Functions

Functions are the fundamental building block of any application in Silicon.

You’ve already seen one of the most important functions in the language: the main function, which is the entry point of many programs. You’ve also seen the fn keyword, which allows you to declare new functions.

Silicon prefers snake case as the conventional style for function and variable names. In snake case, all letters are lowercase and underscores separate words.

src/main.si

extern fn printf(format: string, ...): i32;

fn hello_world() {
    printf("%s\n", "Hello World!");
}

fn main() {
    printf("%s\n", "Calling hello_world function...");
    
    hello_world();
}

Function definitions in Silicon start with fn and have a set of parentheses after the function name. The curly brackets tell the compiler where the function body begins and ends.

We can call any function we’ve defined by entering its name followed by a set of parentheses. Because hello_world is defined in the program, it can be called from inside the main function. Note that we defined hello_world before the main function in the source code.

Function Parameters

Functions can also be defined to have parameters, which are special variables that are part of a function’s signature. When a function has parameters, you can provide it with concrete values for those parameters. Technically, the concrete values are called arguments, but in casual conversation, people tend to use the words parameter and argument interchangeably for either the variables in a function’s definition or the concrete values passed in when you call a function.