Hi, Perhaps I did not understand the question properly, but it looks very straight forward :
oneOrNone x = fmap Just x <|> pure Nothing it will have a type of oneOrNone :: (Alternative f) => f a -> f (Maybe a) In fact, there is a function called "optional" in Control.Applicative[1] which does exactly that. Is this what you are looking for? thanks, Hemanth K [1] http://haskell.org/ghc/docs/6.12.2/html/libraries/base-4.2.0.1/Control-Applicative.html On Fri, Aug 12, 2011 at 1:31 PM, C K Kashyap <ckkash...@gmail.com> wrote: > Hello gentle Haskell folks, > > I happened to read "Beautiful code"'s chapter 1 today and found Brian > Kerninghan's regex implementation. In it he only shows the * meta character. > I can easily understand how + can be built but am having trouble with > building ? (zero or one). I'd really appreciate it if some one could help me > understand it. > > Regards, > Kashyap > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe@haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe > >
_______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
