On Mar 8, 2004, at 11:17, Sven Panne wrote:
Hmmm, using generics seems like massive overkill for option handling. Could you describe what you are exactly trying to achieve?
I am doing command line options parsing. I've defined Flag type with constructor for each possible option: data Flag = Verbose | Input String | Output String | Filter String deriving (Show, Typeable, Data) getOpt returns me a list of such objects. Now I need to look things up there by constructor. For example: .... doSomething fltflag where (Filter fltflag) = findFlag (Filter "none") opts To achieve this I've defined: instance Eq Flag where x == y = toConstr x == toConstr y findFlag :: Flag -> [Flag] -> Flag findFlag f fs = fromMaybe f (find (==f) fs) Sincerely, Vadim -- "La perfection est atteinte non quand il ne reste rien a ajouter, mais quand il ne reste rien a enlever." (Antoine de Saint-Exupery)