node.hs

{-# LANGUAGE LambdaCase #-}

-- | Teaching terrible coding practices with the help of purely functional
-- programming. Today: Node.hs!
module NodeHs where



import           Control.Concurrent
import           Control.Exception
import           Control.Monad
import           System.IO          as SIO



withFile :: SIO.FilePath -> (SIO.Handle -> IO ()) -> IO ()
withFile name
  = nodify (openFile name ReadWriteMode)
           hClose
           (error . show)

nodify
    :: IO resource              -- ^ Acquire resource
    -> (resource -> IO ())      -- ^ Release resource
    -> (SomeException -> IO ()) -- ^ Exception handler
    -> (resource -> IO ())      -- ^ Workhorse
    -> IO ()
nodify acquire release errorHandler action = bracket before after thing
  where
    before = acquire
    after _ = pure ()
    thing resource = void (forkFinally (action resource) (\x -> do
        release resource
        case x of
            Left e -> errorHandler e
            Right _ -> pure () ))