On Sun, Jan 17, 2010 at 7:02 AM, Stephen Tetley
I wouldn't use read instead something either a simple function:
verb :: String -> Maybe Verb verb "Go" = Just Go verb "Get" = Just Get verb _ = Nothing
Or possible a Map:
verb2 :: String -> Maybe Verb verb2 s = Map.lookup s verb_map
verb_map :: Map.Map String Verb verb_map = Map.fromAscList [ ("Go", Go), ("Get", Get) {- .. -} ]
Oh, yeah, I like these better than relying on the Read instance. Relying on Read and Show for program logic has been kind of an implicit smell to me, and I can put my finger on why now: you lose alpha conversion on the program scale. I like the ability to rename with confidence. Plus, this way it is natural to encode synonyms; eg. "take" and "get". Though depending on the vernacular of the game you might not want that. I'm not sure what it means to take out of bed. Luke
You could then do more about say case sensitivity - e.g. add ("get",Get) etc or always convert to upper before querying the map.
verb3 :: String -> Maybe Verb verb3 s = Map.lookup (map toUpper s) verb_map2
verb_map2 :: Map.Map String Verb verb_map2 = Map.fromAscList [ ("GO", Go), ("GET", Get) {- .. -} ]
Best wishes
Stephen _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe