On 2/17/06, Peter
Hello,
For the purpose of familiarizing myself with Haskell, and also because I love Haskell :), I am trying to re-make a script that I made in Python that sends a request to a server and extracts the list of email addresses from a Mailman web-page by using an XML Parser on the page's HTML that has been converted to XHTML by "HTML Tidy".
However, I cannot seem to figure out a way to get the state of a Monad; Specifically I cannot get the value of an "IO String" Monad.
I have read some tutorials on Monads but I guess I must have missed something.
I have read that the >>= operator is the only way to extract the state of an action as a string, and pipe it to a function. So far so good. But, That does not seem to work, because as I understand the >>= operator, it expects the function on the right hand side to return an IO Monad, which completely defeats the purpose here.
So, How am I supposed to get the value of an IO Monad, such as "IO String", without returning an IO Monad?
If this is of any help, here is the function I am stuck on: recv_headers' :: Socket.Socket -> String -> IO [[String]] recv_headers' sock bulk | received == "" = error "Connection died unexpectedly." | received == "\n" && endswith bulk "\r\n\r" = return [["foo", "bar"]] | otherwise = recv_headers' sock (bulk ++ received) where received = (Socket.recv sock 1)
Try: recv_headers' sock bulk = do received <- Socket.recv sock 1 case received of "" -> error ... "\n" | endswith bulk "\r\n\r" -> ... _ -> recv_headers' sock (bulk ++ received) -- Friendly, Lemmih