Separate Compilation is currently considered impossible for Modelica in practice; because several features of stateof-the-art Modelica compilers currently rely on global information. One prominent example for those features is causalization. This particular feature is very important for the generation of fast simulation code. In this work we show how a post-compilation causalization can fit into the operational semantics of a language like Modelica. We present the semantics of a causalizing language system are together with a prototype. This prototype shows that separately compiled models can form a causalized; thus fast; simulation program.