Let's define a tree T: A / \ B C / \ D E Let's say a new node is added to E, yielding T': A / \ B C / \ D E \ G In a mutable language this is an easy task - just update E's children...

Oleg Kiselyov showed how to make a zipper from any traversable by using delimited continuations. His Haskell code is quite short: module ZipperTraversable where import qualified Data.Traversable...

Problem I've been wondering how this could be done efficiently for a while, but for some reason I have been unable to do it. I need to model a rectangular grid, where each field contains some data....

I'm writing a graphical editor for a "model" (i.e. a collection of boxes and lines with some kind of semantics, such as UML, the details of which don't matter here). So I want to have a data struct...

I'm reading Huet Zipper, I cannot understand the go_up method: let go_up (Loc(t,p)) = match p with Top -> failwith "up of top" | Node(left,up,right) -> Loc(Section((rev left) @ (t::right)),u...

I have a few ADT's that represent a simple geometry tree in Haskell. Something about having my operation types separate from the tree structure is bothering me. I'm thinking of making the Tree type...

I am struggling with existential types in my program. I think I'm trying to do something very reasonable however I cannot get past the typechecker :( I have a datatype that sort of mimics a Monad ...

The Zipper data structure is great when one wants to traverse a tree and keep the current position, but what data structure one should use if they want to track more then one position? Let me expl...

I think that the zipper is a beautiful idea; it elegantly provides a way to walk a list or tree and make what appear to be local updates in a functional way. Asymptotically, the costs appear to be...

Lets suppose we have some XML like so: <a> <b> <c>text</c> <d> <e>text</e> <f> ... lots of cruft here .. </f> </d> </b> ...