[Haskell-cafe] Re: Newbied question on IO Monad
bortzmeyer at nic.fr
Tue Sep 12 09:11:36 EDT 2006
On Tue, Sep 12, 2006 at 09:00:19AM -0400,
Sara Kenedy <sarakenedy at gmail.com> wrote
a message of 68 lines which said:
> Maybe what I talk is not clear.
Do not worry, not all the haskell-cafe readers speak english. (I'm
french, for instance.)
> 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".
>From a newbie to another newbie: I do not think it is possible. "There
is no way out of the IO monad, once you're in it."
See the explanations in the page indicated by Henning Thielemann :
This should work (not tested):
update :: String -> IO String
update sss = do
writeFile "myFile.txt" sss
x <- callSystem "myFile.txt"
y <- openFile "result.txt" ReadMode
zzz <- hGetContents y
main = update "Foobar"
More information about the Haskell-Cafe