On 11/18/07, Benja Fallenstein <[EMAIL PROTECTED]> wrote:
> Hi Radosław,
>
> You should be able to write this with MaybeT as follows:
Correction, sorry. The code in my original mail doesn't take care of
converting the 'Maybe's returned by the functions you're calling into
'MaybeT's.
The following should work, but is a little annoying:
getStrip :: IO ( Maybe String )
getStrip = runMaybeT $ do
pageContent <- MaybeT $ downloadFile mainPageAddress
z <- MaybeT $ return $ patternForStrip pageContent
MaybeT $ downloadFile $ mainPageAddress ++ z
Something like the following might feel cleaner, though:
maybeT :: Maybe a -> MaybeT m a
maybeT = MaybeT . return
downloadFile :: String -> MaybeT IO String
downloadFile s = maybeT (parseURI s) >>= liftIO . httpGet
getStrip :: MaybeT IO String
getStrip = do
pageContent <- downloadFile mainPageAddress
z <- maybeT $ patternForStrip pageContent
downloadFile $ mainPageAddress ++ z
Best,
- Benja
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