Here's how I wrote it: ----- beginning of file import IO -- turn a line of the text file into a pair consisting of -- the message triple and the message string -- slight bug: will contract multiple spaces in the message string -- This could be rewritten to avoid this problem, but couldn't make as much use of -- existing prelude functions to do the work. readMessage :: String -> ((Integer, Integer, Integer), String) readMessage line = let (lang:typ:idx:msgWds) = words line msg = unwords msgWds in ((read lang, read typ, read idx),msg) -- An IO action which gets a list of such pairs given a filename. readMessagesFile filename = do hdl <- openFile filename ReadMode cs <- hGetContents hdl return $ map readMessage (lines cs) -- An IO action which gets a lookup function for the message codes given a filename. getMessageLookup :: String -> IO ((Integer, Integer, Integer) -> Maybe String) getMessageLookup filename = do msgs <- readMessagesFile filename return (flip lookup msgs) ----- end of file You can then test this in GHCi with something like msgLookup <- getMessageLookup "messages.txt" msgLookup (1,1,1) which should result in: Just "Error message 1" The values are wrapped in the "Just" constructor, and typed in the Maybe monad, since the lookup might fail, in which case the msgLookup will return the value "Nothing". Also note that this is somewhat inefficient for very large numbers of messages, (lookup will be linear in the number of messages in the worst case.) To get better performance, a Map (see Data.Map) could be constructed, and the lookups done on that, resulting in logarithmic time performance. The interface would remain the same. Hope this helps, - Cale On 26/07/05, Huong Nguyen wrote:

Hello everybody,

Now I am writing a module to handles messages of a system. The messages are stored in a file. The content of each line of the file likes this:

1 001 001 Error message 1 1 001 002 Error message 2 1 002 001 Warning message 1

in which: The first word is the language Code (e.g: 1 is English, 2 is French), the second is type of messages (e.g: 001 is error message, 002 is warning message,etc), the third is the index number of messages, and the last is the message. I need to read 3 first words of each line and assign them to 3 variables. After that, I need to show the error message based on the tuple of those 3 first variable, e.g: errMsg("1","001","001") = "Error message 1"

At first, I tried to read only one first line of the file as follows:

import Prelude import List import Char import IO

main = do hdl <- openFile "message.txt" ReadMode msgLine <-hGetLine hdl --stdMsg: cut space at the begining of the line. let stdMsg = dropWhile(not.isSpace) msgLine -Assign langCode with the first word of the line. let langCode = takeWhile(not.isSpace) stdMsg

However, after that, I do not know how to read second element, third element of the line. And how to read continuous next line after first?

Please help me. Thanks a lot. _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe