module OptionalConfiguration (
OptionalConfiguration(..),
- from_rc )
+ from_rc,
+ merge_maybes )
where
import qualified Data.Configurator as DC (
import System.FilePath ( (</>) )
import System.IO.Error ( catchIOError )
import System.Log ( Priority(..) )
+
import Logging ( log_error )
import TSN.FeedHosts ( FeedHosts(..) )
deriving (Show, Data, Typeable)
+-- | Combine two Maybes into one, essentially mashing them
+-- together. We give precedence to the second argument when both are
+-- Justs.
+merge_maybes :: (Maybe a) -> (Maybe a) -> (Maybe a)
+merge_maybes Nothing Nothing = Nothing
+merge_maybes (Just x) Nothing = Just x
+merge_maybes Nothing (Just x) = Just x
+merge_maybes (Just _) (Just y) = Just y
+
+
-- | The Monoid instance for these lets us "combine" two
-- OptionalConfigurations. The "combine" operation that we'd like to
-- perform is, essentially, to mash them together. So if we have two
-- OptionalConfigurations, each half full, we could combine them
-- into one big one.
--
--- One of the two must take precedence during this mashing, and we
--- choose the second one for no reason.
---
-- This is used to merge command-line and config-file settings.
--
instance Monoid OptionalConfiguration where
cfg1 `mappend` cfg2 =
OptionalConfiguration
all_feed_hosts
- (merge (log_file cfg1) (log_file cfg2))
- (merge (log_level cfg1) (log_level cfg2))
- (merge (password cfg1) (password cfg2))
- (merge (output_directory cfg1) (output_directory cfg2))
- (merge (syslog cfg1) (syslog cfg2))
- (merge (username cfg1) (username cfg2))
+ (merge_maybes (log_file cfg1) (log_file cfg2))
+ (merge_maybes (log_level cfg1) (log_level cfg2))
+ (merge_maybes (password cfg1) (password cfg2))
+ (merge_maybes (output_directory cfg1) (output_directory cfg2))
+ (merge_maybes (syslog cfg1) (syslog cfg2))
+ (merge_maybes (username cfg1) (username cfg2))
where
- merge :: (Maybe a) -> (Maybe a) -> (Maybe a)
- merge Nothing Nothing = Nothing
- merge (Just x) Nothing = Just x
- merge Nothing (Just x) = Just x
- merge (Just _) (Just y) = Just y
-
-- Use only the latter feed_hosts if there are any.
all_feed_hosts =
feed_hosts $ if (null (get_feed_hosts (feed_hosts cfg2)))