    {-# LANGUAGE DeriveDataTypeable #-}
    {-# LANGUAGE CPP #-}
    -----------------------------------------------------------------------------
    -- |
    -- Module      :  Language.Haskell.Exts.Extension
    -- Copyright   :  (c) Niklas Broberg 2009
    -- License     :  BSD-style (see the file LICENSE.txt)
    --
    -- Maintainer  :  Niklas Broberg, niklas.broberg@chalmers.se
    -- Stability   :  transient
    -- Portability :  portable
    --
    -- This module defines the list of recognized modular features
    -- of Haskell, most often (sloppily) referred to as "extensions".
    --
    -- Closely mimicking the Language.Haskell.Extension module from
    -- the Cabal library, this package also includes functionality for
    -- "computing" languages as sets of features. Also, we make no
    -- promise not to add extensions not yet recognized by Cabal.
    --
    -----------------------------------------------------------------------------
    module Language.Haskell.Exts.Extension (
        -- * Language definitions
        Language(..),
        knownLanguages,
        classifyLanguage,
        prettyLanguage,

        -- * Extensions
        Extension(..), KnownExtension(..),
        classifyExtension,
        parseExtension, prettyExtension,

        -- * Extension groups
        ghcDefault, glasgowExts,
        knownExtensions, deprecatedExtensions,

        -- * Semantics of extensions applied to languages
        impliesExts, toExtensionList

        ) where

    #if __GLASGOW_HASKELL__ < 710
    import Control.Applicative ((<$>), (<|>))
    #else
    import Control.Applicative ((<|>))
    #endif
    import Data.Array (Array, accumArray, bounds, Ix(inRange), (!))
    import Data.List (nub)
    import Data.Maybe (fromMaybe)
    import Data.Data

    -- Copyright notice from Cabal's Language.Haskell.Extension,
    -- from which we borrow plenty of features:

    {- All rights reserved.

    Redistribution and use in source and binary forms, with or without
    modification, are permitted provided that the following conditions are
    met:

        * Redistributions of source code must retain the above copyright
          notice, this list of conditions and the following disclaimer.

        * Redistributions in binary form must reproduce the above
          copyright notice, this list of conditions and the following
          disclaimer in the documentation and/or other materials provided
          with the distribution.

        * Neither the name of Isaac Jones nor the names of other
          contributors may be used to endorse or promote products derived
          from this software without specific prior written permission.

    THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
    "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
    LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
    A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
    OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
    SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
    LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
    DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
    THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
    (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
    OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. -}

    data Language =

      -- | The Haskell 98 language as defined by the Haskell 98 report.
      -- <http://haskell.org/onlinereport/>
         Haskell98

      -- | The Haskell 2010 language as defined by the Haskell 2010 report.
      -- <http://www.haskell.org/onlinereport/haskell2010>
      | Haskell2010

      -- | The minimal language resulting from disabling all recognized
      -- extensions - including ones that are part of all known language
      -- definitions e.g. MonomorphismRestriction.
      | HaskellAllDisabled

      -- | An unknown language, identified by its name.
      | UnknownLanguage String
      deriving (Int -> Language -> ShowS
    [Language] -> ShowS
    Language -> String
    (Int -> Language -> ShowS)
    -> (Language -> String) -> ([Language] -> ShowS) -> Show Language
    forall a.
    (Int -> a -> ShowS) -> (a -> String) -> ([a] -> ShowS) -> Show a
    $cshowsPrec :: Int -> Language -> ShowS
    showsPrec :: Int -> Language -> ShowS
    $cshow :: Language -> String
    show :: Language -> String
    $cshowList :: [Language] -> ShowS
    showList :: [Language] -> ShowS
    Show, ReadPrec [Language]
    ReadPrec Language
    Int -> ReadS Language
    ReadS [Language]
    (Int -> ReadS Language)
    -> ReadS [Language]
    -> ReadPrec Language
    -> ReadPrec [Language]
    -> Read Language
    forall a.
    (Int -> ReadS a)
    -> ReadS [a] -> ReadPrec a -> ReadPrec [a] -> Read a
    $creadsPrec :: Int -> ReadS Language
    readsPrec :: Int -> ReadS Language
    $creadList :: ReadS [Language]
    readList :: ReadS [Language]
    $creadPrec :: ReadPrec Language
    readPrec :: ReadPrec Language
    $creadListPrec :: ReadPrec [Language]
    readListPrec :: ReadPrec [Language]
    Read, Language -> Language -> Bool
    (Language -> Language -> Bool)
    -> (Language -> Language -> Bool) -> Eq Language
    forall a. (a -> a -> Bool) -> (a -> a -> Bool) -> Eq a
    $c== :: Language -> Language -> Bool
    == :: Language -> Language -> Bool
    $c/= :: Language -> Language -> Bool
    /= :: Language -> Language -> Bool
    Eq, Eq Language
    Eq Language =>
    (Language -> Language -> Ordering)
    -> (Language -> Language -> Bool)
    -> (Language -> Language -> Bool)
    -> (Language -> Language -> Bool)
    -> (Language -> Language -> Bool)
    -> (Language -> Language -> Language)
    -> (Language -> Language -> Language)
    -> Ord Language
    Language -> Language -> Bool
    Language -> Language -> Ordering
    Language -> Language -> Language
    forall a.
    Eq a =>
    (a -> a -> Ordering)
    -> (a -> a -> Bool)
    -> (a -> a -> Bool)
    -> (a -> a -> Bool)
    -> (a -> a -> Bool)
    -> (a -> a -> a)
    -> (a -> a -> a)
    -> Ord a
    $ccompare :: Language -> Language -> Ordering
    compare :: Language -> Language -> Ordering
    $c< :: Language -> Language -> Bool
    < :: Language -> Language -> Bool
    $c<= :: Language -> Language -> Bool
    <= :: Language -> Language -> Bool
    $c> :: Language -> Language -> Bool
    > :: Language -> Language -> Bool
    $c>= :: Language -> Language -> Bool
    >= :: Language -> Language -> Bool
    $cmax :: Language -> Language -> Language
    max :: Language -> Language -> Language
    $cmin :: Language -> Language -> Language
    min :: Language -> Language -> Language
    Ord, Typeable Language
    Typeable Language =>
    (forall (c :: * -> *).
     (forall d b. Data d => c (d -> b) -> d -> c b)
     -> (forall g. g -> c g) -> Language -> c Language)
    -> (forall (c :: * -> *).
        (forall b r. Data b => c (b -> r) -> c r)
        -> (forall r. r -> c r) -> Constr -> c Language)
    -> (Language -> Constr)
    -> (Language -> DataType)
    -> (forall (t :: * -> *) (c :: * -> *).
        Typeable t =>
        (forall d. Data d => c (t d)) -> Maybe (c Language))
    -> (forall (t :: * -> * -> *) (c :: * -> *).
        Typeable t =>
        (forall d e. (Data d, Data e) => c (t d e)) -> Maybe (c Language))
    -> ((forall b. Data b => b -> b) -> Language -> Language)
    -> (forall r r'.
        (r -> r' -> r)
        -> r -> (forall d. Data d => d -> r') -> Language -> r)
    -> (forall r r'.
        (r' -> r -> r)
        -> r -> (forall d. Data d => d -> r') -> Language -> r)
    -> (forall u. (forall d. Data d => d -> u) -> Language -> [u])
    -> (forall u. Int -> (forall d. Data d => d -> u) -> Language -> u)
    -> (forall (m :: * -> *).
        Monad m =>
        (forall d. Data d => d -> m d) -> Language -> m Language)
    -> (forall (m :: * -> *).
        MonadPlus m =>
        (forall d. Data d => d -> m d) -> Language -> m Language)
    -> (forall (m :: * -> *).
        MonadPlus m =>
        (forall d. Data d => d -> m d) -> Language -> m Language)
    -> Data Language
    Language -> Constr
    Language -> DataType
    (forall b. Data b => b -> b) -> Language -> Language
    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) -> Language -> u
    forall u. (forall d. Data d => d -> u) -> Language -> [u]
    forall r r'.
    (r -> r' -> r)
    -> r -> (forall d. Data d => d -> r') -> Language -> r
    forall r r'.
    (r' -> r -> r)
    -> r -> (forall d. Data d => d -> r') -> Language -> r
    forall (m :: * -> *).
    Monad m =>
    (forall d. Data d => d -> m d) -> Language -> m Language
    forall (m :: * -> *).
    MonadPlus m =>
    (forall d. Data d => d -> m d) -> Language -> m Language
    forall (c :: * -> *).
    (forall b r. Data b => c (b -> r) -> c r)
    -> (forall r. r -> c r) -> Constr -> c Language
    forall (c :: * -> *).
    (forall d b. Data d => c (d -> b) -> d -> c b)
    -> (forall g. g -> c g) -> Language -> c Language
    forall (t :: * -> *) (c :: * -> *).
    Typeable t =>
    (forall d. Data d => c (t d)) -> Maybe (c Language)
    forall (t :: * -> * -> *) (c :: * -> *).
    Typeable t =>
    (forall d e. (Data d, Data e) => c (t d e)) -> Maybe (c Language)
    $cgfoldl :: forall (c :: * -> *).
    (forall d b. Data d => c (d -> b) -> d -> c b)
    -> (forall g. g -> c g) -> Language -> c Language
    gfoldl :: forall (c :: * -> *).
    (forall d b. Data d => c (d -> b) -> d -> c b)
    -> (forall g. g -> c g) -> Language -> c Language
    $cgunfold :: forall (c :: * -> *).
    (forall b r. Data b => c (b -> r) -> c r)
    -> (forall r. r -> c r) -> Constr -> c Language
    gunfold :: forall (c :: * -> *).
    (forall b r. Data b => c (b -> r) -> c r)
    -> (forall r. r -> c r) -> Constr -> c Language
    $ctoConstr :: Language -> Constr
    toConstr :: Language -> Constr
    $cdataTypeOf :: Language -> DataType
    dataTypeOf :: Language -> DataType
    $cdataCast1 :: forall (t :: * -> *) (c :: * -> *).
    Typeable t =>
    (forall d. Data d => c (t d)) -> Maybe (c Language)
    dataCast1 :: forall (t :: * -> *) (c :: * -> *).
    Typeable t =>
    (forall d. Data d => c (t d)) -> Maybe (c Language)
    $cdataCast2 :: forall (t :: * -> * -> *) (c :: * -> *).
    Typeable t =>
    (forall d e. (Data d, Data e) => c (t d e)) -> Maybe (c Language)
    dataCast2 :: forall (t :: * -> * -> *) (c :: * -> *).
    Typeable t =>
    (forall d e. (Data d, Data e) => c (t d e)) -> Maybe (c Language)
    $cgmapT :: (forall b. Data b => b -> b) -> Language -> Language
    gmapT :: (forall b. Data b => b -> b) -> Language -> Language
    $cgmapQl :: forall r r'.
    (r -> r' -> r)
    -> r -> (forall d. Data d => d -> r') -> Language -> r
    gmapQl :: forall r r'.
    (r -> r' -> r)
    -> r -> (forall d. Data d => d -> r') -> Language -> r
    $cgmapQr :: forall r r'.
    (r' -> r -> r)
    -> r -> (forall d. Data d => d -> r') -> Language -> r
    gmapQr :: forall r r'.
    (r' -> r -> r)
    -> r -> (forall d. Data d => d -> r') -> Language -> r
    $cgmapQ :: forall u. (forall d. Data d => d -> u) -> Language -> [u]
    gmapQ :: forall u. (forall d. Data d => d -> u) -> Language -> [u]
    $cgmapQi :: forall u. Int -> (forall d. Data d => d -> u) -> Language -> u
    gmapQi :: forall u. Int -> (forall d. Data d => d -> u) -> Language -> u
    $cgmapM :: forall (m :: * -> *).
    Monad m =>
    (forall d. Data d => d -> m d) -> Language -> m Language
    gmapM :: forall (m :: * -> *).
    Monad m =>
    (forall d. Data d => d -> m d) -> Language -> m Language
    $cgmapMp :: forall (m :: * -> *).
    MonadPlus m =>
    (forall d. Data d => d -> m d) -> Language -> m Language
    gmapMp :: forall (m :: * -> *).
    MonadPlus m =>
    (forall d. Data d => d -> m d) -> Language -> m Language
    $cgmapMo :: forall (m :: * -> *).
    MonadPlus m =>
    (forall d. Data d => d -> m d) -> Language -> m Language
    gmapMo :: forall (m :: * -> *).
    MonadPlus m =>
    (forall d. Data d => d -> m d) -> Language -> m Language
    Data, Typeable)

