My function gets a string of type IO [String] by simple manipulations, and I need a String. For example, display.
How to perform type conversion?

  • one
    IO [String] is not a string, but a list of strings in the IO monad. - andrybak

1 answer 1

An example is a program that concatenates its arguments:

 import System.Environment main = do args <- getArgs putStrLn $ concat args

Type getArgs :: IO [String] .

Write the function f :

 f :: Monad m => m [[a]] -> m [a] fm = m >>= (\ xs -> return $ concat xs)

Let's expand the do notation in the original example:

 main :: IO () main = (f getArgs) >>= putStrLn