Remove mapM usage in monad

Was really a hack.

byg/src/Main.hs

@@ -1,13 +1,18 @@
 module Main where
 
+import Types
 import ComputationM
 
+testSub :: ComputationM TokenNotTraversable Image
+testSub = do
+  inp <- getListElem
+  openImage inp
+
 test :: ComputationM TokenNotTraversable ()
 test = do
   dir <- inject "retter"
   dirContents <- listDirectory dir
-  let dirContents' = makeTraversable dirContents
-  u <- mapM openImage dirContents'
+  u <- mapListTaken testSub dirContents
   pure $ NoToken
 
 main :: IO ()