Change type of program options to 'IO [Options]'
Some options have defaults that depend on the environment, and we could handle these in two ways: - use a place-holder value (e.g. data X a = Default | Custom a) that is later read from the environment - move the options list to IO monad, where it can read the environment, etc. The second option allows also displaying the actual defaults in the `--help' output, even though it's not as nice, so I went with it. This patch only changes the option types, without actually changing any options yet. Signed-off-by: Iustin Pop <email@example.com> Reviewed-by: Helga Velroyen <firstname.lastname@example.org>