[Haskell-cafe] Newbied question on IO Monad
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Tue Sep 12 08:42:24 EDT 2006
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
In this case main :: IO String so you will not see any output (quite
I'd suggest you to have a look at this tutorial that explain quite
well the IO Monad:
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