  We present a new abstract machine, called DCESH, which describes the
execution of higher-order programs running in distributed architectures. DCESH
implements a generalised form of Remote Procedure Call that supports calling
higher-order functions across node boundaries, without sending actual code. Our
starting point is a variant of the SECD machine that we call the CES machine,
which implements reduction for untyped call-by-value PCF. We successively add
the features that we need for distributed execution and show the correctness of
each addition. First we add heaps, forming the CESH machine, which provides
features necessary for more efficient execution, and show that there is a
bisimulation between the CES and the CESH machine. Then we construct a
two-level operational semantics, where the high level is a network of
communicating machines, and the low level is given by local machine
transitions. Using these networks, we arrive at our final system, the
distributed CESH machine (DCESH). We show that there is a bisimulation relation
also between the CESH machine and the DCESH machine. All the technical results
have been formalised and proved correct in Agda, and a prototype compiler has
been developed.
