src/ConnectionString.hs

   1 {-# LANGUAGE DeriveDataTypeable #-}
   2 {-# LANGUAGE OverloadedStrings #-}
   3
   4 -- | Definition of and instances for the ConnectionString type.
   5 --
   6 module ConnectionString (
   7   ConnectionString(..) )
   8 where
   9
  10 -- DC is needed only for the DCT.Configured instance of String.
  11 import qualified Data.Configurator as DC()
  12 import qualified Data.Configurator.Types as DCT (
  13   Configured,
  14   Value( String ),
  15   convert )
  16 import Data.Data (Data)
  17 import System.Console.CmdArgs.Default (Default(..))
  18 import Data.Typeable (Typeable)
  19
  20 -- | A newtype around a string that allows us to give a more
  21 --   appropriate default value for a connection string.
  22 --
  23 newtype ConnectionString =
  24   ConnectionString { get_connection_string :: String }
  25   deriving (Data, Show, Typeable)
  26
  27 instance Default ConnectionString where
  28   -- | This default is appropriate for SQLite databases which require
  29   --   no authentication and live entirely in a file (or in this case,
  30   --   memory).
  31   def = ConnectionString ":memory:"
  32
  33
  34 instance DCT.Configured ConnectionString where
  35   -- | This allows us to read a ConnectionString out of a Configurator
  36   --   config file. By default Configurator wouldn't know what to do,
  37   --   so we have to tell it that we expect a DCT.String, and if one
  38   --   exists, to apply the ConnectionString constructor to it.
  39   convert s@(DCT.String _) =
  40     fmap ConnectionString (convert_string s)
  41     where
  42       convert_string :: DCT.Value -> Maybe String
  43       convert_string = DCT.convert
  44
  45   -- If we read anything other than a DCT.String out of the file, fail.
  46   convert _ = Nothing