gistfile1.hs

module Main where
import qualified Data.Map as Map
import Data.Either (lefts, rights)

data DbColumn = DbColumn { name :: String
                         , tableName :: TableName
                         } deriving Show

newtype TableName = TableName String deriving (Ord, Eq, Show)

type Config = Map.Map TableName [DbColumn]

doWork :: Config -> [DbColumn] -> [Either String DbColumn]
doWork conf input = concatMap (fun conf) input
                    where
                    fun conf x@(DbColumn "id" _) = [Right x]
                    fun conf (DbColumn _ tn) = case Map.lookup tn conf of
                                                    Just x -> fmap Right x
                                                    Nothing -> [Left $ "id for table " ++ show tn ++ " not found in conf"]


good :: [Either String DbColumn] -> [DbColumn]
good = rights

bad :: [Either String DbColumn] -> [String]
bad = lefts


main :: IO ()
main = do
    let result = doWork undefined undefined
    print $ "good " ++ (show $ good result)
    print $ "bad " ++ (show $ bad result)