I have a common pattern in my command-line programs; I start out with a configuration data type, which over-simplified looks like: data Cfg = Cfg { verbose :: Bool } Now, there's usually a default configuration, default :: Cfg default = Cfg False The user can override the defaults one of two ways, either via a config file, or from the command-line. If both are specified, the command-line takes precedence. The way I do this is with, data OptionalCfg = OptionalCfg { verbose :: Maybe Bool } And then I define I Monoid instance for OptionalCfg which lets me merge two ofthem. Once the two OptionalCfgs are merged, I merge *that* with the default Cfg. This all works great, except that when there's 20 or so options, I duplicate a ton of code in the definition of OptionalCfg. Is there some pre-existing solution that will let me take a Cfg and create a new type with Cfg's fields wrapped in Maybe?