empty.hs

import System.Directory
import System.Environment
import Control.Exception
import Data.Typeable
import Data.List 

data InvalidPath = InvalidPath String deriving (Show)
data FileError   = NoSuchFile  deriving (Show, Typeable)
data EmptyFile   = EmptyFile   deriving (Show, Typeable)

instance Exception InvalidPath
instance Exception EmptyFile

readMyFile :: FilePath -> IO String
readMyFile pathToFile = do
    fileIsHere <- doesFileExist pathToFile
    if fileIsHere then do
        content <- readFile pathToFile
        case content of
            [] -> throw EmptyFile
            _  -> return content
    else
        throw $ InvalidPath "Alert: You entered an incorrect path"   

main :: IO ()
main = do
    putStrLn "Введите путь к фалу"
    content <- getLine
    file <- try $ readMyFile content :: IO (Either InvalidPath String)
    case file of
       Left exc  -> print $ show exc
       Right content -> putStrLn content