Roc with Richard Feldman

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Nov 13, 2025

Richard Feldman, creator of the Roc programming language and author of 'Elm in Action', discusses the ambitious goals of Roc: a fast, friendly, functional language for machine code and WebAssembly. He explains the decision to shift the compiler from Rust to Zig, highlighting issues with compile times and the unique advantages Zig offers, such as efficient compile-time features. Richard also reflects on the importance of long-term thinking in design and shares insights on improving the Rust community's focus on user experience.

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INSIGHT

Roc’s Ambitious Language Goal

Roc aims to be a fast, friendly, functional language inspired by Elm but targeting machine code and WASM.
Richard emphasizes simple APIs, purity inference, and being the fastest garbage-collected language in its class.

ANECDOTE

Origin Story From NoRedInk

Richard started Roc after struggling to find an Elm-like language for non-browser domains while at NoRedInk.
He experimented with Haskell but wanted a purity-first language with full type inference for many domains.

ADVICE

Pick A High-Performance Host Early

Choose a host language with a high performance ceiling when building a compiler to avoid future rewrites.
Prioritize long-term compile-time performance as part of UX to keep developer feedback loops fast.

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Building a new programming language from scratch is a monumental undertaking. In this episode, we talk to Richard Feldman, creator of the Roc programming language, about building a functional language that is fast, friendly, and functional. We discuss why the Roc team moved away from using Rust as a host language and instead is in the process of migrating to Zig. What was the decision-making process like? What can Rust learn this decision? And how does Zig compare to Rust for this kind of systems programming work?

About Roc

Roc is a fast, friendly, functional programming language currently in alpha development. It's a single-paradigm functional language with 100% type inference that compiles to machine code or WebAssembly. Roc takes inspiration from Elm but extends those ideas beyond the frontend, introducing innovations like platforms vs applications, opportunistic mutation, and purity inference. The language features static dispatch, a small set of simple primitives that work well together, and excellent compiler error messages. Roc is already being used in production by companies like Vendr, and is supported by a nonprofit foundation with corporate and individual sponsors.

About Richard Feldman

Richard Feldman is the creator of the Roc programming language and author of "Elm in Action." He works at Zed Industries and has extensive experience with functional programming, particularly Elm. Richard is also the host of Software Unscripted, a weekly podcast featuring casual conversations about code with programming language creators and industry experts. He's a frequent conference speaker and teacher, with courses available on Frontend Masters. Richard has been a longtime contributor to the functional programming community and previously worked at NoRedInk building large-scale Elm applications.

Links From The Episode

Zig - Better than Rust?
Rust in Production: Zed - Our interview with Richard's colleague with more details about Zed
Richards blogpost about migrating from Rust to Zig - Sent in by many listeners
Elm - Initial inspiration for Roc
NoRedInk - Richard's first experience with Elm
Haskell - A workable Elm on the backend substitute
OCaml - Functional language, but pure functions only encouraged
F# - Similar shortcomings as OCaml
Evan Czaplicki - Creator of Elm
Ghostty - Terminal emulator from Mitchel Hashimoto with lots of code contributions in Zig
bumpref - A tiny Rust crate that came out of this discussion, providing Arc::bump(), which is an alias for clone().
RAII - Resource acquisition is initialization, developed for C++, now a core part of Rust
Frontend Masters: The Rust Programming Language - Richard's course teaching Rust
Rust by Example: From and Into - Traits for ergonomic initialising of objects in Rust
The Rust Programming Language: Lifetime Annotations on Struct Definitions - Learn from Roc: try to avoid having lifetime type parameters
Rust By Example: Box, stack and heap - Putting objects on the heap can slow down your application
Design Patterns: Elements of Reusable Object-Oriented Software - Seminal book popularising many common patterns in use today, written by the so-called "Gang of Four"
Casey Muratori: The Big OOPs - Game developer explaining why OOP was an obvious mistake for high performance code
Alan Kay - Coined the term "object-oriented" while developing the Smalltalk language in the 70s
Niklaus Wirth - Working on Modula, a modular programming language, at the same time
Kotlin - A new and popular language, basically Java++
Go - Popular "greenfield" language, i.e. not coupled to an existing language, not using the object oriented paradigm
Cranelift backend for Rust - A faster backend than LLVM, but still not released
Andrew Kelly - Creator of Zig
Software Unscripted - Richard's Podcast
GPUI - Zed's own UI crate
Structure of Arrays vs Array of structures - A big source of unsafe code in the Rust implementation of Roc
The Zig Programming Language: comptime - Zig's replacement for Rust's proc-macros, with much broader utility
crabtime - Comptime crate for Rust
Roc - Roc's namesake, the mythical bird
Rust in Production: Tweede Golf - Podcast episode with Volkert de Vries, one of the first contributors to Roc

Official Links