# FrAngel: Component-Based Synthesis with Control Structures

arXiv: https://arxiv.org/abs/1811.05175 · HTML: https://mlsanity.com/paper/1811.05175/

## Key facts

- Cited by 10 papers in the map (data through 14 Oct 2026).
- First posted on arXiv 13 Nov 2018.

## Built on by (most cited first, 10 of 10)

- [Divide-and-Conquer Meets Consensus: Unleashing the Power of Functions in Code Generation](https://mlsanity.com/paper/2405.20092/) (2024)
- [CrossBeam: Learning to Search in Bottom-Up Program Synthesis](https://mlsanity.com/paper/2203.10452/) (2022)
- [ExeDec: Execution Decomposition for Compositional Generalization in Neural Program Synthesis](https://mlsanity.com/paper/2307.13883/) (2023)
- [JavaBench: A Benchmark of Object-Oriented Code Generation for Evaluating Large Language Models](https://mlsanity.com/paper/2406.12902/) (2024)
- [Learning to Combine Per-Example Solutions for Neural Program Synthesis](https://mlsanity.com/paper/2106.07175/) (2021)
- [Compositional Generalization and Decomposition in Neural Program Synthesis](https://mlsanity.com/paper/2204.03758/) (2022)
- [LambdaBeam: Neural Program Search with Higher-Order Functions and Lambdas](https://mlsanity.com/paper/2306.02049/) (2023)
- [AbstractBeam: Enhancing Bottom-Up Program Synthesis using Library Learning](https://mlsanity.com/paper/2405.17514/) (2024)
- [Herb.jl: A Unifying Program Synthesis Library](https://mlsanity.com/paper/2510.09726/) (2025)
- [APRIL: API Synthesis with Automatic Prompt Optimization and Reinforcement Learning](https://mlsanity.com/paper/2509.25196/) (2025)

## Abstract (arXiv)

In component-based program synthesis, the synthesizer generates a program given a library of components (functions). Existing component-based synthesizers have difficulty synthesizing loops and other control structures, and they often require formal specifications of the components, which can be expensive to generate. We present FrAngel, a new approach to component-based synthesis that can synthesize short Java functions with control structures when given a desired signature, a set of input-output examples, and a collection of libraries (without formal specifications). FrAngel aims to discover programs with many distinct behaviors by combining two main ideas. First, it mines code fragments from partially-successful programs that only pass some of the examples. These extracted fragments are often useful for synthesis due to a property that we call special-case similarity. Second, FrAngel uses angelic conditions as placeholders for control structure conditions and optimistically evaluates the resulting program sketches. Angelic conditions decompose the synthesis process: FrAngel first finds promising partial programs and later fills in their missing conditions. We demonstrate that FrAngel can synthesize a variety of interesting programs with combinations of control structures within seconds, significantly outperforming prior state-of-the-art.