I have been following the development of Oberon-07 (and submitted minor fixes to Prof. Wirth) over the years. The compiler's source code is the fruit of refinements and simplifications accumulated over 30+ years (more if you include his compilers for previous languages). His approach for compiler writing, and system design in general, is outstanding. For more information about his compilers see "Compiler Construction - The Art of Niklaus Wirth" [0]

[0] http://oberon2005.oberoncore.ru/paper/art3.pdf