Hello,
Maybe what I talk is not clear.
I want to take the input string sss of "update" to use in: writeFile
"myFile.txt" sss of function "main" and get the value zzz from "main"
to assign for the value return of "update". I think I need to change
the way to declare two functions to get what I want, but I do not know
how.
update :: String -> String
update sss = zzz
main = do writeFile "myFile.txt" sss
x <- callSystem "myFile.txt"
y <- openFile "result.txt" ReadMode
zzz <- hGetContents y
return zzz
S.
On 9/12/06, Andrea Rossato
Il Tue, Sep 12, 2006 at 08:05:42AM -0400, Sara Kenedy ebbe a scrivere:
Hello all,
update :: String -> String update sss = ...
main = do writeFile "myFile.txt" sss x <- callSystem "myFile.txt" y <- openFile "result.txt" ReadMode zzz <- hGetContents y return zzz
I know that function main returns IO String, function update returns String. And my purpose is to get the string zzz from main for the value return of function update. But I do not know which way I can do.
Did you mean something like this?
update :: String -> String update sss = "Hi! " ++ sss
main = do writeFile "myFile.txt" $ update "What are you trying to do?" x <- callSystem "myFile.txt" y <- openFile "result.txt" ReadMode zzz <- hGetContents y return zzz
In this case main :: IO String so you will not see any output (quite useless). I'd suggest you to have a look at this tutorial that explain quite well the IO Monad: http://haskell.org/haskellwiki/IO_inside
Ciao Andrea _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe