diff --git a/ChangeLog.md b/ChangeLog.md
--- a/ChangeLog.md
+++ b/ChangeLog.md
@@ -1,5 +1,11 @@
 # Revision history for ecstasy
 
-## 0.1.0.0  -- YYYY-mm-dd
+## 0.1.0.1  -- 2018-02-14
 
+* Added 'yieldSystemT' for resuming a 'SystemT' computation later.
+* Bumped the upper bound on 'base' to 5 (thanks to nek0).
+
+## 0.1.0.0  -- 2017-12-27
+
 * First version. Released on an unsuspecting world.
+
diff --git a/ecstasy.cabal b/ecstasy.cabal
--- a/ecstasy.cabal
+++ b/ecstasy.cabal
@@ -2,7 +2,7 @@
 -- documentation, see http://haskell.org/cabal/users-guide/
 
 name:                ecstasy
-version:             0.1.0.0
+version:             0.1.0.1
 synopsis:
   A GHC.Generics based entity component system.
 
@@ -37,8 +37,7 @@
   exposed-modules: Data.Ecstasy
   other-modules:   Data.Ecstasy.Deriving
                  , Data.Ecstasy.Types
-                 , Main
   -- other-extensions:
-  build-depends:       base >=4.9 && <4.10, containers, mtl, transformers
+  build-depends:       base >=4.9 && <5, containers, mtl, transformers
   hs-source-dirs:      src
   default-language:    Haskell2010
diff --git a/src/Data/Ecstasy.hs b/src/Data/Ecstasy.hs
--- a/src/Data/Ecstasy.hs
+++ b/src/Data/Ecstasy.hs
@@ -26,6 +26,7 @@
 import           Data.Functor.Identity (runIdentity)
 import           Data.Maybe (catMaybes)
 import           Data.Traversable (for)
+import           Data.Tuple (swap)
 import           GHC.Generics
 
 
@@ -214,6 +215,17 @@
 runQueryT e qt = do
   cs <- getEntity e
   lift $ unQueryT qt cs
+
+
+------------------------------------------------------------------------------
+-- | Provides a resumable 'SystemT'. This is a pretty big hack until I come up
+-- with a better formalization for everything.
+yieldSystemT
+    :: Monad m
+    => SystemState world
+    -> SystemT world m a
+    -> m (SystemState world, a)
+yieldSystemT = (fmap swap .) . flip S.runStateT
 
 
 ------------------------------------------------------------------------------
diff --git a/src/Data/Ecstasy/Types.hs b/src/Data/Ecstasy/Types.hs
--- a/src/Data/Ecstasy/Types.hs
+++ b/src/Data/Ecstasy/Types.hs
@@ -20,10 +20,13 @@
   show (Ent e) = "Ent " ++ show e
 
 
+------------------------------------------------------------------------------
+-- | The internal state of the 'SystemT' monad.
+type SystemState w = (Int, w 'WorldOf)
 
 ------------------------------------------------------------------------------
 -- | A monad transformer over an ECS given a world 'w'.
-type SystemT w = StateT (Int, w 'WorldOf)
+type SystemT w = StateT (SystemState w)
 
 ------------------------------------------------------------------------------
 -- | A monad over an ECS given a world 'w'.
diff --git a/src/Main.hs b/src/Main.hs
deleted file mode 100644
--- a/src/Main.hs
+++ /dev/null
@@ -1,52 +0,0 @@
-{-# LANGUAGE DataKinds                    #-}
-{-# LANGUAGE DeriveGeneric                #-}
-{-# LANGUAGE TypeFamilies                 #-}
-
-module Main where
-
-import Data.Ecstasy
-import Control.Monad (void)
-import Control.Monad.IO.Class (liftIO)
-
-
-main :: IO ()
-main = do
-  e <- runSystemT defWorld $ do
-    void $ newEntity $ defEntity
-        { pos = Just 0
-        , vel = Just 1
-        , ack = Just True
-        }
-
-    void $ newEntity $ defEntity
-      { pos = Just 0
-      , ack = Just False
-      }
-
-    let
-      step = do
-        pos' <- get pos
-        vel' <- get vel
-        pure $ defEntity'
-          { pos = Set $ pos' + vel'
-          }
-    emap step
-    emap step
-
-    efor $ \i -> do
-      with ack
-      pure $ show i
-
-  print e
---   print $ pos e
---   print $ vel e
---   print $ ack e
-
-
-data Entity f = Entity
-  { pos :: Component f 'Field  Int
-  , vel :: Component f 'Field  Int
-  , ack :: Component f 'Unique Bool
-  } deriving (Generic)
-
-