Hello World

Traditionally, the very first program you write when learning a new programming language is one that prints “Hello, World!” to the screen. In Inference, however, we do not have built-in string and printing functionality. Instead, we will write a simple program that returns a magic number from a function. Later, by executing this program, we will see the result in the terminal.

Writing the Program

First, we need to create a new file for our program. Inference uses the .inf file extension for its source code files. Create a new file named hello_world.inf and open it in your favorite text editor. Then, add the following code to the file:

pub fn hello_world() -> i32 {
    return 42;
}

This code defines a function named hello_world that takes no parameters and returns a 32-bit signed integer (i32). The function simply returns the number 42.

Understanding the Code

Let’s break down the code to understand its components:

• pub is a visibility keyword that marks the function as exported from the compiled WebAssembly module, making it callable from outside;
• fn is a keyword used to define a function in Inference;
• hello_world is the name of the function;
• () is a pair of parentheses that groups the function parameters. In this case, there are no parameters;
• -> reads as “right arrow” and indicates the return type of the function;
• i32 specifies that the function returns a 32-bit signed integer;
• return is a keyword used to return a value from a function;
• 42 is the integer value (or literal) being returned by the function.

In the appendix, Language Reference, you can find more information about Inference keywords and data types.

Compiling the Program

To compile an .inf file into a WebAssembly module, use the infs build command. Open your terminal, navigate to the directory where you saved hello_world.inf, and run the following command:

On Linux or macOS:

$ infs build hello_world.inf

On Windows:

> infs build hello_world.inf

The compiler will generate a WebAssembly binary module at out/hello_world.wasm.

Note

You can also use the infc compiler directly as an alternative:

$ infc hello_world.inf

Both commands produce the same output.

Running the Program

To execute the compiled WebAssembly module, we can use any preferred Wasm runtime. In this example and throughout this book, we will use wasmtime, a popular and easy-to-use Wasm runtime. You can install and learn more about wasmtime from its official website.

Once you have wasmtime installed, you can run the compiled module using the following command:

On Linux or macOS:

$ wasmtime out/hello_world.wasm --invoke hello_world

On Windows:

> wasmtime out/hello_world.wasm --invoke hello_world

As a result, you will see the output 42 printed in the terminal, which is the value returned by the hello_world function.

Congratulations! You have successfully written, compiled, and executed your first Inference program. In the next chapters, we will explore more features of the Inference programming language.