diff --git a/Kawaii-Parser.cabal b/Kawaii-Parser.cabal
--- a/Kawaii-Parser.cabal
+++ b/Kawaii-Parser.cabal
@@ -11,7 +11,7 @@
 maintainer: liisikerik@hotmail.com
 name: Kawaii-Parser
 synopsis: A simple parsing library and some additional utilities.
-version: 5.0.0
+version: 5.1.0
 library
   build-depends: base < 4.22, containers, directory, mtl, transformers
   default-extensions: FlexibleContexts, ScopedTypeVariables, StandaloneDeriving
diff --git a/Parser/Files.hs b/Parser/Files.hs
--- a/Parser/Files.hs
+++ b/Parser/Files.hs
@@ -31,7 +31,7 @@
   -- | Relative directory.
   data Directory = Directory [Back] [String]
   -- | Errors.
-  data File_error = Failed_to_find_the_file FilePath | Invalid_file_path | Unexpected_extension Ext
+  data File_error = Failed_to_find_file FilePath | Invalid_file_path | Unexpected_extension Ext
   -- | File extensions.
   type Ext = String
   -- | Relative file path.
@@ -144,7 +144,7 @@
         let file_path' = write_file_path file_path
         file_exits <- liftIO (doesPathExist file_path')
         case file_exits of
-          False -> throwError (Failed_to_find_the_file file_path')
+          False -> throwError (Failed_to_find_file file_path')
           True -> liftIO (read_file' file_path'))
   tokenise :: Tokeniser ()
   tokenise = void (parse_many tokenise_1)
diff --git a/Parser/Parser.hs b/Parser/Parser.hs
--- a/Parser/Parser.hs
+++ b/Parser/Parser.hs
@@ -109,12 +109,12 @@
   filter_error err = Parser (\ tokens -> return (Just (Just (Left err), tokens)))
   -- | Filter parse results - for example, restrict an integer parser to positive numbers. You also have to provide an error.
   filter_parser :: (Eq token, Monoid output) =>
-    (t -> Bool) -> (Location -> error) -> Parser token output error t -> Parser token output error t
+    (t -> Bool) -> (t -> Location -> error) -> Parser token output error t -> Parser token output error t
   filter_parser f err =
     fmap_filter_parser
       (\ x ->
         do
-          check err (f x)
+          check (err x) (f x)
           Right x)
   -- | Filter and transform the parse results in one operation. You also have to provide an error.
   fmap_filter_parser :: (Eq token, Monoid output) =>