Operators for delimiting control and for capturing composable continuations litter the landscape of theoretical programming language research. Numerous papers explain their advantages, how the operators explain each other (or don’t), and other aspects of the operators’ existence. Production programming languages, however, do not support these operators, partly because their relationship to existing and demonstrably useful constructs—such as exceptions and dynamic binding—remains relatively unexplored. In this paper, In this paper, we report on our effort of translating the theory of delimited and composable control into a viable implementation for a production system. The report shows how this effort involved a substantial design element, including work with a formal model, as well as significant practical exploration and engineering. The resulting version of PLT Scheme incorporates the expressive combination of delimited and composable control alongside dynamic-wind, dynamic binding, and exception handling. None of the additional operators subvert the intended benefits of existing control operators, so that programmers can freely mix and match control operators.

Abstract. In this paper, we address the different conceptual and technical difficulties encountered when embedding CHR into an imperative host language. We argue that a tight, natural integration leads to a powerful programming language extension, intuitive to both CHR and imperative programmers. We show how to compile CHR to highly optimized imperative code. To this end, we first review the well-established CHR compilation scheme, and survey the large body of possible optimizations. We then show that this scheme, when used for compilation to imperative target languages, leads to stack overflows. We therefore introduce new optimizations that considerably improve the performance of recursive CHR programs. Rules written using tail calls are even guaranteed to run in constant space. We implemented systems for both Java and C, following the language design principles and compilation scheme presented in this paper, and show that our implementations outperform other state-of-the-art CHR compilers by several orders of magnitude. 1

We describe a derivational approach to abstract interpretation that yields novel and transparently sound static analyses when applied to well-established abstract machines. To demonstrate the technique and support our claim, we transform the CEK machine of Felleisen and Friedman, a lazy variant of Krivine’s machine, and the stack-inspecting CM machine of Clements and Felleisen into abstract interpretations of themselves. The resulting analyses bound temporal ordering of program events; predict return-flow and stack-inspection behavior; and approximate the flow and evaluation of by-need parameters. For all of these machines, we find that a series of well-known concrete machine refactorings, plus a technique we call store-allocated continuations, leads to machines that abstract into static analyses simply by bounding their stores. We demonstrate that the technique scales up uniformly to allow static analysis of realistic language features, including tail calls, conditionals, side effects, exceptions, first-class continuations, and even garbage collection.

MzScheme’s continuation marks provide a flexible mechanism for implementing a number of useful language features and tools. We demonstrate the simplicity and utility of continuation marks by adapting them for JavaScript as frame-based stack marks using the Rhino implementation, showing a simple model of their behavior, and using them to build a toy debugger. Along the way, we discover a few interesting things. First, it requires some thinking—but not much code—to add continuation marks to JavaScript. Second, coupling tail-calling with the “return” of statement-based languages leads to some interesting problems in formulating a semantics. Third, building a debugger based on continuation marks highlights (by its absence) the elegance of Scheme’s simple syntax and hygienic macro system. 1.

The lambda and procedure-application forms in PLT Scheme support arguments that are tagged with keywords, instead of identified by position, as well as optional arguments with default values. Unlike previous keyword-argument systems for Scheme, a keyword is not self-quoting as an expression, and keyword arguments use a different calling convention than non-keyword arguments. Consequently, a keyword serves more reliably (e.g., in terms of error reporting) as a lightweight syntactic delimiter on procedure arguments. Our design requires no changes to the PLT Scheme core

Debugging is a laborious, manual activity that often involves the repetition of common operations. Ideally, users should be able to describe these repetitious operations as little programs. Debuggers should therefore be pro-grammable, or scriptable. The operating environment of these scripts, however, imposes interesting design challenges on the programming language in which these scripts are written. This paper presents our design of a language for scripting debuggers. The language offers powerful primitives that can precisely and concisely capture many important debugging and comprehension metaphors. The paper also describes a pair of debuggers, one for Java and the other for Scheme, built in accordance with these principles. The paper includes concrete examples of applying this debugger to programs. 1

Type-based protection mechanisms in a JVM-like environment must be administrated by the code consumer at the bytecode level. Unfortunately, formulating a sound static type system for the full JVM bytecode language can be a daunting task. It is therefore counter-productive for the designer of a bytecode-level type system to address the full complexity of the VM environment in the early stage of design. In this work, a lightweight modeling tool, Featherweight JVM, is proposed to facilitate the early evaluation of bytecode-level, type-based protection mechanisms. In the style of Security Automata, Featherweight JVM is an event model that tracks interprocedural access events generated by a JVM-like environment. The effect of deploying a typebased protection mechanism can be modeled by a safety policy that restricts the event sequences produced by the VM model. To evaluate the effectiveness of the protection mechanism, security theorems in the form of state invariants can then be proven in the policy-guarded VM model. This paper provides first evidence on the utility of this approach in providing early feedback to the designer of type-based protection mechanisms for JVM-like environments. 1.

Language extensions, such as embedded domain-specific languages, are often implemented by assimilating (rewriting) the extended language constructs to the host language. The result can then be compiled by a standard compiler. This approach is limited by the host language, which may not be designed with code generation in mind. An example of this is Java, which provides insufficient protection against name capture of host language identifiers, and does not provide the same low-level primitives that exist in the underlying Java Virtual Machine. For example, it does not provide equivalents for a jump or jump subroutine instruction, unbalanced synchronization, stack manipulation, or specification of debugging information. Code generated from a language that does not match Java’s structure can therefore require inefficient or laborious alternatives instead. We propose a new open compiler model to provide generators direct access to the underlying compiled code. With conventional open compilers, leveraging the bytecode-generating back-end is an intricate process, requiring adaptations tangled throughout the system. The result is hard to develop, understand, and maintain. By providing a mixed source language of Java and the underlying bytecode instruction language, we can provide access to the back-end at the source-level. Compiled instructions can be used in place of statements or expressions, which can aid language extensions but also applications of separate

Gregory Harold Cooper was born on New Year’s Day of 1978 in South County, Rhode Island. He has enjoyed mathematics and logic since he can remember and was addicted to computer programming by age 7. He was valedictorian of the class of 1996 at North Kingstown High School and a National Merit Scholar and Barry M. Goldwater Scholar at the University of Rhode Island. He also received an honorable mention in the National

As computers are deployed in increasingly diverse, numerous, and critical roles, the need for confidence in their hardware and software becomes more acute. Often, however, computer technologies, such as programming languages, lack a sufficiently formal definition to allow rigorous mathematical analysis of their properties. Even in cases where a formal definition is available, the theorems to be proven and the definition itself tend to have many cases and many details that are easily overlooked when writing a proof by hand. This has created interest in the mechanization of the proof process through the use of automated proof assistants. In this report, we develop a formal definition for a programming language called IntegerPython, which is a subset of the Python language that supports integers, booleans, global variables, loops, modules, and nested functions. The definition takes the form of an operational semantics on a CEKS machine, which we embed in the Isabelle/HOL mechanized logic. We then prove an invariant of the CEKS machine in Isabelle/HOL. The report concludes with strategies for the efficient, executable implementation of the IntegerPython semantics and its extension into a semantics of