patch applied (cabal): Add liftOption for making derived command parsers

[Duncan Coutts]

Tue Feb 26 12:02:15 PST 2008  Duncan Coutts <duncan at haskell.org>
  * Add liftOption for making derived command parsers
  liftOption :: (b -> a) -> (a -> (b -> b)) -> Option a -> Option b
  For example:
  liftOption fst (\a (_,b) -> (a,b)) :: Option a -> Option (a,b)
  Needed to be able to make a CommandUI (a, b) using an existing CommandUI a.
  That's what we want to do in cabal-install where the 'install' command
  to support all the 'configure' flags and some extra of it's own, for example
  --dry-run and probably several more in future.

    M ./Distribution/Simple/Command.hs -1 +12

View patch online:

  http://darcs.haskell.org/cabal/_darcs/patches/20080226200215-adfee-64cb4642ffb5c880e8935c7117062f0e07686b82.gz