Program comprehension tools are often developed for a specific programming language. Developing such a tool from scratch requires significant effort. In this paper, we report on our experience developing a language-independent framework that enables the creation of program comprehension tools, specifically tools gathering insight from deep dynamic analysis, with little effort. Our framework is language independent, because it is built on top of Truffle, an open-source platform, developed in Oracle Labs, for implementing dynamic languages in the form of AST interpreters. Our framework supports the creation of a diverse variety of program comprehension techniques, such as query, program slicing, and back-in-time debugging, because it is centered around a powerful information-flow tracking engine. Tools developed with our framework get access to the information-flow through a program execution. While it is possible to develop similarly powerful tools without our framework, for example by tracking information-flow through bytecode instrumentation, our approach leads to information that is closer to source code constructs, thus more comprehensible by the user. To demonstrate the effectiveness of our framework, we applied it to two of Truffle-based languages namely Simple Language and TruffleRuby, and we distill our experience into guidelines for developers of other Truffle-based languages who want to develop program comprehension tools for their language.

A highly productive platform accelerates the production of research results. The design of a Virtual Machine (VM) written in the Java™ programming language can be simplified through exploitation of interfaces, type and memory safety, automated memory management (garbage collection), exception handling, and reflection. Moreover, modern Java IDEs offer time-saving features such as refactoring, auto-completion, and code navigation. Finally, Java annotations enable compiler extensions for low-level “systems programming” while retaining IDE compatibility. These techniques collectively make complex system software more “approachable” than has been typical in the past. The Maxine VM, a metacircular Java VM implementation, has aggressively used these features since its inception. A co-designed companion tool, the Maxine Inspector, offers integrated debugging and visualization of all aspects of the VM's runtime state. The Inspector's implementation exploits advanced Java language features, embodies intimate knowledge of the VM's design, and even reuses a significant amount of VM code directly. These characteristics make Maxine a highly approachable VM research platform and a productive basis for research and teaching.

Powerful editing systems for developing complex software documents are difficult to engineer. Besides requiring efficient incremental algorithms and complex data structures, such editors must accommodate flexible editing styles, provide a consistent, coherent, and powerful user interface, support individual variations and projectwide configurations, maintain a sharable database of information concerning the documents being edited, and integrate smoothly with the other tools in the environment. Pan is a language-based editing and browsing system that exhibits these characteristics. This paper surveys the design and engineering of Pan , paying particular attention to a number of issues that pervade the system: incremental checking and analysis, information retention in the presence of change, tolerance for errors and anomalies, and extension facilities.