From 938721877d1a4d8d0c304ef43572856b1a39970a Mon Sep 17 00:00:00 2001
From: Kjetil Orbekk <kjetil.orbekk@gmail.com>
Date: Wed, 17 Feb 2016 05:33:34 +0100
Subject: Monad transformers.

---
 src/Lib.hs | 48 ++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 48 insertions(+)
 create mode 100644 src/Lib.hs

(limited to 'src')

diff --git a/src/Lib.hs b/src/Lib.hs
new file mode 100644
index 0000000..9748aed
--- /dev/null
+++ b/src/Lib.hs
@@ -0,0 +1,48 @@
+{-# LANGUAGE TemplateHaskell #-}
+{-# LANGUAGE OverloadedStrings #-}
+{-# LANGUAGE GeneralizedNewtypeDeriving #-}
+module Lib where
+
+import Control.Lens (makeLenses)
+import Control.Monad.Identity (Identity(..))
+import Control.Monad.Reader (ReaderT(..), runReaderT)
+import Control.Monad.Reader.Class (MonadReader(..))
+import Control.Monad.State.Class (MonadState(..))
+import Control.Monad.State.Strict (StateT(..), evalStateT)
+import Data.Default (Default(..))
+
+data Position = Position { _x :: Int, _y :: Int }
+                deriving (Show, Read)
+instance Default Position where
+    def = Position 0 0
+makeLenses ''Position
+
+data Player = Player {
+      position :: Position}
+              deriving (Show, Read)
+instance Default Player where
+    def = Player { position = def }
+makeLenses ''Player
+
+newtype Config = Config String
+    deriving (Show)
+
+data World = World {
+      player :: Player}
+             deriving (Show, Read)
+instance Default World where
+    def = World { player = def }
+makeLenses ''World
+
+newtype App a = App {
+      runApp :: StateT World (ReaderT Config Identity) a}
+    deriving ( Applicative
+             , Functor
+             , Monad
+             , MonadState World
+             , MonadReader Config
+             )
+
+evalApp :: App a -> World -> Config -> a
+evalApp f world config =
+    runIdentity (runReaderT (evalStateT (runApp f) world) config)
-- 
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