import Data.Maybe
import Control.Applicative
import Control.Monad.Trans.Maybe

data Result = Result
getEnv :: String -> IO (Maybe String)
getEnv = undefined
readFileLines :: String -> IO [String]
readFileLines = undefined
result1 :: String -> Result
result1 = undefined
result2 :: String -> Result
result2 = undefined
def :: Result
def = undefined

main = fmap (maybe def id) $ runMaybeT $ asum
         [result1 <$> MaybeT (getEnv "path1")
         ,result2 <$> MaybeT (getEnv "path2")]