S. Günther wrote:
Whether circular or not, sharing values by using a "back pointer" is problematic for any update. Why not use a zipper instead?
I looked into zippers before and the problem I had was that they never really matched the structure which I needed and which led me to think about this whole knot tying thing again.
What kind of structure do you need exactly?
The things I read about them always assumed either a list like (i.e. linear) or a tree like (i.e. existence of a root) structure on the type to be plugged into the zipper.
Viewing the zipper as the derivative of a data type opens up more possibilities. That being said, every algebraic data types has a tree-like structure. The extra invariants like left . right = right . left that the programmer imposes are what make them different from trees.
So I just have to decide whether to use IORefs/Vars (clunky) or to implement zippers for the structure I need (probably too hard for me).
It's not too hard for you. You've got a whole haskell-cafe and #haskell at your fingertips, after all. ;) Regards, H. Apfelmus