diff options
Diffstat (limited to 'libraries/base')
| -rw-r--r-- | libraries/base/Control/Monad.hs | 37 |
1 files changed, 15 insertions, 22 deletions
diff --git a/libraries/base/Control/Monad.hs b/libraries/base/Control/Monad.hs index d9bfdebd54..09066c70cc 100644 --- a/libraries/base/Control/Monad.hs +++ b/libraries/base/Control/Monad.hs @@ -156,33 +156,26 @@ f >=> g = \x -> f x >>= g -- -- ==== __Examples__ -- --- Simple network servers can be created by writing a function to --- handle a single client connection and then using 'forever' to --- accept client connections and fork threads to handle them. +-- A common use of 'forever' is to process input from network sockets, +-- 'System.IO.Handle's, and channels +-- (e.g. 'Control.Concurrent.MVar.MVar' and +-- 'Control.Concurrent.Chan.Chan'). -- --- For example, here is a [TCP echo --- server](https://en.wikipedia.org/wiki/Echo_Protocol) implemented --- with 'forever': +-- For example, here is how we might implement an [echo +-- server](https://en.wikipedia.org/wiki/Echo_Protocol), using +-- 'forever' both to listen for client connections on a network socket +-- and to echo client input on client connection handles: -- -- @ --- import "Control.Concurrent" ( 'Control.Concurrent.forkFinally' ) --- import "Control.Monad" ( 'forever' ) --- import Network ( PortID(..), accept, listenOn ) --- import "System.IO" ( 'System.IO.hClose', 'System.IO.hGetLine', 'System.IO.hPutStrLn' ) --- --- main :: IO () --- main = do --- sock <- listenOn (PortNumber 7) --- 'forever' $ do --- (handle, _, _) <- accept sock --- echo handle \`forkFinally\` const (hClose handle) +-- echoServer :: Socket -> IO () +-- echoServer socket = 'forever' $ do +-- client <- accept socket +-- 'Control.Concurrent.forkFinally' (echo client) (\\_ -> hClose client) -- where --- echo handle = 'forever' $ --- hGetLine handle >>= hPutStrLn handle +-- echo :: Handle -> IO () +-- echo client = 'forever' $ +-- hGetLine client >>= hPutStrLn client -- @ --- --- The @Network@ module is provided by the [network --- package](https://hackage.haskell.org/package/network). forever :: (Applicative f) => f a -> f b {-# INLINE forever #-} forever a = let a' = a *> a' in a' |