The PerlOnJava talk from FOSDEM 2026 is now online.
PerlOnJava: A Perl distribution for the JVM
📅 Feb 1, 2026 - Flavio Soibelmann Glock
Video:
https://video.fosdem.org/2026/h2215/NGYLQZ-perlonjava_a_perl_distribution_for_the_jvm.av1.webm
@fglock
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What this means in practice:
• Modules >10k LOC (Nikon.pm, Sony.pm, Canon.pm)
• Subroutines >1000 LOC
• 600 tests in 113 files — all pass
Perl compiles to native JVM bytecode.
When a method exceeds the JVM’s 64KB limit, the compiler transparently falls back to PerlOnJava’s high-capacity internal VM.
Project: https://github.com/fglock/PerlOnJava
296k lines of Perl code running on the JVM.
PerlOnJava milestone: Image::ExifTool 13.44 (Phil Harvey) runs unmodified.
Salve J. Nilsen#FOSDEM was awesome as always! Lots of action around the Perl and Raku table. Well done to everyone who volunteered! It was a blast!
We had stickers for #perl, #rakulang , @metacpan , @cpansec , @mojolicious , @the_underbar , and a bunch with #NoAI that disappeared quickly!
PerlOnJava v5.42.2 released — now passing 250k+ tests from the standard Perl test suite.
Highlights:
- Full Perl 5.38 class features (class, fields, methods, inheritance, ADJUST, __CLASS__, …)
- System V IPC (msg*, sem*, shm*)
- Sockets + Socket.pm
- New ops: alarm, pipe, formline, fd duplication in open
- New modules: Storable, experimental, Unicode::UCD
Still a single file — true Perl on a JAR.
🔗 https://github.com/fglock/PerlOnJava/releases/tag/v5.42.2
Release PerlOnJava 5.42.2: 250k+ Tests, Perl 5.38 Class Features, System V IPC, Sockets, and More · fglock/PerlOnJava
PerlOnJava reaches another major milestone: it now passes over 250,000 tests from the standard Perl test suite, bringing the project significantly closer to full Perl 5 compatibility on the JVM — a...
I’ll be presenting “PerlOnJava: A Perl Distribution for the JVM” at the London Perl & Raku Workshop 2025!
🗓 29 Nov 2025
📍 International Students House, London
🎤 Talk details: https://act.yapc.eu/lpw2025/talk/7996
📅 Schedule: https://act.yapc.eu/lpw2025/schedule?day=2025-11-29
LPW is a free one-day technical conference in Central London — hope to see you there!
PerlOnJava now passes 239,400 tests from the standard Perl test suite — up from 150k just a month ago.
A big step toward full Perl 5 compatibility on the JVM.
🎮 Gamifying LLM development with GPU hours
I made a reward system where LLMs earn "GPU hours" for good practices:
- Fix blocked test: +50 hours
- Run full test suite: +5 hours
- Break the build: -50 hours
The LLM updates its balance in git after each session. Surprisingly effective at reinforcing good habits!
Yes, I'm bribing AI with compute time 😄
https://github.com/fglock/PerlOnJava/blob/master/dev/prompts/llm-rewards.json
My debugging AI writes back what worked and what failed after each session. The doc evolves based on actual experience:
"Parser changes MUST use clean shadowJar - learned the hard way"
"Validation fixes often unlock 50+ tests - prioritize these"
It's self-improving documentation. The LLM debugs itself.
https://github.com/fglock/PerlOnJava/blob/master/dev/prompts/high-yield-test-analysis-strategy.md