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Last Week in Pony - February 22, 2026

Crank up this week’s theme song — Horse Outside by the Rubberbandits — and settle in. Big week. We welcomed a new committer, shipped three brand-new libraries, and put out ten releases across five projects. There’s also a persistent HashMap bug fix that enabled json-ng to drop its custom null type, three new Pony patterns, and a blog post about teaching Claude to write Pony.

Welcome Orien Madgwick

We have a new Pony committer. Orien Madgwick has been given commit access to the ponylang organization. Welcome aboard, Orien. You’ve been doing great work so far. We look forward to seeing what you do next.

ponylang/uri

ponylang/uri is a new URI library for Pony. Two releases landed this week.

0.1.0 shipped with RFC 3986 parsing, reference resolution, normalization, and RFC 6570 URI template expansion at all four levels. If you need to parse URIs, resolve relative references, or expand URI templates, this is your library.

0.2.0 followed the next day with URI reference resolution per RFC 3986 section 5, IRI support per RFC 3987, URITemplateBuilder for one-shot template expansion, and URIBuilder for fluent URI construction with automatic percent-encoding.

See the release notes for 0.1.0 and 0.2.0.

ponylang/crdt

ponylang/crdt is a new library for conflict-free replicated data types in Pony, based on delta-state replication. It’s mostly an update of Joe’s original jemc/pony-crdt, brought up to date and moved into the ponylang org.

The initial release includes counters (GCounter, PNCounter, CCounter), sets (GSet, P2Set, TSet, AWORSet, RWORSet), registers (TReg, MVReg), and collections (TLog, CKeyspace). Each type supports convergent merging of concurrent updates. All replicas reach the same state without coordination.

If you’re building distributed systems in Pony and need data structures that merge without coordination, this is what you want.

See the release notes.

ponylang/web_link is a new library for parsing RFC 8288 Web Linking HTTP Link headers. It implements the link-value grammar from Section 3 including quoted-string parameters, whitespace handling, and multi-link comma-separated headers. If you’re working with HTTP Link headers (pagination, API discovery, resource relationships), this parses them.

See the release notes.

ponylang/json-ng

Two releases of ponylang/json-ng this week.

0.2.0 adds JSONPath filter expressions, function extensions, and slice-with-step support per RFC 9535. Filters let you select array elements or object values matching a condition: comparisons, existence tests, logical operators. All five built-in function extensions are implemented: match, search, length, count, and value. Two naming changes: JsonType is now JsonValue, and NotFound is now JsonNotFound.

0.3.0 replaces JsonNull with Pony’s built-in None. This was made possible by a fix to Pony’s persistent HashMap that previously used None as an internal sentinel (more on that below). That fix hasn’t shipped in a ponyc release yet, so 0.3.0 requires the latest nightly ponyc builds.

See the release notes for 0.2.0 and 0.3.0.

ponylang/lori

Four releases of ponylang/lori this week.

0.8.2 adds local_address() to TCPListener — essential when binding to port 0 and needing to discover the actual port. 0.8.3 widens send() to accept (ByteSeq | ByteSeqIter) for multi-buffer writev sends and fixes incorrect FFI declarations for exit() and pony_os_stderr(). 0.8.4 adds per-connection idle timeouts using ASIO timer events, no extra actors needed. 0.8.5 fixes an overflow in IdleTimeout where large millisecond values silently wrapped when converted to nanoseconds.

See the release notes for 0.8.2, 0.8.3, 0.8.4, and 0.8.5.

Persistent HashMap Fix

A PR was merged to fix a bug in the standard library’s persistent HashMap. The internal HAMT node lookup used None as a sentinel for “key not found,” which collided with user types that include None. If your map’s value type was (String | None), apply would raise instead of returning the stored None, and contains would return false for keys mapped to None.

The fix replaces the None sentinel with error. It’s a breaking change, but a localized one. It will ship in the next ponyc release.

Teaching Claude to Write Pony

I wrote up how I’ve been teaching Claude Code to write Pony: Teaching Claude to Write Pony. If you’re interested in using AI tools with Pony, give it a read.

Items of Note

Pony Development Sync

The recording of the February 18th Pony Development Sync is available.

The sync covered the json-ng RFC. Joe and Red provided feedback on naming, suggesting JsonValue over JsonType and considering None instead of “JSON null.” The persistent HashMap bug was discussed and classified as a bug worth fixing. There was also conversation about including a panic pattern in the standard library.

Office Hours

Red and I attended Office Hours this week. We discussed ponyc issue #4838, a bug where PonyCheck’s mapped generators segfault during shrinking. Then Red taught me about NixOS.

Pony Patterns

Three Pony patterns were published this week:

Building on Lori

I’ve started repositories for a pure Pony Redis client and an HTTP server called Stallion, both built on ponylang/lori. They’re part of a project to build five different protocols on top of lori: Redis, SMTP, HTTP client, HTTP server, and WebSocket server. The goal is to find commonalities that can be moved into lori itself. No releases yet. Just getting started.

Releases

Last Week In Pony is a weekly blog post to catch you up on the latest news for the Pony programming language. To learn more about Pony, check out our website or our Zulip community.

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