A Core Model for Choreographic Programming

Abstract

Choreographic Programming is a paradigm for developing concurrent programs that are deadlock-free by construction, as a result of programming communications declaratively and then synthesising process implementations automatically. Despite strong interest on choreographies, a foundational model that explains which computations can be performed with the hallmark constructs of choreographies is still missing.In this work, we introduce Core Choreographies (CC), a model that includes only the core primitives of choreographic programming. Every computable function can be implemented as a choreography in CC, from which we can synthesise a process implementation where independent computations run in parallel. We discuss the design of CC and argue that it constitutes a canonical model for choreographic programming.

The Paths to Choreography Extraction

“…The body of X is not projectable (the branches for r are not mergeable, cf. [11]), but it faithfully describes the behavior of the original network.…”

“…We review the languages of Core Choreographies (CC) and Stateful Processes (SP), from [11], which respectively model choreographies and endpoint programs. We introduce labels in the reduction semantics for these calculi to formalize the link between choreographies and their process implementations as a bisimilarity.…”

On Asynchrony and Choreographies

“…Term 0 is the terminated choreography, which we sometimes omit. For a more detailed discussion of these primitives, we refer the reader to [8]. 1 The (synchronous) semantics of MC is a reduction semantics that uses a total state function σ to represent the memory state at each process p. Since our development is orthogonal to the details of the memory implementation, we say that σ (p) is a representation of the memory state of p (left unspecified) and write upd(σ , p, v) to denote the (uniquely defined) updated memory state of p after receiving a value v. Term e ↓ σ (p) v denotes that locally evaluating expression e at p, with memory state σ , evaluates to v. We assume that expression evaluation is deterministic and always terminates.…”

“…Minimal Choreographies are meant to be implemented in a minimalistic process calculus, also introduced in [8], called Stateful Processes (SP). We summarize this calculus, noting that we make the same conventions and changes regarding expressions, labels, and states as above.…”

“…Choreographic Programming [18] is a paradigm for developing concurrent software, where an "Alice and Bob" notation is used to prevent mismatched I/O actions syntactically. An EndPoint Projection (EPP) can then be used to synthesise correct-by-construction process implementations [4,8,21]. Choreographies are used in different settings, including standards [2,23], languages [5,14,20,22], specification models [3,4,16], and design tools [2,20,22,23].…”