diff --git a/byg/src/ComputationM.hs b/byg/src/ComputationM.hs
index d76ddac..476d9c7 100644
--- a/byg/src/ComputationM.hs
+++ b/byg/src/ComputationM.hs
@@ -1,8 +1,11 @@
 module ComputationM
   ( ComputationM
+  , Token
   , evalComputationM
   , inject
   , mapComputationM
+  , mapComputationM_
+  , filterComputationM
   , runFunction
   , runFunctionIO
   ) where
@@ -19,11 +22,13 @@ data TypedRun a b where
   GetListElem :: TypedRun [b] b
   SetListElem :: TypedRun a [a]
   MapComp :: [DependencyUntyped] -> TypedRun [a] [b]
+  FilterComp :: TypedRun ([a], [Bool]) [a]
 
 deriving instance (Show a, Show b) => Show (TypedRun a b)
 
 data Token a where
   Token :: Int -> Token a
+  ZipToken :: Token a -> Token b -> Token (a, b)
   NoToken :: Token ()
 
 deriving instance Show (Token a)
@@ -90,3 +95,13 @@ mapComputationM f input = genDependency' $ \target -> do
         setListElem outp target
   put top'
   pure (Dependency input (MapComp res) target)
+
+mapComputationM_ :: Show a => (Token a -> ComputationM ()) -> Token [a] -> ComputationM ()
+mapComputationM_ f input = do
+  _ <- mapComputationM f input
+  pure NoToken
+
+filterComputationM :: Show a => (Token a -> ComputationM Bool) -> Token [a] -> ComputationM [a]
+filterComputationM f input = do
+  conds <- mapComputationM f input
+  genDependency (Dependency (ZipToken input conds) FilterComp)
diff --git a/byg/src/Main.hs b/byg/src/Main.hs
index 34cec97..48f7f9a 100644
--- a/byg/src/Main.hs
+++ b/byg/src/Main.hs
@@ -3,11 +3,18 @@ module Main where
 import ComputationM
 import Functions
 
+handleRecipeDir :: Token FilePath -> ComputationM ()
+handleRecipeDir dir = do
+  dirContents <- listDirectory dir
+  imageFilenames <- filterComputationM isImageFilename dirContents
+  t <- inject ("hej", "hey.txt")
+  saveFile t
+
 test :: ComputationM ()
 test = do
   dir <- inject "retter"
   dirContents <- listDirectory dir
-  _ <- mapComputationM openImage dirContents
+  mapComputationM_ handleRecipeDir dirContents
   t <- inject ("hej", "hey.txt")
   saveFile t