support for qualified do

support for qualified do notation

indexed-transformers.cabal

@@ -23,6 +23,7 @@ library
   exposed-modules:
       Control.Monad.Trans.Indexed
       Control.Monad.Trans.Indexed.Cont
+      Control.Monad.Trans.Indexed.Do
       Control.Monad.Trans.Indexed.Free
       Control.Monad.Trans.Indexed.Free.Fold
       Control.Monad.Trans.Indexed.Free.Lance

src/Control/Monad/Trans/Indexed/Do.hs

@@ -0,0 +1,35 @@
+{-# LANGUAGE
+    GADTs
+  , NoImplicitPrelude
+#-}
+
+module Control.Monad.Trans.Indexed.Do
+  ( (>>=)
+  , (>>)
+  , fail
+  ) where
+
+import qualified Control.Monad as M
+import qualified Control.Monad.Trans as T
+import qualified Control.Monad.Trans.Indexed as Ix
+import qualified Prelude as P
+
+(>>=)
+  :: (Ix.IndexedMonadTrans t, M.Monad m)
+  => t i j m x
+  -> (x -> t j k m y)
+  -> t i k m y
+(>>=) = P.flip Ix.ixBind
+
+(>>)
+  :: (Ix.IndexedMonadTrans t, M.Monad m)
+  => t i j m x
+  -> t j k m y
+  -> t i k m y
+(>>) = P.flip Ix.ixThen
+
+fail
+  :: (Ix.IndexedMonadTrans t, M.MonadFail m, i ~ j)
+  => P.String
+  -> t i j m x
+fail = T.lift P.. M.fail