Hello Mark [ Literate haskell follows... ]
module Verb where
import qualified Data.Map as Map import Data.Char
data Verb = Go | Get | Jump | Climb | Give deriving (Show, Read)
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) {- .. -} ]
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