Expressions

Expressions are combinations of variables, literals, operators, and method invocations that evaluate to a single value. They are used throughout the language, such as in arguments for component instantiations, in guards of transitions, and as part of statements in the actions of automata.

Context & Setup

To illustrate how expressions work, assume the following types are defined:

  public class Person {
    public int age;
    public String name;
    public Role role;
    public String getFullName();
  }

  public class Role {
    public int id;
  }

And imported into your current model:

import montiarc.types.Person;
import montiarc.types.Role;

Working with Objects

The following examples demonstrate how to use expressions to create objects, access fields, and invoke methods.

// 1. Object Creation
// Declares a variable 'p' of type Person and evaluates the creation expression
Person p = Person.Person();

// 2. Field Access & Assignment 
// Accesses fields on variable 'p' and assigns new values to them
p.age = 35;
p.name = "Max";

// Creates a new Role object and assigns it to the 'role' field
p.role = Role.Role();

// Chained field access: accesses the 'id' field of the 'role' field
p.role.id = 5; 

// 3. Field Reading
// Accesses the 'age' field and stores its evaluated result in a new variable
int currentAge = p.age;

// 4. Method Invocation
// Invokes the getFullName() method on the object referenced by 'p'
p.getFullName();

Operators

The language supports standard mathematical, assignment, comparison, and logical operators.

Arithmetic Operators

Arithmetic operators perform mathematical calculations and evaluate to a numeric value.

Operator	Name	Example
+	Addition	a + b
-	Subtraction	a - b
*	Multiplication	a * b
/	Division	a / b
%	Modulo	a % b

Assignment Operators

Assignment operators evaluate the right side and assign the resulting value to a variable on the left side, or send a message via a port.

Operator	Example	Abbreviation for
=	a = b
+=	a += b	a = a + b
-=	a -= b	a = a - b
*=	a *= b	a = a * b
/=	a /= b	a = a / b
%=	a %= b	a = a % b

Comparison Operators

Comparison operators compare two evaluated values and return a Boolean (true or false).

Operator	Name	Example
==	Equal to	a == b
!=	Not equal to	a != b
>	Greater than	a > b
<	Less than	a < b
>=	Greater than or equal	a >= b
<=	Less than or equal	a <= b

Logical Operators

Logical operators operate strictly on Boolean values and evaluate to a Boolean result.

Operator	Name	Example
&&	Logical AND	a && b
| |
!	Logical NOT	!a