Add API to gather results of multiple computations

src/Strands.hs

@@ -16,6 +16,7 @@ module Strands
     , async
     , waitEvents
     , each
+    , gather
     , sample
     , threads
     , logged

src/Strands/Threads.hs

@@ -8,6 +8,7 @@ module Strands.Threads
     , each
     , sample
     , sync
+    , gather
     --, react
     , threads
 
@@ -537,6 +538,13 @@ gatherResult ref r = do
     liftIO $ atomicModifyIORef ref $ \rs -> (r : rs, ())
     mzero
 
+gather :: (MonadIO m, MonadCatch m) => AsyncT m a -> AsyncT m [a]
+gather m = AsyncT $ do
+    resultsRef <- liftIO $ newIORef []
+    lift $ waitAsync (gatherResult resultsRef) Nothing m
+    r <- liftIO $ readIORef resultsRef
+    return $ Just r
+
 -- | Run an 'AsyncT m' computation and collect the results generated by each
 -- thread of the computation in a list.
 wait :: (MonadIO m, MonadCatch m) => AsyncT m a -> m [a]

test/gather.hs

@@ -0,0 +1,14 @@
+import Control.Concurrent (threadDelay, myThreadId)
+import Control.Monad.IO.Class (liftIO)
+import System.Random (randomIO)
+import System.IO
+
+import Strands
+
+--- Check space leaks
+
+main = do
+    x <- wait $ do
+        y <- gather $ each [1..10]
+        liftIO $ print y
+    print x