Pony (programming language)

Pony (also referred to as ponylang) is a free and open source, object-oriented, actor model, capabilities-secure, high performance programming language.^[6][7] Pony's reference capabilities allow even mutable data to be safely passed by reference between actors. Garbage collection is performed concurrently, per-actor, which eliminates the need to pause program execution or "stop the world".^[8][9][10] Sylvan Clebsch is the original creator of the language.^[11][12] It is now being maintained and developed by members of the Pony team.^[13]

Pony

Paradigm	Actor model, Object-oriented, Imperative
Designed by	Sylvan Clebsch[1]
First appeared	28 April 2015; 10 years ago (2015-04-28)[2]
Stable release	0.59.0 / April 26, 2025; 26 days ago (2025-04-26)
Typing discipline	strong, static, inferred, nominal, structural
Implementation language	C
License	BSD-2.[3]
Website	www.ponylang.org
Influenced by
E[4]
Influenced
Project Verona[5]

History

The language was created by Sylvan Clebsch, while a PhD student at Imperial College London. His professor at that time was Sophia Drossopoulou, who is also well known for her contributions to computer programming, and as a lecturer. According to developers who have talked to Sylvan, he was frustrated with not having a high performance language that could run concurrent code securely, safely, and more simply.^[14]

Language design

At its core, Pony is a systems language designed around safety and performance.

Safety

• Type safety - Pony is a type safe language.^[15]
• Memory safety - There are no dangling pointers and no buffer overruns. There is no null but optional types can be safely represented using unions with the None type.^[6][16]
• Exception safety - There are no runtime exceptions. All exceptions have defined semantics and are always caught.^[17]
• Concurrency safety - The type system employs reference capabilities to ensure (at compile time) that there are no data races nor deadlocks.^{[18][19][20][21]}

Performance

• Lock-free - By design, Pony avoids the need for traditional locking mechanisms, which eliminates the overhead and contention associated with locks.^[14]
• Native code - Pony is an ahead-of-time compiled language. There is no interpreter or virtual machine^[18][16]
• Concurrent garbage collection - Each actor's heap is collected separately and concurrently, avoiding the need to "stop the world" for global collection.^[11][12][21]

Examples

Hello World

In Pony, instead of a main function, there is a main actor. The creation of this actor serves as the entry point into the Pony program.^[6][17]

actor Main
  new create(env: Env) =>
    env.out.print("Hello, world!")

There are no global variables in Pony, meaning everything must be contained within an instance of a class or an actor.^[14] As such, even the environment that allows for printing to standard output is passed as a parameter.^[14][6]