The Goose Programming Language

A memory-safe systems language with no heap allocator, garbage collector, or lifetime annotations. In this repository's benchmarks, Goose runs faster than C++ and Rust while using less memory.

Tutorial · Reference · Specification · Command line · Packages · Samples · Benchmarks · Standard library

Goose has syntax familiar to C and Rust programmers, but there is no heap. Every dynamic value lives inline on data stacks managed by the compiler. Growth advances a pointer, and memory is freed when its scope ends. The language's type and lifetime rules make this memory model safe to use.

Why Goose

• Faster than C++ and than safe Rust, while memory safe. Over sixteen benchmarks Goose runs at 3.3x the speed of idiomatic C++, 1.16x hand-optimized C++ and 1.12x the best safe Rust, and uses 1.9x, 1.3x and 1.2x less memory (results). These gains come from Goose's data layouts and memory model.
• No allocator, no GC, no reference counting, no destructors. Memory is a handful of data stacks that the compiler assigns statically. Freeing a structure with a million elements takes a single store, no matter how deeply it is nested.
• Growth preserves references. A reference into a growing array stays valid for as long as the array does. In the corresponding benchmarks, Goose keeps typed references where C++ must call reserve and safe Rust uses u32 indices.
• Memory safe with zero annotations. There is no lifetime syntax, there are no aliasing or exclusivity rules, and there is no unsafe. The compiler infers what every reference is rooted at and rejects references that could outlive their owners.
• Nested data stays inline. A string, an array of strings, a record with variable-size fields and an array of those records are each stored as one contiguous block that contains no pointers. A example record that takes 160 bytes and one allocation in C++ takes 29 bytes and no allocations in Goose.
• Variable sized Enums. Variable-mode ADTs store each value at the size of its own variant rather than that of the largest variant. On the benchmark that exercises this, they use 4x less memory than a Rust enum and run at 2x its speed.
• Links narrower than pointers. A relative reference stores a typed, checked link as a 1, 2 or 4-byte offset. Structures built from them are position independent, so a data structure can be written to a file as is. Saving it is a single write, and loading it is a single read followed by a verification pass that rejects malformed or hostile data.
• Everything is built in place, guaranteed. A value is constructed at its final destination through any depth of calls. items.push(parse(line)) writes the parsed record directly into the array, and returning a growable array by value does not copy it.
• Returns across multiple calls. return err from load returns from a function any number of frames up the call stack. It is checked statically, and needs no unwinder, no Result type and no ? on every call.
• Threads with no shared memory. A worker is compiled as a separate program with its own memory, and flat values are passed between threads through typed queues with a . Data races, locks, atomics and memory orderings do not exist in the language.

The tutorial walks through all of this by example, the reference covers the whole language topic by topic, the specification has the exact rules, and the benchmarks have the numbers, including the cases where Goose loses.

Features

This section focuses on what distinguishes Goose. The tutorial explains these features in more detail, and the samples show them in thirty-one complete programs.

One memory model: data stacks freed at scope exit

A program has the native call stack, static data and N data stacks, where the compiler works out N. A data stack is a large address-space reservation with a bump pointer, and there is no other memory. At most one resizable value is live per stack and it is always on top, so growth never moves anything and never checks a capacity. All of this is proved at compile time; the runtime tracks only the bump pointers.

for round in 3 {
    var scratch: u8[>..] = [];                        // grow-only: growth is a pointer bump
    for i in 100000 { scratch.push((i % 256) as! u8); }
    print("round ", round, ": ", scratch.len, " bytes");
}                                                     // the free: one store to the stack top

Memory never moves, so references survive growth

struct Item { id: i32, weight: f32 }

var items: Item[>..] = [];
let first .= items.push(Item { 1, 0.5 });             // a reference to element 0
for i: i32 in 2..1000001 { items.push(Item { i, 0.0 }); }
first.weight = 99.5;                                  // still valid, a million pushes later

push returns a reference to the new element, so a program can link elements while building the array. A vector<T> or Vec<T> may reallocate and cannot provide this guarantee. Stable references account for several benchmark gains.

Safe references, no annotations

Every reference and slice has a static root: the variable that bounds its target's lifetime. A reference must not outlive the variable that owns its target or access that target through an incompatible type. The compiler infers roots and specializes functions for them, so no annotations are needed. There are no aliasing or exclusivity rules. When a lifetime check fails, the error names the reference's root and its destination:

fn longest(a: u8[:], b: u8[:]) -> u8[:] { if a.len >= b.len { a } else { b } }

var outer: u8[>..] = [];
var w = outer[..];
{
    var inner: u8[>..] = [];
    format(inner, "inner text");
    w = longest(outer, inner);     // error: storing a reference rooted at inner,
}                                  //        which does not outlive the destination (§9.2)

A slice T[:] lets a function accept a range from any array kind without copying its elements. For example, split returns slices into its input, and a dictionary keyed by u8[:] stores views of strings rather than copies.

Nested data stays inline

There is no single array type. Instead there is a family of array types that differ only in how their size can change. Every member is laid out as [metadata][elements...], inline and packed, never as a pointer to a separate block of elements:

Type	What it is
T[k]	fixed size, known at compile time
T[], T[varint]	sized at construction, frozen after; a fixed or variable-width length
T[..k], T[..]	capacity inline; grows and shrinks within it
T[>..]	grow-only: the most commonly used kind; references into it stay valid
T[>..<]	grow-shrink: stacks, queues, heaps

Strings are u8 arrays: u8[>..] is a builder, u8[] a finished string stored inline in whatever holds it, u8[..16] a small string inside a struct, u8[:] a view. A struct may contain variable-size parts, which are stored inline in declaration order, so a record is a sequence of bytes with no indirection in it:

struct Item  { sku: u8[varint], qty: varint, cents: varint }
struct Order { id: varint, customer: u8[varint], items: Item[varint] }

var book: Order[>..] = [];
book.push(Order { id: 1001, customer: "alice",
                  items: [Item { sku: "SKU-441", qty: 2, cents: 1999 },
                          Item { sku: "SKU-7", qty: 1, cents: 500 }] });

That order is 29 bytes and 0 allocations. As C++ std::string + std::vector<Item> it is 160 bytes and 1 allocation, and as Rust String + Vec<Item> it is 153 bytes and 4 allocations. An entire order book is a single array, so reading it streams through the cache. The trade-off is that an array of variable-size elements is sequential: you can iterate it but not index it (unless you keep a second array of references into it as an index).

Enums in two sizes

Algebraic data types are the only form of dynamic polymorphism; there is no inheritance and there are no vtables. Every ADT can be stored in two ways, chosen at the point of use. Fixed mode (Shape) stores a tag plus room for the largest payload, so values can be indexed and overwritten. Variable mode (Shape..) gives each value exactly the size of its variant. An array of such values becomes sequential and a value never changes variant, but in exchange you may take references into a payload:

enum Shape { Circle { r: f64 }, Rect { w: f64, h: f64 }, Dot }

var packed: Shape..[>..] = [];                 // 9, 17 and 1 bytes, not 17 each
packed.push(Shape.Circle { r: 1.0 });
packed.push(Shape.Rect { w: 2.0, h: 3.0 });
packed.push(Shape.Dot);
for s in packed {
    match s { Rect &r => { r.w += 1.0; }, _ => {} }   // edits the payload in place, inside the array
}

