There are two types of Tyl programs:

• without functions
• with functions

Tyl program without functions is a program that does not have any function in it. In most of the examples in the guide, there are no functions, and they are valid Tyl programs that can run successfully.

Tyl program with functions is a program that has at least one function in it. In functions page, there are examples of programs with functions.

Tyl system gives the programmer the ability to choose between the two options, thus enabling a functionless programming. If you have only activities that are to occur in one function, than there is no need for that function at all, and the module (program) itself is the function.

Tyl program structure:


Tyl program has two optional sections:

• statements
• functions

If the module (program) is functionless, it has only a module statements section that is composed of Tyl statements, such as declaration, assignment, conditional and looping. If it has functions, than module statements section is optional, and the module functions section, that is always after the module statements section, will be composed of functions with their statements.

Say we want to implement traffic lights activity:

A full cycle is shown from first stand to last stand.

Though it works, a better idea is to use an indices list and iterate over it:

indices list holds the scenario of the activity, and if it is only for that scenario, than the program implements it without using any function. So the program has only module statements, and when the program runs, it runs all the statements in it, and that's all program activity.

What if we want to deal with some scenarios?

Obviously, repeating the looping statements in code is tedious and awkward. So in this case we would gather all code that should be repeated in functions:

go function was declared, that plays two scenarios, and play function was declared, that holds scenario functionality. In Tyl, if a program has functions, the system locates the first function. If the first function does not have parameters, the system will run it. go function is the first function in the program, and is parameterless so Tyl system will run it. So in this type of Tyl program, it has functions, and the program runs the first of them.

If we look closely on play function, we can see that it holds actions and lights lists, and declares them each time the function is activated. Usually, when there are static variables in a program, or if there are variables that are used in various places in the program, they should be declared outside any function.

Therefore we will modify the program (including structure comments):

All declarations were moved to module statements section. On program run, these statements will be run first, than go function will run. The result of this program will be the same, but it will work more efficiently, and the variables that were declared in module statements can be used anywhere in the program.