sx/readme.md

sx

An experimental systems programming language with Jai-inspired syntax, compile-time execution, generics, closures, protocols, and an LLVM backend.

Status: Highly experimental. The language and compiler are under active development.

At a Glance

#import "modules/std.sx";

Point :: struct {
    x, y: s32;
    magnitude :: (self: *Point) -> f32 { sqrt(self.x * self.x + self.y * self.y); }
}

main :: () {
    p := Point.{ x = 3, y = 4 };
    print("point: {}, magnitude: {}\n", p, p.magnitude());
}

Key characteristics:

• Jai-inspired declaration syntax: name :: value for constants, name := value for variables
• Compiles to native code via LLVM 19
• Compile-time execution with #run
• Generics via monomorphization
• First-class closures with value capture
• Protocol-based polymorphism (traits)
• Pattern matching on enums, optionals, and type categories
• C interop via #foreign and #import c
• Targets: macOS (ARM64, x86_64), Linux (x86_64, ARM64), Windows (x86_64), WebAssembly

Building

Requires Zig 0.16+ and LLVM 19+.

zig build

On macOS with Homebrew LLVM:

# default path: /opt/homebrew/opt/llvm@19
zig build

Custom LLVM path:

zig build -Dllvm-prefix=/path/to/llvm

Usage

sx run file.sx           # compile and run
sx build file.sx         # compile to binary
sx build file.sx -o out  # compile with output path
sx ir file.sx            # emit LLVM IR
sx lsp                   # start language server

Options:

--target <triple>   target platform (shortcuts: macos, linux, windows, wasm)
--opt <level>       optimization: none, less, default, aggressive
--cpu <name>        target CPU
-o <path>           output path

Language Overview

Types

Type	Description
s8..s64, u8..u64	Signed/unsigned integers (default: s64)
f32, f64	Floating point (default: f32)
bool	true / false
string	UTF-8 fat pointer {ptr, len}
[N]T	Fixed-size array
[]T	Slice (fat pointer)
*T, [*]T	Single / many pointer
?T	Optional
struct, enum, union	Composite types
Closure(args) -> ret	Closure type

Numeric limits. A field-like access on a builtin integer type name folds to a compile-time constant of that type: s64.max → 9223372036854775807, u8.min → 0, s3.max → 3. It works for every width s1..s64 / u1..u64 plus usize/isize, and is usable anywhere a constant of that type is — including array dimensions ([u8.max]T is a 255-element array).

Declarations

// Constants (compile-time when possible)
PI :: 3.14159;
MAX : s32 : 100;

// Variables (mutable)
x := 42;               // inferred type
y : s32 = 0;           // explicit type
z : s32 = ---;         // uninitialized

Builtin type names (s2, u8, bool, string, …) are reserved and can't be used as bare value identifiers. A leading backtick escapes one into a raw identifier — its text drops the backtick and it's never read as a type — so reserved spellings (and keywords) work as ordinary names:

`s2 := 2.5;            // value identifier "s2", distinct from the s2 type
print("{}\n", `s2);    // 2.5

Foreign declarations from #import c { … } are exempt automatically: C names that collide with reserved type names (e.g. s1, s2) import unedited.

Structs

Vec3 :: struct {
    x, y, z: f32;

    length :: (self: *Vec3) -> f32 {
        sqrt(self.x * self.x + self.y * self.y + self.z * self.z);
    }
}

v := Vec3.{ x = 1, y = 2, z = 3 };
v2 := Vec3.{ 1, 2, 3 };              // positional
print("{}\n", v.length());

Structs support field defaults, #using for composition, and methods defined in the body.

Enums (Tagged Unions)

Shape :: enum {
    circle: f32;
    rect: struct { w, h: f32; };
    none;
}

area :: (s: Shape) -> f32 {
    if s == {
        case .circle: (r) => 3.14159 * r * r;
        case .rect: (r) => r.w * r.h;
        case .none: 0;
    }
}

Flag enums with power-of-2 values:

Perms :: enum flags { read; write; execute; }
rw := Perms.read | Perms.write;

Optionals

x: ?s32 = 42;
y: ?s32 = null;

val := x ?? 0;          // null coalescing
forced := x!;           // force unwrap (traps on null)

if v := x {             // safe unwrap
    print("{}\n", v);
}

// Optional chaining
node: ?Node = get_node();
name := node?.name ?? "unknown";

Generics

max :: (a: $T, b: T) -> T {
    if a > b then a else b;
}

List :: struct ($T: Type) {
    items: [*]T;
    len: s64;

    append :: (self: *List(T), item: T) { ... }
}

Generic constraints via protocols:

are_equal :: ($T: Type/Eq, a: T, b: T) -> bool { a.eq(b); }

Closures

make_adder :: (n: s64) -> Closure(s64) -> s64 {
    closure((x: s64) -> s64 => x + n);
}

add5 := make_adder(5);
print("{}\n", add5(100));   // 105

Closures capture by value. Bare functions auto-promote to closures when needed.

