rule. These are used to represent the outermost
    -- quantification in:
    --    * Type signatures (LHsSigType/LHsSigWcType)
    --    * Patterns in a type/data family instance (HsFamEqnPats)
    --
    -- We support two forms:
    --   HsOuterImplicit (implicit quantification, added by renamer)
    --         f :: a -> a     -- Desugars to f :: forall {a}. a -> a
    --         type instance F (a,b) = a->b
    --   HsOuterExplicit (explicit user quantification):
    --         f :: forall a. a -> a
    --         type instance forall a b. F (a,b) = a->b
    --
    -- In constrast, when the user writes /visible/ quanitification
    --         T :: forall k -> k -> Type
    -- we use use HsOuterImplicit, wrapped around a HsForAllTy
    -- for the visible quantification
    --
    -- See Note [forall-or-nothing rule]

    -- | The outermost type variables in a type that obeys the @forall@-or-nothing
    -- rule. See @Note [forall-or-nothing rule]@.
    data HsOuterTyVarBndrs flag pass
      = HsOuterImplicit -- ^ Implicit forall, e.g.,
                        --    @f :: a -> b -> b@
        { forall flag pass.
    HsOuterTyVarBndrs flag pass -> XHsOuterImplicit pass
    hso_ximplicit :: XHsOuterImplicit pass
        }
      | HsOuterExplicit -- ^ Explicit forall, e.g.,
                        --    @f :: forall a b. a -> b -> b@
        { forall flag pass.
    HsOuterTyVarBndrs flag pass -> XHsOuterExplicit pass flag
    hso_xexplicit :: XHsOuterExplicit pass flag
        , forall flag pass.
    HsOuterTyVarBndrs flag pass -> [LHsTyVarBndr flag (NoGhcTc pass)]
    hso_bndrs     :: [LHsTyVarBndr flag (NoGhcTc pass)]
        }
      | XHsOuterTyVarBndrs !(XXHsOuterTyVarBndrs pass)

    -- | Used for signatures, e.g.,
    --
    -- @
    -- f :: forall a {b}. blah
    -- @
    --
    -- We use 'Specificity' for the 'HsOuterTyVarBndrs' @flag@ to allow
    -- distinguishing between specified and inferred type variables.
    type HsOuterSigTyVarBndrs = HsOuterTyVarBndrs Specificity

    -- | Used for type-family instance equations, e.g.,
    --
    -- @
    -- type instance forall a. F [a] = Tree a
    -- @
    --
    -- The notion of specificity is irrelevant in type family equations, so we use
    -- @()@ for the 'HsOuterTyVarBndrs' @flag@.
    type HsOuterFamEqnTyVarBndrs = HsOuterTyVarBndrs ()

    -- | Haskell Wildcard Binders
    data HsWildCardBndrs pass thing
        -- See Note [HsType binders]
        -- See Note [The wildcard story for types]
      = HsWC { forall pass thing. HsWildCardBndrs pass thing -> XHsWC pass thing
    hswc_ext :: XHsWC pass thing
                    -- after the renamer
                    -- Wild cards, only named
                    -- See Note [Wildcards in visible kind application]

             , forall pass thing. HsWildCardBndrs pass thing -> thing
    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.
        }
      | XHsWildCardBndrs !(XXHsWildCardBndrs pass thing)

    -- | Types that can appear in pattern signatures, as well as the signatures for
    -- term-level binders in RULES.
    -- See @Note [Pattern signature binders and scoping]@.
    --
    -- This is very similar to 'HsSigWcType', but with
    -- slightly different semantics: see @Note [HsType binders]@.
    -- See also @Note [The wildcard story for types]@.
    data HsPatSigType pass
      = HsPS { forall pass. HsPatSigType pass -> XHsPS pass
    hsps_ext  :: XHsPS pass   -- ^ After renamer: 'HsPSRn'
             , forall pass. HsPatSigType pass -> LHsType pass
    hsps_body :: LHsType pass -- ^ Main payload (the type itself)
        }
      | XHsPatSigType !(XXHsPatSigType pass)

    -- | Located Haskell Signature Type
    type LHsSigType   pass = XRec pass (HsSigType pass)               -- Implicit only

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

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

    data HsTyPat pass
      = HsTP { forall pass. HsTyPat pass -> XHsTP pass
    hstp_ext  :: XHsTP pass   -- ^ After renamer: 'HsTyPatRn'
             , forall pass. HsTyPat pass -> LHsType pass
    hstp_body :: LHsType pass -- ^ Main payload (the type itself)
        }
      | XHsTyPat !(XXHsTyPat pass)

    type LHsTyPat  pass = XRec pass (HsTyPat pass)

    -- | A type signature that obeys the @forall@-or-nothing rule. In other
    -- words, an 'LHsType' that uses an 'HsOuterSigTyVarBndrs' to represent its
    -- outermost type variable quantification.
    -- See @Note [Representing type signatures]@.
    data HsSigType pass
      = HsSig { forall pass. HsSigType pass -> XHsSig pass
    sig_ext   :: XHsSig pass
              , forall pass. HsSigType pass -> HsOuterSigTyVarBndrs pass
    sig_bndrs :: HsOuterSigTyVarBndrs pass
              , forall pass. HsSigType pass -> LHsType pass
    sig_body  :: LHsType pass
              }
      | XHsSigType !(XXHsSigType pass)

    hsPatSigType :: HsPatSigType pass -> LHsType pass
    hsPatSigType :: forall pass. HsPatSigType pass -> LHsType pass
    hsPatSigType = HsPatSigType pass -> LHsType pass
    forall pass. HsPatSigType pass -> LHsType pass
    hsps_body

    {-
    Note [forall-or-nothing rule]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Free variables in signatures are usually bound in an implicit 'forall' at the
    beginning of user-written signatures. However, if the signature has an
    explicit, invisible forall at the beginning, this is disabled. This is referred
    to as the forall-or-nothing rule.

    The idea is nested foralls express something which is only expressible
    explicitly, while a top level forall could (usually) be replaced with an
    implicit binding. Top-level foralls alone ("forall.") are therefore an
    indication that the user is trying to be fastidious, so we don't implicitly
    bind any variables.

    Note that this rule only applies to outermost /in/visible 'forall's, and not
    outermost visible 'forall's. See #18660 for more on this point.

    Here are some concrete examples to demonstrate the forall-or-nothing rule in
    action:

      type F1 :: a -> b -> b                    -- Legal; a,b are implicitly quantified.
                                                -- Equivalently: forall a b. a -> b -> b

      type F2 :: forall a b. a -> b -> b        -- Legal; explicitly quantified

      type F3 :: forall a. a -> b -> b          -- Illegal; the forall-or-nothing rule says that
                                                -- if you quantify a, you must also quantify b

      type F4 :: forall a -> b -> b             -- Legal; the top quantifier (forall a) is a /visible/
                                                -- quantifier, so the "nothing" part of the forall-or-nothing
                                                -- rule applies, and b is therefore implicitly quantified.
                                                -- Equivalently: forall b. forall a -> b -> b

      type F5 :: forall b. forall a -> b -> c   -- Illegal; the forall-or-nothing rule says that
                                                -- if you quantify b, you must also quantify c

      type F6 :: forall a -> forall b. b -> c   -- Legal: just like F4.

    For a complete list of all places where the forall-or-nothing rule applies, see
    "The `forall`-or-nothing rule" section of the GHC User's Guide.

    Any type that obeys the forall-or-nothing rule is represented in the AST with
    an HsOuterTyVarBndrs:

    * If the type has an outermost, invisible 'forall', it uses HsOuterExplicit,
      which contains a list of the explicitly quantified type variable binders in
      `hso_bndrs`. After typechecking, HsOuterExplicit also stores a list of the
      explicitly quantified `InvisTVBinder`s in
      `hso_xexplicit :: XHsOuterExplicit GhcTc`.

    * Otherwise, it uses HsOuterImplicit. HsOuterImplicit is used for different
      things depending on the phase:

      * After parsing, it does not store anything in particular.
      * After renaming, it stores the implicitly bound type variable `Name`s in
        `hso_ximplicit :: XHsOuterImplicit GhcRn`.
      * After typechecking, it stores the implicitly bound `TyVar`s in
        `hso_ximplicit :: XHsOuterImplicit GhcTc`.

      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.
          See Note [Binding scoped type variables] in GHC.Tc.Gen.Sig.

    HsOuterTyVarBndrs GhcTc is used in the typechecker as an intermediate data type
    for storing the outermost TyVars/InvisTVBinders in a type.
    See GHC.Tc.Gen.HsType.bindOuterTKBndrsX for an example of this.

    Note [Representing type signatures]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    HsSigType is used to represent an explicit user type signature. These are
    used in a variety of places. Some examples include:

    * Type signatures (e.g., f :: a -> a)
    * Standalone kind signatures (e.g., type G :: a -> a)
    * GADT constructor types (e.g., data T where MkT :: a -> T)

    A HsSigType is the combination of an HsOuterSigTyVarBndrs and an LHsType:

    * The HsOuterSigTyVarBndrs binds the /explicitly/ quantified type variables
      when the type signature has an outermost, user-written 'forall' (i.e,
      the HsOuterExplicit constructor is used). If there is no outermost 'forall',
      then it binds the /implicitly/ quantified type variables instead (i.e.,
      the HsOuterImplicit constructor is used).
    * The LHsType represents the rest of the type.

    E.g. For a signature like
       f :: forall k (a::k). blah
    we get
       HsSig { sig_bndrs = HsOuterExplicit { hso_bndrs = [k, (a :: k)] }
             , sig_body  = blah }

    Note [Pattern signature binders and scoping]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Consider the pattern signatures like those on `t` and `g` in:

       f = let h = \(t :: (b, b) ->
                   \(g :: forall a. a -> b) ->
                   ...(t :: (Int,Int))...
           in woggle

    * The `b` in t's pattern signature is implicitly bound and scopes over
      the signature and the body of the lambda.  It stands for a type (any type);
      indeed we subsequently discover that b=Int.
      (See Note [TyVarTv] in GHC.Tc.Utils.TcMType for more on this point.)
    * The `b` in g's pattern signature is an /occurrence/ of the `b` bound by
      t's pattern signature.
    * The `a` in `forall a` scopes only over the type `a -> b`, not over the body
      of the lambda.
    * There is no forall-or-nothing rule for pattern signatures, which is why the
      type `forall a. a -> b` is permitted in `g`'s pattern signature, even though
      `b` is not explicitly bound. See Note [forall-or-nothing rule].

    Similar scoping rules apply to term variable binders in RULES, like in the
    following example:

       {-# RULES "h" forall (t :: (b, b)) (g :: forall a. a -> b). h t g = ... #-}

    Just like in pattern signatures, the `b` in t's signature is implicitly bound
    and scopes over the remainder of the RULE. As a result, the `b` in g's
    signature is an occurrence. Moreover, the `a` in `forall a` scopes only over
    the type `a -> b`, and the forall-or-nothing rule does not apply.

    While quite similar, RULE term binder signatures behave slightly differently
    from pattern signatures in two ways:

    1. Unlike in pattern signatures, where type variables can stand for any type,
       type variables in RULE term binder signatures are skolems.
       See Note [Typechecking pattern signature binders] in GHC.Tc.Gen.HsType for
       more on this point.

       In this sense, type variables in pattern signatures are quite similar to
       named wildcards, as both can refer to arbitrary types. The main difference
       lies in error reporting: if a named wildcard `_a` in a pattern signature
       stands for Int, then by default GHC will emit a warning stating as much.
       Changing `_a` to `a`, on the other hand, will cause it not to be reported.
    2. In the `h` RULE above, only term variables are explicitly bound, so any free
       type variables in the term variables' signatures are implicitly bound.
       This is just like how the free type variables in pattern signatures are
       implicitly bound. If a RULE explicitly binds both term and type variables,
       however, then free type variables in term signatures are /not/ implicitly
       bound. For example, this RULE would be ill scoped:

         {-# RULES "h2" forall b. forall (t :: (b, c)) (g :: forall a. a -> b).
                        h2 t g = ... #-}

       This is because `b` and `c` occur free in the signature for `t`, but only
       `b` was explicitly bound, leaving `c` out of scope. If the RULE had started
       with `forall b c.`, then it would have been accepted.

    The types in pattern signatures and RULE term binder signatures are represented
    in the AST by HsSigPatType. From the renamer onward, the hsps_ext field (of
    type HsPSRn) tracks the names of named wildcards and implicitly bound type
    variables so that they can be brought into scope during renaming and
    typechecking.

    Note [Lexically scoped type variables]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    The ScopedTypeVariables extension does two things:

    * It allows the use of type signatures in patterns
      (e.g., `f (x :: a -> a) = ...`). See
      Note [Pattern signature binders and scoping] for more on this point.
    * It brings lexically scoped type variables into scope for certain type
      signatures with outermost invisible 'forall's.

    This Note concerns the latter bullet point. Per the
    "Lexically scoped type variables" section of the GHC User's Guide, the
    following forms of type signatures can have lexically scoped type variables:

    * In declarations with type signatures, e.g.,

        f :: forall a. a -> a
        f x = e @a

      Here, the 'forall a' brings 'a' into scope over the body of 'f'.

      Note that ScopedTypeVariables does /not/ interact with standalone kind
      signatures, only type signatures.

    * In explicit type annotations in expressions, e.g.,

        id @a :: forall a. a -> a

    * In instance declarations, e.g.,

        instance forall a. C [a] where
          m = e @a

      Note that unlike the examples above, the use of an outermost 'forall' isn't
      required to bring 'a' into scope. That is, the following would also work:

        instance forall a. C [a] where
          m = e @a

    Note that all of the types above obey the forall-or-nothing rule. As a result,
    the places in the AST that can have lexically scoped type variables are a
    subset of the places that use HsOuterTyVarBndrs
    (See Note [forall-or-nothing rule].)

    Some other observations about lexically scoped type variables:

    * Only type variables bound by an /invisible/ forall can be lexically scoped.
      See Note [hsScopedTvs and visible foralls].
    * The lexically scoped type variables may be a strict subset of the type
      variables brought into scope by a type signature.
      See Note [Binding scoped type variables] in GHC.Tc.Gen.Sig.
    -}

    mapHsOuterImplicit :: (XHsOuterImplicit pass -> XHsOuterImplicit pass)
                       -> HsOuterTyVarBndrs flag pass
                       -> HsOuterTyVarBndrs flag pass
    mapHsOuterImplicit :: forall pass flag.
    (XHsOuterImplicit pass -> XHsOuterImplicit pass)
    -> HsOuterTyVarBndrs flag pass -> HsOuterTyVarBndrs flag pass
    mapHsOuterImplicit XHsOuterImplicit pass -> XHsOuterImplicit pass
    f (HsOuterImplicit{hso_ximplicit :: forall flag pass.
    HsOuterTyVarBndrs flag pass -> XHsOuterImplicit pass
    hso_ximplicit = XHsOuterImplicit pass
    imp}) =
      HsOuterImplicit{hso_ximplicit :: XHsOuterImplicit pass
    hso_ximplicit = XHsOuterImplicit pass -> XHsOuterImplicit pass
    f XHsOuterImplicit pass
    imp}
    mapHsOuterImplicit XHsOuterImplicit pass -> XHsOuterImplicit pass
    _ hso :: HsOuterTyVarBndrs flag pass
    hso@(HsOuterExplicit{})    = HsOuterTyVarBndrs flag pass
    hso
    mapHsOuterImplicit XHsOuterImplicit pass -> XHsOuterImplicit pass
    _ hso :: HsOuterTyVarBndrs flag pass
    hso@(XHsOuterTyVarBndrs{}) = HsOuterTyVarBndrs flag pass
    hso

