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{-# LANGUAGE PatternGuards #-}
-- | A Ninja style environment, basically a linked-list of mutable hash tables.
module Development.Ninja.Env(
Env, newEnv, scopeEnv, addEnv, askEnv, fromEnv
) where
import qualified Data.HashMap.Strict as Map
import Data.Hashable
import Data.IORef
data Env k v = Env (IORef (Map.HashMap k v)) (Maybe (Env k v))
instance Show (Env k v) where show _ = "Env"
newEnv :: IO (Env k v)
newEnv = do ref <- newIORef Map.empty; return $ Env ref Nothing
scopeEnv :: Env k v -> IO (Env k v)
scopeEnv e = do ref <- newIORef Map.empty; return $ Env ref $ Just e
addEnv :: (Eq k, Hashable k) => Env k v -> k -> v -> IO ()
addEnv (Env ref _) k v = modifyIORef ref $ Map.insert k v
askEnv :: (Eq k, Hashable k) => Env k v -> k -> IO (Maybe v)
askEnv (Env ref e) k = do
mp <- readIORef ref
case Map.lookup k mp of
Just v -> return $ Just v
Nothing | Just e <- e -> askEnv e k
_ -> return Nothing
fromEnv :: Env k v -> IO (Map.HashMap k v)
fromEnv (Env ref _) = readIORef ref
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