Right, that's what Oliver said and I was reinforcing it with deductive reasoning. It is also not Option. It is something else altogether. Nevertheless, an isomorphism can easily be written with Either alone (ignoring bottoms). So in some loose sense "it is an Either".
-- Tony Morris http://tmorris.net/ S, K and I ought to be enough for anybody. David Pollak wrote: > Tony, > > Can (now Box) is not an Either. > > David > > On Tue, Jan 6, 2009 at 2:37 PM, Tony Morris <[email protected] > <mailto:[email protected]>> wrote: > > > Can is not an Option and to call it so in any way is an error of > misintegration. Indeed it would be an error to "replace Option with > Can" - they are completely different algebras. Either is kinded * > -> * -> * so cannot possible be isomorphic and cannot possibly have > map, flatMap etc (though it can have a bifunctor map being > covariant in both type arguments). However, Either.LeftProjection > and Either.RightProjection are kinded * -> * and are both covariant > functors and monads, hence map, flatMap etc. are available. e.g. > for(x <- either.left) ... is valid, try it. > > Of mild interest, it is possible to construct an isomorphism to Can > using both Either and Option. Indeed, it is possible to construct > an isomorphism to Option using Either e.g. forall A. Option[A] ≡ > Either [Unit, A] so it is possible using Either alone. I'll leave > both as reader exercises. > > > On Dec 21 2008, 5:15 am, Oliver Lambert <[email protected] > <mailto:[email protected]>> wrote: >> Ok so Can is not either an Either or an Option, its a Can. I > kind of >> wondered when I first used Can, and it was described as an > enhanced >> Option, why it wasn't called something like Option+ with > None, Some >> and Failure. >> >> On 21/12/2008, at 5:47 AM, David Pollak wrote: >> >>> Can has map, flatMap, filter etc. So it can be used in a for >>> comphrension. I don't believe Either has those methods. > Further, >>> Can has a bunch of helpers to turn Empty into Failure >> >>> On Dec 20, 2008 10:33 AM, "Oliver Lambert" <[email protected] > <mailto:[email protected]>> wrote: >> >>> Is Can a little less like Option and more like scala.Either, > where >>> the left side is used to indicate failure? On 21/12/2008, at >>> 1:43 AM, David Pollak wrote: > Folks, > > > Over the >>> year that Lift has had Can[T... > > > > > > -- Lift, the simply functional web framework http://liftweb.net > Collaborative Task Management http://much4.us Follow me: > http://twitter.com/dpp Git some: http://github.com/dpp > > > --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "Lift" group. To post to this group, send email to [email protected] To unsubscribe from this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/liftweb?hl=en -~----------~----~----~----~------~----~------~--~---