    knownLanguages :: [Language]
    knownLanguages :: [Language]
    knownLanguages = [Language
    Haskell98, Language
    Haskell2010]

    classifyLanguage :: String -> Language
    classifyLanguage :: String -> Language
    classifyLanguage String
    str = Language -> Maybe Language -> Language
    forall a. a -> Maybe a -> a
    fromMaybe (String -> Language
    UnknownLanguage String
    str) (Maybe Language -> Language) -> Maybe Language -> Language
    forall a b. (a -> b) -> a -> b
    $ String -> [(String, Language)] -> Maybe Language
    forall a b. Eq a => a -> [(a, b)] -> Maybe b
    lookup String
    str [(String, Language)]
    langTable
      where
        langTable :: [(String, Language)]
    langTable = [ (Language -> String
    forall a. Show a => a -> String
    show Language
    lang, Language
    lang)
                    | Language
    lang <- [Language]
    knownLanguages ]

    prettyLanguage :: Language -> String
    prettyLanguage :: Language -> String
    prettyLanguage (UnknownLanguage String
    name) = String
    name
    prettyLanguage Language
    lang = Language -> String
    forall a. Show a => a -> String
    show Language
    lang

    -- | This represents language extensions beyond a base 'Language' definition
    -- (such as 'Haskell98') that are supported by some implementations, usually
    -- in some special mode.

    data Extension =
      -- | Enable a known extension
        EnableExtension KnownExtension

      -- | Disable a known extension
      | DisableExtension KnownExtension

      -- | An unknown extension, identified by the name of its @LANGUAGE@
      -- pragma.
      | UnknownExtension String
      deriving (Int -> Extension -> ShowS
    [Extension] -> ShowS
    Extension -> String
    (Int -> Extension -> ShowS)
    -> (Extension -> String)
    -> ([Extension] -> ShowS)
    -> Show Extension
    forall a.
    (Int -> a -> ShowS) -> (a -> String) -> ([a] -> ShowS) -> Show a
    $cshowsPrec :: Int -> Extension -> ShowS
    showsPrec :: Int -> Extension -> ShowS
    $cshow :: Extension -> String
    show :: Extension -> String
    $cshowList :: [Extension] -> ShowS
    showList :: [Extension] -> ShowS
    Show, ReadPrec [Extension]
    ReadPrec Extension
    Int -> ReadS Extension
    ReadS [Extension]
    (Int -> ReadS Extension)
    -> ReadS [Extension]
    -> ReadPrec Extension
    -> ReadPrec [Extension]
    -> Read Extension
    forall a.
    (Int -> ReadS a)
    -> ReadS [a] -> ReadPrec a -> ReadPrec [a] -> Read a
    $creadsPrec :: Int -> ReadS Extension
    readsPrec :: Int -> ReadS Extension
    $creadList :: ReadS [Extension]
    readList :: ReadS [Extension]
    $creadPrec :: ReadPrec Extension
    readPrec :: ReadPrec Extension
    $creadListPrec :: ReadPrec [Extension]
    readListPrec :: ReadPrec [Extension]
    Read, Extension -> Extension -> Bool
    (Extension -> Extension -> Bool)
    -> (Extension -> Extension -> Bool) -> Eq Extension
    forall a. (a -> a -> Bool) -> (a -> a -> Bool) -> Eq a
    $c== :: Extension -> Extension -> Bool
    == :: Extension -> Extension -> Bool
    $c/= :: Extension -> Extension -> Bool
    /= :: Extension -> Extension -> Bool
    Eq, Eq Extension
    Eq Extension =>
    (Extension -> Extension -> Ordering)
    -> (Extension -> Extension -> Bool)
    -> (Extension -> Extension -> Bool)
    -> (Extension -> Extension -> Bool)
    -> (Extension -> Extension -> Bool)
    -> (Extension -> Extension -> Extension)
    -> (Extension -> Extension -> Extension)
    -> Ord Extension
    Extension -> Extension -> Bool
    Extension -> Extension -> Ordering
    Extension -> Extension -> Extension
    forall a.
    Eq a =>
    (a -> a -> Ordering)
    -> (a -> a -> Bool)
    -> (a -> a -> Bool)
    -> (a -> a -> Bool)
    -> (a -> a -> Bool)
    -> (a -> a -> a)
    -> (a -> a -> a)
    -> Ord a
    $ccompare :: Extension -> Extension -> Ordering
    compare :: Extension -> Extension -> Ordering
    $c< :: Extension -> Extension -> Bool
    < :: Extension -> Extension -> Bool
    $c<= :: Extension -> Extension -> Bool
    <= :: Extension -> Extension -> Bool
    $c> :: Extension -> Extension -> Bool
    > :: Extension -> Extension -> Bool
    $c>= :: Extension -> Extension -> Bool
    >= :: Extension -> Extension -> Bool
    $cmax :: Extension -> Extension -> Extension
    max :: Extension -> Extension -> Extension
    $cmin :: Extension -> Extension -> Extension
    min :: Extension -> Extension -> Extension
    Ord)

    data KnownExtension =

      -- | [GHC &#xa7; 7.6.3.4] Allow overlapping class instances,
      -- provided there is a unique most specific instance for each use.
        OverlappingInstances

      -- | [GHC &#xa7; 7.6.3.3] Ignore structural rules guaranteeing the
      -- termination of class instance resolution.  Termination is
      -- guaranteed by a fixed-depth recursion stack, and compilation
      -- may fail if this depth is exceeded.
      | UndecidableInstances

      -- | [GHC &#xa7; 7.6.3.4] Implies 'OverlappingInstances'.  Allow the
      -- implementation to choose an instance even when it is possible
      -- that further instantiation of types will lead to a more specific
      -- instance being applicable.
      | IncoherentInstances

      -- | [GHC &#xa7; 7.6.3.5] Allow type signatures in instances.
      | InstanceSigs

      -- | [GHC &#xa7; 7.3.8] Deprecated in GHC.  Allows recursive
      -- bindings in @do@ blocks, using the @rec@ keyword.
      | DoRec

      -- | [GHC &#xa7; 7.3.8.2] Allows recursive bindings using @mdo@, a
      -- variant of @do@, and @rec@.
      | RecursiveDo

      -- | [GHC &#xa7; 7.3.9] Provide syntax for writing list
      -- comprehensions which iterate over several lists together, like
      -- the 'zipWith' family of functions.
      | ParallelListComp

      -- | [GHC &#xa7; 7.6.1.1] Allow multiple parameters in a type class.
      | MultiParamTypeClasses

      -- | [GHC &#xa7; 7.17] Enable the dreaded monomorphism restriction.
      | MonomorphismRestriction

      -- | [GHC &#xa7; 7.6.2] Allow a specification attached to a
      -- multi-parameter type class which indicates that some parameters
      -- are entirely determined by others. The implementation will check
      -- that this property holds for the declared instances, and will use
      -- this property to reduce ambiguity in instance resolution.
      | FunctionalDependencies

      -- | [GHC &#xa7; 7.8.5] Like 'RankNTypes' but does not allow a
      -- higher-rank type to itself appear on the left of a function
      -- arrow.
      | Rank2Types

      -- | [GHC &#xa7; 7.8.5] Allow a universally-quantified type to occur on
      -- the left of a function arrow.
      | RankNTypes

      -- | [GHC &#xa7; 7.8.5] Allow data constructors to have polymorphic
      -- arguments.  Unlike 'RankNTypes', does not allow this for ordinary
      -- functions.
      | PolymorphicComponents

      -- | [GHC &#xa7; 7.4.4] Allow existentially-quantified data constructors.
      | ExistentialQuantification

      -- | [GHC &#xa7; 7.8.7] Cause a type variable in a signature, which has an
      -- explicit @forall@ quantifier, to scope over the definition of the
      -- accompanying value declaration.
      | ScopedTypeVariables

      -- | Deprecated, use 'ScopedTypeVariables' instead.
      | PatternSignatures

      -- | [GHC &#xa7; 7.8.3] Enable implicit function parameters with dynamic
      -- scope.
      | ImplicitParams

      -- | [GHC &#xa7; 7.8.2] Relax some restrictions on the form of the context
      -- of a type signature.
      | FlexibleContexts

      -- | [GHC &#xa7; 7.6.3.2] Relax some restrictions on the form of the
      -- context of an instance declaration.
      | FlexibleInstances

      -- | [GHC &#xa7; 7.4.1] Allow data type declarations with no constructors.
      | EmptyDataDecls

      -- | [GHC &#xa7; 4.10.3] Run the C preprocessor on Haskell source code.
      | CPP

      -- | [GHC &#xa7; 7.8.4] Allow an explicit kind signature giving the kind of
      -- types over which a type variable ranges.
      | KindSignatures

      -- | [GHC &#xa7; 7.11] Enable a form of pattern which forces evaluation
      -- before an attempted match, and a form of strict @let@/@where@
      -- binding.
      | BangPatterns

      -- | [GHC &#xa7; 7.6.3.1] Allow type synonyms in instance heads.
      | TypeSynonymInstances

      -- | [GHC &#xa7; 7.9] Enable Template Haskell, a system for compile-time
      -- metaprogramming.
      | TemplateHaskell

      -- | [GHC &#xa7; 8] Enable the Foreign Function Interface.  In GHC,
      -- implements the standard Haskell 98 Foreign Function Interface
      -- Addendum, plus some GHC-specific extensions.
      | ForeignFunctionInterface

      -- | [GHC &#xa7; 7.10] Enable arrow notation.
      | Arrows

      -- | [GHC &#xa7; 7.16] Enable generic type classes, with default instances
      -- defined in terms of the algebraic structure of a type.
      | Generics

      -- | [GHC &#xa7; 7.3.11] Enable the implicit importing of the module
      -- @Prelude@.  When disabled, when desugaring certain built-in syntax
      -- into ordinary identifiers, use whatever is in scope rather than the
      -- @Prelude@ -- version.
      | ImplicitPrelude

      -- | [GHC &#xa7; 7.3.15] Enable syntax for implicitly binding local names
      -- corresponding to the field names of a record.  Puns bind specific
      -- names, unlike 'RecordWildCards'.
      | NamedFieldPuns

      -- | [GHC &#xa7; 7.3.5] Enable a form of guard which matches a pattern and
      -- binds variables.
      | PatternGuards

      -- | [GHC &#xa7; 7.5.4] Allow a type declared with @newtype@ to use
      -- @deriving@ for any class with an instance for the underlying type.
      | GeneralizedNewtypeDeriving

      -- | [GHC &#xa7; 9.6.10] Allow use of any typeclass in deriving clauses.
      | DeriveAnyClass

      -- | [Hugs &#xa7; 7.1] Enable the \"Trex\" extensible records system.
      | ExtensibleRecords

      -- | [Hugs &#xa7; 7.2] Enable type synonyms which are transparent in
      -- some definitions and opaque elsewhere, as a way of implementing
      -- abstract datatypes.
      | RestrictedTypeSynonyms

      -- | [Hugs &#xa7; 7.3] Enable an alternate syntax for string literals,
      -- with string templating.
      | HereDocuments

      -- | [GHC &#xa7; 7.3.2] Allow the character @#@ as a postfix modifier on
      -- identifiers.  Also enables literal syntax for unboxed values.
      | MagicHash

      -- | Binary integer literals
      | BinaryLiterals

      -- | [GHC &#xa7; 7.7] Allow data types and type synonyms which are
      -- indexed by types, i.e. ad-hoc polymorphism for types.
      | TypeFamilies

      -- | [GHC &#xa7; 7.5.2] Allow a standalone declaration which invokes the
      -- type class @deriving@ mechanism.
      | StandaloneDeriving

      -- | [GHC &#xa7; 7.3.1] Allow certain Unicode characters to stand for
      -- certain ASCII character sequences, e.g. keywords and punctuation.
      | UnicodeSyntax

      -- | [GHC &#xa7; 8.1.1] Allow the use of unboxed types as foreign types,
      -- e.g. in @foreign import@ and @foreign export@.
      | UnliftedFFITypes

      -- | [GHC &#xa7; 7.4.3] Defer validity checking of types until after
      -- expanding type synonyms, relaxing the constraints on how synonyms
      -- may be used.
      | LiberalTypeSynonyms

      -- | [GHC &#xa7; 7.4.2] Allow the name of a type constructor, type class,
      -- or type variable to be an infix operator.
      | TypeOperators

      -- | [GHC &#xa7; 7.26.5] Parallel arrays for Data Parallel Haskell.
      | ParallelArrays

      -- | [GHC &#xa7; 7.3.16] Enable syntax for implicitly binding local names
      -- corresponding to the field names of a record.  A wildcard binds
      -- all unmentioned names, unlike 'NamedFieldPuns'.
      | RecordWildCards

      -- | Deprecated, use 'NamedFieldPuns' instead.
      | RecordPuns

      -- | [GHC &#xa7; 7.3.14] Allow a record field name to be disambiguated
      -- by the type of the record it's in.
      | DisambiguateRecordFields

      -- | [GHC &#xa7; 7.6.4] Enable overloading of string literals using a
      -- type class, much like integer literals.
      | OverloadedStrings

      -- | [GHC &#xa7; 7.4.6] Enable generalized algebraic data types, in
      -- which type variables may be instantiated on a per-constructor
      -- basis. Implies GADTSyntax.
      | GADTs

    {- GADTSyntax (the extension name) not yet supported by HSE

      -- | Enable GADT syntax for declaring ordinary algebraic datatypes.
      | GADTSyntax

    -}

      -- | [GHC &#xa7; 7.17.2] Make pattern bindings monomorphic.
      | MonoPatBinds

      -- | [GHC &#xa7; 7.8.8] Relax the requirements on mutually-recursive
      -- polymorphic functions.
      | RelaxedPolyRec

      -- | [GHC &#xa7; 2.4.5] Allow default instantiation of polymorphic
      -- types in more situations.
      | ExtendedDefaultRules

      -- | [GHC &#xa7; 7.2.2] Enable unboxed tuples.
      | UnboxedTuples

      -- | [GHC &#xa7; 7.5.3] Enable @deriving@ for classes
      -- @Data.Typeable.Typeable@ and @Data.Generics.Data@.
      | DeriveDataTypeable

      -- | [GHC &#xa7; 7.6.1.3] Allow a class method's type to place
      -- additional constraints on a class type variable.
      | ConstrainedClassMethods

      -- | [GHC &#xa7; 7.3.18] Allow imports to be qualified by the package
      -- name the module is intended to be imported from, e.g.
      --
      -- > import "network" Network.Socket
      | PackageImports

      | LambdaCase

      -- | [GHC &#xa7; 7.3.20] Allow case expressions with no alternatives.
      | EmptyCase

      -- | [GHC &#xa7; 7.8.6] Deprecated in GHC 6.12 and will be removed in
      -- GHC 7.  Allow a type variable to be instantiated at a
      -- polymorphic type.
      | ImpredicativeTypes

      -- | [GHC &#xa7; 7.3.3] Change the syntax for qualified infix
      -- operators.
      | NewQualifiedOperators

      -- | [GHC &#xa7; 7.3.12] Relax the interpretation of left operator
      -- sections to allow unary postfix operators.
      | PostfixOperators

      -- | [GHC &#xa7; 7.9.5] Enable quasi-quotation, a mechanism for defining
      -- new concrete syntax for expressions and patterns.
      | QuasiQuotes

      -- | [GHC &#xa7; 7.3.10] Enable generalized list comprehensions,
      -- supporting operations such as sorting and grouping.
      | TransformListComp

      -- | [GHC &#xa7; 7.3.6] Enable view patterns, which match a value by
      -- applying a function and matching on the result.
      | ViewPatterns

      -- | Allow concrete XML syntax to be used in expressions and patterns,
      -- as per the Haskell Server Pages extension language:
      -- <http://www.haskell.org/haskellwiki/HSP>. The ideas behind it are
      -- discussed in the paper \"Haskell Server Pages through Dynamic Loading\"
      -- by Niklas Broberg, from Haskell Workshop '05.
      | XmlSyntax

      -- | Allow regular pattern matching over lists, as discussed in the
      -- paper \"Regular Expression Patterns\" by Niklas Broberg, Andreas Farre
      -- and Josef Svenningsson, from ICFP '04.
      | RegularPatterns

      -- | Enables the use of tuple sections, e.g. @(, True)@ desugars into
      -- @\x -> (x, True)@.
      | TupleSections

      -- | Allows GHC primops, written in C--, to be imported into a Haskell
      -- file.
      | GHCForeignImportPrim

      -- | Support for patterns of the form @n + k@, where @k@ is an
      -- integer literal.
      | NPlusKPatterns

      -- | Improve the layout rule when @if@ expressions are used in a @do@
      -- block.
      | DoAndIfThenElse

      -- | Makes much of the Haskell sugar be desugared into calls to the
      -- function with a particular name that is in scope.
      | RebindableSyntax

      -- | Make @forall@ a keyword in types, which can be used to give the
      -- generalisation explicitly.
      | ExplicitForAll

      -- | Allow contexts to be put on datatypes, e.g. the @Eq a@ in
      -- @data Eq a => Set a = NilSet | ConsSet a (Set a)@.
      | DatatypeContexts

      -- | Local (@let@ and @where@) bindings are monomorphic.
      | MonoLocalBinds

      -- | Enable @deriving@ for the @Data.Functor.Functor@ class.
      | DeriveFunctor

      -- | [GHC &#xa7; 7.5.3] Enable @deriving@ for the @Generic@ and @Generic1@ classes.
      | DeriveGeneric

      -- | Enable @deriving@ for the @Data.Traversable.Traversable@ class.
      | DeriveTraversable

      -- | Enable @deriving@ for the @Data.Foldable.Foldable@ class.
      | DeriveFoldable

      -- | Enable non-decreasing indentation for 'do' blocks.
      | NondecreasingIndentation

      -- | [GHC &#xa7; 8.1.4] Enable interruptible FFI.
      | InterruptibleFFI

      -- | [GHC &#xa7; 8.1.5] Enable the 'capi' calling convention in the
      -- foreign function interface.
      | CApiFFI

      -- | GHCJS FFI extension with convenient import patterns,
      -- asynchronous FFI and a JSVal FFI type
      | JavaScriptFFI

      -- | [GHC &#xa7; 7.3.27] Enable explicit namespaces in import/export.
      | ExplicitNamespaces

      | DataKinds

      | PolyKinds

      -- | [GHC &#xa7; 7.3.16] Enable the multi-way if-expressions
      -- extension to accept conditional expressions with multiple branches.
      | MultiWayIf

      -- | [GHC &#xa7; 7.20.3] Allow imports to be qualified with a safe
      -- keyword that requires the imported module be trusted as according
      -- to the Safe Haskell definition of trust.
      --
      -- > import safe Network.Socket
      | SafeImports

      -- | [GHC &#xa7; 7.20] Compile a module in the Safe, Safe Haskell
      -- mode -- a restricted form of the Haskell language to ensure
      -- type safety.
      | Safe

      -- | [GHC &#xa7; 7.20] Compile a module in the Trustworthy, Safe
      -- Haskell mode -- no restrictions apply but the module is marked
      -- as trusted as long as the package the module resides in is
      -- trusted.
      | Trustworthy

      -- | [GHC &#xa7; 7.6.1.4] Allow default signatures in class
      -- definitions. They apply to default methods implemented in this
      -- class.
      | DefaultSignatures

    -- ConstraintKinds not generally supported by HSE. This flag makes RCategory2.hs
    -- pass testing though.

