Definition: A data structure equivalent to a binary tree that is "opened" so that some node is accessible. It consists of a pair: the current node, along with information to reconstruct the tree. Reconstruction information is called the path or context. A move-to-left-child operation returns the left subtree, along with a new path, which has (i) a Left value, (ii) the current node, (iii) the right subtree, and (iv) any previous path. A similar operation moves to the right child. A move-up operation returns a tree rebuilt from the path information and the current node, along with the previous path.
Note: In functional programming languages, a zipper acts as a "pointer" into a tree. The name comes from visualizing the move-to-child operation as unzipping a tree. (Instead of two halves, though, move-to-child keeps the pieces in a k-ary tree: the path.)
A message on Using zippers to handle huge trees.
Gérard Huet, The Zipper, Journal of Functional Programming, 7(5):549-554, 1997.
If you have suggestions, corrections, or comments, please get in touch with Paul Black.
Entry modified 21 March 2005.
HTML page formatted Fri Feb 23 10:06:08 2018.
Cite this as:
Paul E. Black, "zipper", in Dictionary of Algorithms and Data Structures [online], Vreda Pieterse and Paul E. Black, eds. 21 March 2005. (accessed TODAY) Available from: https://www.nist.gov/dads/HTML/zipper.html