diff --git a/app/Main.hs b/app/Main.hs
index 110e2c5..1c939fa 100644
--- a/app/Main.hs
+++ b/app/Main.hs
@@ -159,11 +159,15 @@ world0 = World {
 main :: IO ()
 main =
  do args <- getArgs
-    let name = case args of x:_ -> x; [] -> ""
-    bracket (mkVty =<< userConfig) shutdown \vty ->
-     do
-        loop vty (pure (pickWorld name))
-        pure ()
+    case args of 
+      x:_ | Just w <- Map.lookup x worldList ->  
+        bracket (mkVty =<< userConfig) shutdown \vty ->
+          loop vty (pure w)
+      _ ->
+       do putStrLn "Usage: parabox <worldname>"
+          putStrLn "" 
+          putStrLn "Available worlds:" 
+          mapM_ putStrLn (Map.keys worldList)
 
 loop :: Vty -> NonEmpty World -> IO ()
 loop vty (world :| history) =
@@ -184,13 +188,16 @@ loop vty (world :| history) =
           _ -> loop vty (world :| history)
       _ -> loop vty (world :| history)
 
-pickWorld :: String -> World
-pickWorld "world0" = world0
-pickWorld "small" = smallWorld
-pickWorld "center8" = center8
-pickWorld "center13" = center13
-pickWorld "clone11" = clone11
-pickWorld _ = transfer14
+
+worldList :: Map.Map String World
+worldList = Map.fromList
+  [ ("world0", world0)
+  , ("small", smallWorld)
+  , ("center8", center8)
+  , ("center13", center13)
+  , ("clone11", clone11)
+  , ("transfer14", transfer14)
+  ]
 
 smallWorld :: World
 smallWorld =