src/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 -- System imports.
  11 import System.Console.CmdArgs.Default ( Default(..) )
  12 import System.Log ( Priority( INFO ) )
  13
  14 -- Local imports.
  15 import Backend ( Backend(..) )
  16 import ConnectionString ( ConnectionString )
  17 import qualified OptionalConfiguration as OC (
  18   OptionalConfiguration(..),
  19   merge_maybes )
  20
  21
  22 -- | The main configuration data type. It contains all options that
  23 --   can be set in a config file or on the command line.
  24 --
  25 data Configuration =
  26   Configuration {
  27     backend           :: Backend,
  28     connection_string :: ConnectionString,
  29     log_file          :: Maybe FilePath,
  30     log_level         :: Priority,
  31     remove            :: Bool,
  32     syslog            :: Bool }
  33     deriving (Show)
  34
  35 -- | A Configuration with all of its fields set to their default
  36 --   values.
  37 instance Default Configuration where
  38   def = Configuration {
  39           backend           = def,
  40           connection_string = def,
  41           log_file          = def,
  42           log_level         = INFO,
  43           remove            = def,
  44           syslog            = def }
  45
  46
  47 -- | Merge a Configuration with an OptionalConfiguration. This is more
  48 --   or less the Monoid instance for 'OptionalConfiguration', but since
  49 --   the two types are different, we have to repeat ourselves.
  50 --
  51 merge_optional :: Configuration
  52                -> OC.OptionalConfiguration
  53                -> Configuration
  54 merge_optional cfg opt_cfg =
  55   Configuration
  56     (merge (backend cfg) (OC.backend opt_cfg))
  57     (merge (connection_string cfg) (OC.connection_string opt_cfg))
  58     (OC.merge_maybes (log_file cfg) (OC.log_file opt_cfg))
  59     (merge (log_level cfg) (OC.log_level opt_cfg))
  60     (merge (remove cfg) (OC.remove opt_cfg))
  61     (merge (syslog cfg) (OC.syslog opt_cfg))
  62   where
  63     -- | If the thing on the right is Just something, return that
  64     --   something, otherwise return the thing on the left.
  65     merge :: a -> Maybe a -> a
  66     merge x Nothing  = x
  67     merge _ (Just y) = y
  68