    --------------------------------------------------
    -- | These names are used early on to store the names of implicit
    -- parameters.  They completely disappear after type-checking.
    newtype HsIPName = HsIPName FastString
      deriving( HsIPName -> HsIPName -> Bool
    (HsIPName -> HsIPName -> Bool)
    -> (HsIPName -> HsIPName -> Bool) -> Eq HsIPName
    forall a. (a -> a -> Bool) -> (a -> a -> Bool) -> Eq a
    $c== :: HsIPName -> HsIPName -> Bool
    == :: HsIPName -> HsIPName -> Bool
    $c/= :: HsIPName -> HsIPName -> Bool
    /= :: HsIPName -> HsIPName -> Bool
    Eq, Typeable HsIPName
    Typeable HsIPName =>
    (forall (c :: * -> *).
     (forall d b. Data d => c (d -> b) -> d -> c b)
     -> (forall g. g -> c g) -> HsIPName -> c HsIPName)
    -> (forall (c :: * -> *).
        (forall b r. Data b => c (b -> r) -> c r)
        -> (forall r. r -> c r) -> Constr -> c HsIPName)
    -> (HsIPName -> Constr)
    -> (HsIPName -> DataType)
    -> (forall (t :: * -> *) (c :: * -> *).
        Typeable t =>
        (forall d. Data d => c (t d)) -> Maybe (c HsIPName))
    -> (forall (t :: * -> * -> *) (c :: * -> *).
        Typeable t =>
        (forall d e. (Data d, Data e) => c (t d e)) -> Maybe (c HsIPName))
    -> ((forall b. Data b => b -> b) -> HsIPName -> HsIPName)
    -> (forall r r'.
        (r -> r' -> r)
        -> r -> (forall d. Data d => d -> r') -> HsIPName -> r)
    -> (forall r r'.
        (r' -> r -> r)
        -> r -> (forall d. Data d => d -> r') -> HsIPName -> r)
    -> (forall u. (forall d. Data d => d -> u) -> HsIPName -> [u])
    -> (forall u. Int -> (forall d. Data d => d -> u) -> HsIPName -> u)
    -> (forall (m :: * -> *).
        Monad m =>
        (forall d. Data d => d -> m d) -> HsIPName -> m HsIPName)
    -> (forall (m :: * -> *).
        MonadPlus m =>
        (forall d. Data d => d -> m d) -> HsIPName -> m HsIPName)
    -> (forall (m :: * -> *).
        MonadPlus m =>
        (forall d. Data d => d -> m d) -> HsIPName -> m HsIPName)
    -> Data HsIPName
    HsIPName -> Constr
    HsIPName -> DataType
    (forall b. Data b => b -> b) -> HsIPName -> HsIPName
    forall a.
    Typeable a =>
    (forall (c :: * -> *).
     (forall d b. Data d => c (d -> b) -> d -> c b)
     -> (forall g. g -> c g) -> a -> c a)
    -> (forall (c :: * -> *).
        (forall b r. Data b => c (b -> r) -> c r)
        -> (forall r. r -> c r) -> Constr -> c a)
    -> (a -> Constr)
    -> (a -> DataType)
    -> (forall (t :: * -> *) (c :: * -> *).
        Typeable t =>
        (forall d. Data d => c (t d)) -> Maybe (c a))
    -> (forall (t :: * -> * -> *) (c :: * -> *).
        Typeable t =>
        (forall d e. (Data d, Data e) => c (t d e)) -> Maybe (c a))
    -> ((forall b. Data b => b -> b) -> a -> a)
    -> (forall r r'.
        (r -> r' -> r) -> r -> (forall d. Data d => d -> r') -> a -> r)
    -> (forall r r'.
        (r' -> r -> r) -> r -> (forall d. Data d => d -> r') -> a -> r)
    -> (forall u. (forall d. Data d => d -> u) -> a -> [u])
    -> (forall u. Int -> (forall d. Data d => d -> u) -> a -> u)
    -> (forall (m :: * -> *).
        Monad m =>
        (forall d. Data d => d -> m d) -> a -> m a)
    -> (forall (m :: * -> *).
        MonadPlus m =>
        (forall d. Data d => d -> m d) -> a -> m a)
    -> (forall (m :: * -> *).
        MonadPlus m =>
        (forall d. Data d => d -> m d) -> a -> m a)
    -> Data a
    forall u. Int -> (forall d. Data d => d -> u) -> HsIPName -> u
    forall u. (forall d. Data d => d -> u) -> HsIPName -> [u]
    forall r r'.
    (r -> r' -> r)
    -> r -> (forall d. Data d => d -> r') -> HsIPName -> r
    forall r r'.
    (r' -> r -> r)
    -> r -> (forall d. Data d => d -> r') -> HsIPName -> r
    forall (m :: * -> *).
    Monad m =>
    (forall d. Data d => d -> m d) -> HsIPName -> m HsIPName
    forall (m :: * -> *).
    MonadPlus m =>
    (forall d. Data d => d -> m d) -> HsIPName -> m HsIPName
    forall (c :: * -> *).
    (forall b r. Data b => c (b -> r) -> c r)
    -> (forall r. r -> c r) -> Constr -> c HsIPName
    forall (c :: * -> *).
    (forall d b. Data d => c (d -> b) -> d -> c b)
    -> (forall g. g -> c g) -> HsIPName -> c HsIPName
    forall (t :: * -> *) (c :: * -> *).
    Typeable t =>
    (forall d. Data d => c (t d)) -> Maybe (c HsIPName)
    forall (t :: * -> * -> *) (c :: * -> *).
    Typeable t =>
    (forall d e. (Data d, Data e) => c (t d e)) -> Maybe (c HsIPName)
    $cgfoldl :: forall (c :: * -> *).
    (forall d b. Data d => c (d -> b) -> d -> c b)
    -> (forall g. g -> c g) -> HsIPName -> c HsIPName
    gfoldl :: forall (c :: * -> *).
    (forall d b. Data d => c (d -> b) -> d -> c b)
    -> (forall g. g -> c g) -> HsIPName -> c HsIPName
    $cgunfold :: forall (c :: * -> *).
    (forall b r. Data b => c (b -> r) -> c r)
    -> (forall r. r -> c r) -> Constr -> c HsIPName
    gunfold :: forall (c :: * -> *).
    (forall b r. Data b => c (b -> r) -> c r)
    -> (forall r. r -> c r) -> Constr -> c HsIPName
    $ctoConstr :: HsIPName -> Constr
    toConstr :: HsIPName -> Constr
    $cdataTypeOf :: HsIPName -> DataType
    dataTypeOf :: HsIPName -> DataType
    $cdataCast1 :: forall (t :: * -> *) (c :: * -> *).
    Typeable t =>
    (forall d. Data d => c (t d)) -> Maybe (c HsIPName)
    dataCast1 :: forall (t :: * -> *) (c :: * -> *).
    Typeable t =>
    (forall d. Data d => c (t d)) -> Maybe (c HsIPName)
    $cdataCast2 :: forall (t :: * -> * -> *) (c :: * -> *).
    Typeable t =>
    (forall d e. (Data d, Data e) => c (t d e)) -> Maybe (c HsIPName)
    dataCast2 :: forall (t :: * -> * -> *) (c :: * -> *).
    Typeable t =>
    (forall d e. (Data d, Data e) => c (t d e)) -> Maybe (c HsIPName)
    $cgmapT :: (forall b. Data b => b -> b) -> HsIPName -> HsIPName
    gmapT :: (forall b. Data b => b -> b) -> HsIPName -> HsIPName
    $cgmapQl :: forall r r'.
    (r -> r' -> r)
    -> r -> (forall d. Data d => d -> r') -> HsIPName -> r
    gmapQl :: forall r r'.
    (r -> r' -> r)
    -> r -> (forall d. Data d => d -> r') -> HsIPName -> r
    $cgmapQr :: forall r r'.
    (r' -> r -> r)
    -> r -> (forall d. Data d => d -> r') -> HsIPName -> r
    gmapQr :: forall r r'.
    (r' -> r -> r)
    -> r -> (forall d. Data d => d -> r') -> HsIPName -> r
    $cgmapQ :: forall u. (forall d. Data d => d -> u) -> HsIPName -> [u]
    gmapQ :: forall u. (forall d. Data d => d -> u) -> HsIPName -> [u]
    $cgmapQi :: forall u. Int -> (forall d. Data d => d -> u) -> HsIPName -> u
    gmapQi :: forall u. Int -> (forall d. Data d => d -> u) -> HsIPName -> u
    $cgmapM :: forall (m :: * -> *).
    Monad m =>
    (forall d. Data d => d -> m d) -> HsIPName -> m HsIPName
    gmapM :: forall (m :: * -> *).
    Monad m =>
    (forall d. Data d => d -> m d) -> HsIPName -> m HsIPName
    $cgmapMp :: forall (m :: * -> *).
    MonadPlus m =>
    (forall d. Data d => d -> m d) -> HsIPName -> m HsIPName
    gmapMp :: forall (m :: * -> *).
    MonadPlus m =>
    (forall d. Data d => d -> m d) -> HsIPName -> m HsIPName
    $cgmapMo :: forall (m :: * -> *).
    MonadPlus m =>
    (forall d. Data d => d -> m d) -> HsIPName -> m HsIPName
    gmapMo :: forall (m :: * -> *).
    MonadPlus m =>
    (forall d. Data d => d -> m d) -> HsIPName -> m HsIPName
    Data )

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

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

    -- | Haskell Type Variable Binder
    -- The flag annotates the binder. It is 'Specificity' in places where
    -- explicit specificity is allowed (e.g. x :: forall {a} b. ...) or
    -- '()' in other places.
    data HsTyVarBndr flag pass
      = UserTyVar        -- no explicit kinding
             (XUserTyVar pass)
             flag
             (LIdP pass)
            -- See Note [Located RdrNames] in GHC.Hs.Expr

      | KindedTyVar
             (XKindedTyVar pass)
             flag
             (LIdP pass)
             (LHsKind pass)  -- The user-supplied kind signature
            -- ^
            --  - 'GHC.Parser.Annotation.AnnKeywordId' : 'GHC.Parser.Annotation.AnnOpen',
            --          'GHC.Parser.Annotation.AnnDcolon', 'GHC.Parser.Annotation.AnnClose'

