-- | An abstract interface to a unique symbol generator.
module Data.Unique.Really (
    Unique, newUnique, hashUnique,
    ) where

import Control.Applicative ((<$>))
import Data.Hashable

#if UseGHC

import Control.Exception (evaluate)
import qualified Data.Unique
import System.Mem.StableName

-- | An abstract unique value.
-- Values of type 'Unique' may be compared for equality
-- and hashed into Int.
--
-- Note: Unlike the symbols from "Data.Unique", the symbols from this
-- module do not become equal after reloads in the GHC interpreter!
newtype Unique = Unique (StableName Data.Unique.Unique) deriving (Unique -> Unique -> Bool
(Unique -> Unique -> Bool)
-> (Unique -> Unique -> Bool) -> Eq Unique
forall a. (a -> a -> Bool) -> (a -> a -> Bool) -> Eq a
$c== :: Unique -> Unique -> Bool
== :: Unique -> Unique -> Bool
$c/= :: Unique -> Unique -> Bool
/= :: Unique -> Unique -> Bool
Eq)

newUnique :: IO Unique
newUnique = do
    Unique
x <- IO Unique
Data.Unique.newUnique
    Unique
_ <- Unique -> IO Unique
forall a. a -> IO a
evaluate Unique
x
    StableName Unique -> Unique
Unique (StableName Unique -> Unique)
-> IO (StableName Unique) -> IO Unique
forall (f :: * -> *) a b. Functor f => (a -> b) -> f a -> f b
<$> Unique -> IO (StableName Unique)
forall a. a -> IO (StableName a)
makeStableName Unique
x

hashUnique :: Unique -> Int
hashUnique (Unique StableName Unique
s) = StableName Unique -> Int
forall a. StableName a -> Int
hashStableName StableName Unique
s

#else

import Data.IORef
import System.IO.Unsafe (unsafePerformIO)

{-# NOINLINE refNumber #-}
refNumber :: IORef Integer
refNumber = unsafePerformIO $ newIORef 0

newNumber = atomicModifyIORef' refNumber $ \x -> let x' = x+1 in (x', x')

-- | An abstract unique value.
-- Values of type 'Unique' may be compared for equality
-- and hashed into Int.
--
-- NOTE: You haven't compiled this module with GHC.
-- The functionality will be identitcal to "Data.Unique".
newtype Unique = Unique Integer deriving (Eq,Ord)

newUnique = Unique <$> newNumber
hashUnique (Unique s) = fromIntegral s


#endif

-- | Creates a new object of type 'Unique'.
-- The value returned will not compare equal to any other
-- value of type 'Unique' returned by previous calls to 'newUnique'.
-- There is no limit on the number of times you may call this function.
newUnique  :: IO Unique

-- | Hashes a 'Unique' into an 'Int'.
-- Two Uniques may hash to the same value, although in practice this is unlikely.
-- The 'Int' returned makes a good hash key.
hashUnique :: Unique -> Int

instance Hashable Unique where hashWithSalt :: Int -> Unique -> Int
hashWithSalt Int
s = Int -> Int -> Int
forall a. Hashable a => Int -> a -> Int
hashWithSalt Int
s (Int -> Int) -> (Unique -> Int) -> Unique -> Int
forall b c a. (b -> c) -> (a -> b) -> a -> c
. Unique -> Int
hashUnique