diff --git a/src/parser.py b/src/parser.py
index 74b756d..50d602b 100755
--- a/src/parser.py
+++ b/src/parser.py
@@ -12,9 +12,7 @@ def __init__(
         self,
         grammar=grammar.imperivm,
         visitor=visitor.ImperivmVisitor(),
-        preprocessor=preprocessor.PipelinePreprocessor(
-            [preprocessor.CommentsPreprocessor()]
-        ),
+        preprocessor=preprocessor.PipelinePreprocessor([preprocessor.CommentsPreprocessor()]),
     ):
         self.grammar = grammar
         self.visitor = visitor
diff --git a/src/preprocessor.py b/src/preprocessor.py
index d74f943..1decb12 100644
--- a/src/preprocessor.py
+++ b/src/preprocessor.py
@@ -5,16 +5,14 @@
 
 class Preprocessor(ABC):
     @abstractmethod
-    def process(self, program: str):
+    def process(self, program: str) -> str:
         pass
 
 
 class CommentsPreprocessor(Preprocessor):
     @override
     def process(self, program: str):
-        cleaned_program = map(
-            lambda line: re.sub(r"#.*$", "", line), program.splitlines()
-        )
+        cleaned_program = map(lambda line: re.sub(r"#.*$", "", line), program.splitlines())
         return "\n".join(cleaned_program)