Re: [Haskell-beginners] IO action on a list of [IO a]

On Sat, 06 Oct 2012 19:35:13 +0200 "Henk-Jan van Tuyl" wrote:

On Sat, 06 Oct 2012 16:16:18 +0200, Manfred Lotz wrote:

...

myfor :: (a -> IO () ) -> [IO a] -> IO () myfor _ [] = return () myfor f (x:xs) = do x' <- x f x' myfor f xs

Is there a library function doing just this?

You could use this: import Control.Monad myfor :: (a -> IO () ) -> [IO a] -> IO () myfor f (x:xs) = mapM_ (liftM f) xs

or this: import Data.Functor myfor :: (a -> IO () ) -> [IO a] -> IO () myfor f (x:xs) = mapM_ (f <$>) xs

Shouldn't it be xs instead of (x:xs)? The signatures are the same as in my own myfor. However, when I run my code using your versions of myfor I do not get any output at all. -- Manfred -- Manfred