simplify vm

newtype_deriving.hs

@@ -10,7 +10,7 @@ type Program = [Instr]
 
 type VM a = ReaderT Program (WriterT Output (State Stack)) a
 
-newtype Comp a = Comp { unComp :: ReaderT Program (WriterT Output (State Stack)) a }
+newtype Comp a = Comp (VM a)
   deriving (Monad, MonadReader Program, MonadWriter Output, MonadState Stack)
 
 data Instr = Push Int | Pop | Puts
@@ -20,11 +20,8 @@ evalInstr instr = case instr of
   Pop    -> modify tail
   Push n -> modify (n:)
   Puts   -> do
-    val <- tos
-    tell [val]
-
-tos :: VM Int
-tos = gets head
+    tos <- gets head
+    tell [tos]
 
 eval :: VM ()
 eval = do

writer_impl.hs

@@ -16,10 +16,4 @@ instance Monoid w => Monad (Writer w) where
 tell :: w -> Writer w ()
 tell w = Writer ((), w)
 
-listen :: Writer w t -> Writer w (t, w)
-listen m = Writer $ let (a, w) = runWriter m in ((a, w), w)
-
-pass :: Writer t (a, t -> w) -> Writer w a
-pass m = Writer $ let ((a, f), w) = runWriter m in (a, f w)
-
 main = return ()

zoom.hs

@@ -23,8 +23,7 @@ $(makeLenses ''Particle)
 $(makeLenses ''Vector)
 
 step :: StateT Box IO ()
-step = do
-  zoom (particles.traverse) $ do
+step = zoom (particles.traverse) $ do
     dx <- use (vel.x)
     dy <- use (vel.y)
     pos.x += dx