Draft:Roc (programming language)
Programming language
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Roc is a purely functional, statically typed, general-purpose programming language that compiles to binary.[2] It aims to bring purely functional programming to areas traditionally dominated by imperative languages, such as command-line tools, web servers, and scripts.[3][4]
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|  |
| Roc | |
|---|---|
| Paradigm | Purely functional, statically typed |
| Designed by | Richard Feldman |
| Developer | Roc Team |
| First appeared | 2018[1] |
| Stable release | Alpha 4
|
| Typing discipline | Inferred, static, strong |
| Implementation language | Rust, Zig |
| License | Universal Permissive License (UPL-1.0) |
| Website | www |
| Major implementations | |
| Roc Compiler | |
| Influenced by | |
| Elm | |
Created by Richard Feldman, the language features a unique architecture that separates the application logic from the underlying runtime environment (referred to as the "Platform").[5]
History
Roc was created by Richard Feldman, who is also known for his work in the Elm community and as the author of Elm in Action from Manning Publications.[6] The language began development to address the lack of a purely functional language that offered both the developer experience of Elm and the performance characteristics required for backend and systems software.[7]
The language is in an alpha state. In early 2025, Feldman announced that the team had begun rewriting the compiler from Rust to Zig.[8] The development roadmap focuses on stabilizing the compiler, expanding the ecosystem of platforms, and implementing an editor-agnostic language server.[9]
Design and features
Performance and memory management
Roc compiles directly to machine code (or WebAssembly) rather than running on a virtual machine (VM) or transpiling to another high-level language.[10]
Unlike many functional languages (such as Haskell or OCaml) or managed languages (like Java), Roc does not use a tracing garbage collector. Instead, it utilizes automatic reference counting. The compiler inserts instructions to free memory immediately when a variable is no longer in use. To optimize performance, Roc employs "in-place mutation" optimizations: if the compiler detects that a data structure is being updated and its reference count is one (meaning it is unique), it will mutate the memory in place rather than allocating a new copy. This allows the language to remain purely functional semantically while potentially achieving performance characteristics similar to imperative languages.[10]
Platforms and Applications
A distinctive feature of Roc is its separation of code into "Applications" and "Platforms."[3]
- The Application contains the core logic of the program. It is written in Roc and is purely functional.
- The Platform is a domain-specific compilation framework. It acts as as interface between the application and the operating system and allows code compilation to be optimised for the given domain. It provides low-level primitives for I/O, memory management entry points, and standard library features appropriate for the target.[11] So far the two main supported platforms are a web server platform and a CLI platform, and potential future platforms may include a game engine platform and a GUI platform.[12]
Platforms are often written in low-level languages like Rust, Zig, or C, though they expose a Roc interface to the application.
Developer experience
Roc places a heavy emphasis on "friendliness," largely inspired by Elm. This includes helpful compiler error messages that suggest fixes, a built-in test runner, and a formatter. The type system uses type inference, allowing developers to omit type annotations in most cases while maintaining static type safety.[13]
Syntax and semantics
Roc's syntax was influenced by Elm but has now developed its own distinctive functional style.[14]
Functional patterns
Roc supports standard functional programming patterns, including:
Error handling
Roc does not use exceptions. Instead, it uses an algebraic data type (containing either an `Ok` value or an `Err` value) for operations that can fail.[17]
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