Sword

Sword is a compiled systems language with Go’s syntax and Zig’s memory model. It has no garbage collector, nothing allocates behind your back, and the compiler refuses to build a program where two tasks can touch the same memory at the same time.

import "std/mem"

func square(xs []i64, mut out []i64) {
    for i in 0..out.len {
        out[i] = xs[i] * xs[i]
    }
}

func main() !int {
    mut backing := [4096]u8{}
    mut arena := mem.NewArena(backing[..])

    mut src := mem.Alloc[i64](&arena, 64) orelse return error.OutOfMemory
    mut dst := mem.Alloc[i64](&arena, 64) orelse return error.OutOfMemory
    for i in 0..src.len {
        src[i] = i64(i)
    }

    scope {
        for off, part in dst.chunks(8) {
            spawn square(src[off..off+part.len], part)
        }
    }

    return int(dst[63] % 100)
}

Eight tasks write into eight pieces of the same array. That compiles because chunks hands out pieces that cannot overlap. Slice dst by hand inside the loop instead and the compiler stops you, because then it has no way to know the pieces are distinct.

What the compiler cannot see is the order tasks run in, so the test runner varies it on purpose: shield test -sim runs each test under many interleavings, one thread and a seed each, and a failure comes with the seed that makes it happen again.

Install

git clone https://github.com/swordlang/sword
cd sword
make
make install

That builds the latest release, 0.3.0 “Quench”, from main; develop has what is coming next. What each release changed is in CHANGELOG.md.

import "std/io"

func main() !int {
    try io.Printf("{} workers, {.1}ms each\n", 8, 12.5)
    return 0
}

That puts shield (the compiler) and swordls (the language server) in ~/.local/bin. See docs/install.md for prefixes, editor setup and what the build needs.

Learn it

• Why Sword — what the design buys against Go, C and Rust, and what it costs. Read this before the tour if you are deciding whether to care.
• A tour of Sword — start here. Every section is a program you can run, and they build on each other from hello world to parallel code.
• Concurrency — how tasks, partitions and the race checker fit together, and why they are shaped the way they are.
• HTTP — writing a server and a client with std/http.
• Testing — shield test, and writing tests that sit beside the code.
• Reference — types, operators, keywords, standard library. For looking things up once you know the language.
• Grammar — the syntax in EBNF, token by token, for writing a tool that reads Sword or settling what parses.

What it looks like

Three commitments run through every design decision:

Nothing allocates implicitly. A function that touches the heap takes an Allocator parameter. There is no other way, including in the standard library, so a signature without one cannot allocate.

A task’s lifetime is a lexical scope. spawn only exists inside scope, and the closing brace is the join. That is what makes it safe to lend a task a slice of memory the parent owns.

Immutable by default. x := 1 cannot be reassigned; mut x := 1 can. That is not a style preference — immutable data crosses between tasks with no synchronisation at all, which is what the race checker leans on.

Status

Sword compiles to native code through LLVM and the language is usable, but it is young. Working today: functions with variadic parameters and function values, methods, interfaces with dynamic dispatch, generics over both functions and structs, floating point, top-level constants, atomics, mutex-protected shared[T] with wait and notify, structs, enums, slices, strings, pointers, optionals, error unions, switch with completeness checking over an enum, defer, packages, and the whole concurrency story with a work-stealing scheduler behind it, channels included.

The standard library covers memory (std/mem), byte buffers (std/bytes), byte-level strings (std/strings), UTF-8 and the width of a character (std/unicode), generic containers and sorting (std/collections), exact and compensated sums and elementary functions with the same bits on every machine (std/num), random numbers that do not depend on the number of threads (std/rand), parallel scan, filter, sort and minimum with the same property (std/par), printing and formatting (std/io, std/fmt), JSON (std/json), hashing, HMAC and keys derived from passwords (std/crypto), hex and base64 (std/encoding), arguments and environment (std/os), files, directories and standard input (std/fs), running another program (std/process), C’s types by their C names (std/c), loading a library while the program runs (std/dl), clocks and durations (std/time), scheduler counters (std/runtime), TCP and UDP over IPv4 and IPv6 (std/net), TLS (std/tls), HTTP/1.1 with keep-alive, routing, timeouts, static files and HTTPS, server and client (std/http), and tests (std/testing, run by shield test).

A task has its own stack, so a task waiting on a socket is put down rather than holding a thread: the descriptor goes to a poller and the worker moves on. Measured, on ten cores — 4000 concurrent keep-alive connections at 84 000 requests a second on twelve threads, and 2000 idle ones in 65 MiB.

TLS comes from OpenSSL, found at build time — http.ListenTLS for a server, http.Fetch("https://...") for a client, and http.ListenWith for a server that asks its clients for a certificate of their own. A build made on a machine without OpenSSL says so (tls.Available()) instead of failing to link.

What comes next — packages, speed, smaller machines, and the compiler rewritten in Sword — is in the roadmap.

Contributing

Bug reports, fixes, library code, documentation and editor support are all welcome. A change to the language itself starts as an issue, where it is settled before anybody writes it. CONTRIBUTING.md has how to build, test and send a change, and everyone taking part follows the Code of Conduct.

License

MIT.