Note on Algol and Conservatively Extending Functional Programming

A simple Idealized Algol is considered, based on Reynolds\u27s essence of Algol. It is shown that observational equivalence in this language conservatively extends observational equivalence in its assignment-free functional sublanguage

Non Interference for Intuitionist Necessity

The necessity modality of intuitionist S4 is a comonad. In this paper, we study indexed necessity modalities that provide the logical foundation for a variety of applications; for example, to model possession of capabilities in policy languages for access control, and to track exceptions in type theories for exceptional computation. Noninterference properties of the intuitionist logic of indexed necessity modalities capture the limitations on the information flow between formulas that are under the scope of necessity modalities with different indices. The impact of noninterference is seen in the unprovability of certain formulas. Noninterference is necessary for several applications. In models of capabilities, noninterference facilitates distributed reasoning. In models of exceptions, noninterference is necessary to ensure that the exceptions are tracked conservatively. In this paper, we prove noninterference properties for indexed intuitionist necessity S4 modalities. To our knowledge, this is the first examination of noninterference results for the intuitionist S4 necessity modality (even without indexing)

Particpants' Proceedings on the Workshop: Types for Program Analysis

As a satellite meeting of the TAPSOFT'95 conference we organized a small workshop on program analysis. The title of the workshop, ``Types for Program Analysis´´, was motivated by the recent trend of letting the presentation and development of program analyses be influenced by annotated type systems, effect systems, and more general logical systems. The contents of the workshop was intended to be somewhat broader; consequently the call for participation listed the following areas of interest:- specification of specific analyses for programming languages,- the role of effects, polymorphism, conjunction/disjunction types, dependent types etc.in specification of analyses,- algorithmic tools and methods for solving general classes of type-based analyses,- the role of unification, semi-unification etc. in implementations of analyses,- proof techniques for establishing the safety of analyses,- relationship to other approaches to program analysis, including abstract interpretation and constraint-based methods,- exploitation of analysis results in program optimization and implementation.The submissions were not formally refereed; however each submission was read by several members of the program committee and received detailed comments and suggestions for improvement. We expect that several of the papers, in slightly revised forms, will show up at future conferences. The workshop took place at Aarhus University on May 26 and May 27 and lasted two half days

Type Systems For Polynomial-time Computation

This thesis introduces and studies a typed lambda calculus with higher-order primitive recursion over inductive datatypes which has the property that all definable number-theoretic functions are polynomial time computable. This is achieved by imposing type-theoretic restrictions on the way results of recursive calls can be used. The main technical result is the proof of the characteristic property of this system. It proceeds by exhibiting a category-theoretic model in which all morphisms are polynomial time computable by construction. The second more subtle goal of the thesis is to illustrate the usefulness of this semantic technique as a means for guiding the development of syntactic systems, in particular typed lambda calculi, and to study their meta-theoretic properties. Minor results are a type checking algorithm for the developed typed lambda calculus and the construction of combinatory algebras consisting of polynomial time algorithms in the style of the first Kleene algebra