Release Notes

Each section summarizes what changed for a user of the compiler, runtime, commands, and packages since the previous release. The installation chapter carries the upgrade steps.

0.15.1 (2026-10-17)

A patch release of 0.15.0. Existing installations upgrade in place; no packages need rebuilding.

• An uncaught error prints one line naming the error, the raising function and location, and its details, then aborts with the same status. The full logger event remains available with X2C_DEBUG or a <log> policy. See Handlers and policy.
• $auto on a local that is already managed is a compile-time error instead of a crash at scope exit.
• The REPL continues a list literal across lines, and code it loads boxes classes, expands its own meta functions, and calls protocol defaults as an ordinary build does.
• The book gains this release notes page, and the repository gains a security policy, a pull request template, and a bug report template.

0.15.0 (2026-10-17)

Releases ship for macOS arm64 and x86_64 and Linux aarch64 and x86_64, with the book as a PDF beside the archives. Read Upgrading from 0.14.0 before replacing an existing prefix.

Language

• meta functions run ordinary x2c during translation. A macro body calls one with $helper(...), passes constants or captured syntax, and inserts the code it returns. meta.x supplies the Code and Type operations for inspecting and building code. See Meta Functions and Generating Code.
• Macro values: a macro can select, apply, and collect cases as values, and typed quotations with expression holes build code with its type.
• Stmt macros accept an expression body, and a macro call may begin with a dotted name.
• Module blocks split one translation unit across a directory. The new module storage class is visible in every member file; static stays private to its file.
• Indentation syntax: a .xp file, or #pragma indent in a .x file, groups statements by indentation without braces or semicolons. See Indentation Syntax.
• raise is a statement head, catch accepts patterns as codes, and a variable may supply a raise code.
• Optional reference parameters, GNU statement expressions, threaded thread-local storage, and the contextual in membership operator.
• class types gain alloc and a refusing init, and init takes constructor arguments.
• Twelve language features moved out of the compiler kernel into components under src/components/; their behavior is unchanged.

Library

• lib/regex.x adds regular expressions over the bytes of a String, and every x2c script can use them.
• lib/diff.x computes line differences between two texts.
• The runtime’s canonical pool operations moved from List to Pool.
• Var.truth replaces Var.truthy; List.reduce, Array.reduce, and Iter.reduce are removed in favor of Iter.foldl.
• Compile-time Lisp gains tail calls and a bounded call depth.

Commands and packages

• x2c new creates a starter project that builds and runs.
• x2c repl is a shipped command with line editing, grammar-aware and semantic completion, and named inspection of session values. It evaluates a supported subset of the language. See Experimental REPL.
• Package management, the editor adapter, and project creation are external commands under libexec/x2c/. x2c lint and x2c graph are shipped as experimental.
• Packages record native arguments in <name>.native.rsp instead of <name>.link. Rebuild source packages and replace native bundles.
• Automatic differentiation moved from the runtime to the optional autodiff package; import "autodiff" supplies its types and macros.
• The SQLite package renames Statement to Prepared and Var.statement to Var.prepared.
• Every package manages its handles with $auto, so connections, loops, images, documents, and terminals release at scope exit.
• The C* verification package is removed.

Documentation

• The book adds the x2c Syntax Map for C readers, the syntax specifications with a source grammar and lexical rules, The Region Model, and chapters for meta functions, generating code, the REPL, and indentation.
• The language reference was corrected against the implementation and its repeated rules removed.
• The public site at x2c-lang.dev carries the book under /docs/.

Fixed defects

• A return inside a defer or finally body leaves its exception frame before transferring, so a later raise in the caller is caught.
• Macro bindings retained across package builds, nested empty unit macros, quotation members and splices, and template members in anonymous aggregates expand correctly.
• Parameter redeclaration inside callable bodies and the author-binding extern regression are fixed.
• Constructed raw string segments, nested string literals inside list literals, and negative percent literals in every radix are read as written.
• Pointer arithmetic over pointer typedefs and casts to template typedefs type correctly.
• Project meta payloads, include handling, the failure cache, and host flags are repaired for package builds.