      -- | [GHC &#xa7; 7.40] Allow type class/implicit parameter/equality
      -- constraints to be used as types with the special kind Constraint.
      -- Also generalise the (ctxt => ty) syntax so that any type of kind
      -- Constraint can occur before the arrow.
      | ConstraintKinds

      -- | [GHC &#xa7; 7.25.3] Allow role annotations.
      | RoleAnnotations
      -- | [GHC &#xa7; 7.3.8] Enable giving names to parametrized pattern
      -- schemes
      | PatternSynonyms

      -- | [GHC &#xa7; 7.15] Allow partial specified type signatures.
      -- Note that this extension does not affect parsing. It only affects whether the
      -- program is able to be run with partial signatures.
      | PartialTypeSignatures

      -- | [GHC &#xa7; 7.15.1.2] This extension treats type variables which
      -- start with an underscore as wildcards. For example, `foo :: _x` is
      -- equivalent to `foo :: _`.
      | NamedWildCards

      | TypeApplications

      | TypeFamilyDependencies

      | OverloadedLabels

      -- | Allow multiple @deriving@ clauses, each optionally qualified with a
      -- /strategy/.
      | DerivingStrategies

      | UnboxedSums

      | TypeInType

      | Strict

      | StrictData

      -- | Enable deriving instances via types of the same runtime representation.
      -- Implies 'DerivingStrategies'.
      | DerivingVia

      | QuantifiedConstraints

      | BlockArguments

      deriving (Int -> KnownExtension -> ShowS
    [KnownExtension] -> ShowS
    KnownExtension -> String
    (Int -> KnownExtension -> ShowS)
    -> (KnownExtension -> String)
    -> ([KnownExtension] -> ShowS)
    -> Show KnownExtension
    forall a.
    (Int -> a -> ShowS) -> (a -> String) -> ([a] -> ShowS) -> Show a
    $cshowsPrec :: Int -> KnownExtension -> ShowS
    showsPrec :: Int -> KnownExtension -> ShowS
    $cshow :: KnownExtension -> String
    show :: KnownExtension -> String
    $cshowList :: [KnownExtension] -> ShowS
    showList :: [KnownExtension] -> ShowS
    Show, ReadPrec [KnownExtension]
    ReadPrec KnownExtension
    Int -> ReadS KnownExtension
    ReadS [KnownExtension]
    (Int -> ReadS KnownExtension)
    -> ReadS [KnownExtension]
    -> ReadPrec KnownExtension
    -> ReadPrec [KnownExtension]
    -> Read KnownExtension
    forall a.
    (Int -> ReadS a)
    -> ReadS [a] -> ReadPrec a -> ReadPrec [a] -> Read a
    $creadsPrec :: Int -> ReadS KnownExtension
    readsPrec :: Int -> ReadS KnownExtension
    $creadList :: ReadS [KnownExtension]
    readList :: ReadS [KnownExtension]
    $creadPrec :: ReadPrec KnownExtension
    readPrec :: ReadPrec KnownExtension
    $creadListPrec :: ReadPrec [KnownExtension]
    readListPrec :: ReadPrec [KnownExtension]
    Read, KnownExtension -> KnownExtension -> Bool
    (KnownExtension -> KnownExtension -> Bool)
    -> (KnownExtension -> KnownExtension -> Bool) -> Eq KnownExtension
    forall a. (a -> a -> Bool) -> (a -> a -> Bool) -> Eq a
    $c== :: KnownExtension -> KnownExtension -> Bool
    == :: KnownExtension -> KnownExtension -> Bool
    $c/= :: KnownExtension -> KnownExtension -> Bool
    /= :: KnownExtension -> KnownExtension -> Bool
    Eq, Eq KnownExtension
    Eq KnownExtension =>
    (KnownExtension -> KnownExtension -> Ordering)
    -> (KnownExtension -> KnownExtension -> Bool)
    -> (KnownExtension -> KnownExtension -> Bool)
    -> (KnownExtension -> KnownExtension -> Bool)
    -> (KnownExtension -> KnownExtension -> Bool)
    -> (KnownExtension -> KnownExtension -> KnownExtension)
    -> (KnownExtension -> KnownExtension -> KnownExtension)
    -> Ord KnownExtension
    KnownExtension -> KnownExtension -> Bool
    KnownExtension -> KnownExtension -> Ordering
    KnownExtension -> KnownExtension -> KnownExtension
    forall a.
    Eq a =>
    (a -> a -> Ordering)
    -> (a -> a -> Bool)
    -> (a -> a -> Bool)
    -> (a -> a -> Bool)
    -> (a -> a -> Bool)
    -> (a -> a -> a)
    -> (a -> a -> a)
    -> Ord a
    $ccompare :: KnownExtension -> KnownExtension -> Ordering
    compare :: KnownExtension -> KnownExtension -> Ordering
    $c< :: KnownExtension -> KnownExtension -> Bool
    < :: KnownExtension -> KnownExtension -> Bool
    $c<= :: KnownExtension -> KnownExtension -> Bool
    <= :: KnownExtension -> KnownExtension -> Bool
    $c> :: KnownExtension -> KnownExtension -> Bool
    > :: KnownExtension -> KnownExtension -> Bool
    $c>= :: KnownExtension -> KnownExtension -> Bool
    >= :: KnownExtension -> KnownExtension -> Bool
    $cmax :: KnownExtension -> KnownExtension -> KnownExtension
    max :: KnownExtension -> KnownExtension -> KnownExtension
    $cmin :: KnownExtension -> KnownExtension -> KnownExtension
    min :: KnownExtension -> KnownExtension -> KnownExtension
    Ord, Int -> KnownExtension
    KnownExtension -> Int
    KnownExtension -> [KnownExtension]
    KnownExtension -> KnownExtension
    KnownExtension -> KnownExtension -> [KnownExtension]
    KnownExtension
    -> KnownExtension -> KnownExtension -> [KnownExtension]
    (KnownExtension -> KnownExtension)
    -> (KnownExtension -> KnownExtension)
    -> (Int -> KnownExtension)
    -> (KnownExtension -> Int)
    -> (KnownExtension -> [KnownExtension])
    -> (KnownExtension -> KnownExtension -> [KnownExtension])
    -> (KnownExtension -> KnownExtension -> [KnownExtension])
    -> (KnownExtension
        -> KnownExtension -> KnownExtension -> [KnownExtension])
    -> Enum KnownExtension
    forall a.
    (a -> a)
    -> (a -> a)
    -> (Int -> a)
    -> (a -> Int)
    -> (a -> [a])
    -> (a -> a -> [a])
    -> (a -> a -> [a])
    -> (a -> a -> a -> [a])
    -> Enum a
    $csucc :: KnownExtension -> KnownExtension
    succ :: KnownExtension -> KnownExtension
    $cpred :: KnownExtension -> KnownExtension
    pred :: KnownExtension -> KnownExtension
    $ctoEnum :: Int -> KnownExtension
    toEnum :: Int -> KnownExtension
    $cfromEnum :: KnownExtension -> Int
    fromEnum :: KnownExtension -> Int
    $cenumFrom :: KnownExtension -> [KnownExtension]
    enumFrom :: KnownExtension -> [KnownExtension]
    $cenumFromThen :: KnownExtension -> KnownExtension -> [KnownExtension]
    enumFromThen :: KnownExtension -> KnownExtension -> [KnownExtension]
    $cenumFromTo :: KnownExtension -> KnownExtension -> [KnownExtension]
    enumFromTo :: KnownExtension -> KnownExtension -> [KnownExtension]
    $cenumFromThenTo :: KnownExtension
    -> KnownExtension -> KnownExtension -> [KnownExtension]
    enumFromThenTo :: KnownExtension
    -> KnownExtension -> KnownExtension -> [KnownExtension]
    Enum, KnownExtension
    KnownExtension -> KnownExtension -> Bounded KnownExtension
    forall a. a -> a -> Bounded a
    $cminBound :: KnownExtension
    minBound :: KnownExtension
    $cmaxBound :: KnownExtension
    maxBound :: KnownExtension
    Bounded, Typeable KnownExtension
    Typeable KnownExtension =>
    (forall (c :: * -> *).
     (forall d b. Data d => c (d -> b) -> d -> c b)
     -> (forall g. g -> c g) -> KnownExtension -> c KnownExtension)
    -> (forall (c :: * -> *).
        (forall b r. Data b => c (b -> r) -> c r)
        -> (forall r. r -> c r) -> Constr -> c KnownExtension)
    -> (KnownExtension -> Constr)
    -> (KnownExtension -> DataType)
    -> (forall (t :: * -> *) (c :: * -> *).
        Typeable t =>
        (forall d. Data d => c (t d)) -> Maybe (c KnownExtension))
    -> (forall (t :: * -> * -> *) (c :: * -> *).
        Typeable t =>
        (forall d e. (Data d, Data e) => c (t d e))
        -> Maybe (c KnownExtension))
    -> ((forall b. Data b => b -> b)
        -> KnownExtension -> KnownExtension)
    -> (forall r r'.
        (r -> r' -> r)
        -> r -> (forall d. Data d => d -> r') -> KnownExtension -> r)
    -> (forall r r'.
        (r' -> r -> r)
        -> r -> (forall d. Data d => d -> r') -> KnownExtension -> r)
    -> (forall u.
        (forall d. Data d => d -> u) -> KnownExtension -> [u])
    -> (forall u.
        Int -> (forall d. Data d => d -> u) -> KnownExtension -> u)
    -> (forall (m :: * -> *).
        Monad m =>
        (forall d. Data d => d -> m d)
        -> KnownExtension -> m KnownExtension)
    -> (forall (m :: * -> *).
        MonadPlus m =>
        (forall d. Data d => d -> m d)
        -> KnownExtension -> m KnownExtension)
    -> (forall (m :: * -> *).
        MonadPlus m =>
        (forall d. Data d => d -> m d)
        -> KnownExtension -> m KnownExtension)
    -> Data KnownExtension
    KnownExtension -> Constr
    KnownExtension -> DataType
    (forall b. Data b => b -> b) -> KnownExtension -> KnownExtension
    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) -> KnownExtension -> u
    forall u. (forall d. Data d => d -> u) -> KnownExtension -> [u]
    forall r r'.
    (r -> r' -> r)
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    forall r r'.
    (r' -> r -> r)
    -> r -> (forall d. Data d => d -> r') -> KnownExtension -> r
    forall (m :: * -> *).
    Monad m =>
    (forall d. Data d => d -> m d)
    -> KnownExtension -> m KnownExtension
    forall (m :: * -> *).
    MonadPlus m =>
    (forall d. Data d => d -> m d)
    -> KnownExtension -> m KnownExtension
    forall (c :: * -> *).
    (forall b r. Data b => c (b -> r) -> c r)
    -> (forall r. r -> c r) -> Constr -> c KnownExtension
    forall (c :: * -> *).
    (forall d b. Data d => c (d -> b) -> d -> c b)
    -> (forall g. g -> c g) -> KnownExtension -> c KnownExtension
    forall (t :: * -> *) (c :: * -> *).
    Typeable t =>
    (forall d. Data d => c (t d)) -> Maybe (c KnownExtension)
    forall (t :: * -> * -> *) (c :: * -> *).
    Typeable t =>
    (forall d e. (Data d, Data e) => c (t d e))
    -> Maybe (c KnownExtension)
    $cgfoldl :: forall (c :: * -> *).
    (forall d b. Data d => c (d -> b) -> d -> c b)
    -> (forall g. g -> c g) -> KnownExtension -> c KnownExtension
    gfoldl :: forall (c :: * -> *).
    (forall d b. Data d => c (d -> b) -> d -> c b)
    -> (forall g. g -> c g) -> KnownExtension -> c KnownExtension
    $cgunfold :: forall (c :: * -> *).
    (forall b r. Data b => c (b -> r) -> c r)
    -> (forall r. r -> c r) -> Constr -> c KnownExtension
    gunfold :: forall (c :: * -> *).
    (forall b r. Data b => c (b -> r) -> c r)
    -> (forall r. r -> c r) -> Constr -> c KnownExtension
    $ctoConstr :: KnownExtension -> Constr
    toConstr :: KnownExtension -> Constr
    $cdataTypeOf :: KnownExtension -> DataType
    dataTypeOf :: KnownExtension -> DataType
    $cdataCast1 :: forall (t :: * -> *) (c :: * -> *).
    Typeable t =>
    (forall d. Data d => c (t d)) -> Maybe (c KnownExtension)
    dataCast1 :: forall (t :: * -> *) (c :: * -> *).
    Typeable t =>
    (forall d. Data d => c (t d)) -> Maybe (c KnownExtension)
    $cdataCast2 :: forall (t :: * -> * -> *) (c :: * -> *).
    Typeable t =>
    (forall d e. (Data d, Data e) => c (t d e))
    -> Maybe (c KnownExtension)
    dataCast2 :: forall (t :: * -> * -> *) (c :: * -> *).
    Typeable t =>
    (forall d e. (Data d, Data e) => c (t d e))
    -> Maybe (c KnownExtension)
    $cgmapT :: (forall b. Data b => b -> b) -> KnownExtension -> KnownExtension
    gmapT :: (forall b. Data b => b -> b) -> KnownExtension -> KnownExtension
    $cgmapQl :: forall r r'.
    (r -> r' -> r)
    -> r -> (forall d. Data d => d -> r') -> KnownExtension -> r
    gmapQl :: forall r r'.
    (r -> r' -> r)
    -> r -> (forall d. Data d => d -> r') -> KnownExtension -> r
    $cgmapQr :: forall r r'.
    (r' -> r -> r)
    -> r -> (forall d. Data d => d -> r') -> KnownExtension -> r
    gmapQr :: forall r r'.
    (r' -> r -> r)
    -> r -> (forall d. Data d => d -> r') -> KnownExtension -> r
    $cgmapQ :: forall u. (forall d. Data d => d -> u) -> KnownExtension -> [u]
    gmapQ :: forall u. (forall d. Data d => d -> u) -> KnownExtension -> [u]
    $cgmapQi :: forall u.
    Int -> (forall d. Data d => d -> u) -> KnownExtension -> u
    gmapQi :: forall u.
    Int -> (forall d. Data d => d -> u) -> KnownExtension -> u
    $cgmapM :: forall (m :: * -> *).
    Monad m =>
    (forall d. Data d => d -> m d)
    -> KnownExtension -> m KnownExtension
    gmapM :: forall (m :: * -> *).
    Monad m =>
    (forall d. Data d => d -> m d)
    -> KnownExtension -> m KnownExtension
    $cgmapMp :: forall (m :: * -> *).
    MonadPlus m =>
    (forall d. Data d => d -> m d)
    -> KnownExtension -> m KnownExtension
    gmapMp :: forall (m :: * -> *).
    MonadPlus m =>
    (forall d. Data d => d -> m d)
    -> KnownExtension -> m KnownExtension
    $cgmapMo :: forall (m :: * -> *).
    MonadPlus m =>
    (forall d. Data d => d -> m d)
    -> KnownExtension -> m KnownExtension
    gmapMo :: forall (m :: * -> *).
    MonadPlus m =>
    (forall d. Data d => d -> m d)
    -> KnownExtension -> m KnownExtension
    Data, Typeable)