Case functions provide another way to dispatch on a variant: define one overload per variant. Calls dispatch on the tag through a jump table, and the compiler checks that the overloads cover every variant:

fn area(s: Shape.Circle) -> f64 { 3.14159 * s.r * s.r }
fn area(s: Shape.Rect) -> f64   { s.w * s.h }
fn area(s: Shape.Dot) -> f64    { 0.0 }

for s in packed { print(s, " area ", area(s)); }

Links narrower than pointers

A T& is a machine address: it takes eight bytes and never dangles. A relative reference is the same link stored as a narrow offset. A T&<u32> is measured from the field itself to a target in the same array, so the structure is position independent. A T&<u32 in pool> is measured from the base of a named pool, so other arrays can link into the pool. T&<u32>? uses offset 0 as null. Here is a binary search tree in one grow-only array, with 12-byte nodes:

struct Node { key: i32, left: Node&<u32>?, right: Node&<u32>? }   // 12 bytes, links included

fn insert(pool: Node[>..]&, key: i32) {
    if pool.len == 0 { pool.push(Node { key: key }); return; }
    var cur .= pool[0];                             // .= binds a reference; = would copy the node
    loop {
        if key == cur.key { return; }
        let next = if key < cur.key { cur.left } else { cur.right };
        if next { cur .= next; continue; }          // narrowed by `if`: next is a Node&
        if key < cur.key { cur.left .= pool.push(Node { key: key }); }
        else             { cur.right .= pool.push(Node { key: key }); }
        return;
    }
}

References are transparent (there is no * or ->). .= binds or retargets a reference, and Node? is a nullable reference that if, guard and assert narrow. The insert is one push and one store, and the push cannot invalidate cur. When lifetimes are not nested, a reusable pool pairs a grow-only array with a hidden freelist. alloc_ref reuses a free slot or pushes a new one, and free returns a slot to the pool. Since a slot's memory is never actually freed, a stale slot reads a different value of the correct type rather than corrupting memory.

Saving and loading data as bytes

var image: u8[>..] = tree.to_bytes();           // a framed byte image of the whole array
var loaded, ok = from_bytes<Node[>..]>(image);  // verified before it becomes a value
image[image.len - 3] = 200;                     // tamper with a link ...
var bad, bok = from_bytes<Node[>..]>(image);    // ... and it is false and an empty array

The tree's links are self-relative, so the tree means the same thing wherever it is stored. Saving it writes its bytes and loading it reads them back, with no serializer, no schema and no pointer fixups. from_bytes checks the framing, every tag, every length and every link before the bytes become a value, so a corrupt or hostile file makes it return false, never a wild reference.

In-place construction

The copy-free construction guarantee (spec §4.3) says a constructed value is always built at its final location, which is passed down through calls. A function returning a grow-only array by value writes its elements directly into the caller's variable, or into a field of the record being built inside another array, so out-parameters are rarely needed.

words.push(str("word", i));                    // formatted straight into the new element
let evens = xs.filter() { it % 2 == 0 };       // built straight into `evens`: no temporary
book.push(Order { id: 1001, customer: "alice", items: parse_items("SKU-441:2:1999;SKU-7:1:500") });

Returning errors across calls

struct User { name: u8[..16], age: i32 }

fn load(text: u8[:]) -> User[>..], u8[] {
    var users: User[>..] = [];
    each_split(text, '\n') { users.push(parse_user(it)); };
    return users, "";
}

fn parse_user(line: u8[:]) -> User {              // returns a User: no Result, no error parameter
    let comma = find(line, ",");
    guard comma >= 0 else { return [], str("expected name,age: ", line) from load; }
    let age, ok = parse_int(line[comma + 1..]);
    guard ok else { return [], str("bad age: ", line) from load; }
    let name = trim(line[..comma]);
    return User { name: name, age: age as i32 };
}

return E from f returns E as the result of the innermost active call of f, however many frames up that call is. Every function in between keeps its plain signature. The construct is checked statically: every call of parse_user must lie inside a load call, so nothing can go uncaught at runtime. It is implemented as a hidden discriminant checked in each frame rather than as an unwinder, and the message is built directly where load's caller wants it. The parsers in the samples use it for every syntax error.

