Prologue.Control.Monad.IO

Documentation

putChar :: MonadIO m => Char -> m ()

putStr :: MonadIO m => String -> m ()

putStrLn :: MonadIO m => String -> m ()

print :: (MonadIO m, Show a) => a -> m ()

pprint :: (MonadIO m, Show a) => a -> m ()

getChar :: MonadIO m => m Char

getLine :: MonadIO m => m String

getContents :: MonadIO m => m String

interact :: MonadIO m => (String -> String) -> m ()

readFile :: MonadIO m => FilePath -> m String

writeFile :: MonadIO m => FilePath -> String -> m ()

appendFile :: FilePath -> String -> IO ()

ioError :: MonadIO m => IOError -> m a

type FilePath = String

File and directory names are values of type String, whose precise meaning is operating system dependent. Files can be opened, yielding a handle which can then be used to operate on the contents of that file.

userError :: String -> IOError

Construct an IOError value with a string describing the error. The fail method of the IO instance of the Monad class raises a userError, thus:

instance Monad IO where
  ...
  fail s = ioError (userError s)

type IOError = IOException

The Haskell 2010 type for exceptions in the IO monad. Any I/O operation may raise an IOError instead of returning a result. For a more general type of exception, including also those that arise in pure code, see Exception.

In Haskell 2010, this is an opaque type.