An introduction to metric semantics: operational and denotational models for programming and specification languages

Modern science commonly uses computer modelling. Thousands of scientific model are daily transformed to computers programs and tested. The transformation must overcome the gap between abstract human formal notation and low level semantics of contemporary programming languages. The simultaneous knowledge of specific scientific models and programming languages is an unpleasant necessity for a significant proportion of scientists and practitioners (engineers, economist, etc.). But a solution exists - accommodation of programming languages to mental models of their users. The article discuss one partial solution - implementation of domain specific languages in the heart of existing universal languages by mechanisms of metaprogramming. This mechanism overcomes limitations of classical programming languages and complexity of creation new languages from scratch. However, the support of metaprogramming in contemporary languages is limited to isolated and peripheral constructs in very few languages. These constructs are demonstrated by simplified but real examples (metaobject system of Python, monads in F# and macro-based metaprogramming of Boo language) together with discussion of their advantages and disadvantages. The discussion of examples is aimed to finding requirements for new languages and their implementation in a original (parent) language.

Semantics of programming languages: Using Asf+Sdf

In this chapter we outline a process algebra, whose name — Petri Box Calculus (PBC) — arises from its original Petri net semantics [6, 7]. PBC combines a number of features taken from other process algebras, such as COSY (Concurrent Systems notation, [62]), CCS (Calculus of Communicating Systems, [80, 81]), SCCS (Synchronous CCS, [81]), CSP (Communicating Sequential Processes, [58]), TCSP (Theoretical CSP, [59]) and ACP (Algebra of Communicating Processes, [2]). However, there are some fundamental differences with each of these process algebras since PBC has been designed with two specific objectives in mind: To support a compositional Petri net semantics, together with an equivalent — more syntax-oriented — structured operational semantics (SOS) [89]. To provide as flexible as possible a basis for developing a compositional semantics of high-level concurrent specification and programming languages with full data and control features.

This paper provides an analysis of the meaning–reference problem, as traditionally advanced in the philosophy of language, for imperative programming languages. Addressing the problem is relevant for the philosophy of computer science in the context of the debate of whether simulative programs can be considered representational theories of their simulated systems. This paper challenges the thesis that, since programming languages have semantics, they also have reference, presumably to the external world. First, denotational, operational, game theoretic, and axiomatic semantics are epistemologically analysed to provide a theory of meaning for high-level language programs. It is argued that programming language semantics can be seen, to some extent, under the light of Fregean descriptivism, thereby rejecting the view that it is reference that determines meaning. Secondly, descriptivist, causal, character, and intentionalist theories of reference are examined to argue that meaning is not sufficient for programming languages to determine reference, thereby rejecting the view that meaning determines reference. It is argued that it is the intentions of agents that allow programming language semantics to identify referents. The paper concludes that if the semantics of programming languages may determine their reference, the latter is not to the external world but to the internal operations of the implementation executing them. This does not prevent simulative programs from representing empirical systems, but they do so not on the basis of programming language semantics.

We introduce a new semantics for logic programming languages. It generalises the traditional Herbrand universe semantics, and specialises the semantics of logical relations, as used in analysing parametricity in functional and imperative programming languages. We outline a typed logic programming language, give it this semantics, and show how it supports structured development of logic programs as advocated by Sterling et al. In particular, it gives semantics for some dynamic aspects of logic programs.

We introduce an answer-set semantics for abstract-constraint programs with disjunction in rule heads in the style of Faber, Leone, and Pfeifer (FLP). To this end, we extend the definition of an answer set for logic programs with aggregates in rule bodies using the usual FLP-reduct. Additionally, we also provide a characterisation of our semantics in terms of unfounded sets, likewise generalising the standard concept of an unfounded set. Our work is motivated by the desire to have simple and rule-based definitions of the semantics of an answer-set programming (ASP) language that is close to those implemented by the most prominent ASP solvers. The new definitions are intended as a theoretical device to allow for development methods and methodologies for ASP, e.g., debugging or testing techniques, that are general enough to work for different types of solvers. We use abstract constraints as an abstraction of literals whose truth values depend on subsets of an interpretation. This includes weight constraints, aggregates, and external atoms, which are frequently used in real-world answer-set programs. We compare the new semantics to previous semantics for abstract-constraint programs and show that they are equivalent to recent extensions of the FLP semantics to propositional and first-order theories when abstract-constraint programs are viewed as theories.

The concurrency theory literature contains many proposals for models of process algebras. We consider an example application of the π-calculus, the programming language Pict of Pierce and Turner, primarily in order to see how far it is possible to argue, from facts about the application, that some model is the most appropriate. We discuss informally the sense in which the semantics of Pict relates to the behaviour of actual implementations. Based on this we give an operational model of the interactions between a Pict implementation (considered as the abstract behaviour of a C program) and its environment (modelling an operating system and user). We then give a class of abstract machines and a definition of abstract machine correctness, using an adapted notion of testing, and prove that a sample abstract machine is indeed correct. We briefly discuss the standard of correctness appropriate for program transformations and the induced precongruence. Many of the semantic choices do indeed turn out to be determined by facts about Pict.

In this work we propose to use a Horn fragment of Concurrent Transaction Logic ( ${\mathcal CTR}$) as an intuitive logic framework to specify semantics of concurrent programming languages. Using Horn logic to specify a programming language has been suggested before [5,6,2]. By specifying a programming language we mean writing semantics, all three semantics-operational, denotational, and axiomatic-in Horn logic, which is also executable. Slonneger convincingly demonstrated that, for the specification of denotational semantics, Prolog can be regarded as superior to imperative languages. Gupta [2] expanded on the idea and showed how Horn logic denotations lead to some interesting practical applications, such as automatic program verification and automatic generation of compilers. The work presented here builds on the aforementionedworks and extends that of [2] by providing a Horn logic denotational semantics for concurrent programming languages.

