lens_are_awesome.hs

-- non-lens version (BROKEN)
addNativeFunction :: String -> FunctionData -> Context -> Context
addNativeFunction name fn ctx = newCtx
    where
        newRef :: FunctionRef
        newRef = (\(FunctionRef i) -> FunctionRef (i+1)) $ fst $ Map.findMax (functions ctx)
        ctxWithNewRef = ctx { functions = Map.insert newRef fn (functions ctx) }

        insertNewValue :: TableData -> TableData
        insertNewValue (TableData td) = TableData $ Map.insert (Str name) (Function newRef) td
        newCtx = ctxWithNewRef { tables = Map.adjust insertNewValue (_Gref ctx) (tables ctx) }

-- lens version
addNativeFunction :: String -> FunctionData -> LuaM ()
addNativeFunction name fdata = do
    newRef <- uniqueFunctionRef
    functions . at newRef .= Just fdata
    tables . at gRef . at name .= Just newRef