What are some examples of functors in different programming languages?

What are some examples of functors in different programming languages?

Functors are a concept in functional programming that can be found in many languages. For example, in Haskell, a functor is a type class that implements the fmap function. In JavaScript, you can think of a functor as an object that implements a map method, like in the case of arrays.

Can you give me a specific example in Haskell?

Sure! In Haskell, you can define a functor for a simple data type like Maybe. Here's how it looks:

instance Functor Maybe where
    fmap _ Nothing  = Nothing
    fmap f (Just x) = Just (f x)

This allows you to apply a function to the value inside a Just or do nothing if it's Nothing.

What about in JavaScript?

In JavaScript, you can create a functor using an array. Here's an example:

const functor = [1, 2, 3];
const mapped = functor.map(x => x * 2);
console.log(mapped); // Output: [2, 4, 6]

The map method applies the function to each element in the array.

Are there functors in Python too?

Yes, in Python, you can use the map function, which is a built-in functor. For example:

numbers = [1, 2, 3]
result = list(map(lambda x: x * 2, numbers))
print(result)  # Output: [2, 4, 6]

This applies the lambda function to each element in the list.