    -- | Certain extensions imply other extensions, and this function
    --   makes the implication explicit. This also handles deprecated
    --   extensions, which imply their replacements.
    --   The returned value is the transitive closure of implied
    --   extensions.
    {-impliesExts :: [Extension] -> [Extension]
    impliesExts exts =
        let posExts = [ ke | EnableExtension  ke <- exts ]
            negExts = [ ke | DisableExtension ke <- exts ]

            implExts = impliesKnownExts posExts
         in
    -}
    impliesExts :: [KnownExtension] -> [KnownExtension]
    impliesExts :: [KnownExtension] -> [KnownExtension]
    impliesExts = [KnownExtension] -> [KnownExtension]
    go
      where go :: [KnownExtension] -> [KnownExtension]
    go [] = []
            go [KnownExtension]
    es = let xs :: [KnownExtension]
    xs = (KnownExtension -> [KnownExtension])
    -> [KnownExtension] -> [KnownExtension]
    forall (t :: * -> *) a b. Foldable t => (a -> [b]) -> t a -> [b]
    concatMap KnownExtension -> [KnownExtension]
    implE [KnownExtension]
    es
                        ys :: [KnownExtension]
    ys = (KnownExtension -> Bool) -> [KnownExtension] -> [KnownExtension]
    forall a. (a -> Bool) -> [a] -> [a]
    filter (Bool -> Bool
    not (Bool -> Bool)
    -> (KnownExtension -> Bool) -> KnownExtension -> Bool
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . (KnownExtension -> [KnownExtension] -> Bool)
    -> [KnownExtension] -> KnownExtension -> Bool
    forall a b c. (a -> b -> c) -> b -> a -> c
    flip KnownExtension -> [KnownExtension] -> Bool
    forall a. Eq a => a -> [a] -> Bool
    forall (t :: * -> *) a. (Foldable t, Eq a) => a -> t a -> Bool
    elem [KnownExtension]
    es) [KnownExtension]
    xs
                     in [KnownExtension]
    es [KnownExtension] -> [KnownExtension] -> [KnownExtension]
    forall a. [a] -> [a] -> [a]
    ++ [KnownExtension] -> [KnownExtension]
    go [KnownExtension]
    ys

