Gossamer

Why Gossamer

Expressive and clear syntax

Forward pipes (|>), immutable by default, and one obvious way to do things. Data flows top-to-bottom, the way you wrote it - not nested inside-out.

A Swift-like memory model

Deterministic reference counting - closely modeled on Swift's ARC, with automatic cycle collection added - plus arena { } regions reclaim memory as it goes out of scope. No borrow checker, no lifetimes, no tracing collector.

Real goroutines, colorless functions

go and typed channels on an M:N scheduler. Blocking calls park the goroutine, not the thread. No async, no await, no function colouring.

Run it, or ship it

A bytecode VM and a REPL for fast iteration; a single, dependency-free native binary via LLVM when you ship. Same language, your choice of tier.

Familiar types, fewer surprises

Result / Option / ?, exhaustive match, traits, generics, and no null. If you know Rust, Go, or F#, you can already read it.

Batteries included, extensible in Rust

A broad standard library - HTTP, JSON, crypto, SQL, compression, and more - and a clean path to drop down into safe Rust when you need it.

Examples

Hit Run on any sample - it executes right in your browser, no install. Gossamer's VM is compiled to WebAssembly.

fn double(x: i64) -> i64 { x * 2 }
fn add(a: i64, b: i64) -> i64 { a + b }
fn clamp(lo: i64, hi: i64, x: i64) -> i64 {
    if x < lo { lo } else if x > hi { hi } else { x }
}

fn main() {
    let n = 3 |> double |> add(10) |> clamp(0, 100)
    println!("answer: {}", n)
}

use std::http::router

// A request router - the heart of a web service. Register the route
// table once (note the {id} path parameter), then match each request.
let routes = router::new()
let _ = router::add(routes, "GET", "/")
let _ = router::add(routes, "GET", "/users/{id}")
let _ = router::add(routes, "POST", "/users")

let requests = #[("GET", "/"), ("GET", "/users/42"), ("POST", "/users"), ("DELETE", "/users/42")]
for (method, path) in requests {
    let status = match router::lookup(routes, method, path) {
        Some(_) => "200 ok",
        None    => "404 not found",
    }
    println!("{} {} -> {}", method, path, status)
}

fn fib(n: i64) -> i64 {
    if n < 2 { n } else { fib(n - 1) + fib(n - 2) }
}

fn main() {
    // spawn runs fib on a goroutine; join collects its result.
    let h = spawn(|| fib(30))
    match h.join() {
        Ok(v)  => println!("fib(30) on a goroutine = {}", v),
        Err(e) => eprintln!("worker failed: {}", e),
    }
}

enum Shape {
    Circle(f64),
    Rect { w: f64, h: f64 },
    Triangle(f64, f64),
}

fn area(s: &Shape) -> f64 {
    match s {
        Shape::Circle(r)       => 3.14159 * r * r,
        Shape::Rect { w, h }   => *w * *h,
        Shape::Triangle(b, h)  => 0.5 * b * h,
    }
}

// Top-level statements - no fn main() needed
let shapes = #[Shape::Circle(3.0), Shape::Rect { w: 4.0, h: 5.0 }, Shape::Triangle(6.0, 2.0)]
for s in shapes {
    println!("area = {:.2}", area(&s))
}

use std::collections::{BTreeSet, Map, Set, Deque, Queue, Stack, MaxHeap, MinHeap}

let mut nums = #[]
nums.push(10)
nums.push(20)
let dropped = nums.remove(0).unwrap_or(-1)
println!("[] Vec: len={} removed={} first={}", nums.len(), dropped, nums[0])

let fixed = [1, 2, 3]
println!("[] fixed array: len={}", fixed.len())

let mut scores: Map<String, i64> = {}
scores.insert("ada", 100)
scores.insert("grace", 95)
let old_score = scores.remove("ada").unwrap_or(0)
println!("{} Map: len={} removed={} has_grace={}",
    "{}", scores.len(), old_score, scores.contains_key("grace"))

let mut seen = #{}
seen.insert(3)
seen.insert(5)
let removed_seen = seen.remove(3)
println!("#{} Set: len={} removed={} has5={}",
    "{}", seen.len(), removed_seen, seen.contains(5))

let mut ordered: BTreeSet<i64> = #{}
ordered.insert(4)
ordered.insert(1)
let removed_ordered = ordered.remove(4)
println!("#{} BTreeSet: len={} removed={} values={}",
    "{}", ordered.len(), removed_ordered, ordered.to_vec().join(","))

let mut max_heap = MaxHeap::new()
max_heap.push(5)
max_heap.push(9)
let largest = max_heap.pop().unwrap_or(0)
println!("MaxHeap: len={} removed={}", max_heap.len(), largest)

let mut min_heap = MinHeap::new()
min_heap.push(5)
min_heap.push(2)
let smallest = min_heap.pop().unwrap_or(0)
println!("MinHeap: len={} removed={}", min_heap.len(), smallest)

let mut deque = Deque::new()
deque.push_front(2)
deque.push_back(3)
let front = deque.pop_front().unwrap_or(0)
let back = deque.pop_back().unwrap_or(0)
println!("Deque: front={} back={} len={}", front, back, deque.len())

let mut queue = Queue::from([7, 8])
queue.push(9)
let next = queue.pop().unwrap_or(0)
println!("Queue: next={} len={}", next, queue.len())

let mut stack = Stack::from([7, 8])
stack.push(9)
let top = stack.pop().unwrap_or(0)
println!("Stack: top={} len={}", top, stack.len())

let entry = (1, "widgets", 2.5)
let (id, name, unit_price) = entry
println!("Tuple: {} {} {:.2} (first={})", id, name, unit_price, entry.0)

Coming from another language?

Short, focused guides that map what you already know onto Gossamer.

From Rust → From Go → From Python → From Kotlin → From F# →

Get started

Write a .gos file and run it with the gos toolchain - no build step needed while you iterate:

$ gos run hello.gos
hello, gossamer

$ gos build --release hello.gos   # one native binary, ready to ship

Runs on Linux (x86_64, aarch64, armv7), macOS (Intel & Apple Silicon), and Windows (x86_64).

Install → Read the docs