5 Mar
2009
5 Mar
'09
4:05 a.m.
On 3/5/09, Ryan Ingram
... Here is the problem with your "update":
tree = Fork (Leaf 1) (Leaf 2) ztree = initZ tree
test = fromJust $ do z1 <- moveLeft ztree let z2 = update z1 3 z3 <- moveUp z2 z4 <- moveLeft z3 this z4
I'd expect "test" to equal 3, but I believe with your code that it still equals 1. As apfelmus said, update needs to completely re-construct the zipper structure with the tied knot, which defeats the purpose of using a zipper in the first place.
I got it. I dont't know what your expression "tied knot" is referring to but I got the point. Thanks. Cristiano