1 files changed, 73 insertions, 0 deletions
diff --git a/src/Erebos/Flow.hs b/src/Erebos/Flow.hs
new file mode 100644
index 0000000..ba2607a
--- /dev/null
+++ b/src/Erebos/Flow.hs
@@ -0,0 +1,73 @@
+module Erebos.Flow (
+    Flow, SymFlow,
+    newFlow, newFlowIO,
+    readFlow, tryReadFlow, canReadFlow,
+    writeFlow, writeFlowBulk, tryWriteFlow, canWriteFlow,
+    readFlowIO, writeFlowIO,
+
+    mapFlow,
+) where
+
+import Control.Concurrent.STM
+
+
+data Flow r w = Flow (TMVar [r]) (TMVar [w])
+              | forall r' w'. MappedFlow (r' -> r) (w -> w') (Flow r' w')
+
+type SymFlow a = Flow a a
+
+newFlow :: STM (Flow a b, Flow b a)
+newFlow = do
+    x <- newEmptyTMVar
+    y <- newEmptyTMVar
+    return (Flow x y, Flow y x)
+
+newFlowIO :: IO (Flow a b, Flow b a)
+newFlowIO = atomically newFlow
+
+readFlow :: Flow r w -> STM r
+readFlow (Flow rvar _) = takeTMVar rvar >>= \case
+    (x:[]) -> return x
+    (x:xs) -> putTMVar rvar xs >> return x
+    [] -> error "Flow: empty list"
+readFlow (MappedFlow f _ up) = f <$> readFlow up
+
+tryReadFlow :: Flow r w -> STM (Maybe r)
+tryReadFlow (Flow rvar _) = tryTakeTMVar rvar >>= \case
+    Just (x:[]) -> return (Just x)
+    Just (x:xs) -> putTMVar rvar xs >> return (Just x)
+    Just [] -> error "Flow: empty list"
+    Nothing -> return Nothing
+tryReadFlow (MappedFlow f _ up) = fmap f <$> tryReadFlow up
+
+canReadFlow :: Flow r w -> STM Bool
+canReadFlow (Flow rvar _) = not <$> isEmptyTMVar rvar
+canReadFlow (MappedFlow _ _ up) = canReadFlow up
+
+writeFlow :: Flow r w -> w -> STM ()
+writeFlow (Flow _ wvar) = putTMVar wvar . (:[])
+writeFlow (MappedFlow _ f up) = writeFlow up . f
+
+writeFlowBulk :: Flow r w -> [w] -> STM ()
+writeFlowBulk _ [] = return ()
+writeFlowBulk (Flow _ wvar) xs = putTMVar wvar xs
+writeFlowBulk (MappedFlow _ f up) xs = writeFlowBulk up $ map f xs
+
+tryWriteFlow :: Flow r w -> w -> STM Bool
+tryWriteFlow (Flow _ wvar) = tryPutTMVar wvar . (:[])
+tryWriteFlow (MappedFlow _ f up) = tryWriteFlow up . f
+
+canWriteFlow :: Flow r w -> STM Bool
+canWriteFlow (Flow _ wvar) = isEmptyTMVar wvar
+canWriteFlow (MappedFlow _ _ up) = canWriteFlow up
+
+readFlowIO :: Flow r w -> IO r
+readFlowIO path = atomically $ readFlow path
+
+writeFlowIO :: Flow r w -> w -> IO ()
+writeFlowIO path = atomically . writeFlow path
+
+
+mapFlow :: (r -> r') -> (w' -> w) -> Flow r w -> Flow r' w'
+mapFlow rf wf (MappedFlow rf' wf' up) = MappedFlow (rf . rf') (wf' . wf) up
+mapFlow rf wf up = MappedFlow rf wf up