On Sat, 17 Jan 2009, David Menendez wrote:
instance Applicative f => Applicative (Backwards f) where pure = B . pure f <*> x = B (unB f <**> unB x)
probably should be f <*> x = B (unB x <**> unB f) anyhow, this should be part of Control.Applicative.
This may be terminological confusion. I would have said that a PointedList *is* a zipper.
This is what I thought, and what how I initally advised Jeff. However after carefully reading both <http://en.wikibooks.org/wiki/Haskell/Zippers> and <http://www.cs.nott.ac.uk/~ctm/Dissect.pdf> (Clowns to the left of me, jokers to the right), it is clear that formally a zipper focuses on a sub-list / sub-tree rather than focusing on a particular node of a list or a tree. Hence zippers are not comonads.
-- Russell O'Connor <http://r6.ca/> ``All talk about `theft,''' the general counsel of the American Graphophone Company wrote, ``is the merest claptrap, for there exists no property in ideas musical, literary or artistic, except as defined by statute.'' _______________________________________________ Haskell mailing list Haskell@haskell.org http://www.haskell.org/mailman/listinfo/haskell
