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 import System.Console.CmdArgs.Default ( Default(..) )
  11
  12 import qualified OptionalConfiguration as OC (
  13   OptionalConfiguration(..),
  14   merge_maybes )
  15
  16 -- | The main configuration data type. This will be passed to most of
  17 --   the important functions once it has been created.
  18 --
  19 data Configuration =
  20   Configuration {
  21     database :: Maybe String,
  22     detail  :: Bool,
  23     host :: Maybe String,
  24     password :: Maybe String,
  25     port :: Maybe Int,
  26     username :: Maybe String }
  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           database = def,
  34           detail = def,
  35           host = def,
  36           password = def,
  37           port = def,
  38           username = def }
  39
  40 -- | Merge a 'Configuration' with an 'OptionalConfiguration'. This is
  41 --   more or less the Monoid instance for 'OptionalConfiguration', but
  42 --   since 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     (OC.merge_maybes (database cfg) (OC.database opt_cfg))
  49     (merge (detail cfg) (OC.detail opt_cfg))
  50     (OC.merge_maybes (host cfg) (OC.host opt_cfg))
  51     (OC.merge_maybes (password cfg) (OC.password opt_cfg))
  52     (OC.merge_maybes (port cfg) (OC.port opt_cfg))
  53     (OC.merge_maybes (username cfg) (OC.username opt_cfg))
  54   where
  55     -- | If the thing on the right is Just something, return that
  56     --   something, otherwise return the thing on the left.
  57     merge :: a -> Maybe a -> a
  58     merge x Nothing  = x
  59     merge _ (Just y) = y