            -- For details on above see Note [exact print annotations] in GHC.Parser.Annotation

      | XTyVarBndr
          !(XXTyVarBndr pass)

    data HsBndrVis pass
      = HsBndrRequired !(XBndrRequired pass)
          -- Binder for a visible (required) variable:
          --     type Dup a = (a, a)
          --             ^^^

      | HsBndrInvisible !(XBndrInvisible pass)
          -- Binder for an invisible (specified) variable:
          --     type KindOf @k (a :: k) = k
          --                ^^^

      | XXBndrVis !(XXBndrVis pass)

    type family XBndrRequired  p
    type family XBndrInvisible p
    type family XXBndrVis      p

    isHsBndrInvisible :: HsBndrVis pass -> Bool
    isHsBndrInvisible :: forall pass. HsBndrVis pass -> Bool
    isHsBndrInvisible HsBndrInvisible{} = Bool
    True
    isHsBndrInvisible HsBndrRequired{}  = Bool
    False
    isHsBndrInvisible (XXBndrVis XXBndrVis pass
    _)     = Bool
    False

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

    -- | Haskell Type
    data HsType pass
      = HsForAllTy   -- See Note [HsType binders]
          { forall pass. HsType pass -> XForAllTy pass
    hst_xforall :: XForAllTy pass
          , forall pass. HsType pass -> HsForAllTelescope pass
    hst_tele    :: HsForAllTelescope pass
                                         -- Explicit, user-supplied 'forall a {b} c'
          , forall pass. HsType pass -> LHsType pass
    hst_body    :: LHsType pass  -- body type
          }
          -- ^ - 'GHC.Parser.Annotation.AnnKeywordId' : 'GHC.Parser.Annotation.AnnForall',
          --         'GHC.Parser.Annotation.AnnDot','GHC.Parser.Annotation.AnnDarrow'
          -- For details on above see Note [exact print annotations] in "GHC.Parser.Annotation"

      | HsQualTy   -- See Note [HsType binders]
          { forall pass. HsType pass -> XQualTy pass
    hst_xqual :: XQualTy pass
          , forall pass. HsType pass -> LHsContext pass
    hst_ctxt  :: LHsContext pass  -- Context C => blah
          , hst_body  :: LHsType pass }

      | HsTyVar  (XTyVar pass)
                  PromotionFlag    -- Whether explicitly promoted,
                                   -- for the pretty printer
                 (LIdP pass)
                      -- Type variable, type constructor, or data constructor
                      -- see Note [Promotions (HsTyVar)]
                      -- See Note [Located RdrNames] in GHC.Hs.Expr
          -- ^ - 'GHC.Parser.Annotation.AnnKeywordId' : None

          -- For details on above see Note [exact print annotations] in GHC.Parser.Annotation

      | HsAppTy             (XAppTy pass)
                            (LHsType pass)
                            (LHsType pass)
          -- ^ - 'GHC.Parser.Annotation.AnnKeywordId' : None

          -- For details on above see Note [exact print annotations] in GHC.Parser.Annotation

      | HsAppKindTy         (XAppKindTy pass) -- type level type app
                            (LHsType pass)
                            (LHsKind pass)

      | HsFunTy             (XFunTy pass)
                            (HsArrow pass)
                            (LHsType pass)   -- function type
                            (LHsType pass)
          -- ^ - 'GHC.Parser.Annotation.AnnKeywordId' : 'GHC.Parser.Annotation.AnnRarrow',

          -- For details on above see Note [exact print annotations] in GHC.Parser.Annotation

      | HsListTy            (XListTy pass)
                            (LHsType pass)  -- Element type
          -- ^ - 'GHC.Parser.Annotation.AnnKeywordId' : 'GHC.Parser.Annotation.AnnOpen' @'['@,
          --         'GHC.Parser.Annotation.AnnClose' @']'@

          -- For details on above see Note [exact print annotations] in GHC.Parser.Annotation

      | HsTupleTy           (XTupleTy pass)
                            HsTupleSort
                            [LHsType pass]  -- Element types (length gives arity)
        -- ^ - 'GHC.Parser.Annotation.AnnKeywordId' : 'GHC.Parser.Annotation.AnnOpen' @'(' or '(#'@,
        --         'GHC.Parser.Annotation.AnnClose' @')' or '#)'@

        -- For details on above see Note [exact print annotations] in GHC.Parser.Annotation

      | HsSumTy             (XSumTy pass)
                            [LHsType pass]  -- Element types (length gives arity)
        -- ^ - 'GHC.Parser.Annotation.AnnKeywordId' : 'GHC.Parser.Annotation.AnnOpen' @'(#'@,
        --         'GHC.Parser.Annotation.AnnClose' '#)'@

        -- For details on above see Note [exact print annotations] in GHC.Parser.Annotation

      | HsOpTy              (XOpTy pass)
                            PromotionFlag    -- Whether explicitly promoted,
                                             -- for the pretty printer
                            (LHsType pass) (LIdP pass) (LHsType pass)
          -- ^ - 'GHC.Parser.Annotation.AnnKeywordId' : None

          -- For details on above see Note [exact print annotations] in GHC.Parser.Annotation

      | HsParTy             (XParTy pass)
                            (LHsType pass)   -- See Note [Parens in HsSyn] in GHC.Hs.Expr
            -- Parenthesis preserved for the precedence re-arrangement in
            -- GHC.Rename.HsType
            -- It's important that a * (b + c) doesn't get rearranged to (a*b) + c!
          -- ^ - 'GHC.Parser.Annotation.AnnKeywordId' : 'GHC.Parser.Annotation.AnnOpen' @'('@,
          --         'GHC.Parser.Annotation.AnnClose' @')'@

          -- For details on above see Note [exact print annotations] in GHC.Parser.Annotation

      | HsIParamTy          (XIParamTy pass)
                            (XRec pass HsIPName) -- (?x :: ty)
                            (LHsType pass)   -- Implicit parameters as they occur in
                                             -- contexts
          -- ^
          -- > (?x :: ty)
          --
          -- - 'GHC.Parser.Annotation.AnnKeywordId' : 'GHC.Parser.Annotation.AnnDcolon'

          -- For details on above see Note [exact print annotations] in GHC.Parser.Annotation

      | HsStarTy            (XStarTy pass)
                            Bool             -- Is this the Unicode variant?
                                             -- Note [HsStarTy]
          -- ^ - 'GHC.Parser.Annotation.AnnKeywordId' : None

      | HsKindSig           (XKindSig pass)
                            (LHsType pass)  -- (ty :: kind)
                            (LHsKind pass)  -- A type with a kind signature
          -- ^
          -- > (ty :: kind)
          --
          -- - 'GHC.Parser.Annotation.AnnKeywordId' : 'GHC.Parser.Annotation.AnnOpen' @'('@,
          --         'GHC.Parser.Annotation.AnnDcolon','GHC.Parser.Annotation.AnnClose' @')'@

          -- For details on above see Note [exact print annotations] in GHC.Parser.Annotation

      | HsSpliceTy          (XSpliceTy pass)
                            (HsUntypedSplice pass)   -- Includes quasi-quotes
          -- ^ - 'GHC.Parser.Annotation.AnnKeywordId' : 'GHC.Parser.Annotation.AnnOpen' @'$('@,
          --         'GHC.Parser.Annotation.AnnClose' @')'@

          -- For details on above see Note [exact print annotations] in GHC.Parser.Annotation

      | HsDocTy             (XDocTy pass)
                            (LHsType pass) (LHsDoc pass) -- A documented type
          -- ^ - 'GHC.Parser.Annotation.AnnKeywordId' : None

          -- For details on above see Note [exact print annotations] in GHC.Parser.Annotation

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

          -- For details on above see Note [exact print annotations] in GHC.Parser.Annotation

      | HsRecTy     (XRecTy pass)
                    [LConDeclField pass]    -- Only in data type declarations
          -- ^ - 'GHC.Parser.Annotation.AnnKeywordId' : 'GHC.Parser.Annotation.AnnOpen' @'{'@,
          --         'GHC.Parser.Annotation.AnnClose' @'}'@

          -- For details on above see Note [exact print annotations] in GHC.Parser.Annotation

      | HsExplicitListTy       -- A promoted explicit list
            (XExplicitListTy pass)
            PromotionFlag      -- whether explicitly promoted, for pretty printer
            [LHsType pass]
          -- ^ - 'GHC.Parser.Annotation.AnnKeywordId' : 'GHC.Parser.Annotation.AnnOpen' @"'["@,
          --         'GHC.Parser.Annotation.AnnClose' @']'@

          -- For details on above see Note [exact print annotations] in GHC.Parser.Annotation

      | HsExplicitTupleTy      -- A promoted explicit tuple
            (XExplicitTupleTy pass)
            [LHsType pass]
          -- ^ - 'GHC.Parser.Annotation.AnnKeywordId' : 'GHC.Parser.Annotation.AnnOpen' @"'("@,
          --         'GHC.Parser.Annotation.AnnClose' @')'@

