On Fri, Oct 30, 2009 at 1:33 PM, Yusaku Hashimoto <nonow...@gmail.com> wrote: > Thanks for fast replies! Examples you gave explain why all > Applicatives are not Monads to me. > > And I tried to rewrite Bob's Monad instance for ZipList with (>>=). > > import Control.Applicative > > instance Monad ZipList where > return = ZipList . return > (ZipList []) >>= _ = ZipList [] > (ZipList (a:as)) >>= f = zlHead (f a) `zlCons` (ZipList as >>= f)
This is taking the first element of each list, but you need to take the nth element. Try (ZipList (a:as)) >>= f = zlHead (f a) `zlCons` (ZipList as >>= zlTail . f) -- Dave Menendez <d...@zednenem.com> <http://www.eyrie.org/~zednenem/> _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