            implE :: KnownExtension -> [KnownExtension]
    implE KnownExtension
    e = case KnownExtension
    e of
                        KnownExtension
    TypeFamilies        -> [KnownExtension
    KindSignatures]
                        KnownExtension
    ScopedTypeVariables -> [KnownExtension
    TypeOperators, KnownExtension
    ExplicitForAll]
                        KnownExtension
    XmlSyntax           -> [KnownExtension
    RegularPatterns]
                        KnownExtension
    RegularPatterns     -> [KnownExtension
    PatternGuards]
                        KnownExtension
    RankNTypes          -> [KnownExtension
    Rank2Types, KnownExtension
    ExplicitForAll]
                        KnownExtension
    Rank2Types          -> [KnownExtension
    PolymorphicComponents, KnownExtension
    ExplicitForAll]
                        KnownExtension
    PolymorphicComponents   -> [KnownExtension
    ExplicitForAll]
                        KnownExtension
    LiberalTypeSynonyms -> [KnownExtension
    ExplicitForAll]
                        KnownExtension
    ExistentialQuantification -> [KnownExtension
    ExplicitForAll]
                        KnownExtension
    ImpredicativeTypes   -> [KnownExtension
    ExplicitForAll]
                        KnownExtension
    PolyKinds           -> [KnownExtension
    KindSignatures]
                        KnownExtension
    TypeFamilyDependencies -> [KnownExtension
    TypeFamilies]
                        KnownExtension
    TypeInType          -> [KnownExtension
    PolyKinds, KnownExtension
    DataKinds, KnownExtension
    KindSignatures]
                        KnownExtension
    TypeOperators       -> [KnownExtension
    ExplicitNamespaces]
                        -- Deprecations
                        KnownExtension
    RecordPuns          -> [KnownExtension
    NamedFieldPuns]
                        KnownExtension
    PatternSignatures   -> [KnownExtension
    ScopedTypeVariables]
                        KnownExtension
    DerivingVia         -> [KnownExtension
    DerivingStrategies]
                        KnownExtension
    _                   -> []

    -- | The list of extensions enabled by
    --   GHC's portmanteau -fglasgow-exts flag.
    glasgowExts :: [Extension]
    glasgowExts :: [Extension]
    glasgowExts = (KnownExtension -> Extension) -> [KnownExtension] -> [Extension]
    forall a b. (a -> b) -> [a] -> [b]
    map KnownExtension -> Extension
    EnableExtension [
          KnownExtension
    ForeignFunctionInterface
        , KnownExtension
    UnliftedFFITypes
        , KnownExtension
    GADTs
        , KnownExtension
    ImplicitParams
        , KnownExtension
    ScopedTypeVariables
        , KnownExtension
    UnboxedTuples
        , KnownExtension
    TypeSynonymInstances
        , KnownExtension
    StandaloneDeriving
        , KnownExtension
    DeriveDataTypeable
        , KnownExtension
    FlexibleContexts
        , KnownExtension
    FlexibleInstances
        , KnownExtension
    ConstrainedClassMethods
        , KnownExtension
    MultiParamTypeClasses
        , KnownExtension
    FunctionalDependencies
        , KnownExtension
    MagicHash
        , KnownExtension
    PolymorphicComponents
        , KnownExtension
    ExistentialQuantification
        , KnownExtension
    UnicodeSyntax
        , KnownExtension
    PostfixOperators
        , KnownExtension
    PatternGuards
        , KnownExtension
    LiberalTypeSynonyms
        , KnownExtension
    RankNTypes
        , KnownExtension
    ImpredicativeTypes
        , KnownExtension
    TypeOperators
        , KnownExtension
    RecursiveDo
        , KnownExtension
    ParallelListComp
        , KnownExtension
    EmptyDataDecls
        , KnownExtension
    KindSignatures
        , KnownExtension
    GeneralizedNewtypeDeriving
        , KnownExtension
    TypeFamilies
        ]

    -- Not exported, just used locally in several places.
    allLangDefault :: [KnownExtension]
    allLangDefault :: [KnownExtension]
    allLangDefault = [KnownExtension
    MonomorphismRestriction, KnownExtension
    MonoPatBinds, KnownExtension
    ImplicitPrelude]

    ghcDefault :: [Extension]
    ghcDefault :: [Extension]
    ghcDefault = (KnownExtension -> Extension) -> [KnownExtension] -> [Extension]
    forall a b. (a -> b) -> [a] -> [b]
    map KnownExtension -> Extension
    EnableExtension (KnownExtension
    NondecreasingIndentationKnownExtension -> [KnownExtension] -> [KnownExtension]
    forall a. a -> [a] -> [a]
    :[KnownExtension]
    allLangDefault)

    -- | List of all known extensions, both \"yes\" and \"no\" versions.
    knownExtensions :: [Extension]
    knownExtensions :: [Extension]
    knownExtensions =
      [[Extension]] -> [Extension]
    forall (t :: * -> *) a. Foldable t => t [a] -> [a]
    concat [ [KnownExtension -> Extension
    EnableExtension KnownExtension
    x, KnownExtension -> Extension
    DisableExtension KnownExtension
    x] | KnownExtension
    x <- [KnownExtension
    forall a. Bounded a => a
    minBound..KnownExtension
    forall a. Bounded a => a
    maxBound] ]

    -- | Extensions that have been deprecated, possibly paired with another
    -- extension that replaces it.
    --
    deprecatedExtensions :: [(Extension, Maybe Extension)]
    deprecatedExtensions :: [(Extension, Maybe Extension)]
    deprecatedExtensions =
      [ (KnownExtension -> Extension
    EnableExtension KnownExtension
    RecordPuns, Extension -> Maybe Extension
    forall a. a -> Maybe a
    Just (KnownExtension -> Extension
    EnableExtension KnownExtension
    NamedFieldPuns))
      , (KnownExtension -> Extension
    EnableExtension KnownExtension
    PatternSignatures, Extension -> Maybe Extension
    forall a. a -> Maybe a
    Just (KnownExtension -> Extension
    EnableExtension KnownExtension
    ScopedTypeVariables))
      ]

    -- | A clever version of read that returns an 'UnknownExtension'
    --   if the string is not recognised.
    classifyExtension :: String -> Extension
    classifyExtension :: String -> Extension
    classifyExtension String
    string
      = case String -> Maybe KnownExtension
    classifyKnownExtension String
    string of
        Just KnownExtension
    ext -> KnownExtension -> Extension
    EnableExtension KnownExtension
    ext
        Maybe KnownExtension
    Nothing ->
            case String
    string of
            Char
    'N':Char
    'o':String
    string' ->
                case String -> Maybe KnownExtension
    classifyKnownExtension String
    string' of
                Just KnownExtension
    ext -> KnownExtension -> Extension
    DisableExtension KnownExtension
    ext
                Maybe KnownExtension
    Nothing -> String -> Extension
    UnknownExtension String
    string
            String
    _ -> String -> Extension
    UnknownExtension String
    string

    classifyKnownExtension :: String -> Maybe KnownExtension
    classifyKnownExtension :: String -> Maybe KnownExtension
    classifyKnownExtension String
    "" = Maybe KnownExtension
    forall a. Maybe a
    Nothing
    classifyKnownExtension string :: String
    string@(Char
    c : String
    _)
      | (Char, Char) -> Char -> Bool
    forall a. Ix a => (a, a) -> a -> Bool
    inRange (Array Char [(String, KnownExtension)] -> (Char, Char)
    forall i e. Array i e -> (i, i)
    bounds Array Char [(String, KnownExtension)]
    knownExtensionTable) Char
    c
      = String -> [(String, KnownExtension)] -> Maybe KnownExtension
    forall a b. Eq a => a -> [(a, b)] -> Maybe b
    lookup String
    string (Array Char [(String, KnownExtension)]
    knownExtensionTable Array Char [(String, KnownExtension)]
    -> Char -> [(String, KnownExtension)]
    forall i e. Ix i => Array i e -> i -> e
    ! Char
    c)
      | Bool
    otherwise = Maybe KnownExtension
    forall a. Maybe a
    Nothing