          -- For details on above see Note [exact print annotations] in GHC.Parser.Annotation

      | HsTyLit (XTyLit pass) (HsTyLit pass)      -- A promoted numeric literal.
          -- ^ - 'GHC.Parser.Annotation.AnnKeywordId' : None

          -- For details on above see Note [exact print annotations] in GHC.Parser.Annotation

      | HsWildCardTy (XWildCardTy pass)  -- A type wildcard
          -- See Note [The wildcard story for types]
          -- ^ - 'GHC.Parser.Annotation.AnnKeywordId' : None

          -- For details on above see Note [exact print annotations] in GHC.Parser.Annotation

      -- Extension point; see Note [Trees That Grow] in Language.Haskell.Syntax.Extension
      | XHsType
          !(XXType pass)

    -- | Haskell Type Literal
    data HsTyLit pass
      = HsNumTy  (XNumTy pass) Integer
      | HsStrTy  (XStrTy pass) FastString
      | HsCharTy (XCharTy pass) Char
      | XTyLit   !(XXTyLit pass)

    -- | Denotes the type of arrows in the surface language
    data HsArrow pass
      = HsUnrestrictedArrow !(XUnrestrictedArrow pass)
        -- ^ a -> b or a → b

      | HsLinearArrow !(XLinearArrow pass)
        -- ^ a %1 -> b or a %1 → b, or a ⊸ b

      | HsExplicitMult !(XExplicitMult pass) !(LHsType pass)
        -- ^ a %m -> b or a %m → b (very much including `a %Many -> b`!
        -- This is how the programmer wrote it). It is stored as an
        -- `HsType` so as to preserve the syntax as written in the
        -- program.

      | XArrow !(XXArrow pass)

    type family XUnrestrictedArrow p
    type family XLinearArrow       p
    type family XExplicitMult      p
    type family XXArrow            p

    -- | This is used in the syntax. In constructor declaration. It must keep the
    -- arrow representation.
    data HsScaled pass a = HsScaled (HsArrow pass) a

    hsMult :: HsScaled pass a -> HsArrow pass
    hsMult :: forall pass a. HsScaled pass a -> HsArrow pass
    hsMult (HsScaled HsArrow pass
    m a
    _) = HsArrow pass
    m

    hsScaledThing :: HsScaled pass a -> a
    hsScaledThing :: forall pass a. HsScaled pass a -> a
    hsScaledThing (HsScaled HsArrow pass
    _ a
    t) = a
    t

    {-
    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 [HsStarTy]
    ~~~~~~~~~~~~~~~
    When the StarIsType extension is enabled, we want to treat '*' and its Unicode
    variant identically to 'Data.Kind.Type'. Unfortunately, doing so in the parser
    would mean that when we pretty-print it back, we don't know whether the user
    wrote '*' or 'Type', and lose the parse/ppr roundtrip property.

    As a workaround, we parse '*' as HsStarTy (if it stands for 'Data.Kind.Type')
    and then desugar it to 'Data.Kind.Type' in the typechecker (see tc_hs_type).
    When '*' is a regular type operator (StarIsType is disabled), HsStarTy is not
    involved.

    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
    two constructors of HsTupleSort:

            HsUnboxedTuple                  -> Produced by the parser
            HsBoxedOrConstraintTuple        -> Could be a boxed or a constraint
                                            tuple. Produced by the parser only,
                                            disappears after type checking

    After typechecking, we use TupleSort (which clearly distinguishes between
    constraint tuples and boxed tuples) rather than HsTupleSort.
    -}

    -- | Haskell Tuple Sort
    data HsTupleSort = HsUnboxedTuple
                     | HsBoxedOrConstraintTuple
                     deriving Typeable HsTupleSort
    Typeable HsTupleSort =>
    (forall (c :: * -> *).
     (forall d b. Data d => c (d -> b) -> d -> c b)
     -> (forall g. g -> c g) -> HsTupleSort -> c HsTupleSort)
    -> (forall (c :: * -> *).
        (forall b r. Data b => c (b -> r) -> c r)
        -> (forall r. r -> c r) -> Constr -> c HsTupleSort)
    -> (HsTupleSort -> Constr)
    -> (HsTupleSort -> DataType)
    -> (forall (t :: * -> *) (c :: * -> *).
        Typeable t =>
        (forall d. Data d => c (t d)) -> Maybe (c HsTupleSort))
    -> (forall (t :: * -> * -> *) (c :: * -> *).
        Typeable t =>
        (forall d e. (Data d, Data e) => c (t d e))
        -> Maybe (c HsTupleSort))
    -> ((forall b. Data b => b -> b) -> HsTupleSort -> HsTupleSort)
    -> (forall r r'.
        (r -> r' -> r)
        -> r -> (forall d. Data d => d -> r') -> HsTupleSort -> r)
    -> (forall r r'.
        (r' -> r -> r)
        -> r -> (forall d. Data d => d -> r') -> HsTupleSort -> r)
    -> (forall u. (forall d. Data d => d -> u) -> HsTupleSort -> [u])
    -> (forall u.
        Int -> (forall d. Data d => d -> u) -> HsTupleSort -> u)
    -> (forall (m :: * -> *).
        Monad m =>
        (forall d. Data d => d -> m d) -> HsTupleSort -> m HsTupleSort)
    -> (forall (m :: * -> *).
        MonadPlus m =>
        (forall d. Data d => d -> m d) -> HsTupleSort -> m HsTupleSort)
    -> (forall (m :: * -> *).
        MonadPlus m =>
        (forall d. Data d => d -> m d) -> HsTupleSort -> m HsTupleSort)
    -> Data HsTupleSort
    HsTupleSort -> Constr
    HsTupleSort -> DataType
    (forall b. Data b => b -> b) -> HsTupleSort -> HsTupleSort
    forall a.
    Typeable a =>
    (forall (c :: * -> *).
     (forall d b. Data d => c (d -> b) -> d -> c b)
     -> (forall g. g -> c g) -> a -> c a)
    -> (forall (c :: * -> *).
        (forall b r. Data b => c (b -> r) -> c r)
        -> (forall r. r -> c r) -> Constr -> c a)
    -> (a -> Constr)
    -> (a -> DataType)
    -> (forall (t :: * -> *) (c :: * -> *).
        Typeable t =>
        (forall d. Data d => c (t d)) -> Maybe (c a))
    -> (forall (t :: * -> * -> *) (c :: * -> *).
        Typeable t =>
        (forall d e. (Data d, Data e) => c (t d e)) -> Maybe (c a))
    -> ((forall b. Data b => b -> b) -> a -> a)
    -> (forall r r'.
        (r -> r' -> r) -> r -> (forall d. Data d => d -> r') -> a -> r)
    -> (forall r r'.
        (r' -> r -> r) -> r -> (forall d. Data d => d -> r') -> a -> r)
    -> (forall u. (forall d. Data d => d -> u) -> a -> [u])
    -> (forall u. Int -> (forall d. Data d => d -> u) -> a -> u)
    -> (forall (m :: * -> *).
        Monad m =>
        (forall d. Data d => d -> m d) -> a -> m a)
    -> (forall (m :: * -> *).
        MonadPlus m =>
        (forall d. Data d => d -> m d) -> a -> m a)
    -> (forall (m :: * -> *).
        MonadPlus m =>
        (forall d. Data d => d -> m d) -> a -> m a)
    -> Data a
    forall u. Int -> (forall d. Data d => d -> u) -> HsTupleSort -> u
    forall u. (forall d. Data d => d -> u) -> HsTupleSort -> [u]
    forall r r'.
    (r -> r' -> r)
    -> r -> (forall d. Data d => d -> r') -> HsTupleSort -> r
    forall r r'.
    (r' -> r -> r)
    -> r -> (forall d. Data d => d -> r') -> HsTupleSort -> r
    forall (m :: * -> *).
    Monad m =>
    (forall d. Data d => d -> m d) -> HsTupleSort -> m HsTupleSort
    forall (m :: * -> *).
    MonadPlus m =>
    (forall d. Data d => d -> m d) -> HsTupleSort -> m HsTupleSort
    forall (c :: * -> *).
    (forall b r. Data b => c (b -> r) -> c r)
    -> (forall r. r -> c r) -> Constr -> c HsTupleSort
    forall (c :: * -> *).
    (forall d b. Data d => c (d -> b) -> d -> c b)
    -> (forall g. g -> c g) -> HsTupleSort -> c HsTupleSort
    forall (t :: * -> *) (c :: * -> *).
    Typeable t =>
    (forall d. Data d => c (t d)) -> Maybe (c HsTupleSort)
    forall (t :: * -> * -> *) (c :: * -> *).
    Typeable t =>
    (forall d e. (Data d, Data e) => c (t d e))
    -> Maybe (c HsTupleSort)
    $cgfoldl :: forall (c :: * -> *).
    (forall d b. Data d => c (d -> b) -> d -> c b)
    -> (forall g. g -> c g) -> HsTupleSort -> c HsTupleSort
    gfoldl :: forall (c :: * -> *).
    (forall d b. Data d => c (d -> b) -> d -> c b)
    -> (forall g. g -> c g) -> HsTupleSort -> c HsTupleSort
    $cgunfold :: forall (c :: * -> *).
    (forall b r. Data b => c (b -> r) -> c r)
    -> (forall r. r -> c r) -> Constr -> c HsTupleSort
    gunfold :: forall (c :: * -> *).
    (forall b r. Data b => c (b -> r) -> c r)
    -> (forall r. r -> c r) -> Constr -> c HsTupleSort
    $ctoConstr :: HsTupleSort -> Constr
    toConstr :: HsTupleSort -> Constr
    $cdataTypeOf :: HsTupleSort -> DataType
    dataTypeOf :: HsTupleSort -> DataType
    $cdataCast1 :: forall (t :: * -> *) (c :: * -> *).
    Typeable t =>
    (forall d. Data d => c (t d)) -> Maybe (c HsTupleSort)
    dataCast1 :: forall (t :: * -> *) (c :: * -> *).
    Typeable t =>
    (forall d. Data d => c (t d)) -> Maybe (c HsTupleSort)
    $cdataCast2 :: forall (t :: * -> * -> *) (c :: * -> *).
    Typeable t =>
    (forall d e. (Data d, Data e) => c (t d e))
    -> Maybe (c HsTupleSort)
    dataCast2 :: forall (t :: * -> * -> *) (c :: * -> *).
    Typeable t =>
    (forall d e. (Data d, Data e) => c (t d e))
    -> Maybe (c HsTupleSort)
    $cgmapT :: (forall b. Data b => b -> b) -> HsTupleSort -> HsTupleSort
    gmapT :: (forall b. Data b => b -> b) -> HsTupleSort -> HsTupleSort
    $cgmapQl :: forall r r'.
    (r -> r' -> r)
    -> r -> (forall d. Data d => d -> r') -> HsTupleSort -> r
    gmapQl :: forall r r'.
    (r -> r' -> r)
    -> r -> (forall d. Data d => d -> r') -> HsTupleSort -> r
    $cgmapQr :: forall r r'.
    (r' -> r -> r)
    -> r -> (forall d. Data d => d -> r') -> HsTupleSort -> r
    gmapQr :: forall r r'.
    (r' -> r -> r)
    -> r -> (forall d. Data d => d -> r') -> HsTupleSort -> r
    $cgmapQ :: forall u. (forall d. Data d => d -> u) -> HsTupleSort -> [u]
    gmapQ :: forall u. (forall d. Data d => d -> u) -> HsTupleSort -> [u]
    $cgmapQi :: forall u. Int -> (forall d. Data d => d -> u) -> HsTupleSort -> u
    gmapQi :: forall u. Int -> (forall d. Data d => d -> u) -> HsTupleSort -> u
    $cgmapM :: forall (m :: * -> *).
    Monad m =>
    (forall d. Data d => d -> m d) -> HsTupleSort -> m HsTupleSort
    gmapM :: forall (m :: * -> *).
    Monad m =>
    (forall d. Data d => d -> m d) -> HsTupleSort -> m HsTupleSort
    $cgmapMp :: forall (m :: * -> *).
    MonadPlus m =>
    (forall d. Data d => d -> m d) -> HsTupleSort -> m HsTupleSort
    gmapMp :: forall (m :: * -> *).
    MonadPlus m =>
    (forall d. Data d => d -> m d) -> HsTupleSort -> m HsTupleSort
    $cgmapMo :: forall (m :: * -> *).
    MonadPlus m =>
    (forall d. Data d => d -> m d) -> HsTupleSort -> m HsTupleSort
    gmapMo :: forall (m :: * -> *).
    MonadPlus m =>
    (forall d. Data d => d -> m d) -> HsTupleSort -> m HsTupleSort
    Data

