What are functors and how are they used in different programming languages?

What are functors and how are they used in different programming languages?

Functors are a programming concept that allows you to apply a function to values wrapped in a context, like lists or options. In languages like Haskell, functors are a type class that defines how to map a function over a wrapped value. In JavaScript, you can think of functors as objects that implement a map method.

Can you give me an example of a functor in Haskell?

Sure! In Haskell, the Maybe type is a common functor. It can either be Just value or Nothing. You can use the fmap function to apply a function to the value inside Maybe. For example: fmap (+1) (Just 2) results in Just 3.

How about in JavaScript? What does a functor look like?

In JavaScript, an array can be considered a functor. You can use the map method to apply a function to each element. For example: [1, 2, 3].map(x => x + 1) results in [2, 3, 4].

Are there any other programming languages that use functors?

Yes, many functional programming languages like Scala and OCaml also use functors. In Scala, for instance, collections like List and Option are functors, allowing you to use the map method to transform their contents.