Generics and function blocks

fn twice(x) { x + x }                              // an untyped parameter is a generic one

fn each_pair<T, F>(xs: T[:]) {                     // F is a function value: a compile-time entity
    for i in 0..xs.len - 1 { F(xs[i], xs[i + 1]); }
}

fn first_gap(xs: i64[:]) -> i64 {
    each_pair(xs) { a, b => if b - a > 1 { return a; } };   // returns from first_gap, not each_pair
    return -1;
}

let evens = xs.filter() { it % 2 == 0 };
let total = fold(xs, 0) { acc, x => acc + x };
sort(xs) { a, b => a > b };

Everything is monomorphized. Type arguments are inferred from argument types; type parameters that do not appear in those types can be supplied explicitly. Function values are passed as generic parameters. Every call of a function value is direct and can be inlined, function values cannot escape, and there are no closure objects or function pointers, so a higher-order function compiles to exactly the loop it looks like. A block may return from its lexically enclosing function, and nested functions can use the enclosing function's locals.

Threads with no shared memory

thread_fn worker() {                                // a separate program with its own memory
    loop {
        let job = qget<Job>();                      // blocks on the typed queue for Job
        guard job.n >= 0 else { break; }            // -1 means stop
        qput(Result { n: job.n, digits: count_digits(job.n) });
    }
}

for i in n { ids.push(thread_spawn(worker)); }

There is no shared mutable memory. A thread_fn and everything it calls is compiled as its own program with its own data stacks and its own copies of the globals. Values are passed between threads through typed queues, one per type, and must be flat, with no references at any depth. Passing them is cheap because a flat Goose value is contiguous: a job or a result can carry real data, such as pixels, and passing it is a single memcpy.

A failed check or abort in a worker started with thread_spawn_contained ends only that worker. Its message goes to whoever waits for it, not to stderr, so a supervisor can log it and start another:

var why: u8[>..] = [];
while !thread_wait(thread_spawn_contained(serve, attempt), why) {
    log(why);                                       // "assert failed (serve.goose:12)"
    why.clear();
    attempt++;
}

The first thread_wait(id, msg) for a worker takes the message; a caller that doesn't ask for it loses it.

Compiling to and calling C

extern fn hypot(x: f64, y: f64) -> f64;             // straight from libm
extern fn crc32_bytes(s: const u8[:]) -> u32;       // a slice crosses as { data, len }
extern fn stats_of(xs: i32[:], out: Stats&);        // a struct filled through a pointer

An extern fn binds a Goose signature to a C symbol. The math and os modules use this interface. Only types with supported C representations may cross the boundary; unsupported signatures are rejected at the declaration. The compiler emits one C file for the whole program. The bundled TinyCC backend can compile and run that C inside the Goose compiler's process.

Where the speed comes from

Much of the speed comes from the memory model: no heap allocation or per-object teardown, contiguous data, narrow links, and enums sized for the variant they contain. Every index is bounds-checked, and the compiler removes checks it can prove unnecessary. An assert on a slice length often lets the compiler remove the remaining checks in a kernel, so that the kernel can be vectorized. --bce-lines reports the checks that remain. checkfree fn rejects a kernel if any bounds check remains in it; index types let graph edges keep the validation done while the graph was built. Benchmark measurements use whole-process wall-clock time, including teardown.

Geometric mean over 16 benchmarks	vs idiomatic C++	vs hand-optimized C++	vs best safe Rust
speed, MSVC backend	3.51x	1.24x	1.13x
speed, clang backend	3.54x	1.26x	1.19x
peak memory	1.95x less	1.32x less	1.25x less

The summary explains the gains and losses; results.md has every measurement, and design.md explains what the suite tests.

