1 files changed, 22 insertions, 0 deletions

diff --git a/TraversableT.hs b/TraversableT.hs
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index 00000000..6446fcc9
--- /dev/null
+++ b/TraversableT.hs
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+module TraversableT where
+
+import Data.Traversable
+import Control.Monad (join)
+
+newtype TraversableT m t a = TraversableT { runTraversableT :: m (t a) }
+
+instance (Monad m, Traversable t, Monad t) => Monad (TraversableT m t) where
+    return = TraversableT . return . return
+    m >>= k  = TraversableT $ do
+        a <- runTraversableT m
+        b <- forM a $ runTraversableT . k
+        return (join b)
+    fail s = TraversableT $ return (fail s)
+
+liftT :: Monad m => t a -> TraversableT m t a
+liftT = TraversableT . return
+
+liftMT :: m (t a) -> TraversableT m t a
+liftMT = TraversableT
+
+