What does maintainability look like when the software you’re responsible for is a programming language? José Valim creator of Elixir and founder of Dashbit, joins Robby to talk about software that can “fit in your head,” the importance of clear boundaries, and why maintaining a language requires a different level of restraint than maintaining an application.

José traces Elixir’s origins back to his time on the Rails Core team and a concurrency bug that sent him looking for different approaches to software. That journey led through functional programming to Erlang and the BEAM, where he found ideas around immutability, concurrency, and distributed systems that reshaped how he thought about software. He explains why Elixir was designed to be extensible, allowing communities to build things like Phoenix and Numerical Elixir without continually expanding the language itself.

Robby and José also look at what AI is changing for maintainers. José explains how Tidewave gives coding agents access to context that frameworks already provide to developers, why documentation and good error messages have become unexpectedly valuable to agents, and how AI-generated contributions are changing open-source collaboration. They also explore whether coding agents might change the old calculus around dependencies, SDKs, and choosing a programming language.

Topics and Timestamps

[00:00:53] What Makes Software Maintainable: José compares well-maintained software to good conference Wi-Fi and explains why he values software whose boundaries and moving parts can fit in his head.
[00:03:20] Maintaining a Programming Language: How responsibility changes when thousands of applications depend on the software you maintain, and why language designers have to minimize churn for users.
[00:10:51] The Origins of Elixir: José tells the story of the Rails concurrency bug that changed his career and sent him exploring functional programming, Erlang, and distributed systems.
[00:17:00] Removing the Root Cause: Why José distinguishes between layering a solution over a problem and designing software so the underlying problem disappears.
[00:20:47] Designing Elixir to Be Extensible: Why José resisted making Elixir a web-specific language and instead focused on giving developers the building blocks to extend it into new domains.
[00:25:42] Restraint and the Elixir Ecosystem: José explains why much of his work moved away from changing the language itself and toward helping communities build on top of it.
[00:28:21] Giving Coding Agents Better Context with Tidewave: How Tidewave connects Rails and Phoenix applications with coding agents and exposes information developers already rely on.
[00:33:20] Designing for Humans in the Age of AI: Why José believes programming languages should continue optimizing for humans, and how features that help humans often help agents too.
[00:36:40] Documentation as Infrastructure: How Elixir’s long-standing investment in first-class documentation, HexDocs, Markdown, and searchable package documentation has translated well to AI-assisted development.
[00:41:40] AI and Open-Source Maintenance: José describes the increase in AI-assisted contributions and why AI-generated responses can disrupt the human relationship between contributors and maintainers.
[00:46:22] Rethinking Dependencies and Language Choice: Robby and José consider whether AI makes it easier to bring ideas across ecosystems instead of rewriting applications or depending on large SDKs.

Thanks to Our Sponsors!

Your test coverage says 90%, but that might be misleading. Undercover CI looks at your Ruby pull requests and shows you which parts of your changes weren't tested- not just overall coverage, but what changed and what got missed, down to the method level. Visit undercover-ci.com and use code MAINTAINABLE for 15% off your first billing cycle. Free for public repos. Private repos with unlimited users also available.

Mailtrap is a modern email delivery platform built for developers. Native SDKs, a secure Email API and SMTP, and a free tier with 4,000 emails a month. When you need help, you'll reach real people on 24/7 support, not an AI chatbot. Try Mailtrap for free!

Resources and Links

Subscribe to Maintainable on:

Or search "Maintainable" wherever you stream your podcasts.

Keep up to date with the Maintainable Podcast by joining the newsletter.

José Valim: Designing a Language You Can Maintain for Decades

Maintainable

José Valim: Designing a Language You Can Maintain for Decades