Eff (programming language)

Eff is a functional programming language designed by Andrej Bauer and Matija Pretnar at the University of Ljubljana. Its primary focus is on algebraic effects and handlers as a programming paradigm for managing side effects, control flow, and context management in a structured and composable way. Eff distinguishes itself from other effect-oriented languages by providing a strong theoretical foundation rooted in category theory.

The core concept in Eff revolves around effects, which represent computations that can have side effects or require additional information from the environment. Effects are declared as part of a function's type signature, making them explicit and visible to the programmer. Handlers are then used to interpret these effects, providing the necessary implementation details to execute the computation. A handler essentially defines how to deal with each declared effect when it is encountered during program execution.

Eff supports a flexible and extensible system of effects and handlers, allowing programmers to define their own custom effects and provide multiple interpretations for them. This makes it possible to abstract away implementation details and write code that is independent of the specific environment or context in which it is executed. Different handlers can then be applied to the same code to achieve different results or adapt to different environments.

The language features a type system that tracks the effects performed by functions, ensuring that all effects are explicitly declared and handled. This helps to prevent unexpected side effects and makes it easier to reason about the behavior of programs. Eff's type system also supports type inference, reducing the amount of boilerplate code required to write effectful programs.

Key features of Eff include:

• Algebraic Effects and Handlers: The core programming paradigm, allowing for structured and composable handling of side effects.
• Explicit Effects: Functions declare the effects they may perform in their type signatures.
• Custom Effects: Programmers can define their own effects and handlers.
• Type System with Effect Tracking: Ensures that all effects are accounted for and handled.
• Type Inference: Reduces the amount of type annotations required.

While Eff is primarily a research language, it serves as a platform for exploring the potential of algebraic effects and handlers as a powerful programming paradigm. It offers a clean and principled approach to managing side effects and control flow in functional programming, paving the way for more robust and modular software systems.