Dan Licata wrote: > On Jul25, apfelmus wrote: >> The point is to be >> able to define both zip and pairs with one and the same operator :< . > > There's actually a quite simple way of doing this. You make the view > type polymorphic, but not in the way you did: > > type Queue elt > empty :: Queue elt > cons :: elt -> Queue elt -> Queue elt > > data ViewL elt rec = EmptyL > | elt :< rec > > view :: Queue elt -> ViewL elt (Queue elt) > view2 :: Queue elt -> ViewL elt (ViewL elt (Queue elt))
This is cool! The more so because 'view2' can quite easily be defined in terms of 'view' view2 q = case view q of EmptyL -> EmptyL x :< q' -> x :< view q' so it suffices to provide the one-level 'view' as a library function. Does this scale to views containing multiple nestable constructors? It would, of course, be nice to get rid of having to write view2 altogether... Cheers Ben _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
