bux-lang/docs/LanguageRef.md

Bux Language Reference

This document describes the Bux programming language as implemented by the bootstrap compiler.

---

Table of Contents

1. Lexical Structure
2. Types
3. Variables
4. Functions
5. Control Flow
6. Structs
7. Enums
8. Pattern Matching
9. Methods and Interfaces
10. Generics
11. Error Handling
12. Modules and Imports
13. Async/Await
14. Operators

---

Lexical Structure

Comments

// Single-line comment

/*
   Multi-line comment
   /* Nested comments are supported */
*/

Identifiers

Identifiers start with a letter or underscore, followed by letters, digits, or underscores.

Keywords

func, let, var, const, type, struct, enum, union, interface, extend
module, import, pub, extern, if, else, while, do, loop, for, in
break, continue, return, match, as, is, null, self, super, sizeof
async, await, spawn

String Literals

"Hello"           // String (UTF-8) — escape sequences: \n \t \r \\ \"
c8"Hello"         // *char8 (C string)
c16"Hello"        // *char16
c32"Hello"        // *char32
`raw literal`     // Raw multi-line string — no escape processing
`line 1
line 2
line 3`           // Newlines preserved as-is

Backtick raw strings (`...`) treat all characters literally:

• \n is two characters, not a newline
• Actual newlines in source are preserved in the string
• No way to escape the backtick character itself (use regular strings if needed)

Number Literals

42        // int
3.14      // float64
0x2A      // hex
0o52      // octal
0b101010  // binary
32i8      // int8 literal
1000u64   // uint64 literal

---

Types

Primitive Types

Type	Description
int8, int16, int32, int64, int	Signed integers
uint8, uint16, uint32, uint64, uint	Unsigned integers
float32, float64	Floating-point
bool, bool8, bool16, bool32	Booleans
char8, char16, char32	Characters
String	C-compatible string (const char*)

Composite Types

*T              // Pointer to T
T[]             // Slice (unsized)
T[N]            // Fixed-size array
(T1, T2, T3)    // Tuple
func(T1) -> T2  // Function type

Structs

struct Point {
    x: int;
    y: int;
}

Enums

enum Color {
    Red,
    Green,
    Blue
}

// Algebraic enum (tagged union)
enum Result {
    Ok(int),
    Err(String)
}

Unions

union Bits {
    asByte: uint8;
    asInt: int32;
}

---

Variables

let x: int = 42;       // Immutable
var y: int = 10;       // Mutable
y = 20;                // OK

const MAX: int = 100;  // Compile-time constant

---

Functions

func Add(a: int, b: int) -> int {
    return a + b;
}

// Extern C function
extern func printf(fmt: *char8, ...);

// Generic function
func Min<T>(a: T, b: T) -> T {
    if a < b {
        return a;
    }
    return b;
}

---

Control Flow

If / Else

if x > 0 {
    PrintLine("positive");
} else if x < 0 {
    PrintLine("negative");
} else {
    PrintLine("zero");
}

Loops

while i < 10 {
    i = i + 1;
}

do {
    i = i + 1;
} while i < 10;

loop {
    // Infinite loop
    break;
}

for i in 0..10 {
    // Range 0 to 9 (exclusive)
}

for i in 0..=10 {
    // Range 0 to 10 (inclusive)
}

Break / Continue with Labels

outer: loop {
    loop {
        break outer;
    }
}

---

Structs

struct Rectangle {
    width: int;
    height: int;
}

func Main() -> int {
    let rect: Rectangle = Rectangle { width: 10, height: 5 };
    PrintInt(rect.width);
    return 0;
}

---

Enums

Simple Enums

enum Color { Red, Green, Blue }

let c: Color = Color::Red;
if c == Color::Red {
    PrintLine("red");
}

Algebraic Enums

enum Result {
    Ok(int),
    Err(String)
}

func Main() -> int {
    let r: Result = Result { tag: Result_Ok };
    r.data.Ok_0 = 42;

    if r.tag == Result_Ok {
        PrintInt(r.data.Ok_0);
    }
    return 0;
}

---

Pattern Matching

match opt {
    Option::Some(value) => PrintInt(value),
    Option::None => PrintLine("none")
}

Supported patterns:

• Wildcard: _
• Literal: 42, "hello", true
• Identifier: name
• Range: 1..9, 1..=9
• Enum destructuring: Shape::Circle(r)
• Struct destructuring: Point { x: 0, y: 0 }
• Tuple: (a, b, c)
• Guard: t if t < 0

---

Methods and Interfaces

struct Rectangle {
    width: int;
    height: int;
}

interface Drawable {
    func Draw(self: Rectangle);
}

extend Rectangle for Drawable {
    func Draw(self: Rectangle) {
        PrintLine("Drawing rectangle");
    }
}

// Or extend with standalone methods
extend Rectangle {
    func Area(self: Rectangle) -> int {
        return self.width * self.height;
    }
}

---

Generics

Generic Functions

Generic functions are monomorphized at compile time. Type parameters can be specified explicitly or inferred from arguments:

func Max<T>(a: T, b: T) -> T {
    if a > b { return a; }
    return b;
}

func Main() -> int {
    // Explicit type args
    let m1: int = Max<int>(10, 20);

    // Type inference — T inferred as int from arguments
    let m2: int = Max(10, 20);
    return 0;
}

Generic Structs

struct Box<T> {
    value: T,
}

// Use extend Type<T> for methods on generic structs
extend Box<T> {
    func Get(self: *Box<T>) -> T {
        return self.value;
    }

    func Set(self: *Box<T>, value: T) {
        self.value = value;
    }
}

func Main() -> int {
    let b: Box<int> = Box<int> { value: 42 };
    PrintInt(b.Get());  // 42
    b.Set(100);
    PrintInt(b.Get());  // 100
    return 0;
}

Note: extend Type<T> syntax requires type parameters on the impl block. The compiler propagates them to each method automatically.

