We call language L 1 intensionally more expressive than L 2 if there are functions which can be computed faster in L 1 than in L 2 . We study the intensional expressiveness of several languages: the Berry-Curien programming language of sequential algorithms, CDS0, a deterministic parallel extension to it, named CDSP, and various parallel extensions to the functional programming language PCF. The paper consists of two parts. In the first part, we show that CDS0 can compute the minimum of two numbers n and p in unary representation in time O(min(n; p)). However, it cannot compute a "natural" version of this function. CDSP allows us to compute this function, as well as functions like parallel-or. This work can be seen as an extension of the work of Colson [7, 8] with primitive recursive algorithms to the setting of sequential algorithms. In the second part, we show that deterministic parallelism adds intensional expressiveness, settling a "folk" conjecture from the literature in the nega...

Denotational semantics is usually extensional in that it deals only with input/output properties of programs by making the meaning of a program a function. Intensional semantics maps a program into an algorithm, thus enabling one to reason about complexity, order of evaluation, degree of parallelism, efficiency-improving program transformations, etc. I propose to develop intensional models for a number of parallel programming languages. The semantics will be implemented, resulting in a programming language of parallel algorithms, called CDSP. Applications of CDSP will be developed to determine its suitability for actual use. The thesis will hopefully make both theoretical and practical contributions: as a foundational study of parallelism by looking at the expressive power of various constructs, and with the design, implementation, and applications of an intensional parallel programming language. 1 Introduction Denotational semantics has now been around for about 25 years, which makes...