diff --git a/aoc2022.cabal b/aoc2022.cabal
index fb16dc9..2cb4c3c 100644
--- a/aoc2022.cabal
+++ b/aoc2022.cabal
@@ -45,8 +45,10 @@ library
       Day5.Shared
       Day6
       Day7
+      Day7.Interpreter
       Day7.Parser
       Lib
+      Shared
   other-modules:
       Paths_aoc2022
   hs-source-dirs:
diff --git a/src/Day7.hs b/src/Day7.hs
index 7f3cb58..c27c542 100644
--- a/src/Day7.hs
+++ b/src/Day7.hs
@@ -1,86 +1,10 @@
 module Day7 (
-  buildTree,
-  buildTree',
-  mkdir,
-  Directory (..),
-  calculateSize,
-  filterDirectories,
-  sumUp,
   day7
 ) where
 
 import Day7.Parser
-import Data.Map (Map)
-import qualified Data.Map as Map
-
-data Directory = Directory
-  { sub :: Map String Directory
-  , files :: Map String Int
-  , isRoot :: Bool
-} deriving (Eq)
-
-
-instance Show Directory where
-  show d = show (files d) ++ " - " ++ show (sub d) ++ "\n"
-
-mkdir :: Directory
-mkdir = Directory { sub = Map.empty, files = Map.empty, isRoot = False }
-
-rootDirectory :: Directory
-rootDirectory = Directory { sub = Map.empty, files = Map.empty, isRoot = True  }
-
-buildTree :: [TerminalCommand] -> Directory
-buildTree commands = fst (buildTree' rootDirectory commands)
-
-buildTree' :: Directory -> [TerminalCommand] -> (Directory, [TerminalCommand])
-buildTree'  dir [] = (dir, [])
-buildTree' dir (command:cs) =  case command of
-  Listing entries ->
-    let asFiles = Map.fromList $ toFiles entries
-        newDir = dir { files = asFiles }
-    in buildTree' newDir cs
-  In dirName ->
-   let subFolders = sub dir
-       selectedDir = Map.findWithDefault mkdir  dirName subFolders
-       (replacement, rest) = buildTree' selectedDir cs
-       updatedSub = Map.insert dirName replacement subFolders
-   in buildTree' dir { sub = updatedSub} rest
-  Out -> (dir, cs)
-  Root -> if isRoot dir
-            then buildTree' dir cs
-            else (dir, command:cs)
-
-toFiles :: [ListingEntry] -> [(String, Int)]
-toFiles ((FileListing name size):rest) = (name, size): toFiles rest
-toFiles (_:rest) = toFiles rest
-toFiles [] = []
-
-calculateSize :: Directory -> Int
-calculateSize dir = sum (Map.elems (files dir)) + sum sizes
-  where
-    subFolders = Map.elems (sub dir)
-    sizes = map calculateSize subFolders
-
-flatten :: Directory -> [(String, Directory)]
-flatten dir = flatten' ("/", dir)
-  where
-  flatten' (name, d) = (name, d) : concatMap flatten' (Map.toList (sub d))
-
-sizeOfDirectories :: Directory -> [(String, Int)]
-sizeOfDirectories dir = map withSize allDirectories
-  where
-    allDirectories = flatten dir
-    withSize (name, directory) = (name, calculateSize directory)
-
-filterDirectories :: (Int -> Bool) -> Directory -> [(String, Int)]
-filterDirectories predicate dir = filter (\(_, size) -> predicate size) $ sizeOfDirectories dir
-
-sumUp :: [(String, Int)] -> Int
-sumUp = sum . map snd
-
-forceRight :: Either a b -> b
-forceRight (Left _) = error "forced Right but got Left"
-forceRight (Right b) = b
+import Day7.Interpreter
+import Shared
 
