arXiv subjects

Harrison Goldstein

Publications and source records attributed to Harrison Goldstein.

12 recordsLinked to original sources

arXiv2026

Decision-Oriented Programming with Aporia

AI agents allow developers to express computational intent abstractly, reducing cognitive effort and helping achieve flow during programming. Increased abstraction, however, comes at a cost: developers cede decision-making authority to agents, often without realizing that important design decisions are being made without them. We aim to bring these decisions to the foreground in a paradigm we dub decision-oriented programming. In DOP, (1) decisions are explicit and structured, serving as the shared medium between the programmer and the agent; (2) decisions are co-authored interactively, with the agent proactively eliciting them from the programmer; and (3) each decision is traceable to code. As a step towards this vision, we have built Aporia, a design probe that tracks decisions in a persistent, editable Decision Bank; elicits them by asking programmers design questions; and encodes each decision as an executable test suite that can be used to validate the implementation. In a user study of 14 programmers, Aporia increased engagement in the design process and scaffolded both exploration and validation. Participants also gained a more accurate understanding of their implementations, with their mental models 5x less likely to disagree with the code than a baseline coding agent.

cs.HC↗

arXiv2026

Explorable Theorems: Making Written Theorems Explorable by Grounding Them in Formal Representations

LLM-generated explanations can make technical content more accessible, but there is a ceiling on what they can support interactively. Because LLM outputs are static text, they cannot be executed or stepped through. We argue that grounding explanations in a formalized representation enables interactive affordances beyond what static text supports. We instantiate this idea for mathematical proof comprehension with explorable theorems, a system that uses LLMs to translate a theorem and its written proof into Lean, a programming language for machine-checked proofs, and links the written proof with the Lean code. Readers can work through the proof at a step-level granularity, test custom examples or counterexamples, and trace the logical dependencies bridging each step. Each worked-out step is produced by executing the Lean proof on that example and extracting its intermediate state. A user study ($n = 16$) shows potential advantages of this approach: in a proof-reading task, participants who had access to the provided explorability features gave better, more correct, and more detailed answers to comprehension questions, demonstrating a stronger overall understanding of the underlying mathematics.

cs.HC↗

arXiv2026

Etna: An evaluation platform for property-based testing

Property-based testing is a mainstay of functional programming, boasting a rich literature, an enthusiastic user community, and an abundance of tools~ -- so many, indeed, that new users may have difficulty choosing. Moreover, any given framework may support a variety of strategies for generating test inputs; even experienced users may wonder which are better in any given situation. Sadly, the PBT literature, though long on creativity, is short on rigorous comparisons to help answer such questions. We present ETNA, a platform for empirical evaluation and comparison of PBT techniques. ETNA incorporates a number of popular PBT frameworks and testing workloads from the literature, and its extensible architecture makes adding new ones easy, while handling the technical drudgery of performance measurement. To illustrate its benefits, we use ETNA to carry out several experiments with popular PBT approaches in Rocq, Haskell, OCaml, Racket, and Rust, allowing users to more clearly understand best practices and tradeoffs.

cs.SE↗

arXiv2026

DIRT: Database-Integrated Random Testing

Database management systems (DBMSs) are notoriously complex, making them difficult to test effectively, especially during early development when many features are incomplete. Traditional testing tools like SQLancer and SQLSmith are highly effective for mature databases, but they struggle with high false positive rates and low actionability when applied to evolving systems. We present DIRT, a paradigm designed specifically for testing databases during development, which integrates a testing framework directly into the DBMS, enabling the random testing process to evolve in tandem with the system and reducing false positives by construction. We introduce generation actions, an abstraction for allowing database developers rather than testing experts to specify correctness properties. We evaluate DIRT on Turso, an actively developed SQLite-compatible OLTP engine, and show that it finds 23 unique, confirmed bugs--significantly outperforming off-the-shelf SQLancer variants in terms of true positive rate and usefulness of bug reports. Our results demonstrate that embedding testing infrastructure within the DBMS can dramatically improve its effectiveness and usability during development.

cs.DB↗

arXiv2026

Programmable Property-Based Testing

Property-based testing (PBT) is a popular technique for establishing confidence in software, where users write properties -- i.e., executable specifications -- that can be checked many times in a loop by a testing framework. In modern PBT frameworks, properties are usually written in shallowly embedded domain-specific languages, and their definition is tightly coupled to the way they are tested. Such frameworks often provide convenient configuration options to customize aspects of the testing process, but users are limited to precisely what library authors had the prescience to allow for when developing the framework; if they want more flexibility, they may need to write a new framework from scratch. We propose a new, deeper language for properties based on a mixed embedding that we call deferred binding abstract syntax, which reifies properties as a data structure and decouples them from the property runners that execute them. We implement this language in Rocq and Racket, leveraging the power of dependent and dynamic types, respectively. Finally, we showcase the flexibility of this new approach by rapidly prototyping a variety of property runners, highlighting domain-specific testing improvements that can be unlocked by more programmable testing.

cs.SE↗

arXiv2025

The Search for Constrained Random Generators

Among the biggest challenges in property-based testing (PBT) is the constrained random generation problem: given a predicate on program values, randomly sample from the set of all values satisfying that predicate, and only those values. Efficient solutions to this problem are critical, since the executable specifications used by PBT often have preconditions that input values must satisfy in order to be valid test cases, and satisfying values are often sparsely distributed. We propose a novel approach to this problem using ideas from deductive program synthesis. We present a set of synthesis rules, based on a denotational semantics of generators, that give rise to an automatic procedure for synthesizing correct generators. Our system handles recursive predicates by rewriting them as catamorphisms and then matching with appropriate anamorphisms; this is theoretically simpler than other approaches to synthesis for recursive functions, yet still extremely expressive. Our implementation, Palamedes, is an extensible library for the Lean theorem prover. The synthesis algorithm itself is built on standard proof-search tactics, reducing implementation burden and allowing the algorithm to benefit from further advances in Lean proof automation.

