Hi Benja,
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
This is even neater. However, I fail to implement this. It does not
2007/11/19, Ryan Ingram [EMAIL PROTECTED]:
I am pretty sure that the constructor MaybeT is exactly what you are looking
for.
newtype MaybeT m a = MaybeT (m (Maybe a))
therefore
MaybeT :: m (Maybe a) - MaybeT m a
I swear I tried it. I swear.. Why didn't it worked than and it works now??
Hello,
I am writing some toys programs to learn and try to apply Monads
properties (without success, I must say). Although I spent half a day
on this code:
http://hpaste.org/3957
I couldn't simplify (shorten) getStrip function. After reading Doing
it with class (
Hi Benja,
You can find MaybeT here:
http://www.haskell.org/haskellwiki/New_monads/MaybeT
Thank you, that you spent some time figuring this out. This is exacly
what I have expected. (This print was debug leftovers).
Now I will try to understand how exacly this works.
My big thanks to you
Hi Radosław,
You should be able to write this with MaybeT as follows:
getStrip :: IO ( Maybe String )
getStrip = runMaybeT $ do
pageContent - liftIO $ downloadFile mainPageAddress
let x = patternForStrip pageContent
print x
z - x
liftIO $ downloadFile $ mainPageAddress ++ z
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
