Action semantics in retrospect

This paper is a themed account of the action semantics project, which Peter Mosses has led since the 1980s. It explains his motivations for developing action semantics, the inspirations behind its design, and the foundations of action semantics based on unified algebras. It goes on to outline some applications of action semantics to describe real programming languages, and some efforts to implement programming languages using action semantics directed compiler generation. It concludes by outlining more recent developments and reflecting on the success of the action semantics project

Iraq: The Way Forward—a Political Strategy to Win & End the War in Iraq

The challenges to stability, unity, and democracy in Iraq are typically characterized as factional (sectarian and ethnic) or as struggle against the presence of foreign troops. However, this assumption remains largely erroneous. The problems and challenges in Iraq are actually and overwhelmingly the result of power struggles, and the competition for resources by political elites, and dominant political factions. The political and electoral system emplaced in Iraq incentivizes elites and political entities to undertake factional identities; in doing so, it promotes identity politics. The current system also fails to filter the contests for power through the electoral system. As such, fragmentation within the government is maximized, and the political system in Iraq becomes one that promotes extremism and incorporates extremist views, thus, creating paralysis and hindering progress. Consequently, this study proposes redesigning the Iraqi electoral system in a way that compels elites to secure cross-factional support. Such an approach will force political elites and candidates to undertake median and moderate approaches to win and will promote moderate elites who must gain the support of the people. This will allow reconciliation efforts to progress steadily and will put Iraq on the right path for consolidating its nascent democracy. Vitally important, such a system will provide for democratic consolidation and sustainability without the need of external interference. The challenge, however, is in deciding how to introduce such an institutional redesign due to entrenched interests of parties and elites that are served under the current system. The current political system in Iraq is parliamentarian; it follows the concept of infusion of powers and is based on consensus and informal consociation. The electoral system in Iraq is a closed-party-list proportional representation. This study proposes an alternative political and electoral system. As a substitute political system, this study proposes a hybrid system that largely follows the concept of separation of powers. Under this system the chief executive--as opposed to the head of state--will be directly elected by the people through a customized majoritarian system that conditions victory in elections not only on achieving 50+% of the vote, but also on achieving certain thresholds in 16 out of the 18 Iraqi provinces. Thus, only candidates who are acceptable to all the components of Iraqi society will assume the responsibility of governing Iraq. The Presidency Council--the head of state--can follow the consociational principle, and remain as it is now. At present, the presidency council in Iraq--which will give over power to a President in the next elections--consists of a President and two Vice Presidents. The presidency council\u27s members are representatives of the three major components of the Iraqi society--Shiite, Sunni, and, Kurd. This can remain unchanged, voted in by parliament. In fact, preserving this would check the strong Prime Minister proposed under this system. As such, transparency, accountability, decisiveness, and cohesion, will be combined with oversight. As for elections to the legislature, this study proposes to convert the electoral rules to single-member districts. Districts must be delineated in such a way that candidates will largely compete against people of their own (sectarian or ethnic) identity. Hence, candidates will be unable to invoke their identities as credentials to win elections. Where possible, minorities in districts will be included so that serious candidates competing against others from their-own identity will be forced to appeal also to people other than their identities. This will further compel candidates to undertake moderate stands. Essentially, the proposed system enhances the accountability of elected officials to the electorate; it promotes substantive politics rather than descriptive politics in Iraq; and it allows for the steady consolidation of democracy. The proposed system also maintains unity within the executive branch, and opens the way for reconciliation, reconstruction, the provision of services and security, and political stability

Formal Component-Based Semantics

One of the proposed solutions for improving the scalability of semantics of programming languages is Component-Based Semantics, introduced by Peter D. Mosses. It is expected that this framework can also be used effectively for modular meta theoretic reasoning. This paper presents a formalization of Component-Based Semantics in the theorem prover Coq. It is based on Modular SOS, a variant of SOS, and makes essential use of dependent types, while profiting from type classes. This formalization constitutes a contribution towards modular meta theoretic formalizations in theorem provers. As a small example, a modular proof of determinism of a mini-language is developed.Comment: In Proceedings SOS 2011, arXiv:1108.279

Reusable Components of Semantic Specifications

Semantic specifications of programming languages typically have poor modularity. This hinders reuse of parts of the semantics of one language when specifying a different language – even when the two languages have many constructs in common – and evolution of a language may require major reformulation of its semantics. Such drawbacks have discouraged language developers from using formal semantics to document their designs. In the PLanCompS project, we have developed a component-based approach to semantics. Here, we explain its modularity aspects, and present an illustrative case study: a component-based semantics for Caml Light. We have tested the correctness of the semantics by running programs on an interpreter generated from the semantics, comparing the output with that produced on the standard implementation of the language. Our approach provides good modularity, facilitates reuse, and should support co-evolution of languages and their formal semantics. It could be particularly useful in connection with domain-specific languages and language-driven software development

Control over phase separation and nucleation using a laser-tweezing potential

Control over the nucleation of new phases is highly desirable but elusive. Even though there is a long history of crystallization engineering by varying physicochemical parameters, controlling which polymorph crystallizes or whether a molecule crystallizes or forms an amorphous precipitate is still a poorly understood practice. Although there are now numerous examples of control using laser-induced nucleation, the absence of physical understanding is preventing progress. Here we show that the proximity of a liquid–liquid critical point or the corresponding binodal line can be used by a laser-tweezing potential to induce concentration gradients. A simple theoretical model shows that the stored electromagnetic energy of the laser beam produces a free-energy potential that forces phase separation or triggers the nucleation of a new phase. Experiments in a liquid mixture using a low-power laser diode confirm the effect. Phase separation and nucleation using a laser-tweezing potential explains the physics behind non-photochemical laser-induced nucleation and suggests new ways of manipulating matter

ACTRESS: an Action Semantics Directed Compiler Generator

We report progress on the development of Actress, a compiler generator based on action semantics. It consists of a number of modules, written in SML, that can be composed to construct either an action notation compiler or a simple compiler generator. We also outline current and future developments that will improve the quality of the generated compilers. 1 Introduction We define a compiler generator to be a tool that constructs a compiler automatically, given a syntactic and semantic description of the source language. This definition emphasizes the fact that the compiler is not written by a programmer, but generated from a formal description of the language. Ideally, this formal description is one that was written by the language designer and is consulted by users of the language. We can generate an efficient syntactic analyser automatically from a syntactic description, using tools such as lex and yacc. However, generating a code generator from a semantic description is much more d..