Non-Regular Process Types

                          Franz Puntigam
    Institut für Computersprachen, Technische Universität Wien
           Argentinierstraße 8, A-1040 Vienna, Austria
             E-mail: franz@complang.tuwien.ac.at

Process types specify sequences of acceptable messages. Even if the set
of acceptable messages changes dynamically, a type checker can statically
ensure that only acceptable messages are sent. As proposed so far, all
message sequence sets specified by types can be generated by regular
grammars. We propose to increase the expressiveness so that non-regular
message sequence sets can be specified. Type equivalence and subtyping
take possible type extensions into account.

Keywords: type systems, subtyping, active objects