I was hoping to find some resources on the "zipper" - The article that you reference in your comment has cited this one - http://www.st.cs.uni-saarland.de/edu/s

I was hoping to find some resources on the "zipper" - The article that you reference in your comment has cited this one - http://www.st.cs.uni-saarland.de/edu/seminare/2005/advanced-fp/docs/huet-zipper.pdf http://www.st.cs.uni-saarland.de/edu/seminare/2005/advanced-... [PDF Link] which seems pretty relevant too. Thanks for the pointer