    -- | Located Constructor Declaration Field
    type LConDeclField pass = XRec pass (ConDeclField pass)
          -- ^ May have 'GHC.Parser.Annotation.AnnKeywordId' : 'GHC.Parser.Annotation.AnnComma' when
          --   in a list

          -- For details on above see Note [exact print annotations] in GHC.Parser.Annotation

    -- | Constructor Declaration Field
    data ConDeclField pass  -- Record fields have Haddock docs on them
      = ConDeclField { forall pass. ConDeclField pass -> XConDeclField pass
    cd_fld_ext  :: XConDeclField pass,
                       forall pass. ConDeclField pass -> [LFieldOcc pass]
    cd_fld_names :: [LFieldOcc pass],
                                       -- ^ See Note [ConDeclField pass]
                       forall pass. ConDeclField pass -> LBangType pass
    cd_fld_type :: LBangType pass,
                       forall pass. ConDeclField pass -> Maybe (LHsDoc pass)
    cd_fld_doc  :: Maybe (LHsDoc pass)}
          -- ^ - 'GHC.Parser.Annotation.AnnKeywordId' : 'GHC.Parser.Annotation.AnnDcolon'

          -- For details on above see Note [exact print annotations] in GHC.Parser.Annotation
      | XConDeclField !(XXConDeclField pass)

