diff --git a/byg/src/ComputationM.hs b/byg/src/ComputationM.hs
index 213bb0b..6068aa8 100644
--- a/byg/src/ComputationM.hs
+++ b/byg/src/ComputationM.hs
@@ -1,4 +1,3 @@
-{-# LANGUAGE GADTs #-}
 module ComputationM where
 
 import Types
@@ -16,7 +15,8 @@ data TypedRun a b where
   FIO :: IsFIO f a b => f -> TypedRun a b
   TInject :: b -> TypedRun () b
   GetListElem :: TypedRun () b
-  InList :: ComputationM b -> TypedRun [a] [b]
+  SetListElem :: TypedRun a ()
+  InList :: [DependencyUntyped] -> TypedRun [a] [b]
 
 instance Show (ComputationM a) where
   show _ = "<computation>"
@@ -43,6 +43,7 @@ newtype ComputationM' a = ComputationM { unComputationM :: WriterT [DependencyUn
 
 type ComputationM a = ComputationM' (Token a)
 
+evalComputationM :: ComputationM () -> [DependencyUntyped]
 evalComputationM m = evalState (execWriterT (unComputationM m)) 0
 
 genDependency :: (Show u, Show a) => (Token a -> Dependency u a) -> ComputationM a
@@ -61,6 +62,9 @@ inject x = genDependency (Dependency NoToken (TInject x))
 getListElem :: Show a => ComputationM a
 getListElem = genDependency (Dependency NoToken GetListElem)
 
+setListElem :: Show a => Token a -> ComputationM ()
+setListElem a = genDependency (Dependency a SetListElem)
+
 run :: (Show a, Show b, IsF f a b) => f -> Token a -> ComputationM b
 run f input = genDependency (Dependency input (F f))
 
@@ -76,5 +80,10 @@ convertImage = runIO ConvertImage
 saveFile = runIO SaveFile
 runPandoc = runIO RunPandoc
 
-mapListTaken :: (Show a, Show b) => ComputationM b -> Token [a] -> ComputationM [b]
-mapListTaken f input = genDependency (Dependency input (InList f))
+mapListTaken :: (Show a, Show b) => (Token a -> ComputationM b) -> Token [a] -> ComputationM [b]
+mapListTaken f input = genDependency (Dependency input (InList (evalComputationM m)))
+  where m :: ComputationM ()
+        m = do
+          inp <- getListElem
+          outp <- f inp
+          setListElem outp
diff --git a/byg/src/Main.hs b/byg/src/Main.hs
index da7dfed..a137df8 100644
--- a/byg/src/Main.hs
+++ b/byg/src/Main.hs
@@ -3,16 +3,11 @@ module Main where
 import Types
 import ComputationM
 
-testSub :: ComputationM Image
-testSub = do
-  inp <- getListElem
-  openImage inp
-
 test :: ComputationM ()
 test = do
   dir <- inject "retter"
   dirContents <- listDirectory dir
-  u <- mapListTaken testSub dirContents
+  u <- mapListTaken openImage dirContents
   pure $ NoToken
 
 main :: IO ()