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). The float types f32/f64 expose .min / .max too (with .min = most-negative finite = -max, not C's DBL_MIN) plus the float-only .epsilon (ULP of 1.0, not C#'s denormal Epsilon), .min_positive (smallest normal = C DBL_MIN), .true_min (smallest subnormal — beware flush-to-zero CPU modes), .inf, and .nan. A float-only accessor on an integer (s32.epsilon), or any accessor on a non-numeric type, is a clean compile error. The fold applies only to a bare type-name receiver: a raw identifier that binds a value shadowing a type name (`f64 := … then `f64.epsilon) reads the value's field, not the limit — for a local, global, or module-constant binding alike. This stays an ordinary runtime field read even when it flows into an integer binding or an array dimension, so it truncates (its field value) / is a non-constant count — never the builtin limit. See specs.md → Numeric Limits.

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

A typed constant's initializer must be compatible with its annotation — an integer fits any integer or float, a float a float type, a string string, null a pointer/optional. The check is type-based, so it covers a literal and a constant expression alike: both N : string : 4 and N : string : M + 2 are a compile-time type mismatch error, not a silently-accepted constant. Mixed int+float arithmetic promotes to the float in either operand order (n + 0.5 and 0.5 + n are both f64), so C : s64 : M + 0.5 is rejected regardless of order while F : f64 : M + 0.5 folds to 2.5.

Float → integer narrowing (unified rule). A float flowing into an integer-typed binding without a cast follows the same integral-fold rule an array dimension uses: an integral compile-time float folds to its integer, a non-integral one is a compile error. It holds whether the value is a literal or any compile-time-constant float expression — including one that references a float-typed const (F : f64 : 2.5; y : s64 = F + 1.5 → 4), a builtin float numeric-limit accessor (f64.max - f64.max → 0, while f64.true_min + 0.5 errors), a float % (6.0 % 4.0 → 2, while 5.5 % 2.0 = 1.5 errors), or a float / (6.0 / 2.0 → 3, while 5.0 / 2.0 = 2.5 errors — a float / is always float division, never integer truncation, even with integral operands): the compile-time float evaluator recognises every leaf shape the integer one does, so no constant float form escapes the rule at one site while folding at another — and is uniform across a typed local, a parameter default, a struct field default, a call argument, a typed constant, and an array dimension / count — y : s64 = 4.0, K : s64 : 4.0, y : s64 = M + 2.0, and [F + 1.5]s64 (≡ [4]s64, whether written directly, through a const, or via a type alias) all give 4, while y : s64 = 1.5, N : s64 : 1.5, y : s64 = M + 0.5, y : s64 = F + 0.25 (= 2.75), and [F + 0.25]s64 all error (one wording at the binding sites: cannot implicitly narrow non-integral float …; a dimension instead reports array dimension must be an integer, but '…' is a non-integral float, since the cast escape does not apply in a count position). An explicit xx / cast(s64) is the escape hatch and always truncates (y : s64 = xx 1.5 → 1, y : s64 = xx (M + 0.5) → 2); a genuine runtime float is likewise unaffected.

Builtin type names (s2, u8, bool, string, …) are reserved and a bare spelling can't be used as an identifier at a value-binding or declaration-name site — a value binding (:= / typed local / parameter), a :: constant or function declaration, an impl method definition, or a :: type declaration (struct / enum / union / alias / protocol / …) — each is an error (s2 :: 5 and s2 :: (n) { … } are rejected just like s2 := 5). Member-name positions are exempt: a struct field, a union tag, and a protocol method-signature may be a bare reserved spelling (struct { s2: s64 }, union { u8: … }, protocol { s2 :: () -> s64 }) — they are reached via obj.name, so they never mis-lower. The bare exemption covers only the identifier-classified reserved names (s1..s64, u1..u64, bool, string, void, usize, isize, Any); f32 and f64 are lexer keywords, so even in a member slot they need the backtick (struct { `f32: s64 }). A leading backtick escapes one into a raw identifier: `name is the literal identifier name (the backtick drops out of the text), usable in every position — value, declaration, and type, and optional in the exempt member positions. It is the only way handwritten sx can spell a reserved name in a binding or declaration site.

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

`s2 :: struct { x: s64; }   // declare a type named with a reserved spelling
v : `s2 = ---;              // and reference it as a type — resolves to the struct
x : s2 = 3;                 // bare `s2` in type position is still the int type

It works in every identifier position — local, global, parameter, struct field, union tag, function name, type/alias/import name, a top-level or struct-body constant, and the control-flow / capture / binding forms (destructure, if/while binding, for capture, match capture, catch/onfail tag) — and a reserved-spelled function is bare-callable (s2(10)). A backtick name used as a type resolves to a `name-declared type — including a parameterized template (`s2(s64)) and under pointer/optional wrappers — else a normal unknown type error.

Foreign declarations from #import c { … } are exempt automatically: C names that collide with reserved type names (e.g. s1, s2) import unedited, and a foreign reserved-name function is bare-callable by its C name.

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

When two flat-imported modules each define a function of the same name, every module's own code binds its OWN author — a bare call resolves to the same-name function in the caller's module (or in its single flat import that provides it). A bare call to a name that two or more flat imports both provide is ambiguous and is rejected; qualify it with a namespaced import (m :: #import …; m.fn()).

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, uint_to_string, float_to_string, cstring
• Memory: Allocator protocol, GPA (general purpose), Arena (bump allocator)
• Math: sqrt, sin, cos
• Introspection: type_of, type_name, type_is_unsigned, type_eq, field_count, field_name, field_value, size_of, align_of, is_flags — the type-only builtins (size_of, align_of, field_count, type_name, type_eq, type_is_unsigned, is_flags) require a type argument (a spelled type or a generic T); passing a value is a compile-time error. A runtime Type value (type_of(x)) is currently accepted by type_name and type_is_unsigned only — the other five are compile-time-only (runtime reflection is deferred)

Command-line interface (modules/std/cli.sx)

std.cli builds command-line front-ends over an explicit logical argv ([]string): os_args(buf) reads the real process argv, and parse(args, commands, diag) -> !Parsed does subcommand dispatch + --flag parsing. On top of that it defines the small exit-code / --json contract a CLI program (e.g. dist) relies on:

#import "modules/std/cli.sx";

p, e := parse(args, cmds, @diag);   // (Parsed, !CliError)
if e == error.UnknownCommand {
    log.err("unknown command '{}'", diag.token);   // human text -> stderr
    exit_usage();                                   // usage error -> exit 64
}
if p.json { /* emit ONLY machine output on stdout */ }

• Named exit codes — EX_OK (0), EX_USAGE (64, the sysexits.h command-line-usage code), EX_UNAVAILABLE (70, unsupported platform).
• Terminators — exit_ok() / exit_usage() end the process with the matching code; both route through the canonical process.exit(code: u8).
• --json mode — the reserved global --json flag surfaces as parsed.json (true iff --json is in the argv). Convention: in json mode stdout carries only the machine result; human diagnostics go to stderr.

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