source-code-server-2010.9.1: src/Rika/Type/Default.hs

module Rika.Type.Default where

import qualified Data.ByteString.Char8 as B

import Control.Concurrent.STM

-- BEGIN
-- copy from data.default

import Data.Ratio
import qualified Data.Set as S
import qualified Data.Map as M

import Debug.Trace

-- | A class for types with a default value.
class Default a where
    -- | The default value for this type.
    def :: a

instance Default () where def = ()

instance Default (S.Set v) where def = S.empty
instance Default (M.Map k v) where def = M.empty

instance Default Int where def = 0
instance Default Integer where def = 0
instance Default Float where def = 0
instance Default Double where def = 0
instance (Integral a) => Default (Ratio a) where def = 0

instance Default (Maybe a) where def = Nothing
instance Default [a] where def = []

instance (Default r) => Default (e -> r) where def _ = def
instance (Default a) => Default (IO a) where def = return def

instance (Default a, Default b) => Default (a, b) where
  def = (def, def)

-- END


instance Default (TVar a) where
  def = error "undefined tvar used in default instance"

instance Default B.ByteString where
  def = B.empty