We prove that the observational equivalence of third-order finitary Idealized Algol is decidable using Game Semantics. By modelling the state explicitly in our games, we show that the denotation of a term M of this fragment of IA is a compactly innocent strategy-with-state, i.e. the strategy is generated by a finite view function fM. Given any such fM, we construct a real-time deterministic pushdown automaton that recognizes the complete plays of the knowing-strategy denotation of M. Since such plays characterize (...) observational equivalence, and there is an algorithm for deciding whether any two DPDAs recognize the same language, we obtain a procedure for deciding the observational equivalence of third-order finitary IA. Restricted to second-order terms, the DPDA representation cuts down to a deterministic finite automaton; thus our approach gives a new proof of Ghica and McCusker’s regular-expression characterization for this fragment. Our algorithmic representation of program meanings, which is compositional, provides a foundation for model-checking a wide range of behavioural properties of IA and other cognate programming languages. Another result concerns second-order IA with full recursion: we show that observational equivalence for this fragment is undecidable. (shrink)

The semantics of programming languages tend to be discussed with high levels of formality; much of the previous research—both philosophical and historical—has investigated them from this perspective. In this paper, I draw on the philosophical and cognitive theories of metaphor and use the early work of Adriaan van Wijngaarden as a historical case study to explore the conceptual and discursive surroundings of semantics. I investigate the relationships between the texts of semantics, the abstract entities they denote, and the metaphors, analogies, (...) and illustrative language used to accompany or explain the same. This serves to further understanding of the historical developments of work in this area, the nature of programming languages and their semantics, and the importance of the communicative methods used in dissemination and education of computer science. (shrink)

This chapter is focused on the application of the COC (the criterion of ontological commitment) to the λ\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\lambda $$\end{document}-calculus and the formulation of the functional ontology that underlies it. As the theory λ\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\lambda $$\end{document}is an equational theory, then we can use either Martin’s metalinguistic approach (see Chap. 8) or Anderson’s definition of the existential quantifier in the object-language of the λ\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} (...) \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\lambda $$\end{document}-calculus. In both cases, then theλ\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\lambda $$\end{document}-calculus is exclusively committed (ontologically) withλ\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\lambda $$\end{document}-terms. The ontological reduction implemented by the functional ontology of the λ\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\lambda $$\end{document}-calculus (for both logic and programming) is, then, the following: no abstract objects other than (Curried) monadic functions are needed for science. This powerful functional ontology is more economical than the set-theoretical ontology described by Quine. Moreover, the “Strachey-Quine example” illustrates, in a very effective way, the intersubjective nature of functional ontology. The example shows that using the COC, the programming language ALGOL is ontologically committed to real numbers because they behave like quantified (bound) variables. In contrast, procedures (the ALGOL term for functions) are not admitted in its ontology because they do not behave like quantified variables at all. Two specific lines of code (provided by Strachey) show this difference in the ontology of ALGOL. (shrink)

A wide-ranging history of the intellectual developments that produced the modern idea of the algorithm. Bringing together the histories of mathematics, computer science, and linguistic thought, Language and the Rise of the Algorithm reveals how recent developments in artificial intelligence are reopening an issue that troubled mathematicians long before the computer age. How do you draw the line between computational rules and the complexities of making systems comprehensible to people? Here Jeffrey M. Binder offers a compelling tour of four visions (...) of universal computation that addressed this issue in very different ways: G. W. Leibniz's calculus ratiocinator; a universal algebra scheme Nicolas de Condorcet designed during the French Revolution; George Boole's nineteenth-century logic system; and the early programming language ALGOL, whose name is short for algorithmic language. These episodes show that symbolic computation has repeatedly become entangled in debates about the nature of communication. To what extent can meaning be controlled by individuals, like the values of a and b in algebra, and to what extent is meaning inevitably social? By attending to this long-neglected question, we come to see that the modern idea of the algorithm is implicated in a long history of attempts to maintain a disciplinary boundary separating technical knowledge from the languages people speak day to day. Machine learning, in its increasing dependence on words, now places this boundary in jeopardy, making its stakes all the more urgent to understand. The idea of the algorithm is a levee holding back the social complexity of language, and it is about to break. This book is about the flood that inspired its construction. (shrink)

We introduce a game model for an Algol-like programming language with primitives for parallel composition and synchronization on semaphores. The semantics is based on a simplified version of Hyland–Ong-style games and it emphasizes the intuitive connection between the concurrent nature of games and that of computation. The model is fully abstract for may-equivalence.

• Lisp programs are Lisp data—abstract syntax. Programming languages need functions for their abstract • English is important for its semantics—not its syntax • The largest piece of cake—Kleene µ operator • An elephant never forgets and is faithful. • Resolution considered harmful. • Special provers are just strategies—Davis-Putnam • Programs as logical formulas—Algol 48 and Algol..