Extension.hs

-----------------------------------------------------------------------------
-- |
-- Module      :  Language.Haskell.Exts.Extension
-- Copyright   :  (c) Niklas Broberg 2009
-- License     :  BSD-style (see the file LICENSE.txt)
--
-- Maintainer  :  Niklas Broberg, d00nibro@chalmers.se
-- Stability   :  transient
-- Portability :  portable
--
-- This entire module should be replaced with
-- Language.Haskell.Extension from cabal, but we must
-- wait for a release of cabal that includes the
-- 'XmlSyntax' and 'RegularPatterns' extensions.
--
-----------------------------------------------------------------------------
module Language.Haskell.Exts.Extension (
    -- * Extensions
    Extension(..), classifyExtension, impliesExts,

    -- * Extension groups
    glasgowExts

    ) where


-- | This datatype is a copy of the one in Cabal's Language.Haskell.Extension module.
--   The intention is to eventually import it from Cabal, but we need to wait for
--   the next release of Cabal which includes XmlSyntax and RegularPatterns.
data Extension
  = OverlappingInstances
  | UndecidableInstances
  | IncoherentInstances
  | RecursiveDo
  | ParallelListComp
  | MultiParamTypeClasses
  | NoMonomorphismRestriction
  | FunctionalDependencies
  | Rank2Types
  | RankNTypes
  | PolymorphicComponents
  | ExistentialQuantification
  | ScopedTypeVariables
  | ImplicitParams
  | FlexibleContexts
  | FlexibleInstances
  | EmptyDataDecls
  | CPP

  | KindSignatures
  | BangPatterns
  | TypeSynonymInstances
  | TemplateHaskell
  | ForeignFunctionInterface
  | Arrows
  | Generics
  | NoImplicitPrelude
  | NamedFieldPuns
  | PatternGuards
  | GeneralizedNewtypeDeriving

  | ExtensibleRecords
  | RestrictedTypeSynonyms
  | HereDocuments
  | MagicHash
  | TypeFamilies
  | StandaloneDeriving

  | UnicodeSyntax
  | PatternSignatures
  | UnliftedFFITypes
  | LiberalTypeSynonyms
  | TypeOperators
  | RecordWildCards
  | RecordPuns -- should be deprecated
  | DisambiguateRecordFields
  | OverloadedStrings
  | GADTs
  | MonoPatBinds
  | NoMonoPatBinds -- should be deprecated
  | RelaxedPolyRec
  | ExtendedDefaultRules
  | UnboxedTuples
  | DeriveDataTypeable
  | ConstrainedClassMethods

  | PackageImports

  | ImpredicativeTypes
  | NewQualifiedOperators
  | PostfixOperators
  | QuasiQuotes
  | TransformListComp
  | ViewPatterns

  | XmlSyntax

  | RegularPatterns
  | UnknownExtension String
  deriving (Eq, Ord, Show, Read)


-- | Certain extensions imply other extensions, and this function
--   makes the implication explicit. This also handles deprecated
--   extensions, which imply their replacements.
--   The returned valued is the transitive closure of implied
--   extensions.
impliesExts :: [Extension] -> [Extension]
impliesExts = go
  where go [] = []
        go es = let xs = concatMap implE es
                    ys = filter (not . flip elem es) xs
                 in es ++ go ys

        implE e = case e of
                    TypeFamilies        -> [KindSignatures]
                    RecordPuns          -> [NamedFieldPuns]
                    PatternSignatures   -> [ScopedTypeVariables]
                    XmlSyntax           -> [RegularPatterns]
                    RegularPatterns     -> [PatternGuards]
                    e                   -> []

-- | List of all known extensions. Poor man's 'Enum' instance
--   (we can't enum with the 'UnknownExtension' constructor).
knownExtensions :: [Extension]
knownExtensions =
  [ OverlappingInstances
  , UndecidableInstances
  , IncoherentInstances
  , RecursiveDo
  , ParallelListComp
  , MultiParamTypeClasses
  , NoMonomorphismRestriction
  , FunctionalDependencies
  , Rank2Types
  , RankNTypes
  , PolymorphicComponents
  , ExistentialQuantification
  , ScopedTypeVariables
  , ImplicitParams
  , FlexibleContexts
  , FlexibleInstances
  , EmptyDataDecls
  , CPP

  , KindSignatures
  , BangPatterns
  , TypeSynonymInstances
  , TemplateHaskell
  , ForeignFunctionInterface
  , Arrows
  , Generics
  , NoImplicitPrelude
  , NamedFieldPuns
  , PatternGuards
  , GeneralizedNewtypeDeriving

  , ExtensibleRecords
  , RestrictedTypeSynonyms
  , HereDocuments
  , MagicHash
  , TypeFamilies
  , StandaloneDeriving

  , UnicodeSyntax
  , PatternSignatures
  , UnliftedFFITypes
  , LiberalTypeSynonyms
  , TypeOperators
--PArr -- not ready yet, and will probably be renamed to ParallelArrays
  , RecordWildCards
  , RecordPuns
  , DisambiguateRecordFields
  , OverloadedStrings
  , GADTs
  , MonoPatBinds
  , NoMonoPatBinds
  , RelaxedPolyRec
  , ExtendedDefaultRules
  , UnboxedTuples
  , DeriveDataTypeable
  , ConstrainedClassMethods
  , PackageImports
  , ImpredicativeTypes
  , NewQualifiedOperators
  , PostfixOperators
  , QuasiQuotes
  , TransformListComp
  , ViewPatterns
  , XmlSyntax
  , RegularPatterns
  ]

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



-- | A clever version of read that returns an 'UnknownExtension'
--   if the string is not recognised.
classifyExtension :: String -> Extension
classifyExtension str
  = case readsPrec 0 str of
      [(e,"")]     -> e
      _            -> UnknownExtension str