Incremental Live Programming via Shortcut Memoization

TL;DR

This paper presents Chordata, an incremental interpreter using shortcut memoization that learns and reuses computation patterns to significantly speed up live programming updates, especially for large or complex programs.

Contribution

It introduces a formal semantics for shortcut memoization, implements it in a live programming system, and demonstrates substantial speedups in program execution and editing.

Findings

Achieves a 13.03× speedup over baseline.

Provides a 19.97× memory overhead.

Effective for small changes and complex programs.

Abstract

Live programming systems aim to quickly show programmers the dynamic impacts of program edits. To do so, they re-execute the program whenever it is edited, which poses a computational challenge when programs become large or complex. This has led to the need for incrementality in the implementation of live program interpreters. This paper introduces Chordata, an incremental program interpreter based on shortcut memoization, which learns repeated patterns of computation, called shortcuts, by observing executions of previous versions of a program. It can then apply these shortcuts when the same or a structurally similar program fragment is re-executed. This paper contributes a formal semantics of shortcut memoization for any language with a rewrite-based semantics, with mechanized proofs of key correctness properties. We then express a variant of the Hazel live programming system, expressed as a CEK machine, in Chordata, and develop a number of practical heuristics to learn high-value shortcuts. We evaluate the resulting system on editing traces of students solving simple programming problems. Chordata achieves a speedup of 13.03\times compared to baseline with a 19.97\times memory overhead. For smaller changes and for more complex programs, Chordata achieves even greater speedups. Furthermore, we show that Chordata is capable of providing a speedup even within a single execution, with a faster speedup on a larger input.