Configuration.hs

   1 -- | This module defines the 'Configuration' type, which is just a
   2 --   wrapper around all of the configuration options we accept on the
   3 --   command line.
   4 --
   5 module Configuration (
   6   Configuration(..),
   7   merge_optional )
   8 where
   9
  10 import System.Console.CmdArgs.Default ( Default(..) )
  11 import System.Log ( Priority( INFO ) )
  12
  13 import Backend ( Backend(..) )
  14 import qualified OptionalConfiguration as OC (
  15   OptionalConfiguration(..),
  16   merge_maybes )
  17
  18 -- | The main configuration data type. This will be passed to most of
  19 --   the important functions once it has been created.
  20 data Configuration =
  21   Configuration {
  22     backend           :: Backend,
  23     connection_string :: String,
  24     log_file          :: Maybe FilePath,
  25     log_level         :: Priority,
  26     syslog            :: Bool }
  27     deriving (Show)
  28
  29 -- | A Configuration with all of its fields set to their default
  30 --   values.
  31 instance Default Configuration where
  32   def = Configuration {
  33           backend           = def,
  34           connection_string = def,
  35           log_file          = def,
  36           log_level         = INFO,
  37           syslog            = def }
  38
  39
  40 -- | Merge a Configuration with an OptionalConfiguration. This is more
  41 --   or less the Monoid instance for OptionalConfiguration, but since
  42 --   the two types are different, we have to repeat ourselves.
  43 merge_optional :: Configuration
  44                -> OC.OptionalConfiguration
  45                -> Configuration
  46 merge_optional cfg opt_cfg =
  47   Configuration
  48     (merge (backend cfg) (OC.backend opt_cfg))
  49     (merge (connection_string cfg) (OC.connection_string opt_cfg))
  50     (OC.merge_maybes (log_file cfg) (OC.log_file opt_cfg))
  51     (merge (log_level cfg) (OC.log_level opt_cfg))
  52     (merge (syslog cfg) (OC.syslog opt_cfg))
  53   where
  54     -- | If the thing on the right is Just something, return that
  55     --   something, otherwise return the thing on the left.
  56     merge :: a -> Maybe a -> a
  57     merge x Nothing  = x
  58     merge _ (Just y) = y
  59