1. An embeddable execution engine for embedding in a host process that executes under the control of a programming language subsystem and includes a host interface, the embeddable execution engine comprising: a command unit configured to receive a command from the host process via the host interface to execute a first sequence of instructions in said execution engine in a controlled mode; an execution unit configured to interpret the first sequence of instructions indicated by the command into instructions for execution by a processor until detecting either a break event or an instruction to perform a remote procedure call; and a host call unit configured to call a first procedure in the host interface to handle the break event, if detected, and to call a second procedure in the host interface to handle the instruction to perform a remote procedure call, if detected, wherein the execution unit functions as the programming language subsystem for the host process when the embeddable execution engine is embedded in the host process.