CODEWITHSUNDEEP
haskell
elliptic00
elliptic00

Reputation: 447

copyFile from two lists in Haskell

I'm new to Haskell.

My objective is to copy files from one directory to other directory.

So far what I have:

I have two lists contain full path file names

list1 = ["file1", "file2" ...]
list2 = ["new name1", "new name2"...]

I want to use 

copyFile::FilePath->FilePath->IO()

to copy files from list1 to list2

Note: list2 contains all new full path file names

I know 

zipWith(a->b->c)->[a]->[b]->[c]

and I try to 

zipWith(copyFile) list1 list2

but it doesn't work.

Any suggestion would be appreciated

Upvotes: 2

Views: 99

Answers (2)

jpvillaisaza
jpvillaisaza

Reputation: 440

Since

zipWith :: (a -> b -> c) -> [a] -> [b] -> [c]

and

System.Directory.copyFile :: FilePath -> FilePath -> IO ()

if you zip with copyFile, you get:

zipWith copyFile :: [FilePath] -> [FilePath] -> [IO ()]

that is, given two lists of file paths, you get a list of actions in which each action copies a file. You can evaluate such list of actions using sequence_:

sequence_ :: (Foldable t, Monad m) => t (m a) -> m ()

(in this case, sequence_ :: [IO ()] -> IO ()).

Thus, something like

sequence_ (zipWith copyFile ["foo", "bar"] ["new_foo", "new_bar"])

would work for you.

EDIT: Even better, as suggested by Daniel Wagner, use Control.Monad.zipWithM_ (zipWithM_ copyFile [...] [...]).

Upvotes: 6

lehins
lehins

Reputation: 9767

copyFile is a monadic action so you cannot use zipWith on it, here is what you can do:

mapM_ (uncurry copyFile) $ zip list1 list2

note mapM_'s type signature:

λ> :t mapM_
mapM_ :: Monad m => (a -> m b) -> [a] -> m ()

Upvotes: 0

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