Re: [Haskell-cafe] Either e Monad

19 Sep 2006


      Albert Lai wrote:
...
Deokhwan Kim  writes:
...
Where is the Monad instance declaration of Either e?
It is in Control.Monad.Error as well.  Strange: the doc doesn't state it.
Thanks a lot, Albert! I found the declaration in 
libraries/mtl/Control/Monad/Error.hs of the ghc source distribution:

   instance (Error e) => Monad (Either e) where
           return        = Right
           Left  l >>= _ = Left l
           Right r >>= k = k r
           fail msg      = Left (strMsg msg)

-- 
Deokhwan Kim