https://xolang.dev/docs/spec/Recent content in Specification on Xo LanguageHugoen-UShttps://xolang.dev/docs/spec/core/Mon, 01 Jan 0001 00:00:00 +0000https://xolang.dev/docs/spec/core/<h1 id="xo-language-specification-core">Xo Language Specification (Core)</h1> <p>Status: draft 0.10 (2026-10-10; 0.9 released as toolchain v0.9.0, decision 0089) Edition: 2026 Companion: <code>spec/std.md</code> (prelude methods and standard library surface)</p> <p>Xo is a small, statically typed, garbage collected language for backends and web services. It keeps what makes Go productive (few keywords, one obvious way, fast builds, static binaries, a strong standard library, a compatibility promise) and is designed so that an AI agent can write, check, build, and debug programs for any OS with fast, structured, unambiguous feedback.</p>https://xolang.dev/docs/spec/std/Mon, 01 Jan 0001 00:00:00 +0000https://xolang.dev/docs/spec/std/<h1 id="xo-standard-library-and-prelude">Xo Standard Library and Prelude</h1> <p>Status: draft 0.8 (2026-10-09; the same draft number as <code>spec/core.md</code>, decision 0089) Companion to <code>spec/core.md</code>.</p> <p>Signatures are written in Xo syntax. <code>[var]</code> before a receiver means the method mutates and needs a <code>var</code> binding (core 3.4). Effects are listed with <code>uses</code>. Everything here is part of the 2026 edition compatibility promise once the edition is released.</p> <h2 id="0-conventions">0. Conventions</h2> <ul> <li><strong>Capabilities and fakes are handles.</strong> Copying a <code>Net</code>, <code>Fs</code>, <code>Clock</code>, &hellip; or a test fake shares the same underlying resource. They can be captured in closures and stored in structs.</li> <li><strong>Every error type implements <code>Display</code>.</strong> So any std error converts to <code>Error</code> at a <code>?</code> site.</li> <li><strong>Every error type returned by a blocking operation has a <code>Canceled</code> variant</strong> (core 7.2).</li> <li>Functions that cannot fail have no <code>!</code>. Lookups that may miss return <code>T?</code>.</li> <li>Braces are literal in plain strings (interpolation is <code>${x}</code>), so route patterns are ordinary strings: <code>&quot;GET /users/{id}&quot;</code>.</li> <li>Fields of std structs are <code>pub</code>: they can be read and the structs can be constructed (useful for testing pure functions).</li> </ul> <hr> <h2 id="1-prelude-interfaces">1. Prelude interfaces</h2> <p>Available everywhere without <code>use</code>.</p>