SCALA 2020: Proceedings of the 11th ACM SIGPLAN International Symposium on Scala

Full Citation in the ACM Digital Library

SESSION: Keynote

Towards a sound approximating compiler for numerical kernels (keynote)

Computing resources are fundamentally limited and sometimes an exact solution may not even exist. Thus, when implementing real-world systems, approximations are inevitable, as are the errors they introduce. The magnitude of errors is problem-dependent but higher accuracy generally comes at a cost in terms of memory, energy or runtime, effectively creating an accuracy-efficiency tradeoff. To take advantage of this tradeoff, we need to ensure that the computed results are sufficiently accurate, otherwise we risk disastrously incorrect results or system failures.

In this talk, we present the current state of the tool Daisy which approximates numerical kernels in an automated and trustworthy fashion. Daisy allows a programmer to write exact high-level code and generates an efficient implementation satisfying a given accuracy specification. We discuss Daisy's verification techniques for bounding the effects of numerical errors, and the approximations Daisy can synthesize fully automatically.


ScalaPy: seamless Python interoperability for cross-platform Scala programs

In recent years, Python has become the language of choice for data scientists with its many high-quality scientific libraries and Scala has become the go-to language for big data systems. In this paper, we bridge these languages with ScalaPy, a system for interoperability between Scala and Python. With ScalaPy, developers can use Python libraries in Scala by treating Python values as Scala objects and exposing Scala values to Python. ScalaPy supports both Scala on the JVM and Scala Native, enabling its usage from data experiments in interactive notebook environments to performance-critical production systems. In this paper, we explore the challenges involved with mixing the semantics and implementations of these two disparate languages.

Semantics-preserving inlining for metaprogramming

Inlining is used in many different ways in programming languages: some languages use it as a compiler-directive solely for optimization, some use it as a metaprogramming feature, and others lay their design in-between. This paper presents inlining through the lens of metaprogramming and we describe a powerful set of metaprogramming constructs that help programmers to unfold domain-specific decisions at compile-time. In a multi-paradigm language like Scala, the concern for generality of inlining poses several interesting questions and the challenge we tackle is to offer inlining without changing the model seen by the programmer. In this paper, we explore these questions by explaining the rationale behind the design of Scala-3's inlining capability and how it relates to its metaprogramming architecture.

Kaizen: a scalable concolic fuzzing tool for Scala

Scala is an open-source programming language created by Martin Odersky in 2001 and released under the BSD or Berkeley Software Distribution license. The language consolidates object-oriented and functional programming in one high-level and robust language. Scala also maintains static types that help to reduce tricky errors during the execution time. In this paper, we introduce ”Kaizen” as a practical security analysis tool that works based on concolic fuzzing for evaluating real-world Scala applications.

To evaluated our approach, we analyzed 1,000 popular Scala projects existing on GitHub. As a result, Kaizen could report and exploit 101 security issues; some of those have not been reported before. Furthermore, our performance analysis outcome on the ScalaBench test suite demonstrates a 49% runtime overhead that proves Kaizen’s usefulness for security testing in the Scala ecosystem.

ONNX-Scala: typeful, functional deep learning / Dotty meets an open AI standard (open-source talk)

ONNX (Open Neural Network eXchange) is an open standard for machine learning interoperability, supported by the most widely used tools and frameworks. ONNX-Scala ( brings full support for the ONNX specification, and hence for state-of-the-art deep learning models as well as numerical computing more generally to the Scala ecosystem. Backed by the optimized native CPU/GPU backend ONNX Runtime, with a Scala.js backend coming soon, it offers 2 APIs: A) For off-the-shelf models / performance-critical scenarios, a simple black-box API, B) for everything else (pre/post processing, model customization, internal parameter streaming, etc.) a fine grained API that exposes each ONNX operator as a pure function with type-level encoding of, and constraints on, shapes, axis semantics and data type for each input and output tensor / ndarray. The latter API synthesizes recent progress toward more typeful and functional approaches from across the (Python-dominated) AI ecosystem, implemented using a variety of new features in Dotty / Scala 3 and forms the basis of NDScala (, a NumPy-like API enabling seamless interoperation between ONNX-Scala and other JVM-based offerings via an ndarray type class.