Effective Aspects: A Typed Monadic Embedding of Pointcuts and Advice

International audienceAspect-oriented programming(AOP) aims to enhance modularity and reusability in software systems by offering an abstraction mechanism to deal with crosscutting concerns. However, in most general-purpose aspect languages aspects have almost unrestricted power, eventually conflicting with these goals. In this work we present Effective Aspects: a novel approach to embed the point- cut/advice model of AOP in a statically-typed functional programming language like Haskell. Our work extends EffectiveAdvice, by Oliveira, Schrijvers and Cook; which lacks quantification, and explores how to exploit the monadic setting in the full pointcut/advice model. Type soundness is guaranteed by exploiting the underlying type system, in particular phantom types and a new anti-unification type class. Aspects are first-class, can be deployed dynamically, and the pointcut language is extensible, therefore combining the flexibility of dynamically-typed aspect languages with the guarantees of a static type system. Monads enables us to directly reason about computational effects both in aspects and base programs using traditional monadic techniques. Using this we extend Aldrich's notion of Open Modules with effects, and also with protected pointcut interfaces to external advising. These restrictions are enforced statically using the type system. Also, we adapt the techniques of EffectiveAdvice to reason about and enforce control flow properties. Moreover, we show how to control effect interference us- ing the parametricity-based approach of EffectiveAdvice. However this approach falls short when dealing with interference between multiple aspects. We propose a different approach using monad views, a recently developed technique for han- dling the monad stack. Finally, we exploit the properties of our monadic weaver to enable the modular construction of new semantics for aspect scoping and weaving. These semantics also benefit fully from the monadic reasoning mechanisms present in the language. This work brings type-based reasoning about effects for the first time in the pointcut/advice model, in a framework that is both expressive and extensible; thus allowing development of robust aspect-oriented systems as well as being a useful research tool for experimenting with new aspect semantics

Stream Fusion, to Completeness

Stream processing is mainstream (again): Widely-used stream libraries are now available for virtually all modern OO and functional languages, from Java to C# to Scala to OCaml to Haskell. Yet expressivity and performance are still lacking. For instance, the popular, well-optimized Java 8 streams do not support the zip operator and are still an order of magnitude slower than hand-written loops. We present the first approach that represents the full generality of stream processing and eliminates overheads, via the use of staging. It is based on an unusually rich semantic model of stream interaction. We support any combination of zipping, nesting (or flat-mapping), sub-ranging, filtering, mapping-of finite or infinite streams. Our model captures idiosyncrasies that a programmer uses in optimizing stream pipelines, such as rate differences and the choice of a "for" vs. "while" loops. Our approach delivers hand-written-like code, but automatically. It explicitly avoids the reliance on black-box optimizers and sufficiently-smart compilers, offering highest, guaranteed and portable performance. Our approach relies on high-level concepts that are then readily mapped into an implementation. Accordingly, we have two distinct implementations: an OCaml stream library, staged via MetaOCaml, and a Scala library for the JVM, staged via LMS. In both cases, we derive libraries richer and simultaneously many tens of times faster than past work. We greatly exceed in performance the standard stream libraries available in Java, Scala and OCaml, including the well-optimized Java 8 streams

Abstract-Syntax-Driven Development of Oberon-0 Using YAJCo

YAJCo is a tool for the development of software languages based on an annotated language model. The model is represented by Java classes with annotations defining their mapping to concrete syntax. This approach to language definition enables the abstract syntax to be central point of the development process, instead of concrete syntax. In this paper a case study of Oberon-0 programming language development is presented. The study is based on the LTDA Tool Challenge and showcases details of abstract and concrete syntax definition using YAJCo, as well as implementation of name resolution, type checking, model transformation and code generation. The language was implemented in modular fashion to demonstrate language extension mechanisms supported by YAJCo

A Typed Monadic Embedding of Aspects

International audienceWe describe a novel approach to embed pointcut/advice aspects in a typed functional programming language like Haskell. Aspects are first-class, can be deployed dynamically, and the pointcut language is extensible. Type soundness is guaranteed by exploiting the un- derlying type system, in particular phantom types and a new anti- unification type class. The use of monads brings type-based rea- soning about effects for the first time in the pointcut/advice setting, thereby practically combining Open Modules and EffectiveAdvice, and enables modular extensions of the aspect language

Semantic Web Datatype Inference: Towards Better RDF Matching

International audienceIn the context of RDF document matching/integration, the datatype information, which is related to literal objects, is an important aspect to be analyzed in order to better determine similar RDF documents. In this paper, we propose a datatype inference process based on four steps: (i) predicate information analysis (i.e., deduce the datatype from existing range property); (ii) analysis of the object value itself by a pattern-matching process (i.e., recognize the object lexical-space); (iii) semantic analysis of the predicate name and its context; and (iv) generalization of numeric and binary datatypes to ensure the integration. We evaluated the performance and the accuracy of our approach with datasets from DBpedia. Results show that the execution time of the inference process is linear and its accuracy can increase up to 97.10%. \textcopyright 2017, Springer International Publishing AG

Versatile event correlation with algebraic effects

We present the first language design to uniformly express variants of n -way joins over asynchronous event streams from different domains, e.g., stream-relational algebra, event processing, reactive and concurrent programming. We model asynchronous reactive programs and joins in direct style, on top of algebraic effects and handlers. Effect handlers act as modular interpreters of event notifications, enabling fine-grained control abstractions and customizable event matching. Join variants can be considered as cartesian product computations with ”degenerate” control flow, such that unnecessary tuples are not materialized a priori. Based on this computational interpretation, we decompose joins into a generic, naive enumeration procedure of the cartesian product, plus variant-specific extensions, represented in terms of user-supplied effect handlers. Our microbenchmarks validate that this extensible design avoids needless materialization. Alongside a formal semantics for joining and prototypes in Koka and multicore OCaml, we contribute a systematic comparison of the covered domains and features. ERC, Advanced Grant No. 321217 ERC, Consolidator Grant No. 617805 DFG, SFB 1053 DFG, SA 2918/2-