-----------------------------------------------------------------------------
-- |
-- Module      :  Language.Haskell.Extension
-- Copyright   :  Isaac Jones 2003-2004
--
-- Maintainer  :  libraries@haskell.org
-- Portability :  portable
--
-- Haskell language extensions

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module Language.Haskell.Extension (
        Extension(..),
        knownExtensions
  ) where

import Distribution.Text (Text(..))
import qualified Distribution.Compat.ReadP as Parse
import qualified Text.PrettyPrint as Disp
import qualified Data.Char as Char (isAlphaNum)
import Data.Array (Array, accumArray, bounds, Ix(inRange), (!))

-- ------------------------------------------------------------
-- * Extension
-- ------------------------------------------------------------

-- Note: if you add a new 'Extension':
--
-- * also add it to the Distribution.Simple.X.languageExtensions lists
--   (where X is each compiler: GHC, JHC, Hugs, NHC)
--
-- * also to the 'knownExtensions' list below.
--
-- * If the first character of the new extension is outside the range 'A' - 'V'
--   (ie 'W'-'Z' or any non-uppercase-alphabetical char) then update the bounds
--   of the 'extensionTable' below.

-- |This represents language extensions beyond Haskell 98 that are
-- supported by some implementations, usually in some special mode.

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
--PArr -- not ready yet, and will probably be renamed to ParallelArrays
  | RecordWildCards
  | RecordPuns
  | DisambiguateRecordFields
  | OverloadedStrings
  | GADTs
  | NoMonoPatBinds
  | RelaxedPolyRec
  | ExtendedDefaultRules
  | UnboxedTuples
  | DeriveDataTypeable
  | ConstrainedClassMethods

  -- | Allow imports to be qualified by the package name that the module
  -- is intended to be imported from, e.g.
  --
  -- > import "network" Network.Socket
  | PackageImports

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

  | UnknownExtension String
  deriving (Show, Read, Eq)

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
  , NoMonoPatBinds
  , RelaxedPolyRec
  , ExtendedDefaultRules
  , UnboxedTuples
  , DeriveDataTypeable
  , ConstrainedClassMethods
  , PackageImports
  , ImpredicativeTypes
  , NewQualifiedOperators
  , PostfixOperators
  , QuasiQuotes
  , TransformListComp
  , ViewPatterns
  ]

instance Text Extension where
  disp (UnknownExtension other) = Disp.text other
  disp other                    = Disp.text (show other)

  parse = do
    extension <- Parse.munch1 Char.isAlphaNum
    return (classifyExtension extension)

-- | 'read' for 'Extension's is really really slow so for the Text instance
-- what we do is make a simple table indexed off the first letter in the
-- extension name. The extension names actually cover the range @'A'-'U'@
-- pretty densely and the biggest bucket is 7 so it's not too bad. We just do
-- a linear search within each bucket.
--
-- This gives an order of magnitude improvement in parsing speed, and it'll
-- also allow us to do case insensitive matches in future if we prefer.
--
classifyExtension :: String -> Extension
classifyExtension string@(c:_)
  | inRange (bounds extensionTable) c
  = case lookup string (extensionTable ! c) of
      Just extension    -> extension
      Nothing           -> UnknownExtension string
classifyExtension string = UnknownExtension string

extensionTable :: Array Char [(String, Extension)]
extensionTable =
  accumArray (flip (:)) [] ('A', 'V')
    [ (head str, (str, extension))
    | extension <- knownExtensions
    , let str = show extension ]