The Random Access Zipper: Simple, Purely-Functional Sequences

TL;DR

The paper introduces the Random Access Zipper, a simple, purely-functional data structure that efficiently supports editing and cursor movement in sequences, combining ease of implementation with optimal time bounds.

Contribution

It presents the RAZ, a novel data structure that unifies zipper and tree features, offering simplicity and efficiency for functional sequence editing.

Findings

Supports constant-time edits at cursor

Enables logarithmic-time cursor relocation

Simpler and more concise than existing structures

Abstract

We introduce the Random Access Zipper (RAZ), a simple, purely-functional data structure for editable sequences. A RAZ combines the structure of a zipper with that of a tree: like a zipper, edits at the cursor require constant time; by leveraging tree structure, relocating the edit cursor in the sequence requires logarithmic time. While existing data structures provide these time bounds, none do so with the same simplicity and brevity of code as the RAZ. The simplicity of the RAZ provides the opportunity for more programmers to extend the structure to their own needs, and we provide some suggestions for how to do so.