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

```sx
#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+**.

```sh
zig build
```

On macOS with Homebrew LLVM:
```sh
# default path: /opt/homebrew/opt/llvm@19
zig build
```

Custom LLVM path:
```sh
zig build -Dllvm-prefix=/path/to/llvm
```

## Usage

```sh
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. See `specs.md` → Numeric Limits.

### Declarations

```sx
// 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`.

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.

```sx
`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

```sx
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)

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

### Optionals

```sx
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

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

### Closures

```sx
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

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

### Pattern Matching

```sx
// 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

```sx
// 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

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

### Compile-Time Execution

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

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

### C Interop

Foreign functions:
```sx
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:
```sx
#import c {
    #include "vendors/mylib/api.h";
    #source "vendors/mylib/impl.c";
};
```

### Modules

```sx
#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:

```sx
// 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

```sx
#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`, `field_count`, `field_name`, `field_value`, `size_of`

### 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:

```sx
#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

```sh
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](https://en.wikipedia.org/wiki/Jonathan_Blow) for Jai, the language that inspired this one
- [Andrew Kelley](https://andrewkelley.me) for Zig, which made this compiler a joy to write

## License

MIT