Statically-typed Programming Language Research Articles

Well-typed programs can go wrong: a study of typing-related bugs in JVM compilers

Despite the substantial progress in compiler testing, research endeavors have mainly focused on detecting compiler crashes and subtle miscompilations caused by bugs in the implementation of compiler optimizations. Surprisingly, this growing body of work neglects other compiler components, most notably the front-end. In statically-typed programming languages with rich and expressive type systems and modern features, such as type inference or a mix of object-oriented with functional programming features, the process of static typing in compiler front-ends is complicated by a high-density of bugs. Such bugs can lead to the acceptance of incorrect programs (breaking code portability or the type system's soundness), the rejection of correct (e.g. well-typed) programs, and the reporting of misleading errors and warnings. We conduct, what is to the best of our knowledge, the first empirical study for understanding and characterizing typing-related compiler bugs. To do so, we manually study 320 typing-related bugs (along with their fixes and test cases) that are randomly sampled from four mainstream JVM languages, namely Java, Scala, Kotlin, and Groovy. We evaluate each bug in terms of several aspects, including their symptom, root cause, bug fix's size, and the characteristics of the bug-revealing test cases. Some representative observations indicate that: (1) more than half of the typing-related bugs manifest as unexpected compile-time errors: the buggy compiler wrongly rejects semantically correct programs, (2) the majority of typing-related bugs lie in the implementations of the underlying type systems and in other core components related to operations on types, (3) parametric polymorphism is the most pervasive feature in the corresponding test cases, (4) one third of typing-related bugs are triggered by non-compilable programs. We believe that our study opens up a new research direction by driving future researchers to build appropriate methods and techniques for a more holistic testing of compilers.

ContextJ: Context-oriented Programming with Java

Context-oriented programming (COP) allows for the modularization of context-dependent behavioral variations. So far, COP has been implemented for dynamically-typed languages such as Lisp, Smalltalk, Python, and Ruby relying on reflection mechanisms, and for the statically-typed programming language Java based on a library and a pre-processor. ContextJ is our COP implementation for Java. It properly integrates COP’s layer concept into the Java type system. ContextJ is compiler-based. As confirmed by a benchmark and a case study, it provides both better performance and higher-level abstraction mechanisms than its Java-based predecessors. In this paper, we present the ContextJ language and explain its constructs and semantics. Further, we give an overview of the implementation of our compiler and discuss run-time benchmarks.

Declarative Language Design for Interactive Visualization

We investigate the design of declarative, domain-specific languages for constructing interactive visualizations. By separating specification from execution, declarative languages can simplify development, enable unobtrusive optimization, and support retargeting across platforms. We describe the design of the Protovis specification language and its implementation within an object-oriented, statically-typed programming language (Java). We demonstrate how to support rich visualizations without requiring a toolkit-specific data model and extend Protovis to enable declarative specification of animated transitions. To support cross-platform deployment, we introduce rendering and event-handling infrastructures decoupled from the runtime platform, letting designers retarget visualization specifications (e.g., from desktop to mobile phone) with reduced effort. We also explore optimizations such as runtime compilation of visualization specifications, parallelized execution, and hardware-accelerated rendering. We present benchmark studies measuring the performance gains provided by these optimizations and compare performance to existing Java-based visualization tools, demonstrating scalability improvements exceeding an order of magnitude.

Orthogonal type extensions and reductions

In this paper we present a generalization of Oberon's record type extensions. Our extension mechanism is orthogonally applicable to all the conventional data types found in Pascal-like languages. In order to balance the type system, we present an inverse concept, type reductions, that also can be applied to all the programmer-defined data types. These concepts provide flexible and powerful means for expressing universal subtyping and supertyping in a statically-typed programming language, as well as many possibilities for reuse of data types via a sound mathematical characterization of assignment statements. The presented ideas are under implementation in Alberich, a programming language that can be considered as a natural descendant of Oberon.