-- | Miscellaneous utility functions
module Misc (
  double_just )
where

-- | If given 'Nothing', return 'Nothing'. Otherwise wrap our argument
--   in another 'Just'. This is used when handling optional XML
--   elements that are optionally empty. If the element is missing, we
--   want 'Nothing'. And if the contents are missing, we want
--   'Nothing' then too. But if something is present, we need @Just
--   (Just foo)@ for the types to match up.
--
--   ==== __Examples__:
--
--   >>> double_just Nothing
--   Nothing
--   >>> double_just (Just 2)
--   Just (Just 2)
--
double_just :: (Maybe a) -> Maybe (Maybe a)
double_just val =
  case val of
    Nothing -> Nothing
    just_something -> Just just_something