Re: getOpt return record of type a rather than [a]

18 Dec 2007


      On Dec 18, 2007 11:10 PM, Henning Thielemann
 wrote:
...
The current version of System.Console.GetOpt.getOpt returns a list of
values, where the element type has usually one constructor per option.
 data Flag
     = Verbose | Version
     | Input String | Output String | LibDir String
What I more like to receive is a record consisting of one constructor and
many fields, where optional options are of type Maybe, options with
multiple occurrence are of type list.
data Flag = Flag {
      verbose :: Bool,
      version :: Bool,
      input  :: Maybe FilePath,
      output :: Maybe FilePath,
      libdir :: FilePath
    }
Then we would need
data ArgDescr a =
  NoArg (a -> a)
  ReqArg (String -> a -> a) String
  OptArg (String -> a -> a) String
e.g.
OptArg (\path flags -> flags {input = Just path}) "FILE"
I feel this approach is so natural, that someone must have implemented it
already.
Indeed, we to this in HAppS, for instance. Folding the resulting list
makes the current GetOpt implementation more than adequate.

-- 
Cheers,
  Lemmih