Oberon-0
In the third and last edition of his book on compiler construction, Wirth replaced PL/0 with Oberon-0. The compiler is still presented in its entirety, although the language Oberon-0 is much more complex than PL/0. For example. Oberon-0 offers arrays, records, type declarations and procedure parameters. The publisher of Wirth's books (Addison-Wesley) has decided to phase out all his books, but Wirth revised the third edition of his book in 2005 and the result is now available online.
Read more about this topic: PL/0