What are some practical uses of Functors in Haskell?

What are some practical uses of Functors in Haskell?

Functors in Haskell are used to apply functions over wrapped values. For example, you can use them with lists, Maybe, or even custom data types.

Can you give me an example with Maybe?

Sure! If you have a Maybe value, like Just 5, you can use fmap to apply a function, like (*2), resulting in Just 10. If it's Nothing, it remains Nothing.

What about using Functors with lists?

With lists, you can use fmap to apply a function to each element. For example, fmap (*2) [1, 2, 3] results in [2, 4, 6].

Are there any other data types that use Functors?

Yes, many data types in Haskell are instances of Functor, including Either, IO, and even custom types you define.