Hello, I am developing a small game engine (nothing fancy or professional, it is to test the waters of Haskell). You could say it's a very simple DSL: a user would import a library and use its tool to make a game. The problem I encountered is when defining or getting/setting variables for an instance game. Let me illustrate data GameState = GameState [(String, Int)] This is a very simple and naive gamestate, an association list consisting in (variableName, itsValue). This would mean restricting values to "Int" only, but I can easily enough add any kind of value with: data GameState = GameState [(String, Dynamic)] An example helper function signature would look like getBool :: String -> Either MyError Bool data MyError = NotFound String | TypeMismatch String The problem with this approach is that I loathe picking up those two kind of errors (var not found and type mismatch) at runtime. I would like them to be found at compile time (like "normal" Haskell). I thought that a possible solution was to declare a datatype with the needed variables inside: data MyGameVar = MyGameVar { health :: Int, message :: String } myvars = MyGameVar 1 "Don't forget your umbrella!" This would find at compile time typos in variable names and type errors at compile time, of course. But then I would have to change the GameState to: data GameState = GameState MyGameVar which would be fine if I were developing a *game*, but it is not fine when you develop a *game engine* (that would mean having to rewrite MyGameVar every game you made). So I am left to think if the problem I highlighted is "solvable" or do I have to make compromises? I guess I am not the first to encounter this difficulty, so I am asking here. Any hint or idea is appreciated, thanks! -F