diff --git a/.gitignore b/.gitignore
index 27c9fc8..82536a1 100644
--- a/.gitignore
+++ b/.gitignore
@@ -5,5 +5,5 @@ test_script*
 docs_test/*
 test/*-temp
 result/*
-result/
+**/result/
 notes/*
diff --git a/nix/makePrunedSrc.nix b/nix/makePrunedSrc.nix
index 0da5afa..22f48d3 100644
--- a/nix/makePrunedSrc.nix
+++ b/nix/makePrunedSrc.nix
@@ -3,6 +3,7 @@
   , source
   , filter
   , glibcLocales
+  , lib
 }:
 stdenv.mkDerivation {
   name = "pruned_src";
@@ -12,18 +13,16 @@ stdenv.mkDerivation {
   buildPhase = ''
     export LANG="en_US.UTF-8"
     mkdir $out
-    echo $(locale)
-    echo "treeSurgeon is located: ${treeSurgeon}"
-    if $(${treeSurgeon}/bin/tree-surgeon to-bash -f '${filter}' -s ${source} > call_out 2> call_err); then
+    if $(${treeSurgeon}/bin/tree-surgeon to-bash \
+        -f ${lib.strings.escapeNixString filter} \
+        -s ${source} > call_out 2> call_err);
+    then
         BASHARR="$(cat call_out)"
         cd ${source}
         cp --parents $BASHARR $out/
     else
-        echo "is not working; test char is: │"
         ERRMSG=$(cat call_err)
-        echo "Echoing error"
         echo "$ERRMSG"
-        echo "Exiting"
         exit 1
     fi
   '';
diff --git a/notes/notes.md b/notes/notes.md
index 22f394e..314af3a 100644
--- a/notes/notes.md
+++ b/notes/notes.md
@@ -2,8 +2,6 @@
 ----------
 
 We have three current issues:
-- If you screw up your ts expression in prune, you get crazy error output
-  - An incorrect filter expression doesn't return a non-zero error code
 - Error messages probably still not great
 - It does not seem to work with "endsWith '.cpp' (basename file)", does using '' " " '' though
 - README is incomplete and the documentation doesn't really describe the command-line options.
diff --git a/result b/result
index dfc1ac5..7aed5f5 120000
--- a/result
+++ b/result
@@ -1 +1 @@
-/nix/store/pp79zhm1dcgdsd1vdxrgwcrkq87walks-tstest
\ No newline at end of file
+/nix/store/9h2mqw0srb8gq8rfs5viakqjcj33hg0i-tstest
\ No newline at end of file
diff --git a/src/app/TreeFilter.hs b/src/app/TreeFilter.hs
index 8e6e16d..5c91e5e 100644
--- a/src/app/TreeFilter.hs
+++ b/src/app/TreeFilter.hs
@@ -20,7 +20,6 @@ import Debug.Trace (trace)
 import qualified Data.Text as T
 import System.Directory.Tree
 import System.Exit
-import System.IO (hPutStrLn, stderr)
 import TextShow
 import qualified Lexer as X
 
@@ -65,9 +64,7 @@ applyFilterWith :: FileName -> (DirTree FData -> IO()) -> BS.ByteString -> IO ()
 applyFilterWith dirname ioF filterStr = do
     filteredTreeE <- applyFilter dirname filterStr
     case filteredTreeE of
-        Left (e:_) -> do
-            hPutStrLn stderr $ trace ("to error message: " <> toErrorMessage filterStr e) (toErrorMessage filterStr e)
-            exitWith (ExitFailure 1)
+        Left (e:_) -> die $ toErrorMessage filterStr e
         Left [] -> error "Wie ist es moglich"
         Right filtered -> ioF filtered
 
@@ -75,9 +72,7 @@ applyFilterWithReproduce :: FileName -> (DirTree FData -> IO()) -> BS.ByteString
 applyFilterWithReproduce dirname ioF filterStr = do
     filteredTreeE <- applyFilter dirname filterStr
     case filteredTreeE of
-        Left (e:_) -> do
-            hPutStrLn stderr $ trace ("to error message: " <> toErrorMessage filterStr e) (toErrorMessage filterStr e)
-            exitWith (ExitFailure 1)
+        Left (e:_) -> die $ toErrorMessage filterStr e
         Left [] -> error "Wie ist es moglich"
         Right filtered -> ioF filtered
 
@@ -86,9 +81,7 @@ applyFilterWithComparative dirname ioF filterStr = do
     anchoredTree <- readDirectoryWith return dirname
     filteredTreeE <- applyFilter dirname filterStr
     case filteredTreeE of
-        Left (e:_) -> do
-            hPutStrLn stderr $ trace ("to error message: " <> toErrorMessage filterStr e) (toErrorMessage filterStr e)
-            exitWith (ExitFailure 1)
+        Left (e:_) -> die $ toErrorMessage filterStr e
         Left [] -> error "Wie ist es moglich"
         Right filtered -> ioF (toElements $ dirTree anchoredTree) filtered
 
@@ -97,9 +90,7 @@ applyFilterWithComparativeReproduce dirname ioF filterStr = do
     anchoredTree <- readDirectoryWith return dirname
     filteredTreeE <- applyFilter dirname filterStr
     case filteredTreeE of
-        Left (e:_) -> do
-            hPutStrLn stderr $ trace ("to error message:\n" <> toErrorMessage filterStr e) (toErrorMessage filterStr e)
-            exitWith (ExitFailure 1)
+        Left (e:_) -> die $ toErrorMessage filterStr e
         Left [] -> error "Wie ist es moglich"
         Right filtered -> ioF (toElements $ dirTree anchoredTree) filtered
 
diff --git a/src/call_err b/src/call_err
deleted file mode 100644
index b2f2b3b..0000000
--- a/src/call_err
+++ /dev/null
@@ -1,6 +0,0 @@
-to error message: Error: name endsWit is not a recognized function name
-in original source:
-1 │ endsWit ".cpp" (basename file)
-Error: name endsWit is not a recognized function name
-in original source:
-1 │ endsWit ".cpp" (basename file)
diff --git a/src/call_out b/src/call_out
deleted file mode 100644
index e69de29..0000000
diff --git a/src/result b/src/result
deleted file mode 120000
index ae0b955..0000000
--- a/src/result
+++ /dev/null
@@ -1 +0,0 @@
-/nix/store/0d5y4632ajz3x8b613vldab331ky5rqg-tstest
\ No newline at end of file
diff --git a/tree-surgeon-test.nix b/tree-surgeon-test.nix
index 551b29b..f96baba 100644
--- a/tree-surgeon-test.nix
+++ b/tree-surgeon-test.nix
@@ -4,7 +4,7 @@
 
 stdenv.mkDerivation {
   name = "tstest";
-  src = tsLib.prune ./src/test/test-data ''endsWit ".cpp" (basename file)'';
+  src = tsLib.prune ./src/test/test-data "endsWith '.cpp' (basename file)";
   dontUnpack = true;
   buildPhase = ''
     mkdir $out