[Oberon] Negative integer literals in Oberon

[Andreas Pirklbauer]

   > But I would say that you might want to investigate how the Ada people do it.

Having once been part of an Ada compiler project on VAX/VMS, I can say
that the implementation turned out to be clean, but somewhat complex.

Ada does not provide bit-wise operations (AND, OR, ..) on integer types,
but for so-called “modular types”. A modular type is an integer type with all
arithmetic modulo a specified positive modulus; such a type corresponds
to an *unsigned* type with wrap-around semantics.

See:  http://www.ada-auth.org/standards/12rm/html/RM-4-5-1.html