To be able to overwrite config settings with command line arguments i had to rethink the way we access the config file.
In the new solution i removed the now unnecessary getter functions like getPort :: IO Int
and instead made the Config globally accessible by using the monad transformer ReaderT and keeping the config in the Reader Monad.
Therefore all functions needing config acces now have a type signature of:
(MonadReader Config m, MonadIO m) => a -> m (a)
The config itself can now be loaded with Readers ask function.
Single config records can be accessed via asks as in myVersion <- asks acceptedVersion
Command line arguments
Command line arguments are parsed in a new File calles Args.hs.
it provides a function named parseOpts which if successful returns a Config object as loaded from the config file, where specially specified records like port are overwritten with the command line arguments.
Usage info can be printed with -h or --help and looks like this:
Usage: openage-masterserver [options]...
Options:
-h --help Print help
-c FILE --config=FILE config file to use
-p NUM --port=NUM port to use
Reader Monad
To be able to overwrite config settings with command line arguments i had to rethink the way we access the config file. In the new solution i removed the now unnecessary getter functions like
getPort :: IO Intand instead made the Config globally accessible by using the monad transformer ReaderT and keeping the config in the Reader Monad. Therefore all functions needing config acces now have a type signature of:The config itself can now be loaded with Readers
askfunction. Single config records can be accessed via asks as inmyVersion <- asks acceptedVersionCommand line arguments
Command line arguments are parsed in a new File calles Args.hs. it provides a function named
parseOptswhich if successful returns a Config object as loaded from the config file, where specially specified records like port are overwritten with the command line arguments. Usage info can be printed with-hor--helpand looks like this: