Compiler to interpreter: experiences with a distributed programming language

One interpretive approach for handling concurrency is to provide an interpreter instance for each executing language‐level process. Such an approach has mainly been applied to concurrent implementations of logic and functional languages. This paper describes the use of this approach in constructing an interpreter for an imperative, distributed programming language from an existing compiler and run‐time support system (RTS). Primary design goals were to exploit the existing compiler to the extent possible as well as to have minimal impact on the RTS used to support concurrency. We have been successful in meeting these goals. Additionally, performance results show our interpreter's execution times compare favorably to the times required for compilation, linkage, and execution of small programs or programs with a significant number of calls to the RTS; on such programs, our interpreter's performance also compares favorably to that of the standard Java implementation. However, for larger programs and programs with fewer calls to the underlying RTS, the conventional compiler‐based implementation outperforms the interpreter implementation. For many distributed programs in which network costs dominate, the performances of the two implementations differ little. Copyright © 2001 John Wiley & Sons, Ltd.     

An operational semantics for object-oriented concepts based on the class hierarchy

The formalisation of object-oriented languages is essential for describing the implementation details of specific programming languages or for developing program verification techniques. However there has been relatively little formalisation work aimed at abstractly describing the fundamental concepts of object-oriented programming, separate from specific language considerations or suitability for a particular verification style. In this paper we address this issue by formalising a language that includes the core object-oriented programming language concepts of field tests and updates, methods, constructors, subclassing, multithreading, and synchronisation, built on top of standard sequential programming constructs. The abstract syntax is relatively close to the core of typical object-oriented programming languages such as Java. A novel aspect of the syntax is that objects and classes are encapsulated within a single syntactic term, including their fields and methods. Furthermore, class terms are structured according to the class hierarchy, and objects appear as subterms of their class (and method instances as subterms of the relevant object). This helps to narrow the gap between how a programmer thinks about their code and the underlying mathematical objects in the semantics. The semantics is defined operationally, so that all actions a program may take, such as testing or setting local variables and fields, or invoking methods on other objects, appear on the labels of the transitions. A process-algebraic style of interprocess communication is used for object and class interactions. A benefit of this label-based approach to the semantics is that a separation of concerns can be made when defining the rules of the different constructs, and the rules tend to be more concise. The basic rules for individual commands may be composed into more powerful rules that operate at the level of classes and objects. The traces generated by the operational semantics are used as the basis for establishing equivalence between classes.     

A concurrent abstract interpreter

Abstract interpretation [6] has been long regarded as a promising optimization and analysis technique for high-level languages. In this article, we describe an implementation of aconcurrent abstract interpreter. The interpreter evaluates programs written in an expressive parallel language that supports dynamic process creation, first-class locations, list data structures and higher-order procedures. Synchronization in the input language is mediated via first-class shared locations. The analysis computes intra- and inter-threadcontrol anddataflow information. The interpreter is implemented on top of Sting [12], a multi-threaded dialect of Scheme that serves as a high-level operating system for modern programming languages.     

A language for specifying program transformations

A language is described for specifying program transformations, from which programs can be generated to perform the transformations on sequences of code. The main objective of this work has been to develop a language that would allow the user to quickly and easily specify a wide range of transformations for a variety of programming languages. The rationale for the language constructs is given, as well as the details of an implementation which was prototyped using Prolog. Numerous examples of the language usage are provided     

Neverlang: A framework for feature-oriented language development

Reuse in programming language development is an open research problem. Many authors have proposed frameworks for modular language development. These frameworks focus on maximizing code reuse, providing primitives for componentizing language implementations. There is also an open debate on combining feature-orientation with modular language development. Feature-oriented programming is a vision of computer programming in which features can be implemented separately, and then combined to build a variety of software products. However, even though feature-orientation and modular programming are strongly connected, modular language development frameworks are not usually meant primarily for feature-oriented language definition. In this paper we present a model of language development that puts feature implementation at the center, and describe its implementation in the Neverlang framework. The model has been evaluated through several languages implementations: in this paper, a state machine language is used as a means of comparison with other frameworks, and a JavaScript interpreter implementation is used to further illustrate the benefits that our model provides.     

Software Systems for Computer Graphics

This paper describes some software packages and programming systems for computer graphics applications, in the process considering software features for both passive and interactive graphics. It examines the structure both of subroutine libraries for use with some base language and of complete programming languages, and outlines the advantages and disadvantages of each, along with facilities that should be present in any software package.     

