Expressing contract monitors as patterns of communication

We present a new approach to contract semantics which expresses myriad monitoring strategies using a small core of foundational communication primitives. This approach allows multiple existing contract monitoring approaches, ranging from Findler and Felleisen’s original model of higher-order contracts to semi-eager, parallel, or asynchronous monitors, to be expressed in a single language built on well-understood constructs. We prove that this approach accurately simulates the original semantics of higher-order contracts. A straightforward implementation in Racket demonstrates the practicality of our approach which not only enriches existing Racket monitoring strategies, but also support a new style of monitoring in which collections of contracts collaborate to establish a global invariant.