Skip to content

Component variables

Component variables extend a component's state space. They can store messages and intermediate computation results to record state that is maintained across individual execution steps.

Component variables are declared directly within the body of a component. The declaration of a component variable specifies the variable's type, states its name, and assigns its initial value. A component-variable declaration looks like 

TYPE NAME = INITIAL;

where

  • TYPE is the variable's data type (reference)

  • NAME is the variable's name (defining)

  • INITIAL is an expression defining the variable's initial value

For example,

component SumUp {
  port in int i;
  port in Signal r;
  port out int o;

  int sum = 0;

  automaton {
    initial state S;
    S -> S i / {
      sum = sum + i;
    };
    S -> S r / {
      o = sum;
    };
  }
}

calculates the sum over past inputs using component variable sum of type int. The variable's initial value is 0. Every time the component receives a message on port i it adds it to the value of sum and stores the new value in variable sum. When the component receives a message on port r it outputs the total sum calculated so far on port o.