Debugging hygienic macros

Over the past two decades, Scheme macros have evolved into a powerful API for the compiler front end. Like Lisp macros, their predecessors, Scheme macros expand source programs into a small core language; unlike Lisp systems, Scheme macro expanders preserve lexical scoping, and advanced Scheme macro systems handle other important properties such as source location. Using such macros, Scheme programmers now routinely develop the ultimate abstraction: embedded domain-specific programming languages.Unfortunately, a typical Scheme programming environment provides little support for macro development. This lack makes it difficult for programmers to debug their macros and for novices to study the behavior of macros. In response, we have developed a stepping debugger specialized to the concerns of macro expansion. This debugger presents the macro expansion process as a linear rewriting sequence of annotated terms; it graphically illustrates the binding structure of the program as expansion reveals it; and it adapts to the programmer’s level of abstraction, hiding details of syntactic forms that the programmer considers built-in.     

Programmable applications: exploring the potential for language/interface symbiosis

Programmable applications are software systems that seek to combine the learnability and accessibility of direct manipulation interfaces with the expressive power and range of programming languages. In this paper we explore techniques for creatively integrating language and interface constructs within programmable applications. Using SchemePaint—a programmable graphics application—as a source of examples, we demonstrate how an interface and language can combine symbolically and thereby provide powerful modes of expression within applications.     

Language components for modular DSLs using traits

Recent advances in tooling and modern programming languages have progressively brought back the practice of developing domain-specific languages as a means to improve software development. Consequently, the problem of making composition between languages easier by emphasizing code reuse and componentized programming is a topic of increasing interest in research. In fact, it is not uncommon for different languages to share common features, and, because in the same project different DSLs may coexist to model concepts from different problem areas, it is interesting to study ways to develop modular, extensible languages. Earlier work has shown that traits can be used to modularize the semantics of a language implementation; a lot of attention is often spent on embedded DSLs; even when external DSLs are discussed, the main focus is on modularizing the semantics. In this paper we will show a complete trait-based approach to modularize not only the semantics but also the syntax of external DSLs, thereby simplifying extension and therefore evolution of a language implementation. We show the benefits of implementing these techniques using the Scala programming language.     

An agile approach to language modelling and development

We have developed novel techniques for component-based specification of programming languages. In our approach, the semantics of each fundamental programming construct is specified independently, using an inherently modular framework such that no reformulation is needed when constructs are combined. A language specification consists of an unrestricted context-free grammar for the syntax of programs, together with an analysis of each language construct in terms of fundamental constructs. An open-ended collection of fundamental constructs is currently being developed. When supported by appropriate tools, our techniques allow a more agile approach to the design, modelling, and implementation of programming and domain-specific languages. In particular, our approach encourages language designers to proceed incrementally, using prototype implementations generated from specifications to test tentative designs. The components of our specifications are independent and highly reusable, so initial language specifications can be rapidly produced, and can easily evolve in response to changing design decisions. In this paper, we outline our approach, and relate it to the practices and principles of agile modelling.     

Comparing Parallel Functional Languages: Programming and Performance

This paper presents a practical evaluation and comparison of three state-of-the-art parallel functional languages. The evaluation is based on implementations of three typical symbolic computation programs, with performance measured on a Beowulf-class parallel architecture.We assess three mature parallel functional languages: PMLS, a system for implicitly parallel execution of ML programs; GPH, a mainly implicit parallel extension of Haskell; and Eden, a more explicit parallel extension of Haskell designed for both distributed and parallel execution. While all three languages employ a completely implicit approach to communication, each language takes a different approach to specifying and controlling parallelism, ranging from explicit identification of processes as language constructs (Eden) through annotation of potential parallelism (GPH) to automatic detection of parallel skeletons in sequential code (PMLS).We present detailed performance measurements of all three systems on a widely available parallel architecture: a Beowulf cluster of low-cost commodity workstations. We use three representative symbolic applications: a matrix multiplication algorithm, an exact linear system solver, and a simple ray-tracer. Our results show how moderate speedups can be achieved with little or no changes to the sequential code, and that parallel performance can be significantly improved even within our high-level model of parallel functional programming by controlling key aspects of the program such as load distribution and thread granularity.     

A Tour Through Cedar

This paper^lintroduces the reader to many of the salient features of the Cedar programming environment, a state-of-the-art progrmming system that combines in a single integrated environment: high quality graphics, a sophisticated editor and document preparation facility, and a variety of tools for the programmer to use in the construction and debugging of his programs. The Cedar programming language [8] is a strongly typed, compiler-oriented language of the Pascal family. What is especially interesting about the Cedar project is that it is one of the few examples where an interactive, experimental programming environment has been built for this kind of language. In the past, such environments have been confined to dynamically typed languages like Lisp and Smalltalk.     

On the Expressive Power of Klaim-based Calculi

In this work, we study the expressive power of variants of Klaim, an experimental language with programming primitives for global computing that combines the process algebra approach with the coordination-oriented one. Klaim has proved to be suitable for programming a wide range of distributed applications with agents and code mobility, and has been implemented on the top of a runtime system based on Java. The expressivity of its constructs is tested by distilling from it some (more and more foundational) calculi and studying the encoding of each of the considered languages into a simpler one. An encoding of the asynchronous π-calculus into one of these calculi is also presented.     

