Automated Transpilation of Imperative to Functional Code using Neural-Guided Program Synthesis (Extended Version)

TL;DR

This paper introduces NGST2, a neural-guided program synthesis tool that automatically translates imperative Java and Python code into functional variants using APIs, leveraging trace-compatibility and concolic execution for effective transpilation.

Contribution

The paper presents a novel neural architecture called cognate grammar network and a trace-based pruning method, enabling effective automatic imperative-to-functional code transpilation.

Findings

NGST2 outperforms baseline methods in accuracy and efficiency.

Neural architecture and pruning are crucial for successful transpilation.

Effective translation of imperative Java and Python code to functional APIs achieved.

Abstract

While many mainstream languages such as Java, Python, and C# increasingly incorporate functional APIs to simplify programming and improve parallelization/performance, there are no effective techniques that can be used to automatically translate existing imperative code to functional variants using these APIs. Motivated by this problem, this paper presents a transpilation approach based on inductive program synthesis for modernizing existing code. Our method is based on the observation that the overwhelming majority of source/target programs in this setting satisfy an assumption that we call trace-compatibility: not only do the programs share syntactically identical low-level expressions, but these expressions also take the same values in corresponding execution traces. Our method leverages this observation to design a new neural-guided synthesis algorithm that (1) uses a novel neural architecture called cognate grammar network (CGN) and (2) leverages a form of concolic execution to prune partial programs based on intermediate values that arise during a computation. We have implemented our approach in a tool called NGST2 and use it to translate imperative Java and Python code to functional variants that use the Stream and functools APIs respectively. Our experiments show that NGST2 significantly outperforms several baselines and that our proposed neural architecture and pruning techniques are vital for achieving good results.