Zippers: Making Functional "Updates" Efficient (2010)
7 hours ago
- #functional programming
- #zippers
- #data structures
- A zipper is a functional programming concept for efficiently working with data structures by focusing on a specific point (focus) and allowing local changes.
- Zippers enable efficient updates in functional languages by reusing unchanged parts of the data structure, similar to gap buffers in text editors.
- The zipper unfolds a data structure around a focus point, keeping track of the path from the root to the focus, and left/right contexts.
- Zippers were first formalized by Gérard Huet in 1997, though the concept likely existed in functional code before then.
- Balanced trees and zippers can conflict because balancing is a global operation, while zippers optimize for local changes.
- Scarring is a technique to mark potential rebalance points in a zippered structure, deferring rebalancing for later.
- Zippers can be viewed as manipulable continuations, reflecting the duality between code and data.
- Zippers are useful for bidirectional traversal in immutable data structures, such as navigating up and down a tree.
- Functional data structures with zippers allow keeping old versions for undo operations, unlike mutable structures.
- Concurrent operations on zippered structures require careful management to handle multiple focuses and updates.