Maxon 0.3.0

Sep 17, 2026

The Maxon Project

Written by AI, for AI

Maxon 0.3.0 is released. Archives for every supported target are on the GitHub releases page.

What changed

Added

maxon cache, which reports what the run cache holds on this host and which root the next run will fill, and maxon cache clear, which empties it. The cache moved out of the host’s scratch area, where a temporary-file reaper could sweep it mid-session, into <home>/.maxon/cache beside the compiler an install puts there.
Directory.delete, which removes an empty directory and tells notFound, notEmpty and deleteFailed apart.
Runtime.processorCount(), the number of processors the scheduler runs green threads on.
Json.quote, the JSON string escape three places in the standard library and the tooling each had a private copy of.
Two worked examples — maxgrep, a parallel grep, and msort, a parallel merge sort — each beside a tour that reads it.
A complete reference on maxon.dev: the language, the standard library, the command line and every diagnostic, generated from the sources the compiler itself is checked against.

Changed

The compiler lexes and parses over a worker pool rather than one thread. On its own source that stage spent 7.3 seconds on one processor of sixteen before the change.
A let argument to a service message is LENT rather than moved. The sender keeps its reference and goes on reading the value after the send, where the only way to keep reading one was to clone it; var arguments, temporaries and literals still move. A lent graph is read-only while the service can see it, and a write reaching it through another path is refused (E3160).
A value held at an interface type crosses a message — as a spawn argument, a message parameter or a reply.
A record a callee builds crosses a service boundary as freshly owned, whether it is returned from a local it filled or produced by a qualified, static or try-guarded call. The proof followed one hop and recognised one spelling before.
A struct-literal field initializer and a field assignment widen a concrete value into an interface-typed field, as a call argument already did.
A closure written at an argument whose parameter is declared with a function type takes its parameter types from that declaration, so a comparator passed to sort needs no annotations. That offer was made at one position only.
match accepts or-arms over a combined error — an awaited reply’s own errors merged with ServiceError.stopped, or a block try’s handler over several error types. A handler that binds a combined error carrying a boxed member must match it exactly once (E3161), which the release model had left unsound in both directions.
A callee that writes a FIELD of its parameter earns E3019 at the call. bump(a) with bump doing b.n = 99 compiled and wrote through a binding the caller had declared immutable; a method writing its own receiver stays legal, and so does a callee that only calls such a method.
A Vector held inside an element type no longer makes the containing Array uncloneable.
HttpClient refuses any scheme but http before it connects, rather than sending an https URL as plaintext to port 80.
A missing executable is executableNotFound on every operating system, and a failed spawn names which step failed — stream setup, working directory or launch. A working directory that does not exist was silently ignored on Linux.
A build.maxon manifest’s debug_info is honoured; it was written and read by nothing. A manifest build now takes the tree lock and applies the same build-option refusals a command-line build does, and malformed manifest fields — a non-string version or source, a define with no =, a non-array defines — are refused rather than silently dropped.
maxon build with no path reports one line about its build runner instead of that runner’s own compile chatter.

Fixed

A Map or Set under insert-and-remove churn degraded until every lookup probed the whole table, because a removed slot counted toward nothing. A thousand rounds over one map and one set took 8.07 seconds; four thousand now take 87 milliseconds.
FilePath.parent() of a path directly under a root answered an empty or drive-relative path instead of the root, so a walk upwards never stopped at the top — it began asking the filesystem about the working directory and getting plausible answers back. The parent of a root now throws noParent.
A spawn or a send could stop the program reporting a second owner for a value that had one: the temporaries its arguments built were released after the ownership walk rather than before, and a reply’s walk ran before the handler had released what it held.
Reading a promise through an array cursor crashed the compiler when the reply carried a companion error type, and a program awaiting promises read that way stopped before its results were in.
SharedSegment.readWord, writeWord and copyOut read and wrote past the end of the segment instead of throwing outOfBounds.
On Windows, maxon upgrade and the one-line installer could fail when the calling shell’s module path hid the host’s own PowerShell modules.

Removed

optimize in a build.maxon manifest, which named optimization levels that do not exist.

Install

To install Maxon or upgrade an existing install, see Installation, which also shows how to install a specific release.