    -- | Describes the arguments to a data constructor. This is a common
    -- representation for several constructor-related concepts, including:
    --
    -- * The arguments in a Haskell98-style constructor declaration
    --   (see 'HsConDeclH98Details' in "GHC.Hs.Decls").
    --
    -- * The arguments in constructor patterns in @case@/function definitions
    --   (see 'HsConPatDetails' in "GHC.Hs.Pat").
    --
    -- * The left-hand side arguments in a pattern synonym binding
    --   (see 'HsPatSynDetails' in "GHC.Hs.Binds").
    --
    -- One notable exception is the arguments in a GADT constructor, which uses
    -- a separate data type entirely (see 'HsConDeclGADTDetails' in
    -- "GHC.Hs.Decls"). This is because GADT constructors cannot be declared with
    -- infix syntax, unlike the concepts above (#18844).
    data HsConDetails tyarg arg rec
      = PrefixCon [tyarg] [arg]     -- C @t1 @t2 p1 p2 p3
      | RecCon    rec               -- C { x = p1, y = p2 }
      | InfixCon  arg arg           -- p1 `C` p2
      deriving Typeable (HsConDetails tyarg arg rec)
    Typeable (HsConDetails tyarg arg rec) =>
    (forall (c :: * -> *).
     (forall d b. Data d => c (d -> b) -> d -> c b)
     -> (forall g. g -> c g)
     -> HsConDetails tyarg arg rec
     -> c (HsConDetails tyarg arg rec))
    -> (forall (c :: * -> *).
        (forall b r. Data b => c (b -> r) -> c r)
        -> (forall r. r -> c r)
        -> Constr
        -> c (HsConDetails tyarg arg rec))
    -> (HsConDetails tyarg arg rec -> Constr)
    -> (HsConDetails tyarg arg rec -> DataType)
    -> (forall (t :: * -> *) (c :: * -> *).
        Typeable t =>
        (forall d. Data d => c (t d))
        -> Maybe (c (HsConDetails tyarg arg rec)))
    -> (forall (t :: * -> * -> *) (c :: * -> *).
        Typeable t =>
        (forall d e. (Data d, Data e) => c (t d e))
        -> Maybe (c (HsConDetails tyarg arg rec)))
    -> ((forall b. Data b => b -> b)
        -> HsConDetails tyarg arg rec -> HsConDetails tyarg arg rec)
    -> (forall r r'.
        (r -> r' -> r)
        -> r
        -> (forall d. Data d => d -> r')
        -> HsConDetails tyarg arg rec
        -> r)
    -> (forall r r'.
        (r' -> r -> r)
        -> r
        -> (forall d. Data d => d -> r')
        -> HsConDetails tyarg arg rec
        -> r)
    -> (forall u.
        (forall d. Data d => d -> u) -> HsConDetails tyarg arg rec -> [u])
    -> (forall u.
        Int
        -> (forall d. Data d => d -> u) -> HsConDetails tyarg arg rec -> u)
    -> (forall (m :: * -> *).
        Monad m =>
        (forall d. Data d => d -> m d)
        -> HsConDetails tyarg arg rec -> m (HsConDetails tyarg arg rec))
    -> (forall (m :: * -> *).
        MonadPlus m =>
        (forall d. Data d => d -> m d)
        -> HsConDetails tyarg arg rec -> m (HsConDetails tyarg arg rec))
    -> (forall (m :: * -> *).
        MonadPlus m =>
        (forall d. Data d => d -> m d)
        -> HsConDetails tyarg arg rec -> m (HsConDetails tyarg arg rec))
    -> Data (HsConDetails tyarg arg rec)
    HsConDetails tyarg arg rec -> Constr
    HsConDetails tyarg arg rec -> DataType
    (forall b. Data b => b -> b)
    -> HsConDetails tyarg arg rec -> HsConDetails tyarg arg rec
    forall a.
    Typeable a =>
    (forall (c :: * -> *).
     (forall d b. Data d => c (d -> b) -> d -> c b)
     -> (forall g. g -> c g) -> a -> c a)
    -> (forall (c :: * -> *).
        (forall b r. Data b => c (b -> r) -> c r)
        -> (forall r. r -> c r) -> Constr -> c a)
    -> (a -> Constr)
    -> (a -> DataType)
    -> (forall (t :: * -> *) (c :: * -> *).
        Typeable t =>
        (forall d. Data d => c (t d)) -> Maybe (c a))
    -> (forall (t :: * -> * -> *) (c :: * -> *).
        Typeable t =>
        (forall d e. (Data d, Data e) => c (t d e)) -> Maybe (c a))
    -> ((forall b. Data b => b -> b) -> a -> a)
    -> (forall r r'.
        (r -> r' -> r) -> r -> (forall d. Data d => d -> r') -> a -> r)
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        (r' -> r -> r) -> r -> (forall d. Data d => d -> r') -> a -> r)
    -> (forall u. (forall d. Data d => d -> u) -> a -> [u])
    -> (forall u. Int -> (forall d. Data d => d -> u) -> a -> u)
    -> (forall (m :: * -> *).
        Monad m =>
        (forall d. Data d => d -> m d) -> a -> m a)
    -> (forall (m :: * -> *).
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        (forall d. Data d => d -> m d) -> a -> m a)
    -> (forall (m :: * -> *).
        MonadPlus m =>
        (forall d. Data d => d -> m d) -> a -> m a)
    -> Data a
    forall u.
    Int
    -> (forall d. Data d => d -> u) -> HsConDetails tyarg arg rec -> u
    forall u.
    (forall d. Data d => d -> u) -> HsConDetails tyarg arg rec -> [u]
    forall r r'.
    (r -> r' -> r)
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    (r' -> r -> r)
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    -> r
    forall tyarg arg rec.
    (Data tyarg, Data rec, Data arg) =>
    Typeable (HsConDetails tyarg arg rec)
    forall tyarg arg rec.
    (Data tyarg, Data rec, Data arg) =>
    HsConDetails tyarg arg rec -> Constr
    forall tyarg arg rec.
    (Data tyarg, Data rec, Data arg) =>
    HsConDetails tyarg arg rec -> DataType
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    (Data tyarg, Data rec, Data arg) =>
    (forall b. Data b => b -> b)
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    forall tyarg arg rec u.
    (Data tyarg, Data rec, Data arg) =>
    Int
    -> (forall d. Data d => d -> u) -> HsConDetails tyarg arg rec -> u
    forall tyarg arg rec u.
    (Data tyarg, Data rec, Data arg) =>
    (forall d. Data d => d -> u) -> HsConDetails tyarg arg rec -> [u]
    forall tyarg arg rec r r'.
    (Data tyarg, Data rec, Data arg) =>
    (r -> r' -> r)
    -> r
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    forall tyarg arg rec r r'.
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    (r' -> r -> r)
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    forall tyarg arg rec (m :: * -> *).
    (Data tyarg, Data rec, Data arg, Monad m) =>
    (forall d. Data d => d -> m d)
    -> HsConDetails tyarg arg rec -> m (HsConDetails tyarg arg rec)
    forall tyarg arg rec (m :: * -> *).
    (Data tyarg, Data rec, Data arg, MonadPlus m) =>
    (forall d. Data d => d -> m d)
    -> HsConDetails tyarg arg rec -> m (HsConDetails tyarg arg rec)
    forall tyarg arg rec (c :: * -> *).
    (Data tyarg, Data rec, Data arg) =>
    (forall b r. Data b => c (b -> r) -> c r)
    -> (forall r. r -> c r) -> Constr -> c (HsConDetails tyarg arg rec)
    forall tyarg arg rec (c :: * -> *).
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    (forall d b. Data d => c (d -> b) -> d -> c b)
    -> (forall g. g -> c g)
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    forall tyarg arg rec (t :: * -> *) (c :: * -> *).
    (Data tyarg, Data rec, Data arg, Typeable t) =>
    (forall d. Data d => c (t d))
    -> Maybe (c (HsConDetails tyarg arg rec))
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    (Data tyarg, Data rec, Data arg, Typeable t) =>
    (forall d e. (Data d, Data e) => c (t d e))
    -> Maybe (c (HsConDetails tyarg arg rec))
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    Monad m =>
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    (forall d. Data d => d -> m d)
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    (forall b r. Data b => c (b -> r) -> c r)
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    forall (c :: * -> *).
    (forall d b. Data d => c (d -> b) -> d -> c b)
    -> (forall g. g -> c g)
    -> HsConDetails tyarg arg rec
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    forall (t :: * -> *) (c :: * -> *).
    Typeable t =>
    (forall d. Data d => c (t d))
    -> Maybe (c (HsConDetails tyarg arg rec))
    forall (t :: * -> * -> *) (c :: * -> *).
    Typeable t =>
    (forall d e. (Data d, Data e) => c (t d e))
    -> Maybe (c (HsConDetails tyarg arg rec))
    $cgfoldl :: forall tyarg arg rec (c :: * -> *).
    (Data tyarg, Data rec, Data arg) =>
    (forall d b. Data d => c (d -> b) -> d -> c b)
    -> (forall g. g -> c g)
    -> HsConDetails tyarg arg rec
    -> c (HsConDetails tyarg arg rec)
    gfoldl :: forall (c :: * -> *).
    (forall d b. Data d => c (d -> b) -> d -> c b)
    -> (forall g. g -> c g)
    -> HsConDetails tyarg arg rec
    -> c (HsConDetails tyarg arg rec)
    $cgunfold :: forall tyarg arg rec (c :: * -> *).
    (Data tyarg, Data rec, Data arg) =>
    (forall b r. Data b => c (b -> r) -> c r)
    -> (forall r. r -> c r) -> Constr -> c (HsConDetails tyarg arg rec)
    gunfold :: forall (c :: * -> *).
    (forall b r. Data b => c (b -> r) -> c r)
    -> (forall r. r -> c r) -> Constr -> c (HsConDetails tyarg arg rec)
    $ctoConstr :: forall tyarg arg rec.
    (Data tyarg, Data rec, Data arg) =>
    HsConDetails tyarg arg rec -> Constr
    toConstr :: HsConDetails tyarg arg rec -> Constr
    $cdataTypeOf :: forall tyarg arg rec.
    (Data tyarg, Data rec, Data arg) =>
    HsConDetails tyarg arg rec -> DataType
    dataTypeOf :: HsConDetails tyarg arg rec -> DataType
    $cdataCast1 :: forall tyarg arg rec (t :: * -> *) (c :: * -> *).
    (Data tyarg, Data rec, Data arg, Typeable t) =>
    (forall d. Data d => c (t d))
    -> Maybe (c (HsConDetails tyarg arg rec))
    dataCast1 :: forall (t :: * -> *) (c :: * -> *).
    Typeable t =>
    (forall d. Data d => c (t d))
    -> Maybe (c (HsConDetails tyarg arg rec))
    $cdataCast2 :: forall tyarg arg rec (t :: * -> * -> *) (c :: * -> *).
    (Data tyarg, Data rec, Data arg, Typeable t) =>
    (forall d e. (Data d, Data e) => c (t d e))
    -> Maybe (c (HsConDetails tyarg arg rec))
    dataCast2 :: forall (t :: * -> * -> *) (c :: * -> *).
    Typeable t =>
    (forall d e. (Data d, Data e) => c (t d e))
    -> Maybe (c (HsConDetails tyarg arg rec))
    $cgmapT :: forall tyarg arg rec.
    (Data tyarg, Data rec, Data arg) =>
    (forall b. Data b => b -> b)
    -> HsConDetails tyarg arg rec -> HsConDetails tyarg arg rec
    gmapT :: (forall b. Data b => b -> b)
    -> HsConDetails tyarg arg rec -> HsConDetails tyarg arg rec
    $cgmapQl :: forall tyarg arg rec r r'.
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    (r -> r' -> r)
    -> r
    -> (forall d. Data d => d -> r')
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    gmapQl :: forall r r'.
    (r -> r' -> r)
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    -> HsConDetails tyarg arg rec
    -> r
    $cgmapQr :: forall tyarg arg rec r r'.
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    (r' -> r -> r)
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    (r' -> r -> r)
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    -> r
    $cgmapQ :: forall tyarg arg rec u.
    (Data tyarg, Data rec, Data arg) =>
    (forall d. Data d => d -> u) -> HsConDetails tyarg arg rec -> [u]
    gmapQ :: forall u.
    (forall d. Data d => d -> u) -> HsConDetails tyarg arg rec -> [u]
    $cgmapQi :: forall tyarg arg rec u.
    (Data tyarg, Data rec, Data arg) =>
    Int
    -> (forall d. Data d => d -> u) -> HsConDetails tyarg arg rec -> u
    gmapQi :: forall u.
    Int
    -> (forall d. Data d => d -> u) -> HsConDetails tyarg arg rec -> u
    $cgmapM :: forall tyarg arg rec (m :: * -> *).
    (Data tyarg, Data rec, Data arg, Monad m) =>
    (forall d. Data d => d -> m d)
    -> HsConDetails tyarg arg rec -> m (HsConDetails tyarg arg rec)
    gmapM :: forall (m :: * -> *).
    Monad m =>
    (forall d. Data d => d -> m d)
    -> HsConDetails tyarg arg rec -> m (HsConDetails tyarg arg rec)
    $cgmapMp :: forall tyarg arg rec (m :: * -> *).
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    (forall d. Data d => d -> m d)
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    gmapMp :: forall (m :: * -> *).
    MonadPlus m =>
    (forall d. Data d => d -> m d)
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    $cgmapMo :: forall tyarg arg rec (m :: * -> *).
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    (forall d. Data d => d -> m d)
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    MonadPlus m =>
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    Data

