Writing your first Ybixo program

As is tradition, we'll begin learning Ybixo with the "Hello, World!" program.

Create an empty directory to work on the programs in this book. Inside this new directory, create a new file called hello_world.ob. Enter the following text into the file:

// File: examples/chapter_01_first/hello_world.ob

// Welcome to Ybixo!
fn main() {
    print_line("Hello, World!")
}

Use the Ybixo compiler to run the program and see its output:

$ obc run hello_world.ob
Hello, World!

Remember this command because we'll use it a lot.

This simple program teaches us a few things about Ybixo.

Comments

Two slashes (//) begin a comment. Any text afterwards on the same line will be ignored by the compiler and removed from the Ruby source code produced.

String literals

"Hello, World!"

Strings, sequences of textual characters, are created by writing the text inside a pair of double quotes.

"Literal" just means that there is dedicated syntax in the language to construct a string. There are other kinds of literals for different types in the language, such as integers (e.g. 123) and boolean values (i.e. true and false).

Functions

fn example() {
    expression
}

Functions are declared with the keyword fn, followed by a function name, a pair of parentheses, and a function body inside curly braces. The body is a sequence of zero or more expressions. An expression is anything that can be reduced to a single value.

In our program, main has a body consisting of one expression.

Calling functions

print_line("Hello, World!")

A function is called by writing its name followed by any function arguments in parentheses. An argument is input to the function that changes how it behaves.

Writing to stdout

The function print_line is used to write text to the standard output.

This is what causes "Hello, World!" to appear in the terminal when we run our program.

The main function

When the program runs, if a function named main is defined, it will be automatically executed.