CIF 3

Parametrized automaton definitionsΒΆ

In the previous lesson, automaton definition/instantiation was used to obtain two identical automata, while only having to specify their behavior once. What we have seen so far, is enough for exactly identical automata, but not for nearly identical automata. Consider the following two nearly identical consumers:

automaton consumer1:
  disc list int buffer = [];

  location:
    initial;
    edge provide? when size(buffer) < 2 do buffer := buffer + [?];
end

automaton consumer2:
  disc list int buffer = [];

  location:
    initial;
    edge provide? when size(buffer) < 3 do buffer := buffer + [?];
end

The consumers can accept products that the producer provides (channel provide). They store the identification numbers of those products in a buffer. The two consumers are identical except for the number of products that they can accept: the first consumer can accept two products, the second producer can accept three products. We can still use automaton definition and instantiation to model the consumer only once, but we need to parametrize the automaton definition:

automaton def Consumer(alg int capacity):
  disc list int buffer = [];

  location:
    initial;
    edge provide? when size(buffer) < capacity do buffer := buffer + [?];
end

consumer1: Consumer(2);
consumer2: Consumer(3);

The Consumer automaton definition now has a parameter named capacity that indicates how many identification numbers can be stored in its buffer. The automaton instantiations consumer1 and consumer2 provide an argument (2 and 3 respectively) to match the parameter of Consumer. That is, the instantiations indicate their capacity. Using parameters, the Consumer automaton definition models the behavior of both automata consumer1 and consumer2, even though they have different capacities.

The details of the different kind of parameters of automaton definitions are explained in the next lesson.