Add AccumT example

rhine-examples/rhine-examples.cabal

@@ -84,6 +84,14 @@ executable RandomWalk
     random >=1.1,
     simple-affine-space
 
+executable Accum
+  import: opts
+  main-is: Accum.hs
+  build-depends:
+    transformers,
+    text
+
+
 flag dev
   description: Enable warnings as errors. Active on ci.
   default: False

rhine-examples/src/Accum.hs

@@ -0,0 +1,38 @@
+-- | 'AccumT' example
+
+-- base
+import Control.Monad (void)
+import Control.Monad.IO.Class
+
+-- transformers
+import Control.Monad.Trans.Accum (AccumT, runAccumT, add, look)
+
+-- text
+import Data.Text (Text, pack)
+
+-- rhine
+import FRP.Rhine hiding (add)
+
+personalMessage :: ClSF (AccumT [Text] IO) (Lifting StdinClock) () ()
+personalMessage = tagS >>> arrMCl (pure >>> add)
+
+type Lifting = LiftClock IO (AccumT [Text])
+type EveryTwoSeconds = Lifting (Millisecond 2000)
+
+everyTwoSeconds :: EveryTwoSeconds
+everyTwoSeconds = liftClock waitClock
+
+logSoFar :: ClSF (AccumT [Text] IO) EveryTwoSeconds () ()
+logSoFar = sinceStart >>> arrMCl printLog
+  where
+    printLog t = do
+      add ["Time since start: " <> pack (show t)]
+      l <- look
+      liftIO $ do
+        putStrLn "Log so far:"
+        print l
+
+main :: IO ()
+main = do
+  putStrLn "You can add a personal message to the log."
+  void $ flip runAccumT [] $ flow $ personalMessage @@ liftClock StdinClock |@| logSoFar @@ everyTwoSeconds