Chapter 3: Understanding Cyclone

In this Chapter, we will explain some of the Cyclone language features in detail. This may help you to understand Cyclone better for building your models.

3.1 Variable Types

The value of a variable in Cyclone can be changed from state to state. In the current version of Cyclone, there are five types of variable a user can use.

• int
• real
• bool
• enum
• record

Integer

An integer type variable is declared using keyword int. The range of an integer is the same as the those integers in a general purpose programming language such as Java and C++. That is from -2147483648 to 2147483647. For example, the following piece of code creates an integer type variable called x, and this x is initialized with value of 0.

   int x=0;

Real

A real type variable is declared using keyword real. The range of a real number is from about 3.40282347x1038 to 1.40239846x10-45. For example, the following piece of code simply creates a real number of x,

   real x=-2.32;

When Cyclone produces a trace that has real numbers, by default two digits after a decimal point are preserved. However, one can set a different precision through an option. For example, the following option tells the compiler to preserve 4 digits (after a decimal point) during trace generation.

   option-precision=4;

Currently, Cyclone can preserve 1-6 digits after a decimal point for a real number.

Bool

A bool type variable is declared using keyword bool. Only boolean-typed values (true and false) can be assigned to a bool type variable. For example, the following initialization of a boolean variable is illegal.

   bool b=x+3; //illegal

Enum

An enum type variable is used for a set of predefined constants. This is done through using enum. An enum variable must be equal to one of the predefined constants. You can use a # to assign an enum variable to one of its predefined constants. For example, the following piece of code assigns a constant ON to the variable switch.

   enum {ON, OFF} switch=#ON;

Constant

A constant in Cyclone is very much the same as constants in other programming languages. That is once a constant is defined its value cannot be changed from state to state. To declare a constant data type, one can use the keyword constant. For example, the following code declares 3 different kinds of constants.

 const int A = 3;
 const real PI = 3.1415926;
 const bool B = true;

An enum type is a special constant. Thus, it cannot be declared using the keyword constant.

Record

A record type in Cyclone is a complex data type. It allows users to use a mix of different data field in a single data type. Currently, a user can declare the integer, real, bool and enum data fields within a record. For example, the following record creates a point that contains two integer fields:

 record point {
     int x;
     int y;
   };

We use a dot operator (.) to access its field just like other programming languages. Thus, the following code assigns a 0 to the field x in point.

 point.x = 0;

Each data field declared inside a record type can be associated with a where clause. A field is associated with a where clause is a conditional field (variable). See below.

Conditional Variables

In Cyclone, users can use a special type of variable called conditional variable to build their models. So what is a conditional variable ?

In short, a conditional variable is a variable that is attached to a boolean condition. During computation, a conditional variable must meet the attached condition. Conditional variables are quite useful for limiting the range of a variable. To create a conditional variable, users can create a normal variable first and then use a where clause to specify a condition. For example, the following piece of code creates a conditional variable x

 int x = 1 where x <= 0 && x >= 3;

This variable x is a conditional variable. It is initialized with a value of 1 and attached to a condition: it must stay between 0 and 3 during the computation.

There are some rules when creating a conditional variable:

• where clause can only specify a boolean condition.
• where clause cannot be used for a constant including enum data type.
• The condition described by the where clause cannot use other variables except for itself or a constant.

For example, the following conditional variables are illegal in Cyclone.

 int x where x = x+1; //not a boolean condition
 int y where y > x;//refer to another variable x
 const int z where z > 2;//z is a constant

Semantically speaking, the condition specified by a conditional variable must hold in any computation. This includes each computation in every node/state including initial node/state.

The following piece of code shows a valid conditional variable in use of computing an area of a circle.

 const real PI=3.14159;
 const int MAX=15;
 const int MIN=7;
 int r where r >= MIN && r <= MAX;
 real area = PI * r * r;

During any computation, the variable r must stay between 7 and 15.

3.1.7 Fresh Variables

To keep the design of Cyclone simple, all variables declared in Cyclone are visible to every node/state. Thus, every node/state can use a variable for its own computation. However, sometime we would like to use a variable that does not depend on other states. In other words, this variable is state independent. A user can use fresh variables for state independent variables.