What is the difference between Functor and Applicative in Haskell?

What is the difference between Functor and Applicative in Haskell?

In Haskell, a Functor is a type class that allows you to apply a function over a wrapped value, while an Applicative is a more powerful type class that allows you to apply functions that are also wrapped in a context.

Can you give me an example of each?

Sure! For a Functor, you can use fmap to apply a function to a value inside a Maybe: fmap (+1) (Just 2) results in Just 3. For an Applicative, you can use <*> to apply a wrapped function to a wrapped value: Just (+1) <*> Just 2 also results in Just 3.

Are there any practical use cases for these concepts?

Yes! Functors are often used for mapping over lists or optional values, while Applicatives are useful for combining multiple computations that may fail, like in validation scenarios.

How do they relate to Monads?

Great question! Both Functors and Applicatives are foundational for Monads. Every Monad is an Applicative, and every Applicative is a Functor, but not all Functors are Applicatives.