Hello, World!

Now that you’ve installed the Zirco toolchain, let’s write our first Zirco program! As is tradition, we’ll write a simple program that simply prints “Hello, World!” to the screen.

Project Setup

Zirco’s compilation unit is the file, similar to C. There is no first-class concept of a “project”. This comes with the benefit of placing your source files wherever you want!

To create a Zirco source file, simply create a new file with the .zr extension. It is typical to call the main source file main.zr.

Filename: main.zr

#include <libc/stdio.zh>
fn main() -> i32 {
    printf("Hello, World!\n");
    return 0;
}

Save the file and run the following commands to compile, link, and run the program:

$ zrc main.zr -o main.o
$ ld -lc -lzr main.o -o main
$ ./main
Hello, World!

If you see “Hello, World!” printed to the terminal, congratulations! You’ve successfully written and run your first Zirco program! If you don’t see the expected output, take a look at the installation troubleshooting section.

Anatomy of the Program

Let’s break down the main.zr program to understand what each part does:

#include <libc/stdio.zh>

This line includes the Zirco header file for the C standard library (libc)’s Standard I/O functions. This directive is used to “copy-paste” the contents of a file into another, similar to C’s #include directive. If you check your toolchain’s include/libc/stdio.zh file, you’ll see that it contains “extern” declarations for a bunch of functions, including printf and scanf which we later use.

fn printf(a: *u8, ...) -> i32;
fn scanf(a: *u8, ...) -> i32;

These functions are not defined in Zirco, but they exist here so the compiler is aware of their signatures and can generate the correct code to call them.

fn main() -> i32 {

This line defines a function named main that takes no parameters and returns an i32 (32-bit integer). The main function is the entry point of the program, where all Zirco programs start execution. The function’s return value represents its exit code, where 0 typically indicates success.

    printf("Hello, World!\n");

This line calls the printf function to print the string “Hello, World!” followed by a newline character (\n) to the terminal.

    return 0;
}

This line returns 0 from the main function, indicating that the program executed successfully.

Using the zrx Tool

Oftentimes, for one-off programs (such as many of the examples in this book), it’s more convenient to compile and run the program in one step. The zrx tool does exactly this: it compiles, links, and runs your program with a single command via a JIT.

To run your main.zr program with zrx, simply run the following command:

$ zrx -lzr main.zr
Hello, World!

Many larger Zirco projects choose to use a build system such as make.

Congratulations!

In subsequent chapters, we’ll cover the Zirco language in more depth, but for now, your toolchain is working and you can write and run Zirco programs! In the next chapter, we’ll cover the basics of the Zirco language and syntax.