instance DCT.Configured FeedHosts where
+ -- | This allows us to read a FeedHosts object out of a Configurator
+ -- config file. By default Configurator wouldn't know what to do,
+ -- so we have to tell it that we expect a list, and if that list
+ -- has strings in it, we can apply the FeedHosts constructor to
+ -- it.
convert (DCT.List xs) =
+ -- mapM gives us a Maybe [String] here.
fmap FeedHosts (mapM convert_string xs)
where
convert_string :: DCT.Value -> Maybe String
convert_string = DCT.convert
+ -- If we read anything other than a list of values out of the file,
+ -- fail.
convert _ = Nothing
-