[Haskell-cafe] Wrapping all fields of a data type in e.g. Maybe
michael at orlitzky.com
Wed Jul 17 06:04:18 CEST 2013
On 07/16/2013 08:41 PM, John Lato wrote:
> The suggestion of parameterizing on a functor would be good, however
> there's another approach I've often seen (although it's not quite what
> you've asked for). You can leave your config datatype alone, but
> instead of making it a monoid have your configuration parsers return
> functions with the type (Cfg -> Cfg). You can wrap these functions in
> Endo to get a monoid, combine them together, and then apply that
> function to the default configuration.
I'm using cmdargs for the command-line parsing, and I think (if I don't
want to abandon its magic entirely) that I'm stuck filling a data
I settled on using (Maybe Foo) so that the default value returned by
cmdargs will be Nothing if the user doesn't supply that option; if I use
a plain Cfg object, and the user doesn't pass --verbose, I'll get False
back in its place and then I don't know whether or not that should
override the config file (supposing the user has verbose=True in the file).
Very clever though.
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