Functions

A function declaration looks like

fn NAME() {
  // statements here
}

The fn keyword marks the start of a function.

Next is an identifier that names the function, followed by an empty set of parentheses. Future versions of the language may put things into the parentheses, but in the current version they are always empty.

Finally, we have a set of braces around the code of the function.

The conventional code style for functions is as follows:

• Names are snake_case
• Indentation is 2 spaces
• The opening brace is on the same line as the function name

fn main()

The main function has a special meaning.

After booting, the Game Boy jumps to the "Entry Point" of the ROM ($0100) and begins running there. However, the entry point can only be 4 bytes long, because after that is the rest of the ROM header rather than meaningful instructions. The Entry Point is expected to jump to the actual beginning of the program.

The yagbas compiler always uses di; jp main as the effective code for the entry point. If your program does not include a main function, compilation will cause an error.