harbl-cli/src/Configurator.hs

   1 {-# LANGUAGE FlexibleContexts #-}
   2
   3 module Configurator ( convert_newtype_list )
   4 where
   5
   6 import Data.Configurator.Types (
   7   Configured,
   8   Value( List ),
   9   convert )
  10
  11
  12 -- | Configurator helper function. We often want to parse a list of
  13 --   \"special\" strings; that is, a list of strings with a little
  14 --   more type safett. For example, if we want to read a list of IP
  15 --   addresses and a list of usernames, we don't want to confuse the
  16 --   two. So, we might wrap them in \"Addresses\" and \"Usernames\"
  17 --   newtypes. But then Configurator doesn't know how to parse them
  18 --   any more! This function takes the newtype constructor and the
  19 --   value and does the obvious thing.
  20 --
  21 --   ==== _Examples_
  22 --
  23 --   >>> import Data.Configurator () -- Get predefined 'Configured' instances.
  24 --   >>> import Data.Text ( pack )
  25 --   >>> import Data.Configurator.Types ( Value( String ) )
  26 --   >>> newtype Foo = Foo [String] deriving (Show)
  27 --   >>> let s1 = String (pack "foo1")
  28 --   >>> let s2 = String (pack "foo2")
  29 --   >>> let config = List [s1, s2]
  30 --   >>> convert_newtype_list Foo config
  31 --   Just (Foo ["foo1","foo2"])
  32 --
  33 convert_newtype_list :: Configured b => ([b] -> a) -> Value -> Maybe a
  34 convert_newtype_list ctor (List xs) = fmap ctor (mapM convert xs)
  35 convert_newtype_list _ _ = Nothing