  We present Tierkreis, a higher-order dataflow graph program representation
and runtime designed for compositional, quantum-classical hybrid algorithms.
The design of the system is motivated by the remote nature of quantum
computers, the need for hybrid algorithms to involve cloud and distributed
computing, and the long-running nature of these algorithms. The graph-based
representation reflects how designers reason about and visualise algorithms,
and allows automatic parallelism and asynchronicity. A strong, static type
system and higher-order semantics allow for high expressivity and
compositionality in the program. The flexible runtime protocol enables
third-party developers to add functionality using any language or environment.
With Tierkreis, quantum software developers can easily build, visualise,
verify, test, and debug complex hybrid workflows, and immediately deploy them
to the cloud or a custom distributed environment.
