A considerable amount of implementation work is saved by re-using an existing implementation (the XLISP interpreter). The remaining implementation work is comprised by extending the XLISP interpreter for TCAD purposes and by adding interfaces to all framework components and applications. C code can be added to the XLISP interpreter in a very systematic way. From a historical perspective, the first extension that has been made was a prototype interface to the X Toolkit and Athena widget set, which was followed by the execution of external tools (simulators), coded in LISP, and finally an automatic integration support system for linking C-coded functions has been developed.