Limitations

• You have to think about where data lives: who owns it, and how long its scope lasts. Usually the owner is the function that builds the data, which needs no extra work; when it is not, the data goes in a reusable pool.
• Recursive functions cannot keep growable data across a recursive call. Scratch data must end before the call, and data that outlives the call is passed in as a pool.
• Arrays of variable-size elements can be iterated but not indexed (unless you keep an index of references beside them). A fixed-mode enum cannot be pointed into, and a variable-mode one cannot be overwritten. You make this choice per container.
• There are no escaping closures, no function pointers and no dynamic dispatch beyond ADT tags, and only whole-program compilation is supported.
• A slot that was returned to a reusable pool but is still referenced reads whatever its next owner put there. That is a logic bug, but never memory corruption.

Tutorial §18 is the full list.

Install a release

Prebuilt compilers for Windows (x64), Linux (x64) and macOS (Apple silicon and Intel) are on the releases page, with the graphics, audio, ui and physics packages compiled in. Unpack one anywhere and put its directory on PATH: the compiler finds the standard library, TinyCC's runtime and the packages beside itself, and keeps what it builds under ~/.goose (GOOSE_HOME). The archive also holds these docs, the samples and the VS Code extension.

Running a program in-process (goose file.goose) needs nothing else on Windows. On Linux it needs the C library's headers (libc6-dev, or glibc-devel); on macOS, the SDK of the Xcode command line tools (xcode-select --install). goose build also needs a C compiler: Visual Studio 2022 or later, or clang, on Windows; gcc or clang elsewhere. The Linux compiler needs glibc 2.35 or later (Ubuntu 22.04, Debian 12), and the macOS compiler needs macOS 13.3 or later. macOS keeps a downloaded archive's files from running until xattr -dr com.apple.quarantine is run on the unpacked directory.

Build and run

You need CMake 3.27 or later, a C++20 compiler (MSVC, clang or gcc) and Python 3 for the test and sample runners. TinyCC, which the in-process backend is built from, is part of the tree. The graphics, audio, ui and physics modules are packages in repositories of their own (goose_gfx and goose_physics; docs/design/packages.md). -DGOOSE_BUILTIN_LIBS=all fetches them with git at configure time, at the pinned tags, and compiles them into the compiler, so programs that use them run with nothing else installed. Without that option the compiler is built on its own, and the first time a program imports one of these packages, the package is built into ~/.goose, which needs git, cmake and a C compiler.

git clone https://github.com/aardappel/goose
cd goose
cmake -B build -DCMAKE_BUILD_TYPE=Release -DGOOSE_BUILTIN_LIBS=all
cmake --build build --config Release

GOOSE_BUILTIN_LIBS can also name some of the packages (physics, or gfx, which includes audio and ui too). On Linux, SDL needs the X11 or Wayland development packages (third_party/SDL/docs/README-linux.md); without them the build leaves the gfx module out and says what to install.

The runner scripts prefer build/Release, then build/RelWithDebInfo, then build, then build/Debug. Pass --exe to select a specific compiler; use an explicit Debug executable when testing with compiler assertions enabled. The compiler is build/goose (build/Release/goose.exe with the Visual Studio generator), and it finds the standard library in the source tree it was built from. On Windows 10 version 1903 and later, its embedded manifest selects a UTF-8 process code page so compiler paths do not depend on the system locale. Earlier Windows versions retain their legacy code page. Generated native executables retain their own process settings.

Run a program directly from source, in-process, with no C compiler and no build step (goose run is the explicit form of the same command):

build/goose samples/01_tour.goose

Or build an executable, which is written beside the source. The compiler finds a C compiler on the machine (goose toolchain shows which one) and links the generated C with the runtime and any native modules the program uses, including graphics. Programs that use threads must be built this way, since TinyCC cannot place thread-local storage.

build/goose build samples/01_tour.goose && samples/01_tour
build/goose build samples/27_gfx_cube.goose && samples/27_gfx_cube

goose check only typechecks. --debug turns on the overflow, range and tag checks, each of which names its source line when it fails, and --bce-lines reports the bounds checks that remain on each line. Every resizable value lives on a data stack of 2 GB of reserved address space, committed as it is used, and --stack-reserve 16G changes that size. The command line describes every command and option, including how to write the C for a build system or a C host of your own (goose -o tour.c tour.goose).