    -- | An empty list that can be used to indicate that there are no
    -- type arguments allowed in cases where HsConDetails is applied to Void.
    noTypeArgs :: [Void]
    noTypeArgs :: [Void]
    noTypeArgs = []

    conDetailsArity :: (rec -> Arity) -> HsConDetails tyarg arg rec -> Arity
    conDetailsArity :: forall rec tyarg arg.
    (rec -> Int) -> HsConDetails tyarg arg rec -> Int
    conDetailsArity rec -> Int
    recToArity = \case
      PrefixCon [tyarg]
    _ [arg]
    args -> [arg] -> Int
    forall a. [a] -> Int
    forall (t :: * -> *) a. Foldable t => t a -> Int
    length [arg]
    args
      RecCon rec
    rec -> rec -> Int
    recToArity rec
    rec
      InfixCon arg
    _ arg
    _ -> Int
    2

    {-
    Note [ConDeclField pass]
    ~~~~~~~~~~~~~~~~~~~~~~~~~

    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

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

    {- 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.
    -}

    {- Note [hsScopedTvs and visible foralls]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    ScopedTypeVariables can be defined in terms of a desugaring to TypeAbstractions
    (GHC Proposals #155 and #448):

        fn :: forall a b c. tau(a,b,c)            fn :: forall a b c. tau(a,b,c)
        fn = defn(a,b,c)                   ==>    fn @x @y @z = defn(x,y,z)

    That is, for every type variable of the leading `forall` in the type signature,
    we add an invisible binder at the term level.

    This model does not extend to visible forall. (Visible forall is the one written
    with an arrow instead of a dot, i.e. `forall a ->`. See GHC Proposal #281 and
    the RequiredTypeArguments extension).  Here is an example that demonstrates the
    issue:

      vfn :: forall a b -> tau(a, b)
      vfn = case <scrutinee> of (p,q) -> \x y -> ...

    The `a` and `b` cannot scope over the equations of `vfn`.  In particular,
    `a` and `b` cannot be in scope in <scrutinee> because those type variables
    are bound by the `\x y ->`.

    Our solution is simple: ScopedTypeVariables has no effect on visible forall.
    It follows naturally from the fact that ScopedTypeVariables is already subject
    to several restrictions:

      1. The type signature must be headed by an /explicit/ forall
          * `f :: forall a. a -> blah` brings `a` into scope in the body
          * `f ::           a -> blah` does not

      2. The forall is /not nested/
          * `f :: forall a b. blah`         brings `a` and `b` into scope in the body
          * `f :: forall a. forall b. blah` brings `a` but not `b` into scope in the body

    With the introduction of visible forall, we also introduce a third condition:

      3. The forall has to be /invisible/
          * `f :: forall a b.   blah` brings `a` and `b` into scope in the body
          * `f :: forall a b -> blah` does not

    For example:

       f1 :: forall a. a -> a
       f1 x = (x::a)          -- OK: `a` is in scope in the body

       f2 :: forall a b. a -> b -> (a, b)
       f2 x y = (x::a, y::b)  -- OK: both `a` and `b` are in scope in the body

       f3 :: forall a. forall b. a -> b -> (a, b)
       f3 x y = (x::a, y::b)  -- Wrong: the `forall b.` is not the outermost forall

       f4 :: forall a -> a -> a
       f4 t (x::t) = (x::a)   -- Wrong: the `forall a ->` does not bring `a` into scope

    This design choice is reflected in the definition of HsOuterSigTyVarBndrs, which are
    used in every place where ScopedTypeVariables takes effect:

      data HsOuterTyVarBndrs flag pass
        = HsOuterImplicit { ... }
        | HsOuterExplicit { ..., hso_bndrs :: [LHsTyVarBndr flag pass] }
        | ...
      type HsOuterSigTyVarBndrs = HsOuterTyVarBndrs Specificity

    The HsOuterExplicit constructor is only used in type signatures with outermost,
    /invisible/ 'forall's. Any other type—including those with outermost,
    /visible/ 'forall's—will use HsOuterImplicit. Therefore, when we determine
    which type variables to bring into scope over the body of a function
    (in hsScopedTvs), we /only/ bring the type variables bound by the hso_bndrs in
    an HsOuterExplicit into scope. If we have an HsOuterImplicit instead, then we
    do not bring any type variables into scope over the body of a function at all.
    -}

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

    -- | Arguments in an expression/type after splitting
    data HsArg p tm ty
      = HsValArg !(XValArg p) tm   -- Argument is an ordinary expression     (f arg)
      | HsTypeArg !(XTypeArg p) ty -- Argument is a visible type application (f @ty)
      | HsArgPar !(XArgPar p)      -- See Note [HsArgPar]
      | XArg !(XXArg p)

    type family XValArg  p
    type family XTypeArg p
    type family XArgPar  p
    type family XXArg    p

    -- type level equivalent
    type LHsTypeArg p = HsArg p (LHsType p) (LHsKind p)

    {-
    Note [HsArgPar]
    ~~~~~~~~~~~~~~~
    A HsArgPar indicates that everything to the left of this in the argument list is
    enclosed in parentheses together with the function itself. It is necessary so
    that we can recreate the parenthesis structure in the original source after
    typechecking the arguments.

    The SrcSpan is the span of the original HsPar

    ((f arg1) arg2 arg3) results in an input argument list of
    [HsValArg arg1, HsArgPar span1, HsValArg arg2, HsValArg arg3, HsArgPar span2]

    -}

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

    -- | Located Field Occurrence
    type LFieldOcc pass = XRec pass (FieldOcc pass)

    -- | Field Occurrence
    --
    -- Represents an *occurrence* of a field. This may or may not be a
    -- binding occurrence (e.g. this type is used in 'ConDeclField' and
    -- 'RecordPatSynField' which bind their fields, but also in
    -- 'HsRecField' for record construction and patterns, which do not).
    --
    -- We store both the 'RdrName' the user originally wrote, and after
    -- the renamer we use the extension field to store the selector
    -- function.
    data FieldOcc pass
      = FieldOcc {
            forall pass. FieldOcc pass -> XCFieldOcc pass
    foExt :: XCFieldOcc pass
          , forall pass. FieldOcc pass -> XRec pass RdrName
    foLabel :: XRec pass RdrName -- See Note [Located RdrNames] in Language.Haskell.Syntax.Expr
          }
      | XFieldOcc !(XXFieldOcc pass)
    deriving instance (
        Eq (XRec pass RdrName)
      , Eq (XCFieldOcc pass)
      , Eq (XXFieldOcc pass)
      ) => Eq (FieldOcc pass)

    -- | Located Ambiguous Field Occurrence
    type LAmbiguousFieldOcc pass = XRec pass (AmbiguousFieldOcc pass)

    -- | 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 "GHC.Hs.Pat".
    -- See Note [Located RdrNames] in "GHC.Hs.Expr".
    data AmbiguousFieldOcc pass
      = Unambiguous (XUnambiguous pass) (XRec pass RdrName)
      | Ambiguous   (XAmbiguous pass)   (XRec pass RdrName)
      | XAmbiguousFieldOcc !(XXAmbiguousFieldOcc pass)

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