Haskell Proxies

Haskell Proxies Proxies are special types in the Haskell programming language, often used to pass type-level information during computations. They don’t hold any value; their main function is to provide a way to indirectly feed types to functions, methods, or typeclasses, making them essential tools in type-directed programming.

What is a Haskell Proxy?

A Haskell Proxy is a type that holds no data, but can carry a phantom type variable, utilized for parameterizing functions or data types without using them, in order to guide type inference in function signatures.

Why are Proxies used in Haskell?

Proxies are used in Haskell mainly to improve type inference. By using Proxies, it becomes easier to guide the Haskell compiler through complex type-level computations. Furthermore, they can also be utilized for creating functions where the type variable does not appear in argument list, which can be useful in some Haskell patterns.

How do I create a Haskell Proxy?

In Haskell, a Proxy can be created by simply using the Proxy keyword. For example, you can create a Proxy of Integer type like this: ‘myProxy :: Proxy Integer’. This creates a Proxy that carries the Integer type information, although it does not hold any actual Integer value.