cs.PL↗

arXiv2025

Tuning Random Generators: Property-Based Testing as Probabilistic Programming

Property-based testing validates software against an executable specification by evaluating it on randomly generated inputs. The standard way that PBT users generate test inputs is via generators that describe how to sample test inputs through random choices. To achieve a good distribution over test inputs, users must tune their generators, i.e., decide on the weights of these individual random choices. Unfortunately, it is very difficult to understand how to choose individual generator weights in order to achieve a desired distribution, so today this process is tedious and limits the distributions that can be practically achieved. In this paper, we develop techniques for the automatic and offline tuning of generators. Given a generator with undetermined symbolic weights and an objective function, our approach automatically learns values for these weights that optimize for the objective. We describe useful objective functions that allow users to (1) target desired distributions and (2) improve the diversity and validity of their test cases. We have implemented our approach in a novel discrete probabilistic programming system, Loaded Dice, that supports differentiation and parameter learning, and use it as a language for generators. We empirically demonstrate that our approach is effective at optimizing generator distributions according to the specified objective functions. We also perform a thorough evaluation on PBT benchmarks, demonstrating that, when automatically tuned for diversity and validity, the generators exhibit a 3.1-7.4x speedup in bug finding.

cs.PL↗

arXiv2025

Fail Faster: Staging and Fast Randomness for High-Performance PBT

Property-based testing (PBT) relies on generators for random test cases, often constructed using embedded domain specific languages, which provide expressive combinators for building and composing generators. The effectiveness of PBT depends critically on the speed of these generators. However, careful measurements show that the generator performance of widely used PBT libraries falls well short of what is possible, due principally to (1) the abstraction overhead of their combinator-heavy style and (2) suboptimal sources of randomness. We characterize, quantify, and address these bottlenecks. To eliminate abstraction overheads, we propose a technique based on multi-stage programming, dubbed Allegro. We apply this technique to leading generator libraries in OCaml and Scala 3, significantly improving performance. To quantify the performance impact of the randomness source, we carry out a controlled experiment, replacing the randomness in the OCaml PBT library with an optimized version. Both interventions exactly preserve the semantics of generators, enabling precise, pointwise comparisons. Together, these improvements find bugs up to $13\times$ faster.

cs.PL↗

arXiv2024

Mica: Automated Differential Testing for OCaml Modules

Suppose we are given two OCaml modules implementing the same signature. How do we check that they are observationally equivalent -- that is, that they behave the same on all inputs? One established technique is to use a property-based testing (PBT) tool such as QuickCheck. Currently, however, this can require significant amounts of boilerplate code and ad-hoc test harnesses. To address this issue, we present Mica, an automated tool for testing observational equivalence of OCaml modules. Mica is implemented as a PPX compiler extension, allowing users to supply minimal annotations to a module signature. These annotations guide Mica to automatically derive specialized PBT code that checks observational equivalence. We discuss the design of Mica and demonstrate its efficacy as a testing tool on various modules taken from real-world OCaml libraries.

cs.PL↗

arXiv2023

Stream Types

We propose a rich foundational theory of typed data streams and stream transformers, motivated by two high-level goals: (1) The type of a stream should be able to express complex sequential patterns of events over time. And (2) it should describe the internal parallel structure of the stream to support deterministic stream processing on parallel and distributed systems. To these ends, we introduce stream types, with operators capturing sequential composition, parallel composition, and iteration, plus a core calculus lambda-ST of transformers over typed streams which naturally supports a number of common streaming idioms, including punctuation, windowing, and parallel partitioning, as first-class constructions. lambda-ST exploits a Curry-Howard-like correspondence with an ordered variant of the logic of Bunched Implication to program with streams compositionally and uses Brzozowski-style derivatives to enable an incremental, prefix-based operational semantics. To illustrate the programming style supported by the rich types of lambda-ST, we present a number of examples written in delta, a prototype high-level language design based on lambda-ST.

cs.PL↗

arXiv2022

Parsing Randomness: Unifying and Differentiating Parsers and Random Generators

"A generator is a parser of randomness." This perspective on generators for random data structures is well established as folklore in the programming languages community, but it has apparently never been formalized, nor have its consequences been deeply explored. We present free generators, which unify parsing and generation using a common structure that makes the relationship between the two concepts precise. Free generators lead naturally to a proof that a large class of generators can be factored into a parser plus a distribution over choice sequences. Further, free generators support a notion of derivative, analogous to familiar Brzozowski derivatives of formal languages, that allows analysis tools to "preview" the effect of a particular generator choice. This, in turn, gives rise to a novel algorithm for generating data structures satisfying user-specified preconditions.

cs.PL↗

arXiv2017

Abstractions for AI-Based User Interfaces and Systems

Novel user interfaces based on artificial intelligence, such as natural-language agents, present new categories of engineering challenges. These systems need to cope with uncertainty and ambiguity, interface with machine learning algorithms, and compose information from multiple users to make decisions. We propose to treat these challenges as language-design problems. We describe three programming language abstractions for three core problems in intelligent system design. First, hypothetical worlds support nondeterministic search over spaces of alternative actions. Second, a feature type system abstracts the interaction between applications and learning algorithms. Finally, constructs for collaborative execution extend hypothetical worlds across multiple machines while controlling access to private data. We envision these features as first steps toward a complete language for implementing AI-based interfaces and applications.

cs.PL↗