On Fri, Sep 28, 2007 at 04:38:35PM +0100, Brian Hulley wrote: > > In my oppinion reversor would have type > > > >> reversor :: (Foldable f) => [a] -> f b > >>
> No, this is the wrong type. To find the correct type, if you look at the > type of the input argument in your code it will be the result of > (lines), so from ghci: > > Prelude> :t lines > lines :: String -> [String] > Prelude> > > Therefore (reverseor) has type [String] -> ??? > Now for the output type, you are using (output) as an input to (mapM_ > putStrLn). (mapM_) takes a list and uses its argument to do something to > each element of the list. True. I forgot to mention imports in my code: > import Prelude hiding (foldr, foldr1, reverse, mapM_) > import System.Environment > import Data.List hiding (foldr, foldr1) > import Data.Foldable > import Data.Traversable > import Data.Sequence So the type of mapM_ used in the code is (Foldable t, Monad m) => (a -> m b) -> t a -> m () I'd like to keep the generic Foldable t there when "m" is specialized to IO. I thought this would allow type of "reversor" to be specialized to (Foldable f) => [String] -> f String > For using Data.Sequence to implement reversor, all you need to do is > first convert [String] to Seq String, reverse the sequence, then convert > back from Seq String to [String]. Yes, probably that's how it works under the hood, but the reason I mentioned Foldable is that I'd like to avoid [a] -> something -> [a], but keep the type of output value from "reversor" abstract... For no particular reason, just playing with this idea :) Regards, -- Krzysztof Kościuszkiewicz Skype: dr.vee, Gadu: 111851, Jabber: [EMAIL PROTECTED] Mobile IRL: +353851383329, Mobile PL: +48783303040 "Simplicity is the ultimate sophistication" -- Leonardo da Vinci _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
