12. Using the Library

When programmer make use of a given function in different programs, rather than redefining it in each program they write, they put them in special programs called libraries and they have a way to ensure that their other programs can use the functions that are found in the library.

You are going to use the function turn_right() a lot! Instead of rewriting it each time (remember Rule # 3), what you are going to do is to write it once (more) but, this time, instead of writing it in the editor with the Javascript Code tab, you will click on the Library tab and write it there. Oh, and you should also write turn_around() there as well.

Then, when you want to use the functions defined in your library, you will simply type import_lib() in the Javascript Code editor.

Do this!

After writing the functions turn_right() and turn_around() in the library, go back to the Javascript Code editor (so you no longer see your functions) and write a short program that nonetheless uses them to make sure that they work as expected. If they don’t, go back and fix them. Remember to use import_lib() in your main program.

Hint

With the appropriate functions defined in the library, here is such a program:

import_lib();
move();
turn_around();
move();
turn_right();
move();
turn_around();
move();
turn_left();  // back at starting position

From now on, whenever you define a function that you use more than once, add it to your library so that you don’t have to redefine it every time.

12.1. Reading exercise

Remember the following?

Important

Rule # 2

Write your computer programs to make them easy for people to read and understand.

Can you figure out on your own what the following program does, without copying it in the editor and having Reeborg obey the instructions?:

function a () {
    turn_left();
    turn_left();
}

function b (){
    turn_left();
    a();
}

function c (){
    move();
    move();
}

function d (){
    c();
    b();
}

function e () {
    d();
    d();
    d();
    d();
}

turn_left();
e();
b();

Not so easy, is it?

Test it!

Once you think you have figured out what the above code does, copy it in the editor and run it to confirm your understanding.

This should help you to understand why it is important to write programs for humans, by choosing function names that are meaningful.