3.6 Implementation of VISTA/SFC

 

All modules of the VISTA/SFC environment are coded in VLISP and are run by the VLISP interpreter  of the VISTA framework. The entire VLISP code amounts to approximately 1.8 megabyte of ASCII source text, 1 MB being attributed to the implementation of the core functional modules shown in Figure 3.1 and 0.4 MB each being alloted to the interfaces for currently integrated external tools and to basic functionality for GUI generation, system interface, message handling, and resource handling. Figure 3.2 gives an overview of the various VLISP modules constituting the simulation environment.

 
Table 3.2:   VISTA/SFC VLISP modules.

VLISP was chosen as the implementation language for a variety of reasons that are related to the LISP language itself [WH89], to the XLISP implementation [Bet89], and to various extensions available in VLISP. The following list highlights those aspects that were relevant in the decision process in the context of the VISTA/SFC environment.

• Interpreter allows fast prototyping and code-update and code-reload during sessions.
• Automatic memory management supports problem-oriented programming.
• Run-time code generation capability
• Built-in debugging interface facilitates code development and debugging.
• Runs on various operating systems and platforms.
• Vienna Operating System (VOS)  provides powerful support for file handling and process management tasks in an operating-system independent way.
• Vienna User Interface library (VUI)  provides high-level functionality for defining
  graphical user interfaces quickly and comfortably.
• Built-in error handling and error message system standardizes error handling.
• Built in object classes support object-oriented design.
• Multiple inheritance facilitates the reuse of object classes spread across different
  modules.
• PIF Application Interface (PAI) [FFS91] [Fas94] provides direct access to simulation data stored in PIF format.
• Easily extensible by binding external functions and libraries coded in C or C++ to the interpreter automatically using the Tool Abstraction Concept (TAC).
• Built-in regular expression library simplifies text-based data exchange.
• Byte-code compiler increases speed of execution and enforces syntax and type checking at compile-time.
• Variety of additional LISP data types improve code quality and form basis for compile-time and run-time type checking. Type-specific print and read routines liberate the programmer from handling different types explicitly. Some examples of valuable data type extensions are given in Table 3.3.

 
Table 3.3:   Selected VLISP data types.