Clean up and add documentation

src/EuphApi/CloseableChan.hs

@@ -1,24 +1,39 @@
 {-# LANGUAGE RecordWildCards #-}
 
+-- | Chans that can be closed and reopened.
+--
+-- While a 'CloseableChan' is closed (or locked), it can not be written to or read from.
+-- Calls to 'writeChan' and 'readChan' are non-blocking while a chan is closed.
+--
+-- If a thread is attempting to read from a chan using 'readChan' and that chan is closed,
+-- the call to 'readChan' resumes and @Nothing@ is returned.
+
 module EuphApi.CloseableChan
   ( CloseableChan
-  -- * IO versions
+  -- * IO function versions
-  , newCloseableChan
+  , newOpenChan
+  , newClosedChan
   , writeChan
   , readChan
   , closeChan
+  , openChan
   , emptyChan
-  -- * STM versions
+  -- * STM function versions
-  , newCloseableChanSTM
+  , newOpenChanSTM
+  , newClosedChanSTM
   , writeChanSTM
   , readChanSTM
   , closeChanSTM
+  , openChanSTM
   , emptyChanSTM
   ) where
 
 import           Control.Concurrent.STM
-import           Control.Monad
 
+-- | A 'Chan' that can be closed and opened again.
+--
+-- Attempts to write to or read from a 'CloseableChan' while it is closed result
+-- in a @Nothing@.
 data CloseableChan a = CloseableChan
   { cClosed :: TVar Bool
   , cChan   :: TChan (Content a)
@@ -31,12 +46,21 @@ data Content a = Value a
  - Functions as STM actions
  -}
 
-newCloseableChanSTM :: STM (CloseableChan a)
+-- | See 'newOpenChan'.
-newCloseableChanSTM = do
+newOpenChanSTM :: STM (CloseableChan a)
+newOpenChanSTM = do
   cClosed <- newTVar False
   cChan   <- newTChan
   return $ CloseableChan{..}
 
+-- | See 'newClosedChan'.
+newClosedChanSTM :: STM (CloseableChan a)
+newClosedChanSTM = do
+  cClosed <- newTVar True
+  cChan   <- newTChan
+  return $ CloseableChan{..}
+
+-- | See 'writeChan'.
 writeChanSTM :: CloseableChan a -> a -> STM (Maybe ())
 writeChanSTM CloseableChan{..} a = do
   closed <- readTVar cClosed
@@ -44,6 +68,7 @@ writeChanSTM CloseableChan{..} a = do
     then return Nothing
     else Just <$> writeTChan cChan (Value a)
 
+-- | See 'readChan'.
 readChanSTM :: CloseableChan a -> STM (Maybe a)
 readChanSTM CloseableChan{..} = do
   closed <- readTVar cClosed
@@ -57,11 +82,18 @@ readChanSTM CloseableChan{..} = do
         End     -> readValue -- ignore End while reading normally
         Value v -> return v
 
+-- | See 'closeChan'.
 closeChanSTM :: CloseableChan a -> STM ()
 closeChanSTM CloseableChan{..} = do
   writeTVar cClosed True
   --writeTChan cChan End
 
+-- | See 'openChan'.
+openChanSTM :: CloseableChan a -> STM ()
+openChanSTM CloseableChan{..} = do
+  writeTVar cClosed False
+
+-- | See 'emptyChan'.
 emptyChanSTM :: CloseableChan a -> STM [a]
 emptyChanSTM CloseableChan{..} = do
   writeTChan cChan End
@@ -77,17 +109,43 @@ emptyChanSTM CloseableChan{..} = do
  - Functions as IO actions
  -}
 
-newCloseableChan :: IO (CloseableChan a)
+-- | Create a new open 'CloseableChan'.
-newCloseableChan = atomically newCloseableChanSTM
+newOpenChan :: IO (CloseableChan a)
+newOpenChan = atomically newOpenChanSTM
 
+-- | Create a new closed 'CloseableChan'.
+newClosedChan :: IO (CloseableChan a)
+newClosedChan = atomically newClosedChanSTM
+
+-- | Attempt to write a value into the 'CloseableChan'.
+--
+-- If the chan is open, succeeds with a @Just ()@.
+-- If the chan is closed, fails with a @Nothing@.
 writeChan :: CloseableChan a -> a -> IO (Maybe ())
-writeChan chan = atomically . writeChanSTM chan
+writeChan chan a = atomically $ writeChanSTM chan a
 
+-- | Attempt to read a value @v@ from the 'CloseableChan'.
+--
+-- If the chan is open, succeeds with a @Just v@.
+-- If the chan is closed, fails with a @Nothing@.
 readChan :: CloseableChan a -> IO (Maybe a)
 readChan = atomically . readChanSTM
 
+-- | Close a 'CloseableChan'.
+-- Does nothing if chan is already closed.
+--
+-- Performing this action un-blocks all calls to 'readChan'.
 closeChan :: CloseableChan a -> IO ()
 closeChan = atomically . closeChanSTM
 
+-- | Open a 'CloseableChan'.
+-- Does nothing if chan is already open.
+openChan :: CloseableChan a -> IO ()
+openChan = atomically . openChanSTM
+
+-- | Remove all items currently in the 'CloseableChan' and returns them in a list.
+--
+-- This function also works while the chan is closed.
+-- It is meant as a way to clean up the remaining values in a chan after it was closed.
 emptyChan :: CloseableChan a -> IO [a]
 emptyChan = atomically . emptyChanSTM