Introduction

Yagbas is a programming language that builds programs for the Game Boy, as well as for the other compatible devices: the Game Boy Pocket, Super Game Boy, and Game Boy Color. A lot of useful documentation for this device family can be found in the Pan Docs.

Because of the limited nature of the Game Boy's CPU instruction set, Yagbas does not aim to be a "general purpose" programming language. Instead, it is intended to be close to "assembly with modern syntax".

The language is intended to "look like Rust", when possible.

Language Reference

Tokens

Comments

Multi line comments start with /* and end with */. They can be nested within each other.

/* multi line
comment */

Single line comments start with // and go to the end of the line.

// single line comment

A single line comment marker takes priority over multi line comment markers, and will "comment out" a multi line comment open or close marker that appears after it on the same line.

Registers

a / A
f / F
b / B
c / C
d / D
e / E
h / H
l / L
af / AF
bc / BC
de / DE
hl / HL

Conditions

Conditions can similarly be all lowercase or all caps

c / C
z / Z
nc / NC
nz / NZ

Note that c is both a register name and a condition name. The meaning of the token is always sufficiently clear from the surrounding context.

Keywords

All other keywords only allow a lowercase spelling

break
const
continue
fn
loop
return
static

Numbers

Numbers can be written in decimal, hexadecimal, or binary.

Decimal numbers must start with a digit.
Hexadecimal numbers are prefixed with $
Binary numbers are prefixed with %

123
$AB12
%101011

Underscores can be used within a number literal, and they don't affect the value the literal represents.

1_234 == 1234

Identifiers

Identifiers in Yagbas work essentially like Rust and C style identifiers.

They must start with an underscore or an ascii letter.
They can contain underscores, ascii letters, or digits.
They can't be any other keyword, such as a, nz, or break.

Token Tree Groupings

Certain punctuation will open and close a "token tree" group.

( and )
{ and }
[ and ]
/* and */

Token trees can contain inner token trees, but the group markers must balance out. If they are unbalanced then essentially the entire rest of the file cannot be processed by the parser.

Items

Items are defined at the top level of a source file.

The order that items are defined in has no effect.

Functions

Functions define executable code that runs as part of the program.

fn NAME() {
  // statement 1
  // statement 2
  // ...
  // statement n
}

Each function has a name and a body. The body of the function contains the statements to execute in order to make the program do whatever it's supposed to.

Statements are written one per line. If more than one statement is desired on the same line then a ; can be used, but this is not the standard style.

Statements

Calls and Returns

Function calls are written with the name of the function call followed by parenthesis.

some_function()

A function returns to its caller with the return keyword.

return

Loop, Break, and Continue

A loop is used to execute a block of statements over and over.

loop {
  // statement 1
  // statement 2
  // ...
  // statement n
}

Within a loop, the break keyword can be used to skip the rest of the loop body and jump to after the loop. Similarly, the continue keyword can be used to jump back to the start of the loop body. When one loop is contained in another, break and continue go to the end or start of the innermost loop.

Loops can optionally have a name given to them:

'name: loop {
  // ...
}

When a loop has a name, then break and continue can go to the end or start of that loop by giving that name after the keyword.

'foo: loop {
  loop {
    break 'foo // this goes to the end of the "foo" loop
  }
  return // this line is skipped by the `break` above.
}

This allows the program to jump from one loop nested inside of another "all the way" to the start or end of an outer loop.

The break and continue keywords cannot be used outside of a loop.

Yagbas Language Reference