A program with C of its own lists that C in a sidecar file beside the source, foo.build beside foo.goose: c_sources = ["impl.c"];. Both forms build that C, so an extern fn can call it either way. A program uses a library by writing import name from "source"; in its root file. The source is a directory ("./lib"), or a git repository at a tag or commit ("owner/repo@v1" on GitHub, "host/owner/repo@ref"), which is fetched into ~/.goose and built there once per C compiler (packages).

A program using audio plays procedural mono/stereo PCM through SDL3 without opening a graphics window. See the audio reference.

The test suite and the samples run on Windows, macOS and Linux:

python test/run_tests.py
python samples/run_samples.py

For editing, the VS Code extension gives syntax highlighting, the compiler's language server (goose lsp: errors as you type, hover, go to definition, completion, rename, symbols) and one-key runs through the JIT:

code --install-extension vscode/goose-language.vsix

Other editors can run goose lsp themselves; editors has the configuration for Neovim, Helix and Emacs.

Documentation

• Documentation index: the map of everything below, and the root of the documentation site built from these files (how).
• Tutorial: the friendly introduction, by example. Read this first.
• Language reference: every feature, topic by topic, with a compiling example for each. It covers the whole language and is written to be read.
• Language specification: the exact rules, when you want to know why something did not compile.
• Samples: thirty-one complete programs in reading order, from a tour of the language to a JSON parser, a threaded Mandelbrot, a file tree built from two pools, a spinning cube on the GPU, thousands of boxes raining into a heap and a to-do list in windows of widgets.
• Standard library: fourteen modules, all written in readable Goose under stdlib/. They include gfx for graphics on SDL3's GPU API (how it is built) and physics for rigid body physics on Box3D (how it is built). The ui module provides fonts, text rendering and game HUDs. It also provides windows and widgets on Nuklear, drawn through gfx (how it is built).
• : every command and option of , from running and building to writing the C yourself, the formatter and the language server.

Status

Goose is new. What exists today is a whole-program compiler of about thirty thousand lines of C++, the specification, the standard library, the samples, and a test suite that CI runs on Windows, macOS and Linux with an extra sanitizer job. These are deliberately out of scope for now: moves for resizable values, more than one resizable per struct, labeled break, namespace privacy, and more OS/library access. Open items are tracked in the specification's Appendix B.

License

Goose is licensed under the Apache License, Version 2.0.

Authors

Wouter van Oortmerssen: Language Design, Compiler Design, Coding standards. home page, twitter.

Claude Fable: Compiler implementation, Benchmarking, Sample & Doc writing.

History & Use of AI

This repo was produced almost entirely with AI, from a human language design. I had designed Goose several years ago, and had started to implement it, but running a game startup (which is built on another programming language of mine, Lobster) there was no time to finish it. Which was sad, because I knew Goose could do things other languages can't, and it should exist.

I had not expected AI to help with this until Fable came out. I thought it might be capable enough to do a good job. I made it essentially clone the style and structure of my other recent compiler (Lobster), which is why if you look at the code, it looks rather similar to that. My initial design had left lots of things unspecified, and lots of back and forth with Fable made me decide on all of those, and it is now a better language for it.

It is also an experiment in using AI to implement a new language, rather than reproduce an existing one.

You may wonder why I had it work in C++, if clearly I could have used any language, like Rust, or my own Lobster, or.. Goose itself (that may still happen). With Fable, it was my observation that it is almost equally capable in any language, and the strong guardrails of Rust or other languages are not as pressing as they once were. Since the compiler emits C, you likely already need to have a C/C++ compiler around, so sticking inside one ecosystem would seem to simplify deployment and adoption. I've also integrated libtcc and who knows what other C libraries in the future. And, like I said, to have the compiler code mimic my existing Lobster compiler seemed fun, at least I can read it like it is my own.