OCaml

An industrial-strength functional programming language with an emphasis on expressiveness and safety

Install About OCaml
Latest release: 5.3.0
Long Term Support release: 4.14.2 
# let square x = x * x
val square : int -> int = < fun >
# square 3
- : int = 9
# let rec fac x =
if x <= 1 then 1 else x * fac (x - 1)
val fac : int -> int = < fun >
# fac 5
- : int = 120
# square 120
- : int = 14400
Try the Playground
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The OCaml Compiler has been recognised by SIGPLAN for their prestigious Programming Languages Software Award

Fourteen core OCaml developers are featured for their significant contributions to the project
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Trusted by Industry Leaders

These companies and organisations rely on OCaml every day — along with thousands of other developers. See Success Stories
Facebook
Microsoft
Docker
Jane Street
Bloomberg
Tezos
Ahrefs

Why OCaml?

RELIABILITY

Powerful Type Safety Made Simple

OCaml’s lightweight but highly expressive type system catches more bugs at compile time while garbage collection allows you to focus on application logic instead of memory management. Large, complex codebases become easy to maintain and refactor. OCaml empowers you to create mission-critical software with highest security- and safety-requirements in environments with ever-changing requirements!

An example OCaml program defining nested lists in OCaml. A terminal output also shows the compiler catching a type error where a pattern-match was not exhaustive.
PRODUCTIVITY

First-Class Editor and Tooling

OCaml comes with deep integrations for VS Code, Vim or Emacs to provide type inspection, autocomplete and more. Between Opam, a popular package manager; Utop, a powerful interactive REPL; and odoc, an easy-to-use documentation generator, OCaml programmers have access to a complete, modern developer experience.

VS Code
Vim
Emacs

PERFORMANCE
Fast Compiler and Applications

OCaml offers great runtime performance without compromising on developer experience: The bytecode compiler generates small, highly portable executables blazingly fast; the native code compiler produces highly-efficient machine code. Despite this focus on performance, the OCaml compiler has always been exceptionally reliable and stable

Exceptionally Robust and Reliable

Despite all this testing, we have never had a single XenServer defect reported from internal testing or from the field that can be traced back to a bug in the OCaml runtime or compiler. (During development we did once find a minor compiler bug, triggered when compiling auto-generated OCaml code with many function arguments, but this was already fixed in the development branch by the time we reported it and so no interaction with the maintainers at INRIA was required.)
-- Scott, D. & Sharp, R. & Gazagnaire, T. & Madhavapeddy, A. (2010). Using Functional Programming within an Industrial Product Group: Perspectives and Perceptions. ACM SIGPLAN Notices. 45. 87-92. 10.1145/1863543.1863557.

Releases

Recent Releases

5.3.0 (2025-01-08)

  • Syntax for deep effect handlers
  • Restored MSVC port
  • Re-introduced statistical memory profiling
  • More space-efficient implementation of Dynarray
  • utf-8 encoded Unicode source files and modest support of Unicode identifiers
  • Improved metadata on the pairs of declarations and definitions for merlin.
  • Around 20 new functions in the standard library
  • Many fixes and improvements in the runtime
  • Improved error messages for first-class modules, functors, labeled arguments, type clashes.
  • Numerous bug fixes

5.2.1 (2024-11-18)

  • Bug fixes for 5.2.0
See All Releases

Changelog

Releases & Updates

Compiler and Platform Tools

OCaml-eglot 1.2.0

We are very pleased to present a new version of OCaml Eglot. Many bug fixes to support the new vers...

See full changelog
Dune 3.18.0

The Dune Team is happy to announce the release of Dune `3.18.0`! This release contains changes to s...

See full changelog
OCaml-eglot 1.1.0

We are very pleased to present a new version of OCaml Eglot providing `flycheck` as a configurable ...

See full changelog
See Full Changelog

Users of OCaml

OCaml is used by thousands of developers, companies, research labs, teachers, and more. Learn how it fits your use case.

For Educators

With its mathematical roots, OCaml has always had strong ties to academia. It is taught in universities around the world, and has accrued an ever-growing body of research. Learn more about the academic rigor that defines the culture of OCaml.

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For Industrial Users

OCaml's powerful compile-time guarantees and high performance empower companies to provide reliable and speedy services and products. Learn more about how OCaml is used in the industry: explore success stories and discover companies that use OCaml.

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Curated Resources

Get up to speed quickly to enjoy the benefits of the OCaml programming language across your projects.

Getting Started

Install OCaml, set up your favorite text editor and start your first project.

Language Manual

Read the reference manual of the language and documentation on the compiler.

Books

Discover OCaml books from expert programmers and researchers - from beginner level to advanced topics.

Standard Library

Searchable API documentation.

Exercises

Learn OCaml by solving problems on a variety of topics, from easy to challenging.

Papers

Explore papers that have influenced OCaml and other functional programming languages.

OCaml Packages

Explore thousands of open-source OCaml packages with their documentation.

Explore packages