Working with Applicatives

An Applicative is a type class that is somewhere between a Functor and a Monad. An Applicative takes a Functor one step further. A Functor talks about application of a function a -> b to a data type f a, whereas an Applicative talks about application of a data type of a function f (a -> b) to a data type f a.

In this recipe, we will work with Maybe and Either data types, and see how we can work with Applicative instances in the context of these data types.

How to do it...

1. Create a new project working-with-applicative with the simple Stack template:

        stack new working-with-applicative simple

2. Open src/Main.hs and add the following imports after the initial module definition. The Applicative type class is defined in the module Control.Applicative:

        import Data.Functor
        import Control.Applicative

3. We will use two operators, Functor application <$> (synonym for fmap) and Applicative application <*>. The Applicative function <*> is...