Hi Gilmara, I assume you are trying to do this: main = do map sort $ learquivo "dataFile.txt" which gives you the error you mention. The problem is you are trying to use a "IO [[Int]]" where you want a "[[Int]]". To data out of IO, you must use the "<-" operator. To write a program which reads a line from the user and echos it back you do this: main = do userLine <- readLine putStrLn userLine The type of userLine is "String" (or "[Char]" if you prefer). Similarly, to change your "IO [[Int]]" to an [[Int]] you need to use the <- operator. So your program could become: main = do intListOfLists <- learquivo "dataFile.txt" let sortedSubLists = map Data.List.sort intListOfLists ..... Does this help? If not, read the "True Nature of Return" section of Real World Haskell: http://book.realworldhaskell.org/read/io.html#io.return Hope this helps, Tim ----- Original Message ---- From: Gilmara Pompelli <gilmarampompelli@gmail.com> To: beginners@haskell.org Sent: Mon, October 18, 2010 12:20:21 PM Subject: [Haskell-beginners] Help-me read file Hello I have a file with 100 lists, with 100 ints. I have to read the file and apply the map and sort functions on lists. II did it to read file: learquivo :: FilePath -> IO ([[Int]]) learquivo s = do conteudo <- readFile s return (read conteudo) But now applying the sort, the error appears: <interactive>:1:5: Couldn't match expected type `[a]' against inferred type `IO [[Int]]' how can I fix? Thanks _______________________________________________ Beginners mailing list Beginners@haskell.org http://www.haskell.org/mailman/listinfo/beginners