Programmers of high-performance applications face two major implementation options: to use a high-level language which manages communication implicitly or to use a low-level language while specifying communication explicitly. The high-level approach offers safety and convenience, but forces programmers to give up control, making it difficult to hand-tune communications or to estimate communication cost. The low-level approach retains this control, but forces programmers to express communication at a verbose, tedious, and error-prone level of detail.

We advocate a complementary third approach in which the programmer declaratively, but explicitly, specifies the essence of the communication pattern. The programmer lets the implementation handle the details when appropriate, but retains enough control to hand-encode communications when necessary. In this paper we present Kanor, a language for declaratively expressing explicit communication patterns, and demonstrate how Kanor safely, succinctly, and efficiently expresses both point-to-point and collective communications.