Protocols

Drawable :: protocol {
    draw :: (x: s32, y: s32);
}

impl Drawable for Circle {
    draw :: (self: *Circle, x: s32, y: s32) { ... }
}

shape : Drawable = xx my_circle;   // type erasure via xx
shape.draw(10, 20);                // dynamic dispatch

#inline protocols store function pointers directly (no vtable indirection):

Allocator :: protocol #inline {
    alloc :: (size: s64) -> *void;
    dealloc :: (ptr: *void);
}

Pattern Matching

// On enums
if shape == {
    case .circle: (r) => print("radius: {}\n", r);
    case .rect: (r) => print("{}x{}\n", r.w, r.h);
    case .none: print("nothing\n");
}

// On optionals
if opt == {
    case .some: (val) => use(val);
    case .none: fallback();
}

// On type categories (via Any)
if type_of(val) == {
    case int: print("integer\n");
    case string: print("string\n");
    case struct: print("struct\n");
}

Control Flow

// Chained comparisons
if 0 <= x <= 100 { ... }

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

// For (arrays and slices)
for items: (val) { print("{}\n", val); }
for items: (val, idx) { print("[{}] = {}\n", idx, val); }

// Defer
f := open("file.txt");
defer close(f);

// Multi-target assignment (atomic swap)
a, b = b, a;

Pipe Operator

result := data |> parse() |> transform() |> serialize();
// equivalent to: serialize(transform(parse(data)))

Compile-Time Execution

// Evaluate at compile time
FIBONACCI_10 :: #run fib(10);

// Generate code at compile time
#insert #run generate_lookup_table();

C Interop

Foreign functions:

libc :: #library "c";
printf :: (fmt: [:0]u8, args: ..Any) -> s32 #foreign libc;
write_fd :: (fd: s32, buf: [*]u8, count: u64) -> s64 #foreign libc "write";

Direct C header import:

#import c {
    #include "vendors/mylib/api.h";
    #source "vendors/mylib/impl.c";
};

Modules

#import "modules/std.sx";              // flat import
math :: #import "modules/math.sx";     // namespaced import

Implicit Context

Every program gets an implicit context with a default allocator:

// No boilerplate needed — context is auto-initialized
main :: () {
    list := List(s64).create();   // uses context.allocator
    list.append(42);
}

// Override allocator for a scope
push Context.{ allocator = my_arena } {
    do_work();  // all allocations use my_arena
}

Quick Sort Example

#import "modules/std.sx";

quick_sort :: (items: []$T) {
    partition :: (items: []T, lo: s64, hi: s64) -> s64 {
        pivot := items[hi];
        i := lo - 1;
        j := lo;
        while j < hi {
            if items[j] < pivot {
                i += 1;
                items[i], items[j] = items[j], items[i];
            }
            j += 1;
        }
        i += 1;
        items[i], items[hi] = items[hi], items[i];
        i;
    }

    sort :: (items: []T, lo: s64, hi: s64) {
        if lo < hi {
            pi := partition(items, lo, hi);
            sort(items, lo, pi - 1);
            sort(items, pi + 1, hi);
        }
    }

    sort(items, 0, items.len - 1);
}

main :: () {
    arr : []s64 = .[333, 2, 3, 5, 2, 2, 3, 4, 5, 6, 6, 1];
    quick_sort(arr);
    print("{}\n", arr);
    // [1, 2, 2, 2, 3, 3, 4, 5, 5, 6, 6, 333]
}

Standard Library

The standard library (modules/std.sx) provides:

• I/O: print(fmt, args...), out(str)
• Collections: List($T) (dynamic array)
• Strings: concat, substr, int_to_string, float_to_string, cstring
• Memory: Allocator protocol, GPA (general purpose), Arena (bump allocator)
• Math: sqrt, sin, cos
• Introspection: type_of, type_name, field_count, field_name, field_value, size_of

Cross-Compilation

sx build app.sx --target linux          # Linux x86_64
sx build app.sx --target macos-arm      # macOS ARM64
sx build app.sx --target windows        # Windows x86_64
sx build app.sx --target wasm           # WebAssembly

Acknowledgments

• Jonathan Blow for Jai, the language that inspired this one
• Andrew Kelley for Zig, which made this compiler a joy to write

License

MIT