frequently asked questions (faq)

basics

What languages inspired zo?

Above all Rust-prehistory — Graydon Hoare’s original Rust, the language zo grew out of. Beyond it, zo draws on Carbon, Jai, Erlang, Go, Cyclone, Imba, E4X, and Elm. The specification names each lineage and what it lent.

I’m new to zo. Where should I start?

The quick way is to do the initiation to get a full understanding of specific concept.

Does zo have a playground?

Yes — it ships inside codelord, the zo editor. Download codelord to try zo there — coming soon.

Where can I get support?

Reach the team on Discord — look in the zo category. For bugs and feature requests, open a GitHub issue.

How do I get syntax highlighting for .zo files?

A VS Code extension is available.

usage

Can I use zo for servers?

Yes. The standard library has a non-blocking TCP layer — TcpListener to bind and accept, TcpStream to read and write — and an HTTP/1.1 stack on top: HttpServer::new(addr).listen_and_serve(handler). Each connection runs as a lightweight task, so one server handles many at once without blocking.

comptime

How does zo achieve sub-second compilation speeds?

zo’s speed comes from a short pipeline and owning the whole stack. It runs Tree directly to produce SIR, folding semantic analysis and lowering into one pass rather than several — without skipping any of the safety work a conventional compiler does.

Every stage is hand-written for control over speed, and zo emits the binary itself: its own assembler and Mach-O linker produce a native, code-signed executable directly. So an external system linker — ld or lld, with its startup-and-link cost — never enters the loop.

In the benchmarks, zo compiles faster than clang, gleam, go, odin, and rustc.

memory management

If there is no garbage collector (GC), and no borrow checker, what is the memory management model?

zo gives every value a single owner. When the owner leaves scope, the compiler inserts its destructor, so a Vec, HashMap, String, or any value that owns a resource is freed at the closing brace. There is no garbage collector and no reference counting; the frees are placed at compile time and cost nothing at runtime.

Ownership is affine: a value has one owner, and using it after it moves is a compile-time error. That is the check zo runs in place of a borrow checker.

To release a resource early, call .free(). It consumes the value, so the automatic drop steps aside and nothing is freed twice. One case still needs it: a resource created inside a loop body. Function and block scopes drop automatically today; loop bodies will follow.

templating

How does zo compile a single Ui codebase to native widgets?

The compiler’s parser turns zsx (zo Syntax Extension) into a flat, platform-agnostic stream of user-interface instructions — UiCommands.

Each target lowers that stream to its own native views: UIButton on iOS, android.widget.Button on Android, <button> on the web, and Button::new on desktop.

Layout stays consistent across platforms: the runtime computes it with taffy, which implements the W3C Flexbox specification, fixing the exact geometry of every element. From a single codebase you get full native fidelity — VoiceOver accessibility, native keyboards, and native text rendering.

The gates are open, but this feature is still in development — unifying platforms is hard.

How do I compile to iOS or Android?

Pass the --target flag: zo build <pathname> --target ios. The program must use the #render directive — it tells the compiler to enable the render runtime.

How do I choose the Simulator device?

zo run <pathname> --target ios picks a device automatically: the booted one if any, otherwise the newest iPhone on your machine. To run on a specific device, pass --device with any device name (or UDID) from your Simulator:

zo run app.zo --target ios --device "iPhone 17 Pro"
zo run app.zo --target ios --device "iPad (A16)"
zo run app.zo --target ios --device "Apple Vision Pro"

iPhone, iPad, and Apple Vision Pro simulators can all run the same ios build — visionOS runs it through its iOS app-compatibility layer. The Apple Watch runs its own platform build: use --target watchos and zo compiles, bundles, and launches the same source on a watch simulator (auto-selected, or named with --device):

zo run app.zo --target watchos
zo run app.zo --target watchos --device "Apple Watch Ultra 3 (49mm)"

If a device name does not match the target platform, the error lists every device on your machine able to run the app.

comparison

How does zo compare to Rust?

zo compiles faster. If your feedback loop matters, that alone can make it the better fit. It also carries less friction: no borrow checker, no lifetimes, no function coloring. Concurrency follows Erlang, Go, and Swift — channels, lightweight tasks, and supervision.

At runtime, Rust is faster. We’re working to bring zo’s runtime close to C (clang).

• @SEE @zo-benchmark