> instance Monad m => MonadPlus (MaybeT m) where > mzero = MaybeT $ return Nothing > mplus x y = MaybeT $ do maybe_value <- runMaybeT x > case maybe_value of > Nothing -> runMaybeT y > Just _ -> return maybe_value >
I've not run it so with some caution, I'd expect this to work - the last line is now returning the first answer with 'return' of the wrapped monad. I'm not sure if this is a lawful version of mplus though... _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