 day7 :: IO ()
 day7 = do
diff --git a/src/Day7/Interpreter.hs b/src/Day7/Interpreter.hs
new file mode 100644
index 0000000..3321dbe
--- /dev/null
+++ b/src/Day7/Interpreter.hs
@@ -0,0 +1,80 @@
+module Day7.Interpreter (
+  buildTree,
+  mkdir,
+  Directory (..),
+  calculateSize,
+  filterDirectories,
+  sizeOfDirectories,
+  sumUp,
+) where
+
+import Day7.Parser
+import Data.Map (Map)
+import qualified Data.Map as Map
+
+data Directory = Directory
+  { sub :: Map String Directory
+  , files :: Map String Int
+  , isRoot :: Bool
+} deriving (Eq)
+
+
+instance Show Directory where
+  show d = "DIR " ++ show (Map.toList $ files d) ++ " - " ++ show (Map.toList $ sub d) ++ "\n"
+
+mkdir :: Directory
+mkdir = Directory { sub = Map.empty, files = Map.empty, isRoot = False }
+
+rootDirectory :: Directory
+rootDirectory = mkdir { isRoot = True  }
+
+buildTree :: [TerminalCommand] -> Directory
+buildTree commands = fst (buildTree' rootDirectory commands)
+  where
+  -- executes terminal commands and returns all remaining commands
+  buildTree' :: Directory -> [TerminalCommand] -> (Directory, [TerminalCommand])
+  buildTree'  dir [] = (dir, [])
+  buildTree' dir (command:cs) =  case command of
+    Listing entries ->
+      let asFiles = Map.fromList $ toFiles entries
+          newDir = dir { files = asFiles }
+      in buildTree' newDir cs -- update current directory and return all remaining commands
+    In dirName ->
+     let subFolders = sub dir
+         selectedDir = Map.findWithDefault mkdir dirName subFolders -- select or create folder
+         (replacement, rest) = buildTree' selectedDir cs -- recurse down
+         updatedSub = Map.insert dirName replacement subFolders -- update folder the map of the current directory
+     in buildTree' dir { sub = updatedSub} rest -- continue with updated folder and rest of commands
+    Out -> (dir, cs) -- return to previous caller and return all remaining commands
+    Root -> if isRoot dir
+              then buildTree' dir cs -- return to previous caller as long is current directory is not root
+              else (dir, command:cs) -- keep the Root command because it is not yet completed
+
+-- convert to file-pairs and ignore directories
+toFiles :: [ListingEntry] -> [(String, Int)]
+toFiles ((FileListing name size):rest) = (name, size): toFiles rest
+toFiles (_:rest) = toFiles rest
+toFiles [] = []
+
+calculateSize :: Directory -> Int
+calculateSize dir = sum (Map.elems (files dir)) + sum sizes
+  where
+    subFolders = Map.elems (sub dir)
+    sizes = map calculateSize subFolders
+
+flatten :: Directory -> [(String, Directory)]
+flatten dir = flatten' ("/", dir)
+  where
+  flatten' (name, d) = (name, d) : concatMap flatten' (Map.toList (sub d))
+
+sizeOfDirectories :: Directory -> [(String, Int)]
+sizeOfDirectories dir = map withSize allDirectories
+  where
+    allDirectories = flatten dir
+    withSize (name, directory) = (name, calculateSize directory)
+
+filterDirectories :: (Int -> Bool) -> Directory -> [(String, Int)]
+filterDirectories predicate dir = filter (\(_, size) -> predicate size) $ sizeOfDirectories dir
+
+sumUp :: [(String, Int)] -> Int
+sumUp = sum . map snd
diff --git a/src/Shared.hs b/src/Shared.hs
new file mode 100644
index 0000000..dcc0ff0
--- /dev/null
+++ b/src/Shared.hs
@@ -0,0 +1,6 @@
+module Shared(forceRight) where
+
+forceRight :: Either a b -> b
+forceRight (Left _) = error "forced Right but got Left"
+forceRight (Right b) = b
+
diff --git a/test/Day7Spec.hs b/test/Day7Spec.hs
index 7efbdce..53741b6 100644
--- a/test/Day7Spec.hs
+++ b/test/Day7Spec.hs
@@ -4,8 +4,9 @@ module Day7Spec (spec) where
 import Test.Hspec
 import Text.Heredoc
 
-import Day7
+import Shared
 import Day7.Parser
+import Day7.Interpreter
 import qualified Data.Map as Map
 
 inputPart1 :: String
@@ -72,10 +73,6 @@ cdOutParsed = [
     Listing [FileListing "f" 23, DirListing "foo", DirListing "bar"]
   ]
 
-forceRight :: Either a b -> b
-forceRight (Left _) = error "forced Right but got Left"
-forceRight (Right b) = b
-
 spec :: Spec
 spec =
   describe "Day7" $ do