The LISP interface of the PAI is not built on top of the application layer, since it makes no sense to use LISP for computationally intensive calculations on PIF data. The extension language of the task level is primarily used to generate input PLBs and control information for TCAD tools or to read output values of simulation results for further investigations. Thus the extension language interpreter connects to the interface layer, allowing full access to PBFs. For convenience there is an additional LISP library to support the creation of whole PIF constructs (like generated with the application layer).
Functions of the PIF ToolBox and the high-level libraries are automatically bound to LISP through the Tool Abstraction Concept (TAC) and thus are immediately available to the TCAD shell. The big difference between Application Layer functions and ToolBox functions is that the second get their input from the PLB and write their output back to the same or another PLB. No data manipulation is done in LISP.