    knownExtensionTable :: Array Char [(String, KnownExtension)]
    knownExtensionTable :: Array Char [(String, KnownExtension)]
    knownExtensionTable =
      ([(String, KnownExtension)]
     -> (String, KnownExtension) -> [(String, KnownExtension)])
    -> [(String, KnownExtension)]
    -> (Char, Char)
    -> [(Char, (String, KnownExtension))]
    -> Array Char [(String, KnownExtension)]
    forall i e a.
    Ix i =>
    (e -> a -> e) -> e -> (i, i) -> [(i, a)] -> Array i e
    accumArray (((String, KnownExtension)
     -> [(String, KnownExtension)] -> [(String, KnownExtension)])
    -> [(String, KnownExtension)]
    -> (String, KnownExtension)
    -> [(String, KnownExtension)]
    forall a b c. (a -> b -> c) -> b -> a -> c
    flip (:)) [] (Char
    'A', Char
    'Z')
        [ (String -> Char
    forall a. HasCallStack => [a] -> a
    head String
    str, (String
    str, KnownExtension
    extension))
        | KnownExtension
    extension <- [Int -> KnownExtension
    forall a. Enum a => Int -> a
    toEnum Int
    0 ..]
        , let str :: String
    str = KnownExtension -> String
    forall a. Show a => a -> String
    show KnownExtension
    extension ]

    -- | Parse an enabled or disabled extension; returns
    -- 'UnknownExtension' if the parse fails.
    parseExtension :: String -> Extension
    parseExtension :: String -> Extension
    parseExtension String
    str = Extension -> Maybe Extension -> Extension
    forall a. a -> Maybe a -> a
    fromMaybe (String -> Extension
    UnknownExtension String
    str) (Maybe Extension -> Extension) -> Maybe Extension -> Extension
    forall a b. (a -> b) -> a -> b
    $
          KnownExtension -> Extension
    EnableExtension  (KnownExtension -> Extension)
    -> Maybe KnownExtension -> Maybe Extension
    forall (f :: * -> *) a b. Functor f => (a -> b) -> f a -> f b
    <$> String -> Maybe KnownExtension
    forall a. Read a => String -> Maybe a
    readMay String
    str
      Maybe Extension -> Maybe Extension -> Maybe Extension
    forall a. Maybe a -> Maybe a -> Maybe a
    forall (f :: * -> *) a. Alternative f => f a -> f a -> f a
    <|> KnownExtension -> Extension
    DisableExtension (KnownExtension -> Extension)
    -> Maybe KnownExtension -> Maybe Extension
    forall (f :: * -> *) a b. Functor f => (a -> b) -> f a -> f b
    <$> (String -> Maybe KnownExtension
    forall a. Read a => String -> Maybe a
    readMay (String -> Maybe KnownExtension)
    -> Maybe String -> Maybe KnownExtension
    forall (m :: * -> *) a b. Monad m => (a -> m b) -> m a -> m b
    =<< String -> Maybe String
    dropNo String
    str)
      where
        dropNo :: String -> Maybe String
    dropNo (Char
    'N':Char
    'o':String
    rest) = String -> Maybe String
    forall a. a -> Maybe a
    Just String
    rest
        dropNo String
    _              = Maybe String
    forall a. Maybe a
    Nothing

    -- | Pretty print an extension. Disabled extensions are prefixed with
    -- \'No\'.
    prettyExtension :: Extension -> String
    prettyExtension :: Extension -> String
    prettyExtension (EnableExtension  KnownExtension
    ext) = KnownExtension -> String
    forall a. Show a => a -> String
    show KnownExtension
    ext
    prettyExtension (DisableExtension KnownExtension
    ext) = String
    "No" String -> ShowS
    forall a. [a] -> [a] -> [a]
    ++ KnownExtension -> String
    forall a. Show a => a -> String
    show KnownExtension
    ext
    prettyExtension (UnknownExtension String
    str) = String
    str

    readMay :: Read a => String -> Maybe a
    readMay :: forall a. Read a => String -> Maybe a
    readMay String
    s = case [a
    x | (a
    x,String
    t) <- ReadS a
    forall a. Read a => ReadS a
    reads String
    s, (String
    "",String
    "") <- ReadS String
    lex String
    t] of
                    [a
    x] -> a -> Maybe a
    forall a. a -> Maybe a
    Just a
    x
                    [a]
    _ -> Maybe a
    forall a. Maybe a
    Nothing

    {-------------------------------------------
     -- Transform a 'Language', and possibly a modifying set of'Extension's, into a list
     -- of 'KnownExtension's, to be interpreted as modifying the language you get
     -- when all known extensions are disabled.
     -- Extensions are interpreted in a right-biased fashion, so the last instance
     -- of an occurence of 'EnableExtension' or 'DisableExtension' for a given
     -- 'KnownExtension' takes precedence.
     -------------------------------------------}

    toExtensionList :: Language -> [Extension] -> [KnownExtension]
    toExtensionList :: Language -> [Extension] -> [KnownExtension]
    toExtensionList Language
    lang [Extension]
    exts' =
        let langKes :: [KnownExtension]
    langKes = case Language
    lang of
                        Language
    Haskell98 -> KnownExtension
    NPlusKPatternsKnownExtension -> [KnownExtension] -> [KnownExtension]
    forall a. a -> [a] -> [a]
    :[KnownExtension]
    allLangDefault
                        Language
    Haskell2010 -> [KnownExtension
    DoAndIfThenElse
                                       , KnownExtension
    PatternGuards
                                       , KnownExtension
    ForeignFunctionInterface
                                       , KnownExtension
    EmptyDataDecls
                                       ] [KnownExtension] -> [KnownExtension] -> [KnownExtension]
    forall a. [a] -> [a] -> [a]
    ++ [KnownExtension]
    allLangDefault
                        Language
    HaskellAllDisabled -> []
                        UnknownLanguage String
    s ->
                            String -> [KnownExtension]
    forall a. HasCallStack => String -> a
    error (String -> [KnownExtension]) -> String -> [KnownExtension]
    forall a b. (a -> b) -> a -> b
    $ String
    "toExtensionList: Unknown language " String -> ShowS
    forall a. [a] -> [a] -> [a]
    ++ String
    s
    {-
            addExts = [ ke | EnableExtension  ke <- exts ]
            remExts = [ ke | DisableExtension ke <- exts ]
         in impliesExts $ nub $ (langKes ++ addExts) \\ remExts
    -}
      in [KnownExtension] -> [KnownExtension]
    impliesExts ([KnownExtension] -> [KnownExtension])
    -> [KnownExtension] -> [KnownExtension]
    forall a b. (a -> b) -> a -> b
    $ [KnownExtension] -> [KnownExtension]
    forall a. Eq a => [a] -> [a]
    nub ([KnownExtension] -> [KnownExtension])
    -> [KnownExtension] -> [KnownExtension]
    forall a b. (a -> b) -> a -> b
    $ [KnownExtension] -> [Extension] -> [KnownExtension]
    go [KnownExtension]
    langKes [Extension]
    exts'
        where go :: [KnownExtension] -> [Extension] -> [KnownExtension]
              go :: [KnownExtension] -> [Extension] -> [KnownExtension]
    go [KnownExtension]
    acc [] = [KnownExtension]
    acc
              go [KnownExtension]
    acc (DisableExtension KnownExtension
    x : [Extension]
    exts) = [KnownExtension] -> [Extension] -> [KnownExtension]
    go ((KnownExtension -> Bool) -> [KnownExtension] -> [KnownExtension]
    forall a. (a -> Bool) -> [a] -> [a]
    filter (KnownExtension -> KnownExtension -> Bool
    forall a. Eq a => a -> a -> Bool
    /= KnownExtension
    x) [KnownExtension]
    acc) [Extension]
    exts
              go [KnownExtension]
    acc (EnableExtension  KnownExtension
    x : [Extension]
    exts) = [KnownExtension] -> [Extension] -> [KnownExtension]
    go (KnownExtension
    x KnownExtension -> [KnownExtension] -> [KnownExtension]
    forall a. a -> [a] -> [a]
    : [KnownExtension]
    acc)           [Extension]
    exts
              -- We just throw away UnknownExtensions
              go [KnownExtension]
    acc (Extension
    _ : [Extension]
    exts) = [KnownExtension] -> [Extension] -> [KnownExtension]
    go [KnownExtension]
    acc [Extension]
    exts