diff --git a/reginaldCog/openai_client/models.py b/reginaldCog/openai_client/models.py
index 200b98f..3ec01e3 100644
--- a/reginaldCog/openai_client/models.py
+++ b/reginaldCog/openai_client/models.py
@@ -60,25 +60,22 @@ class Message:
     content: list[Content]
 
 
-@dataclass
+@dataclass(frozen=True)
 class Prompt:
     model: str
     input: list[Message]
 
-    def add_message(self, message: Message):
-        self.input.append(message)
-
 
 @dataclass(frozen=True)
 class Response:
     output: list[Message]
 
 
-def filter_fields(data: dict, filter_by_class: dataclass) -> dict:
+def filter_fields(data: dict, dataclass_type: dataclass) -> dict:
     return {
         i_key: i_value
         for i_key, i_value in data.items()
-        if i_key in tuple(f.name for f in fields(filter_by_class))
+        if i_key in tuple(i_field.name for i_field in fields(dataclass_type))
     }