For operating on nested monads is do:
declare a class MonadIO which contains the IO functions along
with monad monad-transformer lifted versions, for example:
class Monad m = MonadIO m where
ioPrint :: Show a = a - m ()
instance MonadIO IO where
ioPrint = print
instance (MonadIO m,MonadT
G'day Marco.
Quoting Marco Righele [EMAIL PROTECTED]:
How can I achieve the same effect (if it is ever possible)?
I feel like it should be something almost trivial, but I really can't get it.
One approach is to use a monad which works like Maybe, but as a monad
transformer over IO.
You might
Marco Righele wrote:
Hello everyone,
I have some operations that have to be done in sequence, with
each one having the result of the previous as input.
They can fail, so they have signature
a - Maybe b
Checking for error can be quite tedious so I use monadic operations:
f :: a - Maybe b
do
Hello everyone,
I have some operations that have to be done in sequence, with
each one having the result of the previous as input.
They can fail, so they have signature
a - Maybe b
Checking for error can be quite tedious so I use monadic operations:
f :: a - Maybe b
do y - foo x
z
Hello,
I was wondering the same thing, here is what I came up with:
module Main where
import Control.Monad
import Data.Maybe
import System.IO
newtype MaybeIO a = MaybeIO { unMaybeIO :: IO (Maybe a) }
instance Monad MaybeIO where
(=) k f = MaybeIO (do ma - unMaybeIO k
