Systems level liveness with extempore

Live programs can be modified while the program is executing in order to provide a more reactive experience for the programmer. In demanding applications, such programs traditionally utilise pre-defined function calls to compiled libraries. We present a system that enables demanding live programs to be built where the supporting stack of libraries is, itself, live. In such situations, the top level code might be thought of as a simple ``live environment'' that can be created live and that encapsulates code that has ``bubbled-up'' from the supporting libraries. Our system enables this bubbling up to be achieved in an ad-hoc way and with minimal performance penalty. The deep, systems-level liveness that it exhibits is described and compared with other approaches to Live Coding and liveness generally. The work described here has its origins in the artistic Live Coding of computer music and multimedia. We also discuss its wider uses including the development of interactive multimedia installations and the harnessing of scientific simulation.