Developing a distributed application for mobile resource constrained devices is a difficult and error-prone task that requires awareness of several system-level details (e.g., fault-tolerance, ...). Several mobile middleware solutions addressing these issues have been proposed. However, they rely on either significant changes in application structure, extensions to the programming language syntax and semantics, domain specific languages, cumbersome development tools, or a combination of the above. The main disadvantages of these approaches are lack of transparency and reduced portability. In this paper we describe our work on enabling transparent integration between applications and middleware without changing application structure, extending the programming language or otherwise reducing portability. We used the OBIWAN middleware but our solutions are general. To achieve this goal we employ program analysis and transformation techniques for extending application code with hooks for calling middleware services. Application code extension is performed automatically at compile-time by a code extension tool integrated with the development environment tool set. We describe the implementation of our .NET and Java prototypes and discuss evaluation results.

This book – the first of two volumes – explores the syntactical constructs of the most common programming languages, and sheds a mathematical light on their semantics, while also providing an accurate presentation of the material aspects that interfere with coding. Concepts and Semantics of Programming Languages 1 is dedicated to functional and imperative features. Included is the formal study of the semantics of typing and execution; their acquisition is facilitated by implementation into OCaml and Python, as well as by worked examples. Data representation is considered in detail: endianness, pointers, memory management, union types and pattern-matching, etc., with examples in OCaml, C and C++. The second volume introduces a specific model for studying modular and object features and uses this model to present Ada and OCaml modules, and subsequently Java, C++, OCaml and Python classes and objects. This book is intended not only for computer science students and teachers but also seasoned programmers, who will find a guide to reading reference manuals and the foundations of program verification.

In this paper, we present a software module developed for the course Semantics of Programming Languages. This software will be part of the intended comprehensive software package to simplify and make the teaching of formal principles in theoretical computer science more attractive. During the pandemic, the need to support illustrative and illustrative online teaching increased. Our software is designed to illustrate and visualize the translation of a higher-level language into code for the Abstract Machine, the definition of which is based on the structural operational semantics of programs.

There is a large gap between the specification of type systems and the implementation of their type checkers, which impedes reasoning about the soundness of the type checker with respect to the specification. A vision to close this gap is to automatically obtain type checkers from declarative programming language specifications. This moves the burden of proving correctness from a case-by-case basis for concrete languages to a single correctness proof for the specification language. This vision is obstructed by an aspect common to all programming languages: name resolution. Naming and scoping are pervasive and complex aspects of the static semantics of programming languages. Implementations of type checkers for languages with name binding features such as modules, imports, classes, and inheritance interleave collection of binding information (i.e., declarations, scoping structure, and imports) and querying that information. This requires scheduling those two aspects in such a way that query answers are stable—i.e., they are computed only after all relevant binding structure has been collected. Type checkers for concrete languages accomplish stability using language-specific knowledge about the type system. In this paper we give a language-independent characterization of necessary and sufficient conditions to guarantee stability of name and type queries during type checking in terms of critical edges in an incomplete scope graph . We use critical edges to give a formal small-step operational semantics to a declarative specification language for type systems, that achieves soundness by delaying queries that may depend on missing information. This yields type checkers for the specified languages that are sound by construction—i.e., they schedule queries so that the answers are stable, and only accept programs that are name- and type-correct according to the declarative language specification. We implement this approach, and evaluate it against specifications of a small module and record language, as well as subsets of Java and Scala.

Isabelle is a generic meta-logical framework for implementing logical formalisms, and Isabelle/HOL is the specialization of Isabelle for HOL, which stands for Higher Order Logic. In programming language theory, formal semantics is the field concerned with the rigorous mathematical study of the meaning of programming languages. In this paper we develop a relational denotational semantics for a small imperative programming language and implement it as a theory in Isabelle/HOL. We give special attention to the specification of monotonic fix point functional for loops and provide non-trivial proofs of interesting lemmas and properties with the structured proof language Isar.

After a review of semaphores and monitors the principles underlying the programming language OCCAM are outlined. We show how it can also be used as a specification language. We also examine in detail the language CCS, principely by giving examples of processes or specifications. We end with some remarks on the issues raised by these modern languages which on the one hand may be viewed as programming languages for highly parallel architectures and on the other languages for specifying the required behaviour of systems.

For many real-time applications (e.g. command, control, and communications), parallel computers offer a natural computing platform. However, very little attention has been paid to the specification requirements of real-time systems implemented on parallel machines. Towards this end, we propose a specification language PRETSEL (Parallel Real-Time Specification Language). The PRETSEL specification language is based on a traditional two-level view of parallel computing whereby a parallel computation is viewed as a collection of interacting (data) parallel algorithms. This view is naturally reflected in PRETSEL syntax where at the lower level various constructs are provided for the specification of a data-parallel real-time algorithm (data-parallelism). At the upper level another set of constructs is provided to combine such tasks in a variety of way (task-parallelism). Furthermore, the PRETSEL language allows for the specification of performance requirements. PRETSEL is currently being evaluated for real-time avionics applications. We describe the syntax and operational semantics of PRETSEL and establish results relating the functional and the temporal behaviors.