Towards an Operational Semantics for a Parallel Non-Strict Functional Language

Parallel programs must describe both computation and coordination , i.e. what to compute and how to organize the computation. In functional languages equational reasoning is often used to reason about computation. In contrast, there have been many diierent coordination constructs for functional languages, and far less work on reasoning about coordination. We present an initial semantics for GpH, a small extension of the Haskell language, that allows us to reason about coordination. In particular we can reason about work, average parallelism and runtime. The semantics captures the notions of limited (physical) resources, the preservation of sharing, and speculative evaluation. We show a consistency result with Launchbury's well-known lazy semantics.