Define Vervis monad as a newtype over RWST

src/Vervis.hs

@@ -13,12 +13,15 @@
  - <http://creativecommons.org/publicdomain/zero/1.0/>.
  -}
 
+{-# LANGUAGE GeneralizedNewtypeDeriving #-}
+
 module Vervis
     ( User (..)
     , Group (..)
     , IrcChannel (..)
     , Repository (..)
     , Server (..)
+    , Vervis ()
     , subdirs
     , lastChange
     , timeAgo
@@ -27,6 +30,9 @@ module Vervis
 where
 
 import Control.Monad (join)
+import Control.Monad.Fix (MonadFix)
+import Control.Monad.IO.Class (MonadIO)
+import Control.Monad.Trans.RWS (RWST (..))
 import Data.CaseInsensitive (CI)
 import Data.Foldable (toList)
 import Data.Git
@@ -75,6 +81,24 @@ data Server = Server
     , serverRepos  :: HashMap (Either Int Int) [Repository]
     }
 
+data VervisEnv = VervisEnv
+    {
+    }
+
+data VervisState = VervisState
+    {
+    }
+
+newtype Vervis a = Vervis { unVervis :: RWST VervisEnv () VervisState IO a }
+    deriving (Functor, Applicative, Monad, MonadFix, MonadIO)
+
+-- internal func, wrap with API func which hides env and state details
+runVervis' :: VervisEnv -> VervisState -> Vervis a -> IO (a, VervisState)
+runVervis' venv vstate computation = do
+    let rwst = unVervis computation
+    (a, s, _) <- runRWST rwst venv vstate
+    return (a, s)
+
 subdirs :: FilePath -> IO [FilePath]
 subdirs dir = do
     _base :/ tree <- buildL dir

vervis.cabal

@@ -36,6 +36,7 @@ library
                      , hit                  >=0.6.3
                      , hourglass
                      , text                 >=1
+                     , transformers         >=0.4.2
                      , unordered-containers >=0.2.5
   hs-source-dirs:      src
   default-language:    Haskell2010