You want the Map to map from filenames to their contents? Basically you need mapM or foldM, depending in where you want to use getXmlContent. In the below code I used mapM to read the files into a list of pairs, and fold over it (I changed insertRec to take a pair). -- module Main where import Data.List import qualified Data.Map as M import Control.Monad (mapM) insertRec :: M.Map String String -> (String, String) -> M.Map String String insertRec m (key, value) = if M.lookup key m == Nothing then M.insert key value m else m insertRec2 m (key, value) = M.insertWith const key value m createMap :: [(String, String)] -> M.Map String String createMap lst = foldl' insertRec M.empty lst getXmlContent :: FilePath -> IO (String,String) getXmlContent filename = do contents <- readFile filename return (filename, contents) main :: IO () main = do xmlfiles <- mapM getXmlContent ["a.xml","f.xml", "a.xml"] let ht = createMap xmlfiles print ht -- You could also read the files in insertRec instead of in main -- that would make insertRec return an "IO (M.Map String String)" instead of just "M.Map String String". And then you have to use foldM in createMap to use it, because the folding function is monadic now. On 5/11/11, Michael Xavier wrote:

I believe let when you're in do notation is for pure functions. Since c is IO (String String), I think what you might try is:

c <- getXmlContent e k <- fst c v <- snd c

Or even better, use pattern matching:

(k, v) <- getXmlContent e

Someone please step in if I'm misrepresenting how it's done.

On Wed, May 11, 2011 at 11:05 AM, Manfred Lotz wrote:

...

Hi there, I've got a problem creating a map.

I have a list of dataset names and adding those dataset names into a map works fine like this:

<----------------------------snip--------------------------------> module Main where

import Data.List import qualified Data.Map as M

insertRec :: M.Map String String -> String -> M.Map String String insertRec m e = let f = M.lookup e m in if f == Nothing then M.insert e "bla" m else m

createMap :: [String] -> M.Map String String createMap lst = let m = M.empty in foldl' insertRec m lst

main :: IO () main = do let xmlfiles = [ "a.xml","f.xml"] let ht = createMap xmlfiles print ht <----------------------------snap-------------------------------->

However, actually I want to parse the xml files and adding content into the map.

For this I have a function getXmlContent :: FilePath -> IO (String,String)

and would like to do something like this:

<----------------------------snip--------------------------------> insertRec m e = do c <- getXmlContent e let k = fst c let v = snd c M.insert k v m <----------------------------snap-------------------------------->

Unfortunately, this doesn't work because of IO. I have no glue how to get this done.

Any help appreciated.

-- Thanks, Manfred

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