It's not about monads, that this doesn't work. To go point-free you need to understand the types of the expressions you compose. The bind function ((>>=) :: Monad m => m a -> (a -> m b) -> m b) doesn't leave room to take more arguments. Matching the arguments to bind in the expression 'findRegularFiles >>= readFiles' the 'findRegularFiles' should have a type of 'Monad m => m a' and 'readFiles' 'Monad m => a -> m b'. With this type 'findRegularFiles' takes no arguments, but it should take one -- the directory-path. But the 'readFiles' type looks to be right: bind expects a function from 'a' to 'm b', and that's what it gets. So, what you need is some other function than bind (>>=) to compose the functions you have to get the whole expression to have the right type. If you find the type of that function, you'll easily find the composing function itself. Also check the definitions of 'findRegularFiles' and 'readFiles', but at first you can leave them be ... where findRegularFiles :: String -> IO [String] findRegularFiles dir = undefined readFiles :: [String] -> IO [File] readFiles paths = undefined and implement them later. On Sat, Feb 4, 2012 at 12:49 PM, Ovidiu Deac wrote:

I have the following code which works fine:

type File = (String, String) --name and content

readDir :: String -> IO [File] readDir dir = findRegularFiles dir >>= readFiles   where     findRegularFiles = find always (fileType ==? RegularFile)     readFiles paths = mapM readFile paths >>= return.zip paths

...and I would like to write the function readDir like this: readDir :: String -> IO [File] readDir = findRegularFiles >>= readFiles   where ...

...but I get the error: grep.hs:46:32:     Couldn't match expected type `IO [FilePath]'                 with actual type `[FilePath]'     Expected type: IO [FilePath] -> String -> IO [File]       Actual type: [FilePath] -> IO [File]     In the second argument of `(>>=)', namely `readFiles'     In the expression: findRegularFiles >>= readFiles

Can somebody please explain it?

It's not a big deal. I can keep the old version which works fine. My only problem is that I thought I understood the monads better but apparently I don't :)

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