Programmable applications: exploring the potential for language/interface symbiosis

Abstract

Programmable applications are software systems that seek to combine the learnability and accessibility of direct manipulation interfaces with the expressive power and range of programming languages. In this paper we explore techniques for creatively integrating language and interface constructs within programmable applications. Using SchemePaint—a programmable graphics application—as a source of examples, we demonstrate how an interface and language can combine symbolically and thereby provide powerful modes of expression within applications.     

Interpreting computer code in a computer‐based learning system for novice programmers

Although the principles of writing compilers and interpreters are well known, we have found that the ideas needed to develop an interpreter for the express purpose of allowing direct interaction with the running code do not yet appear to have been published in an academic context. We describe a programming method that can be used for the production of an interpreter for common object‐oriented languages such as C++, Java and C#. The main purpose of the interpreter is to parse short, relatively simple programs and allow direct interaction between the user and the running code. Such a system is useful for projects such as OGRE, which is an educational tool allowing students to visualize in three‐dimensional graphics the state of a program as it runs. The interpreter works by first parsing the source code and building up a data structure capable of representing the program's source code in a form that can be used to both run the program and extract detailed information from the running program. This extraction allows for novel uses of the interpreter, such as forming the basis for a visualization system that must display and provide such information to the user as they watch their executing program. This paper considers the construction of such an interpreter specifically for C++, but the principles should be the same for other similar languages such as Java and C#. We cover the main tasks required of the programmer to create and use the data structure, highlighting areas such as its design, initial construction during parsing, and techniques required to use it for interpretation. These include the ability for the data structure to intelligently clone subsets of itself when multiple copies of one of its elements are required by the running program, how it handles C++'s complicated function overloading and overriding rules, and how inheritance and polymorphism can be supported. Copyright © 2005 John Wiley & Sons, Ltd.     

A mechanically verified language implementation

This paper briefly describes a programming language, its implementation on a microprocessor via a compiler and link-assembler, and the mechanically checked proof of the correctness of the implementation. The programming language, called Piton, is a high-level assembly language designed for verified applications and as the target language for high-level language compilers. It provides executeonly programs, recursive subroutine call and return, stack based parameter passing, local variables, global variables and arrays, a user-visible stack for intermediate results, and seven abstract data types including integers, data addresses, program addresses and subroutine names. Piton is formally specified by an interpreter written for it in the computational logic of Boyer and Moore. Piton has been implemented on the FM8502, a general purpose microprocessor whose gate-level design has been mechanically proved to implement its machine code interpreter. The FM8502 implementation of Piton is via a function in the Boyer-Moore logic which maps a Piton initial state into an FM8502 binary core image. The compiler and link-assembler are both defined as functions in the logic. The implementation requires approximately 36K bytes and 1400 lines of prettyprinted source code in the Pure Lisp-like syntax of the logic. The implementation has been mechanically proved correct. In particular, if a Piton state can be run to completion without error, then the final values of all the global data structures can be ascertained from an inspection of an FM8502 core image obtained by running the core image produced by the compiler and link-assembler. Thus, verified Piton programs running on FM8502 can be thought of as having been verified down to the gate level.This work was supported in part by the Defense Advanced Research Projects Agency under DARPA Orders 6082 and 9151, contract MDA904-87-C-H009.     

LexAGen: An interactive incremental scanner generator

This paper describes LexAGen, an interactive scanner generator which is the first component of an interactive compiler generation environment. LexAGen can generate fast scanners for languages whose tokens can be specified by regular grammars. However, LexAGen also supports several context-sensitive programming language constructs such as nested comments and the interaction between floating-point numbers and the range operator in Modula-2. In addition, LexAGen includes a fast new algorithm for keyword identification. However, the most important and novel aspects of LexAGen are that it constructs scanners incrementally and that specifications can be executed anytime for validation testing. LexAGen specifications are expressed and entered interactively in a restricted BNF format (no left recursion). All syntactic errors and token conflicts are detected and reported immediately as LexAGen incrementally constructs a deterministic finite automaton to represent the scanner. At any time, the user can test the scanner fragment which has been entered by supplying text to be scanned. Alternatively, the user can generate a C-code scanner from the automaton. The generated automaton uses a direct execution approach and is quite fast. LexAGen is implemented in Smalltalk-80. Its extensive use of interactive graphics makes it very easy to use. In addition, the object-oriented paradigm of Smalltalk-80 is the basis for the incremental analysis, the error detection scheme and an intermediate representation which can be easily modified to generate scanners in other target languages such as Pascal, Modula-2 and Ada.