We introduce OM-Faust, an OpenMusic library including objects and functions to write, compile and control Faust programs. Faust is a domain-specific functional programming language designed for DSP. The integration of Faust in OpenMusic enables composers to program and compile their own audio effects and synthesizers, controllable both in real-time or deferred time contexts. This implementation suggests a more general discussion regarding the relationship between real-time and off-line processing in computer-aided composition.