---

Gradual Ownership (Phase 8.2) ✅ Implemented

Bux introduces gradual ownership — opt-in borrow checking. By default, Bux is permissive like C. With @[Checked], the borrow checker enforces memory safety rules.

Syntax

// Default: permissive mode (like C/Nim) — raw pointers, no checks
func QuickSort(arr: *int, len: int) {
    for i in 0..len {
        arr[i] = arr[i] * 2;
    }
}

// Opt-in: @[Checked] enables borrow checking
@[Checked]
func Scale(val: &mut int) {
    *val = *val * 2;  // OK: &mut T allows mutation
}

@[Checked]
func Read(val: &int) -> int {
    return *val;       // OK: &T allows reading
}

@[Checked]
func BadWrite(val: &int) {
    *val = 42;         // ERROR: cannot write through shared reference '&T'
}

Reference types

Type	Syntax	Description
Raw pointer	*T	C-style pointer, no checks
Shared ref	&T	Borrowed reference (read-only in checked functions)
Mutable ref	&mut T	Exclusive mutable borrow (allows mutation)
Owned	own T	Ownership transfer (syntax parsed, not yet enforced)

Rules in @[Checked] functions

• &T cannot be used to mutate data (compile-time error)
• &mut T allows mutation
• *T pointers are unrestricted (escape hatch)
• &mut T coerces to &T and *T

---

Compile-Time Function Execution (CTFE) ✅ Implemented

const func functions are evaluated at compile time. Their results can be used in type sizes, array lengths, or other constant contexts.

const func Factorial(n: int) -> int {
    if n <= 1 {
        return 1;
    }
    return n * Factorial(n - 1);
}

const TABLE_SIZE = Factorial(10);  // 3628800 — computed at compile time

func Main() -> int {
    let arr: [TABLE_SIZE]int;  // Array size from compile-time value
    return 0;
}

Supported in CTFE

• Integer, boolean, and string literals
• Arithmetic (+, -, *, /, %)
• Comparisons and logical operators
• if / else with constant conditions
• Calls to other const func functions (including recursion)

Limitations

• No while / for loops (use recursion)
• No mut references or heap allocation
• No non-const function calls

---

Error Handling

Result and Option Types

enum Result {
    Ok(int),
    Err(String)
}

enum Option {
    Some(int),
    None
}

The ? Operator

The ? operator automatically propagates errors:

func Divide(a: int, b: int) -> Result {
    if b == 0 {
        return Result_NewErr("division by zero");
    }
    return Result_NewOk(a / b);
}

func Compute() -> Result {
    let x: int = Divide(10, 2)?;  // If Err, returns immediately
    let y: int = Divide(x, 5)?;
    return Result_NewOk(y);
}

? can be used on Result and Option types in any expression context.

---

Modules and Imports

// Single import
import Std::Io::PrintLine;

// Multiple imports
import Std::Io::{PrintLine, PrintInt};

// Wildcard import
import Std::Io::*;

// Module declaration
module MyModule;

pub func PublicFunc() -> int {
    return 42;
}

func PrivateFunc() -> int {
    return 0;
}

---

Async/Await

Bux supports stackful coroutines via async/await with a round-robin scheduler.

Declaring Async Functions

async func Compute() -> int {
    PrintLine("step 1");
    bux_async_yield();
    PrintLine("step 2");
    return 42;
}

Spawning Tasks

let handle = spawn Compute();

Awaiting Results

let result: int = handle.await as int;

Full Example

import Std::Io::{PrintLine, PrintInt};

async func Compute() -> int {
    PrintLine("Compute: start");
    bux_async_yield();
    PrintLine("Compute: done");
    return 42;
}

func Main() -> int {
    let h = spawn Compute();
    let r: int = h.await as int;
    PrintInt(r);
    return 0;
}

Runtime Functions

Function	Description
bux_async_yield()	Yield control to the scheduler
bux_async_spawn(fn)	Create a new coroutine from a function
bux_async_await(handle)	Block until coroutine completes, return result
bux_async_run()	Run the scheduler (called implicitly from main)
bux_async_sleep(ms)	Sleep for ms milliseconds (non-blocking)
bux_async_return(value, size)	Copy return value into task result buffer

---

Operators

Arithmetic

+, -, *, /, %, ** (power)

Comparison

==, !=, <, <=, >, >=

Logical

&&, ||, !

Bitwise

&, |, ^, ~, <<, >>

Assignment

=, +=, -=, *=, /=, %=, &=, |=, ^=, <<=, >>=

Other

• as — Cast: expr as Type
• is — Type test: expr is Type
• ? — Try / error propagation: expr?
• & — Address-of: &var
• * — Dereference: *ptr
• :: — Path separator: Module::Name
• .. — Range (exclusive): 0..10
• ..= — Range (inclusive): 0..=10
• sizeof — Size of type: sizeof(Type)