SHF: Medium: Collaborative Research: Semantics Engineering for Scripting Languages

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Over the last decade, scripting languages have assumed a huge role. Initially web developers used Perl and Python to enrich the content of web servers; later Ruby on Rails took the scene by storm. Over the same period, JavaScript has become the dominant language on the client side of the web. Additionally, the popularity of scripting language has inspired developers to use them for the construction of many other kinds of systems, including mission-critical real-time systems. While scripting languages are productive tools for the exploration of design ideas, their use also introduces several new kinds of problems into the software cycle. Most basically, scripting languages tend to lack a type system, which tends to raise the debugging and maintenance costs for systems. Worse, even though scripting languages tend to be safe, their flexible primitive operations induce difficult-to-predict behavior in programs and thus creates novel kinds of security holes. At the same time, scripting languages do not come with a well-defined semantics, making it nearly impossible to validate the soundness of a program analysis for safety or security properties.In response to these observations, this proposal promises to re-engineer the semantics of scripting languages. Specifically, the PIs propose to investigate the construction of executable semantics for three scripting languages: JavaScript, Python, and Racket. They will use the language-level test suites to check that the semantics model the implementations adequately. In addition, the PIs will use the semantics to design and validate type systems and program analyses for these scripting languages. Over the long run, the proposal should impact the world at large in three ways. First, the type systems and analyses for scripting languages should help software developers improve the safety of their software and reduce their maintenance cost. Second, the semantics for the scripting languages will help researchers validate their ideas concerning program analyses. Finally, the PIs will develop a process for semantic re-engineering that should be useful to many additional scripting language communities.