What are type classes in Haskell and how are they used in libraries?

What are type classes in Haskell and how are they used in libraries?

Type classes in Haskell are a way to define a set of functions that can operate on different types. They allow for polymorphism, enabling functions to work with any type that implements the type class. Libraries use type classes to provide generic interfaces for various data types.

Can you give me an example of a type class in a library?

Sure! A common example is the Num type class, which includes types that support basic arithmetic operations. Libraries can define their own types that implement Num, allowing them to be used interchangeably with standard numeric types.

How do I create my own type class?

To create your own type class, you use the class keyword followed by the class name and its methods. For example:

class MyTypeClass a where
    myFunction :: a -> String

This defines a type class MyTypeClass with a method myFunction.

What are some popular libraries that use type classes?

Popular libraries that utilize type classes include base (which includes Num, Functor, etc.), lens for functional programming with lenses, and containers for data structures. These libraries leverage type classes to provide flexible and reusable code.