so that it really represents an option and not just a flag.
     It's been renamed to OptionField as it models a field in a flags-like data structure. 
     
        data OptionField a = OptionField {
          optionName        :: Name,
          optionDescr       :: [OptDescr a] }
      
        data OptDescr a  = ReqArg Description OptFlags ArgDescr (ReadE (a->a))         (a -> [String])
                         | OptArg Description OptFlags ArgDescr (ReadE (a->a)) (a->a)  (a -> [Maybe String])
                         | ChoiceOpt [(Description, OptFlags, a->a, a -> Bool)]
			 | BoolOpt Description OptFlags{-True-} OptFlags{-False-} (Bool -> a -> a) (a -> Bool)
      
      An option field can expand to several command line options, which are all defined together.
      For example, the compiler flag is defined as follows.
      
            option [] ["compiler"] "compiler"
               configHcFlavor (\v flags -> flags { configHcFlavor = v })
               (choiceOpt [ (Flag GHC, ("g", ["ghc"]), "compile with GHC")
                          , (Flag NHC, ([] , ["nhc98"]), "compile with NHC")
                          , (Flag JHC, ([] , ["jhc"]), "compile with JHC")
                          , (Flag Hugs,([] , ["hugs"]), "compile with Hugs")])
      
      We can need to use several kinds of OptDescr for the same option, as in the 
      optimization Option (really a extreme case):
      
            ,multiOption "optimization"
               configOptimization (\v flags -> flags { configOptimization = v })
               [optArg' "n" (Flag . flagToOptimisationLevel)
                ....
                ....
                        "Build with optimization (n is 0--2, default is 1)",
                noArg (Flag NoOptimisation) []