Eelco Visser: The Oregon Connection

This paper shares some memories of Eelco gathered over the past 25 years as a colleague and friend, and reflects on the nature of modern international collaborations

Scoped and Typed Staging by Evaluation

Using a dependently typed host language, we give a well scoped-and-typed by construction presentation of a minimal two level simply typed calculus with a static and a dynamic stage. The staging function partially evaluating the part of a term that are static is obtained by a model construction inspired by normalisation by evaluation. We then go on to demonstrate how this minimal language can be extended to provide additional metaprogramming capabilities, and to define a higher order functional language evaluating to digital circuit descriptions.Comment: As accepted for publication at PEPM 202

Semantics of programming languages : a tool-oriented approach

By paying more attention to semantics-based tool generation, programming language semantics can significantly increase its impact. Ultimately, this may lead to ``Language Design Assistants'' incorporating substantial amounts of semantic knowledge

Efficient embedding of strategic attribute grammars via memoization

Strategic term re-writing and attribute grammars are two powerful programming techniques widely used in language engineering. The former relies on strategies to apply term rewrite rules in defining large-scale language transformations, while the latter is suitable to express context-dependent language processing algorithms. These two techniques can be expressed and combined via a powerful navigation abstraction: generic zippers. This results in a concise zipper-based embedding offering the expressiveness of both techniques. Such elegant embedding has a severe limitation since it recomputes attribute values. This paper presents a proper and efficient embedding of both techniques. First, attribute values are memoized in the zipper data structure, thus avoiding their re-computation. Moreover, strategic zipper based functions are adapted to access such memoized values. We have implemented our memoized embedding as the Ztrategic library and we benchmarked it against the state-of-the-art Strafunski and Kiama libraries. Our first results show that we are competitive against those two well established libraries.This work is financed by National Funds through the Portuguese funding agency, FCT - Fundação para a Ciência e a Tecnologia, within project LA/P/0063/2020. The first author is also sponsored by FCT grant 2021.08184.BD

Speculative Staging for Interpreter Optimization

Interpreters have a bad reputation for having lower performance than just-in-time compilers. We present a new way of building high performance interpreters that is particularly effective for executing dynamically typed programming languages. The key idea is to combine speculative staging of optimized interpreter instructions with a novel technique of incrementally and iteratively concerting them at run-time. This paper introduces the concepts behind deriving optimized instructions from existing interpreter instructions---incrementally peeling off layers of complexity. When compiling the interpreter, these optimized derivatives will be compiled along with the original interpreter instructions. Therefore, our technique is portable by construction since it leverages the existing compiler's backend. At run-time we use instruction substitution from the interpreter's original and expensive instructions to optimized instruction derivatives to speed up execution. Our technique unites high performance with the simplicity and portability of interpreters---we report that our optimization makes the CPython interpreter up to more than four times faster, where our interpreter closes the gap between and sometimes even outperforms PyPy's just-in-time compiler.Comment: 16 pages, 4 figures, 3 tables. Uses CPython 3.2.3 and PyPy 1.

Lambda-Dropping: Transforming Recursive Equations into Programs with Block Structure

Lambda-lifting a functional program transforms it into a set of recursiveequations. We present the symmetric transformation: lambda-dropping.Lambda-dropping a set of recursive equations restores blockstructure and lexical scope.For lack of scope, recursive equations must carry around all theparameters that any of their callees might possibly need. Both lambda-liftingand lambda-dropping thus require one to compute a transitiveclosure over the call graph:- for lambda-lifting: to establish the Def/Use path of each freevariable (these free variables are then added as parameters toeach of the functions in the call path);- for lambda-dropping: to establish the Def/Use path of each parameter(parameters whose use occurs in the same scope as theirdefinition do not need to be passed along in the call path).Without free variables, a program is scope-insensitive. Its blocks arethen free to float (for lambda-lifting) or to sink (for lambda-dropping)along the vertices of the scope tree.We believe lambda-lifting and lambda-dropping are interesting perse, both in principle and in practice, but our prime application is partialevaluation: except for Malmkjær and Ørbæk's case study presented atPEPM'95, most polyvariant specializers for procedural programs operateon recursive equations. To this end, in a pre-processing phase,they lambda-lift source programs into recursive equations. As a result,residual programs are also expressed as recursive equations, often withdozens of parameters, which most compilers do not handle efficiently.Lambda-dropping in a post-processing phase restores their block structureand lexical scope thereby significantly reducing both the compiletime and the run time of residual programs.

Semantics of programming languages : a tool-oriented approach

By paying more attention to semantics-based tool generation, programming language semantics can significantly increase its impact. Ultimately, this may lead to ``Language Design Assistants\'\' incorporating substantial amounts of semantic knowledge

Semantics of programming languages : a tool-oriented approach

By paying more attention to semantics-based tool generation, programming language semantics can significantly increase its impact. Ultimately, this may lead to ``Language Design Assistants'' incorporating substantial amounts of semantic knowledge

Towards Unifying Inheritance and Automatic Program Specialization

Inheritance allows a class to be specialized and its attributes refined, but implementation specialization can only take place by overriding with manually implemented methods. Automatic program specialization can generate a specialized, efficient implementation. However, specialization of programs and specialization of classes (inheritance) are considered different abstractions. We present a new programming language, Lapis, that unifies inheritance and program specialization at the conceptual, syntactic, and semantic levels. This paper presents the initial development of Lapis, which uses inheritance with covariant specialization to control the automatic application of program specialization to class members. Lapis integrates object-oriented concepts, block structure, and techniques from automatic program specialization to provide both a language where object-oriented designs can be efficiently implemented and a simple yet powerful partial evaluator for an object-oriented language

Partial Evaluation for Constraint-Based Program Analyses

We report on a case study in the application of partial evaluation, initiatedby the desire to speed up a constraint-based algorithm for control-flow analysis. We designed and implemented a dedicated partial evaluator,able to specialize the analysis wrt. a given constraint graph and thus remove the interpretive overhead, and measured it with Feeley's Schemebenchmarks. Even though the gain turned out to be rather limited, ourinvestigation yielded valuable feed back in that it provided a better understandingof the analysis, leading us to (re)invent an incremental version.We believe this phenomenon to be a quite frequent spinoff from using partial evaluation, since the removal of interpretive overhead makes the flowof control more explicit and hence pinpoints sources of inefficiency. Finally, we observed that partial evaluation in our case yields such regular,low-level specialized programs that it begs for run-time code generation