Re: [Haskell-beginners] How do I map a String and a IO String?

On Thu, Jun 29, 2017 at 02:33:22PM +0200, Jona Ekenberg wrote:

I want to replace lines with the content of a file if the line is a filename

Hello Jonas, you want to user `return`: λ> :t return return :: Monad m => a -> m a which lifts a simple value inside a monad (in this case, a -> IO a), like this: lineOrIO :: String -> IO String lineOrIO cs | (isPrefixOf "./" cs) = readFile cs | otherwise = return cs If this is not a school assignment, consider replacing `isPrefixOf "./"` with something from `System.Directory`. Does this help?